24v from two 12v batteries

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Leading on from a discussion with a chap on FB... can anyone think of a way round the issue that if you have 2 x 12v batteries they share a common earth therefore not allowing you to get 24v AND 12v from the batteries by running them in series?

I kind of feel there must be a way round it (which doesn't involve running a 24v setup and a 24-12v dc:dc converter, or a 12-24v dc:dc converter) but, can't think of one... - oh and that's 12 and 24 at the same time, I could think of a way to have one or the other...
 
Why not connect them up in series and have the connecting positive run through a relay which is operated by a switch. I might be wrong but shouldn't this then mean that when you operate the switch it will open it up to allow 24v
 
the_wolf said:
Why not connect them up in series and have the connecting positive run through a relay which is operated by a switch. I might be wrong but shouldn't this then mean that when you operate the switch it will open it up to allow 24v
Click to expand...

Yes but will change from a full 12v system to a full 24v system which will blow everything that's 12v
 
no, because both earth's are connected together in any twin battery vehicle system... so, if you connect battery 1 neg to battery 2 pos then measure across battery 1 pos and battery 2 neg you still only get 12v as the battery 2 neg is connected directly to the battery 1 neg... so it's just the same as measuring across one battery...
 
Bump said:
no, because both earth's are connected together in any twin battery vehicle system... so, if you connect battery 1 neg to battery 2 pos then measure across battery 1 pos and battery 2 neg you still only get 12v as the battery 2 neg is connected directly to the battery 1 neg... so it's just the same as measuring across one battery...
Click to expand...

that'll give yer 24v.

that's just shorted battery 2 out :eek:

what you tryin to do :confused:
presume its vehicle related, and everything needs to share a common earth?
 
the first battery was wired as per normal and the second battery was wired through 2x barrel solenoids, so in non energised state the second battery would be + to 1st battery + and neg To second battery Neg.when energised the second battery neg would be switched from first battery neg to pos and the pos on second battery removed thus giving 24v between second battery + and chassis. When de energised the two batteries are efectively jumped so both charge off the standard landy set up. I also fitted battery isolators to each battery so i could use alternate batteries when camping ans use the other for starting in the morning.
Im actually thinking of reinstalling it on the new 90 to give 2 speed to the winch, 12 and 24v as good winch do with their set up on bow motors
 
Use a bosch parallel start relay allows 12v charging and 24v starting or winch, completely interlocked and safe from high amperage shorting.
Ive been building challenge motors for a long time and its a proven method
 
pressbrake said:
Use a bosch parallel start relay allows 12v charging and 24v starting or winch, completely interlocked and safe from high amperage shorting.
Ive been building challenge motors for a long time and its a proven method
Click to expand...

Edit: Found them now.

They do look like they'd do the job! Thanks,
 
Last edited:
would this not work??

1224.jpg


if not, can some please explain why not, ive used it on LED lighting systems, where dimming is done on the -ve leg, and used differing supply voltages (in my case was 2 different PSUs.)
 
Last edited:
Bump said:
Leading on from a discussion with a chap on FB... can anyone think of a way round the issue that if you have 2 x 12v batteries they share a common earth therefore not allowing you to get 24v AND 12v from the batteries by running them in series?

I kind of feel there must be a way round it (which doesn't involve running a 24v setup and a 24-12v dc:dc converter, or a 12-24v dc:dc converter) but, can't think of one... - oh and that's 12 and 24 at the same time, I could think of a way to have one or the other...
Click to expand...

Look at ford battery system on there Diesel Pickups might help. I got 2- 12v battery's hooked the negative ground. but the stater is 24 volts. All the other electrics in it are 12v (2005 6.2 liter)
 
SteNova said:
what is the job your trying to do?
Click to expand...

It's hypothetical, guy on FB wanted to run a 24v winch on a 12v landy, was trying to help him out but concluded buying the very cheap 24v winch he has on offer, selling it on ebay then buying a 12v winch was a much better idea for him!

timtheenchanteruk said:
would this not work??

1224.jpg


if not, can some please explain why not, ive used it on LED lighting systems, where dimming is done on the -ve leg, and used differing supply voltages (in my case was 2 different PSUs.)
Click to expand...

If you had a 24v alternator for the 24v charger circuit, yes, however, that would require an unnecessary upgrade to the alternator.

Thor1950 said:
Look at ford battery system on there Diesel Pickups might help. I got 2- 12v battery's hooked the negative ground. but the stater is 24 volts. All the other electrics in it are 12v (2005 6.2 liter)
Click to expand...

Thanks Thor, i knew in theory it would be possible, just, couldn't work it out!
 
I 200 tdi'd my 24 volt lightweight, fitted the 24volt generator to charge but ran the 12 volt electrics for the glow plugs n starter by just wiring to the + and - on the first battery... worked perfectly no relays etc needed... could do the same to run a 24 volt winch

cheers steve
 
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