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Polarity switching issue, first one to resolve gets a one year pro membership, if answered by June 03 2012?

Ok, here's the issue.  years ago i picked up a wireless remote control kit for automotive use.  It consists of a 12v receiver with 4 sets of colour matched wires.  Basically you can turn on and off 4 devices.  Press button 1 on the remote and a on-board 15A relay activates completing the circuit for one set of wires.  Press button 1 again and the same relay cut outs and the circuit is broken.   These wires are designed to interrupt the negative or ground  side of your accessory with the positive lead hooked up to your power source.  The receivers power is hooked up to the 12v battery.  I even went so far as to open up the receiver and discovered the entire circuit to be potted in opaque epoxy (how rude) so no modding of the circuit sadly...

What I can't get my head around is how to utilize this as a polarity reversing unit, or can it.  Now I have messed around with using polarity reversing circuits in a analog style before, I even wrote an instructable on making one with a DIY DPDT switch 

Here's the thing, I live in a remote area of the world and do not have immediate access to what most people are used to, so is this circuit possible to be utilized in the manner I am wanting?  I have access to additional standard 4 pin relays if this helps, but not much of anything else.

First person that provides a detailed anwser, which results in this working the way how I want, utilizing what I have, by the end of JUNE 3 2012 will receive a 1 year pro instructables membership.  With a possible 3 month pro membership to the one who proves most useful in finding a feasible work around by JUNE 5th 2012.  And sadly using alternate supplies is not an option, "pretend I am on the moon, with no transport available in time".

see the pics

Note: in the diagram, the green wires are one switch, the blue wires are another.  Their are 2 more sets of wires but these are being used to control other items and are not shown.

Picture of Polarity switching issue, first one to resolve gets a one year pro membership, if answered by June 03 2012?
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rickharris5 years ago
I assume from your write up - very thorough by the way, that the green and blue wires are just switched on and off. with no voltage applied.

If that's he case you can use an external H bridge set up with relays as in the diagram below

The relays A and B form an H bridge when A is on and B off the motor turns one way - when B is on and A off it turns the other way.

When they are both on or both off the motor stops.

The relays are turned on by the green and blue wires which interrupt the 12 volt supply to the relays.
H bridge again.jpg
iminthebathroom (author)  rickharris5 years ago
so is this using 2 4-pin relays or 1 dpdt?
Yes 2 relays A and B They need to be 2 contact double pole relays. Most are like this.
iminthebathroom (author)  rickharris5 years ago
so for clarity, these are bosch type relays with the 30, 85, 86 87 and sometimes 87a type pin sets
As long as they suit your power supply (12 volts) and the contacts can cope with the current of the motor any type will be suitable.
+1

It's not ideal that turning on circuit 2 doesn't turn off circuit 1. It would be nice to have an extra DPDT (6 connector) relay - that way turning on switch 1 or 2 could cancel the effect of the other switch - with only spdt relays this is the only option.
iminthebathroom (author) 5 years ago
obviously my set dead line for anwser entry had all ready passed, think the questions go through a check stage at instructables HQ, but... Since I still need to know how to do this regardless of time lines I still wish to award a 1 year prize and a 3 month prize. keep the dialogue up if you can, I appreciate it
nothinglabs5 years ago
I suspect the 4-pin relays you have only have NO pins - no NC:

http://www.reuk.co.uk/Automotive-Relays.htm

This makes things extra challenging.

I think it would require 4 relays - but as noted on this page - if you turn on both control lines at once - you'll get a short circuit ("shoot through"):

http://kartikmohta.com/wiki/Tech/HBridge

http://www.dprg.org/tutorials/1998-04a/

You might be able to construct some kind of protection circuit to avoid the shorting issue.

My advice is to obtain a DPDT relay - this instructable I did might offer insight how to wire it:

https://www.instructables.com/id/Super-Easy-Reversible-Motor-Control-for-Arduino-/

wanted to add that I think you can get away with skipping the relays on the positive sides of the motors - and just connect the wires directly to the motors leads instead (so you'd only need 2 relays).

would still suffer from the shoot-through issue as mentioned above.
lsmith2545 years ago
https://www.instructables.com/answers/Dissolving-Epoxy/ My approach would be to pick the epoxy off with a dental pick or pare it with an exacto knife, provided you know where to pick. Best I got!