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Forum Index : Other Stuff : P&F Micro Hydro - charge controller question

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flyingfishfinger
Newbie

Joined: 12/09/2020
Location: United States
Posts: 1
Posted: 03:38am 15 Sep 2020
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Hi,
I'm new to this space - we recently purchased a property with a small stream on it. I was able to pick up a P&F washer for almost nothing after I found the conversion articles on it, so I wanted to give micro hydro a shot.

I'm thinking of wiring it as 7x2C to charge a 12V battery depending on the water flow (we are taking our "summer survey" of that in the coming weeks), but I have some questions regarding a DIY charge controller in general

1) For a water turbine, I know that we don't want any sudden changes in velocity, hence the need for a dump load. However, I'm not 100% certain WHAT should stay constant.

Is it output power, current, rpm, or something else, assuming a constant water flow?

2)I found a PWM charger that looks like it should work with hydro, given an adjustment to the dump load algorithm. Depending on the answer to the above question, that should be fairly simple. is there anything fundamentally wrong with my thinking?

I found this controller I might like to start with (schematic / architecture, not specifically this board): https://www.opengreenenergy.com/post/arduino-pwm-solar-charge-controller-v-2-02

I'd appreciate any thoughts or advice on the matter.

Thanks,
Rafael
 
Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 3371
Posted: 04:50am 15 Sep 2020
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I think first build your dam, pipework, and turbine, and get that rotating.

Now that will produce a fairly uncertain rpm, and have an unknown torque capacity, and the alternator output voltage when rectified needs to fall within a usable voltage range.

If its going to be a 12v system, the dc voltage from the rectifier must be at least 15v, and ideally no more than probably about 30 volts maximum. Two ways you can control that, electrically, by re-configuring the windings, or mechanically through an adjustable ratio  pulley system or a gearbox.

You will need to measure the output power somehow to "tune" the system to generate a suitable range of working voltages before you can even think about a control strategy.

I bought a very nice Turnigy power meter from e-bay which would be an ideal tool for something like this. These work from 4v to 60v and up to 150 amps.

https://www.ebay.com.au/itm/150A-Digital-LCD-Watt-Meter-Power-Analyser-Solar-Caravan-Anderson-Plug-Tool/232109268425?hash=item360aca5dc9:g:w0cAAOSwHVhdy4~c

Run your turbine without any load and measure the max dc output voltage.

Then start adding some load in stages, lamps, resistors, heating elements, whatever junk you can cobble together.  As you add more load, the voltage will be pulled down, and the current rises.  But the power output will peak at some specific value of voltage and current.

That too needs to be within a useful range, ideally around 15v to 20v for instance.

Experiment a bit with different turbine nozzles, pulley ratios, or winding configurations to get an optimum result within the usable range.

When you have all that worked out, you will know four things.
Max voltage running unloaded.
Min fully loaded voltage.
Max full load power.
Max full load current.

When all those figures are known, you can then start thinking about building a control system for it.

My guess is that a low cost bog standard 12v MPPT solar controller should work very well, or at least as well as anything else.
Cheers,  Tony.
 
mab1
Newbie

Joined: 10/02/2015
Location: United Kingdom
Posts: 26
Posted: 08:22pm 15 Sep 2020
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well to try and answer the two specific questions:

1) For a water turbine, I know that we don't want any sudden changes in velocity, hence the need for a dump load. However, I'm not 100% certain WHAT should stay constant?

From my own experience of hydro, I'm not sure that sudden changes in generator 'velocity' are an issue - the velocity of the water in the pipe is more of an issue - hence you need to turn valves off slowly to avoid 'hydraulic ram' effect.

Ideally, RPM will stay near-constant at a speed that best suits turbine & the velocity of the water jet, but to keep RPM constant you need to keep the voltage constant as far as possible. if the generator is connected directly to a battery then the current will be fairly constant but as the voltage on the battery rises, so the RPM of the generator will rise a bit - in practice I don't think this variation is an issue to worry about as the Max-power-point of a hydro turbine is fairly broad.


2)I found a PWM charger that looks like it should work with hydro, given an adjustment to the dump load algorithm. Depending on the answer to the above question, that should be fairly simple. is there anything fundamentally wrong with my thinking?

I did have a quick look at the link but it seemed to me that that controller wasn't a 'diversion' (to dump load) controller but instead just disconnects the 'solar'? - possibly i didn't look long enough to see a diversion setup, and it could be adapted to work as a diversion controller anyway - if it can do diversion then yes it should work.

BUT: if your thinking of using the PWM controller to run the generator at constant voltage that best suits the turbine regardless of the battery voltage? - that should work in theory - I suppose.


Fundamentally though I think Warpspeed is right:- Get it up & running 1st and then you can get a much better idea of what you need to do to get the max power / efficiency.


I use an induction motor as generator and rectify then feed it into a common solar grid-tie inverter - as the GTI has a MPPT function it automatically finds the best load to run the generator to keep the turbine RPM at the max efficiency.
 
Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 3371
Posted: 11:02pm 15 Sep 2020
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For a micro hydro, where you have sufficient fall, but limited water volume, it will require a smaller high rpm turbine.

For something like that, a permanent magnet dc brush motor may be worth considering.
A large treadmill motor might be rated at something like 180 volts, 4,200 rpm, and 10 amps full load.

Now the 10 amps part of the specification must never be exceeded, to prevent overloading and overheating of the windings and commutator.

But the rpm and voltage part are much more flexible and will be proportional.

Voltage will reduce linearly as we slow the beast down.

At roughly one tenth of the rpm, (450-500rpm?) we might expect pretty close to one tenth of the voltage, perhaps about 18 volts dc. Still with our 10 amp current limit.

Its only 180 watts, but over 24 hours its still a healthy 4.32 Kwh which would be a very useful amount to supplement some solar panels in very cloudy weather.
Edited 2020-09-16 09:46 by Warpspeed
Cheers,  Tony.
 
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