1. PREFACE +BATTERY TERMINAL +BATTERY TERMINAL + + + + + + + + + + + + ELECTRICITY AND HWH In the first section of this school, we did an in-depth study of general hydraulics. In section four, we applied hydraulics to HWH systems. In this section, we will discuss the application of DC electricity to HWH leveling and room extension systems. This study will include some basic discussion of electricity but will deal more in-depth with how we use electricity to make our systems function and how to diagnose the problems you may encounter. We will deal with current/voltage/resistance, basic circuits, a discussion of basic electrical and electronic components such as switches and relays (do you really need to know what a diode is made of), test equipment and how to use it, HWH electrical components, the use of electrical wiring diagrams and/or schematics and the general electrical diagnostics of HWH leveling and room extension systems. 2. ELECTRICITY; WHAT IT IS AND HOW IT WORKS 2-1 ELECTRICITY is the flow of electrons from atom to atom in a conductor. Atoms are made up of three particles, electrons (- or negative charge), protons (+ or positive charge) and neutrons (neutral charge). The protons and neutrons are the core of the atom and the electrons are in rings that orbit around the core. The positive charge of the protons attracts the negative charge of the electrons which keeps them in their rings around the core of the atom. Each atom of the same element has an equal number of electrons and protons so in a normal state, an atom is electrically neutral. The number of neutrons in an element is not necessarily the same as the number of electrons and protons in that element. The rule that makes electricity work is like charges repel and unlike charges attract. When some force such as friction causes an electron to leave the outer ring of the atom, it changes the charge state of the atom. The atom gaining an electron becomes negatively charged and the atom that loses an electron becomes positively charged. When a conductor such as a copper wire has a positive charge at one end and a negative charge at the other, the electrons in the conductor will start moving. The positive charge at the end of the conductor will attract an electron (a negative charge) from an atom. That atom will then attract an electron from a neighboring atom leaving that atom positively charged. That atom then attracts an electron and so on and so on with billions and billions of atoms. The electrons flow through the conductor from the negatively charged end to the positively charged end. Now you have electricity. COPPER CONDUCTOR COPPER CONDUCTOR + + + + + + + + + Figure 2 -BATTERY TERMINAL + + + + + + + + + + + + + N N N N N N N N Figure 1 The plus charge attracts an electron which leaves a hole in the outer ring of the atom. The atom is now positively charged. -BATTERY TERMINAL The process is now started and as an electron is pulled from one atom, the charge state of that atom changes and it pulls an electron from another atom. The flow of the electrons is electricity.
2-2 CURRENT, VOLTAGE AND RESISTANCE: Although possibly interesting to some, the previous discussion has absolutely nothing to do with learning to diagnose an electrical issue. The following discussion will also have some useless but interesting facts. BUT this section is important to understand because we will talk about what makes electricity work. There are three basic factors that we deal with when working with electricity. It is important to understand these to perform diagnostics on an electrical system. The three factors are Current, Voltage and Resistance. 2-2.1 Current is the flow of electrons through a conductor. Current is measured in amperes. The following is one of those useless facts. One ampere (from now on we will refer to amperes as amps) is a flow of 6.28 billion billion electrons moving past one point in one second. The number looks like this: 6,280,000,000,000,000,000. Current is the equivalent to flow, gallons per minute, in a hydraulic system. 2-2.2 Voltage is the force or pressure that pushes the current through the circuit. Voltage is to an electrical circuit as pressure is to a hydraulic system. Without pressure fluid cannot flow through the hydraulic circuit. Without voltage, electrons will not move through the electrical circuit. Voltage is a Potential force. This means even if nothing is turned on, there can still be voltage. You can have voltage (pressure) without current (flow) but you cannot have current (flow) without the push of voltage (pressure). A good analogy would be a tank full of water connected to an empty tank through a tube with a closed valve. HIGH PRESSURE NO PRESSURE LOAD NO CURRENT FLOW VALVE OPEN - HIGH PRESSURE FLOWS TO LOW PRESSURE HIGH POTENTIAL (EXCESS OF ELECTRONS) Figure 3 LOAD BATTERY + + + + + LOW POTENTIAL (LACK OF ELECTRONS) The full tank has pressure in it from the weight of the water. The empty tank has no pressure. At the valve there is a potential force because there is pressure on one side of the valve and not the other. The full tank would be the negative side of a battery and the empty tank would be the positive side of the battery. Like the water tanks, voltage (the potential force) exists at the switch even though no electrons are moving. If the valve is opened, the water can flow from the full tank to the empty tank. The same thing happens if you close the switch that isolates the negative from the positive side of the battery. With the switch closed, excess electrons from the negative side can now flow to the positive side. HIGH POTENTIAL (EXCESS OF ELECTRONS) CURRENT FLOW BATTERY LOW POTENTIAL (LACK OF ELECTRONS) Figure 4 When the water level in the two tanks becomes equal, there will be no more flow because there is no differential of pressure to move the water. The potential force is gone. No pressure, no flow. The same thing happens as the battery discharges, that is, loses the potential energy that is voltage. There are no excess electrons to be attracted to the positive side, no difference in potential. No voltage, no current. See the figures on the next page. + + + +
EQUAL PRESSURE NO POTENTIAL FORCE - NO FLOW LOAD NO CURRENT FLOW NO FREE ELECTRONS 0 (ZERO) POTENTIAL BATTERY Figure 5 2-2.3 Resistance is the opposition to the flow of electrical current. The unit of measurement for resistance is the ohm. All materials in an electric circuit create resistance, some more than others. Materials such as platinum, gold, silver and copper have a lower resistance value and are excellent conductors. Copper is the most common of the four to be used as a conductor due to the cost of the other three. Gold and silver are used as contacts in some relays and switches. Aluminum is also used as a conductor but has much more resistance than copper. Materials such as plastic and rubber are very poor conductors and are used as insulators because they prevent the flow of current. We can use the two water tanks to explain resistance. If the two tanks are connected with a large tube, when the valve is opened the water will flow from the full tank to the empty tank quicker than two tanks connected with a small tube. + + + + + HIGH FLOW LOW FLOW Figure 6 The same is true with electricity. A larger diameter copper conductor will have more electrons that can flow through the circuit than a small diameter copper conductor. LARGE CURRENT FLOW SMALL CURRENT FLOW E E E E E E E E E E E E E E E E E E E Figure 7 E E E E In hydraulics, there is a loss of pressure at the outlet end of a hose due to the friction between the fluid and the wall of the hose. The longer the hose, the more friction is introduced into the circuit, the greater the loss of pressure. Again, the same is true with electrical conductors or wires. The longer the wires, the more voltage loss there will be at the load. Some time ago, we did a test up in electrical engineering at HWH where we took a car battery and about 20 feet of 18 gauge wire and connected each end of the wire to one of the battery posts. Nothing happened, the wire did not even get hot (yes, the battery was fully charged). If a wire is too long, there may not be enough voltage to push the current through. If the wire is to small a gauge, the voltage may try to push too much current through. This would create heat in the wire and if the wire is too small, it could possibly melt the wire. This is why wires are protected with fuses rated for the amount of current a wire can carry. E E E
Another piece in an electrical circuit that creates resistance is the load. Light bulbs, a solenoid valve, a relay, an electronic piece of equipment such as a processor or a motor are all examples of a load in the circuit. The larger the load, the greater the resistance is in the circuit. Once again, the two water tanks can be used to represent the resistance a load creates in a circuit. EXAMPLE 1 EXAMPLE 2 NO LOAD LOAD Figure 8 In the first example, we show a paddle wheel between the two tanks after the valve. With only the paddle wheel in the circuit, the load is small and creates little resistance. The water flows to the second tank with only a little interference. In the second example, we have attached a machine to the paddle wheel with a belt. Now the paddle wheel resists the flow of water as it tries to turn the machine. The machine has added resistance to the circuit and the water will not flow to the second tank as quickly as it did in the first example. When the voltage in a circuit is constant, the total resistance in the circuit determines the current. Resistance comes in many different forms besides the type, size and length of the conductor(s) in the circuit or the size of the load(s) in the circuit. The connection points in the circuit (pin connecters, ring terminals, relay posts, etc.) are usually made from different materials than the wire so they would have a different resistance value. They could be brass, steel, stainless steel or tin coated copper, to name a few. The resistance created by good connection points will in most cases be negligible and could probably not be measured with an average voltmeter. Switch contacts and relay contacts can introduce resistance into the circuit, especially if they are pitted, arced or worn. The two main things in an electrical circuit that will create unwanted resistance that is not figured into the design of that circuit are loose connections and corrosion. A loose connection means that less material in the connection will be making contact. Like a smaller wire, the smaller amount of surface contact at the connection allows less current to flow through the connection. A loose connection is usually fairly simple to detect. Connections, whether they are soldiered, pin type, ring terminals or fast-on spade type connections should feel tight when you try to move them (just don t use so much force you create a loose connection). Corrosion is the nasty little thing that can cause a lot of problems and is often overlooked or misdiagnosed. Corrosion is caused by the reaction of the metals in the circuit with air and/or water. Unlike metals can cause a corrosive connection. Contact between aluminum and steel can create devastating corrosion in an electrical circuit. Corrosion can add a very large amount of resistance to any electrical circuit. Even connections that do not appear to be corroded can have corrosion between the contact points of the connection that are not apparent with a simple visual inspection. Switch or relay contacts can be corroded. Wires and pc boards can also be corroded creating resistance. And don t assume a water proof connector is not corroded. This is a common mistake I have seen: The pump motor doesn t run so the pump relay is replaced. Now the pump motor runs. Was the relay really bad or when the wires were removed and attached to the new relay, was a bad connection or the corrosion factor removed? But I get ahead of myself. It s not time for diagnostics yet. It s just that loose connections and corrosion which cause voltage problems are several of the most overlooked and misdiagnosed problems encountered and no matter how many times during this school we discuss it, it is probably not enough.
2-3 OHM S LAW is the mathematical relationship between the amount of voltage, current and resistance in an electrical circuit. A German physicist, Georg Simon Ohm, established this relationship in 1827. Ohm s law is V (volts) = I (amps) x R (ohms or resistance). It takes one volt of pressure to move one amp of current against one ohm of resistance. The following triangle is an easy way to remember Ohm s law and the three ways it can be written. V = I x R V I = V R I R R = V I Figure 9 As long as you know two of the values in the circuit, you can figure the third value by using one of the above formulas that make up Ohm s law. Under standing the relationship between voltage, current and resistance is important when diagnosing electrical issues, but you may never actually use the formulas of Ohm s law when working on an electrical issue with an HWH system. In electricity, power is measured in watts. The formula for figuring power or watts is W (watts/power) = V (volts) x I (current/amps). If you understand the relationships between volts, amps, ohms and watts, it is easier to understand how raising or lowering these values can affect a system. Later, we will use a few examples to show you how lowering voltage or increasing resistance changes how a system performs. 3. CIRCUITS AND BASIC CIRCUIT COMPONENTS 3-1 CIRCUITS: There are three types of electrical circuits, the series circuit, the parallel circuit and the series-parallel circuit. In the discussions of these circuits, we will refer to the resistors in the circuits but these could be any type of load in the circuit, not just a resistor. Series Circuit Parallel Circuit Series-Parallel Circuit Figure 10 3-1.1 Series circuits have only one path for current to flow along. All components in the circuit are connected end to end. Series circuits have the following features: 1. The total circuit resistance is the sum of all resistors in the circuit. (This would include wires, switches, connections and loads.) 2. The current through each resistor is the same. 3. The voltage drops across each resistor is different if the values of the resistors are different. 4. The sum of all the voltage drops in the system will be equal to the voltage source. On the following page, we will show several examples of series circuits. We will also do the math to show circuit resistance, circuit current and voltage drops across the resistance.
Example 1: A series circuit with one 4 ohm resistor 3a The total circuit resistance is 4 ohms. +12 VOLTS 12.0 V 4 The total circuit current the battery supplies is 3 amps. (3 amps) I = 12 volts (V) 4 ohms (R) Example 2: +12 VOLTS 1.2a 3a The voltage drop is 12 volts (12 volts) V = 4 ohms (R) x 3 amps (I) A series circuit with one 2 ohm resistor, one 5 ohm resistor and one 3 ohm resistor The total circuit resistance is 10 ohms R1 2 2 ohms (R1) + 5 ohms (R2) + 3 ohms (R3) = 10 ohms Figure 11 2.4V 6.0V R2 5 The total circuit current the battery supplies is 1.2 amps (1.2 amps) I = 12 volts (V) 10 ohms (R) circuit resistance 3.6V 1.2a R3 3 Figure 12 Voltage drop for R1 is 2.4 volts (2.4 volts) V = 1.2 amps (I) x 2 ohms (R) Voltage drop for R2 is 6.0 volts (6.0 volts) V = 1.2 amps (I) x 5 ohms (R) Voltage drop for R3 is 6.0 volts (3.6 volts) V = 1.2 amps (I) x 3 ohms (R) +12 VOLTS 8a 8a 12.0 V 6a 6a Figure 13 6 R1 12.0 V 2a 2a R2 6 2.4 volts + 3.6 volts + 6.0 volts = 12 volts (source voltage) 3-1.2 Parallel circuits have multiple paths for current to flow. Each resistor in the circuit provides a separate path for current to flow. The resistors are side by side instead of end to end. Parallel circuits have the following features: 1. The voltage drop across each resistor is the same. It will be equal to the voltage source. 2. The current through each resistor will be different if the resistance values of the resistors in the circuit are different. 3. The total current in the circuit is the sum of the individual currents through each resistor. We will again show several examples of a parallel circuit complete with the mathematics showing the different values in the circuit. Example 1: A parallel circuit with a 2 ohm resistor and a 6 ohm resistor Current through R1 is 6 amps (6 amps) I = 12 volts (V) 2 ohms (R) Current through R2 is 2 amps (2 amps) I = 12 volts (V) 6 ohms (R) Total circuit current the battery supplies is 8 amps 6 amps (R1) + 2 amps (R2) = 8 amps Total circuit resistance is 1.5 ohms (1.5 ohms) R = 12 volts (V) 8 amps (I) The voltage drop for R1 is 12 volts (12 volts) V = 6 amps (I) x 2 ohms (R) The voltage drop for R2 is 12 volts (12 volts) V = 2 amps (I) x 6 ohms (R) The voltage drop across each resistor is the same as the source voltage, 12 volts.
Example 2: 9.4a 3a R3-4 12V 12V 3a R2-5 2.4a 2.4a 4a A parallel circuit with a 3 ohm resistor, a 4 ohm resistor and a 3 ohm resistor R1-3 12V 4a 9.4a Current through R1 is 4 amps (4 amps) I = 12 volts (V) 3 ohms (R) Current through R2 is 2.4 amps (2.4 amps) I = 12 volts (V) 5 ohms (R) Current through R3 is 3 amps (3 amps) I = 12 volts (V) 4 ohms (R) Total circuit current the battery supplies is 9.4 amps Total circuit resistance is 1.28 ohms (1.28 ohms) R = 12 volts (V) 9.4 amps (I) The voltage drop for R1 is 12 volts (12 volts) V = 4 amps (I) x 3 ohms (R) The voltage drop for R2 is 12 volts +12 VOLTS (12 volts) V = 2.4 amps (I) x 5 ohms (R) Figure 14 The voltage drop for R3 is 12 volts (12 volts) V = 3 amps (I) x 4 ohms (R) The voltage drop across each resistor is the same as the source voltage, 12 volts. 3-1.3 Series-Parallel Circuits simply have a combination of the two circuits explained above. The circuit has one or more resistors in series with a parallel combination of resistors. Depending on the amount of resistors in the circuit that are in a parallel configuration, figuring circuit resistance or current and voltage drops can be fairly simple to very complex. I will give you some formulas and procedures for figuring values for a series-parallel circuit along with one example, but fortunately this is not something that will be important to remember or even to refer to when dealing with HWH systems. The way to work with this type of circuit is to first figure the total resistance of the parallel circuit then add that to the resistance of the resistor(s) that are in series with the parallel part of the circuit. For the example on the next page that would be R1 + (R2 + R3 + R4). Once we do that, we can use I = V R to figured the total circuit current. This will let us let us figure the voltage drop across R1 and tell us what voltage is available for R s 2, 3 and 4. Then we can figure the current for the individual resistors in the parallel circuit. The reason this is more difficult is because we don t know the voltage for the parallel part of the circuit. We can t use I = V R to figure the parallel circuit resistance as we did with the simple parallel circuit examples because we don t know what V is. It s a catch 22 problem. We can t figure the resistance of the parallel circuit without knowing the voltage drops, but we can t figure the voltage drops without knowing the resistance of the parallel circuit. This is where some new formulas come into play. The way to figure the total resistance of the parallel circuit is fairly simple. The formula for the example on the next page is as follows: 1 1 Total parallel circuit resistance = 1 + 1 + 1 or 1 [(1 R2) + (1 R3) + (1 R4)] R2 R3 R4 If there were more resistors in the parallel circuit, you would just add more R s to the above equation. There is a short cut for this problem if there are only 2 resistors in the parallel part of the circuit. That formula is: The total circuit resistance in a parallel circuit with 2 resistors is the product of the two resistors divided by the sum of the two resistors. Mathematically the formula would look like this: Total parallel circuit resistance with 2 resistors = R x R or (R x R) (R + R) R + R This formula can be used on any parallel circuit with only two resistors.
Example: A series-parallel circuit has a 10 ohm resistor in series with a parallel group of resistors with values of 8 ohms, 4 ohms and 8 ohms. 1a R1-10 10V.25a.5a.25a +12 VOLTS 2V R2 8 2V R3 4 2V R4 8.25a.5a.25a 1a Figure 15 The total resistance of the parallel part of the circuit is 2 ohm. 1 1 [(1 8 ohms [R2]) + (1 4 ohms [R3]) + (1 8 ohms [R4])] = 1 + 1 + 1_ 1 [.125 ohms (R2) +.25 ohms (R3) +.125 ohms (R4)] = R2 R3 R4 1.5. ohm = 2 ohm total parallel circuit resistance. The total circuit current is 1 amp. (1 amp) I = 12 volts (V) 12 ohms (R) [10 ohms (R1) + 2 ohms (total parallel circuit resistance)] The voltage drop for R1 is 10 volts. The current through R1 is 1 amp. (10 volts) V = 1 amp (I) x 10 ohms (R) (1 amp) I = 10 volts (V) 10 ohms (I) The voltage drop for R2, R3 and R4 is 2 volts across each resistor. The current through R2 an R4 is.25 amps. R2 and R4 are both 8 ohm resistors. (.25 amps) I = 2 volts (V) 8 ohms (I) The current through R3 is.5 amps. (.5 amps) I = 2 volts (V) 4 ohms (I) 3-2 BASIC COMPONENTS OF AN ELECTRICAL CIRCUIT: There are four basic components to all electrical circuits, the electrical power source, the load, the wiring and the controls. 3-2.1. The electrical power source. For nearly all HWH systems, the power source will be the battery system of the vehicle. Usually these will be 12 volt systems but some vehicles like the Prevost buses will have a 24 volt system. A large percent of motorized vehicles, especially in the RV industry, will have two separate battery systems. Towable units usually have just one battery system. On motorized vehicles, one system is referred to as the chassis or engine batteries and the other is referred to as the house batteries. In most cases the two systems will be the same voltage but again some vehicles like the Prevost bus may have two different voltage systems available. You are not going to run into too many 24 volt or combination 24/12 volt systems out there but it is important to remember it is possible. Using your 12 volt test light to check a leveling system on a Prevost could be expensive for you depending on what tool company you bought the test light from. Going either way will damage components or equipment but using 12 volt components or equipment on a 24 volt system will cause damage to the components or equipment in a VERY, short period of time. On motorized vehicles, the HWH control systems, light panels or control boxes, are connected to the chassis batteries through the ignition switch. When available, we prefer the use of the accessory side of the ignition switch. The loads for the system, such as the pump motor or valves, can be power by either source. For towable units with just one battery system, it is recommended to use a master switch between the battery supply and the control system. This will eliminate any current draw on the batteries by the HWH system when it is not in use.
3-2.2. The load. The load is any component on the circuit that does some work such as a light bulb or LED, an electrically controlled valve, an electric relay, a processor or the pump motor. Most of the loads in the circuit of an HWH system are a parallel circuit or a simple single load series circuit. The newer automatic systems do use a series circuit with two loads (hydraulic solenoid valves) in series. We will discuss this series circuit in more depth later in the school. Single Load Series Circuit PUMP RELAY CONTACTS M PUMP MOTOR Multiple Load Parallel Circuit 325 CONTROL BOX +12 RR LR RF SOLENOID VALVE LF Figure 16 GROUND 3-2.3. The wiring or conductive path. All the components of the electrical circuit have to be connected. This is accomplished with wires or in the case of printed circuit boards, the traces on the boards. The traces on a pc (printed circuit) board connect the components on the board like wires connect the parts of the system. The gauge (diameter) of the wire being used must be large enough to handle the maximum current the load can use and be able to maintain the voltage needed to operate the load. For example, the resistance of a coil in a large solenoid valve is approximately 1.2 ohms. With 12 volts to the valve, the valve will draw about 10 amps. The guage of wire needed has to be capable of handling 10 amps. But you need to remember the longer the wire, the more resistance the wire adds to the circuit. A longer wire will cause a larger voltage drop. A 14 ga. wire will in most cases handle the load of a solenoid valve. If the length of the wires was extremely long, a larger gauge wire may be needed to reduce the voltage drop even though the smaller gauge wire will handle the maximum current the load may use. Maybe the most important thing to remember about wiring or conductive paths that is the most likely thing to be overlooked is; the ground path for the circuit needs to be the same size or have the same capability as the positive side of the circuit. If the positive side of the circuit needs to be a 2 ga. wire, the conductive capability of the ground side needs to be equal to a 2 ga. wire, whether the conductive path is a wire or a mounting plate or bracket such as for our pump motors. This is true whether dealing with the battery cables or mounting location and brackets for the pump motor; or the smaller wires that supply ignition power to the control box. 3-2.4. The controls. The controls direct or regulate voltage and current to do work such as run a motor, shift a valve or turn on a light. The controls in a circuit can be very simple such as a fuse or the toggle switch used to operate the pump motor on a lever controlled, hand pump landing gear system or more complex like the control box for a 625 series automatic leveling system. Switches come in many styles. There are manual switches such as toggle switches, rocker switches, key operated switches and push button switches. We even use something similar to a knife switch in the joystick valve to supply a ground path to operate the pump relay. There are electrically controlled switches such as relays. Relays are used in control boxes and on the pump assemblies. Relays have an electric coil that causes contacts in the relay to open or close. There are also electronic switches which are called transistors. Often, we use two or more circuits to perform a function. An example would be a joystick leveling system. When pushed to operate the jacks, the joystick lever completes a ground path for the coil of the pump relay. When activated, the contacts of the pump relay supply voltage and current to the pump motor from the battery. In this case, the pump relay acts as both a load and a switch. A computerized system will have two relays to activate the pump motor. There are three circuits used in this operation not counting the control panel to the control box.
These are simplified drawings of the joystick pump operation circuit and an automatic pump operation circuit. Joystick System Automatic System JOYSTICK SWITCH PUMP RELAY COIL M PUMP RELAY CONTACTS PUMP MOTOR CONTROL BOX MASTER RELAY COIL PUMP RELAY COIL MASTER RELAY CONTACTS PUMP RELAY CONTACTS M Figure 17 There are many types of electronic components used in our systems that would be considered controls. These include diodes, resistors, capacitors and processor chips to name a few. These components are used to store, regulate and direct voltage. Normally these components are used on light plates, control panels and in control boxes and are not considered when diagnosing problems in the field. We don t recommend nor is it necessary in most cases to do diagnostics at the board level in the field. We will discuss some of these components in greater detail later in this school. 3-2.5 General circuit diagnostics. One of the meanings of the word circuit in the dictionary is a closed, circular curve. The easy way to say this is a circuit is a circle. For an electrical circuit to function, the circle must be complete. Any break in the circle will cause the circuit to not function. Switches or other controls are used to complete the circle so the circuit can function. An open switch creates a break in the circle. Switches or other controls are designed into circuits to create an intentional break in the circuit to turn the load on and off. The problem is when unwanted breaks in the circle happen. The unwanted break could be a broken wire, a bad connection, a switch (control) problem, blown fuse, a malfunction of the load or a problem with the source (battery). Like with hydraulics, using the process of elimination is the best way to do diagnostics. Using wiring diagrams or schematics, list all the components of the circuit. Then, starting from one end, test and eliminate each component until the break in the circuit is found. For the drawing below the process would be as follows: 1. Do you have + power and ground at the source? Yes. 2. Do you have power to the switch? Yes. 3. Do you have power through the switch? Yes. 4. Do you have power to the load? Yes. 5. Do you have ground to the load? No. The problem is between the load and the ground side of the source. 6. Does the load function? You would only ask this question if the answers to the above five questions were yes. Full Circle - Light On CONTROL Broken Circle - Light Off CONTROL SOURCE LOAD SOURCE LOAD WIRING Figure 18 WIRING
When your testing produces a no answer to one of the above questions, you have isolated the problem. You could also start this process at the load but if you start anywhere else in the circuit, it is hard to eliminate things and the possibility of missing something increases. With the above circuit, the no answer was to the fifth question, Do you have ground to the load? Because there is power and ground at the source, and power to the load but no ground for the load, the break is in the connections or wiring between the source and the load. Admittedly, finding a break in a wire can be a headache, but the connections can be easily checked and then just run a new wire if that would be easier than trying to find a bad spot in the wire. Almost all HWH electrical systems can be treated in this manner. All you have to do is identify all the components that are part of the problem circle. Then eliminate them one at a time until the problem is isolated. 4. ELECTRICAL COMPONENTS. 4-1 MANUAL CONTROL SWITCHES. Manual switches come in many styles and many different contact actions. We use toggle switches, rocker switches, push button switches and key switches. The terminology used to describe the contact actions is important to understand. A momentary switch is a switch that will return to its original position when released. You have to push and hold the switch to keep it activated. A maintained switch is a switch that will remain in the position it is pushed to. This type of switch has to be pushed to return it to its original position. A normally open switch (NO) has contacts that are open in the off position. A normally closed switch (NC) has contacts that are closed in the off position. A single pole switch (SP) controls only one circuit at a time. A double pole switch (DP) controls two circuits at a time. The key switch on our room panels can control three circuits at a time (3P). A single throw switch (ST) only has two positions, off or on. The switch can be normally open or normally closed. A double throw switch (DT) will have several positions. The switch could be a two position switch that is on in both positions or it may be a switch that has three positions, on off on. We use one hybrid switch on the 100 and 110 series (4 lever systems) leveling systems with air dump. That switch is a double pole switch with single throw contacts but it works as an off, on (maintained) and on (momentary) switch. You will see labeling for standard switches that looks like this: SPST-single pole single throw SPDT-single pole double throw DPST-double pole single throw DPDT-double pole double throw The symbols that HWH uses in diagrams and schematics for different switches look like this: SPST NO Single pole, single throw, normally open SPST NC Single pole, single throw, normally closed DPST NO Double pole, single throw, normally open SPDT NO DPDT NO Single pole, double throw, normally open Double pole, double throw, normally open Figure 19
Another important thing to note about switches is their current capacity. Like wires, switches can conduct only so much current without overheating or burning out. The current capability of the switch along with the maximum voltage the switch can be used with is usually indicated on the body of the switch. It is important that these capacities are not exceeded. The contacts of the switch will probably be ruined if its capacity is exceeded. This is why we use relays that can supply large amounts of current to different loads instead of wiring the load directly to the switch. Most of our manual switches are rated for 5 to 10 amps, some up to 15 or 20 amps. It is important that the correct switches are used to maintain correct operation of our systems. Switches also have different types of terminals. The terminals can be soldiered, such as with a board mounted switch or they can be used with fast-on connectors (push on) or ring terminals (screw on). Terminals are usually numbered. The numbers are used to make assembly and repair diagrams to make sure the switches are wired and assembled properly. 4-1.1 Manual switch diagnostics is very simple once the switch action is known. Answering a couple of questions will usually diagnose switch problems. Will the switch stay where it is supposed to if it is a maintain type switch? Will the switch release or does it seem to stick if it is a momentary switch? Do the contacts open when they are supposed to? (There is no continuity between the proper terminals of the switch.) Do the contacts close when they are supposed to? (There is continuity between the proper terminals of the switch.) Or simply, is there power through the switch when there is suppose to be power and is there no power through the switch when there is not suppose to be power? 4-2 ELECTRIC COILS are not an individual component in our systems but coils are used in relays and solenoid valves and it is important to understand how coils function. A coil is nothing more than a long wire wrapped around a spool, like a spool of thread. When power and ground are applied to the opposite ends of the wire, it creates a magnetic field that makes the core move. This opens or closes the electrical contacts of a relay or opens or closes the seat of a valve. All coils have a resistance value which can be checked but there is an easier way to check components that have a coil. Components with coils are rated for a particular voltage, 12 or 24 in our case. These components also have a minimum voltage at which they will operate or pull in and when they will drop out. An example of this is our solenoid valves. The valve must pull in at no more than 8.5 volts and stay energized (not drop out) until the voltage drops to 2 volts or less. If you check components with a coil in this manner, the resistance value of the coil is not needed. If a solenoid valve will not pull in until 9 volts, the valve is bad no matter what resistance the coil is producing. If a valve drops out at 4.4 volts, the valve is bad. Again the resistance does not matter. Sometimes the easiest test to do on a coil is just check continuity between the two sides of the coil. If there is no continuity, the coil is bad. Components with coils can also be affected by the length of time they are on. The wire used to make coils is insulated. This insulation can deteriorate under an excessive heat situation. The longer a coil is on, the more heat can be generated. This depends on the design of the coil. If one of our small valves is on over 20 minutes, the coil can start to deteriorate and damage the valve. The relays we use for our master relay or the valves we use for our air leveling systems can be on for hours without damage. If the coil wire deteriorates enough, this can create a short or an open spot in the coil. A coil with a short will usually blow the fuse that protects that circuit. If there is no fuse or the fuse does not blow, the wires or other components in the circuit can be damaged. If there is an open spot in the coil, the component simply will not work. The coil will show no continuity between the two ends of the coil.
Finally, when the coil is turned off, it will discharge a large amount of voltage. This discharge can cause damage to the switch. By placing a diode in line with the coil, this will allow the voltage to dissipate through the coil instead of through the switch contacts. This is important because a component with a diode installed in the component must maintain the proper polarity when it is wired into the circuit. This is called a back emf diode. If the component is wired in reverse, this will ruin the diode because a direct short is created in the component. This will create a short in the circuit and blow a fuse or damage wiring or other components. Sometimes the diode will be completely destroyed. This will allow the component to work but will now have no protection against the voltage spike when the coil is turned off. Other components can now be damaged. For most components, we have protection built into the control circuit. Our large valves used to have the diode built into the valve. Large replacement valves still have the diode for use in older systems, but this same replacement valve is used for repairs in new systems also. It is just a good rule of thumb to not change the polarity of the wiring in a system. You never know when you may be causing an issue. We will show you examples of coils with and without diodes when we discuss other components such as relays (next component we discuss) or solenoid valves. 4-3 RELAYS. Relays are electrically controlled switches. (They are sometimes referred to as solenoids but if it is use as a switch, it is a relay.) Pictured are several relays presently used by HWH. In the past, HWH has used different styles and brands of relays. Some of the older relays are still available but if not, the present relays can be adapted to any system produced by HWH. Pump or Master Relay Bosch Relay SIDE VIEW FRONT VIEW SIDE VIEW BOTTOM VIEW 85 86 87a 87 30 87 87a 86 85 30 Figure 20 A relay consists of an electrical coil and a set of contacts. The coil is used to produce a magnetic field that moves the contacts. The coil of a relay is designed to work with a specific amount of voltage. If an incorrect amount of voltage is used to operate a relay, the relay will probably malfunction. The coil of the relay will burn out it the voltage is too high or will not function if the voltage is too low. The contacts of a relay have limitations. The contacts will have a maximum amount of voltage and current they can withstand without damaging the contacts. All of the relays we use are non-directional and the contacts can be used to switch + voltage or ground. Either terminal for the relay contacts could be the supply side or the output side. The relay coils are also non-directional. There is no diode installed on the coil of the relays we use. Either terminal for the relay coil could be the + voltage or the ground for the coil. A relay can have normally open contacts, normally closed contacts or both. Some relays can be wired to operate as normally open or normally closed. A relay of this type could be used to control two different circuits, one normally closed circuit and one normally open circuit. Relays are also designed according to the frequency the contacts are operated. There are continuous duty relays. These relays can be on for long periods of time without causing damage to the relay, but should not be turned off and on rapidly in a short period of time. There are intermittent duty relays. These relays are designed to be cycled off and on while being used. It is important that the correct relay is used and although they look similar, one relay maybe continuous duty and the other intermittent duty. Our relays should not be confused with the Ford starter relay or other relays of that type.
RELAY CONTACTS (NO) RELAY COIL M Figure 21 We use relays for many different purposes. We use them to switch large amounts of current that a manual switch or a computer processor will not handle. They are used to send information to computer processors from limit switches or warning switches. They can also be used as a safety switch to interrupt a process that is reaching a critical condition that could create a system or component failure. Many of the relays we use are pc board mounted and are not field serviceable. The main relays we use that are serviceable are on the hydraulic pump motors and on our air compressor assemblies. There are two different types of relays used on the hydraulic pump motors, a continuous duty and an intermittent duty relay. The continuous duty relay is only used with automatic, computerized systems. This relay is called the master relay. Systems that do not use a hydraulic pump may have a master relay. It may be mounted in a control box or remote from the control box. System diagrams or schematics will supply this information. The intermittent duty relay is called the pump relay and is used with any system that has a hydraulic pump motor. The relay used on air compressor assemblies is a continuous duty relay. All three of these relays have normally open contacts. The coil of all pump and air compressor relays is controlled with a + signal except for the pump relay on 400 series leveling systems and 200 series Joystick leveling systems. A switched ground controls these relays. Safety and other relays may be controlled by either a + voltage or ground signal. You should always check system diagrams and/or schematics to determine the control signal for a relay. We use a small Bosch relay as a safety switch with all four cylinder and other pressure sensitive room extension mechanisms. This relay is normally mounted on the pump motor. The Bosch relay can be wired as a normally open or normally closed relay. Check specific system wiring diagrams for use and orientation of the relay contacts. 4-3.1 Relay diagnostics. Before doing the actual diagnostics, it is important to know a few things about the relay and the circuit it is in. Are you switching + voltage or ground? Is the relay a normally open or normally closed relay? Is the relay coil controlled with a switched + voltage or a ground? Most of the relays we use draw less than 1 or 2 amps so operating a relay does not create much of a load, a test light will usually do most of the diagnostics needed or at least give you the basic answers to the tests for relay diagnostics. When helping someone diagnose a relay problem, one statement I frequently get is; my test light will come on when I touch either of the coil terminals. You need to remember that a coil is just one long wire wrapped around a metal rod. If there is + voltage on both relay coil terminals there is no ground for the coil. If there is a ground on both relay coil terminals, there is no + voltage to the coil of the relay. GND +12 VOLTS COIL COIL +12 VOLTS GND +12 VOLTS +12 VOLTS Figure 22
Most of our relays should pull in at a minimum of seven to eight volts and stay on with less voltage. If a relay is chattering or drops out after energizing, the problem is most likely voltage. A chattering relay will cause the relay contacts to stick or burn out. Remember, the ground for the relay could be the problem as easily as the + voltage could be the problem. Whether it is a voltage problem or a grounding problem, low voltage will ruin a relay quicker than most other issues. Also a very common problem with the relays on the pump is loose connections or corrosion. An easy way to test a connection is with a voltmeter. The relays must be on and the pump motor should be running. (This method can be used to test any connection as long as the load for that connection is on.) Put one lead of the meter on the relay post and the other lead on the wire terminal. The meter should show zero voltage. Any voltage reading would indicate an unwanted resistance at the connection. Finally, there should be zero voltage drop between the input and output posts of a relay. GOOD CONNECTION 0.00 RELAY POST WIRE TERMINAL WEAK CONNECTION 0.26 DC VOLTMETER + VOLTAGE FROM BATTERY PUMP RELAY Figure 23 + VOLTAGE TO PUMP MOTOR (MOTOR RUNNING) DC VOLTMETER Connections can also be tested by comparing the voltage at the post to the voltage at the wire terminal. The voltage should be the same when the exact same ground point is used to check the voltage. The main ground point for the system should be used when testing connections this way. The load needs to be running for this test procedure also. Normally open (NO) relay diagnostics. If the relay will not turn on (close the contacts), the following tests should be made. These tests are made with the relay on. This is where a test light will give you the basic answers you are looking for. It is always a good idea to check your test light with a known good voltage and ground source to verify that your test light is working. I speak from experience. 1. Is there + voltage (or ground) to the supply (or input) side of the relay? 2. Is there + voltage to one of the coil terminals of the relay? 3. Is there ground to the other coil terminal of the relay? 4. If 1, 2, and 3 are yes, is there + voltage (or ground) to the output (switched) side of the relay? #2 SOURCE CONTROL BOX #1 SOURCE #3 SOURCE INPUT #1 #2 PUMP RELAY (NO) COIL AND OUTPUT #4 OUTPUT PUMP MOTOR +12 VOLTS #3 COIL GROUND Figure 24 As always, it is a matter of using the process of elimination. If the answer to #1 is no, there is no + voltage or ground to the supply side of the relay, check that source. If the answer to #1 is yes, check #2 then #3. If the answer to #3 or #4 is no, check their source. If the answer to #2 and #3 is yes, go to #4. If the answer to #4 is yes, the relay is good. If the answer is no, there is no voltage (or ground) on the output side of the relay, the relay is bad.
Diagnosing a normally closed relay that is on (contacts closed) at all times is easy to diagnose. All that needs to be done is to remove the control wire or check the control wire for + voltage or ground, whichever is used to control the relay coil. If the control voltage or ground is not present or the control wire is removed and the relay stays on, the relay is bad. It is important to note that sometimes the relay contacts will open if the relay is tapped. It may not take much of a tap to cause the contacts to open. If the relay suddenly starts to function properly after being tapped, it was probably stuck contacts in which case the relay should be replaced. Normally closed (NC) relay diagnostics. Diagnosing a normally closed relay is much the same as diagnosing the normally open relay. You just are looking for some different answers as you perform the tests. When diagnosing a relay that will not turn on, (open the contacts) you start by tuning the relay on to perform the tests. 1. Is there + voltage (or ground) to the supply (input) side of the relay? 2. Is there + voltage to one of the coil terminals of the relay? 3. Is there ground to the other coil terminal of the relay? 4. Is there + voltage to the output side of the relay? PRESSURE SWITCH #3 SOURCE OUTPUT COIL GROUND INPUT BOSCH RELAY (NC) #3 #4 #2 #1 COIL VOLTAGE PUMP RELAY PUMP MOTOR #1 AND #2 SOURCE CONTROL BOX Figure 25 Check #1. If the answer to #1 is no, there is no + voltage (or ground) to the supply side of the relay, check its source. If the answer to #1 is yes, check #2 then #3. If the answer to either is no, check the source for that terminal. If #2 and #3 are answered yes, check #4. (Here is the difference between a normally open and normally closed relay.) If the answer to #4 is yes, the relay is bad. If the answer is no, the relay is good. As with a normally open relay, if the contacts of a normally closed relay will not close, remove the control voltage or ground from the relay. If the contacts remain open, the relay is bad. When diagnosing any relay, it is important to remember that the wire connections to the relay may be the issue and not the relay. Many relays are changed because of a miss-diagnosed problem. A weak connection can seem to be a bad relay. When the relay is replaced, the problem is fixed, not because the relay is bad, but because the connections are fixed when the relay is replaced. When diagnosing a relay using the diagnostic procedure discussed above, put the probes of the test light or meter on the relay posts, not the wire terminals. If connections are weak, that will show up when testing. 4-4 FUSES are an important control device in any electrical system. Fuses are use to protect wiring and components from damage or fire by protecting wires and components from over heating due to excessive current draw because of a faulty component, circuit overload or a short. A fuse, very simply, creates a break in the circuit when its current rating is exceeded. We have used many different types of fuses over the years. We have used automatic circuit breakers, automotive glass fuses, large blade fuses, standard size automotive blade fuses, the newer mini-blade fuses, buss type fuses and poly fuses. The circuit breakers and large blade fuses are no longer used. The poly fuses are only used on pc boards in control boxes or panels. Glass, buss and blade fuses have a conductor that burns and creates a break in the circuit when the current rating of the fuse is exceeded. Circuit breakers have contacts that will open when the current rating of the breaker is exceeded. +12 VOLTS