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MEP802 short circuit?
- Thread starter CDR
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- 3,021
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- 63
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- eldersburg maryland
yes, i think you have at least 2 problems, but sometimes they are related to each other. just start with 1 and solve it. R10 is just 1 of 3, one for each phase, that are to load the sensing transformers so the circuit can see how much current is being generated. the more current the gen puts out, the more current from the sensing transformer is put across one of those resistors, the larger the current the larger the voltage drop so it is an indicator of output current for the gen.
does the gen start and run?
you may have a problem with the malfunction indicator and the only way i know to test that is to swap in a known good one.
Okay now I understand what they do. One wire was broken off that's what I fixed I was wondering if maybe that was the problem it was broken off of R10 the Load meter works last time I tried it generator runs and produces power perfectly.
Hopefully this problem solves everything. I'm betting on it's a frayed wire that's feeding 12 V in to something and giving it a false indication.
Seems so strange to me that I don't even start it and the indicator light goes on
The overload short circuit box I guess could be fed.
Hopefully this problem solves everything. I'm betting on it's a frayed wire that's feeding 12 V in to something and giving it a false indication.
Seems so strange to me that I don't even start it and the indicator light goes on
The overload short circuit box I guess could be fed.
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- eldersburg maryland
keep in mind there are 2 completely different systems here, 1 is the DC system that starts and runs the engine, the other is the AC system that monitors and controls that part of the system.
it seems common for the wires from the main AC contactor to the output lugs to wear thru on the back of the control cabinet. hard to see.
it seems common for the wires from the main AC contactor to the output lugs to wear thru on the back of the control cabinet. hard to see.
glassk
Active member
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- Hampton, GA
Since the system uses those three Resistors to see if the current is in range could be,
- 3,021
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- 63
- Location
- eldersburg maryland
only with the gen running and then there would be an obvious heavy load on the gen. this is a safety for unattended running. in this case it has not been started when it shows short. something in the malfunction indicator has probably gone bad or gotten wet.
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- glasgow,ky
What that light is telling you is that the current going through the current transformer(s) exceeds the allowed current. That black box on the far left inside the control box is controlling this. The current transformer is that grey thing-a-ma-bob that has three sets of wires wrapped through it just above TB4.
So, the most likely culprit is a mis-wired voltage selection switch or a shorted winding in the stator. You say that the only thing you did was wash it -- are you SURE that you didn't change the position of the voltage selection switch during that process. I've seen the short circuit light come on or go off depending on the position of the voltage selection switch. That was caused by a mis-wired wire on a terminal of the VSS. That could be tested by putting the unit in 3 phase and starting it to see if the short light goes out. If it doesn't come on in 3 phase and comes back on in any other phase then you at least have a place to start -- but that isn't necessarily good news, cause it points to the stator.
But if you are certain that the unit is exactly in the same position as before wiring then I'd look for debris in the TB4 / VSS area or a wire that got pushed to one side or the other from the water spray.
Another thing that could have happened is that water got inside the Short circuit - overload black box (far left). It is fairly easy to get water inside, and very difficult to get it out. I've taken one of them apart and there are two relays inside as well as a couple of chips that sense current overloads.
These are good units, and they simply have their own set of problems just like anything else.
The point of the whole short circuit system is to act as a "circuit breaker" to disconnect the load by shutting off the AC interrupt contactor in the situation where the load is shorted somehow. The primary defense for internal-to-generator shorts is the quad windings in the stator and the voltage regulator which shuts down if the quad isn't working or the sense (phase 3) isn't working.
I've washed these units as well, but I always try to avoid getting any water inside the generator unit or the control box. The TB4 area and current transformer areas are the ones that get dirtiest anyway.
good luck
So, the most likely culprit is a mis-wired voltage selection switch or a shorted winding in the stator. You say that the only thing you did was wash it -- are you SURE that you didn't change the position of the voltage selection switch during that process. I've seen the short circuit light come on or go off depending on the position of the voltage selection switch. That was caused by a mis-wired wire on a terminal of the VSS. That could be tested by putting the unit in 3 phase and starting it to see if the short light goes out. If it doesn't come on in 3 phase and comes back on in any other phase then you at least have a place to start -- but that isn't necessarily good news, cause it points to the stator.
But if you are certain that the unit is exactly in the same position as before wiring then I'd look for debris in the TB4 / VSS area or a wire that got pushed to one side or the other from the water spray.
Another thing that could have happened is that water got inside the Short circuit - overload black box (far left). It is fairly easy to get water inside, and very difficult to get it out. I've taken one of them apart and there are two relays inside as well as a couple of chips that sense current overloads.
These are good units, and they simply have their own set of problems just like anything else.
The point of the whole short circuit system is to act as a "circuit breaker" to disconnect the load by shutting off the AC interrupt contactor in the situation where the load is shorted somehow. The primary defense for internal-to-generator shorts is the quad windings in the stator and the voltage regulator which shuts down if the quad isn't working or the sense (phase 3) isn't working.
I've washed these units as well, but I always try to avoid getting any water inside the generator unit or the control box. The TB4 area and current transformer areas are the ones that get dirtiest anyway.
good luck
glassk
Active member
- 998
- 6
- 38
- Location
- Hampton, GA
That is the inside of a Fault indicator for a 30 KW unit, have not looked in a smaller one,
I'd look for debris in the TB4 / VSS area or a wire that got pushed to one side or the other from the water spray.
also something in the push to test/reset contacts could give a light, ???
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Positive I didn't switch the voltage selection switch. The generators always been a little finicky with this. Most the time it went away after a minute after I started it. I sort of just thought that was the way it worked now I'm realizing I probably had a problem along. Now instead of the light ever going off it just stays on the whole time.
I originally thought I found the problem when I saw disconnected wire.
This didn't fix the problem but if the reattaching it the load meter to worked better.
Wondering if it's the black box is shorted need to actually spend more time and investigate this but I really appreciate all the helpful tips you guys are giving me
- 235
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- Location
- glasgow,ky
There is a contactor in the AC interrupt circuit and a small 7.5 amp breaker in the control box, and a tiny third breaker on the right side of the "push to test lamp module". Which one is opening? If the one on the lamp module is going, then that is fairly normal if one draws too much current through the convenience outlets. I've put a load on the convenience outlet several times that caused that breaker to pop. I believe it is ~10 amp breaker.
If you are making electricity and if the unit showed a short circuit intermittantly, or showed a short circuit that eventually went away, then I'd suspect that black box on the far left to be giving a false indication. I've had one of those apart, but there isn't anything inside of it that will give any indication as to whether or not the unit is working properly. If you did take it apart you might find that there is residual water inside which could be causing the problem.
If you could find a known good box and swap it in you could see if things change. Or if you could remove it and find someone who would swap your module in a known good generator you could test it that way as well. A defective short/overload module shouldn't cause any problem in a known good generator except for a short indication whilst your module is installed. It wouldn't hurt the test generator, since it is only a malfunction indicator.
If you are making electricity and if the unit showed a short circuit intermittantly, or showed a short circuit that eventually went away, then I'd suspect that black box on the far left to be giving a false indication. I've had one of those apart, but there isn't anything inside of it that will give any indication as to whether or not the unit is working properly. If you did take it apart you might find that there is residual water inside which could be causing the problem.
If you could find a known good box and swap it in you could see if things change. Or if you could remove it and find someone who would swap your module in a known good generator you could test it that way as well. A defective short/overload module shouldn't cause any problem in a known good generator except for a short indication whilst your module is installed. It wouldn't hurt the test generator, since it is only a malfunction indicator.
- 3,021
- 222
- 63
- Location
- eldersburg maryland
disconnect the wires from the 4 rear right terminals and see that the problem goes away or if it still 'says' there is a problem. also take the box apart and look for water damage as george said. are you sure the cables from the contactor to the output connection have not rubbed thru on the back corner of the control box?
Okay so what you're saying is disconnect the 4 signal wires? The wires have rubbed significantly but they're not through the insulation and it doesn't matter if the breakers closed or not
- 3,021
- 222
- 63
- Location
- eldersburg maryland
right, with the wires disconnected, it cannot know if it has a short or to heavy a load. if it says it does it is the box, if the indicator goes away then maybe it does have a problem with the gen. i don't see how an internal gen head problem would show up since it has to have to much current flowing past the sensor transformer. put a known 5kw load on it and it should act normal.
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So after a four-month hiatus I got ambitious today and figured let me figure this mess out pulled it out of the garage turn the switch to on and started it and it ran perfect no shorts. The diode CR1 still got very hot to the touch. No idea why it's not showing a short now. So aggravating....