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Old 18th July 2003, 04:52 PM   #1
jarthel is offline jarthel  Australia
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Default shorted mains with transformer connected

The primaries of the transformer was connected when it shorted. I have a Hammond 300 series (with plate: 225-0-225V and heater secondaries: 6.3V). When I turn it on, the bridged rectifier connected to the heater secondaries output around 30+V. I think this is completely wrong. Well after awhile, the 100ma 250VAC slo-blo fuse would just give up.

Did I have kill the transformer? How do I test if it still works.
Thanks

jayel
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Old 18th July 2003, 05:45 PM   #2
moamps is offline moamps  Croatia
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Hi,
check your primary connection at site http://www.hammondmfg.com/300series.htm

Primary fuse for 50VA/220V transformer can be rated at 0.5A slow.
You can check windings resistance (primary ca 50ohm, HV secondary ca 100ohm, tube heating secondary ca few ohm).

Regards
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Old 18th July 2003, 05:57 PM   #3
jarthel is offline jarthel  Australia
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Quote:
Originally posted by moamps
Hi,
check your primary connection at site http://www.hammondmfg.com/300series.htm

Primary fuse for 50VA/220V transformer can be rated at 0.5A slow.
You can check windings resistance (primary ca 50ohm, HV secondary ca 100ohm, tube heating secondary ca few ohm).

Regards
Primary connection is alright to me. I followed that hammonds page when I connected it.

when you say test for resistance:

1. my primary is 240VAC. so for me to test the primary resistance, I connect the transformer to its appropriate mains rating and then measure resistance at the 2 primary wires?

2. what about the secondary? the plate and heater secondaries have 3 wires with the middle one usually center-tap. must I measure the resistance at the outside wires (not the center-tap)?

Thank you

jayel
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Old 18th July 2003, 06:11 PM   #4
jarthel is offline jarthel  Australia
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I just tested for resistance according to what I believe is right (above post).

primary has 42ohms
plate secondary = can't determine. I also checked for continuity and doesn't get a beep.
heater secondary = resistance neglible. When I checked for continuity, I get a beep.

Hope this helps.

Thanks

Jayel
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Old 18th July 2003, 06:25 PM   #5
moamps is offline moamps  Croatia
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Quote:
Originally posted by jarthel
1. my primary is 240VAC. so for me to test the primary resistance, I connect the transformer to its appropriate mains rating and then measure resistance at the 2 primary wires?
Between blue and white
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Old 18th July 2003, 06:30 PM   #6
moamps is offline moamps  Croatia
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Quote:
Originally posted by jarthel
[2. what about the secondary? the plate and heater secondaries have 3 wires with the middle one usually center-tap. must I measure the resistance at the outside wires (not the center-tap)?
HV - between red and red/yel and red/yel and another red
heating - between green and green
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Old 18th July 2003, 06:33 PM   #7
jarthel is offline jarthel  Australia
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The reading of 41ohms for the primary seems to be okay. The heater secondary is giving me a value between 0 to 1ohm. When tested for continuity, the volt-ohm meter beeps.

I'll try the plate secondary tomorrow.
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Old 8th March 2004, 05:48 PM   #8
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hello,
Quote:
The primaries of the transformer was connected when it shorted. I have a Hammond 300 series (with plate: 225-0-225V and heater secondaries: 6.3V). When I turn it on, the bridged rectifier connected to the heater secondaries output around 30+V. I think this is completely wrong. Well after awhile, the 100ma 250VAC slo-blo fuse would just give up.
I am in the same situation as you were!

I have a hammond 270cx with 275-0-275 secondary. When i used it in my latest project , it simply went shorted! I didn't put any fuse in the power line, so it smoke a little bit before I unplugged the power.
I think I have already killed it, although it tested ok. My point is that when you power it up and it doesn't give the correct voltage. It's dead!
I am still looking for a reason when it dropped dead. I have use this transformer for many projects already. The wiring is so simple and I checked my wiring many times already. My concluion is either the rectifying diodes doesn't work or the transformer has some internal isolation problem.
I opened the transformer chassis. The construction was poor. The second scenario could be possible...
As for the first scenario, ill-functioniong diodes turing transformer 's secondary leads connected in some sense, it is possible. I am looking for any similar experience here. Anybody wants to say something.
BTW, I am happy to give away this 270cx away considering that somebody can use its steel core to wire a new transfomer or choke.

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