Small House Generator

Charge the field with battery.

Yes, but how?

What voltage should I use and for how long?How about the polarity of the connection? There is a rectifier in the field, what's it function?

See manufacturer's recommendation. If you have 24V battery for engine starting motor, use two wire and and connectr +ve & -ve of batter to F+ & F- terminal of field for some time. there after measure residual voltage of field, if its within recommended value say 8v then its ok. Alternatively you can disconnect avr terminal to field and connect battery as I said above on line.(that is while the engine is running). All above are my on hand practical experience, while I was working with Caterpiller DG set divn.But first thing I will suggest you to read the manual of Alternator, and go by their instruction.

I do not have a manual. There are no markings ( like in the car alternator). It is a 5kw portable gen.

Please . . . Does a generator use permanent magnets?

Kind regards

I do not know, but I do not think so due to the diode.

I am wondering the same thing... I never heard of THAT before.

Bill

This is something I would like to clarify also- everything I have tried to get a Yamaha 500va genset to charge has not worked- (240v, 12v)- I have concluded that shorted windings in the rotor are to blame( this is a self exciting arrangement, with a diode across 2 windings, rotating across the field collection of 2 windings(( also with a common anode 2 diode to supply 12v dc))- a new 15uF is fitted- all continuity, controls ok- I have tried charging cap 440v ac- self disharges when winding plug connected- I have even magnetised the rotor with 12v dc- does not hold magnetism- ) I would like to fix, but new ones are so cheap!.

The only components that I can see are the winding and a diode connected to it (in the rotor). I took the gen apart. What rotor winding resistant should I have ,approximately?

This is the trouble my friend- neither you or I have maker,s specs- in my case the res is about 2 ohms(disconnect 1 leg of diode, also to check diode)- the windings wont hold a charge because diode has volt drop of 0.6v only- this may be the answer- should the rotor windings hold a voltage- seems to make sense they should- in my case they don't- yet there are no obvious shorts to earth(using megger)- I just don't have enough info how this thing is supposed to work- on web about self exciting rotors, some have slinger in contact with rotor windings- some like mine have no direct contact- as to flashing the field, I think some think that we are using the old dc gens where this had to be done- as I said I have charged the 440v ac cap, which immediately discharged on connection of the stator winding so my guess in my case is shorted windings. Ain't worth spending money on in my case, as a new 600va costs A$169 with 2 year r/p warranty.

I just looked at the rotor( a two pole winding) and this is the way it is connected( maybe it will bring some light). One terminal go to a metal plate and the other to the negative of a diode and the positive of the diode to the same plate. There are no slip rings of commutators involved. Suddenly I think that the function of the diode is to provide the charging polarity of the rotor field. What do you think?

I agree with you, they stop any AC being formed in the Rotor field by blocking half with a diode......I see how it works, but I am surprised that it works too!!! Sounds stupid, but it makes sense to me....

Then the generator relies on some residual magnetism in the poles of the alternator to cause some induced electricity in the rotor coil, this in turn has only DC induced as the diode blocks the other half of the AC signal. A current flows in the rotor which starts to generate a voltage in the stator.....or that is my take. Any better offers?

So the fix will be to disconnect the stator fields and connect them for a second or so across a 12 volt battery, "Flashing" the fields is what its called and must only be done for a split second, or the windings will heat up. Make sure that the fields are connected together the same as they would be in a running system (you do not want to flash one in one direction and the other incorrectly with regard to relationship. If you are not sure and each field is separately accessible, flash one only, but DO remember the polarity used. If that does not help, flash using the opposite polarity.

Reconnect and start generator to test....

Before flashing, make sure that the diode is good as if it has gone short circuit, that will preclude any fix and may be the main problem anyway.....it must get at least one leg removed from the circuit for testing!! replace it if your are not fully certain that it is OK......cheap fix maybe!!!

I will try it. Thanks

It seems like we have the same system and problem. I will check for a short.

It is NOT the rotor that needs flashing, it is the stator!!!!!

You may have damaged the diode if it was still in circuit when you did that....

Why the stator and not the rotor? Now Iam more confused!!

It is the stator in your case that must have the residual magnetism, the rotor has a coil that needs to cut across lines of force to have an induced voltage, it cannot cut lines of force of its own, they are turning at the same speed!!!

So it has to be the stator that needs flashing......if it works as I think it does!!!!

In my case the rotor is turned by the gas engine and the output connections come out of the stator. So I figure the field should be in the rotor to cut the stator windings to induce the voltage. Correct me if Iam wrong.

Yes, but first you have to get a "revolving current flowing through the rotor circuit! this can only happen (I believe) if you have a weak magnetism in the stator poles to start with....this causes an AC flow in the rotor, cut to DC with a diode, which then produces a field in the rotor that generates power in the stator.....I hope......otherwise I cannot see how it works.

I have heard you say you have flashed the rotor = did not help.

Diode has been tested, it is good....

So unless someone with more infos on exactly how this generator works, we are both stuck with my theories.....

Thanks a lot for your help.

Does it work??

No thanks.

BUY A CAT GENSET

I don't wish to be rude, but who in the hell would want to buy one of them???

Having had several bad experiences with Cat and their mechanics.........no thank you.

THEN BUY AN FG WILSON SET

Regulator is bad replace it.

I don't think there is a regulator in my gen. i know there is a mechanical governor. I know there is not a magnetic field in my rotor.

Your Small House Generator, looses its Residual Magnetism, when it has been non-operational/ or shutdown for to long. To correct your Problem, your have to Flash the Field, to re-polarize the field winding. Take the posative lead from the start battery, off the starter & momentarily touch it to the field post. You will get a small spark. Place the lead back on the starter post, start the unit, it should show out put. If this doesn't produce alternator output, you may have a faulty diode in the regulator, and that would have also caused the loss of Field Magnetism. I trust, for your sake the first thought works, do too the duration of unit shut down. Carl, retired Power Plant Maintenance Tech. I'll Watch for Replies.

I have the rotor out. The diode is connected to one of the terminal, should I connect the battery positive to the diode end and the other to the remaining end?

I'm lost on this one, how do you know that it ever had "magnetism" in the first place????

I would guess that small AC generators do NOT have permenent magnets, so if that statement is true, there was no magnetism to lose.....

If it did not have magnetic field lines in the rotor to cut the stator windings it would not generate voltage, right?

Check the RR (rotary rectifier) unit and healthiness of diode and fuses. also check exiter winding healthiness, if damaged or shorted. I hope you will find solution out of this.

I will try that

Normally an AC generator "develops" its own DC to energize the rotor, which induces an AC voltage in the field windings.

There are no magnets as such, at least in the larger units. Car alternators (some at least) I am told have magnets.....

A motor (or generator) with magnets can be turned by hand and it "jumps" from alignment point to alignment point. A generator without magnets just turns with no resistance.....

I do believe (as someone else mentioned) that a small mount of residual magnetism is needed in the field coils of the DC side......but I have never had one of these small units apart.....so that I am not really much help here......sorry.

Thanks for your response

Does your unit have slip rings with brushes or a commutator?

Neither. the rotor has two terminals. One of them connected to a metal plate and the other connected to the negative side of a diode and the positive side of the diode connected to the plate mentioned. No slip rings or commutator.

In my case the diode connects between the 2 coils of wire, which are each wound around laminated iron pole pieces on the rotor- the other end of each coil connects together. I have put 12v dc across the windings- the poles magnetise strongly, but don't hold the magnetism, being iron- the windings don't retain any charge either(should they?)- surely the purpose of the diode is to convert ac induced into the rotor windings into dc to magnetise the rotor poles?- so the rotation of the magnetised rotor induces ac in the stator windings- obviously if rotor not magnetised for whatever reason, no ac out. What sort of voltage ? current is induced in the rotor?- would it be 240v?- if so diode could measure ok on dmm test, but fail under the higher volts- use a megger across diode(1 lead disconnected to test). Without info, we are left here to try till find prob- I still think shorted windings in my case, which means BER(beyond economic repair)- as so much stuff these days!.

I will check for shorted winding today.

Where are you located?? I noted one comment of "Just run down to Home Depot and buy another one." or equivalent. If you are located in a tiny village in Boondockistan, the nearest Home Depot might be thousands of miles away.

By giving your location you give us a much better idea of how to solve your problem.

Help us Please!!

Bill

I have to exhaust all the possibilities before buying another

Buying a new one would certainly save a lot of hassle.

There are some very cheap Chinese gen sets available??????

Perhaps it would be better to find out what the problem is with this one!

OR.................. what about one of these

equipments operated by manual power are always good for health.