Topic: Electrical question - Voltage reduction

[Cvillechopper]

I am working on hard-wiring my garage door remote into my truck (going to do more for the bikes this summer) but fried the first one cause I was moving too fast and didn't notice the 3V battery that I took out.  Anyone able to offer some expertise?  I've done some research and it seems that I could wire a 30ohm and a 10 ohm resistor in serial on the positive lead and get to 3v at the remote.  Does that seem correct?

Any help is appreciated.

Thanks
James

[TwoTired]

I think many of the garage remote have microprocessors in them and they like a nice steady regulated voltage to work reliably.  A battery generally provides a stable power source with little noise on the power lines.  It's hard to imagine an auto line that is that stable and has little noise on it.
Most on board computers for car have their own in power condition devices built in, as noise spikes will often damage integrated circuits.  It seems unlikely that a battery driven device would have similar input conditioning.


To calculate the voltage drop across the resistors you need to know either the final load (to know total load presented to source voltage) or know the current being drawn.  Resistors won't drop ANY voltage until current flows through them.
Also know that the charging voltage is likely to be different than the engine stopped voltage.

[kslrr]

You need to design and build a DC/DC regulated power supply, with filtering Capacitors, set @ 3V.

[Cvillechopper]

Thanks guys.  That's what I was afraid of.... it's way above my head to build one
Maybe I can use the 12v accessory power source with a relay between the battery and device.  That way I won't fry to remote and will still get the "only works with the key" functionality.  Any tips/potential issues with relay resistance?

[kslrr]

Just use a relay with a 12vdc coil.

[TwoTired]

Relays have contact ratings.  Some are only signal handling.   Some are power handling, to specify the contact rating, you still need to know the current draw between battery and load.

The relay activation coil must be rated for 12V duty.  The contacts must be rated for the voltage and current the device consumes.

Cheers,

[Spanner 1]

Relay or not, your still providing 12v to your 3v door opener = fried.
Don't get why you want to do this ? as the opener batteries last for years and years and years ( mine is at least 5 years old used everyday)

[bill440cars]

Relay or not, your still providing 12v to your 3v door opener = fried.
Don't get why you want to do this ? as the opener batteries last for years and years and years ( mine is at least 5 years old used everyday)

       Don't know what all is involved, but my 06' Dodge Grand Caravan has a setup in an overhead console, that can be programmed to operate any garage door. Would THAT be a possibility for your purpose? In fact it is set up to have 4 different openers programmed into it. Think about it.  

[Gordon]

How about this for a Rube Goldberg style solution:

Somewhere under the console or behind the dash wire in a small power inverter to a switched power source.  Then directly wire in a 3 volt DC power plug to your garage remote.  Plug DC power plug into power inverter and voila!  You have your garage remote that runs off of the car battery!

[mystic_1]

Don't get why you want to do this ? as the opener batteries last for years and years and years ( mine is at least 5 years old used everyday)

I agree.  I'd be more worried about weatherproofing.

mystic_1

[johnny_from_bel]

Thanks guys.  That's what I was afraid of.... it's way above my head to build one

I bet you can pick one up at an electronics store for less than $15

[TwoTired]

Relay or not, your still providing 12v to your 3v door opener = fried.

No.  He was using 12v to power the relay, and the relay would switch the 3v battery in/out of circuit.  This would isolate 12v from the opener circuits.

A 12v to 3v converter can be had for pretty cheap (under $10).  Just google 12v to 3v converter.

[Spanner 1]

Oh!, that's different then !!

[Cvillechopper]

OK.  I got it worked out.  Quick stop at Radio Shack and $4 later I've got my materials.  Picked up a 12VDC relay and a battery holder.  Used an old light switch cover as my board.  Works like a charm.  Time will tell how durable this solution is but for now it works like it should.  Key on, buttons work, key off, no opening my garage. 

Here's the link to my post on the Tacoma forum if you are interested in seeing the entire project (as small as it was).  http://www.tacomaworld.com/forum/technical-chat/68154-slightly-different-garage-door-opener-mod.html

Parts


Ghetto board




Power feed

[1080]

To step down the 12 volt to 3 volt all you need is a 3 pin 3 volt regulator IC.

12volt in one pin, common ground second pin, 3 volt out third pin.

Very simple electronic device.