804B Odd Problem

[Larry Olson]

After not being able to come up with a megger I took a detailed look at my windings with my regular ohm meter last night. All of the coils are in the 0.2 to 0.3 range and no resistance to ground or each other. I still have the leads free in case I locate a megger but I'm pretty sure the windings are fine. Going to Harbor Freight today to get some space heaters. The saga continues........ Thanks for all the help.

 

[Larry Olson]

I have purchased a UEI Megger. It will be here tomorrow. Never used one before but from what I gather it should be used at the rated voltage of the motor/coils so since the genset is rated at 480V I should use the 500V setting? Scoobyshef said in another post he uses the 1000V setting. Anyone want to chime in on this? I don't want to damage anything. Thanks!

 

[Larry Olson]

Excuse me Scoobyshep.

 

[Ray70]

I'm not the expert in that area, but you definitely don't need to match the operating voltage of the equipment, that's not the intention of the test. Similar to HiPot testing a 12V cable harness at 600V or 1000V. The intention is to accurately measure the winding resistance and accurately measure cable insulation resistance, neither of which require replicating the "operating voltage" of the equipment, typically you will far exceed it, but the current being used is very very minimal, thus the total power being sent through the windings or harnesses is extremely low.
Hopefully one of the experts can explain it better!

 

[Scoobyshep]

Very open ended question anything sensitive? close to the rated voltage. Technically since you are doing each winding its half the voltage so 240 per winding (in high mode the windings are in series) the winding to ground test, if the winding is good no current will pass, if its leaking to ground you dont need to worry about damaging it because its already fu*ked

Now for motors and generator heads. as long as they are not connected to the outside works, 1000v wont hurt them. You get a better chance of finding a bad winding with the higher voltage (be careful what you touch, that thing will knock your dick in the dirt).

The one you need to be careful on with windings is a hipot tester, much higher current and risk of damage.



Also if you need to tag a member here you need a @ symbol like this: @Scoobyshep

 

[Larry Olson]

I'll have some results by Friday at least. I have a feeling the windings are OK but better safe than sorry. I also have the opportunity to buy an 812A (400hz) for $1000 and was wondering if it was worth buying and how much trouble it would be to change out the generator head and VR. I can do the labor easy enough. Guess I'll see what's out there for parts.......

 

[Guyfang]

There are several threads where folks have asked this question. You might want to look for them. Its not quite that simple. Changing the Main Gen and VR are not all that you have to do. At the least, you need to change the entire control panel, (not hard) main gen, (not that hard) and then you need to insure that everything in the Output load section is the same as the MEP-804. You need to look at the UOC for those parts.

 

[Scoobyshep]

Honestly if you want to use a 400 Hertz unit for 60 hertz applications. Your best off buying a solar inverter and feeding it rectified power from generator. You take the 400 Hertz AC through some heavy duty bridge rectifiers to make it DC and you end up with a clean AC source. Depending on the inverter you get you can easily convert three phase to single phase.

Sent from my SM-S908U using Tapatalk

 

[Larry Olson]

Honestly if you want to use a 400 Hertz unit for 60 hertz applications. Your best off buying a solar inverter and feeding it rectified power from generator. You take the 400 Hertz AC through some heavy duty bridge rectifiers to make it DC and you end up with a clean AC source. Depending on the inverter you get you can easily convert three phase to single phase.

Sent from my SM-S908U using Tapatalk

I was thinking that it would be a bunch of trouble. I was once bitten by 115V 400hz inside a test cell control cab and managed to get free. Wasn't pleasant. Thinking I will pass on that genset. Thanks much.

 

[Scoobyshep]

Indeed, quite the project either way.


The higher frequencies do have quite the special tickle.



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[Larry Olson]

It would seem that I need to be smart enough to use a resistance bridge to test my rotor coils according to the -24. Is there a down and dirty way to look at them or do I need to find one and an operator. Seems pretty complicated to me.
Also should I use my megger on the exciter stator or just rely on my regular ohm meter. I'm scared I'm going to damage something. Thanks Much!!

 

[Guyfang]

Open the -24 TM and turn to work package -4-18.1. Start reading there to help get you up to speed on the whole operation. Its really not all that hard.