Author Topic: How to regulate wind generator power to charge battery?  (Read 3374 times)

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zap1

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How to regulate wind generator power to charge battery?
« on: August 29, 2005, 04:53:12 AM »
From www.batteryuniversity.com, lead-acid battery should be charged in multiple stages.

Stage 1 - constant current

Stage 2 - constant voltage

Stage 3 - float charge

How does this applies to wind turbine as the turbine may not be spinning continuously?


Are there any chargers/controllers that will do the above for wind turbine?

I heard about PWM chargers/controller, but they are mainly for solar panel. Are there any PWM chargers/controller for wind turbine?


Thx

Zap

« Last Edit: August 29, 2005, 04:53:12 AM by (unknown) »

Flux

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Re: How to regulate wind generator
« Reply #1 on: August 29, 2005, 01:12:18 AM »
These ideal conditions are difficult to implement in a system when charging and discharging is often going on at the same time, even with solar it is difficult but less so.


With wind you have to take the power when you can get it. As long as the batteries are not undersized there is no need for the constant current phase and it would waste a lot of the available power to use it.


As you near full charge your charge controller provides the constant voltage phase but it is always  a difficult decision to choose the voltage.


For wet batteries that have been well discharged it ought to be about 14.4v but with a varying charge that may stop at any time it becomes difficult to decide when equalising is complete and you need to change to a lower float voltage, say 13.6v.


If the batteries have not been significantly discharged then you don't want the equalising voltage.


Gell cells are even more challenging as they don't like equalising charges.


I have often thought about this and it would be interesting to have other folks views on this.


I tend to settle for a float voltage of 14v and occasionally if the batteries have been low, raise it to about 14.4 for a few hours.


Flux

« Last Edit: August 29, 2005, 01:12:18 AM by (unknown) »

zap1

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Re: How to regulate wind generator
« Reply #2 on: August 29, 2005, 08:44:09 AM »
So is it possible to charge a battery with a wind turbine without a charger/controller? I'll use a dump load to prevent overcharging the battery.


My setup would be like this:


Wind turbine -> rectifier -> battery

Dump load -> battery


Will the battery be damaged if the current from the turbine exceeded the charging current limit of the battery?


Flux, what charge controller do you use in your setup?


Thx

Zap

« Last Edit: August 29, 2005, 08:44:09 AM by (unknown) »

Flux

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Re: How to regulate wind generator
« Reply #3 on: August 29, 2005, 09:50:51 AM »
As long as your battery bank is large enough, which it is normally from the stand by capacity point alone, you can dump all that the windmill can produce into the battery during the bulk charge phase. If you had a large windmill and a small battery you would need a current limit, but normally the battery is large enough to take all that is available.


As the battery charges you reach a point where the voltage will start to rise rapidly with current and this is where your dump load comes into effect. It clamps the voltage to a set value so the battery still takes what it needs to continue charging and the rest of the current is diverted to the dump load.


The final part of the charge cycle takes a fair while, you can't rush it, the battery just won't accept a rapid charge during the final phase.


I don't know exactly how many amps you can put into a battery in a low state of charge but 30 to 40A seems to be ok for a 100AH battery and you normally need more capacity than that for a reasonable storage.


I just use shunt regulators that divert excess charge into resistors as the voltage rises, I think this is common practice, the exact method of operation of various controllers differs, some switch a resistor large enough to dump all available power in at one voltage and switch it off again as a slightly lower voltage, others do it in several steps with a few hundred millivolts between them and others use PWM to alter the ratio of on to off and this has much the same effect as a variable resistor that keeps the voltage constant. Some do this at a few hundred Hz and the dumped current consists of a series of current pulses of differing length. Others chop at a much higher frequency and use a flywheel diode and an inductor to maintain a smooth dc current of the right value to keep the voltage constant.


I build my own but any form of controller designed for wind use will be ok. Don't use a solar controller that open circuits the charging circuit, this is fine for solar but windmills can reach high voltages and speeds and must never be open circuited.


I hope this helps you, chargers designed to charge a battery from the mains can use the 3 stage ideal charge cycle but when you are charging and taking load together you have to use the power when you have it.


As long as you do not let the batteries discharge to far or let the voltage rise much above 14 v there is not a lot more you can do.


At most don't discharge more than 80% and preferably not more than 50% unless you have some back up charger in case of low batteries and no wind.


In remote places I believe they use a large windmill to charge a lot of small batteries for members of the community and they are discharged elsewhwre.


In that case each battery could be charged under near ideal conditions with suitable chargers as long as there was sufficient wind, but that is a special case.


Flux

« Last Edit: August 29, 2005, 09:50:51 AM by (unknown) »

Nando

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Re: How to regulate wind generator
« Reply #4 on: August 31, 2005, 08:15:47 PM »
Flux:


I need to contest your reply, if you have a charger controller that can supply the battery charging current plus the load current, one can do some if not most of the battery charging profiles.


If the load is variable and the charging power is strong enough, the charger will charge the battery in bulk conditions, Float and equalizing may not occur if the load is present but many times at night those will go into operation.


Regards


Nando

« Last Edit: August 31, 2005, 08:15:47 PM by (unknown) »