Need help to identify a component!

[thedeeredoctor]

This is a basic control unit from a tractor. It manages a 12v solenoid which can be energized for hours at a time.The circuit eventually will not energize because of the component in the picture below gets too hot and delaminates.

 

[dave9]

I'm going to guess it's an NTC thermistor, and that hopefully there are markings on it to tell you what value replacement part is needed, or IF it looks EXACTLY like the other one on that PCB, then I'd remove the other one and measure its resistance at 25C temperature to pick a replacement, one that is at least the same physical size or larger.

 

[thedeeredoctor]

Thank you that is excellent. I have since learned that the solenoid that is receiving voltage through that component measures between 10 - 12 ohms at 68f. In addition the amps are between 1 -1.2 A 68f. I know very little about how to purchase the correct thermistor. Any information that I can get will help.Thank you for your help!!

 

[dave9]

I know nothing specific to electrical circuits on a tractor, would do as mentioned above, look for markings on the other thermistor and measure its resistance, with the hope that if they look identical, they are. Once you have that you could look up parts on an electronics supplier's website, for example https://www.digikey.ca/

If this is a common problem you might get better help on a tractor oriented web forum.

 

[Bluejets]

More likely an inductor ( choke) Thermistors rarely if ever are made to carry 1 amp or more as far as I know.There looks like another further over on the same board. If this one is cooked, perhaps the other has some info on it. Also might pay to look for any other apparent fault downstream from there.

 

[dave9]

^ Thermistors are very common above 1A rating. They've been used for years to reduce inrush current in PC power supplies for example. Another random example:
http://www.ussensor.com/inrush-current-limiting-power-thermistors

 

[thedeeredoctor]

The function is to soft start a solenoid so the valve does not open abruptly. Yes there are 2 on this board the one for this solenoid usually becomes intermittent first and then fails completely. The second one is for the hazard lights. This board has a core value of $50. The "reman" sells for $1300. I have 6 of these controllers I have changed over the years. It would be nice to repair these and offer to my clients at a reasonable price.

 

[Bluejets]

So as I said earlier, is there any useful info marked on the good unit?

 

[thedeeredoctor]

No info both are cooked beyond reading anything. That is why I am trying to identify them. Worst case I will buy a reman and open it to get the part id.

 

[73's de Edd]

Sir deeredoctor . . . . .

Definitely a thermal inrush, current limiting thermistor that you have there . . .BUT in a very small power handling profile . . . just looking like its starting its decline, from the very first time powered up and starting a timely decline to result in a failure in a much shorter time than you would want to be expecting. With a final fracturing and a popping off / open connection of one of the solder capped leads.

From what info that you have given, looks like this would be a good fit.

https://www.mouser.com/ProductDetail/Semitec/12D2-10LC?qs=sGAEpiMZZMuBd0%2bwiCVS2waoyKMmx3l3SVq8KGWQqfw=

Only two Amellican dollah . . . a pop . . . BABYCAKES !

This prescribed unit has a multiple upsizing in the thermistor pellet, for 16x enhanced reliability factor.
I think that the units quiescent cold resistance @ 25Degs C would fall in at being 10-12 ohms and shift downward in resistance in ~ 10 seconds and then hold, with solenoid run time, continually pulling current thru it.

If you have or can get access to a laser beam thermometer, and have a good worling unit.

Do these tests:

Take a resistance reading with a DMM to get the cold resistance reading of one of the good . . . albeit . . . somewhat puny . . . .Original Equipment Manufacturer . . . . . themistors.
Watch in probing, them as they are somewhat fragile on the end caps or particularly in bending the leads.
Have a DMM connected in to be reading voltage across the good OEM thermistor, power up the solenoid and immediately take and log down the voltage being read across the implied good thermistor.
Run the activated solenoid for a 30 min to 1 hr " benchmark " test, and retake the voltage reading being across the on time activated and then warmed up thermistor . take the laser beam thermometer and shoot the peak surface temperature of the thermistor pellet.

FIO . . .
A companion unit associated with a series incandescent indicator lamp,. . .it loafs . . . would have NOWHERE near the peak power demand of a solenoid.

A continuance . . .pending feedback . . .

73's de Edd

 

[elebish]

If the resistance of the thermistor is approx. 12 ohms @ 68 f, and gets lower when heated up, it is a NTC type (negative temp coefficient). This is not difficult to check. If the coil of the solenoid has a diode across, that is meant to reduce the dc back emf to keep the coil from re-energizing after the initial energizing. Not often the case with mechanical solenoids but diodes are often used across coils of relays for the same reason. Check the diode if so!

 

[thedeeredoctor]

I want to thank everyone for your help. I have replaced the thermistors and all is well. Thanks again!!