MEP-804A How to change to high voltage?

[robertsears1]

I am asking for help in changing my MEP-804A from 120/208 to 240/416 three phase. I have gone through TM 9-6115-643-10 (the one that came with it) and also TM 9-6115-643-24 which covers maintenance more in depth. Attached should be pictures of the voltage reconnection terminal board front and back. The genset is now running 120/208V. I have not been able to find any procedure on changing to the higher voltages in either TM so far. It could be a case of "if it had been a snake, it would have bit me" but I'm just not finding it.

Robert

 

[m-35tom]

remove the 12 nuts and move the outer board up one row so the arrow (snake) points to the high voltage.

 

[R Racing]

I would have thought the -10 would have had that in it?

 

[robertsears1]

Thanks, I thought the arrows had something to do with it but wanted a more official opinion. As I said in the original post, I have looked through the -10 pretty well but could not get my eyes on it.

Robert

 

[PeterD]

Just curious, why do you want 240/416 volts? Kind of eliminates using it as a backup power source for the house or shop...

 

[robertsears1]

I need the higher voltage to run a 15 hp motor on a compressor. I bought this one for the three phase.

Robert

 

[PeterD]

Makes perfect sense! Why I did not realize that I don't know, I've certainly considered just such a usage myself.

 

[Another Ahab]

I need the higher voltage to run a 15 hp motor on a compressor. I bought this one for the three phase.

Robert

Makes perfect sense! Why I did not realize that I don't know, I've certainly considered just such a usage myself.

No electrician, and the MEP folk all seem to have the know:

- Is there an elementary way of explaining why three-phase power is best for large motors?

That's all I know about three-phase is 1) "3-phase; 4 wire", and 2) preferred for big motors. Maybe I should YouTube it for a tutorial, might try that right now.

 

[Another Ahab]

No electrician, and the MEP folk all seem to have the know:

- Is there an elementary way of explaining why three-phase power is best for large motors?

That's all I know about three-phase is 1) "3-phase; 4 wire", and 2) preferred for big motors. Maybe I should YouTube it for a tutorial, might try that right now.

Figured as much: explaining electricity is is just not anything easily done, but this tutorial is short/ sweet and (maybe) a good start. Good enough for me, anyway. Seem OK to you MEP people (you know for one of the clueless)?

http://youtu.be/2Ndfnta4Y8g

 

[PeterD]

Single phase power is 'static' in that there is no change in the relationship--after all there is only one thing (the one phase) so nothing for it to change against.

Three phase is constantly moving and as such converting that change into rotary motion is easy.

A single phase motor works by changing single phase into two phases (so you get rotation of the phases) using capacitors. That's the start (and run) capacitor working for you.

So we end up with either on single phase converted to two phase (the start and run capacitors) but a bit inefficiently, or three phase where no conversion is needed. No start or run capacitors, no start switches.

 

[robertsears1]

This shows what m-35tom said about moving the board up so that the high voltage arrows (left side of board) are aligned and the voltage confirmed at 416v. The back of the board has a series of copper straps that tie the holes either side of the double rivets together. By moving the board up one row, you tie the second and third rows together.



On another note, I have recently noticed that the voltage between L1-L2 shows 0v. Measuring with a voltmeter at the lugs with the breaker closed shows the proper voltage. I am not sure if this has been the case since I received this genset. I dropped the control panel and wiggled all wires looking for a loose connection but did not find any. Any suggestions on what to look for?

Robert

 

[DieselAddict]

Are the voltages for the other switch positions correct? If so its likely the switch itself. You can try cleaning it by moving it through its positions 10 or 15 times. Switch contacts are usually are self cleaning when actuated.

If you are handy with a VOM - You can double check the diagnosis by reading the voltages off the switch itself with the generator running. Do you have the tech manual?

 

[robertsears1]

Thanks DieselAddict for the advice. I cycled the voltage switch around 30 times and it is working better. Sometimes the voltage between the different phases will vary by around 15 volts. Sometimes the voltage on L1-L2 will show around 240 volts with the Hz dropping from 60 to 58. It seems that if I snap the switch to the next setting vs just turning also works better. This unit had set unused for probably at least three years so maybe the kinks need working out. I have not really loaded it yet. What part of central NC?

Robert

 

[DieselAddict]

Great. Glad to hear that helped. It's always good to cycle all the switches when you do maintenance runs on the machine.

I'm in Efland. Today I was in Apex doing a little work for a friend.