Reduce Alternator Output, Variable Regulator?

[mattnj]

Looking for a way to reduce the alternator output, or better still have it fully variable, as part of the Micro Generator Project:-

http://www.ybw.com/forums/showthread.php?t=241749

Any ideas?

The easiest option that i can think of at the moment is to add a diode (like a split diode setup) which will drop the output voltage and therefore a fair bit of the charge rate/load, but modifying it to be fully variable from nothing upwards would be best.

 

[caiman]

Could you put a rheostat into the field wire feed?(Page 161 12v Doctor's practical Handbook)If you are going for electric start(presumably using a small m/c battery to start the genset) could you diminish the charge output by the field sensing from the charged genset battery rather than the battery the genset is charging?Increase the output by varying the rheostat?
Cheers

 

[Heckler]

Looking for a way to reduce the alternator output, or better still have it fully variable, as part of the Micro Generator Project:-

http://www.ybw.com/forums/showthread.php?t=241749

Any ideas?

The easiest option that i can think of at the moment is to add a diode (like a split diode setup) which will drop the output voltage and therefore a fair bit of the charge rate/load, but modifying it to be fully variable from nothing upwards would be best.

Put a potentiometer in to the excitation circuit, start it on lo excitation, then wind it up whilst you increase the revs.
Stu
PS where does the starter motor fit?

 

[mattnj]

whats the theory to these suggestions?

what does the pot do? reduce the voltage? limit the current? surely a pot will get bloddy hot at 5amps!
how does the alternator decide how much charge its going to output?

i take it the excitation voltage/current decide the charge rate, so i need a variable voltage regulator on the "excitation" circuit so i can vary the charge rate...is that correct? and i leave the regulator as is?

 

[VicS]

Putting a diode or a resistance in series with the load will be a very inefficient method of controlling it and it will result in a lot of heat to dissipate.

The idea of controlling the field current with a variable resistances is better but still rather crude and also somewhat inefficient.

You will find the 12volt Doctors Handbook at http://www.motoren.ath.cx/menus/electrical.php if you want to follow up caiman's suggestion.

What you really need is an electronics wizard to design you a regulator which will replace the inbuilt one and which will give you manual control of the output voltage.
I guess you will only want it to reduce the volts to 12.something at the minimum end but allow you to increase it to the normal 14.whatever that the alternator normally runs at at the top end of it range

 

[White Horse]

Seems a bit daft that

You are using the engine and then limiting the output from the alternator . What a waste Are you going to be running the two together and if so why . Surely the alternator will produce enough power for the boat . Thought your idea of a mini power plant was for when everything was switched off and you needed power . You will blow your alternator if you disconnect the alternator while driving it . They are not happy .....

 

[Heckler]

whats the theory to these suggestions?

what does the pot do? reduce the voltage? limit the current? surely a pot will get bloddy hot at 5amps!
how does the alternator decide how much charge its going to output?

i take it the excitation voltage/current decide the charge rate, so i need a variable voltage regulator on the "excitation" circuit so i can vary the charge rate...is that correct? and i leave the regulator as is?

The regulator varies the excitation voltage which varies the output, it is usually sensed from the output of the alternator, so at the mo you are sensing the battery by virtue of the fact that the battery is coupled directly to the output of the alternator. You can bypass that by adding a wire directly to one of the brushes a la Sterling (you can look Sterling alternator boosters up and follow his instructions to figure out which one) couple the pot in between that and the battery and feed raw voltage in to the excitation circuit. Trial and error will tell you when you get it right.
Very simplistic I know, but I said at the beginning it wouldnt be easy.
Stu
PS in essence you will disconnect the auto regulator and feed manual adjustable voltage in to regulate it, no voltage = no output etc etc.

 

[cimo]

Looking for a way to reduce the alternator output, or better still have it , as fully variablepart of the Micro Generator Project:-

http://www.ybw.com/forums/showthread.php?t=241749

To summarise -
two cheaper options would be
1. alter the field current - between the regulator and field winding by adding variable resistance. Will require some internal rewiring in the alternator most likely.
2. alter the sensing voltage level - between the battery and voltage regulator, by adding a voltage divider (diodes would work well giving 0.7v steps). you may have to change the alternator to be battery sensing if not already so.

The more expensive option 3 is to replace/overide the alternators voltage regulator with a dedicated user variable regulator.

question on my mind is why would you want to vary o/p voltage from zero to max. would a few preset outputs not be more practicle? Can see the point in being able to vary output current from zero to max. DC bench suplies achieve this usiing a variable shunt (variable resistance wired in parallel to the output).

option 4 would be to leave the alternator as is, and install a power supply regulator downstream of the battery. Providing say 5vdc & 12Vdc outputs with full current limiting? This is the easier option, with less pitfalls & a medium expense I think but with a lesser effeicency than options 1, 2 or 3 in my opinion.

nice project by the way. best of fun.
rgds

 

[mattnj]

You are using the engine and then limiting the output from the alternator . What a waste Are you going to be running the two together and if so why . Surely the alternator will produce enough power for the boat . Thought your idea of a mini power plant was for when everything was switched off and you needed power . You will blow your alternator if you disconnect the alternator while driving it . They are not happy .....

no, not limiting it, still makes near the full output, just trying to control it so i can match the engine power curve to the power generated by the alternator. it all works well at the moment, just cant run engine at under say 60% throttle or it stalls (but only just) so i just need to drop the alternator load a small amount at the lower speeds.

would be a much better setup if alternator output was "variable" simply by changing engine speed, so you could choose between idle and say 8amps or full chat at 50amps, or anything in between, by altering throttle, it just that the alternator is a bit too power hungry so needs a tweak..... Its a doddle to make the electronics just need to get my head around the theory.

 

[mattnj]

question on my mind is why would you want to vary o/p voltage from zero to max. would a few preset outputs not be more practicle? Can see the point in being able to vary output current from zero to max.

yes, i didnt really want that, some sort of simple control will be fine, thanks!

 

[Heckler]

yes, i didnt really want that, some sort of simple control will be fine, thanks!

pot on excitation circuit
See here for some more info http://en.wikipedia.org/wiki/Alternator
stu

 

[White Horse]

Barking up the wrong tree

Sorry about that . Thought you were on about the alternator on the ENGINE ..

See the problem now .

 

[VicS]

The best method of achieving the regulation you want is illustrated in sketches 19 and 20 on page 156 of the "12 volt doctors handbook" Sketch 19 is for a negative regulated alternator while sketch 20 is for a positive regulated alternator.

By including a potentiometer in the R1 R2 circuit and selecting appropriate values for the three of them you will be able to control the voltage output from the alternator over what ever range you require.
It does mean however that you will need to disconnect the internal regulator and build a new external one.

 

[cimo]

Vics, I think the simple pot in series with the field winding will resolve the stalling problems at low revs much quicker. Choosing a pot with a range equal to the alternators' field winding resistance will immediately reduce stator current output by almost half (for when engine is on low revs). turning the pot to near zero will return the alternator to near full output when on high revs. May have to play a bit with the pot size to find the sweet spot for the engine.

Different voltage levels would be simply a matter of stepping down the output. As the alternator will always require a battery to load it's output at 12v nominal. Stepdown is easier to acheive downstream of the battery I think.

 

[VicS]

Vics, I think the simple pot in series with the field winding will resolve the stalling problems at low revs much quicker.

yes I think I acknowledged that as a simple but crude method earlier. The pot is going to have to withstand quite a current... I'd budget for up to a couple of amps but perhaps it would be wise to measure the field current beforehand. So it might need something fairly beefy ... probably not the sort of thing that you'll find in Maplins.

The way it behaves might be interesting. Initially as you increase the resistance the regulator will output a higher voltage to try to compensate for the drop in alternator output volts.

I was trying to think out a switched circuit that would bypass the regulator, feeding the field coils via various value resistances directly from the field diodes, but with the final position on the switch bringing the normal regulator back into service. (It could be extended to include boosted outputs as well as reduced outputs)
I thought of too many questions that I could not answer to conclude the idea.

 

[William_H]

Controlling the alternator output

A diode in series with the output is going to drop .7 volt and at 5 amps is going to heat and waste about 3 watts. If you are charging a battery this will dramatically reduce charge current and load on alternator.
What you really want is a variable regulator used in conjunction with an amp meter so you can adjust to load the engine correctly (not too much) while ensuring max charge.
I find it surprising the engine will stall under load because as the alternator slows down output reduces so load on the engine reduces. However if that is what is happening...
You want a regulator (of the field current) which is controlled not by the battery voltage but rather by the engine revs. So if the engine revs too high the field current increases so voltage output of the alterrnator and so load on the engine increases while if engine slows down the field current will reduce so load reduces.
An alternator regulator is simply a power transistor connected between the file excitation supply often an additional 3 diodes from output and the field coil. (via brushes) Some alternators are wired with the excitation supply straight to the field coil and the regulator between field coil and ground.
The power transistor base is driven by the output of another transistor amplifier with a zener diode as voltage reference and the sample of battery voltage. A simple way to do that is using a 741 op amp with zener voltage on + input and sample from battery on -ve input. The sample goes via a potentiometer so can be set to regulate at whatever voltage you want. Once you have built that and it works you can manually adjust regulated voltage. Or build a rev counter circuit for the engine whose output feeds to the sensing circuit.
Or alternatively you could build a current sensing circuit which would regulate to constant charge current.
Which will be adjustable and probably give you the desired outcome.
Or as said just put a variable resistor in series with the field coil and remove the regulator. Field coil generally will take max one amp at 12v so the variable resistor might need to be able to dissipate perhaps 6 watts or so. (control a power transistor with a small pot) PM me for more detail good luck olewill

 

[grumpygit]

Looking for a way to reduce the alternator output, or better still have it fully variable, as part of the Micro Generator Project:-

http://www.ybw.com/forums/showthread.php?t=241749

Any ideas?

The easiest option that i can think of at the moment is to add a diode (like a split diode setup) which will drop the output voltage and therefore a fair bit of the charge rate/load, but modifying it to be fully variable from nothing upwards would be best.

As I said in a earlier post that you will have to overcome the cut in of the regulator. If you had a spec for the alternator you are using you would see the charging curve/revs shown as a graph and that would better explain your problem. With going direct drive I doubt you will overcome this problem. Imo you have gone for a far to higher output alternator than you require. How many amp is the alternator ?

Also by the picture it looks like a Hitachi or Denso alternator, so you have picked probably the worst you could have for internal mods. It will have a 5 or 6 pin regulator and they are a very delicate item and can be destroyed just by to much heat from soldering to it's pins.

Just out of curiosity has/does the alternator you are using need a battery sensing connection? There should be a small diagram on the label along with it's part no. If you are not sure just post them along with part no.

Lets say that a Bosch unit should have been your first choice, easy to work on, regulator external, more options.

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[Plevier]

An alternator regulator is simply a power transistor connected between the file excitation supply often an additional 3 diodes from output and the field coil. (via brushes) Some alternators are wired with the excitation supply straight to the field coil and the regulator between field coil and ground.
The power transistor base is driven by the output of another transistor amplifier with a zener diode as voltage reference and the sample of battery voltage. A simple way to do that is using a 741 op amp with zener voltage on + input and sample from battery on -ve input. The sample goes via a potentiometer so can be set to regulate at whatever voltage you want. Once you have built that and it works you can manually adjust regulated voltage.

Don't you think an LM317 or 337 would be a nice easy way?

 

[mattnj]

the easiest option just has to be add a diode to drop the output voltage by 0.7ish, simple, 2 connections, job done, for now that is......could have it switched in or out and/or use Schotty, or play about to switch then in and out or use different diodes, the heat loss, is irrelavent really, even it is was doing say 20amps at lower speeds, then 20*0.7 drop = 14watts, not a massive amount.

Will start with that and go from there..and work on controlling the alternator at the same time, thanks for all the replies.

 

[grumpygit]

the easiest option just has to be add a diode to drop the output voltage by 0.7ish, simple, 2 connections, job done, for now that is......could have it switched in or out and/or use Schotty, or play about to switch then in and out or use different diodes, the heat loss, is irrelavent really, even it is was doing say 20amps at lower speeds, then 20*0.7 drop = 14watts, not a massive amount.

Will start with that and go from there..and work on controlling the alternator at the same time, thanks for all the replies.

Can you please explain how this diode in the output B+ is going to reduce the rotor current and especially if it's a battery sensed alternator which I'm sure it will be.???

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