Author Topic: generator problems (Read 35411 times)

greenkarson · « **on:** February 28, 2012, 07:53:34 PM »

I have a 5500watt diesel generator its a no name knock off. We used it for a few weeks back about four years ago then one day it quit making electricity. It got thrown in the shed and forgot about untill yesterday. I dug it out and fired it up and checked all the plugs with my multimeter.
It has a 120v plug a 240v plug and a 12vdc connection and here is where it gets weird all three plugs were showing 1v. So i removed the end of the generator its self and tested at the buss bar inside same thing one volt. So im thinking the gen its self is toast but thought i'd get some opinions first before i throw in the towel.

If something is fried in the gen i was wondering why im geting one volt on all three circuits ?

Here is a pic of the end of the gen showing the buss bar

Mary B · « **Reply #1 on:** February 28, 2012, 08:01:04 PM »

Check the brushes. The cheap no-name generators use them a lot.

greenkarson · « **Reply #2 on:** February 28, 2012, 08:10:11 PM »

Is it usually a case of cleaning them or replacing them?

This generator was hardly ever used it would probably have about thirty to fifty hours tops.

Mary B · « **Reply #3 on:** February 28, 2012, 09:23:16 PM »

Maybe just loose, my cheap chinese chopsaw does that all the time. Could be bad too, they don't last long.

greenkarson · « **Reply #4 on:** February 29, 2012, 06:33:36 AM »

I read that last night before i went to bed. In the middle of the night i sat right up in bed thinking. With the coils on the outside like that isnt this a brushless generater?

dinges · « **Reply #5 on:** February 29, 2012, 07:01:42 AM »

Quote

With the coils on the outside like that isnt this a brushless generater?

Unlikely, as it would mean the rotor would need to have permanent magnets then. So unless the rotor has permanent magnets on it it will generate the magnetic field by means of a field coil. If there are copper windings on the rotor, power will need to go to those windings. Can only do that with brushes.

But, it should be easy to tell if it's brushless or not by visually checking for the presence of brushes....

A reading of one volt on all buses means very little if you're using a high-impedance digital multimeter. I get a reading of 2.66Vac just by touching with a finger one of the probes of my DMM, without connecting it to anything else than my body....

You don't give people much information with which to help you; brand of the generator, a few good pictures of details. I do have a copy of 'small AC generator service manual 2nd edition' (Intertec publishing) that has a generator service section on Dayton, Deere, Homelite, Honda, Kawasaki, Kohler, McCulloch, Onan, Pincor, Robin, Tanaka and Yamaha. One thing all these generators have in common is simplicity. A few windings of copper wire and a few diodes. The schematics of these things are amazingly simple. Maybe the more modern ones are different, with inverters, but the few gensets I've dealt with were electrically very simple.

Not much that could be wrong with that, I think.

So, check brushes as Mary-Alana suggested - I'd say 50-60% chance of that being the problem. Then you may want to check the diodes in it. I'd say checking both things should cover about 80% of possible malfunctions. A burnt-out winding is a possibility too, but not the thing I'd expect most likely to be wrong.

You may also want to tighten all screws of electrical connections; the problem could be as simple as a bad contact due to a screw that has vibrated loose.

oztules · « **Reply #6 on:** February 29, 2012, 01:26:15 PM »

"Unlikely, as it would mean the rotor would need to have permanent magnets then. So unless the rotor has permanent magnets on it it will generate the magnetic field by means of a field coil. If there are copper windings on the rotor, power will need to go to those windings. Can only do that with brushes."

No.

The most common gensets I seem to have to fix for folks, are the capacitor excited ones. These have no brushes, but a heap of wire on two poles on the rotor. Each pole winding has it's own diode, and this rectifies the induced emf in the rotor windings and causes the current to flow in the rotor to make the rotor field.

The voltage in the rotor is induced by a winding in the stator, that is paralleled with capacitors (20-80uf usually ) They set up a circuit that resonates with the rotor circuit, inducing the current in the rotor.

This kind of genny has either bad diode/s or bad caps to stop it... very very tough. Also after removal of rotor or not used for very long periods, then flashing the rotor (re inducing a remnant field in the rotor steel) is mandatory to get it to start if it has lost remnance. (12vdc across the out put field will do it when running).

Brush types will have an AVR to drive the brushes. There is usually a small magnet in the rotor that generates a small start field to get the AVR up to voltage to control the rotor. With these they suffer AVR burnout or bad brush contacts. ( have seen fatigue in wire terminations on the rotor as well)

Quick way to check is a 12v battery across the brushes and see the output. If a big change from your AVR, then rotor coils are probably ok... leaving the AVR as problem point. (disconnect brushes from avr for test purposes.... Usually need 50v or so to drive the rotor properly).

Does it have cap/s on the outside? or does it have brush holders... I cannot see either from that pic.

.................oztules
Edit : spelling and diodes to diode

dinges · « **Reply #7 on:** February 29, 2012, 02:05:55 PM »

Quote from: oztules on February 29, 2012, 01:26:15 PM

No.

I stand corrected. The 1.5 gensets I've dealt with had brushes... shouldn't have extrapolated that to all gensets. Good to see incorrect information being immediately corrected.

Had another look at the book at the genset repair book.... lots use brushes, but also many gensets use the self-excitation system.

I've scanned the electrical schematic for a Kohler (450W) brushless genset to show the simplicity of it.

One other thing you could give a quick try is to unplug and re-plug the connector in your image; the problem could be as simple as a bad contact due to dirt, moisture and/or oxidation in the connector.

greenkarson · « **Reply #8 on:** February 29, 2012, 07:18:47 PM »

Thanks everybody for all your help. I never got a chance to open the gen today. I believe its a toledo generator i never heard of it before.

Is it possible for the capacitor to be out and away from the generator its self like in behind the control panel. The reason why i ask is when i was poking around at it the other day i opened the control panel cover a little and peeked in i could see a round thing about three inches long and a inch and a quarter thick. I could'nt see it very well but it looked like capacitor. Now that i think about it i think it may have been porcelain or something.

Hopefully tomorrow i can dig a little deeper and take lots of pics.

Thanks again everybody for putting in the extra effort t help much appreciated.

oztules · « **Reply #9 on:** February 29, 2012, 08:01:18 PM »

Sounds like a cap to me... for 5kw, I expect around 40-50uf. Usually white plastic. They normally make the coloured ones for intermittent electro caps for cap start- cap run units (motors).White for run, blue or black for start.

I have only ever seen 1 tin can/oil filled cap in this application.

..............oztules

greenkarson · « **Reply #10 on:** March 01, 2012, 12:19:39 PM »

Started to dig a little deeper today and tought id post a few more pics before i went any deeper. As it turned out the thing i described is a capacitor. There is a pic of it.

Thanks again everybody!!!

oztules · « **Reply #11 on:** March 01, 2012, 04:14:39 PM »

Hmm, my first instinct was that the cap was too small.... but you are running 60 hz not 50hz, so you have 600 rpm more than we do (3000 vs 3600), and so smaller caps.... so yes I think it is cap excited.

Only two things (apart from open coils somewhere) will stop it. Diodes in the rotor or cap gone open or short.

Best as I can guess from here.

..............oztules

greenkarson · « **Reply #12 on:** March 01, 2012, 04:36:31 PM »

Im in over my head here. Does the cap hz have to match the gen hz or is the cap ok at 50hz with a 60hz gen?

Oztules: you mentioned that i had to flash the the rotor if its been sitting a long time( I'm assuming you didn't mean stand in front of it and drop my pants) is it to much to ask how to do that? As simple as you can.

And what would happen if i was to just buy a new cap and replace the old one. If the cap was the problem is that all i would have to do or would i still need to flash the rotor?

Thanks again everyone and a special thanks to oztules

BooneyLiving · « **Reply #13 on:** March 01, 2012, 05:45:37 PM »

We had a similar problem with a 5500 Generac and we were able to get it working again by replacing the two breakers. They were cheap and it was an easy fix. Don't know if this will solve your problem but I thought I would through it out there.

greenkarson · « **Reply #14 on:** March 01, 2012, 06:28:26 PM »

Done a little more testing after watching a youtube video on the subject. And found out im getting 3.6vac on the leads going to the capacitor does'nt this suggest that the cap is the problem? I think i will try to pick up a new one tomorrow and give it a try.

oztules · « **Reply #15 on:** March 02, 2012, 02:53:56 AM »

"Does the cap hz have to match the gen hz or is the cap ok at 50hz with a 60hz gen?".... no the cap is not usually a hz rated thing. But the cap reactance changes with frequency.... so don't worry about the 50 hz on the cap. The cap (that type) is just two layers of aluminium strips separated by plastic film (mylar etc)..... and wound up into a cylinder........ Nothing exotic inside. If the plastic punctures for any reason, the cap is shot..... can be a total short if the impedance of the circuit is high..... melt down to open circuit if impedance is low

Flashing the rotor is a simple routine to try to get the remnance back. If the rotor suffers an electro mechanical shock (massive o/load) it can cause the rotor to demagnetise, and the alt function will not recover from this,as the remnance is no longer there to recover from a dead short where the magnetising field is completely disrupted.

To flash it, simply run the alt and (it is producing no power anyway) zap, splat whatever you want to call a very short 12v DC across the 110v output. If that was the problem, the unit should get back up to correct volts in half a second or so, as the fields build up slowly then quickly.

If the cap was the only problem then replacement should fix it. The fact you already get 3 volts would persuade me that the remnance is at least good enough to give that...... ie... If the rotor and caps were ok, it should be enough to get the party started.

If you remove the rotor and replace diodes, then flashing may be necessary once replaced and testing .

...................oztules

greenkarson · « **Reply #16 on:** March 02, 2012, 06:39:16 PM »

Well its not the cap. I had it tested its fine so it must be the diodes. I havent removed the rotor yet. Aany ideas if the diodes will be the stud type or some other kind?

dinges · « **Reply #17 on:** March 03, 2012, 04:08:00 PM »

Quote from: greenkarson on March 02, 2012, 06:39:16 PM

Well its not the cap. I had it tested its fine so it must be the diodes. I havent removed the rotor yet. Aany ideas if the diodes will be the stud type or some other kind?

I wouldn't know what kind of diode is in there, but once you've removed the rotor it'll be easy enough to tell, I expect. Not sure why it matters at this stage what kind of diodes are in there if you're not even sure whether it actually is/are the diode(s) that are the culprit. Only one way to tell for sure - by measuring. Anything else is just conjecturing.

If it were my generator I'd first tighten all screws and nuts, and flip the breaker a few times. A bad electrical contact would be the first thing I'd check for. I'd also reseat all connectors I could find. Only after that fails I would start looking how to get at the rotor.

Also it should be pretty easy to tell if it's capacitor excited or whether it uses brushes.... by checking for the presence of brushes. You still haven't established with certainty whether it's capacitor excited or uses brushes to power the fieldwinding on the rotor.

Small but important detail I haven't yet seen mentioned....w.r.t. the topic of 'flashing' the generator.... when you flash a rotor with brushes, make sure you use proper polarity. If you wire it up incorrectly, it may well be the diodes you are 'flashing'.... (read: destroying)

Also, I'm not sure how the battery might confuse matters. If it has been sitting unused for a few years, it's likely to be ruined and at a very low voltage. From one of your pictures I deduce that the 'voltage selector switch' is set to 12V (if I'm not mistaken - hard to be sure). Does flipping that switch from 12Vdc to 120Vac change matters? i.e. do you have 120Vac output? Sorry if that sounds kind of obvious to you - but what is obvious to one person may not necessarily be obvious to someone else.

Edit: and while I'm stating the obvious.... but I assume the first thing you did when the genset malfunctioned was to check that none of the glass fuses were blown?

oztules · « **Reply #18 on:** March 03, 2012, 04:42:25 PM »

I've seen studs, bead diodes, bridges, normal looking ones etc...you name it it may have it.

Dinges,
Flashing the brushless ones............. I don't think the polarity is relevant, as the normal magnetising field is ac anyway.
The rotor is divided into 2 poles, each with it's magnet and diode. One polarises North, and the other South. The diodes would barely see the 12v generated MMF, never mind them being bothered with any damage.

If you think about it, induction motors use the field (stator) to induce emf into the rotor bars, which we short circuit with the aluminium body throughout the rotor to create a strong current that makes a magnetic field in the rotor.... this is similar, except we "short" the rotor windings with diodes, and so the resultant current always flows in the one direction.... unlike the induction example which alternates the fields as they have no diodes.

Flashing brush type alternators......... I have never had to do it. They usually have a weak magnet pressed into the iron core, and that does the trick. If you wanted to flash them, then the brushes are marked + and - so it would be wise to use that orientation, as the AVR could be unhappy about a reverse voltage up it's rear end.

There are no diodes on a brushed rotor to damage or flash... just the wire that the brushes drive with the AVR output.
The diodes on a brushless could care less what you do with the output winding.... because whatever you do they will use it the right way.

I would take Dinges advice re: check out all fittings.... and... is there for certain NO brushes. That was never actually established for absolute certainty.... and no, I cant see why a 10uf 400v ac cap would be there for any other reason than for brushless cap excitation.... except and unless they are trying to create some VARS for power factor correction.....

So it would be nice to know for absolute certainty. ( have never seen cap correction on these things as the resonance may be a real problem.... but you never know. ( yes I still think brushless at this stage).

.................oztules

dinges · « **Reply #19 on:** March 03, 2012, 04:58:39 PM »

Quote from: oztules on March 03, 2012, 04:42:25 PM

I've seen studs, bead diodes, bridges, normal looking ones etc...you name it it may have it.

Dinges, Flashing the brushless ones, I don't think the polarity is relevant, as the normal magnetising field is ac anyway.
The rotor is divided into 2 poles, each with it's magnet and diode. One polarises North, and the other South. The diodes would barely see the 12v generated MMF, never mind them being bothered with any damage.

You're probably right, but I was talking of brushed ones.

Quote

Flashing brush type alternators......... I have never had to do it. They usually have a weak magnet pressed into the iron core, and that does the trick. If you wanted to flash them, then the brushes are marked + and - so it would be wise to use that orientation, as the AVR could be unhappy about a reverse voltage up it's rear end.

Yep, with emphasis on 'weak'. And there are testprocedures to check whether the magnet is still strong enough. And when it's too weak.... flashing is mentioned as the solution.

I've been doing a bit more reading in that genset repair handbook, hence why I made the remark - I'm relaying what it said there. I'm far from an expert - you've repaired much more of them than I have, that's for sure.

Quote

There are no diodes on a brushed rotor to damage or flash... just the wire that the brushes drive with the AVR output.

BTW, the repair manuals of various gensets mention the importance of flashing brushed gensets with the correct polarity. In a few schematics, there *are* diodes connected.

It's not that clearcut. I've seen schematics (I already regret posting a (what I thought was a generic) schematic earlier in this thread, as it may steer a person in the wrong direction) in so many varieties, including brushes and rectifiers (yes!), brushes and capacitors (not just noise-suppressors - real caps), etc. There's much more variety than I had expected. I'm looking at the schematic of an Onan right now - brushes and two diodes.

Hence, I'm not 100% sure Greenkarson's genset is capacitor excited - not till he has positively identified the presence or absence of brushes... So I reckon we'll have to wait on updates from Greenkarson, as all we are doing now is guessing....

ghurd · « **Reply #20 on:** March 04, 2012, 10:13:07 PM »

Quote from: oztules on March 02, 2012, 02:53:56 AM

Flashing the rotor is a simple routine to try to get the remnance back.

Yea, that's what I'd try first.
G-

greenkarson · « **Reply #21 on:** March 06, 2012, 07:42:41 PM »

Well here is what i have come up with. It is a brushless generator. So i pulled the rotor and found two square diodes(at least i think they are) at the motor end of the gen so i done the tested the continuty each way and they seamed to be fine. blocked one way and open the other. Then i noticed one of the wires had been broken off on one of the diodes, looked like it had corroded and broke off with the vibration.

So i was able to solder it back on no problem. I then resembled everthing and started the generater. At first there was no power. So i flashed the 120v plug with a 12v car battery and it instantly tripped the breaker but also started making full power. So i let it run for awhile standing there full of pride looking at the generator i just salvaged. I then shut it off and restarted just to make sure everything was fine. But same thing no power untill i flash the 120 plug with the car battery. I repeated this several times with same results nothing untill flashing the 120 plug. Any ideas what could cause this? I checked all connections everything looked good capacitor connection looked good. How long does it take for a capacitor to charge? And i have taken the battery
off the generator and have just been boosting it with a car batterybut that would no matter would it?

Thanks

greenkarson · « **Reply #22 on:** March 06, 2012, 07:44:51 PM »

Forgot to add the pic of the diode with the broken wire. Kind of hard to tell in the picture but its the wire to the top of diode that was broken.

RP · « **Reply #23 on:** March 06, 2012, 08:37:10 PM »

Make sure you unload the generator before stopping the engine. Killing it while under load will (in many cases) require re-flashing the armature to get it going again.

greenkarson · « **Reply #24 on:** March 06, 2012, 08:38:44 PM »

No load each time

RP · « **Reply #25 on:** March 06, 2012, 08:48:11 PM »

Maybe try flashing it with the opposite polarity on your 12v battery?

greenkarson · « **Reply #26 on:** March 07, 2012, 06:15:41 PM »

Tried flashing again either polarity same results. As soon as i flash instant power but as soon as the motor is turned off i have to flash it again. Any ideas anyone?

DanG · « **Reply #27 on:** March 07, 2012, 07:09:10 PM »

yanno - you should be surging the coils with heavy cable straight battery DC (big spark) without the unit running?

oztules · « **Reply #28 on:** March 07, 2012, 07:34:08 PM »

Something is demagnetising the rotor. If a load is present, then that can do it... but you have no load.

Unloaded..and generating it's 110 or 220 whatever, does the motor sound laboured in any way. I'm wondering if there is a short on the 12v line (diodes?) perhaps.

There is something causing the demag.... or the RPM are not high enough (check frequency, not just voltage).

Try over revving it when it starts and see if that causes it to energise, or bigger cap for a test..... maybe open circuit on the rotor still ( other one you didn't fix). Usually if the rotor has an open on one side/or short, it can still work... but very poor regulation.... all over the place.... but it would be a bit of a coincidence if both went at the same time.

As I understand it, it is supposed to work like this.
When started, the rotor with it's residual mag, starts to generate a small voltage, which is generated in the cap field and the output.

The current in the cap sloshes back and forward between the cap and the coil... this current flow gets stronger, and influences the rotor windings, which is shorted in one direction by the diodes, and so becomes an electromagnet with constant pole orientation.

The whole lot starts to get more current flowing in the rotor, and then very rapidly it builds to full power. The resonance between the coil and the cap keeps the rotor voltage up, as does the current now flowing in the main field. The more current you draw from it, the more magnetic field it projects back into the rotor winding, so in theory it self regulates.

Now if this isn't happening ... why not.

Any load on the output while starting will kill off the cap/coil build up.... by bleeding the voltage away from the tank circuit
Any internal shorting in the cap will do the same.
A short on the dc output will probably be enough to stop it... although this only affects a small part of the primary, or it's own winding (build dependent)... and something should be getting hot.

An open circuit in the cap coil may not stop it running if the main coil can provide the magnetic field to the rotor... but would require some loading on the main field to make a current..

I'm running out of ideas here....

So check the resistance of the cap field, and the run field and the two rotor fields.

Check for shorts to ground in all the coils, I have seen cap coils shorted to ground near the start of the winding, which didn't generate much heat, but as they usually ground one side of the main, then it can be a problem.... auto transformer effect in the cap coil...

Nope... I'm done

all else fails...a push button flash switch

)

.................oztules

Edit just saw Dang post..... dose not work very well like that I would think, as the coil resistance is fairly high, and will limit your "big spark" to only a few amps... not enough to terrify the rotor I suspect.... never tried it though.

Manufacturer states to do it when running for a reason I figure .

greenkarson · « **Reply #29 on:** March 08, 2012, 03:22:16 AM »

Here is a random bunch of stupid questions.

Is it possible that the cap could have been damaged during first startup somehow?

Does polarity matter on a cap?

And once the gen is running for a couple mins should the cap be fully charged?

I don't have a cap setting on my multimeter. First time had cap tested at electronics suppliers shop they said it was fine. I have since taken it back out and shorted it with a screwdriver but there was no spark or anything. Is it possible i could have reversed the polarity and wrecked it or something?

Is it possible these generators use the gen to recharge the starting battery putting a load on it? Or do they just charge from the engine like normal?

Well thanks again

oztules · « **Reply #30 on:** March 08, 2012, 06:46:27 AM »

"Is it possible that the cap could have been damaged during first startup somehow?"........ no. cap couldn't care less

"Does polarity matter on a cap?".... no not on those caps ... they are designed for AC up to at least 450v ac rms or over 600 dc

"And once the gen is running for a couple mins should the cap be fully charged?" no it charges and discharges every 120th of a second once running. (every half cycle)

"I have since taken it back out and shorted it with a screwdriver but there was no spark or anything."... it is in parallel with the cap winding, and discharges into it.... so it will always be fully discharged whenever you stop it. (coil shorts it out dead).

"Is it possible i could have reversed the polarity and wrecked it or something?" not possible at all. It is an AC component. It changes it's polarity every half cycle.

"Is it possible these generators use the gen to recharge the starting battery putting a load on it? Or do they just charge from the engine like normal?".... I expect it uses the normal charging system, or there would be no regulation on the charging of the battery.... and even if they used some other system on the generator coils, the battery would cease charging as the rpm died because it will no longer be a load under the 12v (13.7 or there abouts), so no, even then it would not present a demagnetising load on shut down.

Not very helpful, but there you go.

.................oztules

Edit: As I recall, you found 3v on all the wiring when it is not working properly . This tells me the thing is not de-magnetised, and that something is stopping the cap:coil interaction.. Did you check the 12v diodes on the dc circuit for battery charging ( not the motor battery, but the aux output circuit I think I can see in the pics)

If it can stall the "sloshing " in the tank circuit, it may be enough to stop it getting up to power, and that the flashing pushes it over the line..... look for hot components just after starting it up, something is stealing the start current somewhere I think..... or the cap circuit is open in the coil.

dinges · « **Reply #31 on:** March 08, 2012, 09:38:02 AM »

Quote from: oztules on March 08, 2012, 06:46:27 AM

Edit: As I recall, you found 3v on all the wiring when it is not working properly . This tells me the thing is not de-magnetised, and that something is stopping the cap:coil interaction.. Did you check the 12v diodes on the dc circuit for battery charging ( not the motor battery, but the aux output circuit I think I can see in the pics)

Here's a possible other explanation; if I'm mistaken, Oztules will no doubt gleefully correct me.....

I'm still suspecting the diode on the rotor a little (the one with the loose connection). It's possible that, as the wire vibrated loose, huge voltage excursions and arcing occurred that may damage the diode. Under such conditions, the diode could see much higher voltages than what it may be rated for.

Diodes can fail in strange ways - seemingly measuring ok on the multimeter, but breaking down at, say 15V... or 3V perhaps even?

If you have a suitable replacement diode about (I expect a small 1N540x diode to be fine - 3A at a suitable voltage) I'd try to install that temporarily, instead of the original diode. Then run and see if it magnetizes itself.

greenkarson · « **Reply #32 on:** March 08, 2012, 12:18:37 PM »

Finally some sucess i revved the motor up at start up and it will energize. Do you think that it could be just a matter of raising to idle speed or does it mean there may be another issue?

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Author Topic: generator problems (Read 35411 times)