Relay Help

[hjnorman]

I am working on a push button start for my car using three switches. Two on/off switches which turn on the accessories power, and ignition power. The third switch is a push button which connects the 12+ power wire to the starter wire - connecting the two starts the car. I could not find a push button switch that could handle the needed 30A and was told to wire in a relay with a lesser amp switch. I have no idea how to do this though with a switch and two wires and researching it has only confused me more. Any help, suggestions or how to do this? Or if there is a way to do it not using a relay.

Its a typically automotive relay.

 

[FirefighterBlu3]

your car already has these relays. tap into the ignition circuitry associated with your ignition key switch.

 

[audioguru]

My old Pontiac Sunfire didn't have a relay for the starter motor so it was recalled and a relay was fitted. Some cars had their ignition switch catch on fire before the recall. GM saved a buck then spent millions.

 

[hjnorman]

your car already has these relays. tap into the ignition circuitry associated with your ignition key switch.

I have already tapped this circuitry. So it will be fine to use the push button I already have? It a 95 Land Rover if taht helps any ... I wasn't aware these were already wired it

 

[JimB]

Most UK built cars have a relay in the starter circuit, it is often referred to as the "starter solenoid".
The starter solenoid may be a separate unit, or, it may be incorporated into the top of the starter motor.

JimB

 

[Nigel Goodwin]

Most UK built cars have a relay in the starter circuit, it is often referred to as the "starter solenoid".

I think all cars with electric start have a solenoid, but I don't think that's what they are talking about?. The solenoid itself takes a considerable current, I think they are talking about a relay to feed the solenoid, rather than the ingition switch itself.

 

[FirefighterBlu3]

modern car circuits usually go a bit like this:

ignition key switch activates first relay. this relay may or may not activate a heavy duty relay. if it does not, then it will activate the solenoid itself. all modern starters have a kicker solenoid. this solenoid only takes a few amps and thrusts the drive gear of the starter up to the flywheel and the solenoid remains powered (and pushing the drive gear up to mate the flywheel) until the key is released.

now comes the heavy power part. in older vehicles (see below for newer) the solenoid also closes the circuit for the heavy duty gauge wire that goes directly to the battery. this is the circuit that drives the windings in the starter. this circuit usually draws around 150-250 amps directly off the battery. big engines such as diesels can easily draw several times this. thus you'd find an ~800CCA (cold cranking amps) battery at an auto parts store.

very small engines (geo metro? *grin*) have very small starters that can draw less than this. regardless, it's still a significant current. some modern starters come with the solenoid as parasitic on the main feed and only have one cable that attaches to a power relay and then battery.

obviously there are a good many variations in this design however it's normal to find a two+ stage system to activate the starter.

 

[eblc1388]

Key >> starter relay >> starter solenoid + starter motor.

The information on the internet shows that some starter relays coil are in series with a "Neutral Safety switch" which prevent power from reaching the starter solenoid if the gear lever is not in Neutral.

This could be a curse as the power from the starter motor can get one out of trouble should the car stalled and the engine failed to start on a railway crossing.

 

[FirefighterBlu3]

been there done that, but wasn't on the rails

 

[hjnorman]

OK, so I shouldn't need this extra relay.

However, so that I can understand it because it has been bothering me , how would I wire it up to begin with? Can I even wire in a relay in my situation?

 

[JimB]

I think all cars with electric start have a solenoid, but I don't think that's what they are talking about?. The solenoid itself takes a considerable current, I think they are talking about a relay to feed the solenoid, rather than the ingition switch itself.

OK, but from my experience, the keyswitch powers the solenoid which closes the BIG contacts to power the starter motor.
My current fun car, a Suzuki Vitara works like this, as have all my previous cars where I have got may hands dirty.
How my modern euro box (Ford Mondeo) works is anyones guess!
When you switch off the engine, it stops, but there are all kinds of whirring and clicking sounds from under the bonnet as it tidys its self up!.

JimB

 

[hjnorman]

Thanks for all the help - shouldn't ned one then. Just so I can learn and be less confused and frustrated about relays and things .... how would I wire one in if I needed one? Could I even wire in a relay in this situation?