Generac 7550 no output

[Pcbmann]

I have a Generac 7550. Its about 3 years old. Last year it was running just fine and then, lights out. I had a small over load that should have shut down the output but allowed the unit to fire back up once corrected. The motor runs fine but no output. I have checked the electronics and found that the power regulator board was shorted. I replaced the diode that was shorted and checked it electrically and it seems good now but still no power. I was talking to someone about removing this board completely because this is a known problem in Generac. He was going to send me the info I needed to remove this board and get the unit back working. However I never got the info from him and do not wish to damage anything. If the generator was working one second and not the next could the field need to be flashed because of the short?

Any info would be appreciated.

Thanks,
Pcbmann.

[Pcbmann]

Wow, 69 views and no one has even a guess

[Wayne 440]

Ok, here goes...


(1) I guess there is something more wrong with your regulator board than the diode you replaced.

(2) I guess the regulator board needs to be in there, or Generac would have left it out in the first place as a cost saving measure.

(3) I guess Generac will probably want nearly as much as your set is worth for a replacement regulator board.


Please don't be offended, my real point is that if any viewer of your post had even remotely relevant information for you , they would surely "post up" with it.

Check back in a little while, sometimes these things take some time. The right person has to see your post.

W

[Billy J Shafer]

This is what I was talking about in regards to generac. Very hard to find anyone to work on them. Have you tried flashing the fields. Standard response when you mention Generac around a gen tech.

[Billy J Shafer]

Case in point. The generac section on this site has one page. The Onan site has 46 pages es

[K D Redd]

I fixed a 20 KW generac/ 4 cylinder Chevy powered unit on LP. The local Generac service tech. Took one look at it said all the board you need are obsolete, do you want to buy a new generator. Luckaly I had a new voltage regulator and the service diaghrams. Most of the stuff that was obsolete was the engine control boards. It is now making power. I was able to rigs a "Murphy" so if the engine losses oil pressure it will shut down. The owner uses it to power his race track where we pull garden tractors, race go kart and riding lawn mower. I should have taken pictures when I was working on it.

Kent

[Jim Rankin]

I would say that if a diode shorted and fed the field AC, it may very well need flashing now.

You can check for residual voltage on the output of the generator. If it's only the regulator board, you should still have significant residual voltage output. if you have 120/240 output, the L1 and L2 voltages measured to the neutral should be balanced.

Flash the field and if it builds up then, but doesn't stay up, you will at least know the basic generator end is good.

If no response to flashing, something's wrong with the exciter, field or stator.

[Pcbmann]

Jim, I will work on it this weekend and let you know what happens.
Thank you for pointing me in a direction.

The board that shorted out is the Power control board, it has 2jobs, 1 is to set the output current to only what you need. This way it saves on gas. The other is to shut down the output if an overload is detected. I did have said overload.

Thanks,
Pcbmann.

[Pcbmann]

Ok, this is what happened. I reassebleied everything using the board I had repaired. Checked everything for shorts. Powered up the engine and got 7 volts out of the 110 side. I excited the field with the battery for a second and got 110 out of it, also got 220 out of the 220 side. It will stay that way as long as its running. I put it under load and it held. I let it run for about 10 minuets and all was good. Shut it down and let set for 5 minuets. Started it back up and nothing, no power output. It does not seem to be self exciting any more. Since it held once excited I assume that the field and its power windings are intact. I am going to read and see if I can find the correct way to flash a field.
If you have any further thoughts let me know.
Thank you so much for pointing me in the right direction.
Pcbmann.

[Wayne 440]

When you "excited the field with the battery for a second", you did flash the field. Without schematics this is a WAG, but my intutuion says you have a bad capacitor someplace.

[Pcbmann]

Wayne, your right. I found that the field now has 11 VAC on it. AC, not DC, this means that the diode I replaced is not switching fast enough and is just setting in place until something makes it switch. I have tested this by using a light bulb to drag down the negative side of the field. As soon as the negative side has any load on it the diode switches and the AC becomes DC causing the generator to produce power. Since I can not get the correct diode anyplace (and I wouldent want to just get the same one that has burned up) I am going to order a replacement board. The replacement board is a sub board since they no longer make the bad type. I'm guessing they had to replace to many of them in warranty.
Thanks to everyone for all the information.
Pcbmann.