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Simple car switch question

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HerfGun

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There is a momentary button in my car that I would like to change to an actual on/off switch.

The signal comes out of the gauges. It's +11V 10mA. Pushing the button grounds it to the chassis.

I'm just slightly concerned that leaving it grounded for long periods of time could damage the gauges. I think there are other similar signals coming out of gauges that are grounded for long periods, but I haven't tested them yet to see if they are the same V and mA.

What'da ya think? Should it be OK?

Should I at least put in a diode? Which one?

Thanks,

HerfGun
 
1. Turn the ignition switch off
2. Press and hold the button for a couple of minutes
3. Measure the voltage across the switch

If the voltage is now close to zero, congratulations! Won't run down the battery. If it's still closer to 12v, you may have to do something else.
 
Thanks for the quick reply.

The power coming out is switched, so I'm OK there I think.

I guess I should explain more about the circuit.

When you momentarily push the button it signals the guages to activate a relay.

The relay raises a wing on the back of the car.

When the wing is fully raised it closes a limit switch which grounds another wire coming out of the guages. That signals the guages to stop activating the relay.

Continuing to hold the button or pressing it again doesn't do anything as long as the limit switch is closed. So I don't think that part of the circuit should be a problem.

The problem is if I press the button to put the wing up and then get into traffic and have to slow down for a few minutes it automatically goes down.

I want it to stay up till I put it down.

I could put a switch on the wire to coil of the relay that puts it down, but I would rather ground the button. (there 2 relays one for up and one for down)

I was just worried that whatever component is sourcing the 12V 10mA could overheat if it was left grounded for long periods. My plan B is to make a 1sec on couple min off timer to ground the switch with an optocoupler.

I had the guages apart awhile back and took some pictures. If I can find them I'll post them.
 
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Doubtful it will damage anything at 10ma. Did you verify 10ma with a meter? If so, that's going to be less than an eighth of a watt. Probably a 1.2k "pull-up" resistor or maybe the led current for one of those optos.
 
duffy,
Yes about 10ma from the guage wire to ground.

Speaking of optocouplers, I've never used one. I was looking at digikey and I'm not sure what these values are.

Current - Output/Channel
Current Transfer Ratio (Min) X% @ Yma

I just want to use them as a switch. About 12V 10mA on the input side and the output side fully on or off. The output side current would be pretty small for the things I want to do?

Anyone have a link that explains how to use them?
 
Yes duffy, 10ma from the guage wire to ground.

Anyone have a link that explains how to use an optoisolator? I know how they work I just don't know how to select the values. I just want to use it as a switch.
 
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