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pim asked

Charging battery via MPPT and alternator

Hello people, I’ve got a situation and I’d like to have your advice. My AGM-battery is charged via solar (MPPT) and, when the engine is running, via an alternator (via an Argofet which also charges 2 other batteries). I suspect the battery is not charged enough by the alternator because the Argofet detects a voltage of let’s say 13,5 Volt (caused by the MPPT). So the alternator charges the other batteries which have lower voltages I assume? Is this correct? Of course I want to have this (main)battery is full as possible and this is not happening if this is the case. Because the current from the MPPT can be very low with a minimum of sun

Am I right? Is there a solution?

battery charging
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1 Answer
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Mike Dorsett answered ·

Parallel chargers like the Argofet will always put more charge into the lower voltage battery. If your house bank is also charged by the MPPT, and is a higher voltage than the other batteries, then this will only start to take charge once the charging voltage exceeds the house bank volts. There are several options:

1) Fit a second alternator to charge the house bank

2) Fit additional solar charging / charge relay to charge the other batteries from the solar.

3) fit an isolator switch so as one or the other of the second batteries can be disconnected when charging

4) Fit a high power, small value resistor in the charging line from the Argofet to each of the other 2 batteries. This will cause additional volltage drop, and force more current into the house bank.

Best solution is 1 - though this will involve some engineering.

Easiest solution is 4. The additional resistance could be a length of suitably rated cable. You would need to calculate the lengths carefully to share the load according to normal battery voltages when charging, and desired rate of charge for each battery.

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