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DC breakers from China. Why bother.

efficientPV

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I have several DC breakers from China and decided to test them. These have no agency approvals and who knows how they test them. I have a 55 ohm load and a Xantrex supply that will put out 2A. I set it at 95V which is petty minor duty for something rated at 600V. Just wanted to capture the arc. A word of caution, there seems to be no standard as to which side is the plus or minus. Be careful if you mix and match wiring them all the same. DC breakers have magnets to pull the arc and make it longer when the current creates a magnetic field. Therefore, polarity should be important. Here is the test setup. Next is a trace of the interrupt. Notice the ending arc voltage. Since the magnets and polarity matter, reversing the polarity should be detrimental. Look at the next picture.
This is with polarity reversed. Arc ends sooner and at a higher voltage. I think a single phase AC Square D breaker would do just as well. Both are pretty low ending voltage with two contacts in series. jot108.jpgjot108r.jpg

DCdisconnectTESTs.jpg
 
Any chance you could pop the breaker open to see if it has the expected arc quenching hardware?
Some of the cheapest breakers from China are known to be little more than a crude switch with none of the expected safety features.

I wouldn't write them all off though, there are still some reputable Chinese brands. It's often hard to tell the difference though with plenty of fakes/counterfeits around. Buyer beware.
 
(y) Interesting graphs - have you tested a known good brand as a comparison?
 
(y) Interesting graphs - have you tested a known good brand as a comparison?
Test results shown are probably quite irrelevant. Contact is opening at limited speed in any case. I’d hazard guess that the mechanical contacts are nowhere nearly fully open in 0.00035 seconds.

2 Amps is not going to make much of an arc in the contacts unless you are really unlucky with really bad breaker. Break test at rated current or few thousand amps would be a different matter.
 
Fuses, disconnects, and contactors are enough for me. I think a lot of it is people just wanting to transcribe their AC experience onto DC. Yes a breaker is an attractive concept, but it just doesn't work on DC easily, not for cheap.
 
Any chance you could pop the breaker open to see if it has the expected arc quenching hardware?
Some of the cheapest breakers from China are known to be little more than a crude switch with none of the expected safety features.
This is not proof, but mine I was able to detect the magnet by moving a screwdriver tip along the side. Strength of magnet is quite strong and easily detected on my no-name Amazon breakers.
 
I have three different breaker makes all from China and they have similar results. I get them for free and could break them open, but why should I. External tests are sufficient. Yes, they have magnets and that should increase the arc path shortening the time of the arc. Polarity doesn't seem to have much effect. This is rather minimal voltage and current . The arc time seems much longer than I expected. I don't see how increasing current and voltage will improve things. I was rushed and didn't mention turn on of these breakers. If you slowly press them on, there is no snap action, you can hear them sizzle.
 
Any chance you could pop the breaker open to see if it has the expected arc quenching hardware?
Some of the cheapest breakers from China are known to be little more than a crude switch with none of the expected safety features.

I wouldn't write them all off though, there are still some reputable Chinese brands. It's often hard to tell the difference though with plenty of fakes/counterfeits around. Buyer beware.
Not sure whether to be horrified by that orblaugh hysterically at it.
 
hello - is there a reason not to use DC breaker for AC application ? is the trip point different ? thanks
 
It may not remain a DC breaker after you do. The AC current may demagnetize the internal magnet of the DC breaker. Just a week ago I tested a PV 32A DC disconnect switch. At 60A I gave up after 10 minutes of waiting. At 96A, it did trip in one minute. Plastic had started to melt. Good switch, brakers normally have a time element. It is unlikely a breaker will ever protect one string being overpowered by several other strings.
 
It may not remain a DC breaker after you do. The AC current may demagnetize the internal magnet of the DC breaker. Just a week ago I tested a PV 32A DC disconnect switch. At 60A I gave up after 10 minutes of waiting. At 96A, it did trip in one minute. Plastic had started to melt. Good switch, brakers normally have a time element. It is unlikely a breaker will ever protect one string being overpowered by several other strings.
haven't thought of that, demagnetizing; thank you. Please elaborate the "time element" ?
 
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