Can I pull both 12v and 24v from a battery bank?

[wrybread]

I'm helping a friend who has a battery bank with two 12v batteries wired in parallel. He needs to run an occasional 24v load from them. Is there any danger to adding a wire to series them, and using the battery bank as both a 12v and 24v bank simultaneously (with different connecion points obviously)?

Thanks for any help.

 

[robstrom]

I'm no expert, they will chime in shortly. A 12 volt to 24 volt dc converter would work (like zero breeze AC) wiring from output side of battery bank, through converter.
They're fairly cheap.

 

[wrybread]

I'm no expert, they will chime in shortly. A 12 volt to 24 volt dc converter would work (like zero breeze AC) wiring from output side of battery bank, through converter.
They're fairly cheap.

It's a fairly heavy 24v load though (a boat trolling motor).

 

[Charleswgibbs]

I'm helping a friend who has a battery bank with two 12v batteries wired in parallel. He needs to run an occasional 24v load from them. Is there any danger to adding a wire to series them, and using the battery bank as both a 12v and 24v bank simultaneously (with different connecion points obviously)?

Thanks for any help.

If they are connected in parallel, and you try to connect them in series at the same time you'll have a dead short on your hands. It's the same as running a cable straight across both battery terminals. Sparks will fly, wire insulation may melt, and fuses will blow. Serious damage to the battery could occur.

What you could do is disconnect the parallel cables and then connect them in series to use 24v stuff, then change it back to parallel. But you can't do both at the same time.

 

[MichaelK]

Is the boat fiberglass? The resulting white-hot arc will melt a hole in the bottom of the boat, you'll sink, and possibly drown. Other than that, no problem.

 

[740GLE]

What’s the 12v loads? How’s the battery charged? 12v off the motor?

 

[timselectric]

Two options.
1) build a 24v system and use a DC2DC converter for the 12v loads.
2) build two separate systems.

 

[Texas-Mark]

Just jumper them properly for whichever voltage you need. When in 12v parallel mode, it's as simple as removing one jumper and moving another

 

[MrThisIsME]

Just jumper them properly for whichever voltage you need. When in 12v parallel mode, it's as simple as removing one jumper and moving another

He is talking about running both at the same time.

 

[740GLE]

And typical boat batteries aren’t the easiest to access.

How did the 24v trolling motor come into play did he order the wrong one or just have laying around?

 

[MrThisIsME]

It's a fairly heavy 24v load though (a boat trolling motor).

If I understand correctly the two 12v in parallel are the start battery? If so must be a large motor. More so, running a trolling motor off a start battery sounds like a recipe for disaster. Put in another set of batteries, or sell the unit and buy a 12v.

 

[MrThisIsME]

Some of those 24v trolling motors can draw 60+ amps. Even if you could find a DC convertor that size, it would be cheaper to put in another battery bank, I would think

 

[Texas-Mark]

He is talking about running both at the same time.

Well, depending on the 12V load, it would be easy enough to tap off of one of the series 12V batteries. If the 12V load has it's own isolated lines, a double pole A/B switch could even be used to keep the batteries balanced while drawing from them.

 

[MichaelK]

Well, depending on the 12V load, it would be easy enough to tap off of one of the series 12V batteries. If the 12V load has it's own isolated lines, a double pole A/B switch could even be used to keep the batteries balanced while drawing from them.

I can't think of a better way to make batteries go seriously out of balance and ruin them. Mr. Murphy just loves the idea of manually switching back and forth between batteries to keep them balanced!

 

[schmism]

Two options.
1) build a 24v system and use a DC2DC converter for the 12v loads.
2) build two separate systems.

+1

 

[Texas-Mark]

I can't think of a better way to make batteries go seriously out of balance and ruin them.

I said "depending on the load". People sometimes overthink things.

Of course some people here said that mixing new FLAs in with an older bank would kill the bank "in no time" and yet I have been doing that for over a decade with zero issues. Real world vs "thinking" something won't work. <shrug>

 

[MichaelK]

I said "depending on the load". People sometimes overthink things.

Of course some people here said that mixing new FLAs in with an older bank would kill the bank "in no time" and yet I have been doing that for over a decade with zero issues. Real world vs "thinking" something won't work. <shrug>

Good that you have to attention for detail to stay on top of things.

I myself forget to return library books, have left the irrigation valve open in the orchard, flooding my trees, and forget important telemeetings, so I tend to mistakenly assume that everyone else is as forgetful a slob as I am.

 

[Texas-Mark]

My point is that often here (and on other forums too), there are always people who say something won't work, can't be done, etc. And then someone will come along and show how they have been doing exactly what they said would not work (this is very prevalent on car and gun forums). Just like the many threads here where someone asks about mixing FLAs and LiFePO4s, and many will say absolutely no, but yet we know people have been doing it successfully for years.

 

[32 volt boater]

I'm helping a friend who has a battery bank with two 12v batteries wired in parallel. He needs to run an occasional 24v load from them. Is there any danger to adding a wire to series them, and using the battery bank as both a 12v and 24v bank simultaneously (with different connecion points obviously)?

Thanks for any help.

It will short out.




Look at the left (parallel), what's going to happen if you connect the blue to it like on the right at the same time? You just shorted it out bigtime.

With this gismo you can do it maybe, I got to think about it, my thinking is stuck, might need 2 of them.

Lets see what the forum comes up with.



Its one way valve for electric, I am still stuck though. Need to use it different then in diagram.

My point is that often here (and on other forums too), there are always people who say something won't work, can't be done, etc. And then someone will come along and show how they have been doing exactly what they said would not work (this is very prevalent on car and gun forums). Just like the many threads here where someone asks about mixing FLAs and LiFePO4s, and many will say absolutely no, but yet we know people have been doing it successfully for years.

Exactly.

 

[schmism]

My point is that often here (and on other forums too), there are always people who say something won't work, can't be done, etc. And then someone will come along and show how they have been doing exactly what they said would not work (this is very prevalent on car and gun forums). Just like the many threads here where someone asks about mixing FLAs and LiFePO4s, and many will say absolutely no, but yet we know people have been doing it successfully for years.

And for each of these examples I can point you to the entire forum of failures we have for people who "thought it would be ok" and it wasn't|

The issue is people take the shady advice of cutting corners only to have complete failures a short time later and then want to blame the shady advice they got on the internet. Who you going to blame, the people not smart enough to understand why the advice was shady, or the people that offered the shady advice.