dbbls wrote:
Won't work. When your onboard generator is running your batteries will show full charge because the converter is putting power to them. A separate battery charger will read this as a fully charged battery and will not provide any power to the battery.
If that happens with that charger then all you do is turn off the converter (how to do that depends on the RV ) start the portable charger, then turn the converter on.
It depends on charging voltages whether they will add their amps and in what proportion. Say the charger can do 14.4 but the converter does 13.8 and the battery is at 12.2 at first. Also the battery must accept that many amps.
Both charger and converter will add their amps till battery voltage reaches 13.8 when the converter no longer contributes. Its amps will taper as battery voltage nears 13.8 then will stop as there is no more voltage spread. Meanwhile the charger will still be cranking out its amps to get the battery voltage to 14.4. Its amps will taper according to the charger's usual "charging profile"
If both have the same voltage, they share the amps all the way. Say the battery can accept 80a and you have two 40a chargers of same voltage. Each does 40a till battery acceptance drops below 80a then each charger's amps taper.
If one charger has slightly higher voltage then one will taper more than the other, so when battery will accept say 50a, one charger might be doing 30 and the other 20. It is proportional to the "spread" each charger has between its voltage and the rising battery voltage.
The generator needs enough watts to run all the chargers. Once one charger is doing/can do it all, you might as well turn off the other.
If two 40a chargers are each down to 20a, you can turn one off and the other will jump back to 40a and taper from there again.
