bfellows

Just a quick one..... Just been to Maplins (like radioshack) and found a push switch with blue lens to match alarm armed led for my kickdown override. It is rated 1.5amps @ 240v, 3amps at 110v. My question - would it be OK with say 5 amps (kickdown circuit?) at 12v? Would rather not fry my car finding out the hard way!

Thanks in advance!

Brett

karl ruiter

Many switches have a 24VDC current rating that is the same or actually lower than their 120VAC current rating, so you are probably marginal on the switch. You are almost certainly saved by the facts that: 1) you probably don't need millions of cycles. 2) I kinda doubt your will really be drawing 5A(thats 60Watts which seems like a lot...more like a headlight) and 3)switches and resistors are pretty forgiving to overload while capacitors and FETs are not at all. If there is a problem it will likely not hurt the car, but rather the contacts on the switch will get fried and it will fail open. A good idea would be to put a large capacitor across the switch. Otherwise, if you are really switching 5A, you may get arching as the switch closes and opens which will likely soon oxidize the contacts on the switch and cause it to fail. You might have to play around to find the optimal value but I would start with a 15V, 1000uF elecrolitic. Make sure you get the polarity right or the cap will fry and smell like dead fish! If you are sure you really need 5A and don't want to exceed the rating on the switch I recommend digikey.com or mouser.com. Both stock thousands of different varieties of switches and ship same day.

BrianG

I had an under-rated switch fail closed... I think the contacts basically welded themselves together. Guess that's what I get for running a pair of 4509Q's in my truck!

Anyway, just be aware that failure mode could be either way.

John Speake

Brett,
That switch is not beafy enough. Use it to trigger the coil of a standard "53" type relay (like fuel pump etc) and let the relay switch the current to the kick down solenoid.

Regards

bfellows

Many thanks - will have to give it a bit more thought! I have considered a mini relay and house the lot under the parking brake cover - less wiring the better?

John Speake

Just check the "mini-relay" is rated for the d.c. current you need to switch, and that it has a 12v coil to activate.

bfellows

John, in light of what you've pointed out, i'm guessing my best bet would be to just source a more suitable switch - simplicity if not so aesthetically pleasing!