Alternator charging light staying on. Renogy DCC50S

[fred_jb]

You know what Fred, but I've got that same shunt to fit! I bought it all in May, but with one thing and another, I've not the time to fit it all.

I've got the DCDC50S fitted to mine now, and was just wanting to see it working before I fit the shunt and lithium.
with the engine and ignition off, does your DCDC50S charge from the starter battery? (Far left hand LED lit up red) Mine does, albeit only drawing small current, until the starter battery drops to 12.6V. It seems strange to deplete charge from the starter battery.

Is yours a smart alternator?

Hoping you can help me out here!

There is a bit of a problem with the terminogy used with these kind of units. When they refer to an alternator input it is not a direct connection to the alternator, instead it is a connection to the starter battery +ve which in turn connects to the alternator. So, if it says it is charging from the alternator, in reality it is charging from the starter battery. Unless you connect a proper D+ signal it has no way of knowing if the alternator is actually charging the starter battery and so has to infer this from the level of the starter battery voltage which can obviously be misinterpreted in various scenarios. This can lead to charge being taken out of the starter battery when the alternator is not providing charge to it which is what seems to happening with yours.

My van has a smart alternator and I have connected the D+ signal to the B2B, but would have done so even if it wasn't a smart alternator. As far as I can tell the B2B now only operates to take charge from the starter battery and send it to the leisure battery if the engine is actually running, which is what I want.

Interestingly if the leisure battery is fully charged and you have solar panels connected it seems that it will use the solar input to charge the starter battery instead, and I think I saw this happening the other day. To me this raises the question of how suitable this charging regime is for the AGM starter battery as you can only specify battery type for the leisure battery and I have that set to lithium.

These are my current readouts, with the weak winter sunshine only providing about 45W from my 280W solar panel array!

I have disabled the Electroblock trickle charging of the starter battery, so am relying on the Ablemail unit to keep it topped up, though that, the B2B and the shunt seem to disagree slightly on the voltage reading. The Ablemail unit basically passes charge to the starter battery if the leisure battery is above 13V and the starter battery is below 12.5V.