On Tuesday, June 17, 2014 10:47:48 AM UTC-4, jamesgang wrote:
On Saturday, April 9, 2011 12:23:47 PM UTC-4, Steve Turner wrote:

On 4/9/2011 10:59 AM, The Daring Dufas wrote:

On 4/9/2011 10:48 AM, Steve Turner wrote:

On 4/9/2011 9:12 AM, wrote:

On Apr 8, 10:05 pm, wrote:

On 4/8/2011 8:44 PM, Tony Hwang wrote:



Steve Turner wrote:

A continuation of the "Why does the 115V-24V transformer keep blowing

on my Trane XB80?" discussion I started on 04/02/2011.



...



... Buy one of hevier one(bigger size and really heavier in

weight than stock) If it blows again, something on the load side is

wrong.



I'd venture something is already wrong...



--



I'd agree. Responding to his first post and before he put this

latest transformer in I recommended measuring

how many amps are being drawn on the low voltage side.

This is electricity 101. So, he comes here asking for advice

and instead of listening, he justs puts another transformer in

and blows it too..... Go figure. Time to either get educated

or hire a pro.



In case you hadn't noticed, I've been getting LOTS of (much appreciated)

advice from many people, but it's also been very contradictory with no

single suggested approach. It's been an interesting and informative

discussion, and I've been happy that nobody's been a jerk about it....

until *now*. And I DID listen; plenty of people suggested that the

original transformer was likely to be under-rated and to replace it with

something more heavy-duty. Also, it seems to me that having a working

transformer is a pre-requisite to following your advice of measuring the

amp draw on the low voltage side, no? Unfortunately, time constraints

prevented me from being there to perform those measurements when the

unit was running, and unfortunately again the transformer blew in my

absence. But of course, I'm repeating myself...





Steve I really hope you can figure out the problem with the furnace and

I can understand the bit about time constraints. Installing a fuse in series

with with either side of the transformer is cheap insurance to

keep from losing another transformer. The fuse holders are inexpensive

and it's a lot less of a hassle to replace a blown fuse.



TDD



Yes, I would be more than willing to do that, but my electricity training is

not quite up to the 101 level that trader4 seems to think I should have; can

you suggest a specific fuse rating that I should use? Thanks!



Fuse depends on the transformer rating. Typically they specify a va rating on the secondary.

He said it's 70VA.

Sometimes an amperage. If you have a secondary amperage then that's the fuse size you want. If they give you a va rating, say 50 divide that by the voltage to get the fuse amps. You can get an inline fuse holder and a fuse at radio shack. Use a slo-blo because there will be a surge when the outside unit contactor gets pulled. Most likely you will end up with a 2 amp fuse.


I agree, that's a good idea, except it should be 3 or 4 amps. It would rule out any long over-current draw as the cause.






In the ac mode the transformer is powering the control board and the compressor contactor in the outside unit. If you have a smart thermostat that doesn't run on batteries then it's powering that too.



Most vom's won't measure amperage high enough to check it on the secondary side.

70VA is 3 amps at 24V. IDK about most. Maybe some won't do that,
but all the ones I've used will, including cheap ones. Any decent one
should. But I guess all that's a moot point, based on his last
response.


You can measure the amperage on the primary and multiple by 4.8 to get the approximate secondary amperage.



You have a gas furnace so you only have 115 at the furnace. So fluctuating 115 would have also causes light bulbs to burn out around the house.

You would think so and also, voltage would have to fluctuate a lot to screw the transformer. Given that others are having similar problem, my money would be on these just being cheap, crap parts, but who knows.