DBA Forum (B) - David Beaumont
2014-08-08 14:25:13 UTC
That operation sounds correct to me if I have understood you correctly - you want to always charge your auxillary bank and only charge your main bank when the aux goes over 27.4V?
When you connect a flat battery to a fully charged one there will be a massive flow of amps, dropping the voltage of your main one. This is why car jump starter leads get hot and why you should leave your donor car engine running. When the two batteries get nearer in charge the flow will be a lot less and your relay will settle down.
I do wonder if this is really what you want to do though. If your main is completely flat I don't think wiring it to a fully charged battery is a good idea, even if through a fancy VSR. It could even be dangerous. You might be better finding a way to gently transfer amps from your aux to main. Perhaps via some heavy duty resistors or via a 24V charger, or via a more frequent connection. I think your existing solution is only advisable if you can guarantee that the state of charge difference between the aux and main will always be small. Jump starting flat batteries is not good for the jumper or the jumpee battery.
David
When you connect a flat battery to a fully charged one there will be a massive flow of amps, dropping the voltage of your main one. This is why car jump starter leads get hot and why you should leave your donor car engine running. When the two batteries get nearer in charge the flow will be a lot less and your relay will settle down.
I do wonder if this is really what you want to do though. If your main is completely flat I don't think wiring it to a fully charged battery is a good idea, even if through a fancy VSR. It could even be dangerous. You might be better finding a way to gently transfer amps from your aux to main. Perhaps via some heavy duty resistors or via a 24V charger, or via a more frequent connection. I think your existing solution is only advisable if you can guarantee that the state of charge difference between the aux and main will always be small. Jump starting flat batteries is not good for the jumper or the jumpee battery.
David