The most likely cause is that your split charging system is allowing a huge amount of current flow to a leisure battery when it needs a decent charge. Split relays I believe are more often than not purely voltage sensing to work out when to open the taps from the main battery to the auxiliary battery which in turn has no opinion on what the charge current limit is on your leisure battery or its state of charge.
If you imagine your poor leisure battery would ideally like different current and voltage depending on its state of discharge then split chargers just don't consider this at all. Take my advice and install an intelligent DC to DC charger and then set the charger for the leisure battery type that you have and be done with it. You already have the wiring in place so it should be easy.
We use the Victron Orion bluetooth one that supplies 30amps and actually smart charges the battery as you drive. They are around £200 but you can get cheaper ones though I personally have no recommendations on those. We have a 60amp fuse in-between this and the battery itself and as well as another between the alternator and the DC DC charger.
If it is fact not the reason that you are blowing fuses then at least you are now charging your batteries properly..
Quote: Originally posted by SoggySteve on 02/6/2022
The most likely cause is that your split charging system is allowing a huge amount of current flow to a leisure battery when it needs a decent charge
Would you care to put a value on this huge amount of current, assuming it
is a 'wet' lead acid battery in good condition?
------------- Never argue with fools........They drag you down to their level, then beat you with experience.
Quote:
Would you care to put a value on this huge amount of current, assuming it
is a 'wet' lead acid battery in good condition?
Not really. I have never clamp metered the leisure battery feed from a split charger at different states of charge. A typical alternator will provide maybe 100amps at high revs though I'm not saying that a battery will accept such a high current all the time any more than the vehicle battery.
I think my main point is that having a DC to DC charger will not under current the battery and will provide the correct voltage and current based on the battery technology such as wet LA being AGM or even Lithium at a given state of charge. You probably know that AGM needs the high voltage which a standard alternator usually cannot provide. Split chargers are not like diodes either so the current can flow both ways depending on the voltage of either cell.