Charging Dissimilar Batteries in Parallel

[99yam40]

I read lots of funky information over on the other site. For instance, to be charged in parallel, batteries must be of the same type (flooded lead acid or AGM lead acid), must be of the exact same size, must be about the same age, etc., etc., Otherwise, one battery will either be discharge or will over charge the other battery.

Knowing just a tad of ohms law, that made me suspicious. Furthermore, ACR's/VST/Isolators/Combiners/Etc. are doing this daily with apparently no reported ill effects. So I decided to install some volt meters and amp meters to see what is to be seen. I am not seeing what folks are saying.

Think about it. In your house you have one power supply (wall outlets usually) and many different loads. Clocks, fans, refrigerators, lamps, etc.. Plugging in one device is putting it into parallel with any other devices that are plugged in. One device does not affect the others. Well maybe a refrigerator or air conditioner may momentarily affect the voltage but the system quickly recovers. Why would charging batteries be any different?

My comments relate to when two or more batteries are being charged. Power supply having a higher voltage than either battery. If they are in parallel and no power supply, all bets are off.

Am I missing anything?

I use to know what all all of the different flooded cells should be maintained at for station batteries( per cell), but have to look it now a days.
I am sure gel cells are a little different too, most have set voltages for stand by and cycle usage.
float, equalize, and just nominal cell voltages are different for different material make up of cells

So I could see how mixing some batteries on the same charge system could be a problem.

I am not sure I would want to be in a boat off shore with lithium batteries on board if they decided to burst into flames.
just like I would not like to be in a plane up in the sky with them.
as long as I could quickly stop and get off/away safely on dry land I am good with those at this point.

[boscoe99]

Well, YES and no.. in a real life scene such as on a boat with a small, wimpy outboard alternator, undersize cable runs. Ground faults and a host of other possible varible's.. the answer your seeking grass hopper might be more defined so as I can give you the correct answer.. This is my forta and am a Electrical spe******t. Love doing diagnostics and system design. As soon as the two "Battle Born" 100 ah lithium Batterys show up I doing a sweet install. Custermer has cked my refs and had a easy 'energy audit'. More or less open check on my refs for all the required parts.. yes haw.. no cutting corners on three batt solar system with 1kw pure sine wave inverter. The battery company is running behind with high demand since the hs covid scare. And now the solar company that I'm sourching with has offered to higher me in my local market.. I'm already working 7 days. Jeeze. I could hire 3/4 electrical techs but,, there are none
Major crisis. Anyway what exactly are you trying to figure out ??????

I guess that I am trying to figure out if current can flow out of one battery into another battery while both are receiving current from a power source.

Similar to pumping water into two tanks while having water flow from one tank to another I suppose.

[boscoe99]

Here are a couple of scenarios. One motor (A) charging a flooded lead acid battery. Same motor (B) charging an AGM lead acid battery. Same motor (C) charging both a flooded lead acid battery and an AGM lead acid battery at the same time.

As long as the motor (C) maintains an output of 14.5 volts to both the flooded lead acid battery and the AGM lead acid battery, how does one battery go about affecting the other battery?

[99yam40]

Seem to me that if the power from a motor charging system is higher than all of the batteries the current will flow from the charging system to all of the batteries.
now how they share the current would depend on the internal resistance of the batteries and what state of charge they are at.

there is the possibility of over charging a battery if the output voltage of the charging system or any of the other batteries that are paralleled with it is higher than the battery is suppose to take.
I have not found a battery that has opened up internally before from what I can remember,
but have seen bad cells short out so that the extra voltage for that cell is now shared by the other 5 cells in that battery

when batteries are paralleled and one is at a higher voltage than the others then the higher voltage will flow current into the lower ones when charger is off.

if one battery ends up with a bad cell then the other batteries should flow current to that bad battery when the charging system is off line if there is nothing there to block it
when charger is running and higher than all of the batteries it sends current to all as mentioned above.

Is that not the reason Yamaha put in that auxiliary battery charge wire, so that the start and house are not tied together.?
and the reason for a battery switch is to be able to use the house battery to start the motor if the start bat dies?
I see no reason to have the switch to both at any time if you have them both hooked up to be charged in a different manner.

I never really thought much about how many batteries a multi motor boat should have.
does the boat need a battery for each or not?

[boscoe99]

Seem to me that if the power from a motor charging system is higher than all of the batteries the current will flow from the charging system to all of the batteries.
now how they share the current would depend on the internal resistance of the batteries and what state of charge they are at. I agree. I think. Until someone proves that I am wrong.

there is the possibility of over charging a battery if the output voltage of the charging system or any of the other batteries that are paralleled with it is higher than the battery is suppose to take. I agree. 14.5 volts output from most outboard motor electrical generation systems seems to be par for the course. Maybe not ideal according to the battery type but from what I know it will not damage a battery.
I have not found a battery that has opened up internally before from what I can remember,
but have seen bad cells short out so that the extra voltage for that cell is now shared by the other 5 cells in that battery I suppose a cell could fail open. In which case no output from the battery?

when batteries are paralleled and one is at a higher voltage than the others then the higher voltage will flow current into the lower ones when charger is off. I agree. But for my assessment I am only interested in batteries that are being charged. And which will be unparalleled as soon as the charge voltage terminates.

if one battery ends up with a bad cell then the other batteries should flow current to that bad battery when the charging system is off line if there is nothing there to block it
when charger is running and higher than all of the batteries it sends current to all as mentioned above.

Is that not the reason Yamaha put in that auxiliary battery charge wire, so that the start and house are not tied together.? Convenience mostly. And something to sell. The Yam isolator lead does just one a combiner/ACR/VSR does. It just does it on the motor instead of at the battery.
and the reason for a battery switch is to be able to use the house battery to start the motor if the start bat dies? Yes.
I see no reason to have the switch to both at any time if you have them both hooked up to be charged in a different manner.

I never really thought much about how many batteries a multi motor boat should have.
does the boat need a battery for each or not? Recommendation from Yamaha is one battery per motor. In my view, one battery could serve several motors. But if I ever own twins I will have one battery per motor. Plus a house battery.

I appreciate your comments.

Think I need to consult with folks on an electrical forum.

[oldmako69]

Drunk-guy.gif

WHAT IN THE HELLAREYALL TALKIN ABOUT???


(Great thread)