Author Topic: Generator Problems - keeps blowing avr??  (Read 42246 times)

0 Members and 1 Guest are viewing this topic.

ace

  • Newbie
  • *
  • Posts: 6
  • Country: za
Generator Problems - keeps blowing avr??
« on: December 29, 2012, 05:54:42 PM »
Hi all,
I am in desperate need of some help. I am living "off grid" due to unforseen circumstances for the past 4 months now. I purchased a 3.6kw 24V Inverter, 8 X 200ah deep cycle batteries & 5Kw Diesel generator (no name chinese make). Basically I run the genny during the day to charge up batts, warm the geyser & do laundry. 2 days ago whist charging, I heard the inverter click over to inverter mode. I went outside & saw the volt meter on the generator was 0. I shut it down and started checking wiring, fuses etc... to no avail. I started it up again & noticed the Voltage gradually building up to 220 then falling back down to 0 continuously (motor running stable). I left it for a few hours & started it again - No voltage. I searched on-line & came to the conclusion it must be the avr. I took out the avr (it looked fine to me), went out & bought another one. Installed it - No voltage! I then decided to flash the genny by putting 12V dc on the brushes whilst motor was running, then reconnect avr - It came to life.... sort of. The voltage gradually rose to 220v, but after about 10 minutes or so, the voltage started jumping around (never more than 220V though), then back down to 0 & hasn't worked since. I managed to get some voltage out of it again by applying 12V directly to the brushes while the motor is running. The voltage is stable as long as I keep the 12v supply on the brushes, but doesn't work at all with the avr connected. Can anyone possible help point me in the right direction. All the tool hire shops are closed until after new year. My family & I are starting to take strain now. I have read a few threads on this forum & noticed "oztules" seems to be a genny repair guru. But any help from anyone will be greatly appreciated. Thanks in advance.... & sorry for such a long first post.

ChrisOlson

  • SuperHero Member
  • ******
  • Posts: 3642
  • Country: us
Re: Generator Problems - keeps blowing avr??
« Reply #1 on: December 29, 2012, 09:30:25 PM »
Check for voltage coming from the exciter winding and the exciter diode.  It is possible the exciter has gone bad.

Typically the field voltage will be 80-120 volts DC.  12 volts to the brushes will usually get you enough field current to get the voltage to normal levels, or thereabouts, without a load.  But as load on the generator increases, the field voltage also goes up to make the field stronger.
--
Chris

ace

  • Newbie
  • *
  • Posts: 6
  • Country: za
Re: Generator Problems - keeps blowing avr??
« Reply #2 on: December 30, 2012, 03:23:12 AM »
Hi Chris, thanks for your prompt response. I hope this doesn't sound too stupid but where is the exciter diode normally found & which is the exciter winding? Coming from the stator I have a plug with 4 wires (2 blue, 1 white & 1 yellow) which is going to the avr. 1 black & 1 red with seperate lugs which connects to the brushes. There is also another plug with 2 green cables which goes to the ignition switch panel (which runs through diodes & goes to Black & Red 12V posts for a separate 12V supply. I presume the exciter windings will be either the 2 blue or the white & yellow from the plug. On a side note, I did pull the generator apart & do a visual inspection, the windings looked absolutely perfect with no signs of burning etc.... I was too sure what the impedance should be, but measuring all the coils I found no open circuits, they all seemed to have a really low resistance +-2 - 4 ohms. The rotor however had a resistance of about 50 ohms. Should I measure the exciter windings in ac or dc ? Thanks again.

ace

  • Newbie
  • *
  • Posts: 6
  • Country: za
Re: Generator Problems - keeps blowing avr??
« Reply #3 on: December 30, 2012, 03:57:17 AM »
Ok, just a quick correction. The impedance on the 2 blue wires is really low 0.6 ohms. I also just measured the voltage on the 2 blue & 2 white (one looked yellow but it is actually white). No voltage in dc. Ac voltage on the blue wires while motor is running is 4.5v. Ac voltage on the white wires while motor is running is 1v. When putting 12V on the brushes, both go up to about 80V. I'm soo confused.

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Generator Problems - keeps blowing avr??
« Reply #4 on: December 30, 2012, 04:07:32 AM »
Difficult to help with no drawings and little information but you have done well trying to help yourself. I think you have proved conclusively that the alternator is  fine. If it had burnt windings somewhere it would smoke when you excite it from the battery.

You won't have a separate exciter, you are right that the excitation comes from those windings connected to the plug. Probably the excitation from one pair and the supply for the circuitry from the others and possibly the voltage sensing will be from the exciting winding or the other leads.

I think there may be a clue in the fact that you say there is a supply from the battery ( green cables). I strongly suspect this is part of the build up circuit and if it has failed it would explain why you needed to flash it. It may be that this AVR needs that supply permanently as part of its operation. It may explain why it was unstable when you got it running. Check the supply to that part and check the diode you mentioned.

The only other thing is to check the engine speed if you have a tacho, I would expect you to notice a difference in sound if the speed has dropped but still worth checking.

I am beginning to suspect that the AVR builds up via that battery supply and diode ( just as you are doing by feeding the rings direct).As Chris said the 12v may be enough to supply near nominal volts on no load, then the AVR will increase the filed to that needed to maintain the load. When you are flashing it straight on the rings it builds up and most normal AVRs will take control from this point but this one may not hold it when you aplying the load if it is just compounding the base excitation from the battery.

My guess,  supply to the green leads or that diode has failed ( most likely o/c as it doesn't build up). Change it for a good diode.  It is still possible that the initial problem may have killed both AVRs but you might be lucky

thirteen

  • Hero Member
  • *****
  • Posts: 980
  • Country: us
  • Single going totally off grid 1,1, 2013
Re: Generator Problems - keeps blowing avr??
« Reply #5 on: December 30, 2012, 04:14:39 AM »
Do you  possibly have a broken brush, spring, or they are not making good contact or wornout. If things get bad you could charge the batteries with the battery system off of the genset if it is seperate system. You would have to be careful hooking it up correctly fo reach batterey. I am asuming it is a 12v system or possible 24v system charged by an alternator just for the genset.  But it would work. Just a few ideas to ponder 13
MntMnROY 13

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Generator Problems - keeps blowing avr??
« Reply #6 on: December 30, 2012, 04:23:56 AM »
Your update came in as I posted. That sounds to be normal.

The filed supply will come from those windings, they may be taps on the main winding or may be separate windings. There will be no dc, that comes from the AVR. 4v will be residual ( and I suspect it is too low for build up when you loose volts in the AVR diodes and control elements).  The 80v will be something like the running volts for those windings and this voltage is rectified in the AVR to produce the dc field which could be in the 50v dc plus region and will change with load.  The AVR maintains just enough field to hold the 220v line volts as trhe load changes.

I strongly suspect that a pair of those wires supply the excitation and the others are the reference voltage. Without drawings I wouldn't know which is which and they may even interconnect.

You say that there is about 0.6 ohm resistance in the windings ( makes sense). Is there any connection between those  windings and between each of them and the ac output?

It makes life easier for the designer if either the exiitation or the reference is isolated ( I still wouldn't know which would be which).
Your new tests add more confirmation that the actual alternator is fine.

Flux

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Generator Problems - keeps blowing avr??
« Reply #7 on: December 30, 2012, 04:32:13 AM »
How old is this machine and how much running has it done? When I saw Thirteens commnets it reminded me that these Chinese things are prone to brush troubles and to broken leads from the slip rings to the field winding. You must have some sort of a circuit to get it to build up with tha battery so I dodn't consider that point, but if the brushes are near gone it does tie in with the fluctuation when you had it running and the fact that it gets worse the longer it runs.

Take a good look at the rings and brushes, checking the brushes are long enough to still have spring pressure and check that they are free in the boxes. The rings should be an even brown or black colour, if you see irregular surfaces with brass or copper colour in places then you may have contact trouble.

Flux

ace

  • Newbie
  • *
  • Posts: 6
  • Country: za
Re: Generator Problems - keeps blowing avr??
« Reply #8 on: December 30, 2012, 04:46:52 AM »
Hi Flux, thanks for your help.
The two green wires I mentioned aren't connected to anything else apart from 4-diodes (basically a rectifier) and then go straight to black & red terminal posts on the front panel. Just doing a continuity test with my multimeter. Both the blue & white wires are connected directly to the main output windings on the stator. That is the blue wires are connected to the black output wires. The white wires are connected to the red output wires. The main output wires share a common wire, although there are four terminals on the buss bar, only three are used. I will take some photos quick & post them. The avr is a very common black half moon shaped unit.
Thanks so much for your time.

ace

  • Newbie
  • *
  • Posts: 6
  • Country: za
Re: Generator Problems - keeps blowing avr??
« Reply #9 on: December 30, 2012, 05:06:18 AM »
Hi again. The genny is about 4 months old, but does have some serious hours on it. I use it for about 4 hours per day. I did replace the brushes, although the old one did still have plenty of travel. How would I check the rings, visually the look ok. I took some photo's, but they were too big to put up here. So I used image shack. The last picture is a voltage regulator for charging the battery. It has it's very own generator which is on the flywheel side. The output is measured at 13.8V.







Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Generator Problems - keeps blowing avr??
« Reply #10 on: December 30, 2012, 05:25:58 AM »
Thanks that helps a bit.

It seems as though the engine has its own charging system not connected to the alternator and with its own regulator.

The green wires are from another tap or winding and are just rectified to provide a dc output from the main alternator for charging external batteries or small load supplies, from your description it doesn't seem to be any form of AVR build up.

It does very much look as you have two faulty AVRs, sometimes these things happen and it really does mess up the thought process.

At the moment I don't see any other issues, the alternator seems fine, as far as I can see it is a stand alone unit with no assistance from the starting battery so it doesn't leave much else.

If you have changed the brushes, I doubt that there is any problems with the slip rings and you partly confirm this by getting it to build up with the battery. Just check the connections to the rings where they go to the rotor and wiggle them a bit to make sure they are fine. Don't know what more you can do other than try yet another AVR.

You seem to have done everything sensible. If the thing was in front of me I may have a few more ideas but I have little more to offer.

If you find any other things worth discussing let me know.

Flux

ace

  • Newbie
  • *
  • Posts: 6
  • Country: za
Re: Generator Problems - keeps blowing avr??
« Reply #11 on: December 30, 2012, 05:47:19 AM »
Thanks for all your Help Flux.
I was just reluctant to get another one in case there was something else causing it to blow. It certainly does seem as though everything else is fine though. I will get another AVR & let you know the outcome.
Thanks again.

ChrisOlson

  • SuperHero Member
  • ******
  • Posts: 3642
  • Country: us
Re: Generator Problems - keeps blowing avr??
« Reply #12 on: December 30, 2012, 09:53:24 AM »
Well, I think your problem has been diagnosed overnight while I was sleeping   :D

The type of generator head you have has been used since, what I call, "Moby Dick was a minnow".  It has a separate exciter winding in the generator head that supplies AC to the AVR and reference (that the AVR uses to control the field current) from one main winding in the head.  It starts up from residual magnetism in the core to get the field going, and then is self sustaining once the generator comes up to normal output voltage.  The exciter diode is in the AVR, along with control circuits for the field and capacitors to smooth the DC output to the brushes and rotor field.

There are some newer heads, such as used in our Honda EM-series generator, that do not have an exciter winding.  Instead they are brushless with a CT (Current Transformer) sensor and digital voltage regulation.  These are usually used on gensets with an electronic governor, as the engine governor is also tied in with the field control in the generator head.  This type is very complicated and they are designed to maintain exact voltage and frequency at all times, no matter what the load.  It is usually only found on high-end, more expensive generators.

It seems you have two bad AVR's in a row.  However, I did work on one older Honda generator once that did what you describe and there was nothing wrong with the AVR.  The head, for whatever reason, failed to hold any residual magnetism to get the field going.  I never did determine what was wrong with the head, but instead installed a manual exciter button on it that I had to push to start the field from the battery.  Once manually excited it would take off and operate fine.
--
Chris

OperaHouse

  • Hero Member
  • *****
  • Posts: 1308
  • Country: us
Re: Generator Problems - keeps blowing avr??
« Reply #13 on: December 30, 2012, 01:42:24 PM »
A friend of mine has a construction company and he had three non working generators stored away.  All three of them had brushes just like that with the identical problem.   The carbon brush had melted the plastic holder.  Brush lenght was sufficient so it wasn't exactly worn out from use.  I found replacements on ebay $18 + shipping.  That seemed way over priced.  The listing gave an expected life of 500 hours.  That seemed way too low.  I can only gather from this experience that if the brush assembly had been taken out and cleaned periodically it could have lasted longer.   Suggest you take this oppertunity to check and clean your brush assembly.

TheEquineFencer

  • Full Member
  • ***
  • Posts: 162
  • Country: us
Re: Generator Problems - keeps blowing avr??
« Reply #14 on: January 29, 2013, 08:05:45 PM »
Well, I think your problem has been diagnosed overnight while I was sleeping   :D

The type of generator head you have has been used since, what I call, "Moby Dick was a minnow".  It has a separate exciter winding in the generator head that supplies AC to the AVR and reference (that the AVR uses to control the field current) from one main winding in the head.  It starts up from residual magnetism in the core to get the field going, and then is self sustaining once the generator comes up to normal output voltage.  The exciter diode is in the AVR, along with control circuits for the field and capacitors to smooth the DC output to the brushes and rotor field.

There are some newer heads, such as used in our Honda EM-series generator, that do not have an exciter winding.  Instead they are brushless with a CT (Current Transformer) sensor and digital voltage regulation.  These are usually used on gensets with an electronic governor, as the engine governor is also tied in with the field control in the generator head.  This type is very complicated and they are designed to maintain exact voltage and frequency at all times, no matter what the load.  It is usually only found on high-end, more expensive generators.

It seems you have two bad AVR's in a row.  However, I did work on one older Honda generator once that did what you describe and there was nothing wrong with the AVR.  The head, for whatever reason, failed to hold any residual magnetism to get the field going.  I never did determine what was wrong with the head, but instead installed a manual exciter button on it that I had to push to start the field from the battery.  Once manually excited it would take off and operate fine.
--
Chris

Just and idea, If it has electric start and I think this one does, you can also run a wire from the starter solenoid wire to the + terminal on the brushes with a diode blocking the voltage from going back to the starter and it will flash the field everytime you start it.