On Sat, 09 Apr 2011 11:23:47 -0500, 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!
1.5 amp fast blow for the secondary, no more than 500ma for the
primary if the original was 35va. full rated load would be about .3
amps, so a 250ma would be boarderline. (but the transformer should NOT
be running full rated load, either)

Take the va rating and devide by the voltage to get the current rating
in amps. 40va at 24 volts= 1.66 amps. 40va at 115 volts = .347 amps.
40 va at 127 volts = 0.315, etc.