Thank you Johann you have been most helpfull will try get quotes on that product in the link you provided. I looked at the details and it looks like it would be better.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
This will not work as the unit needs to be mobile and the pack I have with the batteries I have are sufficient and does the job well. My only reason for wanting this setup is to remove the mechanical copper change over lever that tends to burn away once current is passed through it due to the gaps in it.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.
Sorry but that will also not work as I need to have it so that one person alone can jump start a machine so having a toggle switch that can stay in either 12v or 24v would be what I need. So basically how it will be used is as followsIs 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.
1) Pull the battery pack to the machine.
2) Insure the switch is in the middle(off).
3) Unroll the jumper cables and connect the positive to positive and negative to negative.
4) Toggle the switch to the correct voltage.
5) Get in the machine and start it.
6) Get out the machine and toggle the switch back to the middle(off).
7) Disconnect the jumper cables starting with negative first than positive.
8) Roll up the jumper cables again and move battery pack out of the way.
9) Move machine.
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