At a regional last year, a mentor from another team said that they had discovered that the Rev 40A breakers (40A ATO Auto-resetting Breaker - 4 Pack - REV Robotics) had significantly variability in their performance, enough that they specifically selected ones with longer trip times for their drivetrain motors. They mentioned there was a CD thread on this but I couldn’t find one. This experience matches the trip time curves on Rev’s datasheet (trip times for 60A range from a little over 10 seconds to over 1000 seconds) and I was wondering if any other teams had experienced something similar.
What would be the easiest setup for us to test our own breakers? Can we measure the resistance or other properties of the breaker at low current, or would we have to hook the breaker up to a large load and measure the trip time? Is there any suggestions for an cheap and easily adjustable load from 40 to 80A?
12 Volt halogen bulbs are a decent scalable load/current regulatir/resistor. 12 Volt PTC heaters (with fan) worked for a 50 Amp battery testing load.
Make sure your sockets and bulbs match, and get the high wattage bulbs for more current.
What you really need is a high current, low Voltage adjustable power supply. Maybe look for a 3 Volt or 5 Volt one?
You would want some resistance in the circuit to make it sorta stabke, but this might work. You also need a decent current measurement.
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To be clear, any setting off of the breaker measurably changes the performance of the breaker, so by testing them you will be changing their properties.
When I was testing the old style breakers with a heavy duty power supply I didn’t see much resistance change from new vs multiple cycles. BUT, I wasn’t hunting trip time data. IIRC the Rev ones tested similarly.
I was NOT using anything inductive, so no nasty sparks during a trip
It’s got a fan so it should run continuously, and a shroud so you won’t be sending students (or mentors to the ER, nor summoning the fire department. Best for teams working winters in Chicago or Maine, although I see your team is in Calif.
R619-A allows Snap-Action ATO fuses in the PDH, they’re the same company that makes the physically bigger PDP resetting breakers. I know from experience they’re slow to trip; I can’t speak about their consistency.
A context question: are you planning to run your motors approaching the amp rating of the breakers, or is your concern circuit-protection?
Thanks for the good suggestions. The main thing I wanted to do is to understand how much variability these breakers have, and see if other teams have had experience with this. 60A for 10 sec won’t burn up a NEO/Kraken, and I wouldn’t be too concerned about 10awg wire, but it will trip the breaker, and that doesn’t seem ideal to me. And if some percentage of the breakers are out of spec, then it could definitely matter.
$150 to test this is a bit out of our price range though, especially since our team doesn’t push the limits. If it was as simple as measuring the resistance of the breakers though…
I did a bunch of cycles on a range of breakers, but I wasn’t looking for trip current or time; just contact resistance. Note that these were sorted; that spike at the end is an artifact of sorting, not end of life…
So for the old 20A, for example, did you have one 20A breaker that you tested 18 times, or 18 different 20A breakers? And is this just resistance measured with a multimeter?
Each trace is a single breaker that got repeated tests. I had a rather limited set of REV breakers to play with at this point.
I used a high current precision power supply to drive the breakers to opening. I tested with both a 4 wire milli-Ohm meter and also high precision bench meters for Amps and Volts to calculate the resistance. I found my milli-ohm meter lined up very well with the dual meter method.
As part of this I was wondering if the test current would affect the results, or if pre-conditioning would change them. A couple of kilo-Amps did not change the resistance of a SB50 connection enough to measure. I used a spot welder for that one The cables MOVED due to the Lorentz forces! Bonus!
to the ER, nor summoning the fire department. Best for teams working winters in Chicago or Maine, although I see your team is in Calif.
The cables MOVED due to the Lorentz forces! Bonus!