I have a general electric-no puns intended-question regarding wiring a couple of batteries(12 volt SLA's) for series and parallel(not simultaneously) operation in a discrete circuit design.The switch/s needed-S.P.D.T.electromechanical and/or
S.S.-will need to pass 30-75 amperes of current(max),and will need to be wired
so the relays are N.O. in series mode,and(if I mix solid state with N.C.
electromechanical relays)the S.S. are wired in parallel mode!!
This circuit's relays will-both S.S. and E.M. or only E.M.-will be actuated by the same switch;so,what schematic source(or forum member )can help me in
creating this circuit with a minimum of discrete components and wiring

 

You won't be happy to hear this. The only relay I could find that will handle that current is an Omron G9EA-1-CA-DC12. It's good for 100 amps and has a 12 volt coil. But it is SPST-NO only, and costs $119.13/ea.

If you have AC power available, definite purpose contactors might be a slightly lower cost alternative.

I wonder is some IGBT's might be able to do the reconfiguration?

 

There are SPDT, DC coil contactors here that should work, for less than US $100. I just did a quick Google search for "100 amp relay".

 

You COULD use two SPDT relays. However, when the coil fails on one of them (or the relay gets "stuck" in the NC position) you will wind up putting a dead short across one of the batteries, and there will be an earth-shattering *kaboom* as the battery self-destructs and sprays acid everywhere.

It's not a question of IF, but WHEN, as ALL electromechanical devices will eventually fail.

You really either need to find a DPDT relay, or perhaps you could use one of those "Frankenstein laboratory" DPDT knife switches. Those things will handle a good bit of current, and you're running at low voltages.

Here's a company that specializes in those types:
http://www.filnor.com/html/products/knife.html

They also have "field discharge" switches, which will help if you have an inductive load, such as a motor.

Capacity up to 2000 Amperes.

 

You COULD use two SPDT relays. However, when the coil fails on one of them (or the relay gets "stuck" in the NC position) you will wind up putting a dead short across one of the batteries, and there will be an earth-shattering *kaboom* as the battery self-destructs and sprays acid everywhere.

Either that or flash-vaporisation of conductors, resulting in a fiery spray of molten copper or aluminum. Either scenario will be life-altering for the families of the operator.

If remote or automatic operation is not required, you could use a simple 100 Amp transfer switch. They can be had for less than $150.00