Power supply for a 4 wire resistance measurement on a tractor solenoid's wire - Page 1
Forum section: electronics / repair

author: gg64
author_rank: Regular Contributor
timestamp: December 05, 2020, 10:29:51 pm
content: Hey,So I have two tractors that got solenoid triggering issue (clicking noise but not clucthing, occasionnally starting, the brushes are for sure ok).Those are really similar, same brand, same series not the same model though.But the wiring are highly similar and got jerry rigged over the years by someone else than me.When I power the solenoid wire a screwdriver or a wire by taking the positive on the starter terminal we can still start.And recently I changed one starter, and I checked for battery acid density and charge on one it is fine.We can no longer use the stock way to start reliably the tractor from the "cockpit".I won't go into much more details about the other one (I changed the switch for the other but I don't remember that helped...), but basically this issue has been going on for about 3-4 years now.Therefore I'll like to fix it. Hence my question:I'll like to do a 4 wire measurement to pin down what wire/terminal connection is faulty.What kind of power supply specs would I need for such application ?I would like to do the measure at least (I think that would be 15v 0-5A).Ideally I would like to measure what is the current/voltage requirement for the solenoid to work properly (15v 10A).I'll like to keep it under 200eur if possible.What do you guys think where I should get the power supply ?Since I am French I might get from conrad.fr (good but honest price not cheap) or amazon (<- trust issue electronic wise).Maybe this one, but I have no idea about the amperes:https://www.conrad.fr/p/alimentation-de-laboratoire-reglable-basetech-bt-305-0-30-vdc-0-5-a-150-w-nbr-de-sorties-1-x-1-pcs-513812And measure the amps with a amp clamp is tricky IMO. But I can give it a try.

author: bob91343
author_rank: Super Contributor
timestamp: December 05, 2020, 11:25:14 pm
content: Almost any power supply should work. It just needs the current capacity.A battery would do as well.

author: Tom45
author_rank: Frequent Contributor
timestamp: December 05, 2020, 11:59:14 pm
content: You would probably be better off looking at voltages while the starter switch is closed.Watch the voltage at the control terminal of the solenoid to see if it stays close to the nominal battery voltage. Then same for the output terminal of the solenoid.

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: December 06, 2020, 07:55:59 am
content: As Tom45 suggests, you should be able to debug this using just a multimeter. A clamp meter that will read a few 100A DC is useful for checking the full starter motor draw, while the regular multimeter probes will likely be good for the solenoid current. This sort of problem is commonly caused by bad connections/corrosion on earth connections or through the positive line from battery to ignition/starter switch to solenoid. You can just check drop from battery positive to each positive connection, closing and opening the starter switch as appropriate. Another common cause is damage to the internal solenoid contact points from frequent switching/arcing. Depending on the solenoid construction it's often possible to dismantle it, clean the contacts, test for good continuity when they're in contact, and put it back together. There's lots of online advice on this sort of problem.It is possible for the symptoms you describe to occur when there's a corroded connection between battery -ve and the earthing point of the chassis. Used to be quite common on old Toyota 4WDs, especially if they saw a bit of water. Simple cleanup with file/emery paper does the job.

author: SMdude
author_rank: Frequent Contributor
timestamp: December 06, 2020, 10:07:15 am
content: It is quite common for the clutch or neutral switch to go bad. Check the voltage in/out from any switches that are in the starter circuit.A good method I have used to diagnose starter problems is to fit a light bulb, such as a 55w 12v globe to the start trigger wire(disconnect it from the starter) and use a volt meter to measure the voltage to the start trigger wire. Then get someone to hold the key in the start position with the clutch down etc then wriggle any plugs in the harness until the bulb starts to brighten up and the volt reading starts to fluctuate. As it has been said earlier, connectors can corrode/tarnish causing a bad connection to the starter.Also what brand/model is the tractor? This can help to get more specific information.

author: gg64
author_rank: Regular Contributor
timestamp: December 09, 2020, 12:15:07 am
content: Hum, I have several headlight bulbs, that might actually be a really cheap and feasible way to do diagnose.I might give it a try tomorrow.

author: SMdude
author_rank: Frequent Contributor
timestamp: December 09, 2020, 08:23:18 am
content: It works really well!And if you don't have anybody available to help you, just jump the start wire at the back of the ignition switch to provide constant 12v(obviously make sure that you have disconnected the start trigger wire from the starter!!)Most common will be the clutch pedal switch(or neutral switch), followed by the pto switch and or a bad connection is an open(non weatherproof) plug.