three phase immersion heater

[SparkyTris]

I have an idea but I'm sure I am missing something possibly to do with efficient power transfer, hopefully some of the erudite contributors to this forum can comment:
Consider a cheap "chinese" wind turbine. nominally 24V 400W, price about £140 ex ebay. They are what they are. Ive got experience with them and imo they are good value for money. I think in practice they realise 100W through winter in northern scotland.
I have been using them "as purposed" to keep a set of batteries charged for DC power of low power off grid wifi cameras. Fine.

My thought is to try to use one of these wind turbines to heat a mass (lets say water in the first instance owing to ease of coupling) in as SIMPLE a configuration as possible.
these chinese turbines are based on a rotating permanent-magnet alternator. there are 3 wires coming out of the turbine which I think you would say provide "wild AC" at varying amplitudes/frequencies depending on windspeed.
I would like to connect the three wires directly to a 3 phase immersion heater.

1. I cannot find a 3 phase / of-the-order-of-100W immersion heater to buy-off-the-shelf which makes me think that what Id like to do is fundamentally a non starter but I cant see why

2. I *can* find a 3-phase 9kW immersion element, but clearly my chinese windmill wont touch the sides with that

3. I *can* find various 12/24V DC immersion heaters (as seen in waste-oil-heater preheat tanks) So I am considering simply rigging 3 of them up in star configuration to suck it and see. I am slightly concerned that being DC there might be problems when feeding with wild AC but no idea what. Yes, I could simply use the windmill to charge the 24V battery bank then use the DC from that to feed the little element but I want to make the power delivery system as simple as possible.

 

[flameport]

A 3 phase immersion heater is just 3 individual elements connected together in star or delta, depending on the voltage of the elements and the supply.
There is nothing special about them.
AC or DC won't make any difference either, it's just a length of resistance wire sized for a certain power output when a particular voltage is applied to it.

 

[ericmark]

Easy option is to rectify and then connect to single phase heater.

 

[Alec_t]

AC or DC won't make any difference either

..... providing there isn't some DC-expecting electronic thermostat inside the heater.

 

[SparkyTris]

Easy option is to rectify and then connect to single phase heater.

this thought crossed my mind too but that will lose precious watts won't it? plus wanted to keep it as s i m p l e as poss.

 

[Jackrae]

There will be some loss due to the diode forward voltage but if you use schotty diodes that can be kept to a minimum. One problem you will come across is that a permanent immersion load will act as a brake on the turbine and prevent it turning in all but a good breeze. In my system I had to install a voltage control switch (thyristor) which kept the immersion heater disconnected until the turbine was producing sufficient voltage (typically 50% of rating) before the immersion was connected.

 

[ericmark]

@Jackrae makes a good point, I tried to make a few wind generators, and a standard alternator is designed to run at 6000 to 10,000 revs, even with re-winding it still needed gearing up, and the problem was the rotating weight, if a gust hits the blades with no load, they spin, but if a heavy load, they bend back, and rap themselves around the pole unless braced in some way.

So the PWM and MPPT controllers are used, these are inverters which allow the wind charger or solar panel to vary the output voltage to best match the output, so the wind charger may be producing between 6 and 60 volt, but the output to devices and battery is maintained at 12 volt.

With solar panels they are DC to start with, with wind chargers it is more likely AC, even the bicycle hub dynamo is AC in spite being called a dynamo, but the frequency varies with speed, so any transformer will waist power, transformers work best at one frequency, so to convert the energy to a usable form, we turn in into DC then into AC at the frequency we want to transform it at, then into DC again and then back to AC at the frequency we want to use it at, this is the basis of most switch mode power supplies, many MPPT controllers are designed for combined wind and solar power.