Using solar charge controller with AC battery charger

Maine Sail · Apr 23, 2013

weinie said:
I have a solar charge controller and an AC shore powered charger that are both connected to my house bank.

My question is, should I disconnect one while using the other in order to provide maximum charging speed as well as acceptable float voltage charging?

I understand that the each charger only "sees" the highest voltage on the circuit. For example, if the engine is off and the battery is at a resting voltage of 12.5 volts, and the (somewhat dumb) solar controller is charging at 14.4 volts, then the AC battery charger will see the 14.4 volts of the solar controller and not the 12.5 of the battery. Hence, the more efficient AC charger (a promariner sport), may be in a float phase rather than a more useful absorption phase.

Each item will vow for "voltage supremacy" BUT only when the bank has been brought up to target absorption voltage. Eventually the one with the highest voltage setting wins and "finishes" charging the bank.

In bulk (this is before either charger or controller has hit a limiting/absorption voltage) both items will be pumping out all they can. This is good because it gives you faster charging in bulk.. Once the "target voltage" has been hit the device with the highest voltage setting will shut the other device down, if it can maintain and hold the voltage above the other device.

Lets say the solar controller is set for 14.45 but the charger is only set for 14.42V. Once at 14.42V (approx) the charger will shut down and wait for the voltage to drop back to 14.40V (approximation) before resuming charging.

If the solar controller can in-fact hold the voltage at a level above the charger, all on its own at that SOC, then there is no need for the charger. Often the voltage will begin to fall once the other device stops pumping current. The lower voltage device kicks back on until you get to a point in the charge state where the solar panel can keep and hold its target voltage.

There is no problem running two charge sources because all they know is voltage. If one can't hold or maintain the voltage the other device will kick back in...

Maine Sail · Apr 23, 2013

weinie said:
Right, but how does one device "know" that the target voltage of the battery has been reached when all it senses is the higher voltage of the other charging device?

Because the other device has already been able to bring it to target absorption voltage.

weinie said:
If my solar controller is set at 14.4 volts it might only be putting out about 1 amp on the average on a partly sunny afternoon. When I plug in the charger, my thought is that it would only "see" the 14.4 volts of the solar controller and not the depleted voltage of the battery.

If your solar with a 1A output has brought the bank to 14.4V then you are well into the very high 90's as a state of charge or your batteries are beyond sulfated.

The relationship between current and voltage goes hand in hand. The smaller the current source the longer it takes for the bank to reach "target voltage". Conversely the larger the current source the faster you hit "target voltage". With a big enough charge source you can hit voltage limiting/absorption at 70-80% SOC. With a 1A source on a 100Ah battery for example you are not going to hit 14.4V until you are at 98%+/- SOC..

weinie said:
And instead of kicking in and charging with up to 20 amps of current that it is supposedly rated for, the AC shore charger is taking the day off!

If a 1A charge source is holding your bank at 14.4V there is no physical way 20A of additional current is going in...

weinie said:
I would imagine this would get even more interesting if I upgraded my solar panel controller to one with four phases!

It has nothing to do with stages and everything to do with current and how much current is needed to maintain a voltage at a specific SOC.

This video may help, may not..

Ron20324 · Apr 23, 2013

And in the same general theory, this is why my owners manual says to not run the charger off shore power when the engine is running. They're bucking each other.

FourPoints · Apr 24, 2013

Ron20324 said:
And in the same general theory, this is why my owners manual says to not run the charger off shore power when the engine is running. They're bucking each other.

You didn't read MS's post, or watch the video, did you?

Maine Sail · Apr 24, 2013

Ron20324 said:
And in the same general theory, this is why my owners manual says to not run the charger off shore power when the engine is running. They're bucking each other.

This statement in "some" charger manuals really has nothing at all to do with "bucking". It has to do with chargers being fried from motor starting when improperly wired or when a manufacturer uses the cheapest components possible on the output rail. Some manufacturers cover their butts with statements like that because they know that the charger may not be able to handle the starting of the motor without damage.

A good quality modern charger such as the Sterling Pro-Charge Ultra or ProMariner Pronautic P are unaffected by motor starting and can be left on while starting a gen set or engine.

There are thousands upon thousands of installations out there with multiple charge sources running at the same time and it's a non-issue. I have one customer, a world cruiser, who has hydro, wind, solar, engine alt and gen set charging via two 60A shore chargers, and he often uses them all at once and can do his bulk charging in about 40 minutes.....

Mike B1026 · Apr 24, 2013

Maine Sail - Great information. I knew that you could connect to multiple chargers but your explanation on how they actually work really helps.

chp · Apr 24, 2013

Also thanks. I've had the same thoughts when running my small outboard with my solar. Also will be going on a trip in June and may have to augment with a genset. Glad to know I don't have to disconnect and reconnect cables.

ifmdalvey · Apr 24, 2013

Mainesail
that video was the best and easiest to understand description of the relationship of voltage/current i have ever seen, thank you.
One quick question, why should i not set my external regulator to a slightly higher voltage to get the batteries back up to full charge quicker?

Maine Sail · Apr 24, 2013

ifmdalvey said:
Mainesail
that video was the best and easiest to understand description of the relationship of voltage/current i have ever seen, thank you.
One quick question, why should i not set my external regulator to a slightly higher voltage to get the batteries back up to full charge quicker?

You should ideally set it as high as your batteries and your maintenance level will tolerate. Higher voltages means faster absorption changing but more water use.