Micro 12v Generator Project

[danfoley]

Another reminder that insulting other members is not acceptable. Let's stick to the subject, if you really can't stand someone's post/attitude then there's always the ignore option. If you want to discuss further send me a PM as I'm sure everyone wants this thread to stay on topic.

 

[mattnj]

dynostart means dynamo start, a DC device. Most (for the toothsuckers I am speaking in generalities) DC motors, if you turn them will produce voltage with out any further add ons. Voltage to the brushes, it turns, turn them and they produce voltage. They are not as efficient as power producers, thats why dynamos were superceded by alternators.
Stu

we are talking about using an alternator with an electric speed controller as a motor, its a different thing all together....dont think you understand....

 

[Leonidas]

Whats funny about insinuating somebody is a w anker?
Stu

You are absolutely right and I fully agree with you. If one has something clever to contribute to this interesting exercise, this is the forum to do it. Cheap and rude remarks have no place here and I think the administrators should cut in at this stage and call for some order.
So far , the majority of us have been enjoying the difference of opinions ,suggestions , the solutions to technical challenges and inovations ,the occasional tangential deviation and generally the healthy debate on the pros and cons of an otherwise interesting project. Let's keep it this way and see whether the mini genny, the Aussie off the shelf hi/low current mini 12v alternator or Matts efforts will carry the day. Whilst inovation is the mother of progress and the way forward, over complication kills the reliability.It seems to me that this where this project is heading for. The maxim of KISS (Keep It Simple Stupid) has always served us well in all aspects of engineering and marine in particular.

 

[mattnj]

You are absolutely right and I fully agree with you. If one has something clever to contribute to this interesting exercise, this is the forum to do it. Cheap and rude remarks have no place here and I think the administrators should cut in at this stage and call for some order.
So far , the majority of us have been enjoying the difference of opinions ,suggestions , the solutions to technical challenges and inovations ,the occasional tangential deviation and generally the healthy debate on the pros and cons of an otherwise interesting project. Let's keep it this way and see whether the mini genny, the Aussie off the shelf hi/low current mini 12v alternator or Matts efforts will carry the day. Whilst inovation is the mother of progress and the way forward, over complication kills the reliability.It seems to me that this where this project is heading for. The maxim of KISS (Keep It Simple Stupid) has always served us well in all aspects of engineering and marine in particular.

agreed, not sure its that over complex, has all the bits you would find in a normal alternator/engine/suitcase genny except the water cooling, cant think of anything extra....

they have just been modifed or tweaked. electronics are mega reliable....no one should be afraid of adding them to stuff as it may "reduce the reliability" they can often increase it.

 

[caiman]

Humour, is a bit like beauty, or bravery-it is in the eye of the beholder.
If you've missed it,I regularly state in my posts that I sail single handed.
I thought that you would be 'holding on' with the other hand?Like I do?
Cheers
Skipper Stu,I offer my complete apologies if I have offended you in any way,if I have offended,it was not my intention,and I reiterate my apologies.

 

[caiman]

I was about to start on a microgen myself.I've bought a GX31 from Seddons through the link on this thread.The 30amp Landy alternater in the celler,however, turns out to be a 55amp Sierra alternater.I only want to be able to charge at 10 amps.Do you think that the GX31 has enough grunt to power a 55amp alternater?
However,I was given a non working Honda ED250 yesterday.If I can get that going that will be the end of the problem.It is about the same weight as the 2 stroke 'Wolf' that I've recently bought,but certainly more compact.I'll work on the 'noise' if I can get it to make some!!
I find it interesting that Honda have percieved a market for 6,12,24volt generaters since 1965,and have marketed them alongside their 240v generaters.The only thing wrong is the price tag.Why don't other manufacturers make them?(Antipodeans aside)
Cheers

 

[mattnj]

I only want to be able to charge at 10 amps.Do you think that the GX31 has enough grunt to power a 55amp alternater?

No, it will stall it for sure, if the battery is flat, you need to make the adjustable regulator circuit and repalce the built in one, easy enough, £10 of bits, and an afternoons work.

Set the engine speed manually, then increase charge manually, and adjust engine accordingly, i ended up doing that all with a PIC, but only cos i kinda knew how to do it already, otherwise probably wouldnt have bothered.

Whatever you end up doing you will need an adjustable regulator (unless you have say 4hp engine), trust me, spent a while on this now!

 

[ianj99]

The 30amp Landy alternater in the celler,however, turns out to be a 55amp Sierra alternater.I only want to be able to charge at 10 amps.Do you think that the GX31 has enough grunt to power a 55amp alternater?

there does seem to be some confusion between alternator rating and what current you want from it.
It doesn't matter what the rating is provided its larger than your requirements. You just need to limit the current with an adjustable regulator.
This also means it won't stall the engine if you tried to charge a flat battery.

Without an adjustable regulator to limit the current a flat battery is almost a dead short so any alternator would be maxxed out* and stall the generator.

Also, alternators are probably only about 50% efficient at converting mechanical input into electrical output so 55amps at 13v is 715watts (0.95hp)which needs at least a 2hp motor.

* the current would only be limited by the internal resistance of the winding so the actual current would be more than 55amps.

 

[pvb]

there does seem to be some confusion between alternator rating and what current you want from it.....

* the current would only be limited by the internal resistance of the winding so the actual current would be more than 55amps.

There is confusion. Alternators can only convert mechanical energy (ie rotation) into output current. You can't get more current out than the maximum rating of the alternator. And, if you're talking about stalling an engine, as soon as the revs start to drop, so does the current.

 

[caiman]

Thanks for the replies.Mattnj,in an earlier reply,someone suggested that you might put together and sell a small 'kit' of the bits required,plus some instructions?I don't know whether this was suggested sarcasticaly,but, have you considered it?I would be interested if you do.If not a kit,a pointer to the suppliers of the appropriate bits and the instructions?If so,how much?My work restricts me to being in town so I'd have to get the stuff mail order anyway.
I'm still going to have a go at the ED,engines I'm ok with,I am not very good with electronics.(what's a PIC)
Cheers

 

[VicS]

And, if you're talking about stalling an engine, as soon as the revs start to drop, so does the current.

Surely the trouble is that as you reduce the revs the engine power drops but the alternator, unless having the benefit of MAARS (Mattnj's Advanced Alternator Regulating System) still generates at its regualted voltage and therefore still tries to supply the same current to the same load.
If the engine power falls below the power the alternator is trying push out divided by its efficiency the engine will tend to stall.

But perhaps i'm still not understanding all of this!

 

[pvb]

Surely the trouble is that as you reduce the revs the engine power drops but the alternator, unless having the benefit of MAARS (Mattnj's Advanced Alternator Regulating System) still generates at its regualted voltage and therefore still tries to supply the same current to the same load.

The alternator can only convert mechanical energy into electrical energy. The alternator's current output is related to the speed it's turning at. Energy in; energy out. You can't defy the basic laws of physics.

 

[ianj99]

There is confusion. Alternators can only convert mechanical energy (ie rotation) into output current. You can't get more current out than the maximum rating of the alternator. And, if you're talking about stalling an engine, as soon as the revs start to drop, so does the current.

The quoted alternator current will be a continous rating. The short circuit (overload) current will be considerably higher.

Although the engine rpm and hence current will drop, this isn't enough to prevent the motor stalling or there would not be a need for an adjustable (current controlling) regulator.

 

[VicS]

The alternator's current output is related to the speed it's turning at.

.

Yes but if that current multiplied by the volts, ie the power ( adjusted for the alternator efficiency) is greater than the power being developed by the engine then it will tend to stall.

Wasnt that Mattnj's original problem with the alternator he started with coupled to his GX25 as soon as he wanted to run the engine at less than full speed.

 

[pvb]

The quoted alternator current will be a continous rating. The short circuit (overload) current will be considerably higher.

Interesting. But if the alternator is simply turning rotational energy into output current, how do you think it suddenly finds more current?

 

[mikefleetwood]

Ohms Law, dear boy!

Ignoring the regulator for the moment..
The alternator output voltage ia roughly proportional to the RPM.
The Current is proportional to the internal resistance of the alternator and the load resistance (in this case a battery, which complicates things a bit).
Current drawn from the alternator show as a torque load on the motor. If the load is too high for the motor, the RPM will drop, reducing the voltage. This will reduce the current in proportion, and if the loading is still too high, the RPM will drop further, until either the motor can cope or it stalls.
The current rating is a thermal characteristic of the alternator, not a measure of the current it can, or will, produce.
If the alternator voltage is lower than the battery voltage, no current will flow, but the current will increase rapidly once the alternator voltage is higher than the battery.

I have ignored the fact the alternator output is AC not DC, as most have a rectifier internally. The regulator controls the output voltage of the alternator so that it is just higher than the battery, so charging current is controlled within limits to prevent damage to battery or alternator.

Hope the info helps explain some misconceptions.

 

[pvb]

The alternator output voltage ia roughly proportional to the RPM.

I'd have said that the power output of the alternator is proportional to the rotational speed.

The regulator controls the output voltage of the alternator so that it is just higher than the battery, so charging current is controlled within limits to prevent damage to battery or alternator.

Hope the info helps explain some misconceptions.

The regulator sets the output voltage of the alternator, it's not relative to the battery - it's an absolute. The regulator has no way of controlling the charging current. I think, rather than explain, you've introduced some misconceptions.

 

[mikefleetwood]

I'd have said that the power output of the alternator is proportional to the rotational speed.

but then you'd have been wrong, 'cos it isn't. It depends on other things as well, that's what I was explaining. Voltage, current and power are all different parameters and the relationship between them is not simple in this set-up. You start using terms in the wrong way in a technical discussion and it just gets confusing.

If anything, the power output is proportional to the square of the rotational speed.

The regulator sets the output voltage of the alternator, it's not relative to the battery - it's an absolute. The regulator has no way of controlling the charging current. I think, rather than explain, you've introduced some misconceptions.

Maybe I should have said "... voltage just higher than the nominal voltage of the battery...", but I thought perhaps that was obvious.

 

[mattnj]

i think what happens in reality is this:-

engine speed say 5000rpm, engine capable of say 500w at this speed, all running, no load.

You turn on the alternator/regulator and it applies a field voltage/current to hold say 14.2v, this causes the engine to slow down, so the voltage drops from 14.2v to say 13.9v the regulator then increases the field current/voltage to try to up the output voltage again to 14.2v, which slows it down ever more, until it stalls, the only way round it is to:-

a) have an engine with enough power to run the alternator at full load.
b) have an adjustable regulator, that will allow to match the alternator output with the engine power graph.

 

[Pagetslady]

well I have just spent a wonderful hour reading all the posts, I hope it all works out it all way above my head but I want one. I did have a small 2 stroke engine mounted in a wooden cradle connected up to a dianamo with a regulator, I got it out of a skip but could not start the engine but at the time I thought it was a great idea. Thanks again for a great thread.
Mike