In my split charge system, if a fully charged starter battery is connected to an empty leisure battery, what would the maximum in-rush current be? I assume that a battery will have some form of self-limiting maximum charge rate, otherwise it would be like a short circuit. I'm guessing that regarding the split charge relay and fuses the above scenario is the worst case.
From posts on here 30A fuses are mentioned, I have 40A for no good reason. I remember someone had 20A and had to go to 30A so it didn't blow under those circumstances. I'm guessing it depends on the size of the LB too, again I dont think most people have more than 110Ah.
Lead acid accumulators have a fairly high internal resistance, so that should limit the current. I'd think a 30A relay should be fine. The fuse'll pop in extreme cases.
This spec sheet is showing an internal resistance of just 3 mohm. http://www.power-sonic.com/images/p...s_psg_series/12volt/PS-121400FR_11_Feb_21.pdf I've decided to buy a 12V 50A digital ammeter and run a test. I'm very confused by this. If a typical car battery can deliver say 2,000A on short circuit, suggesting a very low internal resistance, what prevents a fully charged battery discharging at this rate into an empty battery. Is the resistance during charging different to the resistance during discharge? Discharge at 2,000A suggests and internal resistance of 0.006ohm, while charge at say 10A suggests a resistance of 1.2ohm. All-in-all this just highlights how thick I am.
The empty battery has a resistance too, the full battery will have 12.6v and the empty one 10 or 11V or thereabouts, a potential difference of 1 to 2V. I dont know how to do the calculation, but I am sure that is has a bearing on the inrush current. Normally batteries are charged at 14.4v... I think boats with a massive capacity LBs difference in the capacity have some sort of protection to stop the starter being immediately flattened, diodes or something similar.
some bed time reading but basically the resistance changes Discharge http://www.mpoweruk.com/performance.htm Charging http://www.mpoweruk.com/chargers.htm
Yes, boat systems have diodes or MOSFET switches which stop any cross-flow of current - the alternator feeds the lowest voltage battery, there is never a metal connection across between the batteries. I have a boat MOSFET battery charge splitter in the bus because I got one for the boat then didnt use it. It cost £120 new. I think I got for £10 with a 1200W sinewave inverter and a 120AH AGM leisure battery which is too long to go in the bus or the boat. :-( While charged lead-acid batteries will discharge with huge currents into a short, the voltage on the battery while charging rises very rapidly with current so you dont get a massive flow for long, the fuse will hold out for long enough for the voltage to rise to the point where the current drops off.
Used to be a auto electrician, always use 30amp fuse to charge a dead leisure battery (30amp fuse will take 45amps peak)
