Author Topic: Cheap 100A 12V disconnect autopsy (big pics notice lol)  (Read 2403 times)

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Offline MadScientist267

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Cheap 100A 12V disconnect autopsy (big pics notice lol)
« on: August 21, 2016, 01:35:02 pm »
100A 12V Cheap (everywhere but the wallet... ok so 20 bucks... lol) auto parts stores disconnect switches...

6074-0

Started getting hot and developing between 300 and 400mV drop in the 30 and 40A range. Decided to see what the problem was, expected to find oxidized contacts or evidence of sizzling... Nope, just cheap!

6062-1

The bridge bar is about as thick as a US nickel... couple mm or so. Didn't measure it exactly. Anyhow, it's slightly curved back away from the target contact plane and as you can see, just rubbing really small spots toward the plunger. A simple extruded bar of copper.

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... and a closeup of each side...

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Then there's the target contacts... They look to me like they were extruded as well, but along the stud axis, with no milling, doming, or possibly even just looked at for a half second with wishful thinking in mind... Absolutely nothing done other than whatever was involved in creating the threaded studs on the other side.

Couple of close ups of those...

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I've got 2 more of these things in the mix, just "heavier duty"... supposedly good for 300A. I shiver at the possibilities with just one early system stress test where I was in the ~150A mark for a less than trivial amount of time (again, not thru this particular one, but the others aren't THAT much different).

Moral of the story... save the headache that 20 bucks buys at your local auto parts store (or possibly worse, online), and cough up a few bucks for a real switch... at the very least, one with wiping action in some form... All exercising these things does is make them worse.

Steve
Wanted: Schrödinger's cat, dead and alive.

Offline bj

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Re: Cheap 100A 12V disconnect autopsy (big pics notice lol)
« Reply #1 on: August 22, 2016, 07:55:10 am »
  Another example of the cheap stuff being passed of as useful.  Include ignition switches, relays,---
basically anything with contacts.
  Takes a lot of trial and error to find good stuff.
  Only indicator I have found is how well a company stands behind their stuff.  And even that doesn't
work until you actually try to send something defective back.  Sometimes there is so much red tape
that it isn't worth it.  Pretty sure that is the way they intended it.
  If I sound a bit bitter about it,  it's because I am.   
  This kind of thing has wasted a lot of my time/money.
  end of rant.
"Even a blind squirrel will find an acorn once in a while"
bj

Offline Pete

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Re: Cheap 100A 12V disconnect autopsy (big pics notice lol)
« Reply #2 on: August 26, 2016, 07:50:51 pm »
Looks like a typical case of over enthusiastic manufacturer specs.
It looks way too small to carry 100 amps. I use switches designed for boats, they have to be pretty large and have decent sized bolts to connect the cables to before I would trust them. Even so , If a switch is rated at 300 amps, it is probably OK for 100 amps.
It seems that we are on the end of a foreign currency grab, where the manufacturers will try to sell anything just to get hold of our money.
Reminds me of the 1960's with the junk that used to come out of Japan, then they caught on and decided to make great stuff.
It is the Chinese companies turn now to make junk. I was bolting something up on my car this morning, the 10 mm bolt I was using stripped its thread way before it got anywhere near tight.
Guess they make their steel out of plasticine too.
Pete

Offline bj

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Re: Cheap 100A 12V disconnect autopsy (big pics notice lol)
« Reply #3 on: August 27, 2016, 06:17:41 am »
  I have seen some good Chinese stuff, so I think some of the blame lies with North American firms
putting their name on parts that were ordered with only cheap cost in mind.  The Chinese aren't
idiots--if they don't meet order spec, they don't get paid.  That said, they also tend to bend
spec representation on off the shelf stuff.
  One has to be careful I guess.
"Even a blind squirrel will find an acorn once in a while"
bj