Power Transformer PT009 - CTM 33302 info
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Lani
- Breadboard Brother
So I picked up 7 of these on the Bay for a great price thinking they would be good in tube amp projects. I measured all the resistances for them (see below image) and I'm pretty confident I know what wires are the primary and what are the secondary. The primary is a little strange and worries me because you would think the resistances would be the same on both halves which they aren't. Is there a conventional color coding scheme with the wires? I know black & white for the primary is Line & Neutral but I'm unsure on brown (maybe a 100v tap option). I'm planning on feeding it with another transformer, say 6VAC (I know, I need a Variac) and take measurements and do the math, (don't worry, I've been an electrician for 25 years now) but first wanted to post here to see if anyone knows where to get a datasheet or if I'm way off base here. Am I correct that the manufacturer is CTM? Searched Google all morning for info on it and found notta. It does look like it has a high voltage CT winding as well as a low voltage CT winding. Any help would be appreciated! Time to go snow blow the driveway.....
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lolbou
- Old Solderhand
Actually the extra coils (BK to BR) may be to switch between 115 or 120 input and or 230 / 240 when you use the primaries in series or parallel..
You can also use a signal generator at 60 (or 50) Hz and measure the secondaries, and if you don't have a variac, use another transformer to get some 12V AC input (you'll be isolated from the grid regarding current).
The outputs looks center tapped as you mention, but the 300V you're after will then have to be rectified from the opposite ends of the secondary with a full wave rectifier.
TBH I wouldn't expect very high voltages...
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.
- Uh, no, I'm a mocker.
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george giblet
- Resistor Ronker
Technically the manufacturer's spec for the primaries could be 0V (WH), 110V (BR), 115V (BK) or 0V (WH), 115V (BR), 120V (BK). It's hard to split that difference.
To get the full transformer rating you normally need to parallel the primaries for nominal 115V etc. supplies. So if you use the White + Black primary both White's connect together and both Black connect together. Similarly if you use the White + Brown primary both White's connect together and both Browns connect together.
My guess is the transformer rating is around 80VA to 100VA. Perhaps a better estimate could be given if we knew the core outer dimensions (width and height) and the total thickness of the laminations (the stack).
What you don't know is if both secondaries. are rated at 50VA. You can estimate that once you measure the actaual secondary voltages.
Regulation of a transformer that size is likely to be around 6.5% to 7%. That means with no load the output voltage are 6.5% to 7% higher than the manufacturers secondary voltage rating.
From the winding resistances, and assuming 240V in (both WH + BK = 120V, in series), it looks like the secondaries are 500Vct (250-0-250V) and 40Vct (20V-0V-20V). This is a very unreliable estimate with a lot of assumptions. You have to measure the output voltages directly.
When using a full-wave rectifier and a filter you need to derate the DC current.
To get the full transformer rating you normally need to parallel the primaries for nominal 115V etc. supplies. So if you use the White + Black primary both White's connect together and both Black connect together. Similarly if you use the White + Brown primary both White's connect together and both Browns connect together.
My guess is the transformer rating is around 80VA to 100VA. Perhaps a better estimate could be given if we knew the core outer dimensions (width and height) and the total thickness of the laminations (the stack).
What you don't know is if both secondaries. are rated at 50VA. You can estimate that once you measure the actaual secondary voltages.
Regulation of a transformer that size is likely to be around 6.5% to 7%. That means with no load the output voltage are 6.5% to 7% higher than the manufacturers secondary voltage rating.
From the winding resistances, and assuming 240V in (both WH + BK = 120V, in series), it looks like the secondaries are 500Vct (250-0-250V) and 40Vct (20V-0V-20V). This is a very unreliable estimate with a lot of assumptions. You have to measure the output voltages directly.
When using a full-wave rectifier and a filter you need to derate the DC current.
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Lani
- Breadboard Brother
Thanks for getting back to me guys. I will test with a small AC voltage in the morning and report back what I find.
Core dimensions are roughly 55mm x 55mm Laminations are W=85mm L=72mm H=28mm.
Thanks again!
Core dimensions are roughly 55mm x 55mm Laminations are W=85mm L=72mm H=28mm.
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george giblet
- Resistor Ronker
Those dimensions look fairly consistent for that size transformer.Core dimensions are roughly 55mm x 55mm Laminations are W=85mm L=72mm H=28mm.
The core size: EI86x29
Based on standard temperature winding, I estimate rating is in
the order of 80VA to 85VA. Higher temp windings will increase
the rating but there's no simple way to know this is the case
and it's a high risk to make this assumption.
The primary resistance of 18.6 ohm is indicating a 60Hz transformer.
For 50Hz, even if the primaries limited to 230V max (115V + 115V)
it still looks like the core is pushed a little too hard (ie. high Bpk).
It will take some detailed measurements and testing to resolve
the finer points for 50Hz.
Transformer regulation is in the order of 5% to 6%.
(Easy to measure actual with a dummy load.)
Keep in mind these are estimates. It's very difficult to know categorically
what the manufacturer's specs are. It's a good idea to use the low
VA estimate.