Bizarre electrical issue w/ starter solenoid

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MrWOT
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Bizarre electrical issue w/ starter solenoid

Post by MrWOT » Sat Mar 28, 2015 3:01 pm

This one has me well and truly stumped. I've been playing with it for almost a week

Okay, first the basics.

It's a small Craftsman tractor, circa 90. 12hp Briggs, 12v system.

It won't crank when you turn the key.

I verify voltage at the exciter terminal on the solenoid and it has 12.52v, direct battery voltage is slightly higher (~12.6).

Bypassing the solenoid from B+ on solenoid to starter, starter engages just fine.

Ordered 2x OEM Craftsman solenoids (trombetta), just to have a backup since the old one wasn't very old.

Same symptom. With BOTH new solenoids.

I verified the voltages umpteen times, no continuity across the solenoid with power to the exciter.

Yesterday, I said goodbye to the OEM solenoid and put a premium Standard solenoid in (bottom mount Ford style).

Same thing.

The solenoid will not energize with 12.5v at the exciter.

The battery is new (spends the night on a maintainer too), I made the cables myself with 4ga and soldered the lugs. Less than 0.1 ohms, same with the starter to solenoid cable.

Jumping from B+ on the solenoid to the exciter directly has the same effect. The solenoid(s) will not energize. No continuity from B+ to S terminals, no voltage.

Thinking it must be a grounding issue I have brushed every connecting piece of metal down to clean bare, connected and sealed, verified resistance from the frame below the solenoid to B- at 0.3 ohms.

Still nothing.

I attached a ground directly from the solenoid base to B- verified less than 0.1 ohms. Still nothing.


I'm more than a little mystified here.

The odds of getting 3 bad OEM or better solenoids is astronomical, and I suspect the original is still good too.

I've also replaced the ignition switch, but you get the same voltage at the exciter wire with the new and the old, no problems found.

Anybody? I'm going a little mad here.

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Re: Bizarre electrical issue w/ starter solenoid

Post by BCjohnny » Sat Mar 28, 2015 6:41 pm

Are you checking the observed voltage (12.5v) at the 'exciter' cable with the cable attached to the solenoid terminal or removed?

If you're checking with it connected you either have four faulty solenoids (unlikely) or you still have earthing issues. An easy way to test is to make up a short jumper cable and bridge the B+ cable/terminal on the solenoid with the 'exciter' (pull in) terminal. If the solenoid doesn't pull in, assuming the solenoid is good, you have a bad ground. If it does you have a bad exciter.

Are you sure all the solenoids you've used are base grounded (earthed) and not insulated, requiring a separate earth? If they have more than one 'small' terminal (ie not the two larger B+ & Starter stud terms) just drop an ohmeter across them and see if you have a circuit (resistance of about 6-8 ohms). If so one needs excitation, the other grounding. Post up pics of the solenoids anyway.
"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

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Re: Bizarre electrical issue w/ starter solenoid

Post by MrWOT » Sat Mar 28, 2015 8:54 pm

Testing is with the wire attached to the solenoid.

The Trombetta solenoids do have two terminals. They have continuity and I see 12v at both terminals whenever one is powered.

The Ford style solenoid is this. Image

It is wired as such
Image


I'll put up pictures this evening.

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Re: Bizarre electrical issue w/ starter solenoid

Post by joe 90 » Sun Mar 29, 2015 12:06 am

What's the terminal marked N/A?
Shouldn't that be earthed?

How hard can it be?
There's 1 coil with a connection at each end. It's got to get 12v across it to magnetise.
There's 2 relay contacts to switch 12V to the starter motor.
You don't even need to connect the starter to test it, if the solenoid works , you'll hear a loud clunk.

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Re: Bizarre electrical issue w/ starter solenoid

Post by MrWOT » Sun Mar 29, 2015 12:53 am

Well... I got home, finished cleaning and re-gap on the plugs, and turned the key to check voltage yet again.

Imagine my surprise when it then turned over and roared to life. I about threw the multimeter and almost fell over.

I've been banging my head into a wall all day over this and I get home. And it just decides to work.

I wiggled everything afterwards, everything is still tight.

I officially have no clue how electricity works. And I'm going to bed.

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Re: Bizarre electrical issue w/ starter solenoid

Post by BCjohnny » Sun Mar 29, 2015 4:27 am

The Trombetta solenoids do have two terminals. They have continuity and I see 12v at both terminals whenever one is powered.
The reason they have continuity and you 'see 12v at both terminals whenever one is powered' is because you have two ends of the same cirucit. If, out of interest, you put this solenoid back on (you also have a spare) just put your 'exciter' wire to one terminal and make a permanent small jumper wire and ground the other terminal to the solenoid ground wire you've already installed. It's a 'base insulated' solenoid.

Just drop your ohmmeter across it and you should see continuity (a circuit ~6-8 ohms ish) prior to re-fitting to prove.

'Remote', non-engaging, solenoids normally only have one winding, so are simple enough. Pre-engaging solenoids normally have two (shunt and series), as do 'throttle/pull' solenoids, and can confuse the unwary.......
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Re: Bizarre electrical issue w/ starter solenoid

Post by 2seater » Sun Mar 29, 2015 10:53 am

That terminal marked n/a on the Ford solenoid is likely the ignition bypass circuit used to provide extra voltage to the coil during starting. If it isn't required to act as ground to pull the solenoid in, it likely shows B+ when the solenoid is activated.

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Re: Bizarre electrical issue w/ starter solenoid

Post by BCjohnny » Sun Mar 29, 2015 11:40 am

2seater wrote:That terminal marked n/a on the Ford solenoid is likely the ignition bypass circuit used to provide extra voltage to the coil during starting. If it isn't required to act as ground to pull the solenoid in, it likely shows B+ when the solenoid is activated.
Judging by the fact that the Ford solenoid (base ground) now works, that's what it is, given different names but here known as the 'cold start' terminal.

[On ballasted systems that place a resistor before the coil, giving ~8v nominal running voltage (which the coil is specifically designed to operate on) there's a Cu/Be spring internally that taps off the main solenoid moving contact, giving cranking voltage ~9-10v directly to the coil, bypassing the resistor. Hotest spark when needed most. Once the sol drops out, so does the bypass. Simple, effective system.]
"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

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Re: Bizarre electrical issue w/ starter solenoid

Post by MrWOT » Sun Mar 29, 2015 2:09 pm

BCjohnny wrote:
The Trombetta solenoids do have two terminals. They have continuity and I see 12v at both terminals whenever one is powered.
The reason they have continuity and you 'see 12v at both terminals whenever one is powered' is because you have two ends of the same cirucit. If, out of interest, you put this solenoid back on (you also have a spare) just put your 'exciter' wire to one terminal and make a permanent small jumper wire and ground the other terminal to the solenoid ground wire you've already installed. It's a 'base insulated' solenoid.

Just drop your ohmmeter across it and you should see continuity (a circuit ~6-8 ohms ish) prior to re-fitting to prove.

'Remote', non-engaging, solenoids normally only have one winding, so are simple enough. Pre-engaging solenoids normally have two (shunt and series), as do 'throttle/pull' solenoids, and can confuse the unwary.......
I'll give it a shot just for grins when I have a minute.

The original solenoid was identical to the new ones (dual term) and did not have a ground wired to the second terminal. No markings on it to indicate which should be grounded. Nor does the wiring diagram I have indicate one should be present. It was naked and I have seen it started/stopped a few times previously. Terminal is corroded and no sign anything ever WAS on it.

Now I can't figure out when it DIDN'T work before. I did nothing to this thing between the night before last and last night and it turned over on the first try last night.

Scared the hell out of me when it did :oops:

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Re: Bizarre electrical issue w/ starter solenoid

Post by BigBlocksOnTop2 » Wed Apr 01, 2015 5:21 pm

1990's? The problem could be a wire that is broken in two. Handling the wire may allow you to read continunity and moving the wire back on to the terminal may cause the wire to open. Corrosion, especially where the wire crimp is, could be an avenew to travel. Is there a relay(s) in the circuit some where? Could be that the contacts need cleaning (burnishing), (600 grit sand paper). The seat switch, maybe a sw. in the pedal, hard to say. Those old machines can be brain pickers.

Bill

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