dummy load / test load for Victor speed controller
 

We'd like to build a test setup for the Victors. Anybody have a suggestion for a cheap fixed resistance dummy load? I don't want to use a motor because the motor is not fixed resistance and it's hard to measure motor power output. Would like to have the ability to set the resistance to about 0.32 ohms to get a 40 A max current test, and also to something like 2.5 ohms for a 5 A max current test. Would like to use a fixed resistor that would spread the heat dissapation over a large area so it doesn't get dangerously hot (500+ watts for the 40 A test).

I can put a big resistor in a can of oil like we do in RF power testing. Anybody got a better idea?

Bill

Re: Victor Burnouts
 

I passed your query on to one of our electrical sub-system mentors.
Our electrical group mostly use the ribbon-style power resistor with a fan blowing on it. The ribbon style are easier to get, cheaper and take a lot of abuse. Between Ebay and online surplus vendors, this can be done on the cheap.
http://www.milwaukeeresistor.com/pdf/ribwound.pdf

There is a chassis mount style which one of our electrical mentors has used at work as well. These are aluminum cased and can be mounted to a finned or water cooled plate, but are more expensive.

Re: dummy load / test load for Victor speed controller
 

How about a 500' roll of #10. An RF load would not get you to the current you want to draw but you could parallel 10 resistors, 5 ohm at 10 watt and drop them in the oil for cooling and be OK I bet.

Re: dummy load / test load for Victor speed controller
 

For discharging our Prius battery packs for our electric airplane project, we use 6 electric water heater elements in a trashcan full of water. Unfortunately, I think their resistance is somewhere around 10-15 ohms, which wouldn't be very doable to achieve .32 ohms.

Re: Victor Burnouts
 

A long time ago, we tested fuel cells by placing two electrical plates into a small swimming pool filled with water and then added rock salt until the resistance was what we wanted. I'm sure that a small garbage can could be used in this case. Some experimentation is required and must be done in a ventilated area (possibility of electrolysis).

Mike

Victor load testing
 

This sure provoked some interesting suggestions! My favorite is the salt water swimming pool...

At lunch I went over to the electronics store and bought 10 3.6 ohm 25 watt resistors. We'll wire them in parallel, in two banks of 5 each, so we can test with either (approx) 450 or 225 watts load at full power (12.8 volts). This should give a max current through the Victor of about 36A, a reasonably safe 10% below max rating for it. These are rectangular concrete resistors, so we can cool them with a slab of steel laid across all of them that will have pretty good surface contact, and keep the full power tests reasonably brief, since at max the resistors will be dissipating about 46 watts of heat each, substantially over their 25 watt rated limit. The steel will also protect from the shrapnel if they blow up....

Thanks again for the ideas.

Bill

Re: Victor load testing
 

I remember seeing a DIY battery tester that used steel banding for the load. A suitable length of steel banding that is used to secure crates was attached to a piece of plywood in a zigzag pattern. The resistance might ba a little low for this project though.

Re: Victor load testing
 

Bill,
I would add a fan to your setup blowing under the steel plate. 25 watt resistors are conservative rating in an enclosed space so with the plate and fan you should be OK for the dissipation. Of course, if you wanted to go the "swimming pool" route, a trip to the store for a couple of gallons of distilled water should add some margin of safety. Pure distilled water does not conduct and is easier to dispose of than mineral oil. When you are done, just add some coffee or tea, sugar and cream to taste, donuts optional.

Re: Victor Burnouts
 

we had to change 3 Victor right be for a demo, we were getting shocked very badly we think think static was the problem. is there a good legal way to ground the robot

Re: Victor Burnouts
 

Colin,
There is no real effective way to do that. In 2003, the "ice" produced incredible sparks so we dragged a tail (the outer shield of a braided coax without insulation or center conductor) and that helped a little when the robot contacted the ramp. (made of copper plated steel) This method was determined to be legal by FIRST for that year only.

Re: Victor load testing
 

Bill;
Check out this link.
http://www.harborfreight.com/cpi/cta...emnumber=90636

This is an auto battery/charging system analyzer but cheap enough to modify for your purposes. You might even rescale the meter and get some sort of go/nogo test rig setup. Enjoy, Larry U.

Re: Victor load testing
 

Remember the old adage about " if it looks to good to be true it is"? I think that is the case here.

Re: Victor load testing
 

Chief Delphi has (or had a few years ago at least) one of these rigged with a standard FIRST battery connector. It is (was ) a good way to know if the battery was charged - it is not perfect but it is a lot better than going by unloaded voltage which is the way many folks try to tell if a battery is fully charged.

But to the matter at hand, they have a coil that literally glows like a toaster when enough current is passed through. I don't know what the current that makes the thing glow is, I but am pretty sure it is above the 36A you are trying to test. I would think that you could calibrate the PWM value of your Victor tester to give you the 36Amp test current.

Anyway, in my opinion, it possible that this tester could dispate the amount of electrical power you are looking for especially if you are only looking for short time periods. A toaster is typcially 1000W or more, you are talking about 36A at perhaps 12V, clearly under 500W.

For $20, it seems to be worth at least a shot.

For what it's worth.

Joe J.

Re: Victor Burnouts
 

We have fried 3 Victors on one motor this year, and the 40 AMP fuse has not tripped... I suspect it is because a short on the motor, because everything else seems fine.

There is another idea.

Re: Victor Burnouts
 

Neil,
It is clearly a problem with that motor if there are other motors on your robot with similar transmissions. It is entirely possible for there to be a mechanical problem that is causing the failures. However, do not rule out the possibilty that the mounting position for that Victor allows it to gather dust thrown up by the motor. I have encountered teams that had positioned the Victor directly in line with the main gear in their transmission which threw little bits of metal into the Victor every time they ran the robot.