So what's the preferred 8 ohm high power audio dummy load these days? - Page 1
Forum section: electronics / testgear

author: cvanc
author_rank: Frequent Contributor
timestamp: February 23, 2018, 11:18:46 pm
content: I have some from many years ago that are good up to maybe 200 watts, but I'm on the hunt for something that can handle at least 400 watts. And of course I don't want it to cost a fortune or be overly complex (liquid cooling is a no-go, even a dedicated fan would be nice to avoid).What are people buying these days to fit that need? I see lots of these extruded aluminum casings with resistors embedded inside coming out of China - are they any good?Thanks...

author: Hydron
author_rank: Super Contributor
timestamp: February 23, 2018, 11:28:41 pm
content: Well you said that liquid cooling is a no-go, but i wouldn't call Mike's method expensive or overly complex...

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 23, 2018, 11:33:56 pm
content: I would get four of those aluminum 8-ohm, 100W resistors (in series-parallel for 8 ohm total.)I would put them into a gallon can of white mineral oil like the classic Heathkit Cantenna.The oil will dissipate more than your 400W with no noise.Ref:https://www.orcadxcc.org/content/cantenna_va7jw.pdf

author: Terry01
author_rank: Frequent Contributor
timestamp: February 24, 2018, 12:03:12 am
content: What would you be running where you need to dump 400+ watts? Just curious, I am still very new to electronics and 400+ watts seems like a hell of a lot to me! Is it a lot or am I being naïve?Sorry if that sounds nosey or anything but it peaked my interest

author: chriswebb
author_rank: Unknown
timestamp: February 24, 2018, 12:19:02 am
content: From this link, I found out about these elements you can get for pretty cheap:https://www.eevblog.com/forum/beginners/dummy-load-for-audio-amplifier/Quote from: Shock on November 04, 2017, 09:42:10 amAvailable on amazon for like 11 bucks.

author: nctnico
author_rank: Super Contributor
timestamp: February 24, 2018, 12:27:16 am
content: You can run resistors pretty hot so a large sink should do. A fan which runs slow can provide extra cooling without making a lot of noise. If you add a temperature controller to the fan then it only turns on when necessary.

author: Cerebus
author_rank: Super Contributor
timestamp: February 24, 2018, 12:50:39 am
content: Quote from: Terry01 on February 24, 2018, 12:03:12 amThat's a medium size amplifier for most sound reinforcement (PA) systems. For a decent sized rig you might be running 10-20 amplifiers at that power level.

author: nanofrog
author_rank: Super Contributor
timestamp: February 24, 2018, 12:57:15 am
content: The element from a clothes dryer works well for this. Cooling is nothing more than a bucket of water.

author: Electro Detective
author_rank: Super Contributor
timestamp: February 24, 2018, 02:16:27 am
content: Whatever way you choose, just make sure it's isolated from earth/ground pathsPlastic bucket with plastic handle to the rescue...

author: TMM
author_rank: Frequent Contributor
timestamp: February 24, 2018, 04:53:13 am
content: If you search ebay for "braking resistor" you can find ones rated at "1000W" for relatively cheap (<$40). Perhaps de-rate it by a factor of 2 or 3 to account for chinesium build quality.

author: Terry01
author_rank: Frequent Contributor
timestamp: February 24, 2018, 08:38:53 am
content: Quote from: Cerebus on February 24, 2018, 12:50:39 amThank you

author: Lightages
author_rank: Unknown
timestamp: February 24, 2018, 03:31:54 pm
content: For an 8ohm load I used e appropriate length of telephone wire randomly bunched up inside a bucket with a lid and filled it with water. It would go for a long time before the temperature changed enough to raise the resistance. It was cheap too.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 24, 2018, 04:32:51 pm
content: Quote from: cvanc on February 23, 2018, 11:18:46 pmyou can search for multi hundreds dollars dummy load but in the end you'll put the 8 ohm speaker on your circuit. you can get the 400W speaker for similar price or even cheaper than the dummy load. any impedance changes due to electromagnetic interaction will be simulated perfectly. you can then adjust your circuit respond as real as like when you wake up from a dream. if you care about the noise and boom boom that will be generated during the circuit development, then you can interconnect bunches of power resistors and put it in liquid bucket as few members suggested above. the reason people want dummy load device is because they wantadjustablecurrent, resistive load etc.

author: Cerebus
author_rank: Super Contributor
timestamp: February 24, 2018, 04:52:07 pm
content: Quote from: Mechatrommer on February 24, 2018, 04:32:51 pmNo, the reason most people want an 8 ohm dummy load is so they don't go deaf while running tests and they don't blow up a succession of speakers when something goes wrong. An 8 ohm dummy load is much more resistant to abuse than a paper/polypropylene speaker cone.Adjustable electronic loads are for playing with batteries and power supplies, they are worse than useless as load simulators for LF amplifiers. Often they'll have next to no control loop gain above a few thousand or 10s of thousands Hertz.And as for "multi hundreds dollars dummy load" - resistive loads tend to be cheap compared to active loads, especially when you're talking 400W. What's the cheapest 400W active load you can find?

author: bitseeker
author_rank: Super Contributor
timestamp: February 25, 2018, 12:11:16 am
content: Quote from: chriswebb on February 24, 2018, 12:19:02 amThat's handy. Here's the current link to it at Lowe's, for those who have one nearby.https://www.lowes.com/pd/Utilitech-Water-Heater-Screw-Element/3693202$8.58

author: David_AVD
author_rank: Super Contributor
timestamp: February 25, 2018, 02:58:15 am
content: I made up an air cooled unit in a rack case with switching (via relays) for 4, 8 and 16 Ohm operation.It's 2 channel so can parallel them for larger loads or when i need to test at 2 Ohms.The resistors are 8 Ohm 100W non-inductive units from WES Components and were not all that expensive.

author: Cerebus
author_rank: Super Contributor
timestamp: February 25, 2018, 03:34:46 am
content: Quote from: David_AVD on February 25, 2018, 02:58:15 amOne tends to forget how inexpensive some components are nowadays. I bought a couple of 100W resistors last year so I had the wherewithal to fully exercise a 200W secondhand bench power supply I'd picked up - just to check performance over its full specified range. I didn't even spend a tenner.The expensive bit is always going to the other hardware for something more permanent - connectors, an enclosure and cooling. For my particular use a temporary setup was OK and I just used a spare bit of 300x300x3mm aluminium sheet as a heatsink and some oil to act as a thermal conductor while I was working, and the resistors went into the parts box once I'd done.

author: Dwaine
author_rank: Frequent Contributor
timestamp: February 25, 2018, 05:08:46 am
content: Yeah, that cool. I think I will make one.