Learn me 12V automotive relays

I'm looking at 12VDC automotive relays and I see they carry two ratings, NO and NC.

My question is, does "normally open" or "normally closed" have anything to do with the relative amount of time they are in the open or closed state? Or is it purely related to whether the relay passes current when the control (trigger? IDK the correct term) is energized or not energized?

thanks!

Normally open and Normally closed are only the designation for NON-ENERGIZED coil trigger condition. There may be a time feature included in the specs, but I have not looked for it, since I am not usually looking for high speed switching mechanical relays. That would be the realm of solid state relays.

Yeah, timing has nothing to do with this.  Sitting on your desk, NC = it's closed right now, energize to open.  And inverse for NO.  

thanks guys, i appreciate the info.  back in the day, power for pretty much everything used to go through the ignition switch and headlight switch.  i'm adding relays for the engine and the headlights.  may be overkill for a challenge car but it might have a life after the event so i'm trying to do it right.  No high-speed switching required, just going to use the original switch outputs to trigger the relays.

Sounds like you're mostly going to want normally open, single throw relays, either single or double throw jobs depending on how you want to deal with the loads.  But really there are all sorts of relay configurations out there, so just get the electrics diagramed and then go find the relays that work for what you need.  Lots of good sources for these sorts of parts.  You aren't stuck with 12V nominal rated parts, either, as there's 24V rated relays (that are really good for more than that, but that's where they fit on vendor websites).  

Many automotive relays have both a NO and a NC path. Which is why they have 5 pins.

In reply to Robbie (Forum Supporter) :

Yep, hence the "50/30" rating for example. The 50 is NO and the 30 is NC.

Are there any cheap options for solid state relays?

I need to switch some power-side controlled solenoids with pull-down transistors.  The only way to make them negative side controlled would be to make the vehicle positive ground.  So I am looking for solid state relays to use to switch it to power side control.

I probably could get away with using regular relays but I might want to use PWM on them, maybe

Pete. (l33t FS) said:

Are there any cheap options for solid state relays?

Cheap? No...

Pete:  Can you draw what you're wanting?  Is sounds like you want to ground-side switch the control side of the relay.  Is that accurate?

Pete. (l33t FS) said:

Are there any cheap options for solid state relays?

I need to switch some power-side controlled solenoids with pull-down transistors.  The only way to make them negative side controlled would be to make the vehicle positive ground.  So I am looking for solid state relays to use to switch it to power side control.

I probably could get away with using regular relays but I might want to use PWM on them, maybe

There are some hella fan relays for the jeePs that are likely inexpensive enough for this (PWM able SSR)

In reply to Paul_VR6 (Forum Supporter) :

Are those factory junkyard type items?

Paul_VR6 (Forum Supporter) said:

Pete. (l33t FS) said:

Are there any cheap options for solid state relays?

I need to switch some power-side controlled solenoids with pull-down transistors.  The only way to make them negative side controlled would be to make the vehicle positive ground.  So I am looking for solid state relays to use to switch it to power side control.

I probably could get away with using regular relays but I might want to use PWM on them, maybe

There are some hella fan relays for the jeePs that are likely inexpensive enough for this (PWM able SSR)

Ooh, perfect.

I'd rather not have to buy two high side driver units from DIYAutotune.  I have more than four transmission solenoids to control, and the solenoids all have only one wire, grounding through their mounting bolts.

Big solenoids and SSRs sometimes don't play nice.   You may need to add a component or two to protect the SSRs from the inductive spike. 

GeddesB said:

Big solenoids and SSRs sometimes don't play nice.   You may need to add a component or two to protect the SSRs from the inductive spike. 

 

 

Seems irrelevant anyway, as the apparently referenced relays I found were more expensive per output than the HSD unit ($109 for four outputs)

There are about seven solenoids that need to be controlled, only two of which seem to need PWM.  I could probably get by with one HSD and use standard relays for the rest.

i have seen reference to people using no computer at all, just diodes and the range position sensor to control the solenoids, but I want an electronic shifter and ignition retard on shift.