Charge both banks together?

kloudie1 · Apr 20, 2011

If the start batt is a "maintenance free" batt then no, don't charge together. if it is a regular wet cell deep cycle like the 6V ones, then yes Charge together

Stu Jackson · Apr 20, 2011

Wiring

Stephen, It All Depends on How Its Wired. Really. Most likely your alternator is wired to the C post of the 1-2-B switch, which is the way it most likely came from the factory unless the PO or you changed it. We just don't know. If you don't have a combiner or echo charger between your house and reserve bank, that's probably the way it is. In order to charge both banks together, you'd need to use the ALL switch position, because the alternator output goes to the C post of the switch, and the switch is determining where the charge current goes.

You may want to read the topics linked in my "Electrical Systems 101" topic, including links to Maine Sail's electrical articles.

http://c34.org/bbs/index.php/topic,5977.0.html

Johnb · Apr 20, 2011

If you have AC power at your dock then a simple, inexpensive (< $100) battery charger (e.g schumacher ship n shore) should be in your toolkit. This has settings for multiple type of batteries combined with multiple type of charges and is a way more effective way of bringing those batteries back than running your engine.

If those batteries are both seriously flat then connecting them together and running the engine (how do you get it started?) for a few hours won't hurt them but won't properly charge at least one or maybe both. In general connecting different type of batteries together is a bad idea.

sailaway78 · Apr 20, 2011

Time

It's gonna take a looooooooooooong time to get them fully charged. Depending on the alt. size, you should be able to get them up to around 80% in a reasonable amount of time, but the last 20% to fully charged is gonna take a while.

Johnb · Apr 20, 2011

When the batteries are connected together they will be forced to have the same voltage across them. If one has more charge than the other current will flow from that one to the other until its voltage rises to the point where if they were separated the voltage would be the same.

This takes place quite quickly and provided there is'nt a huge mismatch e.g. 10 ampere hour battery connected to 200 ampere hour battery the amount of current circulating between them will do no harm. This happens every time a car is jump started for example.

Once a source of charge is applied, current is being forced into the combination of the two batteries and whichever would have the lower voltage if they were separated will be taking more from the charger than the other (again assuming they are approximately matched iin size and wiring).

If the banks are not identical then one of two things will happen. If the charging device is matched to the battery that would be fully charged at a lower voltage than the other one, it will be fully charged and the other will not. If the charging device is matched to the battery that should have the higher voltage it will over charge the other one.

Over charging will wreck a battery quite quickly unless the electrolyte can be replenished (before the plates are uncovered). Under charging will eventually shorten the battery life by sulphation.

(Battery voltage is not actually all that good of an indicator of state of charge. It is dependant on temperature to the point where if you don't know the temperature of the inside of the battery you don't really precisely know what the state of charge is).

The good news is the probability that you will do any harm by connecting them together and running the engine for a few hours is very low. The bad new is you may not get a very good charge.

If you can add distilled water I would make sure the levels are good before you start and check them again afterward. If at least the starting battery is small enough to make removal and charging on shore practical I would do that.

Maine Sail · Apr 20, 2011

Stephen Trapani said:
No dock, I'm on the hook! I thought I read that they WILL both charge adequately if combined and that the battery with the higher charge will constantly flow to the lesser until they are both full. No? (I am going to start the motor with a boost battery)

You are correct and safe to charge on ALL but with dead batts watch the temp of your alt. Small stock alts are not the best when demanded of full output for long periods, as is what happens with two dead banks. It will take a long time to charge both banks but will work if you just monitor the temp of the alt and let it get some air..

Maine Sail · Apr 20, 2011

Stephen Trapani said:
Hey thanks everyone! My alternator is 60A, 82A max rated, non-stock. I will keep tabs on the temp. Too hot to touch=bad? And what about the theory that it's actually better for the batteries to charge them combined?

Please explain the theory, I have not heard that one? Perhaps you mean combined as a single bank? Charging batteries combined with ALL or an ACR device is fine so long as they are similar type with similar charging voltages, wet/wet, gel/gel, agm/agm.

Alts can run 200 +/- degrees when really worked hard...

Maine Sail · Apr 20, 2011

Stephen Trapani said:
What is too hot?

You'll start to smell it.

zeehag · Apr 21, 2011

mine all charged well on mooring when i charged all together---- once i return to allbatteries of same age--replacing them bank by bank--i will again do the all together method....worked great for me, both with honda 2k and with engine alternator(80 amp)