MEP805A regulator

[fredy2]

Weather has precluded test for days... I have come up with one other modification I am installing. I am putting a "polyfuse" in the field lead. I am doing this by putting lugs on the polyfuse and connecting that to terminals 1 and 2. The wire that went to 1 is then put on terminal 2 which is an unused terminal that becomes a tiepoint. A polyfuse is a resettable passive fuse. The one I am trying is a 240 volt one that will hold 1.5 amps and open at a little over 3 amps. I am leaving the retrofitted 3 amp fuse in the circuit as well. If this works out I will create a video of the retrofit method showing the steps on a second unit I have. My test regulator unit is a restored unit that had burned up due to run away voltage.

 

[fredy2]

I tested regulator on the generator today. This was with the generator unloaded. I could regulate the voltage between 200 and 250 as displayed on the meter. The voltage to the field appeared to be about 20 volts, however this is a pulsed drive from the SCR's and the Harbor Freight meter could be lying. If I went below 200 volts with the adjust dial, the unit dropped suddenly to 50 volts. Re-charging the field with the start switch brought it right back up. I think without a load the transient behavior saturates the feedback and the SCR's are shutdown and then the supply voltage to the regulation circuits is too low to maintain operation until field is re-flashed with the start switch. At settings above 200 volts the voltage is stable. The polyfuse seems to work fine and provide additional protection over the three amp retro fitted fuse.
I did find a TRC regulator on Ebay for $85 and will analyze it. It appears to have three large electrolytic caps which over time could cause problems. Also there are three 50 ohm, 55 watt power resistors that would add heat to the box. Notably missing is the bi-filar noise choke in the field circuit. There are two large transistors or SCR's that are driven from one output of an LM324 op amp through 1K resistors. If the two large transistors or SCR's I cringe seeing 1K resistors in the gate or base of these. High impedance in this noisy environment is a design no-no. The TRC board layout at least looks professional More than that will have to wait till I disassemble it to trace the circuitry.

 

[Suprman]

There are 2 nearly identical regulators one is 60hz and one 400hz. The cheaper ones are usually 400hz. Aircraft ground power gens only. They are not compatible with 60hz gens. But I have heard of the 400hz regulators being modified to work in 60hz gens. The generator should have under and over voltage protection and unless in battle short mode it will normally turn off the output contactor and give an error light under either condition.

 

[fredy2]

I have the schematic for the Libby 50/60 Hz unit traced out. There is a design fault that is easily corrected and a board layout problem easily corrected with a jumper wire on the board..
I looked at photos of Libby 50/60 and 400 Hz and there are slight differences.
The initial look on the TRC control looks like they have 150 ohms of power resistor across the field... Possibly putting a pre-load on the field supply regulator and maybe damping the inductance of the field.
On my unit the frequency adjust is not working so I will have to troubleshoot that problem. Frequency is stuck at 59 Hz. My temp gauge is defective... during a run the sensor dropped to 100 ohms but the gauge never got off the low peg.

 

[Guyfang]

Most of the 400 hertz sets can be traced back to Patriot Air Defense.

 

[Suprman]

I thought they used them to power aircraft electrical on the ground when the engines were off. Most of the civ ground power units are all large like 70k and up.

 

[Guyfang]

Some are used by the Zoomies, for radar, and aircraft, but the Air Defense world uses the majority. If I remember right, and it's been a while, a typical Patriot batterie used:
2 X150 KW gen sets for the radar and ECS and AMG
6 X 15 kW gen sets for launchers
1 X 15 kW for BMG

There were three firing batteries per battalion. Then the battalion had:
6 X 30 kW gen sets for another three AMG's
3 X 30 kW gen sets for the fire control ECS
I may have forgot something. In the day, there were 7 battalions here in Germany alone. All these sets were 400 hertz. And then came the gen sets we needed for 120 volt systems, and 24 volt systems!!

HAWK had even more sets per battalion. And the number of HAWK battalions was very large. There were other units that had 400 hertz, but it's been too long to remember.

 

[pbplus9]

I'm new to the forum and impressed by the knowledge I'm reading hear. Hope I don't make anyone mad by jumping in here on this thread, but my issues seem to be related to this topic. I am not smart enough either I guess to start a new thread, as I couldn't figure that out either.

I just purchased a MEP-805a that I planned on using to power a 460 volt steam cleaner with. Didn't come with any manuals, but have found a -10 and -24 online. Haven't helped much. Finally thru this forum figured out how to switch to the higher voltage. Generator seemed to be working fine. Adjusted to 460 output, (I'm hoping that isn't a problem, as I've read it is supposed to be adjustable up to 480 volts) and tried the steam cleaner(haven't been able to try it before either. Bought it used and just trying it for first time). The steamer pump wouldn't pump much water and heater portion wouldn't work. I assumed that was because the pump wasn't building enough pressure and there might be a safety on it to keep from heating if not sensing enough pressure(no book came with it either and what I found online didn't explain much). I also noticed the AC interrupter relay wouldn't stay engaged, so had my son closing it again so could mess with the pump. Finally shut the generator down to try find out why the pump wouldn't work. Found some issues and turned generator back on to try again and it wouldn't work at all. After releasing start switch the frequency gauge would climb to peak and then stop entirely, tripping a low voltage light. After looking at wiring diagram and looking thru the machine, I found the 3 amp fuse between the voltage regulator and field blown. After reading about the upgrades that were supposed to be done in the past, it appears mine was done as it has the fuse and a TRC regulator. (One other issue with the generator is that the voltage gauge is missing and I assumed that wouldn't be a problem as it was for reference only and I used my multi-meter to set the voltage).

Questions: Could the blown fuse and auto tripping AC interrupter all be related to a probable problem with the steamer? What are you thoughts on the most likely issue with the steamer? Do you think and how would I check for other damage on the generator besides the fuse? Where can one find fuses, as it looks like one I haven't seen before? Could the missing voltage gauge cause a problem?

Thanks for your input. I am not an electronics guy, but do understand some basics. I haven't found the manuals very helpful though, as they don't get very specific and I've been having to glean bits and pieces from all over the manuals to get a few basics.

 

[fredy2]

You will find that those fuses are expensive. You will have to replace the fuse before doing anything. Switching inductive loads like motors on and off may cause transients causing regulator to put out full current and blow the fuse. I have NOT traced out the regulator but it could have some of the same design faults as the Libby regulator. Never shut the generator down wit a load connected. I am going to video rebuilding a Libby regulator and incorporating a "poly fuse" in series with the other fuse. The Poly fuse is a self resetting fuse about the size of a quarter.

 

[Guyfang]

No, you don't need the AC volt meter to run the set. It has no other function than to read AC voltage and it cant affect anything else.

All the manuals you need for this gen set are in the SS manuals Forum. The manuals you found, may not be the latest. The manuals in the SS forum, are the latest. Yeah, they could use some work. But that's going to happen.

Put a 3 amp fast blow fuse in it and see if it pops. Buy several fuses, as you may need them!! Maybe a pack of ten? Do not use a load in your testing, until you have corrected the voltage problem. That way, any problem in the steam cleaner is separate from the gen set.

When you say your adjusted it to 460 volts, you mean you used the AC volt rheostat to adjust it up, or the pot on the volt regulator? The only way to correct your problem is to start with the under voltage problem. I think that will correct the rest. You can follow the procedures in the -24 book to test your K-1 output relay, to insure its working correctly and not damaged.

And like Fredy said, do not turn the set off, without shutting down the load first.

 

[pbplus9]

OK, thanks for the ideas. I adjusted the output with the AC voltage rheostat on the front panel, measuring between output lugs with my multi-meter, but one problem may have been I had the steam cleaner hard wired in, but off. I assumed with it off it wouldn't affect anything, but I am thinking now there must be a problem with it, as it would kick the AC interrupter off, even with the steamer off. I had just switched the unit over to the high voltage setting and wasn't sure if that may have been what was opening the AC interrupter. I'll do the next testing with the steamer disconnected. My goal is to eventually have a mobile unit with the steamer mounted on the trailer and I don't have a plug to wire in, thus the direct connection to the steamer.

I'll get some fuses and let you know what I find.

 

[fredy2]

Be aware that I have discovered discrepancies in the technical manuals. One I just discovered is inconsistency in labeling of "Plugs" and "Jacks". Example is they are reversed for J5 and P5 from the schematics on my unit. I hope to make a video on rebuilding the Libby regulator and fixing the design flaws.

 

[pbplus9]

Got my generator going. Seems to be fine. Replaced the 3 amp fuse with a 2 amp(that's all they had in town). Blew that on first start. But once I got the correct fuse it works fine after(I had the steam cleaner disconnected). Turns out, I believe, having the steam cleaner connected didn't work, because the steamer drew a small load for the control circuit. That apparently was enough to cause problems with the generator on start up(the AC interrupter would stay closed). I ended up putting a fused disconnect on the machine, so after getting the generator up and running with voltage set, I could flip on the disconnect, then the steamer would be ready to go.

Thanks for ideas and suggestions. I'll be interested in seeing what you come up with, fredy2, on your rewired circuit. That stuff makes my head spin, but I find it interesting.

 

[fredy2]

There are two problems with the Libby regulators. One is they put diodes in the gate circuit of the SCR's. This allows the gates to float and be subject to transients and false triggering. The second problem is a long circuitous path on the circuit board for the output drive of the unijunction transistor. This also can result in false triggering and run away. I am planning on doing a video of the retrofit of the regulator. I also have a TRC regulator and I want to trace out the circuit of that. From observation it appears that they drive the gates of the SCR's with an IC instead of the unijuntion. They also have three power resistors which appear to be a pre-load on the field drive.

 

[fredy2]

On consideration of the problem you have had, I think it might be that you are running the unit with voltage near the upper limit of its design. You might consider using some "control" transformers to permit operation at around the 416 design and say add another 24 or 48 volts to each phase with an autoformer connection. Auto formers are very efficient connection. Since they would be boosting the voltage about 10% they would only need to be rated at about 10% of a phase capability or in this case 1KW each. The contactor in the generator disconnects everything unless in parallel generator mode, so an external contactor/switch should NOT be required. If it seems to work with an external switch and doesn't with the internal contactor (interrupter), this implies a switching noise problem which is likely to be intermittent and MAY be back.

 

[fredy2]

Got my generator going. Seems to be fine. Replaced the 3 amp fuse with a 2 amp(that's all they had in town). Blew that on first start. But once I got the correct fuse it works fine after(I had the steam cleaner disconnected). Turns out, I believe, having the steam cleaner connected didn't work, because the steamer drew a small load for the control circuit. That apparently was enough to cause problems with the generator on start up(the AC interrupter would stay closed). I ended up putting a fused disconnect on the machine, so after getting the generator up and running with voltage set, I could flip on the disconnect, then the steamer would be ready to go.

Thanks for ideas and suggestions. I'll be interested in seeing what you come up with, fredy2, on your rewired circuit. That stuff makes my head spin, but I find it interesting.

These are my changes to improve the Libby voltage regulator:

Upon investigation, it appears that the original design was overdriving the gates of the SCR's.
The following are changes I have made:

1. Replace the diodes CR16 and CR17 with 260 ohm, 1/4 watt resistors. This reduces the drive to the gates below the maximum allowed per the data sheet. It also holds the impedance of the gates closer to ground than the diodes which may have allowed triggering due to noise spikes.
2. Run a short jumper wire from Q1 cathode (lead nearest CR12) to R20 (end nearest the SCR's). This avoids a very circuitous path for the return of the SCR gate drives that may permit noise to trigger the SCR's.
3. Install outboard a varistor on terminal lugs between the terminal connections 1 and 3 on the external connection terminal board. The purpose of this is to limit transients from damaging the varistor Z1 inside which often burns up and takes the circuit board with it. I used a 270 volt, 40 Joule device.

 

[fredy2]

I have the schematic for the Libby 50/60 Hz unit traced out. There is a design fault that is easily corrected and a board layout problem easily corrected with a jumper wire on the board..
I looked at photos of Libby 50/60 and 400 Hz and there are slight differences.
The initial look on the TRC control looks like they have 150 ohms of power resistor across the field... Possibly putting a pre-load on the field supply regulator and maybe damping the inductance of the field.
On my unit the frequency adjust is not working so I will have to troubleshoot that problem. Frequency is stuck at 59 Hz. My temp gauge is defective... during a run the sensor dropped to 100 ohms but the gauge never got off the low peg.

Temp gauge problem required replacing the sending unit... Unless one wants to take all the covers off, you have to do it by feel. Make sure you get the correct sending unit... It has a larger thread than some. Have new ready to slam in as coolant will leak when you take old one out.