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12v dc motor reverse

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haris_216

Member
hi there all
it's first time am posting to ask for help so I'd appreciate your understanding if am doing something wrong.
the problem I am facing is generated by my silly head that doesn't go for the simple solution:) and it is car related.
to be more precise, in my car I decided to install a spal aftermarket power window set. if I'd go for the usual switches everything would be ok but I found another pair of switches (of "delicate" nature) that won't allow much current to go through (but they are sooo cute). so, relays are the only way, if I am not wrong. I'd go for the DPDT type (2 per door I guess) but I don't seem to find any that could rate at 20A, and of course not cost as much as the window set itself.
so I wonder whether there is a way to operate the window motor (up/down) through some more common relays as I will have the signal (up/down) coming from the (cute/delicate) switch:)
I have been through other similar post replies but I don't think they cover me. so any idea would be most appreciated.
thanks a lot for getting into the trouble of reading my post in the first place
 

BrownOut

Banned
Forget relays. Power mosfets like the IFRZ34 will handle your current requriements, and can be configured into an H-bridge for foward/reverse motor drive. And, they are listed in Jameco for less than a buck a throw. Just pay close attention to heat sinc requirements.
 

haris_216

Member
many thanks to both of you for quick and helpful response. the mosfet approach is very interesting and silent (no clicking) but am worried, as you already pointed out, about the adequate heat extract. so probably I'll stick to the relay solution.
do you think there would be any problem regarding wearing off or "welding" contacts?
once again thank you very much
 

BrownOut

Banned
Well, just my opinion that any clunky-mechanical contraption won't be as reliable as a well-designed solid-state solution. Just keep a couple spare realys at hand.
 

tblo163

New Member
Polarity reversing

You are right about needing relays to cope with the ampage.Simple reversing switches will burn out.It's quite simple to reverse a DC motor with 2 CO Relays.
The relays are 5 pin,marked-30,85,86,87,&87a .if you look at the picture on the
relay casing,you will see see that 87a is ON, & 87 is OFF, when the relay is not energised.if you look at my pdf,you will see that both motor terminals are connected to ground when off,when ONE of the relays is energised,the motor
will run.& by energising the other relay,the motor will run in the opposite
direction.The best source of suitable relays is your local breakers yard, relays rated at 16 Amps will be more than adequate for the job,
Good luck Terry.
 

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tblo163

New Member
update on your question

Hi haris, I assume you will be using the cool reversing switches that you have.
They should have 5 pins,but you can still use them for the 3 pin function,
Simply connect pin 4 to negative,pin1 to relay#1 & pin2 to relay#2.pins 3 & 5
are not connected.you can use a lighter gauge wire to energise the relays.
SEE DIAGRAM, Hope this helps,let me know,
Terry:D
 

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haris_216

Member
hello all. I am sorry I got "lost" but due to vacations and work responsibilities, i wasn't able to finish my project and most of all to thank you for your valuable help. although I haven't decided yet which approach to follow, all your suggestions were interesting and definately educated me more into the fascinated world of electronics. so a big (late:eek:) THANKS to all that put time and effort in trying to help me.
 
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