Author Topic: Advice needed building a dump load for 10' windmill (Read 7542 times)

Tink · « **on:** October 23, 2009, 07:49:02 AM »

I'm building the dump load for my 10' Axial Flux windmill . I'm using 6 of the Ohmite C300KR50E resistors for a heating element wired series and parellel to give me 1850 watts (24 volts) at full blast. I don't know how hot this thing is going to get so I'm at a loss as to what wire I can use to wire it up with. Someone local said I should use kiln wire. I've mounted the resistors in a 'main box' that I gutted out. I don't know if it will get hot enough to fry the gray paint on the box or not. Included is a photo of the box with resistors mounted. I'm wondering if I'll need a shield mounted behind the resistors. Where can I get kiln wire? What should I use to connect the 2/0 wire to this unit?

Any suggestions?

Thanks in advance, this fourm is invaluable to us guys who don't know what the heck we are doing. I've uploaded a photo but haven't been able to figure how to insert it into the post yet.

Tink

DanB · « **Reply #1 on:** October 23, 2009, 07:56:45 AM »

What sort of controller are you using, and can you tell us the ratings of your resistors (the resistance, and the power rating)?

Tink · « **Reply #2 on:** October 23, 2009, 08:09:58 AM »

OK, these are 300 watt each and .5 ohm. I'm using the Xantrex C-60 set for dirversion load. My solar system consists of the Xantrex SW4024 inverter. C-60 controler for the 10 120watt panels and a Crown 935amphour 24volt battery.

Resistors:

12 volt d.c. 300 watt (.50 ohm) air heating diversion load made in

the U.S. by OHMITE.

Model # C300KR50E.

Watts: 300

Ohms: 0.5

Also known as a Vitreous Enameled Resistor.

These loads can be wired in series to increase voltage or parallel

to increase amperage.

Mounting feet are included with each unit as seen in the picture above.

A simple way to utilize excess power from a solar array, wind generator

or hydro-electric generator.

For the most efficient operation, they should be mounted vertically to

take advantage of the convection movement of the air when they heat up.

You can wire multiple units together in series or parallel or

series/parallel to get any combination of voltage and amperage

you need.

Length = 8.5"

Always mount on a non-combustable surface.

This item is RoHS compliant.

Thanks,

Tink

ghurd · « **Reply #3 on:** October 23, 2009, 08:26:37 AM »

I don't see how they will be wired to stay in spec for themselves and the controller and 1850W.

Only thing I can figure is they could be wired to total 0.75 ohms, to dump about 38A for 1100W.

I connect the wires using unusual sized battery type terminal, held to the resistors with brass bolts.

If I am worried about the wire being too hot, I use long bolts and a couple extra nuts to hold the wire terminal a couple inches away from the resistor terminal.

G-

Tink · « **Reply #4 on:** October 23, 2009, 08:47:27 AM »

ghurd,

I was told to wire them as 3 strings of 2 each wired parellel to achieve 1850 watts. Wouldn't this give me the 24 volts I need for my system and the rated 1850 watts? The advice I got may be wrong. My only experience in wiring up series/parallel circuts is with battery banks. I like your suggestion to use the long brass bolts. What type wire do you use? How do you connect the incoming wire from the dirvision load controller to the heating unit?

Thanks,

Tink

ghurd · « **Reply #5 on:** October 23, 2009, 10:07:59 AM »

With 2 in series, the 3 pairs in parallel, that's 0.33 ohms.

Dumping at 28.8V, that's 86A, which is way past the 60A the controller can handle.

That is a total of 2488W, or 415W in each 300W resistor.

Not good.

Wired 3 in series for 1.5 ohms, then paralleled with the other set, that's 0.75 ohms.

Dumping at 28.8V, that's 38.4A, 1106W or 184W per resistor.

That's fine.

Except that's pretty light on the dump capacity for a 10', unless you furl early like recommended, maybe round 800W.

It would keep the duty cycle down, so at the worst the resistors would be averaging about 134W. The 300W resistors will not get super hot with 134W in them.

I would not want that box sealed with a lid if it was mine.

That 800W average is about the same amount of heat as some of the Hi/Lo 1750W electric heaters set on Low. Meaning still quite a bit of heat.

"How do you connect the incoming wire from the dirvision load controller to the heating unit?"

Uh, crimp-on ring terminals?

Not sure what you mean. I'd bring in a heavy wire, join it (I'd solder them) to 3 lighter wires to go to the resistors.

I used brass toilet bolts with the goofy heads. Long, cheap, and available everywhere.

The holes in the resistor's terminals will need drilled out, just a hair.

The extra nuts will hold the wire out away from the heat. Common wire would be fine, IMHO.

Don't let wire touch the ceramic part.

I considered adding another pair of nuts and a brass fender washer half way between the resistor and wire a time or 2, sort of like a heat sink, but they were not needed because I design my stuff to stay cooler than most people do.

G-

SparWeb · « **Reply #6 on:** October 23, 2009, 12:44:37 PM »

My dump load's resistors are Ohmite 2.0 ohm, rated at 300W each, connected in parallel. In case you can't read the displays, it's 34.4 degrees Celcius, and the voltage across the bank is 5.1 volts. A bit of math gives me a current of about 10.2 amps. The IR thermometer was touching the resistor. I can take my glove off and put my bare hand on the resistor. If it's dumping more than 10 amps, doing that gets very uncomfortable.

SparWeb · « **Reply #7 on:** October 23, 2009, 01:30:49 PM »

Uh, did I mention that the resistors are neatly enclosed inside a steel box? Yes I forgot to mention that. Please imagine a steel box around those resistors. They aren't screwed to the plywood wall any more. Got an earful from the other board members the first time they saw that picture, I don't want another lecture!

:^P

Tink · « **Reply #8 on:** October 24, 2009, 06:39:29 AM »

ghurd,

Thanks for the info. Now I'm going to get out my Ohm's Law and digest all this and get back to you later. I'm wondering if it is possible to wire as you said and add another string of 3 to get up to the wattage I need. It looks like the guy I got these from didn't know his Ohm's Law. I should have done the math myself.

Tink

Tink · « **Reply #9 on:** October 24, 2009, 06:45:18 AM »

SparWeb,

Your Ohmite resistors look just like mine (C300KR50E) what is the model # of yours? Great picture, I haven't figured how to get my photos in the post yet, any suggestions? I was able to upload it but can't see how to insert it in the post.

Tink

ghurd · « **Reply #10 on:** October 24, 2009, 07:42:37 AM »

Sellers are usually just Salesman.

"It says 300W right on it, so it will dump 300W". Wrong.

Or they do the math with 24.0V instead 29V.

Adding another string of 3, the same as the ones you have, will be pretty close to the max rating of the C60. And will probably go past it during equalization. A little to close for my personal taste.

Myself, if I was using the same model resistors, I would add another string of 2 resistors at 1 ohm each.

C300K1R0E ($28 at Mouser)

At 29V, /2 ohms, is 14.5A, 210W per resistor.

The C60 will carry 38.4A from the existing set, 14.5A for the new pair, total of 53A.

I think that's about as good as it gets, without getting overly complicated.

G-

PS- Link to the photo,

http://www.fieldlines.com/images/scimages/13185/IMG_0155.JPG

Tink · « **Reply #11 on:** October 24, 2009, 08:27:46 AM »

ghurd,

OK, got it and thanks for the upload tip. The light came on in my brain...

Mouser just sent me their hugh cataloge so I'll be ordering those C300K1ROE next payday. As for today I'll be removing the gray paint from the box and re-painting it with stove pipe paint (1200 degrees)and no lid just a mesh screen over it.

Thanks again for the fine advice from all you guys.

Tink

coldspot · « **Reply #12 on:** October 24, 2009, 12:39:17 PM »

tink-

I'd put two 12 vdc 80-120mm computer fans

blowing air across the resistors and out of the box

maybe one in and one out.

(fans wired in series, for 24v)

$0.02

{maybe I use to many salvaged computer fans?}

maybe I just have to many salvaged piles?

Tink · « **Reply #13 on:** October 24, 2009, 12:57:37 PM »

Coldspot,

I was going to put some kind of fan across them. The 12Vdc are good since I have a few laying around anyway. thanks for the input!

Tink

willib · « **Reply #14 on:** October 24, 2009, 06:57:40 PM »

Here ya go Tink, i can link it for you .

http://www.fieldlines.com/images/scimages/13185/IMG_0155.JPG

ps Just click on your photo in your FILES , and copy the link , then paste it here.

Ungrounded Lightning Rod · « **Reply #15 on:** October 26, 2009, 05:05:17 PM »

Hook 'em in parallel with the resistors and they'll only come on when you have power to burn. B-)

Tink · « **Reply #16 on:** October 26, 2009, 05:43:39 PM »

ghurd,

I follow your math but since i'm using the 10' with the heavy duty stator with the round magnets shouldn't I use another string of what I have (3 of the half ohm resistors) to give me 1682 watts and 58 amps dumping 187 watts to each resistor at 29volts? Do you think this would be too much for the C60?

Tink

ghurd · « **Reply #17 on:** October 26, 2009, 06:12:55 PM »

Do I think it would be too much for a C60? Yea, I personally do. I suppose most people would not.

I have heard of some doing fine for a while carrying many more amps than they are rated.

Then again, I have heard of some less than flattering stories too.

It would most probably be OK.

Lame answer. Tough question.

G-

wellusee · « **Reply #18 on:** October 27, 2009, 04:59:54 PM »

Ah! Were in the same boat here.

For now I'm using 10 # 100Watt 24Volt truck bulbs . Its really rewarding to see them light up. The TS60 Morningstar begins a little buzzing for about seven seconds then they all come on together for about twenty seconds depending on wind. I suppose its one way to show someone that the system is working. Now before (experts) ye wag that index finger at me!!! I know, I know it's not the ideal dump load, bulbs blow .

A resistor is the way to go and from a previous posting Volvo Farmer sent a great way of making such http://www.fieldlines.com/comments/2009/9/2/151837/8282/5

I see that nichrome wire is not that expensive on EBay thing is what length and thickness

of it do I need to wind my own 1k resistor for the 24Volt stator?

Anyway I had a posting few weeks ago called Dump Load if you go through it you'll find some good photos of homemade resistors.

Paddy .

ghurd · « **Reply #19 on:** October 27, 2009, 08:21:46 PM »

Not an ideal load because bulbs have a high surge current.

From 6.4.1

"Do not use light bulbs... will fail OR cause the TriStar to disconnect the load.

From 6.1

"The most important factor for successful diversion charge control is the

correct sizing of the diversion load. If too large, the controller's protections

may open the FET switches and stop diverting current from the battery."

That buzzing you hear is the controller PWM trying to start cold bulbs. It is not good.

G-

wellusee · « **Reply #20 on:** October 28, 2009, 12:15:13 PM »

Thanks for that G.

That makes me scratch the back of me head ,so that's what that buzzing is (jeepers).

It would be a tremendous help to turbine builders if there was a set plan to making a reliable 1k resistor like in the way they explain how to wind the coils

(9 coils 14 gauge 70 winds) nice neat easy to follow. For instance so many meters nichrome at? mm thickness wound around ? Diameter secured by ceramic tile or lengths

of windings in parallel .

Probably different for each controller but perhaps not a problem for them guys who don't have to scratch the back of their heads to figure things out.

I think we could be on the cusp of solving this one . One small step for Man.....

Thanks for any ideas.

Paddy.

wellusee · « **Reply #21 on:** October 28, 2009, 01:52:38 PM »

Hi Ghurd and Tink!

I'm following or should I say trying to follow with bamboozled amazement.

When ye get this contraption sorted out could you explain it in Bog English for me.

I imagine when the book is published it will look like the instructions for the Rubik cube. So far ye have been a tremendous help so thanks for taking the time to share your knowledge.

Paddy

Tink · « **Reply #22 on:** October 28, 2009, 09:13:34 PM »

wellusee,

I'm learning as I go on this one. I've never built a DC dump/heater thing before. I need to order two of those 1 ohm resistors as ghurd advised and that will take a week or so to get in but I'll definatelly post photos and explinations of it all so be looking for that. I am really learning a lot from these guys on this fourm.

Tink

Tink · « **Reply #23 on:** October 29, 2009, 07:58:51 AM »

Steven,

What wire are you using to connect the resistors? I see a black and white but what gauge and what temp rating is the plastic covering on the wire? I like the way you have the wiring up away from the resistors. Do yo have a photo of the completed box?

Thanks,

Tink

ghurd · « **Reply #24 on:** October 29, 2009, 09:18:54 AM »

The more I know about nichrome, and the more I try to use it...

The more I Love power resistors.

Everything about nichrome is here, including the stray parts, math and math examples.

I never bought anything there.

http://www.heatersplus.com/nichrome.htm

G-

ghurd · « **Reply #25 on:** October 29, 2009, 10:04:58 AM »

Be careful what type of fan you choose to run from the PWM dump terminals.

A fan with a "regular" motor may burn up in short order.

I have had good luck with brushless (muffin / computer type) fans.

Like I said, I try to design my stuff to stay cooler (not need a fan).

But if you want to use a 12V fan, it needs a series dropping resistor to get rid of about 15V.

For 100ma, that is a 150 ohm 3W resistor.

For 200ma, that is 2 x 150 ohm 3W resistors in parallel.

For 300ma, that is 3 x 150 ohm 3W resistors in parallel.

etc

That said, and the price of 3W resistors and S&H...

Might check ebay for 24V fans. Pretty easy to get one delivered for less than some places will charge in just S&H for the dropping resistors.

Could also use a snap disk thermostat. Maybe 115 or 125F?

If it gets to that temp in the box, then there is plenty of spare power to run a 'normal' motor fan, avoiding the issues related to PWM and over heated motors.

Just stray thoughts,

G-

Tink · « **Reply #26 on:** October 30, 2009, 08:55:42 AM »

G.

Thanks for that source! I've ordered the 1 ohm resistors you recomended from Mouser and should have them in a few days. Then for the wiring it all up.

Tink

wellusee · « **Reply #27 on:** November 01, 2009, 05:46:19 AM »

This is brilliant. It's as close to what I need as I've seen yet.

Will you be able to post some photos of the finished unit?

How many would I ned?

Whats the link to order them ?

I will order them Ohmite resistors but will you still be around if I need help putting them together you know about parallel and series.

Thanks

Paddy.

wellusee · « **Reply #28 on:** November 04, 2009, 03:55:47 PM »

Hi Think . Is it finished yet ? any photos?

Paddy

Tink · « **Reply #29 on:** November 06, 2009, 06:49:28 AM »

ghurd:

I got it done and it works great! Your suggestion did the trick. I got the 2 extra 1 ohm 300 watt resistors and wired it all up as you said and tested it by direct connecting it to an old bank of L16's wired for 24 volts. This old bank I connected to my solar system after disconnecting the big battery. I turned on the solar array and threw the switch for the DC heater/dirversion load. At 22.6 volts and 38 amps it was putting out 450 degrees over the .5 ohm resistors and 475 degrees over the 1 ohm resistors. That works out to 858 watts at 22.6 volts. Here is the photo:

http://www.fieldlines.com/images/scimages/13185/IMG_0156.JPG

Thanks to everyone who offered advice on this. Now I need to wire this into my bathroom for the winter to help heat the cold part of the house, at least when the wind blows.

Tink

ghurd · « **Reply #30 on:** November 06, 2009, 07:23:57 AM »

Looks Good!

G-

wellusee · « **Reply #31 on:** November 06, 2009, 05:19:22 PM »

Very good Tink .

So this is what I need for my 10' .

Thats a good photo .Will you stay tuned in if I build this resistor bank ?

Whats the link to buy the resistors?

My stator is 24Volt.

Paddy .

Tink · « **Reply #32 on:** November 06, 2009, 07:46:48 PM »

I think Mouser.com is the best place. They are prompt and have a great catalogue.

Tink

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Author Topic: Advice needed building a dump load for 10' windmill (Read 7542 times)