Generator Output Voltage Low

I don't know if this is true on your generator, but on mine, it is possible to lose enough residual magnetic energy retained in the iron, if it was stopped under a load.

According to my manual, I can "prime" the magnetic field using a car battery to create the starting point I need. After that, the rotating field will provide the additional energy for maintaining the magnetic field.

Most of the time, a question such as yours can be answered by reading the manual. If you don't have a manual, try the manufacturers web site.

1. Lack of knowledge of the operator.

2. Lack of knowledge of the operator in manual reading.

3. Lack of knowledge of the operator in following the troubleshooting guide in the manual.

4. Lack of knowledge of the operator regarding how to contact the manufacturer.

5. Lack of knowledge of the operator regarding how to describe the problem.

6. Lack of knowledge of the operator on how to check the speed of the generator.7

7. Lack of knowledge of the operator on how to check the output.

8. Lack of knowledge of the operator on how to use a search engine to find the manufacturer's website to ask for help.

9. Lack of knowledge of the operator in the use of a telephone to contact a technician to fix it.

After you have remedied these problems, let us know if any progress has been made.

Have tried turning the key and running it? just wondering

Useful answer, and a very good troubleshooting startpoint, Good Answer Dhayanandhan !

Dear Mr.Yahlasit,

Thank you for your comment.

DHAYANANDHAN.S

Dear Mr.Yahlasit,

Thank you for your comment.

DHAYANANDHAN.S

Is this homework?

What's the application? Is it automotive, 12 or 24 volt? Is it a DC generator, with commutator and exteral regulator (dynamo in UK) or an alternator?

Or is it an industrial alternator? If so, what power output?

You have not giving any information about the generator. On old 6v and 12v automotive generators, output varies with speed.

If you look at current as the output of a modern car alternator, the maximum current varies with speed as well......at tickover its a lot less than at say 2000RPM.

As current is also a component affected by voltage difference, then you can say that the voltage is STILL affected even today. It is physically impossible for it not to be!!!

Alternators, depending upon their physical design though, can be made to have a drooping characteristic (usual in my experience) or a flat (I have never seen such an output) or even a rising voltage output (also never seen, but possible) with load.

Its simply a question of design.

...but the question was about an unknown generator...

It still is!!

I think its a school boy/girl!

Can you explain why an alternator is self-limiting for current, unlike a dynamo? I've asked various electrical engineers over a few years, including on this forum, and haven't heard a satisfactory answer.

Dynamo has separate regulator contacts for voltage and current, and if the current contacts are held together at low battery voltage the dynamo can soon burn out. Alternator only has a voltage regulator, and current levels off to rated output at about 10000 alternator rpm (2 - 3 x engine rpm). But I can't see any obvious reason why.

I never knew it was, assuming I understand you correctly.

In a normal alternator, the regulator does this in a correctly running machine.

As far as I am aware, assuming for a moment that the load is ever increasing, and the controller holds the voltage stable (long after it should have stopped/dropped offline), then eventually the alternator windings will over heat due to the over current being drawn.....

Controller/regulators are usually set up to only allow a certain maximum current to flow.....that is they control the current flowing through the rotor....and monitor the output voltage...

Maybe I misunderstood what you meant, if so, sorry!

Alternator has a voltage regulator only. On reaching regulated voltage, the current to the rotating field (via the sliprings) is reduced to maintain constant volts. There is no regulation depending on the output current. The voltage regulator can be bypassed (useful for testing) and then the output current rises to rated figure if the speed is high enough, but no more. I don't know much about larger industrial alternators, but I think they do the same.

Dynamo regulator has 3 bobbins, cutout, voltage reg and current reg. (Earlier versions had 1 regulating bobbin, but it had coils for both voltage and current). The dynamo ouput flows through a coil on the current bobbin. The field supply goes through both regulator trembling contacts in series. If the current regulator contacts are held together and the engine revved the current goes as high as you like and can burn out the dynamo.

I don't understand why they should be different. The alternator stator and dynamo rotor both consist of coils of wire, so both should see excessive current if given high enough volts. No doubt there is an explanation but I haven't seen it yet

0 volts out 0 amps. The alternator regulates the voltage and by doing this regulates the current. As you load the alternator so the voltage will start to drop a little. The AVR will make the corrections so where Volts x amps = power the more power you require either the volts or the amps have to rise. Volts is controlled therefore amps rise.

The 3 bobbin regulator used to regulate the field voltage and from memory was a scary box of tricks!

With a dynamo, just after starting the engine the battery voltage is likely to be down, so if there were no current regulator, in order to reach regulated voltage the current could be well above what the dynamo could stand, hence need for a current regulator. So if you measure volts and amps, just after starting the volts is below reg value, the amps = reg value. As the battery charges the volts rise, amps stays constant until reg volts is reached, after that volts stays constant and amps falls.

With an alternator, the pattern is similar, but the current is not controlled by the regulator, amps is self-limiting. I don't understand why this is.

Principle of regulation is same for both - machine output is fed to the field via the regulator. In a dynamo the field is stationary, main output goes through the brushes (and commutator). In an alternator the field is rotating and the smaller field current goes through the sliprings, with advantages we're all aware of.

You have a mind set that I seemingly cannot change, that is the problem as your statements are simply wrong in both theory and practice.

As you appear to have little interest in changing your opinion, neither have I.

You are on your own unless someone else here is kind enough to try and teach you something.

Byeeeeee.

The current will change depending upon the load it has to supply, which is still a function of voltage.

The voltage will only be stabilized once the alternator is being turned fast enough to generate the voltage required, to supply the current needed........which is being adjusted by the regulator.....

You must observe both at the same time.....at least in your head, so to say, they interact with each other depending upon load being drawn...

If the developed voltage is too low, lower than the battery for example, no current will flow. Back flow is prevented by diodes.

Once the alternator voltage exceeds the battery voltage AND the maximum allowed battery voltage has not been reached, the battery will start to be charged. This will usually be (on a car) till a max of around 14.4 volts.

The lower the state of charge of the battery, the earlier the charging starts. Its the difference in voltage between the battery and the alternator that sets the current flow within the maximum possible. No difference, no flow.....

Once the battery is charged/floating on the alternator at 14,4 volts, the alternator will now supply all the cars electrical needs at that set max voltage.

Sudden increases in current usage may be met by the alternator on its own, or with the aid of the battery in parallel.

As long as current usage is within the capabilities of the alternator, the load will be met and the battery will remain fully charged.....

I agree with most of that, but it doesn't explain why a dynamo needs a current regulator but an alternator does not. If you look at alternator wiring diagram there is no current regulation.

If battery voltage is low, or if enough load is connected to the system, without the current regulator a dynamo will burn out. An alternator will not, the amps will not exceed its rated output.

Last time.

The design of an alternator (and a dynamo) decides its characteristics under no load and load.

Alternators are generally designed with a "droop" with load, though it is possible, if wished to, to design the droop out, or even have a rising characteristic.

I am of the opinion that dynamos are generally designed, with a regulator, that they have a flat characteristic at a set RPM, a rising one with increased RPM. Its too long ago that I learned it to be sure today.....I was then a teenager, now I am retired.

I have not worked on a dynamo car regulator since the '60s....but they control the voltage and current within certain bounds, as does a car alternator....

By the way, do you even understand what droop is? (Many wives do!!) Its important and maybe the answer to your question I feel, but as you did not understand it the first time I mentioned it, I have doubts that you will understand it the second time.

Are you talking about an alternator with fixed magnets or a coil (and DC supply) as the rotor?

You forgot to specify and there are slight differences in theory, major ones in practice, but nothing a normal brain cannot handle

My patience is wearing thin, an important factor as well!!!

I asked this question hoping to get an answer. It has nothing to do with having fixed ideas. As you clearly do not know the reason, wouldn't it be better to admit it rather than resort to rudeness? Which of my statements are wrong, in your opinion?

In spite of my explanations, you seem incapable of grasping the concept that a dynamo has a current regulator but an alternator does not.

Ref your #26, automotive dynamos are designed so that the output voltage exceeds cut-in volts (about 13.5 volt), when neither regulator setting is reached, so full output volts is applied to the field, at about 1200 engine rpm. As the engine often runs much faster, the system is then entirely dependent on the regulator to avoid over-voltage or over-current.

If you had read my posts it would be clear I'm talking about alternator with rotating field supplied via sliprings, main output from the stator via a rectifier. Just to be clear, the maximum current output (with voltage regulator bypassed) increases with speed, as you would expect, but it levels off at a certain speed (I said 10000 rpm in earlier post) so it will not over-amp at any speed (without a current regulator!). I'm looking at a graph of output vs speed right now.

Droop has nothing to do with my query. Droop is about controlling speed and output of a number of alternators in parallel, close to synchronous speed. A vehicle alternator stands alone, and it has to work at any engine speed.

Ref your #25, I think I'm more likely to be doing the teaching than the learning on this subject. I've worked on automotive dynamos, regulators and alternators more years than I care to remember.

I'm tempted to make a comment on your lack of patience, but I won't.

You have been given answers that you sadly do not understand.

But look at your question for the reason, a single line of text:-

Team, please what will or can be the contributing factors to make a generator output voltage low.

It shows a complete lack of knowledge on the subject, you do not even mention the type of equipment you want to understand!!!! How childish!!!

You speak in your other posts as though current is independent of voltage or vice versa.......in fact, by controlling one you control the other to a degree AT THE SAME TIME!!!

They are totally mixed with each other my friend. You need to understand how both work!!! TOGETHER!!!

Usually, current is NOT controlled per se, it is monitored to be within certain bounds according to the Generating equipment's set parameters by the manufacturer, what IS controlled is the voltage and with AC, the frequency.

s more current is drawn the regulator will boost the voltage back up to where it should be, otherwise drawing more current would cause a voltage drop on most generator designs AC and DC.

Most of your comments up to now demonstrate a severe lack of good schooling on this subject.....not even a high diploma I would guess, or the equivalent!

Tell us your schooling level so that we may address the answers to your level of knowledge and understanding.

Have you ever worked on AVRs on ANYTHING?

I have worked and was taught on DC Generators each supplying up to 22,000 Amps at 220 Volts on RN Aircraft Carriers with Ring Main supply systems and 10 of these generators, some running in parallel..

I have worked on Alternators of 10 MegaWatt and more also on RN ships, and naturally been fully trained on them and how they work, intimately. Also some running in parallel.

I learnt my trade in a 5 apprenticeship on both land and sea.....to University level mathematics for example....I continued later with my studies at the OU.

Its not me that needs to learn, its you.

You cannot see the wood because there are too many trees in the way!!!!

I was right to give up on you before, you are both rude, ungrateful and a slow learner......

Goodbye.

What a ridiculous tirade! I thought my #15 was fairly clear that I wasn't responding directly to the OP but asking a separate question as I thought somebody might be able to help. And that I was talking about automotive equipment, if not in #15 then in #18 and later.

It's clear you do not know the answer, whatever your CV says. But instead of admitting it you make irrelevant comments and insults, but cannot identify anything I have said that you think is wrong. I know you can't have amps without volts but that doesn't affect my description of operation of dynamos, regulators and alternators.

Who started the rudeness? I'd be grateful to anybody who answered my question, or made constructive comments, but it clearly isn't you.

Goodbye to you too!

Master Germany. Did you start bad into the new year? Codemaster is not OP. If you reverse back a bit you will see that you responded to Codemaster in a overly arrogant way based on your thinking that he is OP and does not know nothing.

We sometimes see what we want to see and not what is clearly there. The only way to get over this is to step back, look at it from a different angle, clear the mind and think again!

Please do so and you will find that there will be never ever an answer on CR4 that will be able to replace a full text book and years of learning and studying.

Codemaster and you are long enough here to know how it works. Get over it!

Thanks IdeaSmith, much appreciated! Good to get support from an outside observer.

AndyG - I never wanted to get into this exchange. If you're happy to forget about it, so am I.

Posted twice and removed-

For generators after about 1945, that's only true up to a certain speed, not much above idle. Above that, maximum volts and amps are limited by controlling field supply via a trembling-contact regulator, to about 15.5 volts and 25 amps for a typical car.

But as you say, we don't know much about the OP's generator yet!

Need to throw the dogs a bone on this.

I've got an alternator on my car. Little cutie it is giving out about 14V at up to 100A. I've also worked with 350MVA generators at 15.5kV and squillions of amps.

So what have you got in front of you?

Exactly what is the machine?

Probably got the gist of where this is going

Over and out

The Fox

To save any more in fighting ...

This is how the regulator box works:

Technical Bulletin Old Car Dynamos Page

2 of 3G4APL GB7CIP 8.6.2006 VOLTAGE REGULATING. There are 2 types of regulator a 2 relay & 3 relay. They are really much the same in operation. When the dynamo voltage reaches 16V the OVER-VOLTAGE relay momentarily operates breaking the current in the dynamo field winding. This reduces the dynamos output to the point were this relay is constantly breaking the current to maintain the voltage. On breaking the field winding current, the back EMF is dumped into a resistor (e.g. 100Û 3W) to stop sparking. CURRENT LIMITING. Regulators with 3 relays have one for OVER-CURRENT with just a thick high current winding, like the OVER-VOLTAGE RELAY this also breaks the dynamo's field winding current to limit the current to a safe level say 20 Amps for that dynamo rating.

Fault finding

FAULTING DYNAMO SYSTEMS. If there is no charging (e.g. ign lamp stays on). With ignition OFF, disconnect the 2 Dynamo connections. Using a car headlamp bulb from battery to :- 1/ Armature terminal, Lamp should light brightly (same as an earth) If not Brushes faulty. 2/ Turn dynamo around slowly (hand crank engine), lamp may flicker but never go out! If not Brushes/Commutator/Armature faulty. 3/ Field winding. Lamp should dimly light. If not check connections. If brightly check for shorts. If all OK dynamo should be OK. Now use the headlamp bulb to earth & the 2 leads off the dynamo test the regulator with the ignition ON, connect lamp to:- 4/ The thick Lead, Lamp should not light. If it does RECTIFY RELAY contact welded closed! Disconnect battery & break apart. 5/ With lamp still on thick lead, manually operate RECTIFY RELAY. Lamp should light fully. If it does not check terminals & wiring. 6/ Connect lamp to thin lead, manually operate RECTIFY RELAY. Lamp should light fully. If it does not check for dirt OVER VOLTAGE RELAY contact, & if 3 relay type the OVER CURRENT RELAY contact. Also check wiring. 7/ With the lamp still on the thin lead, manually operate both RECTIFY & OVER- VOLTAGE RELAYS. Lamp should go out (or very dim). If not check adjustment of OVER-VOLTAGE RELAY contact. 8/ If 3 relay type repeat 7 but with RECTIFY & OVER CURRENT RELAYS operated. Result should be same. If 4-8 are OK the regulator it should be working. Reconnect the dynamo & retest to see it you have cleared an intermittent or dirty connector fault. REGULATOR ADJUSTMENT. Technical Bulletin Old Car Dynamos Page 3 of 3G4APL GB7CIP 8.6.2006 A/ RECTIFY RELAY spring adjustment, should be set to operate @ 12.5V & release @ 12V. B/ OVER-VOLTAGE RELAY contact adjustment should be set to give 16V at full revs on a charged battery with no loads (other than ignition). C/ OVER-CURRENT RELAY if fitted, with a low ohm/clip on DC ammeter in circuit. Connect a separate heavy load across the battery (not existing headlights!) to hold the battery voltage down (e.g. a 30A load of 6x 5A headlamps). Rev up & adjust relay contact for the maximum current for the dynamo rating (normally stamped on casing).

Thanks for that.

I'd just add - on the 2-relay box the regulator bobbin has both a voltage and a current winding. It doesn't actually regulate at 16V during normal operation. To adjust it the lead out to the battery is disconnected, and all loads switched off, so the current is negligible (just the ignition circuit on a petrol engine). Then adjusted to 15.8-16.7V from the data I have. So in normal operation with a charged battery, 2-3 amp trickle charge, the voltage is 15-15.5V-ish due to the additional effect of the current coil.

Last part of your Fault finding is similar but implies the battery is charged but still connected (if not connected it doesn't matter whether it's fully charged or not). But then there is still a load due the trickle charge, which interferes with the adjustment.

That's the gist of it, there might be slight variations for vehicles with different connections. The current setting is built-in and cannot be adjusted.

My comments on charging in #21 refer to a 3-relay box (constant amps, rising volts up to reg volts, constant volts, falling amps after). On a 2-relay box the corner of the graph is rounded off as both windings affect the output. Advantage of 3-relay, slightly faster charging.

Hello Cr4 people

let me understand that ,,, generator when you switch it on without load it ... the voltage is low ...( here a reasons that cause the low voltage ):

1) low speed of the engine : it might be the air filter, governor stuck, diesel injectors might need cleaning, fuel pump trouble ... all these can be seen in the RPM of the engine .... if the RPM of the engine is stable like a manual says ... then it could be another reasons.

2) AVR ... sometimes the AVR adjuster button is unfasten or rotate during the vibration of the engine (( try to adjust it again with a very little turn with any direction just to make sure that the button is the cause )) and fix it .

3) Rotating Diodes ... try to test it .. and there are steps to test the diodes, I think it is familiar ( sometimes the diodes will not make the voltage is low ... but it will make it very low less than 30% of the total voltage .

4) If the voltage is very very low during the normal RPM of the engine and the generator is with diodes ... Try the # (2) and # (3) steps . But if the generator is with brushes (( old one )) try to check the connections of the brushes and the connections of all the exciting system that includes AVR and BRUSHES ... AVR and Diodes

Those steps are from my humble experience in diesel generators if there are any additions or any wrong with the steps that I mentioned ... please let me know.

BUT if the generator shows the low voltage during the loading ... that would be another reasons not that different from what I have mentioned But a little additions.

THIS question used from the employer in the interview

Best Regards