Windmill direct to H2O heater

[stellrecht]

Greetings,

I'm working at hooking my 12 volt wind generator output directly to my 100 gallon water heater. The generator's output varies with wind speed from 0 to ~50 volts (rectified DC voltage with < 10% ripple). I'm expecting wattage to vary from 0 to 500 watts based on typical wind in my area. When I connect a 12 volt 600 watt water heater element to the generator, it stalls and won't push more than a couple volts. Is there a cheap way to avoid stalling and maximize the output to the heater element? My goal is to avoid batteries and inverters and stick to a K.I.S.S. principle. Thanks in advance for any ideas.

Moved to Newbies. TW

[Flux]

With wind nothing is simple and most things work backwards. KISS usually means a severe compromise along the way. If you can live with that then ok.

You don't get a good direct match with heaters. Ideally you need to hold the heaters out of circuit during the start up phase where the prop is stalled. As you seem to be using rectified dc your best option would be a series mosfet switch but you are violating your KISS principle. Mechanical relays are also possible and for some they fall within the KISS requirement but I regard them as added trouble to be avoided where possible. Static relays ( triac based) may work on dc but the wind would need to drop very low to release it.

With the load switched off during start up you remove the big problem. You may or may not get a good enough match over your wind speed range with a fixed value heater. For your tiny set up it will most likely be ok as in light winds you will produce no useful heat. Matching the high winds over a limited range should be ok.

Dave B has done work on this try looking at what he has done and no doubt I will have given information in those posts.

Flux

[Dave B]

Hello,

  How big is your diameter and what type of blades ? The first step is to accept the amount of power capable for your size machine. A decent 10' machine could generate 500 - 1000 watts in 20 MPH winds. It takes a lot of power and or time to effectively Pre-heat / heat water. Without a controller it will be a give and take.

 Obviously you need less load (higher resistance) to allow start up of your machine. Adjusting the load will basically give you 2 scenarios. Either you will have a machine that starts and runs in lower wind and tops out when the real wind starts or you might be able to tweak the load so your machine starts in higher winds only giving you more output in the upper wind speeds but spends most of it's time stalled out never running.

 There is no substitute for swept area when trying to heat with the wind. Your blade design will also have a large impact on the amount of start up and run torque available. The flat type blades with little twist seen mostly on this site are basically fairly fast running designs. The power from these really comes on after getting up to speed. These work quite well for charging batteries as there is little or no load until they get up to battery voltage so they free wheel in low winds.

 A direct resistive load without a controller will need start up torque in these low winds to get started. Again, raise the resistance (value) and or use a blade designed for higher torque in the lower wind speeds. At a constant 500 watts it would take approx. 12 hours to increase the temperature of 50 gallons of water 50 degrees F. It takes a lot of power and or time to heat with the wind.

 I think if you search a bit on this site you will find more useful information on heating. I've been heating direct for quite some time now, it is a totally different thing from the norm here of charging batteries.  Dave B.

 

[stellrecht]

Diameter is 5' in a 6 flat blade configuration. It appears that I have more research to do and perhaps I need to reconsider my power availability. A variable resistance heater element that would decrease resistance with increased temperature might do it, but is probably vapor-ware and would seem to leave the KISS principle behind.  Thanks for your input, I'll continue to search the previous posts.

[electrondady1]

there has been some experimental work done using large capacitors as an aid in startng under load.

http://www.fieldlines.com/story/2006/9/14/17359/1190

http://www.fieldlines.com/story/2006/9/16/225354/917

[electrondady1]

here's another link

http://www.fieldlines.com/story/2006/10/29/201016/09