12-24 Volt

[Don S]

Below is a drawing. I know it should work in theory, but will it in the real world?

I know using the 12V acc will pull amperage out of battery A, but won't both battery A and B equalize voltage as A gets lower?
And what will happen if the 24v trolling motor gets used at the same time as the 12v acc?

 

[TerryMSU]

Re: 12-24 Volt

Sorry Don, but they will not equalize. The reason why, is because for them to equalize, they need to transfer charge from the high one to the low one. Because they are in series, they cannot transfer charge. If they could, one battery would need to have a massive static electricity charge. Since that obviously does not happen, you are out of luck. That said, as long as the accessory does not draw a lot of current, there should not be an issue.

TerryMSU

 

[Don S]

Re: 12-24 Volt

Sorry Don, but they will not equalize. The reason why, is because for them to equalize, they need to transfer charge from the high one to the low one. Because they are in series, they cannot transfer charge.

That is the part I was not sure about. I knew they would equalize when wired in parallel, just not sure about series.

 

[fishrdan]

Re: 12-24 Volt

The batteries won't equalize, but there's nothing wrong with connecting an accessory like,,, the accessory will just see 12V.

The only problem you might run into is if the accessory pulls too much current from the battery and drags down batt A while batt B is still completely charged, the TM won't run well due to the low voltage of batt A. But,,, that accessory (big stereo...) would have to pull a lot of current to make a difference, compared to how much the TM draws.

I run my boat like that ^ when I flip the batt switch over to "B", all of the accessories running off batt A while I'm using the 24V TM. Never had an issue with it.

 

[Don S]

Re: 12-24 Volt

The batteries won't equalize, but there's nothing wrong with connecting an accessory like,,, the accessory will just see 12V.

The only problem you might run into is if the accessory pulls too much current from the battery and drags down batt A while batt B is still completely charged, the TM won't run well due to the low voltage of batt A. But,,, that accessory (big stereo...) would have to pull a lot of current to make a difference, compared to how much the TM draws.

I run my boat like that ^ when I flip the batt switch over to "B", all of the accessories running off batt A while I'm using the 24V TM. Never had an issue with it.

Kind of what this thread is about, what happens when you put a motor and it's charging system on that single battery to keep it fully charged from the motors charging system. Or maybe one of those batteries as a house battery, and one a starting batter, maybe even a battery isolator (not an ACR) to keep both at the same charge. Not even thinking about battery switches at this point, just the use and charging of the batteries.

 

[fishrdan]

Re: 12-24 Volt

I have batt A (in the diagram) being charged by the engine's alternator, but batt B (as in the diagram) has no way to get charged since it's connected in series. The series connection would need to be broken first, then a parallel connection created. I've posted this before, but I'm using a Marinco 12/24 receptacle and plugs to make/break the series and parallel connection, so I can charge the 24V bank off the alternator.

I don't think you could use a battery isolator due to grounding issues, big sparks and balls of fire.

One not perfect solution might be a MinnKota alternator charger,,, if it has independent outputs. Connect batt A to the engine and alternator normally, then connect the MK Alternator charger to batt B, so that the single battery gets 10 amps as the engine is running. Not a great solution as it requires the engine to be running, and it's only 10 amps...

 

[bruceb58]

Re: 12-24 Volt

It would be no problem having the motor/accessories hooked up to one of the 12V batteries if the load is fairly low. What you would want to do is to charge the two batteries up at the end of the day with a 2 bank charger though. Not they really make one, but a 24V series charger would harm the less discharged battery.

ACRs can't work here because the 2 batteries would need a common ground which obviously isn't possible if they stay in series.

I would probably rotate the battery which is used as the 12V battery with the other one every few months as the one battery that is getting discharged more than the other one won't be lasting as long.

 

[Barnacle_Bill]

Re: 12-24 Volt

I have ran accessories that way for many years. {but not electronics} Install an on-board 2 bank charger and your good to go.

 

[UncleWillie]

Re: 12-24 Volt

We often focus on Amps and/or Volts; But it is always really about POWER/Watts!

Consider the trolling motor drawing 40 amps and the House load at 5 amps.
The left battery sees a 45Amp load and the right battery sees a 40A load.
If the House load is removed after an hour, both batteries now see a 40A load.
After a Second hour the left battery will have delivered 85AH and the right only 80AH.
Batteries in series always have equal current passing through them. They will never equalize until recharged.

If charged in series, at 24v, the Right Battery will top out first and "Boil Water" until the left one caught up.
If charged in parallel, at 12v, the Right Battery will Top Out first but its charge current would drop below the Left battery as they equalized.

 

[Don S]

Re: 12-24 Volt

I redrew the picture, and it looks to me like using an isolator should work if you did it like this.



Then I got to thinking about the ground comment by Bruce and looked at the picture and though about if someone put a ground wire from the 12v panel to the 12v engine and thought about what would happen. Not good.

 

[bruceb58]

Re: 12-24 Volt

Battery A wouldn't get charged.

You would need one of those MinnKota devices that fishrdan mentioned. It basically is a DC to DC convertor so the result is two separate grounds and 2 separate outputs to charge the two batteries.
http://store.minnkotamotors.com/products/419589/MK_2_DC_(2_bank)
here is the manual
http://store.minnkotamotors.com/media/document/2377137_revH_english_alt_manual_100129.pdf

 

[UncleWillie]

Re: 12-24 Volt

Battery A wouldn't get charged....

Either would Battery "B"!
Except for One Diode in the Isolator, the Alternator is looking at a dead short!

 

[gm280]

Re: 12-24 Volt

When I looked at your diagram I thought about NiCad battery packs. So often In series circuits with chargeable batteries one or more will start failing before the pack does. And you end up having a pack that will not charge up to full potential anymore. I've seen it over and over with series chargeable packs too many times. I've even seen reverse charges on NiCad cell in packs before. The only way to solve those problems is to draw down all cells involved and short them out 'til they read zero voltage. Then remove the shorts and recharge. But since you would only have two batteries in a series circuit (of course still a lot more cells involved then just two batteries) You could get to the batteries to solve your problem. But if you do use up capacity from one battery more then the other, the output series voltage has to go down. And like previously posted, current is the same in any series circuit. So one battery will petter out well before the other and the remaining voltage will be reduced proportionally as well. Cell imbalance IS a huge problem in aircraft systems all the time. Maybe a viable solution to this dilemma is to install a third battery for the accessories and leave the 24 volt series circuit solely for the TM... Just a suggestion...

 

[Don S]

Re: 12-24 Volt

You would need one of those MinnKota devices that fishrdan mentioned. It basically is a DC to DC convertor so the result is two separate grounds and 2 separate outputs to charge the two batteries.
MK 2 DC Alternator Charger (2 bank)
here is the manual
http://store.minnkotamotors.com/media/document/2377137_revH_english_alt_manual_100129.pdf

Now we're getting somewhere. I have heard the "Charger" used, but always assumed it was an AC charger and never really looked into after that. I have to really look at that and understand it better.

Battery A wouldn't get charged.

In my drawing, (assuming a perfect world and no interconnecting grounds) why would B get charged and A wouldn't?

 

[bruceb58]

Re: 12-24 Volt

In my drawing, (assuming a perfect world and no interconnecting grounds) why would B get charged and A wouldn't?

No return path from the negative side of Battery A to the engine.

Not only that, but you have short circuit from output of isolator port B1 to ground of the engine.
EDIT: I see Willie already mentioned that too.

 

[Don S]

Re: 12-24 Volt

Either would Battery "B"!
Except for One Diode in the Isolator, the Alternator is looking at a dead short!

View attachment 202766

Duh :facepalm: I never gave it a thought about the current going the direction your arrows show. Guess I had by blinders on a little too narrow.

 

[bruceb58]

Re: 12-24 Volt

Now we're getting somewhere. I have heard the "Charger" used, but always assumed it was an AC charger and never really looked into after that. I have to really look at that and understand it better.

Basically, what is does is converts the DC of your alternator to AC and puts it through isolation transformers to get it away from the engine ground reference, then sends that to two independent chargers inside after the voltage gets rectified back to DC. I will try to find a picture or make one for you that explains that better.

 

[Don S]

Re: 12-24 Volt

Maybe a viable solution to this dilemma is to install a third battery for the accessories and leave the 24 volt series circuit solely for the TM... Just a suggestion...

That is the only thing I have ever considered recommending to people.

This subject comes up so often, I just wanted more opinions on the setup from others with more experience with dual voltages. Plus, it puts a lot of information here in this forum for others to learn from too. When some one asks "Why not".

 

[Don S]

Re: 12-24 Volt

Basically, what is does is converts the DC of your alternator to AC and puts it through isolation transformers to get it away from the engine ground reference, then sends that to two independent chargers inside after the voltage gets rectified back to DC. I will try to find a picture or make one for you that explains that better.

That would be great, if you can find one. My head hurts.

 

[UncleWillie]

Re: 12-24 Volt

... I've even seen reverse charges on NiCad cell in packs before. ... But if you do use up capacity from one battery more then the other, the output series voltage has to go down. And like previously posted, current is the same in any series circuit. So one battery will petter out well before the other and the remaining voltage will be reduced proportionally as well. ... Maybe a viable solution to this dilemma is to install a third battery for the accessories and leave the 24 volt series circuit solely for the TM... Just a suggestion...

+1

The big problem with the imbalance is the Cell Reversal.
Once the First Battery gives all it has to give; the other battery in series continues to push current.
Because the POS is connected to the NEG of the other battery it is the same situation as hooking up a charger with the wires reversed.
The weaker battery is essentially being charged in reverse.
It doesn't just go to Zero, it goes to Minus 12v! Destruction is imminent.

If you don't monitor the Batteries very closely, and continuously, and never allow Either one to go flat; A destroyed battery is almost a certainty.

The best and most realistic option is to dedicate two equivalent batteries to the 24v Trolling circuit, and a separate Start/House Circuit with a Combined or Separate House and Start Batteries. 3 or 4 batteries will be needed.