BIG MISTAKE
Feb 28, 2006 at 1:27 AM Thread Starter Post #1 of 24

bperboy

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I accidently shorted the vout and ground on my STEPS while measuring with my dmm, and now the output reads about 50vdc from 26vdc originally. I quickly turned the unit off, but is there anything I should check for? Or should I just let it cool off and then turn it on later? PLEASE HELP FAST! Thanks,
bperboy
 
Feb 28, 2006 at 1:53 AM Post #3 of 24

Xakepa

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I think it's safe to turn it on again, and hopefully it will work. AFAIK, 317 is pretty well protected.
 
Feb 28, 2006 at 2:06 AM Post #4 of 24

mono

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Go ahead and turn it on... anything that might happen, already did if it did.

Hadn't you previously posted (in another thread) that you had measured this high voltage? Whatever became of that? I'm just wondering if shorting it had done something or if you had some kind of intermittent fault that may not entirely depend on your shorting the output?
 
Feb 28, 2006 at 2:58 AM Post #5 of 24

bperboy

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The high output was (I think) due to a fault in measurement last time. THis time I accidently shorted the inner and outer sleeves of the output cord and there was a rather large spark. I think it definetely depended on this particular short for the high voltage this time. I will wait overnight and then test again, and see if time remedies anything. Maybe. Hopefully....
 
Feb 28, 2006 at 5:03 AM Post #7 of 24

ericj

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The only way to 'bypass' the 317 would be if the protection diodes were reversed. Since it was working properly before this event, I'm going to guess that something failed.

Since diodes don't usually exhibit a failure mode where they become a dead short (and in any case a dead short across output and ground would not imply a forward potential across them), and they jump out of the board and plug themselves back in backwards only very rarely, I'm gonna put my money on it being a cooked 317.

Congratulations. You discovered that the lm317t does not have enough over-current protection to make it survive a dead short between output and ground.

You've won an all-expenses-paid (by you) trip back to your parts bin (or vendor) for another regulator. I hope you enjoy your trip.
 
Feb 28, 2006 at 6:43 AM Post #8 of 24

jl123

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Quote:

Originally Posted by ericj
Congratulations. You discovered that the lm317t does not have enough over-current protection to make it survive a dead short between output and ground.

You've won an all-expenses-paid (by you) trip back to your parts bin (or vendor) for another regulator. I hope you enjoy your trip.



That's cute man...real cute.
 
Feb 28, 2006 at 11:21 AM Post #9 of 24

bperboy

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Does anyone have a spare regulator lying around, because I don't have any other parts I need and I don't really just want to place one order for just that. THanks,
bperboy

EDIT: I know they're only 47cents but, I don't want to pay 5 dollars shipping. Are we pretty darn sure that that is what the problem is? Is there a better regulator that functions the same but has better short protection?
 
Feb 28, 2006 at 11:25 AM Post #10 of 24

amb

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Quote:

Originally Posted by bperboy
Does anyone have a spare regulator lying around, because I don't have any other parts I need and I don't really just want to place one order for just that. THanks,
bperboy



Radio Shack carries the LM317T.
 
Feb 28, 2006 at 2:26 PM Post #11 of 24

ericj

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Quote:

Originally Posted by bperboy
Does anyone have a spare regulator lying around, because I don't have any other parts I need and I don't really just want to place one order for just that. THanks,
bperboy

EDIT: I know they're only 47cents but, I don't want to pay 5 dollars shipping. Are we pretty darn sure that that is what the problem is? Is there a better regulator that functions the same but has better short protection?



If you're in a major bind (no radioshack in town) I can mail you one. I have about 20 National LM317T-P+ that i paid 30 cents each for. No charge, since i had some fun at your expense.
 
Feb 28, 2006 at 2:45 PM Post #12 of 24

bperboy

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Yeah, that'd be great if you could send me 1 or 2, just in case of another meltdown.
smily_headphones1.gif

I pm'd you the address.
 
Mar 1, 2006 at 12:25 AM Post #14 of 24

ericj

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Yeah, wasn't any time for me to get stuff to the post office today. Will mail tomorrow.
 

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