Author Topic: Load bank querry  (Read 4504 times)

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Frank S

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Load bank querry
« on: July 25, 2014, 05:47:01 PM »
 I have been thinking that I would like to have a small load bank for testing generators and welders.
 At this point I'm not sure what amperage or wattage I am going to want .
 perhaps one that I can add to later
 I work on a few engine driven generators and welders from time to time  so I would like to add a load test panel to my collection of junk.
 I have several small 1000 to 1800 watt radiant heaters (maybe 6 or 7) that could be cannibalized for a resistance load.
 and a few large resisters salvaged from old welding machines I also have several transformers removed from ac cracker-box welders  a couple of variable core transformers taken out of 250 amp ac welders,   and a pile of ceramic insulators,plus  maybe 20 ft of 500MCM cable 10 ft of 0000 cable 200 ft of #2 cable plus other cable.
 I am thinking the load center will need to start off capable of applying a full load to at least a 10K 120/240v AC generator or 250 amps current load @28vDC then withstand a 1 hour full current test without burning out
  So I am thinking the unit will need to have around 100% overload cap for 15 minutes.
 beyond these parts and possibly a couple of shunts to connect meters to.
 What else do you guys see that I'll need before I start to construct this thing? 
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joestue

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Re: Load bank querry
« Reply #1 on: July 25, 2014, 06:04:46 PM »
If you arrange binary weighted loads and can remember how to count in binary, you don't need that many resistors, or switches. --the problem being its not easy to switch them in real time, without accidentally switching too many on, or turning the load off when you intend to just add a few more watts.

1k, 2k, 4K and 8 K load per phase makes 4 switches per phase for 15Kw load.

ceramics are cheap, get some arts student to fire a bucket full of them in a kiln lol. Nichrome can radiate something like 10KW per pound of wire if you let it get that hot.
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SparWeb

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Re: Load bank querry
« Reply #2 on: July 25, 2014, 10:51:33 PM »
How about a few cooling fans.

Rather than planning an "overload", why not just plan for a maximum power level your equipment can possibly apply, and include enough resistors to do it?

Re-configuring the same load bank to operate at 240VAC or 120VAC or 28VDC will require extensive re-wiring or heavy switching, since you won't want it de-rated at different voltages.  A few fat copper bars and large brass screws for common connections.  If you mean to switch on the fly, well the AC isn't difficult (common power relays will do), but I'd love to see what you do to switch up/down the load on DC if it's carrying hundreds of amps.  pricey.

Nichrome...   maybe you can just collect half a dozen heater elements from electric clothes dryers and make a resistance bank wired for each of your requirements.
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Frank S

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Re: Load bank querry
« Reply #3 on: July 26, 2014, 12:46:46 AM »
 I used to have access to a shop made load bank that could place a 150% load on up to a 1000 amp welder or load up to a 30KW 3 phase generator.
 Switching loads on DC was never done under load the resistance value would be preset then a very large knife switch would be thrown.
 the bank had several large rotary knife switches scavenged from old welding machines There were also 3 large variable pile transformers in it  additionally it had many different sized connection lug sets that lead to preset loads.
 in 1982 I bought a new Hobart mega arc 400 amp diesel driven machine with a 12 KW 3 ph option  to seat the rings of the engine and check the generator/ welder out put they set the resistance load to 800 amps fired up the machine and spun the knobs to max the amp-meter showed  that the machine was putting out the full 800 amps @ 28v they left it there for several minutes then allowed it to cool down then placed it on a 400 amp load and let it run for 10 hours  then we mounted it on my truck which was where it stayed for 11 years when I sold the machine it had 14,000 hrs on it . I sold it for nearly 2/3rds of what I paid for it and had never had any problems with it.
  I want to build the load bank so I can test these small welders & generators that I rebuild from time to time.
 Right now I am using lengths of copper pipes or several electric heaters to do this.
 I feel that a good burn in at rebuild is far better than letting a machine go out having only been lightly loaded  to be burned down later when someone needs it to be loaded heavy and the machine cannot take it
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AzSun

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Re: Load bank querry
« Reply #4 on: July 27, 2014, 07:28:05 PM »
Up until the 50's domestically and maybe still in third world countries, a salt water box was used to load test locomotive alternators. Below is a link describing the operation.

http://en.wikipedia.org/wiki/Liquid_rheostat


Flux

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Re: Load bank querry
« Reply #5 on: September 15, 2014, 03:44:09 AM »
I seem to remember ours using washing soda, (sodium carbonate) rather than salt but the idea was the same.

Our big resistor banks were fan cooled, it increases the rating dramatically.

Flux