keep losing the primary of my transformer

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keep losing the primary of my transformer

Postby jnicholas1 » Sun Dec 26, 2010 1:09 am

I have a ruud heat pump 1.5 ton with electric backup. The other day it blew the primary in the transformer. I put another one it it and when the sequencers kicked on the amerage went up quite a bit. I changed one of my sequencers. I engauged both of them but only found a small resistance on one set of the contacts. put it back together and about half a day later it did it again. Any ideas on where the overcurrent is coming from? The three element ran with 12.3 amps in them and the primary of the transformer had .35 amps
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- keep losing the primary of my transformer

Postby jnicholas1 » Sun Dec 26, 2010 10:40 am

if I have a short in the low voltage wouldn't the secondary of the transformer blow?
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- keep losing the primary of my transformer

Postby jnicholas1 » Sun Dec 26, 2010 11:28 am

okay I wasn't picturing that in my mind but you are right. I will take your advice and add a fuse to the secondary while I try to find the short. A three amp fuse should be plenty for a 40va transformer.
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- keep losing the primary of my transformer

Postby hvaclover » Wed Jan 05, 2011 4:15 am

In cases where trans are not factory protected by a fuse I find it handy to mini breakers instead of fuses.
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- keep losing the primary of my transformer

Postby nomadpeo » Fri Jan 14, 2011 12:25 pm

you might try the following 'divide and conquer' approach.

- install a 3 amp fuse in transformer secondary.

- measure and record total secondary current in heat pump mode only (call for heat 1 degree above room temp).

- measure and record total secondary current in emergency heat mode only.

- measure and record total secondary current in heat pump plus aux heat mode ( run heat 5 degrees above room temp). the transformer should be able to handle all this current and the current should not exceed 1.6 amps (40va / 24v)

you can then run heat in each mode separately. if there is a current spike, the fuse may blow and you can focus on outside or inside.

if it is determined the problem is occurring outside, install a fuse in the common wire outside and jiggle the wire bundle. if the fuse blows, look for a break in insulation outside.

the current limit for the 40 va transformer is approx 1.7 amps (40va / 24 v). a direct short will blow a 3a fuse. an increase to 2 amps, however may take out another transformer. ultimately, you may need to look for an overheating relay or sequencer.
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- keep losing the primary of my transformer

Postby nomadpeo » Fri Jan 14, 2011 9:26 pm

purpose would be to locate the problem.
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