Any ideas on Powertech generator not always producing power? (Again)

[belfert]

I have an issue with my Powertech 8KW generator not always producing power.  It will produce about 3 volts instead of 120 volts.   It usually has to be stopped and started several times before it produces power.  It is not the transfer switch as I measure 3 volts right at the generator.  Any ideas?  I've asked before and unfortunately none of the answers really helped.  The generator has about 700 hours on it.

One Powertech tech said to reseat the connections to the power regulator.  I called again after that and another technician said that reseating wouldn't help and the brushes were probably an issue.  Anyone know how I verify if the brushes are an issue?  It appears I have to basically remove the entire cabinet to get to the brushes.

[Frank @ TX]

Hi Belfert,
I don't have a Powertech but I do have a Martin gen set.
Last summer while on the road ( 100 deg in TX ) mine started doing the same thing : making low voltage.
Some times it was 5 volts and other times it was 30 votes.
The problem was the voltage regulator.  Put in a new one and set the controls and no problem since.  On a Martin the voltage reg does a few things other than just hold the voltage steady.  About $200 to Martin and I'm in business again.
BIG tip for you : the engine will keep itself cool thru the radiator BUT you have to have LOTS of air circulating in the cabinet to cool the generator and the voltage regulator.
Do what you can to move lots of air thru.
Frank

[belfert]

The regulator is mounted in a spot where air doesn't normally circulate at all.  Powertech kinda put a separate box on top of the main box and put all the controls in there.  I wouldn't mind replacing the regulator as long as I knew it was bad and I wasn't just throwing parts at it.

Heat might be an issue here.  It first acted up when it was about 108 degrees outside.  We had to shut down the generator for a few minutes to rewire something and the generator would not put out power upon restart.  I played around with things for a while and it finally started working again.  It is only 80 degrees out right now so I suspect it will work just fine at this point.  I might try heating things up with my heat gun a little bit to see what happens then.

[bobofthenorth]

I dunno jack about generators despite having worked constantly on them since we bought the bus.  The best advice I have found (this site excepted, naturally) has been here. 

[luvrbus]

The voltage regulator regulates the AC power it has nothing to do with the DC current going to the exciter fields on a Powertech that comes from the rectifier as with all DC systems probably a bad ground wire  

I would flash the generator first and work from there if the exciter fields don't get enough 12 v low AC volts are what you get,

I would say the PowerTech guy is on the right end lol    

good luck

[belfert]

I did a little bit of research on flashing the field and it doesn't appear it is something one should do unless as a last resort on a completely dead generator.  The need to flash a generator is often because it hasn't been used for a long time.

Would flashing the generator still be indicated even if the generator is running in the morning and doesn't run later that day?  I've always been able to get power by shutting the generator down and then restarting it a few times.  It sounds like I might be just as well off having a professional take a look at it instead of me spending the whole summer chasing after an intermittent problem.  I'd prefer not to spend the money on a professional, but I can't fix everything.

[belfert]

I went out and started up the generator and it produced power just like it should.  I ended up running it for about an hour under load.  The generator has not acted up since last fall.  The only thing I did during that time is to re-seat the terminals on the voltage regulator.  None of the terminals seemed loose that I recall.

I'm kinda stumped right now.  I suppose I should take the enclosure off and check the brushes, but I first have to figure out how to do that.

[gus]

Go online at their website and see if you can get a maint manual with troubleshooting in it. I did this for my Westerbeke and found my problem to be a shorted field coil.

The manual gives a very easy to follow, step by step troubleshooting guide which will at least narrow down your problem.

I thought at first it was a dead rectifier, don't know if yours has a separate rectifier like mine or it is built into the control box. These little rectifiers are prone to failure, their function is to provide low voltage DC field current.

Anyway, the troubleshooting section enabled me to boil it down to the field which appears to have a short. Mine is '82 vintage and was on a boat so some corrosion in afield coil is no surprise.

Having said all that, my guess is it was just heat soaked. After being overheated most gensets take up to half an hour before they can be restarted. The post about high air flow over all the genset is wisdom to heed, there is no such thing as too much airflow in really hot weather.

I'm no expert on gensets but having gone through four in two buses I'm getting there!! I still have two and the one that works is in the bus. I'm in the process of reawakening the other.

[belfert]

I've been through most of the troubleshooting procedures in the manual and nothing has come from it.  If this was a constant problem it would probably be an easy fix.  The frustrating part is that it is intermittent and hasn't happened since last fall.

The problem is it will probably act up when I'm in the middle of nowhere on a weekend when I can't get technical support or any parts.

[gus]

Brian,

I was having similar intermittent problems with my engine alternator, turned out to be two broken copper connectors which were impossible to see until I shook the wires.

This went on for weeks and weeks!

[Ncbob]

Brian,

You have an exitation problem which is intermittant. If there's enough wiring, solder new spade connections on the VR leads and read them with a quality VOM. You should be reading the resistance of the rotor.

If you don't have a Powertech manual for your unit you should get one post haste. We're all prettygood mechanics but don't always understand what the guys who engineered these things are trying to tell us.

Best of luck,

NCbob

[belfert]

Yes, I have a manual for the generator.  I have attached a page from a PDF manual I got from Powertech that has a wiring diagram.

I'm confused on how to measure the resistance of the rotor.  The resistance chart they provided doesn't list which wires to check for the rotor.  Unfortunately, I am not a generator expert.

[belfert]

I had to give up working on the generator tonight after only an hour or so as the skeeters are getting thick.  Many thanks to those who provided help so far.

It looks like the entire generator head has to come out to replace the brushes or to do anything with the head.  I am not going to do anything more with uncovering the head until someone says I absolutely need to get into the head.

[gus]

Brian,

I wasn't able to download the pdf file for some reason?

3 volts output is normal residual output, which means the field is getting nothing from the rectifier because it is bad or the VR is bad since it regulates the field voltage. (Residual means that the only field strength is from the magnetism remaining in the field iron and it is getting nothing from the rectifier.) In other words it is a only a weak permanent magnet instead of the strong electromagnet it normally is when provided with DC voltage.

So, what I am saying is, since your genset is so new,  I think you have a field problem and not a rotor problem. Since it is intermittent I suspect a loose connection at the rectifier, the VR or in the field wiring. It could be a shorted out field coil which is exactly the problem I have with my Westerbeke right now! It has the same weak output as yours but it is not intermittent, it is steady.

Rotor resistance is checked at the brush rings on the rotor, usually three or four rings, and the rotor shaft, but the brushes may have to be lifted off the rings. Your manual should cover this.

It could be worn brushes, but I doubt it since it is so new. On the other hand, it is not unusual to find a broken brush since they are so brittle.

Unless the PT is a really different animal the rectifier provides DC to the field and the VR controls that DC voltage. It could get DC directly from a battery but have never seen one that does. Have never seen a VR that controls at the AC output although it senses the AC output to tell the VR what to do?

If there is anything connected to the output it will mess up any ohm readings so they will need to be disconnected for accuracy.

If you open it and have a look you may be able to see any shorted or disconnected wires.

OR, it may just be a loose connection at the genset controller. These things vibrate a lot and loose connections and broken wires are not all that unusual.

Without knowing more I would hesitate to even open up the head, especially since it is working well now!! I definitely would not do any soldering to rotor wires.

This is really frustrating, it took me half an hour to type this because the page keeps locking up, bummer!

[belfert]

I talked to Powertech service this morning and they suspect the brushes are sticking.  The only way to get at the brushes is to open the end of the head.  I spent this evening unbolting the generator and moving it so I could pull the panel off that covers the end of the head.  It is unclear how the end of the head comes off.  It is getting late so I decided to call Powertech tomorrow morning.

I would not be surprised if the brushes are sticky based on the amount of dust and dirt in and around the generator.  I need to do a better job cleaning out the dust and dirt after going out to the desert each fall.