Burned 4WD Solenoid

[jericho]

Have a 4WD M8200 and just bought our third 4WD/BiSteering hydraulic valve.
The 4WD solenoid coil is so hot when energized that you can barely keep your fingers on it. Kubota Corporate has no answer for me. They won't sell the solenoid coil separate and you have to buy the whole valve. It's pretty expensive. The dealer told me to check the diodes. I see diodes on the schematic but I can't find them yet. Anyway, I just ran 12v from the battery to the solenoid coil... It get's hot so there is no question of a diode being involved. If I reverse the polarity there is no change... It still gets hot. If I run 12v to the other solenoid coil, next to it on the same valve (the Bi Speed one) it does not get hot. My understanding of dc solenoids is that the inrush current is the same as the holding current, so there should be no question about the valve not stroking to it's full travel. Do I seem to be the only one to be burning up 4WD/Bi Speed solenoids???

 

[Daren Todd]

Are there any linkages that hook to the selonoid? Or does it just open to allow fluid through?

Just trying to visualize how it works and what it controls

 

[jericho]

No linkages. Just two coils that oppose each other on the same valve. If I figure out how to post a picture, I will do that.

 

[Daren Todd]

No worry's was just curious on how it worked. I deal with some selonoids at work that control linkage movements, and if the linkage isn't adjusted right to allow a full throw they'll give you fits and fail early. It was just plain morbid curiosity

 

[BravoXray]

When you energize a coil you create a magnetic field. There is no current flow for a short time, until the field is established. When you remove power from the coil the magnetic field collapses. All of the current that was stored in the field now rushes back into the circuit. The diodes are there to bleed this current off safely. My guess is that if you read the resistance through both coils there will be a big difference. I suspect that a diode is open, and every time that the coil is de-energized the excess current is melting away some of the insulation on the coil windings. Without a schematic it's just a guess, but it might be the diode for the good coil that is open, and it is burning up the opposite coil.
Good luck!

Jerry

 

[bxray]

Like Daren said,

If the linkage or plunger (hydraulic or other fluid) does not make it all the way in it will cause the coil magnetic flux to be off.
This is a part of the resistance of the circuit and will cause over current.

You said you are getting the complete valve.
Or are you just changing the coil?

There may be debris in the plunger or bend in the stem.
Can you take the valve apart?

Put power on the coil and watch the plunger.
It should move freely.
Compare it to the other one.

Ray

 

[MadMax31]

When testing, make sure you have it installed, or a heavy screw driver through the coil. Or you'll burn it up real quick. In the HVAC world solenoids can get pretty hot, but its normal.

 

[North Idaho Wolfman]

I would really like to see the part! send me a PM or email if you can't post it and I will.
I just got done going through all the diagrams for an M8200 and None have BI speed steering and None have anything other than a mechanical front diff lock, so I'm completely baffled on what your dealing with.
Are you sure it's an M8200?

 

[jericho]

O.K. I'll post a picture as soon as I can.

Meanwhile to answer a couple of points:

1. My understanding is that DC coils don't get hot if they don't get the solenoid to shift all the way, but AC coils do.

2. I think I eliminated the question of a diode being involved when I simply energized the coil directly from the battery with a two-lead jumper. I started to get hot right away, just like it does when I energize it hooked up in the normal system.

 

[Daren Todd]

Dc coils can get scalding hot when bad, or simply won't work. Depends if the guts develop quite a bit of resistance or just burn out. Usually if your getting quite a bit of heat, then the valve isn't opening completely. On the ones at work, it's a sign that the linkage is out of adjustment and not letting the rod make full contact with the magnet. Or the rod has a little grit or rust starting and needs to be cleaned and lubed.


If you can, double check the model number, and if need be post the full serial number so north idaho wolfman can work his magic with the parts and electrical diagrams

 

[BravoXray]

No, you didn't disprove the diode by hitting it with the battery. Read the Wikipedia article on flyback diodes and you'll have a better understanding of what I am thinking. You need to put an ohmmeter on both coils, or just keep buying new solenoids. Any one of the responses that you have recieved might be correct. But I would start with the easiest tests first. HVAC solenoids are almost always operated on alternating current, so that post doesn't directly apply to your problem, although he is correct. You might have a valve or hydraulic problem, as others have suggested, but I still submit that it is easier to rule out a simple electrical failure first. Also, I would suggest sending Wolfman a photo, in my experience on this forum, he is often the most knowledgeable.

Jerry

 

[ShaunRH]

Well, if someone else with the same unit could test the heat levels of their coil it would help us know if it is this unit or the whole line. It wouldn't be the first time something got mis-engineered.

It may be that the coil is just getting too much current. Coils are essentially dead shorts and can pull a lot of current. BravoXray has explained a lot of the electronic side of it, but you can also try reducing voltage to it. If the coil is just activating a solenoid mechanism, it may not need all that voltage or current to get the job done. You might try hooking it up to a power supply capable of lowering the voltage and see if the coil still triggers properly.

If you can get away with a lower voltage, or limiting the current (like with a resistor) then it will run cooler.

Someone with a good head for electronics could help you out with this.

The only other way I could think of to reduce the heat would be to pulse the signal at a rate higher than the field would collapse but low enough to cut the total wattage to the coil down.

 

[jericho]

I hope these all came though. The black wire coil is 4WD. The green one is Bi Speed. Both coils measure 7.5 ohms. If I energize the Green wire one it does not get hot. If I energize the black wire one it gets hot. I put the copper disks on myself to try to draw the heat. The one in place is the third one. It's brand new. The second one lasted 6 years.

Hope you can figure it out.

 

[North Idaho Wolfman]

Let me guess, you have a M8200DTN or a M8200SDTN.
In other words a Narrow!

Ok shooting from the hip, but I think I have your issue narrowed down some.
Are the new coils the same OHMS?
Did you check the 2 diodes under the seat?
Have you taken the base of the valve out and made sure the orifice was clean and unobstructed?
Is there a switch that controls the valve and if so, What does the switch say?

 

[jericho]

O.K. Wolfman,

Yes it is a narrow.
Yes both coils are 7 ohms.
What orifice? The valve volts to the casting. I see no orifice.
Bent??? I've had trouble with three valves. They all work for a while.
Can't post another picture of the Bi Speed diode passing 12v, but it acts just like the 4WD diode.

 

[North Idaho Wolfman]

Test the diodes on OHMS in both directions, one way should show infinite ohms and the other should show low ohms.
There is 2 orfices in yellow.

 

[jericho]

Did that test on the diodes. They seem o.k.

 

[jericho]

I see the orifices that you marked. I'll have a look.

 

[North Idaho Wolfman]

Three things come to mind why it would keep burning up the solenoids.
Anything that causes a low power (high impedance or high resistance) situation will cause the solenoids to overheat.
I would replace both the diodes at $24 (that's stupid expensive for those), and I would replace the 2 relays $46 that control the solenoids, also check all wiring connections at all points.
check and clean the orifices just to make sure there is no trash that is obstructing there flow, but if both sections are working good I doubt that is your issue.

A bad or intermittently bad diode (which job is to) protects the relay and/or a bad relay set of contacts will cause the resistance to so high enough to not power the solenoid to there proper potential thus causing them to overheat.
Measuring them and getting an accurate account of the feed power failure is hard because of the way the system works, you can measure voltage , but the real failure point is not voltage, but loss of amperage, or ultimately wattage due to resistance building up via a fault and the rise in Impedance due to heat build up in the coil, so it's adding to it's own problem and making it worse.

 

[bxray]

FYI, if the diodes check out fine they do not need to be replaced.

Their in the circuit to give the electro magnetic energy somewhere to go when the coil is turned off. As the field collapses it creates power in reverse polarity. i.e. The cathode is on the positive.
When the power is on they do nothing.
And if the diodes were bad/shorting they would blow a fuse as they are in Parallel.

In the first post 12 volts was applied right to the coil thus bypassing any relay/switch and diode and it still heated up.

When a coil is first energized the current is higher than normal, this helps pull the plunger into it.

When the plunger is in its proper place the coil dynamics change and the resistance/impedance increase lowering the current.

So I would be Checking the offices and plunger. If there is back pressure the plunger will not retract all the way due a hydraulic lock.

And seeing this is a two stage valve, make sure that only one coil is on at a time.
If one coil is holding the plunger the other can not take over. This would be a relay problem.

Ray