foxy Posted March 2, 2014 Share Posted March 2, 2014 can anyone please enlighten me as to the correlation of battery voltage and amps. my control panel states that I have a 12.5 volt battery but the capacity is 45 % it is a 100 amp battery so this must be 45 amps left in the battery,, so why is the voltage showing as a full battery? Link to comment Share on other sites More sharing options...
colin Posted March 2, 2014 Share Posted March 2, 2014 Because 12.5v is not a full charge. Link to comment Share on other sites More sharing options...
Tracker Posted March 2, 2014 Share Posted March 2, 2014 There is no real correlation as I understand it but I'm no techy and doubtless someone will have a better explanation. Consider a battery to be like a water tank but with the the depth (aka capacity) gauge reading in volts which is around 12.7 when full and around 12.2 when empty. When you open a tap on the tank the water flows at whatever rate is dictated by the size of the opening and would be shown as amps - anything between a trickle at under 1 amp with a small bulb to full flow of hundreds of amps when turning a starter motor. In general terms for the purpose of this example that flow will continue largely undiminished until the battery - or the water tank - is completely depleted of it's capacity to supply so it matters not what the voltage is in relation to the current - or water - flow. The theoretical capacity of a battery may well be 110 amp hours (ah) but in reality given issues like incorrect or incomplete charging, age of the battery, losses through resistance in connections the actual usable capacity is often more like half to two thirds of the nominal capacity - which is maybe like having the tap outlet half way up the tank instead of close to the bottom or perhaps like have lime scale in your pipes slowing the flow. Hope that makes sense to you - it is very simplistic but it might help? Link to comment Share on other sites More sharing options...
spospe Posted March 2, 2014 Share Posted March 2, 2014 A fully charged '12 volt' battery, will show about 14.7 volts for a flooded lead-acid type and 14.4 volts for a gel type. Link to comment Share on other sites More sharing options...
Tracker Posted March 2, 2014 Share Posted March 2, 2014 spospe - 2014-03-02 7:17 PM A fully charged '12 volt' battery, will show about 14.7 volts for a flooded lead-acid type and 14.4 volts for a gel type. Yes but if you take it off charge, after a while that will drop back to more like 12.7 / 12.8 volts with no load applied. Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 2, 2014 Share Posted March 2, 2014 If the battery is not being used or charged, and if it has been allowed to "settle" for about two hours, it should show about 12.8 Volts when fully charged. As the indicated voltage is 12.5 Volts it is partially discharged, possibly at about 80% capacity. It should not be allowed to fall below 12.25 Volts as under this Voltage the battery may become permanently damaged. I'm a bit puzzled that yours is giving the Ah readout it is at that voltage, but that is quite possibly due to the relative sensitivity of the panel meter. That is about the extent of my understanding. If either Clive or Jon (Brambles) picks up yout quesr tye will be able to give chapter and verse on the battery and the meter. Hope this helps. Link to comment Share on other sites More sharing options...
Robinhood Posted March 2, 2014 Share Posted March 2, 2014 foxy - 2014-03-02 5:59 PM can anyone please enlighten me as to the correlation of battery voltage and amps. my control panel states that I have a 12.5 volt battery but the capacity is 45 % it is a 100 amp battery so this must be 45 amps left in the battery,, so why is the voltage showing as a full battery? I believe from previous posts you have recently changed your 'van to a brand new one. It would be useful to know what your new 'van is, and what control panel is fitted. A number of panels have the capability to program the battery capacity (Ah) into them, and it is not unknown for this to be incorrectly set, and subsequent capacity display estimates will be wrong. As previously noted, a 'static' real reading of 12.5v does not denote a fully charged battery. which should be in the region of 12.7-12.8v. What makes you believe it is fully charged at this reading? Link to comment Share on other sites More sharing options...
foxy Posted March 2, 2014 Author Share Posted March 2, 2014 just got a Auto trail Mohawk. It had ben in the show room for a while, I noticed the battery amp reading on the control panel was reading about 25% and well into the red .It will be fully charged sir when you pick it up. It wasn`t, so I spent a few nights away to try things out. The charger put the battery up to 75% but not long after I got home I noticed the battery had dropped to 30%. I was going away again shortly so I managed to get a battery on loan while they checked the original battery. I received a call to say what is wrong with the battery it is showing 12.7v. So Iam confused as the capacity was showing 30amps. To me the battery isn`t holding its charge, but I am told there is nothing wrong. Link to comment Share on other sites More sharing options...
artheytrate Posted March 2, 2014 Share Posted March 2, 2014 I picked my new Auto Sleeper Broadway up yesterday and when I got home my reading was 42% which I couldn't understand, I have had it on hook up since and it's only reading 60% after 30 hours on charge. John. Link to comment Share on other sites More sharing options...
Robinhood Posted March 2, 2014 Share Posted March 2, 2014 From your description, I suspect your 'van is fitted with an EC480 control panel. This can be programmed for the size of leisure battery fitted (which will, of course, have an effect on the %ge reading you see). There is also an AH start point setting which affects the display (and note the default setting for this is 50%, which may be relevant in your case). I think it would be worthwhile checking what capacity has been programmed in, and also the secondary AH start point. I suspect the user is not supplied with the "advanced setting" documentation for this panel, but it can be gleaned from the "dealer" document here: http://www.sargentltd.co.uk/EC500%20Dealer%20Guide%20Issue%201.pdf I would be inclined to leave the battery on charge for some time, then use the advanced settings to check/configure the correct battery size, and set the AH start point to 100%. HTH Link to comment Share on other sites More sharing options...
foxy Posted March 2, 2014 Author Share Posted March 2, 2014 cheers robin, will have a read. Link to comment Share on other sites More sharing options...
artheytrate Posted March 3, 2014 Share Posted March 3, 2014 Thanks also Robin as my new motorhome as exactly the same set up. John. Link to comment Share on other sites More sharing options...
Robinhood Posted March 3, 2014 Share Posted March 3, 2014 I hope it helps both of you. Whatever the circumstances and the programmed values, it would be worth taking an independent check of the battery charge state when you *think* it is fully charged (either by testing the specific gravity, or checking the voltage with a multimeter when it has been off-charge and off-load for some time (as above, this should be 12.7-12.8v). This should give some confidence that there isn't (also) an issue with the battery. I'm always suspicious of the state of the leisure battery in new vehicles, especially if they've been in the showroom for some time, having seen many such vehicles with well-depleted readings following tyre-kickers having left lights, etc. switched on. The level shown has often made me doubt that the fitted battery would subsequently recover fully. Link to comment Share on other sites More sharing options...
Tracker Posted March 3, 2014 Share Posted March 3, 2014 Robinhood - 2014-03-03 7:37 AM I'm always suspicious of the state of the leisure battery in new vehicles, especially if they've been in the showroom for some time, having seen many such vehicles with well-depleted readings following tyre-kickers having left lights, etc. switched on. The level shown has often made me doubt that the fitted battery would subsequently recover fully. Me too - many is the van I have bought with the leisure battery allegedly fully charged because it was on hook up for a day or two before I collected it only to find it flat the following morning. I too consider that this it had been allowed to go so flat whilst standing, and this applies to new vans as well as used, that it was irreparably damaged and unable to fully recover. To be fair most dealers replaced the battery without too much hassle although some had to be pushed and even then some of the replaced batteries were no better and had to be replaced again. I don't know why but I suspect incorrect storage and maintaining of charge had something to do with it - or just poor quality cheap and nasty batteries in the first place maybe? Link to comment Share on other sites More sharing options...
mikejkay Posted March 3, 2014 Share Posted March 3, 2014 If you take a water hose as an analogy the voltage is equivelant to water pressure and the amp(eres) is equivelant to flow. When your butt is almost empty there will be little pressure and not much flow. AS others have said a low voltage reading indicates that your battery is discharged. Link to comment Share on other sites More sharing options...
hallii Posted March 3, 2014 Share Posted March 3, 2014 It is perfectly possible for a battery that has low capacity ( i.e." wearing out") to show a voltage on a meter that indicates that it is "fully charged". Since it is low capacity it cannot be "fully charged" at least it cannot be fully charged to it's rated capacity (Ah). So a battery that has low capacity (Ah) can have "normal" voltage, but a low capacity battery can have a lower voltage which indicates something is wrong. Your meter cannot measure capacity (Ah) directly so it measures voltage and the electronics, after being calibrated or set by the user, provides an approximation of the Ah left based on the voltage. From the foregoing you will deduce that any meter indicating the Ah capacity of a battery can only be an approximation. With a brand new battery and properly calibrated you should get a reasonable idea of what is left in the battery. With an older or worn out battery it's like "sticking your finger in the air".. Your best bet is to have the battery (ies) tested by someone with the correct equipment, then you can decide on what to do. H Link to comment Share on other sites More sharing options...
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