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Forum Index : Electronics : Dump Loads
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eirbyte Newbie  Joined: 19/11/2008 Location: IrelandPosts: 16 |
Hi has anyone made their own dump load resistors for water or air heating. The reson I ask is if we want ceramic resistors they come from the usa (I'm in Ireland) and a 24v 55a load costs around 200euro that's a lot when people are trying to build their turbines on a tight budget. One friend put coper wire in his concrete slab and it worked for a few months only. Thanks Jimmy Education isn't everything; for a start it isn't an elephant. Spike Milligan BuildYourOwnWindTurbine.com |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
If you make your own dump loads, they should be insulated, especially if the load is DC. Gordon. become more energy aware |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Bryan posted his project not too long ago: http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?T ID=1380&PN=1 Peter. |
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oztules Guru  Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Yes. This afternoon I wound 20meters of "twitching wire" (about 1.2mm galvanised wire to "twitch/tie" fencing wire to posts). I quickly wound it using the lathe onto about 1 1/2 inch pipe, shook it off and used it as an air coil heater on the ground to test with. It dropped about 20A@48v.. about 1kw. It got hot (as expected), but not stinky hot, and did the job very well. To use this as a fixture, I thought I would get some 1" pipe and wrap it in glass cloth. Make up some sloppy plaster, and make a 1/4" thick glass/plaster former for the coil to sit on. It should be both rigid, and heatproof. When heat dried (by the coil perhaps), it should resemble a poor mans ceramic resistor... we'll see. The coil is about 700mm long. It should last forever, as it does not get hot enough to denature the steel, but just enough to give the gal a cause to worry. May have to put higher voltage through it for a while to burn the gal off. I will leave the 1" pipe inside for mounting purposes. On the next one I will make the pipe/glass/plaster former, and wind directly onto that in the lathe. For 24v, obviously 1/2 the length. Comments on the workability of this scheme is welcome. I will need about 3 of these... for 3kw.... and no I haven't mixed plaster with glass before... should be interesting. I may go to a larger diameter to get the length down a bit. ..........oztules Village idiot...or... just another hack out of his depth |
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| eirbyte Newbie Joined: 19/11/2008 Location: IrelandPosts: 16 |
Sounds good any photos Education isn't everything; for a start it isn't an elephant. Spike Milligan BuildYourOwnWindTurbine.com |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Yes and No. I haven't done the pipe and glass/plaster bit yet, but here are some piks of the test load. I put a fluro tube inside the wire just to hold it all together for testing. I guess if you cut the tit inside the end piece to relieve the internal gas so that there is no pressure when heating..... I don't know how the glass would respond long term. Seems a bit flimsy to me, but ok to test with. Also depends how hot you design your load. I will try to get the pipe and glass matting bit done soon. So here is the wire resistor on the fluro tube.: 
Here it is dumping @ 20A: 
Close up of the twitching wire: 
And (by changing the meter leads) here is the incoming power @57v.. 25A 
So the chainsaw blades are still working. (I am still waiting for Niall to get his in the air.) I'll need two of these at most now I have the furling point lowered. ..........oztules Village idiot...or... just another hack out of his depth |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Oztules, try thicker gal wire and you get a much more robust coil load. I made one out of 3mm gal wire. Wound it on my lathe on a 25mm pipe former, using the screw cutting set up to drive the carriage at a set pitch (6mm I think it was). That produced a very neat coil, very strong. I needed it for general testing and 600mm of spiral got only warmish when passing 50 Amps for a short time. Do take care when winding thick wire like that, there is a lot of stored spring energy released when the chuck is loosened - could do some very nasty injury. The thick wire coil is just about self supporting when bent into a ring with the ends fixed on an insulating board. A sliding hosepipe clamp like takeoff could provide an adjustable load. Klaus |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
"600mm of spiral got only warmish when passing 50 Amps for a short time." I'm guessing this must have been for 12v. @48v thats over 2kw of power. It has to give up that as heat no matter how thick. Seems like a good system. For that thickness, I would wind it close wound (side by side) to make a "solid" spring, and then pull uniformly to get the spacing... less room used on the lathe. Good one Tinker .........oztules Village idiot...or... just another hack out of his depth |
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