wire gauges, resistance, amps... do you know these guys?

[xp190]

Hi guys

I was wondering, even though this is not really related to a specific car problem, if someone could shed some light on electronics for me.

my 190E has an aux fan, which is electronic, and since my ac is dead, and will probably remain that way for a while, I wanted to hook up a switch in the cabin so I can turn on that fan manually.

I'm quite sure this will help the motor stay a bit cooler in hot summer traffic weather, plus it should not be too hard to do, I have all the components already,

BUT, I don't want to set anything on fire.

I know how the circuit should look like, this is not a problem, but my main concern is numbers, and how you go about figuring them out.

If I have a switch connected up to the battery which is then connected up to the aux fan, where would I place the fuse? What rating fuse should I use so that nothing gets damaged, and what gauge wire should I be using to do all this?

Would anyone be able to show me the math behind this? I have taken electronics, but only in theory, and even with my books I am not sure about figuring this out.

Any help will be greatly appreciated.

TIA

xp

[xp190]

Thank you tkamiya

that information will definately help. I will go get a relay tonight and some 12 gauge wire.

I'm guessing that if I follow the wireing pattern already in the car, I should be fine. I don't want to modify it but rather replicate somethign similar. That circuit also has a relay.

Thanx again, I will post when I make some progress.

xp

To know what Amp rating you should build this circuit for, simply find the aux fan fuse and see what size it is. If it is a 20 Amp fuse, then use components including wire and switch that are rated for at least 20 Amps.

Good luck,

[olpos]

there is a much easier way for your car. search for a (ch92) or the (cool harness). jim sells something that just plugs right into your fan switch and does not need the ac to work. also does not need to be minded.
good luck
rich

[xp190]

I almost have everything ready

I didn't know about the cool harness but thanx for the info olpos.

Here is what I did. I got a relay that controls the fan, it's a heavy duty relay so it can handle the currents no problem. 12 gauge wire going from battery, fused of course to the relay, and from the relay to the fan.

Then I have a switch in the cabin, using 14 gauge wire, just because that's what I had handy, I have it grounded and connected to the relay, but I have a problem finding a power source for it.

At the moment it is hooked up, to the same place as the fan itself, there is a small socket box next to the battery, this is what I used. The switch is not fused, and it operates at any point, ignition on or off.

I was wondering if anyone knows a good ignition controlled power source for a small switch like this. I'm not sure how to exactly track this one down. I had the entire fusebox apart but that didn't help much.

Thanks so much for the input, this is the first mod I did to my car other then for repairs

xp

[csnow]

If I understand your design, you can tie it to pretty much anything in the fusebox that is switched by the ignition. It will draw very little current, since it just fires the relay.

You would generally not want to operate the fan at highway speeds. Not that you would need it, but something to remember with a manual switch.

[Arthur Dalton]

<
I'm quite sure this will help the motor stay a bit cooler in hot summer traffic weather, plus it should not be too hard to do, I have all the components already, >>

If you simply want to control the fan manually from the cabin, you should just use the existing circuit. [ the relay, wiring, fusing and complete circuitry are already there. Just put a switch in the cabin and run the 2 leads up to the a/c drier high pressure switch.
When the switch is On , the a/c aux fan will come on using the stock components...cost you $2-3 ...

[xp190]

Since I'm no electrician, I didn't want to modify pre-existing circuits in order to accomplish this, this is why I made another circuit, if you can call it that, just a few wires really, but alright.

I made it so that at any point you can plug it back in and restore it to it's original condition.

I just tested the new setup, it sure makes a difference. Now I just need to change the power input for the switch and fix one of my turn signals, I probably nudged something while working under the dash.

Next step is to put a microcontroller in there that will smooth out the heat curve for the engine.

It should be an interesting project.

xp