MEP-803a overload circuit

[jamawieb]

Just got in a nice 803a and was load testing the unit. As I was increasing the load, the percent load gauge barely moved and after approximately 60 seconds the interrupter tripped and the overload indicator lite up. The amperage on both legs were 43 amps and the percent load gauge was reading about 30%. I assume the percent load gauge and the overload circuit have something in common, causing the problems. Any help would be appreciated.

 

[Korgoth1]

How long before it trips?

This could be your am/vm switch, need to test it. Test all your burden resistors. You will unfortunately have to desolder them to get an accurate reading.

 

[jamawieb]

Its about 45 seconds before it trips.
Do the burden resistors correlate to the problem I'm having with the percent load gauge?

 

[kloppk]

Yes - the burden resistors are used in the current measuring circuit as well as the AM/VM switch.
Sometimes just exercising the AM/VM switch will correct the problem.
Any corrosion on it's internal contacts will result is poor connection which will result in the incorrect amount of current load being detected by the meter and generator.

 

[TNriverjet]

I've got a similar problem with my 803a. It will run under load (50-70%) for 10-15 min and then trip the overload. If I load it up to 100% or more it trips within a few minutes. With advice from jamawieb, I've taken the top cover off and used electrical contacts cleaner on the reconnection switch. I've also tightened connections. I'm thinking I have an issue with something in the circuitry, but have not been able to track it down. I found page 2-58 of the -24 TM describes testing of the short circuit/overload relay. I have yet to do that, but am also interested in learning more about testing the burden resistors.

...scanning my schematics, trying to learn nomenclature and locations of the electronic wizardry behind the panel...

 

[Haoleb]

I had a somewhat similar issue with my 803. The % current meter seemed accurate but it would trip the overload way too early. I thought perhaps a bad current transformer or overload circuitry. On the advice of members here I took the top off and cleaned the reconnection switch with about a full can of deoxit sprayed every which way inside the switch and turning it back and fourth a ton of times.. Worked like a charm. In-fact just yesterday I ran it at 100% output for several hours on my load bank no problem at all.

 

[TNriverjet]

I've used nearly a full can of good quality electrical parts cleaner. I may have to try "deoxit". I need to leave the top cover off until this problem gets solved as suggested by others.

An interesting note here, my previous 802a would load up to 125% and chug black smoke. I never tripped the O/L on that unit. It might have had the opposite problem... that said, I don't feel like this 803a has the same tendency. It seems kinda lightweight in its ability to handle load due to this problem. Do others with working 803a's see them loading up and pulling the engine down a bit? I read in the TM that the O/L circuit was set to trip over at 100 or 110% load per leg. (Can't remember exact number) It would be the same for the 802a's correct?

 

[Guyfang]

Just got in a nice 803a and was load testing the unit. As I was increasing the load, the percent load gauge barely moved and after approximately 60 seconds the interrupter tripped and the overload indicator lite up. The amperage on both legs were 43 amps and the percent load gauge was reading about 30%. I assume the percent load gauge and the overload circuit have something in common, causing the problems. Any help would be appreciated.

Assuming will always get you into trouble. In fact, these two things have nothing to do with another. The gauge indicates what it senses for a percentage of max load being pulled. When the gage reads 125, or 130 %, it doesn't send a signal to the overload relay to shut down the K1.

If you want to test the K8 (overload/short circuit) relay, simply start the set. Flip up the S7, (battle short) switch and then apply load, to see what happen. Keep in mind, the K8 has TWO functions. When the overload portion trips the K1 out, its because of an overload. BUT, when the gen set scenes a short circuit, the same relay shuts K1 off. So you may be having a problem that has nothing to do with overload.

 

[TNriverjet]

Guyfang, so if I run your K8 test with no O/L tripping, what does that mean?

I see two possible outcomes, correct me if I'm wrong:
1. K8 test with normal loading and no O/L tripping
2. K8 test with immediate trip?

Also, I am using an old electric range for a load. All four burners on high and broil on the oven = 100% load. Maybe the range starts to overheat and feeds back something quirky on the two load wires? I'm just trying to heavily exercise a low hour unit and can't seem to keep it loaded up. Maybe I need to build a better load bank.

 

[Triple Jim]

Maybe the range starts to overheat and feeds back something quirky on the two load wires? I'm just trying to heavily exercise a low hour unit and can't seem to keep it loaded up. Maybe I need to build a better load bank.

It's very unlikely that the range would overheat, or that its load is anything but a nice, resistive one. In fact, a range should make a very good load bank.

 

[Dwnorton1]

[QUOTE

Also, I am using an old electric range for a load. All four burners on high and broil on the oven = 100% load. Maybe the range starts to overheat and feeds back something quirky on the two load wires? I'm just trying to heavily exercise a low hour unit and can't seem to keep it loaded up. Maybe I need to build a better load bank.[/QUOTE]



I use and old stove for my load bank as well. With all burners on high, oven on and door open it will pull right at 42FLA 240vac. Keep in mind this is an inductive load at 1.0 PF and gens are rated at .8 PF, so it gives the gen a pretty good load close to its rated capacity My 803 was experiencing the same symptoms until i exersised the AM/VM switch, multiple times. What I really like about the stove is that I set the burners at different ranges so the load varies from 32fla to 42 fla. It is more of a reactive type load closer simulating equipment starting and stopping. I

 

[TNriverjet]

That's what I thought too. Thanks for confirming. The unit seems to handle the fluctuating load well when burners are set on something less the "high". I usually keep the oven door open and run a fan off the convenience outlet to keep air moving around the range.

I'll go get a can of deoxit and try using that while exercising the main switch.

...note to self, don't completely reinstall the top cover off until a fix is confirmed...

 

[Guyfang]

I just want to see if K8 is properly working. If you run the set and turn on the S7, then put the set under load, if the K-8 is operating right, the idiot light should come on, but the set should continue to run. If not, its possible the fault indicator is bad. Doesn't happen often, but have seen it a few times.

Lets also not forget that you may have a short circuit someplace on the set also.

 

[Haoleb]

If it does turn out just to be a dirty switch I think the deoxit will probably help. I have used all kinds of different contact cleaners found at automotive stores, and brands like techspray but the deoxit is probably one of the best out. That stuff has brought back many a piece of vintage audio equipment as well. Most contact cleaners tend to vaporize and dry off immediately. The deoxit is different it will stay there and help lubricate and clean instead of drying off in 2 seconds. I blasted out the switch with air after cleaning it and also let it set overnight before trying it out so that it would dry out since I really deuched that thing.

 

[csheath]

Guyfang,
Did you ever receive a new unit with defects and return it under warranty or did the military just fix or shove them aside?

I just wonder if some of these super low hour units were delivered with defects and just put aside. I think I prefer a unit with some time on the clock.

 

[Dwnorton1]

...note to self, don't completely reinstall the top cover off until a fix is confirmed...

Another note to self might should be buy riv nut gun. Lol. Putting the nuts on some of these screws is real PITA. My unit has some forklift dents and dings and I have been fighting the urge to pull it apart to straighten out. I learned my lesson when I pulled some panels off a 802 I had. Told myself never again. Will be purchasing equipment for this in next week are so. Still researching which unit.

 

[Daybreak]

I've used nearly a full can of good quality electrical parts cleaner. I may have to try "deoxit". I need to leave the top cover off until this problem gets solved as suggested by others.

An interesting note here, my previous 802a would load up to 125% and chug black smoke. I never tripped the O/L on that unit. It might have had the opposite problem... that said, I don't feel like this 803a has the same tendency. It seems kinda lightweight in its ability to handle load due to this problem. Do others with working 803a's see them loading up and pulling the engine down a bit? I read in the TM that the O/L circuit was set to trip over at 100 or 110% load per leg. (Can't remember exact number) It would be the same for the 802a's correct?

Howdy,
You know the MEP-803A can handle a lot of load. Look back at my thread with the load bank.

Acquired a Military surplus load bank (running MEP-803A hard)

Watch the video through the end. I have the unit handling 67.2 amps per leg single phase 120/240 on the load bank. Watch the percent rated meter. I throw a bunch of different loads on it. Some, way over spec, but for only a second or two.

Then farther along in the thread I have written up a generator time and temp and load log for MEP-802A and MEP-803A.

 

[TNriverjet]

Ok I'm running the gen with S7 (battle short) flipped up. After 10-15 min the overload light still came on. Guyfang, I know this tells me something significant about where to look for the problem based on your previous messages. Please elaborate based on my conditions if you don't mind helping me wrap my brain around this.

 

[Guyfang]

guyfang,
did you ever receive a new unit with defects and return it under warranty or did the military just fix or shove them aside?

we had a warranty system in the army, and it was used somewhat, but mostly we just took stuff as is, because the warranty started when the equipment was turned over to the army. Sometimes it took 6-8 months to get equipment out to gaining units, so most of the warranty was no longer good. This was a warranty between the manufacture and the army.

There was no warranity between cecom, or the old troscom when they issued us equipment. In theory, but when new gen sets were delivered to a unit, normally someone, or even a team, when there was enough sets to justify it, came along. The gaining unit gave the equipment a ti, (technical inspection) and then began the hog swapping. Depended on the gaining commander, and his command structure. Some units were told "take it" from the gods on high. And that just what happened. Some commanders, and chains of command told the issuing unit/organization, "if it ain't right, sorry charlie". And that's what happened.

Normally, and i was in this situation several times, we didnt take anything deadlined. Flat out no. We might take a "checks in the mail" on small stuff. But mostly we said that the issuing unit had to bring the equipment to an operational condition. Nothing less. But that was always new stuff, and it was "normally", (i keep using that word) a non problem. The army pulled out all the stops, to issue us 100% operational equipment.

But when you want to see a real blood letting!!!!!!!! Watch two units handing over old beat up junk!! Oh boy, we had some fun!

I once gave 6 gen sets to another, "sister" unit, in exchange for 6 trashed out, beat up, pieces of junk. And then the gaining unit wanted every gig fixed. 100% fixed. It took 2 weeks, and much time, effort and money. The gaining unit needed equipment to pass a nato inspection. They got it. And the best part of the story is that after we tore all that junk up, went through and fixed it, that was some of the best running gen sets i ever had. One of the sets, old 303, that had 18 thousand hours on the clock, had to get turned in because of "excess hours". I drilled out the rivets on the data plate, and swapped it with a real dog. Made up a new log book and sent away my dog. We still had old 303 when we went to improved hawk, and swapped out every piece of equipment in the battalion.

i just wonder if some of these super low hour units were delivered with defects and just put aside. I think i prefer a unit with some time on the clock.

 

[Guyfang]

Ok I'm running the gen with S7 (battle short) flipped up. After 10-15 min the overload light still came on. Guyfang, I know this tells me something significant about where to look for the problem based on your previous messages. Please elaborate based on my conditions if you don't mind helping me wrap my brain around this.


The K8 relay, works on a thermal process. I am having difficulty translating this stuff in my head, back to english. So bare with me. Inside the K8 are three thermal contacts. Each one for a leg on the main gen. When the contacts get hot, there can only be two reasons. Short circuit, or Overload. These contacts get their signal from the CT1, CT2 and CT3 current transformers. As its easier, I would start with the K8. Make sure its wired right. Then the current Transformers. I would also check to see if the output load wires are wound through the CT's the right number of times. The CT's are the same between the 802 and 803. The only difference is how many times the wires are wound through the CT's. Maybe one of the other guys out there can take a picture of the CT and send it in. Or remember how many times the wires are wrapped. I am not at home, using a stupid notepad and don't have my schematics., so I cant look. If you can get another known good K8 and try it, its nice. But I don't know if that's an option. I suppose you might have a bad CT. It breaks down after getting hot. That would be VERY rare. Get out the -24 manual and read up on test procedures for the K8 and CT. I wish I could be of more help, but I am not home right now.
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