I have this feeling that you guys are going to disappoint me on this, but I have to try:
Given a double-pole switch with a current rating X per contact, what current could you safely design for if you run the two contacts in parallel?
It's for DC -- I'm interested in the answer both for switching the thing at low current (which is the normal use case) and for those moments when the user shuts the thing off when it's pulling close to the rated current.
-- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Den onsdag den 25. maj 2016 kl. 21.51.22 UTC+2 skrev Tim Wescott:
For DC, the make and break conditions will be defined by the ratings of each
*individual* contact (for obvious mechanical reasons). I.e., worst contact governs. (keep in mind how "worst" is a criteria that changes as the product ages)
But that's only for AC, I did not see anytihng about DC. AC has a Zero crossing that affect make and break.
DC, you might draw an arc that does not extinguish. So, I would stick with the max contact rating for parallel.
Cheers
1.5x the rating of one contact. Or if you add some lead wire resistance to equalize the currents, 2x.
I just made those up.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Den onsdag den 25. maj 2016 kl. 22.09.56 UTC+2 skrev Martin Riddle:
isn't that basically what it says; make/break rating is not increased by paralleling
-Lasse
John Larkin is a pimple on the ass of mankind.
I just made that up.
I've never had pimples there. Is it painful?
Since you can't invent anything electronic, that will have to do.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
One contact is going to open before the other. The question is: how much before? If close enough, an arc will start on the first-opening one also & the load shared. If not, the 2nd one will have to break the full load itself - a no-go. So, you gots to ax yourself: Am I feeling lucky?
I don't think that I've ever seen a spec for the timing between contacts.
Current rating matters most at make & break times. At those times, due to switch bounce there's no way the 2 switches are operating synchronously. Thus the current rating of a parallel pair is the same as of a single switch, not greater.
Current rating while remaining on will be higher with 2 parallel paths. If you're willing to tolerate reduced life you could often run with 2x, but you'd pay a price in MTTF.
NT
At least he isn't making stuff up and pawning it off as "inventing any thing electronic".
-- Rick C
The reference specifically refers to DC in the series case.
I'd like to see hard data on that though. If it was that easy....
RL
Thank you all. I found a suitable switch that has the right current rating on each contact, and isn't too big for my application.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Why do you say such things? I have no idea but it seemed like a good first guess. (and he said he was making it up... what more can you ask for?)
George H.
First I know nothing of this... so perhaps a silly question.
There is some switch bounce time.. (perhaps different times for different switches.) ~100 us to ~1ms? If the second contact.. (I'm thinking a double pole toggle) closes within that time, then can there be some sharing?
George H.
I would think the problem is on opening under load:
If one pole opens before the other, the remaining pole will have to break more than its rated load. The arc could be more than it can handle.
kevin
The numbers are both reasonable. There is no exact answer.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
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Because just pulling numbers out of the ass, good advice would have been to contact an engineer at the manufacturer of the switch.
Ahh OK, Then the answer may be no better than a single.
George H.
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