Got one of these: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91129
Works great, but want to modify it to work continuously, or atleast for a few minutes at very high current. Has anyone here done something similar? Any ideas?
Simplest way I guss is to drill a hole and use a spray bottle to cool the element. Air cooling probably won't cut it.
I cant agree that spraying water on an electric device is a good idea, granted there isnt much in there but your just asking for problems with corrosion at the least. I dont really see any hope for it running more than 30 seconds at a time, maybe more maybe less. 500 amps at 12 volts is 6000 watts, they dont make space heaters that can plug into an outlet that size. Even at 100 amps you have 1200 watts that is a space heater. If you dont mind it not lasting very long i dont think spraying water directly on the resistance would pose much of a problem as long as you keep the gauge dry and anything else that might be in there.
my two cents
Joe
Andrew,
Why would you want it to work continuously?
Until latter,
Gman
Peace Out, <img src="http://tinyurl.com/ysafbn">
Gman
So this gadget cannot be used to, say, test a battery at 20 amps for an hour or so?
I'm not sure...20 amps at 12 volts is 240 watts, it just might be able to take it continuously, but I have a 12v car defroster that takes about 10 amps for slow discharge testing.
"Andrew,
Why would you want it to work continuously?
Until latter,
Gman"
I want to see how certain batteries hold up under high discharge currents throughout the discharge cycle and exactly how much each type varies, e.g., how much better Hawkers are than B&B under very high discharge rates. I also want to see how my results compare to the manufacturer claims.
[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri
spraying water on hot carbon is likely to crack it and doesn't carry away the heat. you just get a one-time phase change energy loss then it's gone. the way to cool something like this is an oil bath. if you can find a way to immerse the element in oil you can probably use it for as long as you like. I would use mineral oil from the drugstore, because it will not get rancid like vegetable oil, but that would work too. oil is not a conductor so you could immerse everything but the meter movement if you had to. (take off the fan of course) just watch the oil temp and if it gets too hot you just need a bigger tank of oil. if you have a gallon of oil 1200w will take quite awhile to heat it up. if the oil heats too much you could run some tubing through it and run water through the tubing, or you could put in convection cooling tubes, or just toss in some frozen french fries. good luck.
-bob
Andrew,
How many amps does a car headlight draw?
Also, to get good discharge curve, do you have to adjust the resistance to keep the amps constant as the voltage drops? Or, does a lamp filament self-compensate for this by cooling (and thus lower it's resistance) as it dims with decreasing voltage? Any idea?
Paul D.
Thats a really good idea, all except for the mineral oil french fries :-) (always wondered why theyre french)
I have a feeling that using an oil tank to place the elements in is more than he bargained for, but its the best idea ive heard. Perhaps actually using an old deep fryer filled with mineral oil would be best theyre already meant to hold roughly a gallon of very hot oil. Would simply require removing the old element, perhaps you could solder to existing wiring if you cant, then drill a hole above the oil line for the leads and seal around them with silicone.Doesnt seem very safe to have a gallon of hot oil in the garage but hey people make french fries. Im already imagining welding up a sheet metal tank roughly three gallons then weaving copper tube around the inside, then using a windshield washer pump and car radiator for cooling.
Joe
When I ran remote controlled boats we used the water from the lake to cool the motor. We would take some copper tubing and wrap it around a larger piece of copper tubing and attached the two together with solder. The large copper tube was just big enough to go around the motor. Forcing water through the small tube would cool the motor. This worked so well you could feel the warm water coming out of the return tube which was put back in the lake. This gives your cooling system a sealed system so nothing inside your unit will get wet. The small tube we used was about 1/8", this carried enough cooling water to keep us from burning up motors that would normally burn up in just 2 to 3 runs. Now you could run the boat as long as you wanted. These were electric powered boats.
If you could make a coil to fit around the resistor in your unit, you could keep it cool with water through a tube.
Here is a picture of one you can buy for boats. The size might not be right but it might give you an idea.
Click for more details.
Keep cool,
Chas S.
I've done a lot of load testing with various batteries, and I usually use inverters for 12 V loads. A 750 W inverter can pull a good 50 amps, and if you want more current, add extra inverters. You can get fancy and use a datalogger to get accurate discharge curves, but a simple way is to use an inverter with a low voltage disconnect (usually 10.5 V) and plug a clock (old school) into it. Turn it on, and come back when it's off - you discharge time will be waiting for you. The loads can be choosen for the application - I like 500 W halogens, or space heaters for the big ones. I am curious about why you want to test with such high loads; unless you're hill-climbing, even a Perm or Etek will only pull hundereds of amps for a few seconds.
Patrick