Solenoid Amperage for Wilson Switch (1 Viewer)

[CaptBeardilocks]

I've read a lot of threads on here on Wilson Switch set-ups but haven't seen much about specific solenoids used. Most refer to a "Ford" starter solenoid that seems to have been unchanged ~1958-1991 but seem to be made by dozens of makers.

I found one mention to "around 10A per glow plug". And one member (Mudder? WTH do we call members on here?) who uses a Cole Hearse 200A that was alluded to as being overkill. Is there a good rule of thumb for solenoid amperage?

Thanks!

 

[Feistl]

I have measured glow plugs in a hilux at around 8amp for the first second or two, then around 6amp constant draw when on.
So assuming 6 cylinders you’d probably want a 50amp contactor.
You should easily be able to find a 12v contactor to do the job for around $20-50 depending on what quality you want.

basically any external style starter relay or contactor will do the job. Just ensure it’s mounted properly, use decent gauge wiring (measure the actual copper size and not the insulation diameter) and good quality crimps (buy a crimping tool :-D)

just ensure you fuse it!

and if you live in really cold climates/require the glow plugs to start the car then perhaps buy a second contactor/solenoid to keep as a spare.

 

[CaptBeardilocks]

I have a 65A Solenoid kicking around. I was debating using that or moving up to an 85A. I wasn't sure how much "extra" you might need over the 10A/plug I had read about.

I'm definitely going to throw a fuse or circuit breaker in the mix for it as well.

 

[Feistl]

The other question is do you have a multimeter? Most multimeters will measure up to 20amp current draw, so you can test one glow plug to get an accurate idea.

and while it’s highly recommended to run a relay/contactor with ample capacity, the rated capacity is at 100% duty cycle.
Eg a relay that is rated for 50amps can probably handle 60-70amps for a second or two during start up. It’s prolonged current draw that will cause heat/potential issues.
That said, it’s not that expensive to just use the correct parts...

but I would be comfortable using that solenoid. (Again though, probably worth measuring the specific glow plugs you plan to use. They might draw more than the ones I measured in the hilux...

 

[CaptBeardilocks]

I have a collar-style meter for measuring higher amps. I've never tried it in an auto application but in theory it should work. The only problem is that there's currently no wiring under the hood on my swap, so my the first glow I could test would be the first glow on whatever I have installed as a solenoid...

 

[Feistl]

Hook it direct to battery while you measure... a solenoid/contactor/relay just gives you the flexibility to operate it via a small switch remotely. Again just make sure you don’t have any short circuits between the wire and glow plugs.
What engine is this for?

 

[CaptBeardilocks]

It’s a 1HDT swapped FZJ80.

I’ll give that a shot before I order a solenoid. Thanks.

 

[CaptBeardilocks]

So I did a bit more research on glow plug draw to try to source how much of a fuse/circuit breaker and solenoid are really necessary to run the glow plugs. General consensus is around 8-12A max per glow plug (in general, I couldn't find Toyota-specific numbers). Looking at the factory wiring book, I see that the only thing in the system on the GP side of the ignition is a "1.25B" fusible link. A little Google-Fu and 1.25B translates to about 80A cut off.

So in my understanding (PLEASE correct me if I'm wrong here) running an 80A circuit breaker and an 85A Solenoid should be plenty for the system as the ~80A fusible link would be the first domino to fall anyway.

Now I just need to measure the wire gauge in the factory harness and set up a place to mount it all on the truck.

 

[paul r]

I would feel pretty comfortable with an 85 Amp solenoid if it were me.

For additional context, I know in the industrial world, the same relay will often have different ratings for different load types (might be a 15 amp rating for an easy load and 6 amp for inductive for example). Inductive loads like motors or heater coils (glow plug) are often the most difficult types of load to switch as there is typically fairly high instantaneous inrush current (maybe 7-10 times normal load for fractions of a second) that is not always easy to measure unless you have tracking on a scope and watch for it. The goal I think in the derate is typically to get the contact pad size on the switch load to a larger surface area to prevent premature failure with the higher inrush.

If you already have the 65A solenoid there would be little harm in trying it out if you have no other use for it. Glow plugs are not likely to leave you stranded and you can always use jumper cables or something like that if you had a hard time starting until you could get a larger solenoid. The only risk you would face is if the contacts welded shut and the relay gave constant power to the plugs causing them to burn out. However, your diagram as drawn would have the glow light on so you would likely see that in time to take care of it.

 

[CaptBeardilocks]

Going over the old harness I have here on my parts truck, the wiring off the battery to the glow circuit goes through the fusible link and then through the 50A AM1 breaker in the fuse box before going to the first GP Relay.

Can anyone see any reason to add an addition fuse or circuit breaker to the system?

I plan on setting up my Wilson-style switch using the same wiring in the harness that exists to the glow plugs and just cut out the 2nd Relay and the computer. I might replace or upgrade the solenoid relay but the stock one still works.