Dummy Loads

[jbeckva]

So hey all yooze-guys...

How many of you have made a dummy load before? What kind of power rating do you have on it? Any pics?

Thinking that would be a good addition to the 'trons bench here...

 

[laatsch55]

I have 4 100 watt 2 ohm Ohmitesin series and a 360 watt made out of a bunch of 4 ohm 20 watt Ohmites, both 8 or 4 ohm. Now, Dave and i had a few chats about that 360 watter.

 

[laatsch55]

Now dave will probably link an AK thread where EW suggests an all resistive test load is not a good thing,.....Dave......??

 

[stuwee]

Snicker, sincker, and here I thought this was about the IQ level of the 'giver'

If they're stupid, I let stuwella have them, if they're smart I might let them give me a pearl necklace

 

[laatsch55]

Never can get one by ya!!!

 

[avionic]

Now dave will probably link an AK thread where EW suggests an all resistive test load is not a good thing,.....Dave......??

Dave..Dave...Daves Not Here!!!..LOL Showing my age again..


What Lee is refering to is the use of non-inductive Vs inductive wirewound resistors.
I had a couple (inductive)200 watt clarastat 8 ohm resistors that work OK for just monitoring the sinewave for clipping. Where you may run into issues is measuring THD.
I pulled the trigger on the big bad boys
2 each 4,8 & 16ohm/ 300 watt/Arcol aluminum incased --NH series (non-inductive)
from Mouser.
http://www.mouser.com/ProductDetail/Arc ... SpuqQRc%3d" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
Roughly $460 worth of resistors. Mounted the 16's and the 4's on a forklift battery charger heatsink with heatsink compound and 6 each 1/4-20 socket head screws. The 2 8's I mounted on a big-ass heatsink from a 3-phase AB Freq drive using the same compound and fasteners. Of course depending how I wire them in various series - parallel configurations.Like..

2 -- 8 ohm 300watt
2 -- 8 ohm 600watt
2 -- 4 ohm 300watt
1 -- 4 ohm roughly 900watt
http://www.audiokarma.org/forums/showpo ... stcount=23

and as long as I can keep the heatsinks cooler than 150 degrees F. I can fudge the amount power..

 

[avionic]

At the time I was requested to check the output power of a Yamaha PC5002M. 138 pounds of pro Yamaha. That nearly puts out 1Kwatt into 4 ohm at 1Khz before clipping occurs..960watts.

Needless to say.Loads got hot , real fast..even with a fan blowing on the sinks.

 

[laatsch55]

55 gallon drum of mineral oil next time

 

[avionic]

Sure .That would work. Where in the hell would I put a 55 gal drum full of enviormentally unfriendly oil.With second containment concerns.Don't need the EPA on my ass.Way to much hassle..LOL

 

[Web Police]

The thread title sounds like a Technical name for Stuwee.

 

[avionic]

Sounds like a Technical name for Stuwee.

Thats "not right"...

 

[stuwee]

I'm new to all this, but really want to learn. Why would you spend $460 on resistors for a dummy load, when you could just hook a big amp up? Are you trying to use a specific output load? Ie; 500w, 400w etc....150F on a heatsink sounds pretty hot for electronics.

What is the purpose of having a specific load for a test?

 

[jbeckva]

Kind of related to that "specs" thread, Stu. Basically specs are typically measured with a specific resistance (load) on the amp. So the load goes in place of the speakers. Non inductive = doesn't vary with frequency. Also.. say you wanted to burn an amp in for awhile but didn't want to HEAR it burn in... hook a dummy load up and you're set.

Besides... testing out something like Larry's PL with actual speakers would've prolly turned Lee deaf after a day or two... heheh (another advantage. yadon't HEAR the watts.. )

 

[avionic]

150F on a heatsink sounds pretty hot for electronics

Thats on the dummy load heatsink..Believe me,you hook up a 150 watt amp to a 300watt load at WOT..And let it set there for 10 min. or so. Its going to get real warm.
When measuring max power or distortion levels, resistors don't shift in impedance (resistance) like a speaker would .Also a 1000 hz test tone would get awful annoying at max power.

 

[avionic]

Why would you spend $460 on resistors for a dummy load, when you could just hook a big amp up?

You hook up the load resistors to the big amplifiers outputs instead of speakers. When working on BIG amplifiers ,it takes BIG resistor power handling capacity with precision loads.Those that I purchased measure "deadnuts" at 4,8 & 16 ohm..I could have went with a bunch of smaller resistors . But believe it or not it was cheaper and easier to go with the 300 watt Arcols.

 

[avionic]

If your going to work on audio gear alot..Like I do.I go with quality testing gear.The Load is just another piece of test gear.

 

[laatsch55]

hard to argue with someone who's right, unless Stu's your name , innaneness his game.

 

[stuwee]

Except for that last reply . Great info, that makes sense, I can understand better. Although I don't expect to be tearing something apart and puttin' it back anytime soon

 

[avionic]

It was a pretty large investment.But they should last forever. When the majority of the stuff I work on is from 90-250 watts.

 

[avionic]

For the benefit of those banned from AK...