Off Topic big time LOL 12v charging 24v...............

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Post  Martin R on Thu Mar 21, 2019 4:30 pm

I need some help with a 12v charging vehicle and a 24v air compressor
My work vehicle is used for Road side service and I was able to buy a 24v A/comp that is military spec

My question is this

If I have a 12v battery that currently gets charged every time the vehicle starts up , could I add a 2nd battery to make 24v?? ??
No springs to mind as the 12v system would get fried straight away , what if I used a Battery isolating solenoid to stop the feedback entering the 12v system
Off Topic big time LOL 12v charging 24v............... 34qpfdk

If both Batteries are being charged at 12v , and the 24v bridge is disconnected everything is it save for 12v

However if I were to turn off the feeding 12v solenoid and activate isolating solenoid that will give me 24v right, right

As some of the tools run of 12v , I should be able to connect those to the leading battery and the 24v air compressor to the 24v leads

So if we do have any auto elecs here could you correct me if I'm wrong PLEASE


Cheers Marty

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Post  ivanll on Thu Mar 21, 2019 5:28 pm

DC/DC Converter Regulator 12V step Up to 24V.

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Post  Martin R on Thu Mar 21, 2019 5:42 pm

Yes I know
However at 140amp draw I'd like think outside the square

Marty

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Post  ivanll on Thu Mar 21, 2019 5:54 pm

There is another easy solution but it to require logic thinking Exclamation

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Post  peterinaust on Thu Mar 21, 2019 6:43 pm

When you activate the isolating solenoid to make 24volt, what will happen to the earths on the lead battery?? I would think there will be a dead short!

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Post  Martin R on Thu Mar 21, 2019 6:58 pm

This why I'm asking

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Post  bicter on Fri Mar 22, 2019 7:53 am

Can be achieved using a double pole changeover relay rated at the necessary current draw.
The normally closed contacts connect the two batteries in parallel with the wiper contacts connected to the auxiliary battery, the first normally open contact is wired out to the compressor and the second normally open contact is wired to the start battery positive.
Ensure suitable fusing is used to protect the wiring.
Hopefully this is sufficient for you to wire up a solution
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Post  boobook on Fri Mar 22, 2019 9:10 am

The problem to my way of thinking is in the earth isolation of the lead battery before the series connection of both.
In the use of solenoid isolators, any lag in the disconnect/connect may result in a dead short to earth, however brief. This is sure to cause a problem.
My solution would be to use 2 manual keyed isolators with 1 key. One between lead battery/earth, other between +/- both batteries
Isolate lead batt. earth first, remove key.
Install key in series connection (+/-), 24v. available.
Disconnect in reverse.
The "key" is to use only one key, but must remember to disconnect series connection and re connect lead batt. earth.
mike

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Post  Dozer on Sat Mar 23, 2019 10:20 pm

American trucks in the 70's used a series parallel switch to activate the starter on 24volt. Normal running was at 12 volt. I used to have the circuit diagram somewhere but a
simple internet search should show what you want. The actual switch used to be a big beast of a thing. I have no idea what a modern version will look like. Delco used to make a good one so ebay will be your friend. Starter flash current would have been up to 1000 amps and settle to 400-600 so it should handle your load easily.
Only issue will be that you can't run the motor while the compressor is running, so you risk your batteries getting too flat to start the vehicle after using the compressor.
You state the current draw as 140 amp. At 24 volt that is over 3 kw's which is a serious motor. What is the duty cycle?
You will only get to run the compressor for two to three minutes max before the batteries are flattened. You also need to think about what type of batteries can handle that sort of treatment. Standard car type batteries will not be happy and their life expectancy will be seriously diminished.
Petrol or diesel powered compressors are the norm for roadside assist for good reasons.

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Post  Martin R on Mon Mar 25, 2019 7:25 am

I pick it up today shall let you know

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Post  pablop on Mon Mar 25, 2019 10:30 am

Dozer wrote:
You will only get to run the compressor for two to three minutes max before the batteries are flattened. You also need to think about what type of batteries can handle that sort of treatment. Standard car type batteries will not be happy and their life expectancy will be seriously diminished.
Petrol or diesel powered compressors are the norm for roadside assist for good reasons.

Yep energy in versus energy out.  I don't think an ordinary vehicle battery isn't going to last long with that beast.
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Post  Martin R on Mon Mar 25, 2019 3:09 pm

Ok so the draw isnt as bad as I was told it would be
At 50amp draw I might get away with something like this eBay item number:322979953006

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Post  peterinaust on Mon Mar 25, 2019 6:14 pm

Looks a good little compressor. Bet your happy with that.

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