DIY 12V generator

[Chalky]

You could set the engine to run at its most fuel efficient rpm, then use a power converter to sort out the voltage.

[Sir Nibble]

That heatsink looks to be about 20cm long, would you agree?

 

If it is that sort of size, then even at 10 amps, it's going to get to at least 125 degrees C above ambient.

I've not actually seen the photo but the units I'm used to working with are, as I say about the size of a fag packet.

 

The heatsink you see on the pic is the rectifier, it has no regulator (as yet).

 

I regulate by manually adjusting rpm to give me the voltage I need.

 

I think effective automatic regulation would need to include a servo to adjust the throttle. It seems very ineffective to have the engine run at full power all the time and just burn up the excess energy as heat.

 

Pieter

That would be interesting, but how are the motor windings connected? Can you get at both ends of all phases? even if you can't get to both ends it does give scope for mucking around with connections to select output "tappings". In fact, I've got a shrewd idea there is a way of controlling the output from two phases by mucking about with dc into the other. Have to have a think about that.

As for an actuator on the throttle, how about a solenoid acting in concert with the governor spring?

[Gibbo]

The heatsink you see on the pic is the rectifier, it has no regulator (as yet).

 

That's what I thought. There's simply no way it's big enough to have a shunt reg on it.

[pistnbroke]

I think some of you have lost the plot here ( not Pieter ) I am talking of a series regulator with a pulsed MOSFET not a shunt regulator and the motor /generator running to produce say 18v which is regulated by the mosfet to 14.4v...the engines speed regulator will control the throttle so only sufficient petrol will be burnt to match the output required

[Gibbo]

I think some of you have lost the plot here ( not Pieter ) I am talking of a series regulator with a pulsed MOSFET not a shunt regulator and the motor /generator running to produce say 18v which is regulated by the mosfet to 14.4v...the engines speed regulator will control the throttle so only sufficient petrol will be burnt to match the output required

 

That's not a series regulator. A series regulator is, by definition, a linear regulator.

 

If you use anything other than a shunt regulator, the output of the alternator will go sky high when the load is removed and start letting smoke out because there is no automatic engine speed control.

 

Edit: Who's lost the plot?

Edited March 9, 2011 by Gibbo

[Nickhlx]

Bike alternators..

 

Of the more modern bikes, the BMWs are generally thought to have the higher outputs - somewhere around 800 watts for the 1200/1300 cc bikes.

 

My FJR1300 is a mere 550 watts and the Fazer 600 is about 350 watts

 

Nick

[Gibbo]

You forgot the Goldwing at 1300 watts. Though I suppose one could argue it's actually a two wheeled car

[Nickhlx]

You forgot the Goldwing at 1300 watts. Though I suppose one could argue it's actually a two wheeled car

 

I didn't know that one - you could weld with that !!

 

Nick

[pistnbroke]

I still say you lost the plot Gibbo ..this is a 4 stroke honda so its governed or limited ...and on this type of generator /motor its 230 rpm per volt ...so output does not go sky high .....I am talking either three MOSFETS combined with 3 diodes in the rectifier or a MOSFET in series with a standard 9 diode 3 phase rectfier which is pulsed on/off so the dissipation is minimal .....

 

Pieter has given us a good idea and once again its getting myred by experts...have any of you actually got one of these and tried it in the lathe or variable speed drill? why are we getting multiple irrelavent posts on motorbikes for gods sake

Edited March 9, 2011 by pistnbroke

[Gibbo]

I still say you lost the plot Gibbo ..this is a 4 stroke honda so its governed or limited ...and on this type of generator /motor its 230 rpm per volt

 

That's when it's running as a motor at rated load.

 

...so output does not go sky high .....

 

Believe me, it will. Just like an alternator does when it's open circuited. There is no difference.

 

I am talking either three MOSFETS combined with 3 diodes in the rectifier or a MOSFET in series with a standard 9 diode 3 phase rectfier which is pulsed on/off so the dissipation is minimal .....

 

Won't work. You can't open circuit them. That's why wind turbine regs don't work that way.

[Robin2]

 

... Just like an alternator does when it's open circuited. There is no difference.

 

 

What is the smallest load that will prevent an alternator from blowing up its diodes if the rest of the load is removed?

 

For example if a bulb (or a resistor) consuming 1 amp was connected across the alternator output would it matter if you removed all of the rest of the load?

[WotEver]

What is the smallest load that will prevent an alternator from blowing up its diodes if the rest of the load is removed?

 

For example if a bulb (or a resistor) consuming 1 amp was connected across the alternator output would it matter if you removed all of the rest of the load?

See post #21:

When the battery is fully charged the reg somehow has to get rid of 430 watts (and that's a best case scenario).

 

Tony

[pieter]

I've not actually seen the photo but the units I'm used to working with are, as I say about the size of a fag packet.

 

 

That would be interesting, but how are the motor windings connected? Can you get at both ends of all phases? even if you can't get to both ends it does give scope for mucking around with connections to select output "tappings". In fact, I've got a shrewd idea there is a way of controlling the output from two phases by mucking about with dc into the other. Have to have a think about that.

As for an actuator on the throttle, how about a solenoid acting in concert with the governor spring?

No can't get to both sides of the windings, although there are motors where you can (which means you could make them switchable between star and triangle), but they were much more expensive.

 

Interesting idea about the solenoid. Can you get solenoids with a variable movement/output? For some reason in my mind they are associated with on/off, i.e. one position or the other but nothing in between.

 

If you use anything other than a shunt regulator, the output of the alternator will go sky high when the load is removed and start letting smoke out because there is no automatic engine speed control.

 

I am sure you are right re alternators, but the brushless motor and rectifier do fine without load.

Edited March 9, 2011 by pieter

[Robin2]

See post #21:

 

 

Tony

 

I was thinking of the usual automotive type of alternator which has a voltage regulator so would reduce its load automatically but may have to deal with a short term high voltage spike when it was open-circuited.

[WotEver]

I was thinking of the usual automotive type of alternator which has a voltage regulator so would reduce its load automatically but may have to deal with a short term high voltage spike when it was open-circuited.

Snib or Gibbo would be the best to answer this, but here goes my best guess:

 

There's no load that could be put across the alternator output to protect it in the even of going OC that wouldn't adversly affect the charging. If a 100A alternator was working flat out into batteries in bulk there would be something in the region of 1300W being consumed. Assuming the voltage to be in the region of 13V that means that the alternator is 'seeing' an apparent load of approximately 0.13 ohms. Therefore a 1300W r13 resistor could 'replace' the batteries and prevent the Alt trying to reach the sky in order to put out it's max output. This resistor would be around half a metre long and would need to be bolted to the baseplate as a heatsink. Alternatively, the alternator output could be grounded, which is I believe how 2nd alternators on new marine engines are supplied. Obviously, neither of those 'solutions' would work in an installation.

 

Maybe I've missed something, in which case I'm sure someone will be along shortly to correct me. (It's not unknown for me to be fully confident and entirely wrong.)

 

Tony

 

Can you get solenoids with a variable movement/output? For some reason in my mind they are associated with on/off, i.e. one position or the other but nothing in between.

In my mind too. I wonder if Snib meant a stepper motor? Snib?

 

Tony

[Gibbo]

I am sure you are right re alternators, but the brushless motor and rectifier do fine without load.

 

As a sanity check, last night I removed the motor from my RC plane. It's a 3 pole brushless. I ran it up on the lathe until it was producing about 10 amps at 11 volts (it just happened to be a convenient load). When I disconnected the load the output voltage went to 64 volts.

 

So yes, they do rocket the output when unloaded.

 

Now I don't think for one moment it will bother the motor, but the rectifier might have a bit of an issue with it.

 

What is the smallest load that will prevent an alternator from blowing up its diodes if the rest of the load is removed?

 

For example if a bulb (or a resistor) consuming 1 amp was connected across the alternator output would it matter if you removed all of the rest of the load?

 

It depends how much current it was producing at the time the load is removed. If it's running at full hoot, and the load is removed, then it will literally need about (it's a guesstimate so don't ask for calculations because it depends on the breakdown voltage of the diodes and a million other things) half load to stop the output voltage going so high that it damages the diodes.

[Robin2]

 

It depends how much current it was producing at the time the load is removed. If it's running at full hoot, and the load is removed, then it will literally need about (it's a guesstimate so don't ask for calculations because it depends on the breakdown voltage of the diodes and a million other things) half load to stop the output voltage going so high that it damages the diodes.

 

Doesn't something pretty close to a loss of full load happen when my microwave switches off? The load seems to go from 70amps to 2amps instantly?

[Gibbo]

Doesn't something pretty close to a loss of full load happen when my microwave switches off? The load seems to go from 70amps to 2amps instantly?

 

No. Stick a scope on it, monitoring the current, and you'll find that it doesn't. It will reduce over a short period of time. Even reducing the current from full to nothing over 500mS is long enough to prevent the large voltage spike.

[WotEver]

No. Stick a scope on it, monitoring the current, and you'll find that it doesn't. It will reduce over a short period of time. Even reducing the current from full to nothing over 500mS is long enough to prevent the large voltage spike.

If the batteries remain connected won't they in fact act as a huge quenching capacitor even if a load were to be instantaneously removed?

 

Tony

[Gibbo]

If the batteries remain connected won't they in fact act as a huge quenching capacitor even if a load were to be instantaneously removed?

 

Yes, that's precisely what stops the voltage spike when a large load is remove.

 

The size of voltage spike is directly inversely proportional to the rate of change of current. The internal capacitance of the alternator affects it a little bit but that's tiny in comparison.

[Sir Nibble]

In my mind too. I wonder if Snib meant a stepper motor? Snib?

 

Tony

No, a solenoid. If you put a solenoid so that when energised it works to slacken the governor spring tension and then power it through a meaty zener then excess current will be dumped to the solenoid. The more excess current is dumped the more the solenoid slackens the spring and the slower the motor runs reducing the current to be dumped and a feedback loop is set up. I have seen diesel gens governed by varying current through a throttle mounted solenoid achieve speed control to + or - 0.01%.

of course component selection is all.

[WotEver]

No, a solenoid. If you put a solenoid so that when energised it works to slacken the governor spring tension and then power it through a meaty zener then excess current will be dumped to the solenoid. The more excess current is dumped the more the solenoid slackens the spring and the slower the motor runs reducing the current to be dumped and a feedback loop is set up. I have seen diesel gens governed by varying current through a throttle mounted solenoid achieve speed control to + or - 0.01%.

of course component selection is all.

Gotcha. So the solenoid is effectively pulling against the spring tension, yes?

 

Tony

 

edited for fat fingers

Edited March 10, 2011 by WotEver

[pieter]

As a sanity check, last night I removed the motor from my RC plane. It's a 3 pole brushless. I ran it up on the lathe until it was producing about 10 amps at 11 volts (it just happened to be a convenient load). When I disconnected the load the output voltage went to 64 volts.

 

So yes, they do rocket the output when unloaded.

 

Now I don't think for one moment it will bother the motor, but the rectifier might have a bit of an issue with it.

 

 

 

It depends how much current it was producing at the time the load is removed. If it's running at full hoot, and the load is removed, then it will literally need about (it's a guesstimate so don't ask for calculations because it depends on the breakdown voltage of the diodes and a million other things) half load to stop the output voltage going so high that it damages the diodes.

 

OK, just checked my rectifier. It is rated at upto 1000V, so that might be the reason I had no problems, rather than the voltage not sky-rocketing. Sorry for the confusion.

 

No, a solenoid. If you put a solenoid so that when energised it works to slacken the governor spring tension and then power it through a meaty zener then excess current will be dumped to the solenoid. The more excess current is dumped the more the solenoid slackens the spring and the slower the motor runs reducing the current to be dumped and a feedback loop is set up. I have seen diesel gens governed by varying current through a throttle mounted solenoid achieve speed control to + or - 0.01%.

of course component selection is all.

 

Get you know! Indeed component choice will be crucial.

[Sir Nibble]

Gotcha. So the solenoid is effectively pulling against the spring tension, yes?

 

Tony

 

edited for fat fingers

Yes.