Author Topic: NICHROME WIRE (Read 5137 times)

2windy · « **on:** September 20, 2006, 10:43:59 PM »

I am building a dump load for my 12 volt wind genny.

I have some .15 ohms per foot nichrome wire. I need about 1000 watts of dump, so I am going to shoot for around 1300 watt dump load. I read that if you coil the nichrome (1/2 inch coil dia) wire you will only get half the amps. Did I misunderstand this or is this correct? If so why? My other question is has any one did this that can explain to me how to do it. According to Ohms Law 1 foot of this is 900 watts at 80 amps. Should I parallel about four pieces about a foot long? I don't know much about nichrome but it says 17 gauge witch I have is good for 25 amps at 1800 degrees. I'm assuming that means per foot. I think I'm lost here. Thanks for the help!

JW · « **Reply #1 on:** September 20, 2006, 06:03:54 PM »

Hi 2windy,

" I read that if you coil the nichrome (1/2 inch coil dia) wire you will only get half the amps. Did I misunderstand this or is this correct? If so why?"

"I have some .15 ohms per foot nichrome wire."

Alot of times the comparison is made that a strand of wire out in air, can dissipate heat better than a coil. You must look for an operating temerature specification @ ohms per foot.

I run some nichrome wire in some infared heaters. 6000w of it @240v 3phase, to be exact.(not an RE application) Its wound in 3/8in glass tube. When you mention 12v that makes me concerned, because this stuff has a high operating temp and gennerally is a resitive load. But very stable once its at operating temp. Inherently its not opimized for low volts. But people do use it on 12v systems. What wire size gauge is it?

Ok 17gauge, Yes you could parallel the strands to get more of a dump load.

25amps @ 1800*f at what type of volts?

Just try it, start with one strand see what happens. I assume you are diverting from the battery. Id take some 18ga and coil 4ft of it, in a half inch coil (about an inch long?, id preffer 3/8 dia thou)and put that in a glass tube and start from there, just diverting from the battery. Its hard to know the dynamic impeadence of that stuff, but if its red hot its working like it should. This could cause a problem with cut-in speed at start up. If so, use more than 5ft wound in the coil. 'If you use to much length'(to start with and try) it will be the same effect as a fully charged battery. Just cut down the size, after running it for a while. It should turn red hot in a strong wind gust. If it does turn red hot anywhere along the coil of wire that you wound, then parallel what you have, to control mill speed for that average wind speed. If you cant get it to turn red hot at all, use a smaller gauge of wire and start over. Its definitly easier to use nichrome with higher voltages.

using 12volt light bulbs would be easier. Use 1000w of 12v lightbulbs and impeadence will be optimized. It would be much easier to do the same thing. but no matter what, the cut-in will be affected from a dead stop. Try a search on "staging dump loads" here on the board.

JW

JW · « **Reply #2 on:** September 20, 2006, 06:12:29 PM »

Dam,

Uknow, I just did a search for "staging dump loads", and got 0 results... it seems to me, ziener diodes were discussed to stage progressive elements for this type of dump load.

Anyhow just do a search of the board for "dump loads" I know that one works. Theres alot of good info there.

JW

vawtman · « **Reply #3 on:** September 20, 2006, 06:37:54 PM »

Dont they make relays for staging electric heaters?

JW · « **Reply #4 on:** September 20, 2006, 06:42:31 PM »

Yes, the relays work good, but something has to complete the circuit to the coil of the relay. the ziener dosent conduct untill a preset dc volt such a 12.5

2windy · « **Reply #5 on:** September 20, 2006, 07:01:28 PM »

This is going to be hooked up to the diversion side of my C-40 controller. I am assuming that 12 volts only comes out of the controller to the diversion load, its the current (amps) that I have to get rid of. Would someone correct me if I'm wrong.

JW · « **Reply #6 on:** September 20, 2006, 07:11:38 PM »

If I was about to hook something into the diversion side of my C-40. Id use 12volt light bulb. Instead of an unproven ni-chrome filament. Resistance could be to low at the wrong time and hurt something. But but thats just me. Arent there any recomendations in the book for a dump load with that thing.

JW

JW · « **Reply #7 on:** September 20, 2006, 07:33:49 PM »

Just to be clear, im talken about 4 old style auto head-lamp-bulbs in parellel. Seems to me, one can go to the junkyard and buy a dozen of these, for a buck.

JW

2windy · « **Reply #8 on:** September 20, 2006, 07:41:44 PM »

That thing recomends using only resistive loads such as air or water cooled heating elements. It also says do not use light bulbs for diversion loads.

harrie · « **Reply #9 on:** September 20, 2006, 08:07:47 PM »

Yes, that is what they say, and they are probley right. I however use 12 volt light bulbs for my c-40, along with a 600 watt parabolic resistant heater. seem to work fine as long as my 8 year old granddaughter came over one day and thought she would do me a favor, and shut off the lights. ha I guess she heard shut the light of by her dad once too often ha. This of course resulted in overchargeing my bank to a tune of 15.8 volts before I caught it. I dont think they were hurt tho.

JW · « **Reply #10 on:** September 20, 2006, 08:08:02 PM »

Hmmmmm,

Try this then.

http://www.cetsolar.com/12vdirectheater.htm

Its only 300watts but its a start.

JW

2windy · « **Reply #11 on:** September 20, 2006, 08:24:53 PM »

Believe it or not but I have one of those heaters. Its only 300 watts though. It looks pretty simple thats why I thought maybe I could build one myself with a little help from here on the board.

JW · « **Reply #12 on:** September 20, 2006, 09:12:23 PM »

Ok,

This seems to have gone full circle

Most posts dont get that far.

By all means take the thing apart and let us know what you find in there...

I think some trial and error is in order here. A 300watt heater could pull as much as 25amps@12vdc. How many amps at 12v are you looking to pull, over a hundred? I doubt these units use standard nichrome wire. Even if you cant figure out what the alloy is, four elements could be cooled with one fan, but you would have to try wiring them in both series and parallel and let us know the end result. It may come down to the reason no other heater's are available @12vdc over 300watts. perhaps theres an inherent limitation there. Id hate to find out its only because nobody needs a 1500watt 12 volt heater.

JW

Shadow · « **Reply #13 on:** September 20, 2006, 10:06:05 PM »

Heres a link that I found interesting. It may be of some help.http://www.fieldlines.com/story/2006/2/28/114556/473

2windy · « **Reply #14 on:** September 20, 2006, 10:36:27 PM »

Why didn't I think of that.Will take it apart in the morning. Will let you know whats inside. Thanks JW

2windy · « **Reply #15 on:** September 20, 2006, 10:42:27 PM »

Thanks Shadow, I've search the board for that posting for two nights with no luck. I knew it was there cause I had read it before. How did you find it?

Shadow · « **Reply #16 on:** September 20, 2006, 10:50:35 PM »

I kinda remembered it being in a Diary, so I hit search,Find in: Diaries, dump load, then scrolled down. Theres probably more in that search that mey be helpful. Good Luck

Darren73 · « **Reply #17 on:** September 21, 2006, 01:21:58 AM »

we had some low voltage nichrome heaters on site a few years back for a trial and they had multiple strands of wire twisted together into a rope to take the current, from memory they were around 9kW at 48v.

I have personally wound a number of different heating elements from nichrome, if you take a 1/4" round bar and a cordless drill, with a little practice you can make nice elements.

to reduce the heat the end terminations experience I usually double up on the last 1 to 2" of the element or crimp it onto some stainless rod

ie =--------------------=

where = is the doubled heating wire and - is the normal strand.

Regards

Darren

Darren73 · « **Reply #18 on:** September 21, 2006, 01:56:20 AM »

Just took another look at this over coffee, how much wire do you have?

If you have enough I wouldn't run above 15A which at 12 v means each element will be around 180w and cool enough to stay reasonably constant on resistance and provide enough of a safety margin for the typically higher voltage that the dump load is likely to experience.

Each coil would require an element length of 64".

Using 1/4" round bar as the former provides nice tight coils which tend to hold shape well, This when wound on a 1/4 rod should be 64 turns give or take a turn, wind an extra 4 to 6 turns which allows for the termination, ie 4 turns would allow you to uncoil 2" off each end (double this over and twist together firmly to form roughly 1" of "cold" end for termination.

Stretch the coil from the approx. 3.5" formed length to about 8" long, this will allow for roughly 25w per inch of dissipation.

I'd try 1 first and see how it performs, if you are happy then 1300w would be 7 elements.

Mount the elements at least 1" apart in free air, and make sure they can't be touched while operating, one of the guys I know managed to touch an electric fire element as a toddler, and having seen the scars and knowing the years of surgery and pain he must have been through I wouldn't wish it on anyone. have fun but remember keep it safe, you only get one life.

Any further queries I'll be more than happy to answer

Flux · « **Reply #19 on:** September 21, 2006, 03:26:17 AM »

C40 controller is only 40A. Maximum load should not exceed 500W.

For a dump load you will do better to run the wire below red heat, so use longer lengths in parallel rather than run each strand red hot.

At low temperatures it makes no difference if the wire is straight or coiled. At red heat you will have higher temperature for the same watts if you coil the wire so that is why there is a derating.

I would use strands about 3 ft long and parallel up until you reach the limit of the C40. Running cooler there will be much less change in current between switch on and running and will put less stress on the controller.

Flux

Opera House · « **Reply #20 on:** September 21, 2006, 06:19:13 AM »

Lamps have a ten to one increase in resistance as they heat up. That means a single 5A lamp can asily draw 30A for a ignifigant period. Put a couple lamps in parallel and it initially looks like a dead short to the controller and could zap the output semiconductor. If you put a couple lamps in series, the change in resistance will be less.

I'd run less than 10A in that nichrome wire. At high temperature the wire will need a lot of support. Everyone thinks nichrome, but this is really a very poor choice unless you are looking for a high temprature heating element. A better choice is steel where the resistance is lower and that gives you more surface area. Off hand, a hacksaw blade would make a nice resistive element. Convenient size, large surface area, and a mounting/connecting hole on each end.

paulpic · « **Reply #21 on:** September 21, 2006, 06:23:26 AM »

I had the same situation at trying to find a way of dumping 1000 watts or so for a 12v system.

I went to the local rubbish tip and got an old oven element,and by squashing it with a hammer the powder inside comes out and it leaves a tightly formed nichrome wire.

Slowly pull this out in about 16" lengths and carry out tesing with clamp meter to give a current reading for 1 wire.Just simply add more wire to give the desired load.

I made 2 bundles of wire and by changing them from series to parallel i can dump 60amps or 120amps.

These are submerged (insulated of course)in water mounted on 2 brackets in and a drum then seal welded.

I have 2 dump loads 1 @ 14.3 volts 18 amps (air cooled )and second 60 amps @ 15.1 volts (water cooled). This works good for my system.

Heres some pics.

http://www.otherpower.com/images/scimages/351/dump_load.jpg

http://www.otherpower.com/images/scimages/351/dump_load_.jpg

http://www.otherpower.com/images/scimages/351/contoller_with_dump_load.jpg

Paul.

2windy · « **Reply #22 on:** September 21, 2006, 07:26:51 AM »

Just got it apart, it has some type of square bricks in it.(about 1"x1"x1/4" with tiny holes in them) There are 3 in a row and 3 rows totaling 9 bricks. There are 2 wires going to each row and they read 1.7 ohms each. The 3 sets of wires are then paralleled and then go to a relay then to the switch. Guess I won't be copying this.

phil b · « **Reply #23 on:** September 21, 2006, 12:05:45 PM »

Hi paulpic,

"These are submerged (insulated of course)in water mounted on 2 brackets in and a drum then seal welded."

Can you expain further how you did this? maybe some pics?

Thanks

Ungrounded Lightning Rod · « **Reply #24 on:** September 21, 2006, 03:10:17 PM »

I think the issue with light bulbs is that they burn out and then you have no dump load.

(Might also be excessive inrush current on turnon, since their cold resistance is significantly lower than their operating resistance.)

jmk · « **Reply #25 on:** September 22, 2006, 10:06:08 AM »

I think it was the Xantrex manual that stated, light bulbs can fool the controller and cause it to stop dumping. Then because it was fooled it needs to turn back on again. This can repeat many times and cause the bulbs to burn out leaving you without a dump load.

JW · « **Reply #26 on:** September 22, 2006, 11:08:41 PM »

Hi paulpic.

Are you refering too-

http://www.otherpower.com/images/scimages/351/dump_load_.jpg

Because theres no insulator or isolators, between the drum and the filaments, OR inbetween the 2 strands, for each circuit. Why to you have 2 filiments shorted to the same circuit and 4 wires feeding them, when you only need two wires to energize both filaments in series-parallel, the way you have it wired in the pic. Not only that, but the barrel is shorting that in parallel. If you install insulators, please rename your pic, so we can compare the difference. You need 4 insolators(washers) and non-conductive bolts to isolate all your circuits, for the 4 wire feed.

Yes, we know air is just as good of an insulator, as pure water, but that doesnt explain the lack of isolation washers, in your pic. Is this just a mock-up picture by mistake?

JW

Darren73 · « **Reply #27 on:** September 24, 2006, 01:41:49 PM »

JW,

I agree the elements do not appear to be shrouded, but look carefully, the flat sections that the elements are bolted to look like tufnol to me, ie an insulating material used for electrical work.

Darren

paulpic · « **Reply #28 on:** September 25, 2006, 06:08:42 AM »

Darren 73

That is correct,the mounting brackets material insulates each element

which isolates them internally that allows me to vary the load externally.

JW · « **Reply #29 on:** October 01, 2006, 05:26:21 PM »

Ya, I thought that was 1/8 copper plate. Thanks for the correction.

Im still mysified by this response-

"Re: NICHROME WIRE (3.00 / 0) (#22)

by 2windy on Thu Sep 21st, 2006 at 07:26:51 AM MST

(User Info)

Just got it apart, it has some type of square bricks in it.(about 1"x1"x1/4" with tiny holes in them) There are 3 in a row and 3 rows totaling 9 bricks. There are 2 wires going to each row and they read 1.7 ohms each. The 3 sets of wires are then paralleled and then go to a relay then to the switch."

I bet the people that make this alloy, sell it. too bad we cant idenify what it is. Seems to me this stuff could do wonders in the 12volt dumpload catagory.

JW

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Author Topic: NICHROME WIRE (Read 5137 times)