pjcoleman Posted January 17, 2013 Share Posted January 17, 2013 Can someone tell me if starter batteries and leisure batteries have to have the same Ah? They both receive a charge from the same alternator. I would like to install a new leisure battery with a greater Ah. Change from 85Ah to 105Ah. Link to comment Share on other sites More sharing options...
lennyhb Posted January 17, 2013 Share Posted January 17, 2013 No, within reason you can fit whatever leisure battery you want. The leisure battery only receives a small portion of the alternator output. As larger leisure battey will just take longer to charge. Link to comment Share on other sites More sharing options...
Brambles Posted January 18, 2013 Share Posted January 18, 2013 Sorry Lenny, not strictly true a larger battery wil take longer to charge. The charge rate is dependant on the voltage supplied and the capacity of the battery, limited only by the power the alternator can output. As the alternator is capable of many times more power then the charge rate of the batteries, it can be all but ignored. So if you say, double the leisure battery capacity it will charge at approximatly twice the current and charge in the same time as half the capacity. There wil be a slight effect because of volt drops in the cables being slightly higher as twice the current flows but will only be small amount. In effect having a larger capcity means for a given power usage from the battey, you will actually replace that charge faster with a larger battery. e.g. If you have a 100Ah battery and take out 5 Ah and then drive off to recharge it. Lets say for sake of argument it charges at 5 amps. That is 1 hour to recharge fully. Now, same scenario but a 200Ah battery or two 100Ah batteries in parallel. Now again we take out 5 Ah. Thats 2.5Ah per 100Ah capacity. As the batteries %age wise is not so deeply discharged the current will average a lot less so lets say it recharges at less than twice the curremt. Say 8 Amps. Then thats 37 minutes to recharge, not an hour with half the capacity. The above is an example to demonstrate what happens and is not actual figures or correct ratios of charge, but shows the principle of increasing your battery capacity actually benefits the recharge time for a given power usage. The battery has not been so deeply discharge so will last longer as well. Therefore going from 85Ah to 105Ah will have benefits in recharge time. Jon. Edit - some spelling and typos.....must start using google chrome more often which has spell checking built in. Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted January 18, 2013 Share Posted January 18, 2013 Perhaps Brambles could answer this for me and others. I cannot understand why the engine alternator takes forever to re-charge the leisure batteries, I assume it's because it goes through a split charge relay and is only capable of so much current. So here's the thing, why could you not simply have cables run directly from the engine battery to the leisure batteries, with perhaps an isolation switch to prevent their use for engine starting, or am I missing something. Link to comment Share on other sites More sharing options...
Tracker Posted January 18, 2013 Share Posted January 18, 2013 1footinthegrave - 2013-01-18 7:44 AM Perhaps Brambles could answer this for me and others. I cannot understand why the engine alternator takes forever to re-charge the leisure batteries, I assume it's because it goes through a split charge relay and is only capable of so much current. So here's the thing, why could you not simply have cables run directly from the engine battery to the leisure batteries, with perhaps an isolation switch to prevent their use for engine starting, or am I missing something. No doubt others will correct me for this non techy answer but as I see it, under the guise of 'elfnsafety the charge rate to the leisure battery(s) is restricted to about 10 amps either by the size of cables feeding it(them) or by some other electronic means? I know this to be so because using a 20 amp multimeter to check charge rates on partially discharged leisure batteries on more than one occasion and on different vans the engine alternator charge rate has never been found to exceed about 12 amps and is more often than not 10 or less amps. One of the reasons given is the risk of hydrogen gas being given off inside the van if the charge rate is higher but to me this is a bit of a red herring as it is very easy to either build in an external battery locker or seal batteries in a locker and vent them externally. My perception is that most vans are built with site use in mind and the intention of using electric hook up to keep the batteries topped up so when we start wandering off site without hookup the systems simply are not designed for this type of use? But I could be wrong? Link to comment Share on other sites More sharing options...
pjcoleman Posted January 20, 2013 Author Share Posted January 20, 2013 :-D Thanks for the information, that's what I needed to know. Link to comment Share on other sites More sharing options...
hallii Posted January 21, 2013 Share Posted January 21, 2013 Reference "Trackers" reply. I think (but I may be wrong) that the switching to charge the leisure batteries is simply a relay that is switched "on" when the alternator produces enough voltage. So a direct connection should go to the leisure battery. The amperage delivered is dependant upon the state of charge of the battery, a battery at 75% will not take a full on charge, rather something less tapering off until it is almost fully charged. I say almost as the full theoretical charge cannot be reached with just the alternator, a proper seperate charger would be required particularly with a gel battery. To overcome this and to shove a lot more amps into a leisure battery the "battery to battery" devices up the voltage to the leisure battery to around 14.4v. This increases the charge current by about 5 times. All well and good, but the battery will be accepting a charge rate above what it was designed for, maybe the battery will not last as long? My solar panels output 160w in Spanish sunlight, thats about 11 amps at 14.4v, they (the panels) keep my batteries fully charged most of the time. H Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted January 21, 2013 Share Posted January 21, 2013 And that's the catch 22 situation as far as I can see, the only times I need extra 12 volt power are when off mains hookup and in the sorter daylight hours of the year, and invariably under gray skies, at least in the UK. If I was buying another van it would not have one of those stupid blown air heating systems sucking away the amps as they do, and as we've got, I really miss the convector type of heater, that together with LED lighting would solve nearly all these lack of 12 volt power issues if on the move every week or so. oh well. Link to comment Share on other sites More sharing options...
Tracker Posted January 21, 2013 Share Posted January 21, 2013 The simplest and most cost effective way to gain extra 12 volt capacity has always been to fit a second or even a third leisure battery. This is reliable if done properly as there is nothing electronic to go wrong plus it is not complicated to fit or wire up and it works. The only thing to remember is that you only get out what you put in so either charge them fully whenever you can from ehu or drive enough miles to keep them charged. Unless you want to add to the complication (and the cost) by adding a solar panel and regulator - which is also generally reliable and also works - as long as you get enough strong daylight. Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted January 21, 2013 Share Posted January 21, 2013 Yes I know that Tracker, I've got two 85 amps, both new last year, but in my experience unless there's something amiss with my split charging relay I have to drive at least 100 miles to get a reasonable amount of charge back in, but even then if I'm straight on to a mains hookup the batteries will continue to charge for around 12/18 hours to get back up to capacity, I put it down to that blow air heating when we have to use it of hookup, seems to hammer the batteries, oh well. Link to comment Share on other sites More sharing options...
lennyhb Posted January 21, 2013 Share Posted January 21, 2013 You are doing well mike before I fitted the solar panel I used to reckon 200-300miles to get the batteries fully charged. On their own the Truma heaters aren't that bad 5-6 amps on start up after a few minutes drops to 2-3 amps then after about 15 minutes & the fan slows down drops to 1-1.5 amps but when you add that to the other bits & pieces drawing currents the batteries don't last long. Bit of a backward step making everything electronic from the point of view of a Motorhomer not everyone wants to plug into a hook-up I certainly don't and I know you don't. Vans now days take about ½ amp with control panel/charger, electronic controls on the fridge, the Truma dump valve, radio & TV sat receiver. Stay put for a couple of days don't turn anything on 24 amp hours gone. Link to comment Share on other sites More sharing options...
chas Posted January 21, 2013 Share Posted January 21, 2013 Would I be right in asuming that to get a quicker charge to my liesure battery when leaving site is to turn off the 12 v supply to the fridge and rely on it keeping its contents reasonably cold while driving to another location ,say 2hr drive, I rarly use EHUs. Link to comment Share on other sites More sharing options...
Tracker Posted January 21, 2013 Share Posted January 21, 2013 1footinthegrave - 2013-01-21 1:01 PM Yes I know that Tracker, I've got two 85 amps, both new last year, but in my experience unless there's something amiss with my split charging relay I have to drive at least 100 miles to get a reasonable amount of charge back in, but even then if I'm straight on to a mains hookup the batteries will continue to charge for around 12/18 hours to get back up to capacity, I put it down to that blow air heating when we have to use it of hookup, seems to hammer the batteries, oh well. It sounds as if something is not right as the blown air heating blower (I think) only takes about an amp - what does the handbook say? As I said earlier you won't get much above 10 amps from the engine alternator into the leisure batteries so if your theoretical 170 ah batteries are half depleted and in need of 80 ah to top them up it will take up to 8 hours driving. Have you checked the system? Starting with the fuses on the split charge relay which can become corroded and not allow the current to pass, on to the battery fuses and their connections and the battery terminals all of which can also over time become dirty or loose. Check the battery voltage both with and without the engine running as the voltage should rise to well above 13 if the charging circuit is working properly and drop back to below 13 once off charge. Apologies if you know all this and have done it! Link to comment Share on other sites More sharing options...
myshell Posted January 21, 2013 Share Posted January 21, 2013 I think we may be confusing the OP with all this tech talk about battery / alternator charging rates, all he or she wanted to know was can they replace their 85 Ah leisure battery with a 105 Ah one ? well PJ Colman the short answer is YES YOU CAN. The main thing to check is that if your current 2 batteries (engine & leisure) are both Gel maintenance free then your new replacement leisure battery must also be Gel, if on the other hand they are both wet (ie you can top them up with distilled water) then your replacement battery must also be the wet type. Link to comment Share on other sites More sharing options...
Tracker Posted January 21, 2013 Share Posted January 21, 2013 myshell - 2013-01-21 4:43 PM I think we may be confusing the OP with all this tech talk about battery / alternator charging rates, all he or she wanted to know was can they replace their 85 Ah leisure battery with a 105 Ah one ? well PJ Colman the short answer is YES YOU CAN. The main thing to check is that if your current 2 batteries (engine & leisure) are both Gel maintenance free then your new replacement leisure battery must also be Gel, if on the other hand they are both wet (ie you can top them up with distilled water) then your replacement battery must also be the wet type. Always assuming there is enough space to fit a larger battery? Some wet batteries are fully sealed and do not ever need topping up? Your van's charging system might give you the choice between gel and wet! The handbook should tell you whether you can change the charge regime? The battery should have a label on it somewhere stating which type it is? Confusing innit! Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted January 21, 2013 Share Posted January 21, 2013 With apologies to myshell, of course he can add another battery, although I'm told they are best replaced in matched pairs at the same time, and although gone of topic you can bet he'd probably find the other contributions useful information. As to my question replied to by Tracker amongst others, just underlines the catch 22, you could have 500 amps of battery capacity, but at some point they all need to be charged, and that opens another can of worms that has happened to me with the addition of another battery, Mmmmmm Link to comment Share on other sites More sharing options...
Tracker Posted January 21, 2013 Share Posted January 21, 2013 1footinthegrave - 2013-01-21 6:27 PM As to my question replied to by Tracker amongst others, just underlines the catch 22, you could have 500 amps of battery capacity, but at some point they all need to be charged, and that opens another can of worms that has happened to me with the addition of another battery, Mmmmmm We have 2 x 110 ah batteries and although we never use a site or ehu we do have a small 50 watt solar panel which serves mainly to keep all three batteries topped up mainly when the van is not in use. Allowing for using a microwave via 1500 watt inverter most days we enjoyed four weeks away in Germany last year without ever running low on battery power and it was not sunny all the time! Which is what makes me wonder if your batteries and charge system are working to full capacity? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted January 21, 2013 Share Posted January 21, 2013 myshell - 2013-01-21 4:43 PM ...The main thing to check is that if your current 2 batteries (engine & leisure) are both Gel maintenance free then your new replacement leisure battery must also be Gel, if on the other hand they are both wet (ie you can top them up with distilled water) then your replacement battery must also be the wet type. From a purist point of view, it might be best for a motorhome's starter-battery and leisure-battery not to be different types but, in reality, they very often are... The norm (historically and currently) for motorhomes is to have a 'wet-acid' starter-battery. In the past this would usually be 'maintainable' in that its electrolite level could be checked and, if necessary, topped up. Nowadays it's much commoner for the starter-battery to be a maintenance-free wet-acid battery whose electrolite level cannot be checked/topped up. Where motorhome leisure-batteries are concerned, it's far from rare for the converter to choose a gel battery (or more recently an AGM battery). The advantages of gel/AGM batteries for leisure-vehicle use are that, besides being sealed and maintenance free, there is no possibility of them leaking in the event of an accident and they can be installed in any orientation (even upside-down if one wished). Although received wisdom is that multiple leisure-batteries should be all of the same type, this advice really relates to the different charging regimens that a motorhome's on-board battery-charger may be able to provide. If multiple leisure-batteries are a mixture of 'wet', gel or AGM types, if the battery-charger is set to a gel charging regimen, the 'wet' battery may be damaged. Alternatively, if the battery-charger is set to a 'wet' charging regimen, the gel/AGM battery may not be optimally charged. So, where multiple leisure-batteries are concerned, the wisest thing is not to mix types and (where it's selectable) to select the charging regimen setting of the motorhome's on-board battery-charger so that it matches the leisure-batteries' type. As the norm is for a vehicle's starter-battery to be wet-acid type, the charging regimen provided by a motorhome's alternator will be suitable for a wet-acid battery. This charging regimen won't damage a gel/AGM battery so, when the motorhome is being driven and its alternator is charging both the starter- and leisure-battery (or batteries), it won't matter whether the leisure-battery is 'wet' or gel/AGM. Basically, there's no potential harm in having a 'wet' starter-battery and a gel/AGM leisure-battery, or vice versa. Where care should to be taken is to avoid using a battery-charger (continuously) on a gel setting to charge 'wet' batteries. Link to comment Share on other sites More sharing options...
Pete-B Posted January 21, 2013 Share Posted January 21, 2013 Being a bit of a numpty on all things that use electrickery, when we talk of alternaters or solar panels producing 10amps or 2amps or whatever is this per hour? Link to comment Share on other sites More sharing options...
lennyhb Posted January 21, 2013 Share Posted January 21, 2013 chas - 2013-01-21 1:45 PM Would I be right in asuming that to get a quicker charge to my liesure battery when leaving site is to turn off the 12 v supply to the fridge and rely on it keeping its contents reasonably cold while driving to another location ,say 2hr drive, I rarly use EHUs. Strictly speaking it shouldn't make any difference but in reality it depends on how the van has been wired and the size of cables used. If the manufacturer has skimped on cable size and the feed from the alternator/engine battery to the split charge relay/charger is on the small side when the fridge is running on 12v you will get a bigger volt drop reducing the charge to the leisure battery. Easy way to check is with the engine running see if the voltage across the leisure battery drops when you turn on the fridge. Link to comment Share on other sites More sharing options...
Tracker Posted January 21, 2013 Share Posted January 21, 2013 Pete-B - 2013-01-21 7:29 PM Being a bit of a numpty on all things that use electrickery, when we talk of alternaters or solar panels producing 10amps or 2amps or whatever is this per hour? If we compare the flow of electricity to water in a pipe and compare 10 amps to 10 gallons, that means that in an hour 10 amps will flow through the cables which is equal to 10 amp hours (ah), in the same way that 10 gallons will flow through the pipe at the rate of 10 gallons per hour (gph). Does that help? Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted January 21, 2013 Share Posted January 21, 2013 Tracker - 2013-01-21 7:43 PM Pete-B - 2013-01-21 7:29 PM Being a bit of a numpty on all things that use electrickery, when we talk of alternaters or solar panels producing 10amps or 2amps or whatever is this per hour? If we compare the flow of electricity to water in a pipe and compare 10 amps to 10 gallons, that means that in an hour 10 amps will flow through the cables which is equal to 10 amp hours (ah), in the same way that 10 gallons will flow through the pipe at the rate of 10 gallons per hour (gph). Does that help? Yes, then all you've got to do is find out how much each individual 12 volt item consumes and you've cracked it, blimey life was so simple with gas mantles and a pump foot operated water pump :D Link to comment Share on other sites More sharing options...
Pete-B Posted January 21, 2013 Share Posted January 21, 2013 It's now all makes sense, thanks. (lol) Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.