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Old 4th February 2014, 11:20 PM   #11
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All i need this for is to run the amps at or near clipping for a period to ensure a good repair and make sure no hidden problems will arise once the amp warms up or is put through a workout. I also would like it to do some power tests via clamping and/or the new SMD AMM-1 when I finally getting around to buying one.

So the heaters will suffice. REALLY REALLY wish I could find some 120V 3500W water heater elements. Largest Ive seen is 3000W. I could use the 240V 3500W ones, but I would need twice as many of them to get a 4/2/1 ohm load than if they were 120V.
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Old 4th February 2014, 11:51 PM   #12
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Dummy Loads
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Old 5th February 2014, 12:59 AM   #13
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any junk yard/scrap yard is full of hot water heaters just asking for the elements to be taken out.

Then there are electric ovens...
Also old "rotisseries".

Wirewound is superior to the aluminum "Dale" type resistors for high power testing. Unless you ramp up the temp slowly there is the danger of blowing the ends out of the aluminum case type. I avoid them wherever possible. Too bad, because they *look* good.

You can make a wirewound GLOW red and it is ok usually.

As far as getting the extra 500watts out of the 3000watt element?
Put in a metal can water bath. Or oil if you pick the right type...

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Old 5th February 2014, 01:05 AM   #14
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The extra 500W was not a dissipation concern. It was the fact that a 120V 3000W element would yield a 4.8 ohm load. At 3500W it would be a 4.1 ohm load. As close to multiples of 2 the better. (2.0, 4.0, 8.0)
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Old 5th February 2014, 02:41 AM   #15
laplace is offline laplace  Australia
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What about obtaining a couple of old busted toasters and using the nichrome wire and glass formers they're wound on? You can tap off at whatever point gives you the right R. Add a fan to make it a little more linear/consistent

Hell, a new toaster costs what, $10?
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Old 5th February 2014, 08:53 AM   #16
AndrewT is offline AndrewT  Scotland
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One could buy replacement wire coils for infra red heater tubes.
They were relatively cheap. Don't know if they are still available.
Need special flux to solder to the ends.
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Old 5th February 2014, 09:09 AM   #17
Pulse-R is offline Pulse-R  Australia
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I'd have thought an inductive load (like a speaker) would be the ONLY way to test real performance of an amplifier...

I mean really, who cares what a nice sine wave you have in a non-inductive load if it goes haywire when a speaker is connected?

Just my 2c.

I use cheap kettles (jugs) in parallel to give lower ohms. at only $5 a pop, you can't get much cheaper
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Old 5th February 2014, 09:26 AM   #18
AndrewT is offline AndrewT  Scotland
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A speaker load is indeterminate.

A simulated speaker load could be set as a standard. ESP and others discuss this.

But designers have an array of predictable test procedures using standard value components and techniques that can identify poor performance and lead the competent designer (without interference from the accountant) to adopt all the compensations that ensure exemplary performance into any simulated or actual speaker load.
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Old 5th February 2014, 05:45 PM   #19
infinia is offline infinia  United States
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Quote:
Originally Posted by Troy Dionne View Post
All i need this for is to run the amps at or near clipping for a period to ensure a good repair and make sure no hidden problems will arise once the amp warms up or is put through a workout. I.
burn in testing for repairs use any value around 3 ohms ( for 4 ohm car stuff )
value not critical. dial in the power you want via input level. remember the heater resistance is somewhat variable depends on temp


depending on how long you burn in and tank size, the water can be boiling off. it would be ideal to re-use the heat of course. The rating without water is prolly 10-20%

three or four old 1500W space heaters in parallel ( coiled wire types with fan ) they have 2 way switches to adjust tap selection.
$40 new or less used . could be the easiest to modify IMO
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Last edited by infinia; 5th February 2014 at 05:48 PM.
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Old 5th February 2014, 06:02 PM   #20
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Quote:
Originally Posted by Troy Dionne View Post
The extra 500W was not a dissipation concern. It was the fact that a 120V 3000W element would yield a 4.8 ohm load. At 3500W it would be a 4.1 ohm load. As close to multiples of 2 the better. (2.0, 4.0, 8.0)
rather irrelevant, imo.

Don't see why the exact value matters all that much...
1/2 power is only 3dB.

At that power level it either works or smokes pretty much, and the line voltage will probably cause more variation than that impedance difference.

Oh, right, this is a car amp, so unless the internal supply maintains the voltage precisely, the power out will vary a bit...

but also a little exercise, if you used say 4 x those elements (series parallel) to result in a load that at 3kw did not shift resistance very much if at all, how much *shunt* resistance would be required to pull it to 4.0 ohms, and what *power* resistor is needed for this job?

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Last edited by bear; 5th February 2014 at 06:10 PM.
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