What relays to use?

**Dutch2** · 02-09-2007, 02:55 PM

What relays should I use to control things in the car?

Would 8 Amps be enough for most things like windows and lights, or does it really take a 25 Amp relay to control most things in the car?

Thanks in advance,

D2.

**bimmerman** · 02-09-2007, 05:57 PM

Your best best is to just buy "automotive rated" relays. The coils will handle 12V and it isnt going to hurt anything if you run 2A through a 40A relay but going the other way around could create some bad problems. It just gives you a lot of head room.

any of these should work fine.
https://www.jameco.com/webapp/wcs/st...egoryId=353505

I use something like this one to run anything that I control in my car.
https://www.jameco.com/webapp/wcs/st...oductId=148582

**Ryann** · 02-10-2007, 12:23 AM

would a TTL signal triigger any of them relays? ^^^^

**Dutch2** · 02-10-2007, 09:34 AM

No TTL won't drive those relays. TTL can only deliver a few mA at 5 Volt and these relays require 150 mA at 12V.

The reason I was asking is because I wanted to put together a relay pack to control my windows, locks, and sunroof.

All the wiring diagrams show switches and relays but of course no currents. Based on the fuses I thought 8 Amp relays would be enough.

Just looking for some input

D2.

**vfinterceptor** · 02-10-2007, 12:34 PM

I hope you're not planning to have the comp as the only way to control those things.
I'm not sure I'd want to trust a comp with such important items!

(I'd like to get out but I can't unlock the doors or open the windows!)

Cheers

BJ

**bimmerman** · 02-12-2007, 01:10 PM

Originally Posted by Dutch2

No TTL won't drive those relays. TTL can only deliver a few mA at 5 Volt and these relays require 150 mA at 12V.

The reason I was asking is because I wanted to put together a relay pack to control my windows, locks, and sunroof.

All the wiring diagrams show switches and relays but of course no currents. Based on the fuses I thought 8 Amp relays would be enough.

Just looking for some input

D2.

8A should be more than enough to run those things, but you have to watch out for things like stall current on the window which is usually closer to 25A (something is stuck in the window and it tries to drive more current to keep it moving, but hopefully a fuse would blow first.) Check the ratings on the fuses that control the circuit. If the power window circuit uses a 10A fuse, then an 8A relay should be fine as that is the "Constant current rating" and not the instantaneous peak. I usually buy a large handfull at a time, so I just go for the bigger ones as I can use them on anything and they are still fairly cheap. But if you are using them on lower power circuits, you dont need that heavy of a relay.