MEP-003 Rectifier Board Burn

[truckfest]

Have a good running MEP-003 set, have test run several hours. After a cold start and 3-4 min. warm up (idle ,no load) Bridge Rectifier Board Resistor started smoking badly I am unsure how to procede other than to repair board and try again,but do not want to smoke any more parts. Any thoughts would be greatly appreciated!!

 

[Speddmon]

The problem was more than likely that you were running it at idle.

When you first start the set up, by moving the main switch to the start position you "flash" the generator field. This allows the generator to start producing power, from there out it is self excited, meaning it rectifies it's own power to feed the DC to the field. The voltage regulator "regulates" for a lack of a better term, the DC voltage to maintain the output voltage. I don't remember right off hand what the supplied voltage is exactly, but I think you are supplying 12 volts to the field to maintain the proper output voltage. By allowing the set to run at idle, you are not able to generate enough voltage to be rectified, meaning the voltage regulator has to draw harder on the bridge resistor to get the power it needs. You will be very lucky if you did not damage the voltage regulator as well.

I have a set that was like that when I picked it up from the base. Check very carefully around the board especially on the post of the 3 phase breaker nearest to the board...when I dug into the one I bought, the resistor has fried a terminal on the three phase breaker as well....I hope you don't have this problem.

It's a PITA to get to, but I say, pull the rectifier board, and repair it. The -34 TM shows the components needed. You may need a diode or two as well. Check it over really well. When you replace the board, after you start the set, get it up to 1800 RPM's right away and leave it there. That's the way these sets were designed to be run. Idling them is NOT GOOD!!!

 

[Carl_in_NH]

It's a painful lesson - but reading the TMs carefully is important before operating equipment.

They mention to not idle except under certain conditions like starting - and then, only for a few seconds before going to governed speed - on most gensets.

 

[truckfest]

Thanks for info. This unit idled very fast (considerably faster than any unit I've dealt with in the past) So I "Fixed" that.!! As I understand your response battery voltage (24V), has nothing to do with this part of the system once Field is "flashed". Could holding the switch in the start/flash position too long contribute to this problem? (Some units seem to take longer to satisfy oil pressure switch). I will have to change my warm up and cool down idling habits, but hate to run an engine at operating speed too soon.

Thank you very much.!!
Truckfest

 

[Speddmon]

As long as you are holding the start switch in the start position, yes it does play a part in the rectifier board. Again, that's why the TM says not to hold it for longer than 15 seconds. In actuality, 15 seconds is a pretty long time when you actually time it.

I know what you mean about not liking to have the engine run right up to 1800 RPM's after a cold start, but that is really what these beasts were designed to do. As for a shutdown sequence, these are not turbo charged engines so there is no more need to idle them down before shutdown, than you would in your car. I know it seems hard on the engines, but I feel they can take it...I've read too many posts about people buying "scrap" sets or "non repairable" sets from GL and having no problems with them at all. These really are beasts of burdon and can handle almost anything you throw at them.

 

[Gnoz]

As long as you are holding the start switch in the start position, yes it does play a part in the rectifier board. Again, that's why the TM says not to hold it for longer than 15 seconds. In actuality, 15 seconds is a pretty long time when you actually time it.

I know what you mean about not liking to have the engine run right up to 1800 RPM's after a cold start, but that is really what these beasts were designed to do. As for a shutdown sequence, these are not turbo charged engines so there is no more need to idle them down before shutdown, than you would in your car. I know it seems hard on the engines, but I feel they can take it...I've read too many posts about people buying "scrap" sets or "non repairable" sets from GL and having no problems with them at all. These really are beasts of burdon and can handle almost anything you throw at them.

Do you know what type of resistor goes on the bridge rectifier for MEP 002A?

 

[Triple Jim]

Do you know what type of resistor goes on the bridge rectifier for MEP 002A?

The parts manual says it's part number 5905-00-081-7350. Searching for that number turns up suppliers that specify it as a wirewound resistor, 56Ω, 6.5 watts. A higher power rating would be OK, but not a lower one.

 

[Keith_J]

Also, the injection pump timing is fixed, optimized for 1800 RPM. Running at lower speed could cause issues

 

[Gnoz]

The parts manual says it's part number 5905-00-081-7350. Searching for that number turns up suppliers that specify it as a wirewound resistor, 56Ω, 6.5 watts. A higher power rating would be OK, but not a lower one.

Do you think this FROM Radio shack would work?:10W056 56 OHMS CERMET POWER WIREWOUND RESISTOR

 

[Keith_J]

Do you think this FROM Radio shack would work?:10W056 56 OHMS CERMET POWER WIREWOUND RESISTOR

Your link didn't work too well, I did a search. That is a 10 watt 56 ohm, the required minimum heat capacity is 6.5 watts, it will work. If it were a 2 watt, it would overheat but a 10 watt won't. Basically, higher power dissipating resistors are physically larger.

 

[Gnoz]

I rebuild the board with new diodes and 20 W 56 OHM resistor and I got voltage and RPM, but the resistor started burning again. I turned the generator off and turned it back on with no out put. I am assuming that the bridge rectifier is fried again. I am not sure what is causing this. Any input would be appreciated. I know the wattage on the resistor is a bit to high but that's all that is available where I am.

 

[Gnoz]

I have replaced the components of the bridge rectifier and the resistor got really hot within seconds, again. When I first re-installed the part, I got voltage and rpm but when I noticed the resistor getting hot, I turned the unit off. Upon restarting it, I got no voltage. I wonder what is causing the problem. I know I am not having an idle issue because both times, the unit was running at 1800 rpm. I would like to know what powers up the bridge rectifier because I am assuming that the problem is before the bridge.
Thanks

 

[LuckyDog]

Did you down load the TM's from Speddemon's signature lines? They may not look like links but they are. The TM5-6115-585-34 has a better schematic of the electrical system. It is for the MEP-003a but they are the same schematics and it is easier to read than the MEP-002a scan.

I am thinking you have a short somewhere. That resistor should not be connected to anything once the generator is up to speed. The starter disconnect switch (S7) should open when the generator is up to speed. Maybe it is stuck closed? Just an idea.

 

[Gnoz]

Did you down load the TM's from Speddemon's signature lines? They may not look like links but they are. The TM5-6115-585-34 has a better schematic of the electrical system. It is for the MEP-003a but they are the same schematics and it is easier to read than the MEP-002a scan.

I am thinking you have a short somewhere. That resistor should not be connected to anything once the generator is up to speed. The starter disconnect switch (S7) should open when the generator is up to speed. Maybe it is stuck closed? Just an idea.

Where is (S7) located? I have looked for it and I cannot find it. I can see it on the schematics but I have hunted for it to no avail. Also, the starter has been stocking and sometimes it takes a little knock with a wrench to get it to work---could that related to the problem?

 

[LuckyDog]

TM 5-6115-584-12 Page 4-31 Section 4-28 at the bottom.

That should help. It is mounted on the outside of the blower housing next to the IP.

 

[Gnoz]

Your link didn't work too well, I did a search. That is a 10 watt 56 ohm, the required minimum heat capacity is 6.5 watts, it will work. If it were a 2 watt, it would overheat but a 10 watt won't. Basically, higher power dissipating resistors are physically larger.

Hi, I just replaced the bridge rectifier on my ME 002A and upon installing the new one, I noticed that the resistor on the bridge rectifier was starting to get really hot. So, I took off the battery terminal to cut off the DC power to the system. Later when I put the terminal back up, I did not notice any heat. I cranked the generator and the engine started fine, but no AC output until I flashed the excited by holding the start switch on the start position. I notice if I flash the excited for a while, it will continue to produce AC power when I let go of the start switch. But I would have to repeat the process every time I start the generator. I also noticed that the emergency DC switch does not function. I pulled it while the generator was running and it kept on running.

Any advice on how to resolve these issue?
Thanks

 

[LuckyDog]

Hi, I just replaced the bridge rectifier on my ME 002A and upon installing the new one, I noticed that the resistor on the bridge rectifier was starting to get really hot. So, I took off the battery terminal to cut off the DC power to the system. Later when I put the terminal back up, I did not notice any heat. I cranked the generator and the engine started fine, but no AC output until I flashed the excited by holding the start switch on the start position. I notice if I flash the excited for a while, it will continue to produce AC power when I let go of the start switch. But I would have to repeat the process every time I start the generator.

You'll need to check the wiring. Sounds like the CB is broken or by-passed. This is the Circuit Breaker on the engine control panel correct? Not the one down by the electrical outlet.

I also noticed that the emergency DC switch does not function. I pulled it while the generator was running and it kept on running.

Any advice on how to resolve these issue?
Thanks

Do a search on in this forum. IIRC, this is not an unusual problem. If there is not enough residual magnetism in the exciter field, it will require reflashing. Most of the time it is enough to just hold the master switch in the start position until the oil pressure is up. That is why S7 (Starter Disconnect Switch) is there. It prevents the starter from trying to engage once the engine is running at proper speed.

I don't know if it is a problem, but I always start my 002 with the main AC circuit breaker (CB1) in the off position. I don't want to try and start the engine with any load apply.

 

[GREENMV]

Hello to my fellow Steel Soldiers, I am jumping on
this past post with similar problem. Short story, I needed to sell a Mep-003a 10Kw
to a friend today for his portable logging mill. I knew it would run but not
produce power, I knew that It was probably the Voltage Regulator and it did not
have a working frequency gauge, so In my wisdom I took a control box off my
Mep-002a that I knew was in 100% working condition. I swapped the control box’s
and it worked on the 10kw like a champ. Now I needed to put the 5Kw back together,
so I installed the non working control box onto the 5Kw and put In a “New”
Voltage Regulator (Lakeland) and a working Frequency Gauge I had for another
Generator. I started the 5Kw up with no problems and was showing around 240v power
at the gauge and the Frequency gauge was showing around 62 Hz, perfect. “NOT” I
walked to my toolbox to get my Fluke to double check voltage’s and by the time
I walked back to the running generator 1 min tops, I smelled the OH Sh-t smell
and seen smoke coming from the AC Control box.
I shut down the generator and took the AC Control Box cover off to see
what the problem was. I Smoked the Bridge Rectifier Resistor. So I know it’s
not the VR so does anyone have an Idea what else could smoke the Resistor?

 

[Triple Jim]

Greenmv, it's late and I'm tired, but I assume something is causing that resistor to keep trying to supply exciter current after you're done cranking the engine. I wonder if terminal 5 of the diode board isn't connected to terminal 12 of the regulator (ground), so it's trying to ground through the resistor all the time. In any case, something is causing that resistor to stay active after you release the master switch from the "start" position.

 

[GREENMV]

Triple Jim, Whatever It Is I know its in the Control Box. I just finished reading for the past 5 hours and nothing is jumping out at me. I replaced the Bridge Rectifier Board before I closed up garage tonight and next I am going to change the start switch and try again. Cross fingers, will see Monday, If It smokes again? I know it's the wiring or something In that Box. I am done for today myself. Thanks