The battery as power source

Transcription

1 TECHNICAL BACKGROUND The battery as power source There are differet kids of rechargeable batteries. The most commo type is the lead acid battery. A less familiar oe is the ickel-cadmium (NiCad) battery, which ca still ofte be foud i old emergecy power systems. Due to the high charge voltage required by a NiCad battery, ad the fact that they are very evirometally ufriedly, these batteries are ot suitable for use oboard a vessel or car/truck. Priciple of the lead acid battery A battery is a device that stores electric power i the form of chemical eergy. Whe ecessary, the eergy is agai released as electric power for DC cosumers such as lightig ad starter motors. A battery cosists of several galvaic cells with a voltage of 2 Volt each. For a 12 Volt battery, six cells are liked i series ad fitted iside a sigle casig. To achieve 24 Volt, two 12 Volt batteries are liked i series. Each cell has positive oxidised lead plates ad egative lead metal plates, ad has a electrolyte cosistig of water ad sulphuric acid. Durig dischargig, the lead oxide o the lead plates is coverted ito lead. The acid cotet decreases because sulphuric acid is required for this process. To recharge the battery, a exteral power source - such as a battery charger, alterator or solar pael - with a voltage of aroud 2.4 V per cell must be coected. The lead sulphate will the be coverted back ito lead ad lead oxide, ad the sulphuric acid cotet will rise. There are limits set for the charge voltage to prevet the release of a excessive amout of hydroge. A charge voltage of more tha 2.4 V per cell, for istace, releases a lot of hydroge gas, which ca form a highly explosive mixture with the oxyge i the air. The upper limit o charge voltage for a 12 V battery is 14.4 V, ad the correspodig value for a 24 V battery is 28.8 V at 20 C. The relatioship betwee how full a battery is ad the specific gravity of the water/sulphuric acid mixture is as follows: percetage charged battery voltage Differet types of battery - i terms of the thickess ad umber of plates per cell - correspod to differet applicatios. The maximum curret that ca be delivered is determied by the total plate surface. The umber of times that a battery ca be discharged ad recharged - the umber of cycles - depeds o the thickess of the plates. A battery ca feature either may thi plates or a few thick oes. specific gravity percetage discharged 0% V ± 100% 20% V ± 80% 40% V ± 60% 60% V ± 40% 80% V ± 20% 100% V % The starter battery A starter battery has may thi plates per cell, leadig to a large total plate surface. This type of battery is, therefore, suitable for deliverig a high level of curret over a short period of time. The umber of times that a starter battery ca be heavily discharged is limited to aroud But as startig the egie uses oly a small part of the eergy stored (aroud 0.01%), the battery lasts for may years. This type of battery is geerally usuitable for cyclic use. 174

2 BATTERIES The Lithium Io battery Util recetly Lithium Io batteries were maily available as chargeable batteries with a small capacity, which made them popular for use i mobile phoes ad laptops. Mastervolt offers Lithium Io batteries with large capacities. Our Lithium Io batteries have a high eergy desity ad are perfect for cyclic applicatios. Compared to traditioal lead acid batteries, Lithium Io batteries offer savigs of up to 70% i volume ad weight, while the umber of chargig cycles is three times higher, compared to semi-tractio lead acid batteries. A added beefit is that Lithium Io batteries ca supply a costat capacity, regardless of the coected load. The available capacity of a lead acid battery is reduced i case of higher discharge currets. Lithium Io batteries ca be discharged to 80% without affectig their lifespa, whereas lead acid batteries are more affected by deep discharge. Lasts loger Lithium Io batteries also offer major beefits compared to ickel-cadmium batteries, such as a much larger power desity ad a loger lifespa. Ad because lithium is the lightest metal, Lithium Io batteries are also more lightweight. They ca also be charged at ay time, while ickel-cadmium batteries require complete discharge for a optimal performace ad to prevet memory effect. Furthermore, Lithium Io batteries ca be charged with a very high curret, up to 100% of the capacity, resultig i a very short chargig time ad o memory effect. Battery Maagemet System Mastervolt Lithium Io batteries are equipped with a Battery Maagemet System that automatically compesates for the imbalace betwee the cells ad icreases the lifespa. The tractio battery (Mastervolt does ot have this type of batteries i its portfolio) The semi-tractio battery This type of battery has eve fewer, but very thick, flat or cylidrical plates. It ca therefore be discharged may times ad fairly completely ( full cycles). This is why wet tractio batteries are ofte used i forklifts ad small electrical equipmet such as idustrial-grade cleaig machies. But wet tractio batteries require a special charge method. Because these batteries are mostly tall, they are sesitive to the accumulatio of sulphuric acid at the bottom of the battery cotaier. This pheomeo is called stratificatio ad occurs because sulphuric acid is deser tha water. Acid cotet icreases i the lower part of the battery, locally itesifyig plate corrosio, ad decreases i the upper part, reducig capacity. The battery is discharged uevely, sigificatly reducig its lifespa. I order to spread out the acid evely agai, the battery has to be purposefully overloaded usig excessive voltage. This geerates a large amout of hydroge gas, which will form a dagerous mixture with oxyge i the air. The voltage required to recharge these batteries is aroud 2.7 Volt per cell, or 16.2 Volt for a 12 V system ad 32.4 Volt for a 24 V system. These high levels of voltage are extremely dagerous for the coected equipmet ad the large amout of gas geerated makes these batteries usuitable for use i vessels ad vehicles, except for propulsio. A semi-tractio battery has fewer but thicker plates i each cell. These batteries supply a relatively lower starter curret, but ca be discharged more ofte ad to a greater extet (200 to 600 full cycles). This kid of battery is highly appropriate for the combied fuctio of starter ad service battery. 175

3 TECHNICAL BACKGROUND Frequetly asked questios about batteries How log will it take before my battery is discharged? This depeds o its capacity ad the amout of power cosumed by the coected equipmet. As a rule, the faster a battery is discharged, the less power it supplies. This also works the other way aroud: The loger it takes before a battery discharges, the more eergy you ca get from it. A 100 Ah lead-acid battery supplies a curret of 5 amps for 20 hours, durig which time the voltage does ot drop below 10.5 Volt. This amouts to 100 Ah. If a load of 100 amps is coected to the same battery, the battery will be able to power it for oly 45 miutes. After this time the battery voltage will fall to 10.5 Volt ad the battery will be empty, havig supplied o more tha 75 Ah. I cotradictio to the lead-acid batteries, the capacity of Lithium Io batteries will ot be effected by the load coected. A Li-io battery will always supply 100% capacity, idepedet of the coected load. What is series coectio ad parallel coectio? A series coectio is used to icrease voltage, while keepig capacity at the same level. Two serially coected 12 V/120 Ah batteries make a combied battery set of 24 V/120 Ah. I a series coectio, the positive pole of oe battery is coected to the egative pole of the other, with the poles that remai at the eds beig coected to the system. Batteries with differet capacities should ever be liked i series. Examples The examples below apply to the use of ormal 12 V batteries. Mastervolt also supplies 2 V, 6 V ad 24 V batteries; the priciple of series ad parallel coectig remais the same. Series coectio Series coectio 24 V/200 Ah. Series coectio 48 V/200 Ah. How log will my battery last? The lifespa of a battery is related to how ofte ad to what extet it is discharged. Proper chargig with the right charger is also crucial. At a ormal use for holidays ad weekeds, a lifespa of betwee five ad seve years is quite commo for gel ad AGM batteries. Whe batteries are frequetly discharged you will eed to adjust the capacity. There is also a optio to use 2 Volt cells. A lifespa of 15 years is ot exceptioal for this type of battery as log as they have the right capacity ad are properly charged. Lithium Io batteries are top of the bill. You ca discharge ad recharge them super fast ad they last up to three times as may cycles tha other types of batteries. 176 Parallel coectio Parallel coectio is used whe you eed to icrease your capacity. The positive leads are coected together, as are the egative leads. The cablig from the battery to the system should be: Positive from battery 1 ad egative from battery 2 (or the last i the parallel coectio). Series/parallel coectio If you eed a 24 V battery set with a higher capacity, you ca combie series ad parallel coectios. The cables from the battery to the system must be crossed: Positive from battery 1 ad egative from battery 2 (or the last i the parallel coectio). Make sure there is sufficiet space betwee the batteries whe istallig multiple batteries: There should be a figer of space betwee them to allow the heat to be diverted. Parallel coectio 12 V/400 Ah. Series/parallel coectio 24 V/400 Ah.

4 BATTERIES What NOT to do with batteries, especially gel ad AGM Icorrect charge voltage. Too low a voltage meas that the battery caot charge to 100% - the sulphate the hardes o the plates ad the battery loses its capacity. Excessive voltage causes the batteries to geerate gas, leadig to water loss ad dryig out. Excessive dischargig. Dischargig a battery further tha its capacity shortes its lifespa. Too large ripple o the charge voltage. Cheap ad old-fashioed chargers ofte have a sigificat voltage ripple (voltage variatio) i the output voltage. The use of a alterator without 3-step regulator, a high ambiet temperature or chargig without temperature compesatio. Ca I leave the batteries oboard durig witer? This is fie for all batteries as the lower temperature will actually prolog their lifespa. Remember to charge the batteries completely ad to esure that o cosumers are left o. Voltmeters, timers ad car radio memory are some of the stealthy cosumers to look out for i this respect. Wet batteries have to be regularly topped up ad charged to avoid freezig. It is advisable to coect the power oce every two to three weeks so the batteries ca be fully recharged. If you do ot have access to power durig the witer we advise you to fully charge the batteries before the witer ad the discoect the battery poles so small users caot discharge your battery. We also advise chargig your battery every two moths. How should I maitai gel, AGM ad Lithium Io batteries? Gel, AGM ad Lithium Io batteries do ot eed maiteace, which meas they ca be istalled aywhere. However, we recommed checkig all the coectios oce a year to make sure that they are properly attached, ad to clea the top surfaces with a slightly moist cloth. The batteries also eed to be completely charged every time for a maximum lifespa. What are maiteace-free batteries? Various types of batteries are used, each with its ow specific characteristics. Here is a summary: The gel battery With wet lead acid batteries, that use a liquid electrolyte of water ad sulphuric acid, the water is seperated ito hydroge ad oxyge durig chargig, mostly at the ed of the chargig cycle. These gases subsequetly escape through the filler cap. This meas water is used ad distilled (battery) water eeds to be added.the electrolyte i a gel battery is a gel that bids the water with the acid. While the batteries are beig filled, the gel is heated ad liquefies. After the battery has bee filled with the liquefied gel, the gel cools ad solidifies. This process results i tiy hairlie cracks i the gel betwee the plates. Durig the chargig process, oxyge O 2 is geerated o the positive plate ad hydroge H 2 o the egative plate. The cracks i the gel let the gases combie to create water. The gel the absorbs the water so that o water disappears from the system ad o gases are produced. Gel batteries are ot a ew techology ad have bee i use sice the late 1950s. The most importat applicatios are i emergecy power systems, telecommuicatios systems, power supply ad, for the last years, as service batteries i various systems. Gel batteries come i two differet versios. The 12 Volt desig is appropriate for regular use ad available i capacities up to 200 Ah. The secod desig is a 2 Volt tractio battery, available i capacities up to 2700 Ah ad highly suitable for systems with frequet ad sigificat dischargig where a log lifespa is eeded. For a battery of 12 or 24 Volt, six or twelve gel batteries eed to be coected i series to provide the required voltage. Major beefits of gel batteries iclude very limited self-dischargig, the possibility of a short chargig time, ad the lack of gas productio uder ormal circumstaces. All of this makes gel batteries very suitable for heavy cyclical applicatios. 177

5 TECHNICAL BACKGROUND The AGM battery A differet type of lead acid battery is the AGM (Absorbed Glass Mat) battery. I this model, the electrolyte (water ad sulphuric acid) is absorbed ito a extremely delicate glass fibre mat. Just like with ay other battery, chargig geerates hydroge gas ad oxyge, which are trasported through the capillary tubes of the glass fibre mat. Oce the two gases are recombied, water is oce agai obtaied ad subsequetly reabsorbed ito the glass fibre mat. The recombiatio process is the complete. The glass fibre mat also serves as isulatio betwee the plates, allowig the plates to be close together ad leadig to very low iteral resistace. This meas that a high discharge curret is o problem. The charge curret could be a little lower tha with gel batteries (approx. 30%) because the glass fibre mat is also a efficiet heat isulator, ad heat geerated by chargig is gradually coducted to the outside of the case. This requires the charge curret to be somewhat restricted ad results i a slightly loger chargig time. AGM batteries are highly suitable for applicatios requirig a high discharge curret, such as a bowthruster or wiches ad for medium cycle use. The AGM battery is etirely closed ad therefore maiteace free. If the AGM battery is overcharged, for istace due to the use of a (cheap) uregulated battery charger, a small amout of hydroge gas is formed. This gas escapes through a special vet i the battery casig that is desiged to prevet oxyge from eterig the battery. Icorrect chargig will reduce the battery s lifespa. Coclusios ad recommedatios The low iteral resistace of AGM batteries makes them highly suitable for powerig wiches, widlasses ad bowthrusters, for startig egies, ad for limited cyclic use. The Lithium Io battery Mastervolt s Lithium Io batteries are based o Lithium Io iro phosphate, which has a eergy desity of three times higher tha that of lead acid batteries. Although there are materials with a eve higher eergy desity, these are geerally cosidered less safe. Mastervolt s Lithium Io batteries are the safest batteries of their kid. A uique feature is their built-i Battery Maagemet System (BMS). The system cotrols cell voltage ad temperature, ad guaratees optimal safety. Lithium Io batteries are MasterBus compatible ad up to 15% more efficiet tha lead acid batteries. This gives you: Shorter chargig times. Less geerator time required for chargig. More power tha from a traditioal battery of the same dimesios. A ormal ope lead acid battery, for example, has a DOD (depth of discharge) of 50%. This meas that you ca oly use up to 200 Ah from a 400 Ah battery. A Mastervolt Lithium Io has a DOD of 80%, almost 60% more usable battery capacity. With this percetage, a battery of 400 Ah supplies 320 Ah, or 120 Ah more. Lithium Io batteries are also ideal for electric ad hybrid propulsio. Mastervolt Lithium Io batteries ca be paralleled up to te uits. Aother beefit is that Lithium Io batteries weigh less ad require less space. Gel batteries are very suitable as service batteries due to the fact that they ca be quickly charged ad have a log lifespa, eve with may charge/ discharge cycles For a service battery you ca choose for either a 6 Volt, 12 Volt or 24 Volt versio or the 2 Volt model. Mastervolt batteries are completely maiteace free ad i ormal circumstaces do ot release acid or geerate dagerous gas. They are easy to istall aywhere oboard, such as ext to the bilge or i the egie room (reduced lifespa due to higher temperatures). Special battery cases or exteral vetilatio is usually uecessary as atural vetilatio will suffice. Lithium Io batteries save up to 70% i space ad weight, last three times loger ad ca be recharged ad discharged very quickly, 2000 charge cycles is o exceptio. 178

6 BATTERIES Determiig lifespa The average lifespa of a 12 Volt gel or AGM battery is up to six years if the battery remais uused ad is kept i a charged state. After five or six years of float voltage at a average ambiet temperature of 25 ºC, the battery still retais 80% of its origial capacity. Higher average temperatures will shorte the lifespa of the battery. The umber of charge ad discharge cycles of a 12 Volt battery is strogly correlated to its structure ad quality. Mastervolt s 12 Volt gel batteries ca take aroud 500 full cycles of beig discharged dow to 20% ad charged back to full capacity. Most maufacturers cosider batteries to be spet at a remaiig capacity of 80%. This does ot, however, mea that the battery has to be replaced immediately. For example, the battery ca still be used if oly 50% of the battery capacity is actually required. It is therefore ot ecessary to replace the battery after six years or 500 full cycles. A average use of seve years is perfectly ormal for 12 Volt gel batteries. 2 Volt tractio gel batteries The lifespa for 2 Volt tractio gel cells is aroud 10 to 15 years ad the maximum umber of full cycles is whe dischargig to 20% of capacity. These batteries are therefore highly suitable for larger systems that require itesive use ad a very log lifespa. Lithium Io batteries Mastervolt Lithium Io batteries have a lifespa of more tha 2000 cycles, which is three times loger tha most stadard lead acid batteries. This ca be attributed to a wide rage of features icludig cell maagemet, the egligible self discharge, the absece of memory effect ad a discharge to 20%. Trasport Trasportatio of Mastervolt gel ad AGM batteries Mastervolt gel ad AGM batteries are cosidered as o-spillable batteries. This meas that they ca be trasported as o-dagerous goods as they are exempt from Dagerous Goods Regulatios which cover trasport by road, rail, sea freight or air cargo. So they ca be set to ay destiatio i the world quickly ad relatively cheaply. Trasportatio of Mastervolt Lithium Io Ultra batteries Extra care is to be take for proper trasport of Lithium Io batteries. Mastervolt s Lithium Io batteries ad their packagig have udergoe all the required safety testigs as prescribed by the Uited Natios ad the trasport authorities (both road, rail, sea ad air) to achieve this. Below you will fid the techical details of what this meas. The Mastervolt Lithium Io batteries have bee tested accordig to UN Hadbook of Tests ad Criteria, part III, sub sectio 38.3 (ST/SG/ AC.10/11/Rev.5). For trasport the batteries belog to the category UN3480, Class 9, Packagig Group II ad have to be trasported accordig to this regulatio. This meas that for lad ad sea trasport (ADR, RID & IMDG) they have to be packed accordig to packagig istructio P903 ad for air trasport (IATA) accordig to packagig istructio P965. The origial packagig of the Mastervolt Lithium Io batteries satisfies these istructios. 179

7 TECHNICAL BACKGROUND 3-Step+ chargig This moder chargig techology allows a battery to be quickly ad safely charged i three phases (steps). The first step is the BULK PHASE, i which the battery is charged quickly. The output curret of the battery charger is at maximum (100%) durig this phase ad the battery voltage depeds o the chargig degree of the battery. The duratio of this phase depeds o the ratio of battery to charger capacity, ad o the degree to which the batteries were discharged to begi with. The bulk phase is followed by the ABSORPTION PHASE, which begis oce a battery has bee charged to ± 80% (90% for gel ad AGM batteries), ad eds whe the battery is completely full. Battery voltage remais costat throughout this stage, ad the chargig curret depeds o the degree to which the battery was iitially discharged, the battery type, the ambiet temperature, ad so o. With a wet battery this phase lasts some four hours, with gel ad AGM batteries aroud three. This does ot apply to Lithium Io batteries as these are charged to 100% with full curret. Oce the battery is 100% charged, the Mastervolt charger automatically switches to the FLOAT PHASE. I this step, the batteries are kept i optimal coditio ad the coected users are supplied with power. If power cosumptio is higher tha ca be supplied by the battery charger, the remaiig power is supplied by the battery. The battery is the (partly) discharged ad the charger automatically switches back to the bulk phase. If cosumptio is reduced, the charger will start chargig the battery agai via 3-step+ chargig. A battery charger with 3-step+ chargig ca remai coected to the battery, eve i witer, ad esures a log lifespa for your batteries as well as beig safe for the coected equipmet. Absorptio time The duratio of the secod phase i the chargig of a battery. The battery will, i geeral, be charged from 80 to 100% durig this phase, which lasts aroud four hours with a wet lead battery, ad three hours with gel ad AGM batteries. With Lithium Io batteries the absorptio time is very short as they ca be charged to 100% with full curret. This phase is automatically set for Mastervolt battery chargers. 3-Step+ chargig characteristic (IUoUo) 180

8 3 STEP+ CHARGING Charge factor The charge factor idicates the efficiecy of a battery. The efficiecy of the average wet battery is approx. 80%, which meas it must be recharged 1.2 times the evetual capacity i Ah to get the same capacity. This traslates ito a charge factor of 1.2. The lower the charge factor or the higher the battery efficiecy, the better the quality. Mastervolt s gel ad AGM batteries have a efficiecy of > 90% ad a low charge factor of 1.1 to 1.15 ad offer the very best quality. Discharge factor This is also kow as Peukert s Law, ad allows you to determie how log a battery ca be used at a give load before it eeds rechargig. Cycle A battery oly lasts a certai umber of charge/discharge cycles, depedig o its type ad quality. I theory oe charge/discharge cycle is the process of dischargig a battery to 0% of capacity ad rechargig it back to 100%. Twice rechargig after dischargig to 50% is also oe cycle, as is four times dischargig to 75% ad rechargig. A starter battery, for istace, ca take aroud 50 to 80 cycles, which may seem little but is i practice more tha sufficiet: While the curret used for startig a egie is high, it oly lasts a short time ad represets of a cycle. I other words, a egie ca be started 80,000 times before a battery is wor out. A high-quality semi-tractio battery lasts for aroud 250 to 300 cycles. If the battery is oly discharged to 50% of capacity, 600 cycles are available. Assumig 25 weekeds of sailig (50 days) plus 20 days of holiday ad dischargig oly to 50%, the battery will go through 70 half cycles or 35 full cycles. 181

9 TECHNICAL BACKGROUND Chargig batteries Charge voltage Gel (12 ad 2 Volt) ad AGM (6 ad 12 Volt) batteries eed to be charged with a voltage of 2.4 Volt per cell at a temperature of 25 ºC. For a 12 Volt battery set, this correspods to 14.4 Volt, ad for a 24 Volt battery set to 28.8 V. The maximum time that a battery ca be charged at this voltage is four hours, after which the voltage has to be reduced to 2.2 Volt per cell, or ad 26.5 Volt, respectively. Lithium Io batteries eed to be charged with a voltage of 29.2 Volt for a 24 Volt system ad 14.6 Volt for a 12 Volt system. The float voltage is 26.5 ad respectively. With emergecy power systems, where gel batteries ca be i float coditio for log periods of times (years), the float voltage eeds to be slightly icreased to 13.8 ad 27.6 respectively at a temperature of 25 ºC. Mastervolt supplies DC-DC coverters that regulate the oboard voltage to a lower level (13.8 or 27.6 Volt) thus esurig that (haloge) lamps do ot fail durig chargig. The charge curret A rule of thumb for gel ad AGM batteries states that the miimum charge curret should be 15 to 25% of the battery capacity. Coected equipmet usually also eeds to be powered durig chargig, so iclude the power used for that purpose i the abovemetioed figure. This meas that, with a battery set of 400 Ah ad a coected load of 10 amps, battery charger capacity has to be betwee 70 ad 90 amps i order to charge the battery i reasoable time. The maximum charge curret is 50% for a gel battery ad 30% for a AGM battery. For a Lithium Io battery the charge curret ca be the same as the capacity. A 180 Ah Lithium Io battery, for example, ca be recharged with 180 amps. The charge system Esurig the logest possible lifespa for gel, AGM ad Lithium Io batteries requires a moder battery charger with 3-step+ chargig ad a sesor for measurig battery temperature. These battery chargers will costatly regulate charge voltage ad charge curret ad adapt the charge voltage to the battery temperature. As there is always equipmet oboard such as refrigerators that draw power from a battery eve whe it is beig charged, a maximum charge voltage has bee set to protect the coected appliaces. This maximum is Volt for a 12 Volt system ad 29.1 Volt for a 24 Volt system, which is also the charge voltage applicable at a ambiet temperature of 12 ºC. Mastervolt s moder battery chargers come with a temperature sesor for attachig to the battery, which allows the charger to automatically regulate the charge voltage i accordace with battery temperature. Adjustig voltage to high or low temperatures is ot ecessary with Lithium Io batteries. I order to prevet premature failure of the battery, the ripple voltage of the battery charger has to stay below 5%. If the battery also powers avigatio or commuicatio equipmet such as GPS or VHF, the ripple voltage must be less tha 100 mv (0.1 Volt) or problems may occur with the equipmet. Aother advatage of a low ripple voltage is that oboard power systems will ot be damaged if a battery pole is corroded or icorrectly attached. A low ripple voltage eve allows the charger to power the system without beig coected to a battery. Mastervolt chargers are, of course, all equipped with a excellet voltage regulatio that keeps ripple voltage below 100 mv. For GMDSS (Global Maritime Distress Safety System) systems oboard larger ocea-goig vessels, the battery charger also ca be equipped with a amps ad voltmeter plus a alarm cotact. The alarm cotact is coected to the ship s alarm system so that ay iterruptios to the operatio of the charger due to a cut i the 230 Volt supply, for istace are detected o time. The optioal Mass Charger Iterface makes Mass chargers very suitable as GMDSS chargers. 182

10 CHARGING BATTERIES Calculatig chargig time Various factors have to be take ito accout whe calculatig the chargig time for a battery. The first cosideratio is battery efficiey. With a stadard wet battery, efficiey is about 80%. This meas that 120 Ah has to be charged ito the battery i order to be able to draw 100 Ah later. With gel, AGM ad Lithium Io batteries the efficiey is higher - 85 to 90% - so there is less losses ad chargig time is shorter compared to wet batteries. Aother issue that has to be cosidered whe calculatig chargig time is the fact that the last 20% of the chargig process (80-100%) takes ± four hours (this does ot apply to Lithium Io batteries). I the secod stage, also kow as the absorptio phase, the battery dedicates how much curret it eeds to absorb idepedetly of the output of the battery charger. The followig formula ca be used to calculate the chargig time of a gel or AGM battery: The amout of power depeds o the type of battery (wet, AGM, gel or Lithium Io) ad other factors such as the extet to which it was charged to begi with, temperature, lifespa ad the ambiet temperature. Lt = Co x eff Al - Ab + 4h 25 ⁰C referece temperature Lt = chargig time Co = capacity draw from the battery eff = efficiecy; 1.1 for a gel battery, 1.15 for a AGM battery ad 1.2 for a wet battery Al = battery charger curret Ab = cosumptio of the coected equipmet durig the chargig process Takig a battery that is discharged to 50% ad applyig the example of a 400 Ah gel battery ad a 80 amps charger, chargig up to 100% will take: chargig voltage i V float absorptio Lt = 200 x 1, h 7h battery temperature i ⁰C Temperature compesatio curve 183

11 TECHNICAL BACKGROUND Checkig the remaiig capacity of a sealed AGM or gel battery The simplest way to check the remaiig capacity or coditio of a battery is with a Ah meter, such as Mastervolt s MasterShut or BTM-III battery moitor. I additio to charge ad discharge curret, the moitor also tracks battery voltage, the umber of amp-hours cosumed ad how much loger the battery has before it eeds rechargig. The device also provides data o how ofte the battery has bee discharged ad to what extet, with both the average ad highest discharge level show. The MasterShut is easy to coect to the MasterBus etwork ad, with its itegrated system clock combied with commad-based evets, you ca program the system to your preferece. Peukert s Law O the surface it seems easy to calculate how much loger a battery will cotiue to supply sufficiet power. Oe of the most commo methods is to divide battery capacity by discharge curret. I practice, however, such calculatios ofte tur out to be wrog. Most battery maufacturers specify battery capacity assumig a discharge time of 20 hours. A 100 Ah battery, for istace, is supposed to deliver 5 amps per hour for 20 hours, durig which time voltage should ot drop below 10.5 Volt (1.75 V/cell). Ufortuately, whe discharged at a curret level of 100 amps, a 100 Ah battery will deliver oly 45 Ah, meaig that it ca oly be used for less tha 30 miutes. This pheomeo is described i a formula Peukert s Law - devised more tha a cetury ago by the battery pioeers Peukert (1897) ad Schroder (1894). Peukert s Law describes the effect of differet discharge values o the capacity of a battery, i.e. that battery capacity is reduced at higher discharge rates. All Mastervolt battery moitors take this equatio ito accout so you will always kow the correct status of your batteries. Peukert s Law does ot apply for Lithium Io batteries as the coected load will have o effect o the available capacity. A differet but very imprecise method of checkig your battery is to measure the voltage, which ca oly be doe whe the battery has ot bee used (discharged) or charged for at least 24 hours. While measurig voltage provides a rough estimatio of how discharged a battery is, small variatios i voltage make a accurate digital voltmeter essetial. The Peukert formula for battery capacity at a give discharge curret is: Cp = I t Cp = battery capacity available with the give discharge curret remaiig battery capacity battery voltage 25% betwee 11.7 ad 12.3 Volt 50% betwee 12.0 ad 12.6 Volt 75% betwee 12.1 ad 13.0 Volt 100% betwee 12.6 ad Volt I = the discharge curret level log T2 - logt1 = the Peukert expoet = log I1 - log I2 T = discharge time i hours This method is oly 15-20% accurate ad gives a rough idicatio of the power remaiig i the battery. I1, I2 ad T1, T2 ca be foud by carryig out two discharge tests. This ivolves draiig the battery twice at two differet curret levels. Oe high (I1) - 50% of battery capacity, say - ad oe low (I2) - aroud 5%. I each of the tests, the time T1 ad T2 that passes before battery voltage has dropped to 10.5 Volt is recorded. Carryig out two discharge tests is ot always simple. Ofte, o large load will be available or there will be o time for a slow discharge test. 184

12 CHARGING BATTERIES Vetilatio Uder ormal coditios, gel, AGM ad Lithium Io batteries produce little or o dagerous hydroge gas. The little gas that escapes is egligible. However, just like with all other batteries, heat is geerated durig chargig. To esure the logest possible lifespa, it is importat for this heat to be removed from the battery as quickly as possible. The followig formula ca be used to calculate the vetilatio required for Mastervolt battery chargers. Q = Q = 0.05 x I x f1 x f2 x required vetilatio i m³/h I = maximum charge curret of the battery charger f1 = f2 = 0.5 reductio for gel batteries 0.5 reductio for closed batteries = umber of cells used (a 12 Volt battery has six cells of 2 Volt each) Returig to the example of a 12V/400Ah battery set ad a 80 amps charger, the miimum vetilatio ecessary will be: Q = 0.05 x 80 x 0.5 x 0.5 x 6 = 6 m³/h This air flow is so small that ormally atural vetilatio will be sufficiet. If the batteries are istalled i a closed casig, two opeigs will be eeded: Oe o the top ad oe udereath. The dimesios of the vetilatio opeig ca be calculated usig the followig formula: A = 28 x Q A = opeig i cm² Q = vetilatio i m³ I our case, this amouts to 28 x 6 = 168 cm² (aroud 10 x 17 cm) for each opeig. Lithium Io batteries do ot produce ay hydroge gas ad are therefore safe to use. Whe batteries are charged quickly there is some degree of heat productio, i which case the above formula ca be used to remove the heat. Cotact your istaller for larger systems with multiple battery chargers. 185