mrlots2do said:
VA will go down, but not halved, because secondary wires are overdimensioned.
Moamps could tell you what you can expect, he used transformers with primary's in series a number of times and measured max output.
For big transformers he named 70 to 80% of nominal VA.
You can measure the diameter and resistance of the secondaries, and look in a wire chart how much current is acceptable
If you need even lower voltage after putting the orimaries in series you can unwind the secondaries without hurting the VA number.
I found this on Plitron's website. The information appears to be very useful to all trying to determine VA rating of toroid.
Temperature Rise
Figure 11 illustrates the rise in temperature of a Standard Power toroidal transformer in relation to output loading. PLITRON’s Standard Power Transformer Line is designed to 40 deg. C temperature rise above ambient. Temperature rise drops drastically with load: at 50% load, temperature rise will be about 25% of the rise at full load.
So....
50% transformer va will have a temperature rises of 10 degrees above ambient temperature. Sounds easy to check, anyone try this with know VA values.
New subject, fuse sizes, haven't found calculation for that yet.
120v primary of 240VA transformer, would I install 2 amp primary fuse.
24v secondary of 240VA transformer, would I install 10 amp secondary fuse.
Temperature Rise
Figure 11 illustrates the rise in temperature of a Standard Power toroidal transformer in relation to output loading. PLITRON’s Standard Power Transformer Line is designed to 40 deg. C temperature rise above ambient. Temperature rise drops drastically with load: at 50% load, temperature rise will be about 25% of the rise at full load.
So....
50% transformer va will have a temperature rises of 10 degrees above ambient temperature. Sounds easy to check, anyone try this with know VA values.
New subject, fuse sizes, haven't found calculation for that yet.
120v primary of 240VA transformer, would I install 2 amp primary fuse.
24v secondary of 240VA transformer, would I install 10 amp secondary fuse.
Hi,
I doubt the transformer will start with a 1A fuse so just try it with a 2A.
Until you know more about you transformer I would rather you fitted lower rated secondary fuse, try 3A or 5A.
Another thing to do to protect yourself and the transformer is fit an inline light bulb in the primary circuit. Only heard about this recently on DIYaudio and it's so simple and foolproof that I went & built one.
I doubt the transformer will start with a 1A fuse so just try it with a 2A.
Until you know more about you transformer I would rather you fitted lower rated secondary fuse, try 3A or 5A.
Another thing to do to protect yourself and the transformer is fit an inline light bulb in the primary circuit. Only heard about this recently on DIYaudio and it's so simple and foolproof that I went & built one.
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