Good Day. I am a mechanic for Earthmoving Machines. Most of them require a jump start in order to get them running. Now I have a battery pack with 2x Heavy duty 12v battries installed. The wires are connected in a way allowing with the flip of a mechanical switch to close the circuit allowing either 12v or 24v to go to the jumper leads. My problem is the on the 12v side the one battery gets drained more and takes most of the work beceause of how it is wired. I was thinking of using body soloniods or high current relays to make it so the if you select 24v the battries are connected in parallel giving you 24v and then if you select 12v the battries are then connected in series allowing for 12v but higher amp output. I have designed a diagram in paint(forgive me have basic knowledge of automotive electricals) and was wondering if someone could take a look at it and tell me if they feel it can work no problems or if there is a alternitive way of doing it. Keeping in mind that the machines that will be connected to the pack have a high current draw and that I also need a 3 position switch in it so that if the switch is in the middle there is no power being drawn out allowing for safe connecting of the jumper leads.
Thank you in advance

 

From the center of the switch you have a fine red line going to a red circle on the right and then a fat red line going to what seems to be a ground between the two right batteries. A similar mistake seems to be on the left red circle. This black bar among the batteries is very confusing because batteries don't have 3 or 4 terminals. Bottom line is, I can't read your drawing or it is very wrong. Please try again.

ps, you said in writing that you have 2 batteries, but the drawing shows three. More confusion is the result.

pps, It's nearly 4 A.M. where I am. Please excuse me if I fail soon. There are several other competent people here to help you...but probably not in 30 minutes or less.

 

I appologise I have edited it allowing for better understanding.

 

Switching between series and parallel can be done with a simple DPDT (double pole double throw) switch.

No need for the solenoids.

 

I understand what you are saying but I also need a off as stated. They need to handle high current draw

 

I can see a small problem with the "signal" wiring. It can not be connected to both batteries, because the wiring effectively connect the two + poles permanently together. Connect the two way switch centre pole only to the left hand battery + pole in your diagram.The signal circuit (or control circuit) is 12V and should be kept like that say using one battery for the purpose. Don't mix-up the 24V and the 12V.
Your idea is correct, except that for the 12V you need to put the two batteries in parallel (not series) and for the 24V the two batteries need to be in series (not parallel).
You DO need the solenoids because of the high current requirement.

 

Thank you Johann. So if I understand you correctly it should look like this?

 

This looks more like it! You may just have to confirm the labeling on your 2-way switch. It might be the other way round. You'll have to switch it and test which side connects to the centre and when. Other than that, I don't see why it shouldn't work. Good luck!

 

So here is my list of items I need other than the wires. Please click on each item and tell me if they would work
3 x Insulated Continuous Duty 12V SPST Solenoid
1 x Toggle Switch SPDT On-Off-On
2 x 12v Battery (This is the battries I already have)

 

Hi SILENT001,
As long as you don't rely on the battery pack only to do the starting; i.e. the earth moving equipment will still have its own battery also, I believe the solenoids shown will make it (85A).
Next, see that you always connect the batteries to a good, regulated battery charger to keep them in good shape and to prevent sulfating.
The SPDT toggle switch with centre zero (off), looks good.

 

What would happen if I started a machine using only the battery pack? Would the current draw be to much for the solenoid to handle? I am busy working on quotes for the parts to make it happen. Currently we using a mechanical copper change over lever which burns away on the 24v side

 

All depends on the CCA (cold cranking amps). Usually this is a few hundred amps, so you'll need:

1. Heavy duty welding cables with good quality clamps at the vehicle end of them
2. Solenoids to match the cranking current.
3. It will help if the switch is switched on before your starting attempt and to only switch it off after the starting attempt, in other words, do not interrupt the circuit from the battery pack while cranking.

 

The battries have a CCA of 1400. Have thick cables about 1 inch in diameter. Also would it make a difference if I use a 12v solenoid to pass 24v through it pole? IE. using the 12v Solenoid to complete the 24v circuit but only applying 12v to the coil section?

 

The battries have a CCA of 1400. Have thick cables about 1 inch in diameter

Yea, that is the CCA of the batteries. No problem here. The question is how much current is drawn by the equipment starter motor while cranking? Try to measure this with a DC clamp-on ammeter. It should give you a good indication of how long your solenoids will last. Usually the time taken to start is not very long and the solenoids proposed might last........., but then they might not....

 

Also would it make a difference if I use a 12v solenoid to pass 24v through it pole? IE. using the 12v Solenoid to complete the 24v circuit but only applying 12v to the coil section?

 

It does not matter if the control side (coil) of the solenoid is 12V, it's the contact rating in amps that counts.
Here is a bigger one

http://www.colehersee.com/home/item/cat/189/24812/

 

if you select 24v the battries are connected in parallel giving you 24v and then if you select 12v the battries are then connected in series allowing for 12v but higher amp output.

It's the other way around. You want parallel connected batteries for 12V operation and series connected batteries for 24V operation.

 

This issue was already addressed.

 

As far as peak amps go I wouldn't worry about it too much being regardless of what type of battery clamps you are going to use they are going to be the biggest current limiter.

Odds are unless you are directly bolting your booster leads to the vehicles starting system you wont get much more than 400 - 500 amps out of your system at best.

To be honest the best thing you could do for boosting vehicles would be to build your unit with four 8 volt batteries so you have either ~15 volts or 30 volts open circuit which will put a good charge back into what ever battery you are boosting.

By doing that you could get by with smaller gauge leads and solenoids plus have a few extra volts to your advantage when cranking that make up for lead and clamp losses.

 

Is the center off switch momentary?
If not, you might want to make the switch momentary so the solenoids won't be inadvertently left on.
Otherwise you would likely burn out the solenoids (starter solenoids are usually momentary rated for low duty-cycle) and/or drain the battery.
You could add a momentary push button switch in series with the common terminal of the selector switch for that purpose.