Alternator vs solar charging priority

[kingofcary]

Hi Folks … I have a magnum charger/inverter. Have 2x 285w solar panels. Lifepo house battery. Start battery is charged with alternator etc and I use dc to dc charger. All has been good. Question is when underway motoring with lots of sun what is the priority to charge, is it alternator or solar since there is both avail. I guess when on shore power same for shore or solar. Hope this question makes sense!! Tx

[DeepSeeDiver]

Theres a lot of variables to unpack here and I don't think theres a single answer. Basically, I base the priority on whichever method is best for the lifespan of the battery itself. So I'm usually just thinking about when will I need to charge and what what my situation might be. I read this article recently which calibrated my personal decision matrix to prioritize whatever was necessary for prolonging the life of the battery bank. If I didn't need to charge I didn't do it or worry about 'topping off the bank'.

Regardless of where you are solar will be a passive means of charging versus alternator or shore power. You can't just switch on the sun at your discretion. So I consider our solar panels to be bonus charging.

[hjohnson]

Originally Posted by kingofcary

Hi Folks … I have a magnum charger/inverter. Have 2x 285w solar panels. Lifepo house battery. Start battery is charged with alternator etc and I use dc to dc charger. All has been good. Question is when underway motoring with lots of sun what is the priority to charge, is it alternator or solar since there is both avail. I guess when on shore power same for shore or solar. Hope this question makes sense!! Tx

As a rule, they're all equal. A while back, for gits and shiggles, I let my 460AHr bank drop down to about 25% SoC. When I got back to the dock, my Inverter/Charger was pushing in 50A, my alternator was pushing in 60A, and my solar was pushing in another 10A. I did turn the engine off after a while because burning diesel to charge when you have free shorepower is silly. But it was interesting to see what would happen.

The point is there isn't really priority, they'll all push into the system if they can.

Because we have a wakespeed regulator on our alternator, we can flip a toggle switch and put it into "Zero amp" mode, where it drives the alternator field just enough to keep the battery amps at zero. In that mode, it basically just supplies the house loads minus the solar current.

[noelex 77]

Leaving on both charging sources is the best solution. Some set the alternator voltage charge points a little lower than the alternator controller. This means when both charge sources have more power than the battery can accept, the charging current will be mainly from the solar panels. This is preferable, as charging from the alternator slightly reduces the engine power and heats up the alternator, potentially shortening its life. Charging from solar has no negative impact.

Likewise, it is preferable to take energy from solar rather than shore power if the the shore power is metered.

[sailorboy1]

If running the engine/alternator a long time why does it even matter whether solar or the alternator is doing the real charging? All that matters is you are charging.

[RaymondR]

The batteries don't care the charging DC comes from as long as they get enough and are not being over charged.