ThePog Posted December 21, 2022 Share Posted December 21, 2022 Yea so I had a voltage switching relay lying around from the initial solar install in my bus that i never bothered to use. Then the bus wasnt getting used much over covid so I decided to install it to keep the start batteries topped up from the solar, but this doesn't seem to be working, in fact I suspect the batteries are a bit fucked now. This could be normal as they are a few years old and have been flattened and left for a bit without me knowing once or twice. Could it be the solar is charging the boys at too high a voltage? Is there a better way? Quote Link to comment Share on other sites More sharing options...
Stu Posted December 21, 2022 Share Posted December 21, 2022 Rather than the switching relay it may pay to use a charge controller instead as they have different charging profiles to maintain the batteries ie absorption charging, desulphation cycles, float charging etc. Are the batteries not holding a good charge now? 1 Quote Link to comment Share on other sites More sharing options...
ThePog Posted December 21, 2022 Author Share Posted December 21, 2022 They are very weak, i had a read up and the relay probably isnt a great way to do it. Quote Link to comment Share on other sites More sharing options...
ThePog Posted December 21, 2022 Author Share Posted December 21, 2022 I just replaced them, the old as fuck one is fine, the larger/newer battery is down to 11 volts. They were different brands/size/ratings so probably not surprising. Quote Link to comment Share on other sites More sharing options...
ThePog Posted December 21, 2022 Author Share Posted December 21, 2022 5 hours ago, Stu said: Rather than the switching relay it may pay to use a charge controller instead as they have different charging profiles to maintain the batteries ie absorption charging, desulphation cycles, float charging etc. Are the batteries not holding a good charge now? I have a wee solar controller, will the agms provide enough voltage to charge the lead acids? 1 Quote Link to comment Share on other sites More sharing options...
Thousand Dollar Supercar Posted December 21, 2022 Share Posted December 21, 2022 8 hours ago, ThePog said: I suspect the batteries are a bit fucked now. This could be normal as they are a few years old and have been flattened and left for a bit without me knowing once or twice. Yeah that could do it. Lead acid batteries don't like being discharged below a certain voltage and they don't like being left flat. There may be various techniques you could use to try to rejuvenate them, but if they're old and mismatched, replacement would be ideal. 7 hours ago, ThePog said: Could it be the solar is charging the boys at too high a voltage? What peak voltage does it produce, and is it grunty enough to boost the batteries up to that voltage? 46 minutes ago, ThePog said: the old as fuck one is fine, the larger/newer battery is down to 11 volts Terminal voltage under no-load conditions isn't a reliable indicator of battery condition - the one which is 'fine' could have a high internal impedance so its voltage drops away under load, and the one at 11V could just be flat. Testing the batteries under load (once they're charged) is the easiest way to get an idea if they're OK. 50 minutes ago, ThePog said: They were different brands/size/ratings so probably not surprising. Don't mix different brands/sizes/ratings/ages of batteries in series (I'm assuming your bus batteries are in series, but I have no idea if this is likely to be true or not). When you apply a charging voltage to the series string, the voltage won't get distributed evenly between the batteries due to their different characteristics, so some batteries will get cooked and others will be undercharged. 48 minutes ago, ThePog said: will the AGM batteries provide enough voltage to charge the lead acids? Don't use a fully-charged battery to charge a flat battery. I can see two problems - the initial current could be too high (nothing to limit it), and then the final voltage will be too low. I don't know the first thing about buses, off-grid domestic solar/battery/inverter systems etc, but Stu's charge controller sounds like a sensible solution. 2 Quote Link to comment Share on other sites More sharing options...
ThePog Posted December 21, 2022 Author Share Posted December 21, 2022 I bought new batteries today, these are 24v in series. I have disconnected the vsr for now. The solar setup is standalone, has panels and its own controller, this is also 24v with two 12v batteries in series. I have a seperate wee solar controller I could install in place of the VSR, but I am not sure the agms will have voltage to charge the lead acids. Probably wouldnt hurt to try as the controller can be set up to charge lead acids. Quote Link to comment Share on other sites More sharing options...
h4nd Posted December 22, 2022 Share Posted December 22, 2022 circuit diagram pics (sketch on napkin, and faxed from your uncles' shop is traditional) of wiring and model numbers of bits rather helps if want opinions. 1 Quote Link to comment Share on other sites More sharing options...
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