How many little fuses do you have to blow... - Page 3
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  1. #27
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    1,949
    I bought one of those little poppers for around $10, after it took out the second transformer, different jobs, I threw it away and bought a couple of 3.2A mini circuit breakers for Carrier rooftops. They cost about $3 and havent lost a transformer since when checking for low voltage shorts.

    If the system doesn't have a low volt fuse in it to protect the transformer I ussually wire one in.

  2. #28
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,131
    Quote Originally Posted by ICanHas View Post
    Controls is my forte and Fluke meters use a special 11A fuse with 20,000A interruption capacity on the high-A range (as opposed to mA range). That fuse is such that it can safely interrupt up to 20,000A of fault current should you accidentally try to measure voltage across phases on 480v bus bars without the meter turning into a fireball but it would just as easily blow if you were to accidentally try to measure current across a cordless drill battery too.
    All that safety is great... but the catch is, that fuse cost like $13/piece.

    I would use two automotive 1156 bulbs(12v 2A or so) wired up in series so that you'd end up with a 24v 2A bulb, simply because 24v bulbs are hard to find. You could leave it connected in a short indefinitely and no harm would be done. The bulbs would simply remain lit indefinitely.

    You know there is a short when the bulbs come on brightly. If you can't be near it, have another person tell/radio you that bulbs lit up.

    It might barely glow with pilot, turn a bit brighter with call for main valve (and might actually drop out with bulbs in place) and light up bright if there's a short.

    If the two bulbs glow like you hooked them up directly to the transformer, there's a short.

    It is more productive than resetting breakers over and over since there's no resetting ever and there is a visual indicator. If it flickers, you've got a chaffed wire in a conduit or something.

    Use it for a while and you'll learn how to eyeball abnormal draw by looking at how bright the bulbs glow.
    +1 for the bulbs, shame that 24V bulbs aren't an off the shelf product. Bulbs are nice to use because if there is a small load the resistance is low, resistance increases as the load does.

  3. #29
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,131
    Quote Originally Posted by Glennhvac View Post
    I love a fried board! Nothing like not having to wonder. Truthfully though I am shocked at how long so many of these boards last. You have relay contacts that might be 1/8" at most switching 3/4 HP motors in many cases. Often for thousands and thousands of cycles. Look at what most compressor contactors look like after a few years and it's a miracle they are not welding together left and right on these boards.
    The board typically won't complete it's power on initialization if any of the relays are shorted. The relay outputs are monitored and if there is voltage when there shouldn't be the board just shuts down. Tech goes to check it and sees no response, replaces board to fix problem. It is surprising though that the relays last as long as they do...

  4. #30
    Join Date
    Dec 2007
    Location
    north suburbs of Chicago
    Posts
    513
    Quote Originally Posted by 54regcab View Post
    +1 for the bulbs, shame that 24V bulbs aren't an off the shelf product. Bulbs are nice to use because if there is a small load the resistance is low, resistance increases as the load does.
    No kidding on 24v bulbs. I am making a pilot light set up to signal in the bedroom when I left the garage door open again at night! Unless I wanted to spend a ton of many I finally found some small 24v leds from probably China.

  5. #31
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,131
    Quote Originally Posted by Glennhvac View Post
    No kidding on 24v bulbs. I am making a pilot light set up to signal in the bedroom when I left the garage door open again at night! Unless I wanted to spend a ton of many I finally found some small 24v leds from probably China.
    If they are the ones on eBay for $6 or so for a 10 pack they are decent LEDs for the price. The diode and resistor are heatshrinked on one of the leads. They even have 1/4" spades preinstalled.

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