mep 002a kicking my butt

[hahnkl]

Hope someone can help...I posted before about issues I had with my Mep 002a which resulted from starting my machine up an letting it idle at low speed -- resulting in voltage regulator damage. Speeddmon and Ike informed of the issue with running the genset below 1800 rpm. Per their advice I replaced the output transistor on the voltage regulator, ( commercial version 2N3584). At the same time, I installed a Hardy digital Hz/V meter which I use to set the engine RPM. I set the rpm for 60 Hz reading on the meter and never touched it again. The genset worked fine with just a few lights hooked up so I thought everything was fine. Today, I started the genset up as usual, let the Hz stabilize at 60 Hz (just about 15 sec) then threw the main breaker on. I turned on mutiple lights (more than I have in the past and also turned on a blower fan (1/3 hp). The Govenor worked fine, maintaining output at 60 Hz. Ran everything for about 5 minutes and voltage needle was rock solid stable. As I began shutting light switches off, I noticed movement of the voltage meter and a slight strob affect with the lights. Then when I turned the blower fan off, my one last remaining light that was on began a strong strob affect and the voltage needle began jumping more radically. I shut down the genset, restarted and everything worked fine again as as I turned lights on and the blower fan on. Ran for about 10 mins - all ok, then as I described above, as I began shutting lights off and the blower fan off, the voltage meter jumped and the remaining light began the strob affect again.

 

[Isaac-1]

This still sounds like the output transistor, although it could be another component on the voltage regulator or even a rectifier diode going bad. Before searching too far, I would replace the output transistor again, they are relatively cheap, you may have bought a bad one, it happens. Also did you use caution to not overheat the transistor while soldering it in place (using pliers, etc. as a heat sink on the transistor package, and using short bursts of solder?)

Ike

 

[hahnkl]

This still sounds like the output transistor, although it could be another component on the voltage regulator or even a rectifier diode going bad. Before searching too far, I would replace the output transistor again, they are relatively cheap, you may have bought a bad one, it happens. Also did you use caution to not overheat the transistor while soldering it in place (using pliers, etc. as a heat sink on the transistor package, and using short bursts of solder?)

Ike

Thanks for the info Ike...I ordered 2 output transistors so will replace. In the event that this does not work, do you know anyone that does repair work on these voltage regulators. I feel I can replace the output transistor. But when it comes to testing the VR components to pinpoint the problem, I would be in over my head.

I will try a new transistor.

 

[Speddmon]

Like Ike said, the problem is definitely with the VR. Just because you used a "new" transistor, doesn't mean it was good. I've said for many year of electrical work, and even more so today with the cheaper manufacturing processes..."New only means it's never been used, not that it's any good"

I recommend like Ike said, if you can rest the VR upside down with the transistor resting on something metal as a heat sink. What I do is melt some of the solder on the tip of a hot iron, and then just touch it to where the post and board meet. This is usually enough to quickly heat up the post and board and the solder will flow and make your joint.

 

[Speddmon]

One more question...

I assume that you leave the speed set at 60 Hz from the last time you shut it down, so there is no throttle adjustment needed or idling of the engine.

My question is, how long are you holding the start switch in the "start" position? You should hold it no longer than 10 to 12 seconds max!!! If the oil pressure has not build up enough to keep the machine running by that point, let off the switch for 30 seconds and then do it again. Holding it too long is detrimental to your bridge board and can damage the VR as well.

 

[doghead]

Holding it too long is detrimental to your bridge board and can damage the VR as well.

Ed, Could you explain why you say that?

 

[hahnkl]

One more question...

I assume that you leave the speed set at 60 Hz from the last time you shut it down, so there is no throttle adjustment needed or idling of the engine.

My question is, how long are you holding the start switch in the "start" position? You should hold it no longer than 10 to 12 seconds max!!! If the oil pressure has not build up enough to keep the machine running by that point, let off the switch for 30 seconds and then do it again. Holding it too long is detrimental to your bridge board and can damage the VR as well.

Correct, my throttle is set for 60 Hz and I do not change this after shutting down or prior to start up.

My genset starts very quickly--I always run the glow plugs for 60 sec prior to cranking the engine--(even in warm weather) and so it fires right up. I have never timed the cranking time but I would say I never hold the switch more than 10-12 seconds.

Thanks again for your help and suggestions!

 

[hahnkl]

Mep 002a Still kicking my butt

Today...I replaced the output transistor. This makes the second new one. The outcome was the same as in my original post. Voltage output is stable e as I turn lights and power equipment. The needle on the voltage meter is rock solid, until n I start shutting off lights and the power equipment. Then the voltage meter needle starts jumping and any remaining lights that are on start having the strob light affect.

Any suggestions what to try next. Is there anywhere that I can send the VR panel to have it tested and repaired.

thanks

 

[Isaac-1]

The next step I would try is checking the output diodes in the rectifier bank, instructions should be in the TM. The thing I worry about is they may test good, but are just getting to the point of starting to break down under load. With luck one or more will test marginal compared to the others and you can swap it out. If all the diodes test good (and more importantly in this case, consistent compared to each other) I would move back to suspecting something in the AVR circuit board. If all test good at this point it will likely be something very obscure and the easiest testing method may be to start swapping parts (AVR and diodes), if that still does not fix it you may have an issue in the wiring, either in the harness, a connection or in the rotor or stator windings themselves. Another option may be to connect a large resistive load (heating element, etc.) and run it for a few hours, hopefully until the point of complete failure which will make finding the problem much easier, although the same may not be said for fixing it.

Ike

p.s. I can think of a couple of tests to narrow this problem down, the thing is they would require a fairly well stocked electronics test bench, probably including a dual trace oscilloscope and a variable AC power supply. (Hmm maybe just a variable AC power supply and a good current meter and a good multimeter)

 

[derf]

If you plan to keep the gen and are thinking of checking the diodes in the rotor you may as well just get new ones and replace the old ones. You have to take them out of the circuit to test them and if you have them out you may as well spend the $20 or so on new ones.

 

[Speddmon]

Today...I replaced the output transistor. This makes the second new one. The outcome was the same as in my original post. Voltage output is stable e as I turn lights and power equipment. The needle on the voltage meter is rock solid, until n I start shutting off lights and the power equipment. Then the voltage meter needle starts jumping and any remaining lights that are on start having the strob light affect.

Any suggestions what to try next. Is there anywhere that I can send the VR panel to have it tested and repaired.

thanks

I didn't think of this earlier, but if the strobe effect is happening when you are removing the load, it could be as simple as your VR is "Hunting". Read the TM on the proper adjustment of the VR. There is a section on there about adjusting it, and it mentions that if it is out of adjustment, it will "hunt" when you remove loads. That could be what you have happening.

 

[hahnkl]

Mep 002a Still kicking my butt--no more!!

I am happy to report that my Mep 002a is no longer kicking my butt. As I had indicated in my earlier posts I had issues with my voltage regulator. I attempted suggested repairs and tests (multiple times) and nothing worked. I then learned that Delk's surplus sales used and new VR for the mep 002a. I decided not to take any chances so I bought a brand new VR from Delks ($275). A set of instructions came with the new VR which outlined which terminals needed to be bridged on the VR for 60Hz or 400 Hz. For 60 Hz, bridged terminal groups are: 1,2 and 3; 4 and 5; and 8 and 9. I noticed right away that 4 and 5 were not bridged on my old VR. So decided to bridge the 4 & 5 terminals on the old VR to see if it the old VR would work. Bingo, that was the solution. I ran the genset several hours today and the voltage needle was rock solid stable. What a relief!! I now have good working genset and a brand new VR as a back up should I ever need it.

 

[rosco]

Great find! So any clues or guesses, as to how or why the terminals should have become "unbridged"? You got the unit this way? How many hours on it?

 

[hahnkl]

Great find! So any clues or guesses, as to how or why the terminals should have become "unbridged"? You got the unit this way? How many hours on it?

I bought the genset this way. Why the bridge was removed from the 4-5 position I have no idea.

 

[Triple Jim]

My MEP-003A has none of the jumpers in place. The board looks like it's been replaced, so I assume the person who did it was lazy and/or didn't read the instructions. It's on my list to put them on and verify the adjustment of the pots, but it seems to regulate OK the way it is.

 

[Grega]

Could it be that the older boards ,"the tan ones" dont have the jumpers like the newer green VR boards? Mine are like this. Sent mine to Gulf Coast Trucks to see if mine can be fixed. "Strobe light effect",but all the time.

 

[Triple Jim]

Did you adjust R15 (or R16) as described in TM5-6115-585-34.pdf, page 6-8? You turn it counterclockwise until the voltage becomes unstable, then turn it clockwise until it stablilzes, then turn it two additional turns. In your case I guess it was already unstable, so you can skip a step.