60 amp Circuit Breaker Info
Posted by Thomas A. Frank at 1/8/2001 6:56 PM EST
Engineer on team #121, The Islanders/Rhode Warrior, from Middletown (RI) High School and Naval Undersea Warfare Center.
I had the pleasure of testing these breakers for FIRST over the summer, to verify they would work on DC (not all circuit breakers will respond correctly), and how they would behave under robot-like conditions.
They are very nice for this application :-)
From memory, here are the results we got:
Test 1: serious overload. If we consider maximum possible load to be the point where the battery voltage drops to just under 9 volts (the point where the robot controller drops out), then battery in the kit can provide about 200 amps for a modest period of time (we unfortunately demonstrated this in the 2000 NJ Regional). Shorted it will drop below 8.5 volts, and is good for about 225 amps (measured).
Anyway, the 60 amp breaker will hold for about 8 seconds at 200 amps. Test was repeated several times, and the results were consistant. It made a horrible squeeling noise when undergoing this test.
Test 2: big spikes followed by reasonable operation. What if your machine spikes 200 amps at start up, and once you overcome friction it settles into a reasonable current draw of 50 amps. During a match, you might see a couple of spikes, but mostly average oepration.
This test consisted of 2 seconds at 200 amps, 28 seconds at 50 amps, 2 seconds at 200 amps, then 28 seconds at 50 amps, then 2s at 200a, 28s at 50a, 2s at 200a, 28s at 50a (2 minutes total). The breaker did not trip under this condition.
Test 3: OK, maybe you draw more than 60 amps, say 100 amps. How long will the breaker hold that?
Answer: 1 minute and 50 seconds at 100 amps continuous.
These were the primary electrical tests. Then I went over to the shock and vibration group.
Test 1: attach breaker rigidly to 800 pound table. 400 pound hammer is free to swing against table from the side. The blow is aligned such that the shock has the highest chance of tripping the lever to off.
Results: 1 foot drop - no effect
1.5 foot drop - no effect
2 foot drop - toggle barely tripped
2.5 foot drop - toggle tripped 'smartly'
3 foot drop - small cracks noted in body
5 foot drop - breaker shattered
The table is spring mounted, so that the 1 foot drop is approximately 100 g's. Therefore, I don't expect that collisions between robots will trip the breaker. However, if you tape or otherwise lock it so that it cannot accidentally be tripped, this does NOT appear to affect the devices ability to interrupt an overload, as there appears to be an internal clutch (I recommended this, but I haven't read the manual far enough to know if it is approved or not).
I also recommended to Eric that the breaker be mounted with double-sided foam tape to isolate the breaker a bit from shock...and I haven't read the manual far enough to know if he took my advice!
As for vibration, the 70 amp model I tested (after destroying the 60, see above) did not seem sensitive to any reasonable levels of vibration. It bounced (and continues to bounce) around in my car without trouble, and on a shaker table for several minutes without incident. Unfortunately, I can't quantity the numbers for the vibration; however, this should not be a concern. In the off season (and during buildup), we have been using a similar (but not identical) breaker in our machines since the switch from drill batteries.
I hope this answers any questions people might have about this part.
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