Pulse Width Modulation Diversion Regulator latest

[design4p]

Hi,

I'm new to the forum but already got solar panels and would like a wind turbine.  Theonly job the turbine needs to do is to power an immersion heater (or combination of heaters) in my Heat Bank cylinder.  From there the hot water can be used for DHW and underfloor heating.

I am very impressed with the forum and I have read many messages from experts like Ivan, Jack, marbert and lots lots more informed people.

What I would like to know is the latest situation on the Pulse width modulation diversion regulator design.  I know there is an interest in such a device and I have even read that Navitron maybe developing such a device.

Regards John in North Wales

[aa44]

I'm in the same position as design4p.  Is there a box of tricks available now that allows a small (1kw) wind turbine to be connected to an immersion in a thermal store?

Thanks very much.
AA

[Justme]

Yes its called a wire (as long as the turbine output is rectified to dc or ac & not "wild" 3 phase) & as long as you spec the turbine & immersion size to the storage tank & heat load demand properly no control system needed.


You could add a simple stat to the tank so when its up to full heat it either breaks the turbine or diverts the power to a dump load.

[aa44]

Justme, I fear that you assume that I have a load more knowledge about how to set these things up than I actually possess.

[Ivan]

Justme, unfortunately that won't work. The load will be too great to ever start the turbine (like trying to start a car moving in 5th gear).

[Baz]

In a bit more detail; - a typical wind generator is 48v (other voltages are available) so it can only drive about 250W into a normal mains voltage (240) heater element.  Low voltage elements are available but expensive. Then as mentioned the resitance of an element designed for 1kW at 48v is so low that it provides a very high retardation effect whent he wind is low, so the generator can barely get going.
Perhaps you already understand that which is why you ask for a PWM diversion regulator.
The electronics would not be difficult but potentially not commercially viable. It still needs the special heater element so all in makes wind to DHW even less ecenomic sense. I think it would be interesting for an air cooled load ( say 300 W) together with switched loads thus reducing the strain on the transistors and effect of circuit failure. A fully variable load allows optimisation to the pwer curve of the turbine and power extraction at low wind speeds.

What I think is better is a mains inverter (ie 48v to 240v) whose output voltage is variable depending on generated capacity thus controlling the power delivereed into a standard heater element. This enables the element to be used on grid too. Every other application wants fixed output voltage so this just isn't available.

[EccentricAnomaly]

In a bit more detail; - a typical wind generator is 48v (other voltages are available) so it can only drive about 250W into a normal mains voltage (240) heater element.

120 W, surely?

240v/48v = 5.  5 squared is 25 (1/5th voltage, 1/5th current).  3000 W / 25 = 120 W.

Or is it past my bedtime?

[ericw]

Don't you really want a variation on the buck-boost converter (http://en.wikipedia.org/wiki/Buck-boost_converter)  with a control circuit that increases the output voltage (and hence the load current) to keep the input voltage fixed (eg 48v) ?

[peter999]

 Would it not be easyer to power the heating element from the MAIN battery bank ie when the main battery bank reaches the desired max voltage say 14.6v for a 12v system the dump load controller connects the heating element to the MAIN battery bank untill the battery bank voltage drops to the desired voltage say 12.7v for a 12v system, this way the turbine is always loaded by charging the batteries and the battery bank takes the load of the heating element thus not stopping the turbine from spinning but still provides heat to the water and protects the the battery bank from over charging.

or have I missed somthin.  KISS  Keep It Simple because im Stupid principal

[aa44]

If I went down the battery bank route and my sole purpose was to use the turbine to heat water, then what would be the smallest battery bank that I could get away with?  (My planning application includes a 1 kw turbine).  I don't have any requirement to store any of the energy, I just live in a windy place (Shetland) and it seems a pity not to use the available wind power to help with the hot water to the house.

Thanks very much.
AA

[peter999]

 How much water are you trying to heat and to what sort of temperture and how ofter?

form this we can work out what size of battery bank you require or if you can get away with a small battery bank just as a feeder supple a bit like a large capacitor or if you will need a full battery bank. do you know the average annual wind speed for your location at 10m?

regards Peter

[aa44]

The average wind speed is about 7 m/s.  My plan is to have a thermal store with an air source heat pump getting the store up to about 45 degrees (for the UFH) and the immersion adding a bit to the top for the DHW (say up to 60 degrees).  I am not expecting the wind powered immersion to do everything, just push a bit more heat into the store when the wind is blowing.   

Water use tends to be one bath and one shower in the morning and then small amounts for washing up during the rest of the day.  I might set the ASHP up so that if the store is not at, say, 55 degrees at 6 a.m. then it will feed the top of the store for a while at 55 degrees so that the store will be hot enough, regardless of the weather.

[johnrae]

AA
A 1KW 48volt immersion heater element with a standard 21/4" boss will cost you about £40 (see ebay) which is a darned site cheaper than any battery or invertor concept will cost. 

If you have continuous good wind then simply connect the turbine directly to this element (without any thermal switch)  If you think that the set-up might over-heat your tank then fit a tank stat and use this to control a circulating pump which will then circulate a water circuit through the cylinder into a dump radiator.  This will then take away any excess heat capability.

Although the permanent load of circa 2.3ohms will place a brake on the turbine to inhibit it's starting you can overcome this by instaling a voltage relay which disconnects the load until about 20 volts is being generated.  At this volts the turbine will be running nicely and will tolerate the load then being applied.  You can use a thyristor or similar to do this and once "closed" will remain closed until the turbine eventually stops running.  (I use such a set-up and it works very successfully).   An alternative to a simple voltage switch would be a PWM system to control the "connection" to match the wind power but this would be a much more complex system and simplicity should remain the mandate.

jack

[aa44]

Thanks for that, Jack.

I understand the principle of what you are suggesting but wouldn't have a clue on how to build such a thing.  Is this something that I can buy pretty much off the shelf?

Thanks
AA

[johnrae]

AA
Don't think so but others might know better.  If you want I can send you a simple circuit via PM and you can try an search out a friendly electonics guru.  By the way, I see the immersion prices have now risen to around £80, (they were £40 when I bought mine) apologies on that one.

jack