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Forum Index : Electronics : Diversion/ dump load options (re-purpose)
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KarlJ Guru  Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Thanks Pete, bought a 50A SHunt and panel meter for $20 I figured this was cheaper than the $55 that Plasmatronics want for theirs to suit the PL20. As for the relay, impatience got the better of me and although solid state relays are nice, contacts rated for 65A on the Jaycar ones, cheap and I did the deed... Made the "out of control Jezus dump" Adjustable in 400W increments upto 1600W 
Funnily enough the resistance barely changes with this one from hot to cold, ran it at 60V, gets pretty hot but not glowing. Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Karl That would make a nice room heater on a cols windy night. Bob Foolin Around |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Hi Karl, Good to hear you made some choices. Where did you get the meter from? sureelectronics?? I have bought a lot from them over time and is always been hassle free and i think a good price. About 7 days delivery and its taken longer for stuff out of Perth. With your relay, there is a trick of placing a small capacitor across the contacts to reduce arcing, at make and break so they dont weld the contacts together. Hopefully Gordon or someone else will jump in on this with a value of cap to use, and where to put it. Im dont remember the detail now. Pete. Ps. If you can keep your elements below 1/2 their watt rating -- so parrallel 2 rather than run one flat out. Your thermal run away will be not such an issue. Maybe why the later element is more stable. Sometimes it just works |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
I think i'm about 1/2 their watt rating, each resistor was 2400W 1m long cut into ~3rds for about 8Ohms each that means they did take 800W and now ~400-450W yes bought it (the ammeter) from sureelectronics. I knew I kept mobile phone chargers for good reason, perfectly regulated 5V output to drive the ammeter from 240VAC, wouldnt have bought it as making volt reg not worth the hassle or brain drain but easy for you guys! Luck favours the well prepared |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Karl, Just had another look at your dump resistors and it looks like something the mad professor put together 
I see you did master the bending into a tight coil after all. Now that one looks neat. You might want to watch the weight of the wires and terminal block being unsupported when the resistive wire gets hot and soft in the element. Pete. Sometimes it just works |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Ah the really tight one was the bend already there. The first three you see were cut from MY dishwasher element which was the roughest one I've seen yet, bit rusty but it was real easy to bend I broke a few trying to straighten them out and then re-bend them into something that looks nice. Hence, may be a little ugly but they all fit into a small ish space. Need more elements! for the BBQ! Relay circuit came up trumps went for a 10W 470Ohm, so that plus the coils resistance of 120Ohm gives 590Ohm and at 61V =103mA thus under the G terminal max 120mA Voltage on the coil at 64V came in at 13.8V, so coil will live a long time, has a nice solid thunk. I was surprised how warm the resistor gets just to trip a little coil, certainly too hot to touch after 5mins. i guess its dropping 50V so to be expected. Luck favours the well prepared |
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| kalamidas Newbie  Joined: 19/02/2010 Location: GreecePosts: 21 |
helo I'd Like some help if you can. I'm trying to make a dump load 150w-200w for my wind mill. I have 10 1,5ohm power resistor rating 17w if i put them in parallel i will have 170w this will be ok. My consideration is the ohm 1,5 do theese work for 12-15v. Thank you in advance |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
the sums you need to do are VxV / Ohms to give you the Watts dissipated, divide this by the voltage again to get current drawn. at 17W they will not take much to burn up as 15Vx15V / 1.5 Ohms = 150W. pooooff gone. You'll need to run the lot in series / parallel will only dissipate 225/7.5 =30w x2 =60W lastly I'd imagine by now you've already smoked one so three pairs of three would give 150W dissipation 15*15/4.5 =50W right on their limit. keep them cool as surprisingly enough 150W is quite a bit of heat,more than enough to burn fingers. playing with 1KW dumpload heaters is FUN! seriously give the heater elements a go they're free in hardrubbish everywhere and fun to boot Luck favours the well prepared |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Hi kalamidas What you are asking is based on ohms law and it might be advised you have a look and understand how to calculate what you want to know. Ohms Law Here The watts you ask about is "power" in the circuit. You might like to look up Resistors in Parrallel to as its not just a matter of adding the values together this only works for resistors in series. 5 minutes reasearch and you will be much more wiser than us telling you it wont work like that. Pete. Sometimes it just works |
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