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Is this resistor ok for a dummy load?

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    Posted: 14 June 2018 at 11:51pm
So I’m contemplating building a dummy load to test my amps with. Starting off small scale first, I’m aware that the Re of most 8 ohm speakers can be anything between 5 and 7 ohms (ish), but a fixed resistor won’t necessarily behave in the same way as a speaker, when asked to dissipate the output from an amplifier!! I’m thinking in terms of a modular setup using a number of these resistors:

Starting initially with 2, then going to 4 then 8 as funds allow, so I will be able to patch them in series/parallel to adjust resistance/power handling. I chose 10 ohm as I thought it would be a bit easier on the amp when spanking the nuts off it!!

Your thoughts/advice please folks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2018 at 8:46am

I use 4 ohm resistors as it is easier to configure (2,4 or, 8 ohms) and reflects the load the manufacture uses to measure their amplifier(s). 

Best Regards, 

Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2018 at 9:25am
Sure, they'll work. Being wirewound they'll offer a slight inductance which slightly helps to mimic a voicecoil too. Mount them safely and away from your work area if you're doing high power testing is all I'd suggest. On something flameproof preferably.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2018 at 7:11pm
And stick in a fan or two as well. They can get hot.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2018 at 7:22pm
or just buy some electric kettles, should be part way to a cuppa tea with decent amp when ur done.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2018 at 7:40pm
I used to recommend electric kettles - buuuut, they change resistance quite a lot as they heat up. You'd want to have them hot before you start, and you'd have to measure their actual resistance at temperature to have any idea of how much power you are actually delivering. 
There are some good looking 1kW "braking resistor" units on eBay for about £25, that come in 2, 4 and 8 ohm flavours, and are encased in an aluminium heatsink. I think they would work well, unless anyone wants to correct me?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TMH Music Quote  Post ReplyReply Direct Link To This Post Posted: 15 June 2018 at 9:26pm
Thanks for the replies folks. @Studio45, did you mean these resistors on the bay:


They look quite the bargain, 1Kw wire wound, easy mounting for less than £25 a piece!!! Are the ones I linked to from RS that much better? Is it a case of you pays your money you takes your choice? Is it just that the eBay ones are the resistor equivalent of QTX? Am I asking too many questions?!! (Probably) Hmmm Confused
What are the collective’s thoughts??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pinyorouk Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2018 at 5:47pm
I used stove elements from ebay. Not exactly multiples of 4 ohms but sufficient for load testing amps. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2018 at 6:45pm
I would go with the open wirewound style as per the original post.  The advantage of those is that they have massive short term overload capability.  You can pretty much run them glowing red hot!

Stick them in a case with some big fans.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2018 at 10:26pm
Originally posted by ceharden ceharden wrote:

I would go with the open wirewound style as per the original post.  The advantage of those is that they have massive short term overload capability.  You can pretty much run them glowing red hot!

Stick them in a case with some big fans.
.... or a tub or oil(?) Used to do something similar Emersing motherboards with overcooked (pun intended) processors and would run warm enough to almost cook chips (2nd pun fully intended)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2018 at 10:55pm
Oil is messy but you could if you wanted.

Edited by ceharden - 16 June 2018 at 10:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 17 June 2018 at 9:26am
You can just buy resistive wire. Find inductance calculator on web. Wire part of the wire to get the right inductance. Rest of the wire wound with half circles one direction half reverse so you wont get inductance like this.Wink
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