water heater element as air heater

[dscheckman]

Hello All, I'm looking for a cheap, easy, short term solution for a dump load for my newly online micro hydro. A 2000 watt 120 volt water heater element translates to the right load for the 48 volt =/- 300 watt output of my system, and is well within the limits of the tristar 45amp controller I'm using . However, for the moment I'd like to avoid a plumbing project. Can I use the hot water heater element as a resistor, mount it safely and just heat air with it? Thanks for any advice folks can give me on this question.

[vawtman]

I wouldnt use a water heating element there designed to be in water.

 Maybe a stove burner.

[wooferhound]

It would work if it were submerged in water.

[ghurd]

Will the system be expanded, or is there another reason not to go to a permenent dump load now?

Hmmm... Is the dump load needed greater than 310W, or ~5.6A at ~56V?

G-

[jimovonz]

I wouldn't recomend it. Water has a thermal conductivity around 25 times that of air (temperature dependant). Without getting too hung up on convection etc, I would guess that the element would experience around the same temperature rise at 2000/25=80W dissapation in air as it would at 2000w dissapation in water.

It's not hard to make a dump load of practically any size, cheaply and from common parts. I have made four in a similar fashion to this: http://www.fieldlines.com/story/2006/2/28/114556/473 for around $US10 after a bit of scrounging around. I would add that on the 1st one I made the nichrome has become rather brittle and a few of the pieces have broken off (possibly when something has hit them in the wind). I would further de-rate the nichrome when making another to limit the temperature.

[dscheckman]

Only reason not to go permanent now is time and work. I'm looking for a quick [very], cheap solution so I can run the system now. During the building season I have very little extra time or energy. In the long run, I have a salvaged solar hot water system to set up that I will add an element to as a dump load and supplement to the solar. 310 watts @56volts would be cutting it close. I haven't run the system under enough conditions to know the absolute max, so I'm adding a bit to the 250-300 watts we were getting last weekend. thanks.

[dscheckman]

I found a couple of different replacement commercial stove or warmer elements 2000 watts 120 volts. Any comments on those for the above purpose? About $50. More than I'd like but might be quick and easy to set up. Seems like the air heater units they sell for diversion loads are about $235 and more watts than I need. Thanks for any comments

[jimjjnn]

I bought a 220 Volt dryer assembly for my daughter's Sears clothes drier fo $29 at Sears parts store. Seems alot cheaper that way and can be cut down to whatever resistance you need. There were 2 elements on the frame.

[jimovonz]

If your really up for a quick and dirty solution then why don't you just drop the heating element into a reasonable size bucket as wooferhound suggests? The water will limit the temp to around 100degC which may make a plastice bucket softer but shouldn't compromise it. As a precaution I'd rig up a wire support to keep the element from touching the sides (or use a steel bucket/drum). 20l(~5.3USGal) buckets are common here. Without considering any losses to ambient, it would take approx 1.9kWh to raise 20l water from 20degC to 100degC (not boiling). This represents over 6 hours continuous at your max anticipated output of 300w. In reality you would never get there because your bucket would loose heat too fast once it warmed up. There is absolutely no chance of boiling it as this would take a further 12.5hours at a continuous output of 300w (with no loss to ambient). Some water will be lost however due to vaporisaton so you would have to top it up periodically.

[luv2weld]

Several others already said--No to using the heater you have already unless it's

in water. It will probably self-destruct. But as jimovonz and wooferhound say-

drop it in a bucket or barrel of water. I'd use a barrel, anywhere from 20 to

55 gallon. That way you don't need to check every 30 minutes to make sure there

is still enough water in it. Oh, and put the heater at the bottom of the barrel--

not the top!!

The other options mentioned are all excellent. Just remember to protect air-type

elements from accidental contact with things. Don't want to burn the place down!!

Ralph

[Ungrounded Lightning Rod]

It's a micro HYDRO.  Why a bucket?  You've got all this water flowing whenever you need to dump power.  Put it in the water downstream of the turbine - with a guard screen to keep the fishies a few inches away.

And don't worry too much about thermal pollution.  On the average the heat would have ended up in the water without the mill anyhow, due to friction.  (If your controller is bang/bang you might end up heating the water from battery power when it's flowing slowly - but not for long.)