Optimizing generator to work with hydro system?

[Kyle T]

Put this in newbies on account of never having posted here before - didn't want to step on any toes.

Skip to the last paragraph for the important bit

I'm looking to supplement an existing solar system at an off the grid cabin with hydro. Power demands are quite low; existing loads are just the starters on some propane appliances (stove/fridge/water heater), but we'd like to string up some LED lights and could no doubt use any excess power for other "projects".

We have roughly 110' of static head on a 900' run, and we plan to use either 1" or 1-1/4" pipe - the stream is more than adaquate to supply this. The best option I've found to date would be to use a turgo runner from: http://h-hydro.com/ .

Based on our site and the spreadsheets he has available, the point of highest efficiency for the runner is about 2100rpm resulting in a max of 64W shaft work (assuming 1" pipe and 80% turbine efficiency).

The part I'm having the hardest time figuring out is the generator. I have essentially no power tools (hand tools or otherwise) available, so I would basically have to beg, borrow, or buy anything needed, which means making my own generator is pretty much the final option on my list. I only need a (small) fraction of that 64W shaft work though so this shouldn't be a big deal.

The best available options seem to be either an alternator or a tape drive motor like http://www.svigs.com/servomotors . Any other suggestions here would be more than welcome.

Now for either an alternator, or a tape drive motor (I suspect this isn't possible for the tape drive) is it possible to control the torque at a given voltage level required to spin the motor so that we can get it to spin at 2100rpm at 15V? The idea then would be to take whatever current we can get out of that. I guess I'm wondering if its possible to control the power going into the magnetic field of the alternator (or somehow adjust the magnetic field of the tape drive) in order to maximize the efficiency of the turbine, and how I would go about doing this.

Cheers,

Kyle

[zeusmorg]

  Probably the easiest alternative would be to use an automotive alternator, at 2100 rpm you have the speed to generate about 75% of it's rated amperage. It may not be the most efficient solution but probably the easiest to convert.

 The regulator that is built in most alternators will do what you want, without building an outside control system.

 You have done your homework it seems.

[Warren]

Hello,

Look at the post under the topic "Semi homemade hydro power". It may help some.

I do have experience with using a Delco Alternator but not when producing only about 5 amps. You can adjust the field coils to regulate the power produced but that will use up part of the power you produce. You can not use the regulator in the alternator.

My system had an electronic controller for the field coils but it is not available anymore. They now use a rheostat at the alternator to regulate the field current and then a diversion load controller like the Xantrex C 30 at the batteries to look after the battery voltage.

I don't know how much more efficient a self excited induction motor system would be, as described in the above noted post. It isn't as simple as the alternator system.

Hope some of this helps,

Warren

[Kyle T]

Thanks for the input guys

Warren,

I should preface this by saying that I am decidedly not a car guy and have precisely 0 experience with alternators.

I was already aware that we'd need a diversion load controller and I didn't realize there was even an alternative so no loss there. To what are you referring when you say "You can not use the regulator in the alternator"?

If, as stated, they have a rheostat to control the field current, can't I just stick in an ammeter and keep turning the knob or screw or whatever it is until the current peaks? I'd kinda been assuming they (the field coils) were stuck at a fixed voltage level out of the factory.

Also, do the field coils excite themselves, or do I somehow have to provide a power supply to them in order to start things working, and if so how would I do this?

The induction motor idea is good - but efficiency is not #1 on the bill, simplicity gets priority for now - even 1 amp would more than fill our needs for the time being.

Thanks again,

Kyle

[Flux]

I would avoid the self excited induction generator for small power levels.

In your case I tend to agree with the others that a car alternator will do the job. 2100 rpm is reasonably within its range for the sort of power you want.

If you run it with full field it will probably start charging at near 1000 rpm and most of the power you produce will go into the field winding, but you may still get what you want.

As you reduce the field volts ( current) the alternator will speed up, match the turbine better, take less field power and give you more charging current.

Ideally you need a low loss method of reducing the field current. A buck converter will do this with over 80% efficiency but it is probably out of your reach. You will most likely have to make do with resistors or lamps to drop the field current. As you are not likely going to need to work with very low field currents the loss will not be as detrimental as if you were working at much higher speeds.

The main objections of using the internal regulator are that it will almost certainly hold you on full field and reduce your speed to a point where the turbine is poorly matched. If the battery volts come up ( say from solar) the regulator will reduce field and the speed will rise, possibly higher than is good for the turbine. Also the internal regulator will limit you to about 13.8v, which is only float charge and you will need more to fully charge the batteries in a reasonable time.

If you can get a high power variable resistor ( rheostat) of about 5 ohms and rated for 4 amps or more then you can feed the field through it, Start with full field, then increase resistance to give you maximum charge. Failing this you can use car lamps but they are not 100% reliable in the long run and loss of field will run the turbine over speed.

You could most likely get a 2 or 3 times improvement with a decent high quality permanent magnet alternator matched to the turbine, but you will not have any latitude for errors and you will most likely have to build it.

[Kyle T]

Alright, thanks Flux; a few more questions then

-How do I bypass the control circuit in an alternator in order to control it with my rheostat?

-I just want to confirm that the field coils in an alternator will energize themselves without me provide an initial current through them - yes, no?

-With the rheostat in place I'll still need the shunt load controller right? I'm guessing that the field will collapse when the batteries aren't charging if I hook this up to the typical solar controller - which we already have.

-Suggestions for part sourcing for the alternator and rheostat? I live in Canada so some of the US retailers aren't available to me. What kind of alternator should I be looking for? new model? old model? car? truck? any vehicle in particular? And some quick googling seems to indicate that 5 ohm rheostats are typically rated for lower power or current levels (i looked for either 4 amp or 60 watt)... where would you suggest I get one? I'd definitely prefer to go with a rheostat over car lamps.

Cheers,

Kyle

[Flux]

This is where it becomes difficult, if you have no basic idea of car alternators you may struggle. I am not familiar with the alternators available in N America, they are all basically the same but there are significant small detail changes that will confuse a newcomer.

There is a fair bit of information on the internet about modifying car alternators for engine driven battery chargers. Try to find a site that gives exact details of a type that you can get.

You effectively feed the slip rings from the battery via the rheostat, that may mean a bit of messing in some cases as the regulator may be part of the brush gear. You may have to snip a few wires.

It is highly unlikely that it will self excite from the auxiliary diode bridge at that speed without some assistance such as the typical warning light but it should stay excited if you just flash it across to the battery. With hydro if it is running all the time you can ignore the auxiliary diodes and just supply the field from the battery, possibly with a switch to cut the field if you need to shut it down.

You will need a shunt controller, don't try feeding the alternator through the solar controller you will kill it. You will probably do better to remove the series solar controller and use a bigger diversion ( shunt ) controller to handle both then you can let one controller look after the whole charging sequence.

If you have something such as a C40 it can be reconnected to diversion mode. If solar only then you will need to look for a diversion controller.

Sorry I can't help with parts I am in the UK.

Flux

[Kyle T]

Alright, well assuming I can figure out how to modify the alternator, how did you come to the 4 amp, 5 ohm rating on the rheostat? This place (reasonably close to me): http://www.sphere.bc.ca/test/loads.html sells 5 ohm, 50Watt rheostats, and 10 ohm, 100 watt rheostats. They both have the same 3.16A current rating of course, but I'd imagine they're actually sized by power dissipation rather than current, so I should be able to safely put 4.5 amps at 5 ohms through the 100 watt rheostat if necessary, right? however, if I can get away with the 50 Watt version, that'd be nice because they're half the price. - and If I'm dumping 50 watts of my 64 watt shaftwork into the rheostat, something is pretty screwy.

[Flux]

The field coil of a typical alternator has a resistance of somewhere near 3 ohms, so that it takes about 4 A at 12v. A 5 ohm rheo would let you reduce the field volts to below 6v and that you should be adequate for you. If you needed to add 1 ohm to get the speed up, then you would be reducing the field current to 3 amps. You will have reduced the field consumption from 48W down to 36. If you can add 3 ohms then you drop the field consumption to 24W.

It is inevitable with a car alternator that you will waste power in the field and that is one reason why they are pretty useless for wind power. For efficient hydro again they are pretty bad but as you only wanted a modest output then you should get away with it. In addition to the field loss the car alternators are not very efficient but running at low output you should have less loss.

The reason I suggested an electronic regulator for the field is that it would drop your field current without incurring the loss of the rheostat, but most of your loss will be in the field itself. The rheo needs to be able to carry the full field current and your 3.16 A is close but you should not need to run at full field current so it should be ok.

The 50W is the maximum dissipation based on rated current at the full resistance value. Your rheo will only drop a few watts but you need the current rating. Most of your loss will be in the field and that is inevitable with a car alternator. You could convert it to permanent magnet but that means lots of work and no chance of altering the characteristics if you get it wrong.

Flux

[Kyle T]

Ah, I see. I didn't realize the resistance of the rotor was that low, for some reason I expected it to be higher, not that it makes any sense.

Could you take a look at this and tell me whether I'm on the right track or if you'd do something differently? - my circuitry skills are a little subpar but I can follow a diagram well enough, heh.

[Flux]

Yes that looks fine. Traditionally I would have put the rheo in the positive side but it doesn't really matter.

Flux

[Kyle T]

Good stuff!

one more diagram then - imagine this one appended to the right side of the other one with about 200' of wire run in between ;-)

I still am not sure about how to get those field coils going.

Is this a good or bad idea? how would you do it? should there be some diodes in there as well as the switch?

-Kyle

[Kyle T]

Whoops, that should be a single throw switch of course, probably a momentary one.

[Flux]

I thought we established that you can't use a series solar charge controller with this set up. A controller used in diversion mode looks directly at the battery. The hydro will not be aware that it exists so you have no need to bypass it.

A diversion controller just connects directly to the battery and when the volts rise to a set level it diverts the excess charge to a dump load. Charging sources solar and hydro are connected direct to the battery.

Flux

[Kyle T]

Ah, I see.

when you said "It is highly unlikely that it will self excite from the auxiliary diode bridge at that speed without some assistance such as the typical warning light but it should stay excited if you just flash it across to the battery. "

I assumed the flashing across part involved something of this nature.

[Flux]

As you have drawn it you have not used the aux diodes but have supplied the field from the battery. That is fine as long as it is always running and there is no need to do any tricks to start it.

If you want to retain the aux diodes then yo can do this:-

You only need to close the switch for a second or so and it should remain excited. If it stops then it will shut its field off.

Sorry about the crappy drawing.

Flux

[Kyle T]

Ah, now I understand. I'll probably try to do what you've drawn so that if the turbine stops for any reason the battery won't drain, it will probably depend on how easy the various components are to isolate when I open up the alternator.

Thanks for spending all the time Flux, much appreciated.