Starter solenoid

[terry1]

Does anyone know, or has anyone measured, how much
current a starter solenoid draws.
Terry K

[Kirk Morgan]

I have never checked how much amperage a solenoid draws. That being said, it should be only a few amps depending on if it a Ford or GM solenoid. A old school GM would be the most.What it is energizing is what is going to cause the most amps drawn. Modern permanent magnet starters will draw about 150 amps while cranking. That would be on a small block engine with 10 to one compression. The initial amperage draw would be about 20 to 25 amps more.

[FED 387]

initial amperage is about 30 A ---8-10 A to keep the starter drive engaged

[terry1]

I always thought that the solenoid was basically a relay.
This relay closes a set of contacts that allows the/a battery
wire to engage the starter.
If this is true, the actual solenoid should only require enough
current to keep it engaged.
I suspected an amp or less.
Terry K

[kansas stocker]

FED is correct given a few amps either way. It acts like a relay but it is not.
Pete

[Dragsinger]

To be more specific, a Ford starter solenoid and a GM solenoid or a typical aftermarket mini starter solenoid are all different in design and different in amp draw.

*The Ford solenoid/relay is, as stated above, only "making" a set of high amp carrying contacts. With this design, the amperage load is small, only a few amps.

*The GM factory style solenoid serves two purposes. First, it engages the starter drive mechanically through a lever link that is moved to engage by magnet action from the solenoid. Second, it "makes" the contacts that power the starter motor. As stated above, this design draws much more.

*The popular mini-starter design is like the GM dual function but does draw somewhat less load because of design differences.

*Just for info, another solenoid design it the 100% duty cycle style. This is what we use when installing the solenoid activated master switch.

[Eman]

Originally Posted by terry1

Does anyone know, or has anyone measured, how much
current a starter solenoid draws.
Terry K

What brand car, which starter solenoid. Quick giveaway is the size of the wire the factory used to activate the solenoid.
Another thing that comes into play especially on a GM starter mounted solenoid is the heat.

[Dragsinger]

Eman has a good thought in ref to factory wire size. A SWAG could be ascertained in that Ford has an 18 gauge wire to bring in the solenoid whereas GM employes a 12 gauge wire.

[FireSale]

i have one of those red MSD starters that probably came off a 747 based on the torque it provides. It doesn't require a Ford style relay/solenoid and has a wiring diagram that allows a 12 gauge wire to basically be connected directly to a start switch. Only problem was that this provided for the big wire on the starter to be connected directly to the battery at all times when the car was on. My steering shorted it out making a hard turn to get to the staging lanes. Burned out a 150 amp cutoff switch. I wound up wiring in a Ford solenoid to manage the battery power during start. My current headers won't clear the starter and I don't miss the drama.


On a side note, I have found that continuous duty Ford style solenoids make very good relays. They cost more but are very reliable.


Another trick: If you use a Ford style solenoid fender mounted to send power to the starter, there is a reverse voltage surge that travels on the small wire back to the starter button when the switch is released. This is caused by the collapse of the magnetic field in the solenoid and can damage the starter switch or wire to it. I replaced a push button with thin gauge wire with a beefy momentary toggle switch and 14 G wire because of this. You can also wire a diode in that small wire to block reverse current if you understand those things.

[Eman]

Originally Posted by FireSale

Another trick: If you use a Ford style solenoid fender mounted to send power to the starter, there is a reverse voltage surge that travels on the small wire back to the starter button when the switch is released. This is caused by the collapse of the magnetic field in the solenoid and can damage the starter switch or wire to it. I replaced a push button with thin gauge wire with a beefy momentary toggle switch and 14 G wire because of this. You can also wire a diode in that small wire to block reverse current if you understand those things.

This is a good point, I've had it happen but not with every GM starter when you use a Ford solenoid.
Another thing you can do is use a Ford style solenoid and use it as a relay to trigger the 12ga wire to the GM solenoid on the starter. You should use a relay on a GM starter switch circuit if you use a micro switch for a neutral safety switch.