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DocJC



Joined: 16 Mar 2006
Posts: 90
Location: Cleveland, OH
Posted: 05 March 2009, 2:37 AM    Post subject: Reply with quote
Since the spec's on the IR3310 so far exceeded the circuit's needs it was easier just to raise the shut down limit. My biggest concern was the current capability of the circuit board traces. Thus far, no problems.

JC
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spamiam



Joined: 13 Nov 2005
Posts: 689
Posted: 05 March 2009, 12:40 PM    Post subject: Reply with quote
DocJC wrote:
Since the spec's on the IR3310 so far exceeded the circuit's needs it was easier just to raise the shut down limit. My biggest concern was the current capability of the circuit board traces. Thus far, no problems.

JC


It was hard to see all the power traces on the board in the photo, but I could see large areas of silver around the connectors and fuses.

Having fuses in inaccessible places is a potential problem as you clearly already know. In a place like this, I'd install a fuse that was sized just below the maximum surge handling capability of the weakest link on the board. The fuse would be there to protect the board only.

Usually the fuse is to protect the WIRING, but that could be done elsewhere in a more easily replaced location. Another option would be to use self-resetting circuitbreakers on the circuitboard. That way you would "never" have to open up the inaccessible box. The circuitbreakers are not all that much larger than the typical auto fuse, so they probably would fit easily.

-Tony
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DocJC



Joined: 16 Mar 2006
Posts: 90
Location: Cleveland, OH
Posted: 05 March 2009, 17:17 PM    Post subject: Reply with quote
Hi Tony,

Actually each circuit had an in-line fuse, external to the box, as well. I used "automotive" in-line fuses, and about a year later one circuit was intermittant. Turns out there was corrosion on the (cheap) spring loaded terminals inside the fuse holder. I filed them all clean, and then went looking for "marine" grade in-line fuse holders. These were easier to reach, but not easy.

Live and learn.

I do recall looking for self resetting mini circuit breakers, but did not find any with 20A ratings, hence the fuses. If I every re-do it I'll look harder.

JC
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spamiam



Joined: 13 Nov 2005
Posts: 689
Posted: 05 March 2009, 19:04 PM    Post subject: Reply with quote
DocJC wrote:

I do recall looking for self resetting mini circuit breakers, but did not find any with 20A ratings, hence the fuses. If I every re-do it I'll look harder.
JC


http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=302-1244-ND

Here is one. There is a family of similar units in varying ratings. Of course, they are out of stock of the 20 amp type!

I found some reasonably cheap ones at Pep boys auto store a while back.

-Tony
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DocJC



Joined: 16 Mar 2006
Posts: 90
Location: Cleveland, OH
Posted: 06 March 2009, 6:47 AM    Post subject: Reply with quote
Tony,

Thanks for the link.

Man, they don't come cheap, but they sure are convienent!

JC
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Don_Kirby



Joined: 15 Oct 2006
Posts: 329
Location: Long Island, New York
Posted: 07 March 2009, 1:04 AM    Post subject: Reply with quote
Wouldn't a PTC be appropriate here?

-Don
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spamiam



Joined: 13 Nov 2005
Posts: 689
Posted: 07 March 2009, 4:44 AM    Post subject: Reply with quote
Don_Kirby wrote:
Wouldn't a PTC be appropriate here?

-Don


Well, maybe, but I don't see any rated to hold at 20A. They seem to have a "slow blow" effect. Their "trip" values are rather larger than their "hold" values, so it seems that there is a significant time coefficient to the determination of how soon it will "blow" between the "hold" and "trip" values. This is not necessarily a problem, but a 15A hold value might be.

-Tony

Last edited by spamiam on 07 March 2009, 20:10 PM; edited 1 time in total
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DocJC



Joined: 16 Mar 2006
Posts: 90
Location: Cleveland, OH
Posted: 07 March 2009, 17:27 PM    Post subject: Reply with quote
Hi Don,

Thanks for the input. I'll have to take a closer look at their spec's and their Vmax rating, as well.

It is always good to have options!

JC
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