Would like help with voltage boost circuit for Wind Generator.

[charles25]

Hi, I've built a wind generator from a 99 volt low rpm DC motor. I'm trying to charge a 24 volt battery bank with it, along with some PV panels. I have an expensive inverter feeding 120v AC into my home, it is also capable of selling power back to the utility.
My project is to build a forward converter or boost converter of some sort to boost the voltage output of the wind genny X2. The reason is to get a 24 volt charge voltage(and hopefully current) sooner in the wind speed curve. Right now I get a solid 12 volts (o.c) at 10-15 MPH wind. I would like to double that to get some charge into the batts.
The circuit needs to be fairly robust to handle some charge current say 10 amps. Also it needs to have a fairly wide input voltage range say 0 to 20 volts DC. Any thing above 20 volts or so I could use a voltage limit of some kind (zener diode) to switch a relay and charge directly from the generator.The input is very wide ranging and the current requirements are ,potentially quite large. Not so much at low wind conditions though it could get cranking in high winds. The motor I'm using for a generator is capable of currents to 1kW I'm told. I'l probably never see it though.
Any thoughts on a circuit I could build to try this ? I can build my own PCBs and populate them. I cannot design it on my own.
Thanks in advance.
CjK

 

[HarveyH42]

I've only study on this a little, as I've considered building one myself. Huricane season kind of concerns me though, so I don't get too serious. Sounds like you really need to spin the motor faster to get more power. Doesn't sound like you are getting no where near full capacity. We can only guess at how you set it up, so many factors. But realistically, a circuit board won't create more energy, just convert it, power in - power out...

 

[philba]

I believe what he is trying to do is get usable energy at lower wind speeds and not creating energy. Pretty reasonable.

You might be able to find a design with a very wide input range but at the expense of efficiency in some part of the range. Basically, I think the solution is to have 2 different switch mode power converters, one for low speed and one for high(er) speed. National and Linear have lots of designs for SMPS. check out national's webbench. You can just plug in your requirements and it will (er, may) spit out a circuit. A tachometer could be used to decide when to switch between the two though switching based on actual voltage would be better. Given the current needs, I'd probably use a relay. A latching one would consume less current. hysteresis would need to be used.

Each power converter would have a range of inputs (overlapping in the hysteresis region).

To spin it faster would probably take a major redesign. I believe that some (most?) wind power machines use variable pitch blades to get the best possible performance and handle over-speed wind.

 

[justDIY]

check out the SEPIC design for a switchmode circuit ... the input and output voltages don't need to be related, so in periods of low wind speed, and your genny is only putting out 10v, your sepic circuit will boost that to 24v ... on a high wind day, your genny might put out 30v+ and the sepic will buck that down to 24v.

although I'm not sure this sort of setup is recommended by the wind generator folks... most of the computerized generator controllers I've read about have a cut-in speed and an over-speed limiter ... when the wind is low, the controller lets the genny spin freely (open circuit), trying to catch the wind... once the rpms come up, the controller switches in the charging circuit, which loads the generator down... if the winds are too strong, the controller switches in some diodes or a heavy resistive load to slow the generator down (regen braking), before applying mechanical brakes ... too much speed and the genny will self destruct since it's pretty big and heavy.

 

[charles25]

Thanks for the suggestions. I found a PWM kit in allelectronics.com catalog. It has an input range 2.5-35vdc and an adjustable output of 8-35vdc 6.5 Amps Not too shabby.
Can anyone think of a reason that a PWM converter would not work as a battery charger?
Thanks

CjK

 

[Oznog]

Can anyone think of a reason that a PWM converter would not work as a battery charger?
Thanks

CjK

Well here's a problem. The wind generator can only put out so much power. Look at how a boost DC-DC works. It increase the ON time where the inductor's shorted across the source until it makes the required output voltage. The current only flows to the output during OFF time.

With the battery low, it will try to increase the ON time to draw more current which may drag down the gen's output voltage. Hopefully your PWM chip has a limit so it won't leave it at 100% ON time. Still, it could get stuck in a situation where the generator COULD have put out at most 500mA @ 14V (7 watts) @ 30% ON time at a certain windspeed, but the converter was determined to make 24v and the batteries would need 8 amps to get there. So the PWM converter increases ON time until it's at 95%, the gen puts out 600mA but is dragged down to 2v (only 1.2 watts). It's missing the maximum power point that finds the best loading for the genny at a given windspeed and delivers the maximum chare current to the battery possible for that condition.

 

[charles25]

Right. The batteries rarely get low though. They are there for backup in case of power outage. The inverter sells or pushes access generator and solar power back out the AC input to reduce load and will sell back if the loads on the AC side are low. SO the batteries are always at 25.6 volts or higher. Any thing above that will get pushed out the input on the ac side.That being said. I am trying to get the generator up to charge voltage of 25.6+ using the PWM circit mentioned. The wild voltage nature of the input does make this a challenge. Companies that make these controllers probably use computer software and algorithms that I don't have a clue how to implement. I would be happy to see a little charge at low wind though.20 + MPH winds will give me plenty. I just want to pick up a small amount at low RPM.
I have another generator that will give me 28 volts at about 1/3 the rpm as the one Im using. Problem is I'll need a bigger blade to turn it. Thats an upgrade I will do later. I will play with the small one and get all I can from it first.Thanks
CjK

 

[eblc1388]

I have an expensive inverter feeding 120v AC into my home, it is also capable of selling power back to the utility.

Are you sure you can do that?

I'm sure that you can reduce your power consumption from utility by providing part of your household loading via other means. You can also feed power back to the utility grid as there is nothing(in electrical sense) to prevent you from doing so, but as far as I know most household energy meters would not "reverse" when energy is flowing backwards. So in effect you are doing so for free(to the utility).

 

[Nigel Goodwin]

Are you sure you can do that?

I'm sure that you can reduce your power consumption from utility by providing part of your household loading via other means. You can also feed power back to the utility grid as there is nothing(in electrical sense) to prevent you from doing so, but as far as I know most household energy meters would not "reverse" when energy is flowing backwards. So in effect you are doing so for free(to the utility).

Presumably you have to arrange this with your Electricity company?, I doubt they use your exisitng metering for the purpose.

BTW, most electricity meters work quite happily backwards, the old mechanical ones! - which are by far the most common (mine's LCD, the readers hate it! )

 

[eblc1388]

BTW, most electricity meters work quite happily backwards, the old mechanical ones! - which are by far the most common (mine's LCD, the readers hate it! )

Yes, the rotating disc does revolve backwards as it should but the "digital" counter or pointers don't. There is some mechanical means to prevent it counting backward.

In fact, backward power flow is a "protection" or tempering prevention feature of energy meters.

 

[bryan1]

Hiya Charles,
With that first motor you mentioned have you done a lathe test to see what voltage and current output it does at different rpm. Also you haven't mentioned what blades you are using like how many blades, what diameter they are and what's the T.S.R. rating of them. I'm into making my own wind gennies and so is a number of my friends and we have never bothered trying to double the voltage output, we just design a genny to output what we want in the design stage. I've found plenty of DC motors and only 1 sofar has made it as a wind genny. That one is an old tape drive motor off a mainframe and it's running a 8 foot 2 bladed prop to get the speed for charging a nicad battery setup. If you supply some more info on your setup like I've mentioned above then maybe we help a bit more.

Cheers Bryan

 

[Nigel Goodwin]

Yes, the rotating disc does revolve backwards as it should but the "digital" counter or pointers don't. There is some mechanical means to prevent it counting backward.

In fact, backward power flow is a "protection" or tempering prevention feature of energy meters.

It wasn't on old ones!.

 

[philba]

On the subject of "turning the meter backawards" - I know that this is done in a number locations. Usually it is manadate by law as part of a package to encourage alternate small scale energy production. Selling your excess back to the power company is a definite incentive though I have heard there are very few takers. I believe (with no real basis other than anecdotes) that it involves a special meter.

I attended an atmel seminar about a year ago and they went over a case study of electic meters. There has been a huge amount of effort put into anti-tamper, anti-circumvention in the last few year. Most of the code in a modern meter is for that. The guy stated that "most products are designed for third world countries". I thought it was an odd and somewhat non-PC statement.

 

[Oznog]

BTW, most electricity meters work quite happily backwards, the old mechanical ones! - which are by far the most common (mine's LCD, the readers hate it! )

Yeah they have to. You don't pay for reactive power... which means that during a part of the waveform it must run backwards.

An electronic meter could be modified to stop counting backflow that occurred for more than one cycle, but they'd have to go out of their way to disallow it.

At the current prices per kw/h, you can't make a great deal of money at it. Although... wait, this is badly OT, look for me starting another thread about my friend in Houston where the apt management company made up exorbinantkw/hr prices.

 

[charles25]

I use the ametek 99 motor as recommended by this guy; www.tlgwindpower.com I am also running the quadraflex AL blades offered by him. He has as much on homebrew wind gennys as I"ve found anywhere. I have a larger motor from a DC powered Clarke brand floor scrubber . Low RPM high volts are what you want for a good generator. I'm getting a larger rotor soon to try the clarke motor. Mean time the wind quit blowing here in Iowa. But the sun is shining. I'm waiting on my PWM DC convertert kit to arrive so I can try that out.
Later CjK

 

[verytricky]

Yes, the rotating disc does revolve backwards as it should but the "digital" counter or pointers don't. There is some mechanical means to prevent it counting backward. In fact, backward power flow is a "protection" or tempering prevention feature of energy meters.

This is not always the case. On the farm we have eight power meters. Only one has the reverse block ratchet.....