I'm sure this is semi-basic and I think I know the answer but want to double check. I have two transformers that I want to wire up to an IEC socket. Both transformers have dual primaries and dual secondaries. I'll be wiring this up for 115VAC. I figure I'll bunch up the appropriate wires, solder them together, use a little bit of heat shrink tubing and wire them to the IEC and Power Switch. Furthermore, I'm using both secondaries on one transformer and one of two secondaries on the other trafo. I'll take the unused secondary and tie it off and wrap it in electrical tape and heatshrink. If I'm going for 2x15VAC and 1x9VAC would I be wiring up the secondaries in parallel? I definitely know I'm not wiring them up in series. This is what I'm thinking would work for my primaries...
For secondaries this is what I would think if they need to be in parallel...
Does this make sense?
For secondaries this is what I would think if they need to be in parallel...
Does this make sense?
The short answer - is to parallel the primaries down stream from the IEC connector. The secondaries are dependent upon how and what they are going to feed. IOW, your diagram looks correct. 🙂
Phasing? I'm not quite following. Do you mean which terminals its plugged into on each supply? If that's the case from looking at the Sigma 25 supplies I'm using there is no indication of phase relationship -- just two ~ indicators.
Two things:
Firstly, for safety reasons, the switch should come before the fuse. You don't want someone thinking that the fuse is safe to work on if the power switch is turned off when it isn't.
Secondly, each traffo should have its own fuse, rated for its current. Sharing one fuse means it has to be over-rated, and if one traffo develops a fault, the fuse might not protect from overload and fire.
Firstly, for safety reasons, the switch should come before the fuse. You don't want someone thinking that the fuse is safe to work on if the power switch is turned off when it isn't.
Secondly, each traffo should have its own fuse, rated for its current. Sharing one fuse means it has to be over-rated, and if one traffo develops a fault, the fuse might not protect from overload and fire.
The fuse should come before the switch as currently shown on the line side of the IEC connector. Standard practice here in North America. All consumer gear I've seen with UL/CSA labels applied are built this way. (I've also designed consumer and medical gear for this market) Switches have been known to short to the chassis, and depending on a distant circuit breaker to interrupt the current is considered a means of last resort. (Unlike the UK we do not have fused plugs except on Christmas decorations 😀 ) Anything that is being worked on should be disconnected from mains.. Standard bulkhead mount fuse holders used here are intended to wired with the mains connection at the far end of the holder so that inadvertent human contact is impossible.
Individual fuses per transformer are not a bad idea at all, however I've rarely done this on home projects and have yet to loose a transformer this way. Also consider what each transformer is powering and make sure if one fuse blows and another doesn't that no further mischief will ensue.
Individual fuses per transformer are not a bad idea at all, however I've rarely done this on home projects and have yet to loose a transformer this way. Also consider what each transformer is powering and make sure if one fuse blows and another doesn't that no further mischief will ensue.
This is what I will do. I hope it is safe enough. Add up the VA of both transformers and divide by 120v. 10VA+7VA/120V = 0.141A. I ended up buying a few .2A slow blo fuses. I'll put it before the switch. I guess Andrew's option seems uber protective though.
two sub 10VA transformers probably don't need separate fuses.
I mistakenly assumed you were referring to power transformers.
Don't bother with soft start for these small transformers (check primary resistances). Just use normal fusing of THREE times total VA / supply voltage.
I mistakenly assumed you were referring to power transformers.
Don't bother with soft start for these small transformers (check primary resistances). Just use normal fusing of THREE times total VA / supply voltage.
Ditto. Agreed
If using panel mount fuse enclosures, yes. If using PCB mount, then I disagree. Look at any computer PSU for examples.
Its a good idea,
To fit surge protection NTC on power Tx's..the magnetization current can and does take out fuses that are close rated even slow blow "T" type. It can also weld the power switch closed and if these are high VA that will happen and you will not be able to switch the equipment off. So MOV for back EMF and NTC is the way to go. Toroid Tx's are prone to high Magnetization "On" surge.
Regards
M. Gregg
To fit surge protection NTC on power Tx's..the magnetization current can and does take out fuses that are close rated even slow blow "T" type. It can also weld the power switch closed and if these are high VA that will happen and you will not be able to switch the equipment off. So MOV for back EMF and NTC is the way to go. Toroid Tx's are prone to high Magnetization "On" surge.
Regards
M. Gregg
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I'm sure this is semi-basic and I think I know the answer but want to double check. I have two transformers that I want to wire up to an IEC socket. Both transformers have dual primaries and dual secondaries. I'll be wiring this up for 115VAC. I figure I'll bunch up the appropriate wires, solder them together, use a little bit of heat shrink tubing and wire them to the IEC and Power Switch. Furthermore, I'm using both secondaries on one transformer and one of two secondaries on the other trafo. I'll take the unused secondary and tie it off and wrap it in electrical tape and heatshrink. If I'm going for 2x15VAC and 1x9VAC would I be wiring up the secondaries in parallel? I definitely know I'm not wiring them up in series. This is what I'm thinking would work for my primaries...
For secondaries this is what I would think if they need to be in parallel...
Does this make sense?
That wont work. The PSUs should be connected one to GREEN and RED and the other to BROWN and BLUE.
if that was my amp. i will wire two transformer
primaries in parallel and whatever small traffos are used
and connect it to a single fuse...
there is no electrical code that that says
each transformer needs separate fuses....
using two fuses, if one fuse blows, there is
no point using the equipment if only one traffo is alive...
eventually you will have to trun the thing off anyway
to replace the busted fuse...
primaries in parallel and whatever small traffos are used
and connect it to a single fuse...
there is no electrical code that that says
each transformer needs separate fuses....
using two fuses, if one fuse blows, there is
no point using the equipment if only one traffo is alive...
eventually you will have to trun the thing off anyway
to replace the busted fuse...
The top transformer wiring is correct.
The lower transformer shows taps from two different windings. You need the taps from the same winding for the lower supply.
The other pair of taps on the unused winding need to be insulated separately, not tied off.
The lower transformer shows taps from two different windings. You need the taps from the same winding for the lower supply.
The other pair of taps on the unused winding need to be insulated separately, not tied off.
the fuse can be installed at the other side of the IEC inlet..
this arrangement is typical for american type equipment...
for European, switches must be able to disconnect both sides of the line,
fuses are also provided to both sides, I have seen IEC inlets that had two fuses instead of just one...
WRONG. Look at the transformer connections carefully.
If the OP is suggesting using the transformer as CT then I agree but as shown the wiring is incorrect.
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Yes these are low VA toroid transformers. I wrote the wrong values... they are 15VA and 7VA for a total of 22VA. According to my maths and Andrew's calculation that leads to .550mA fuses. My diagram is misleading because I was borrowing someone else's drawing.
Ok so then I don't want to wire my secondaries in parallel then? From Amveco's PDF, which is where I got their schematic (which is shown in both examples), they mention either wire things in parallel or series. I'm not looking to do center tap though. I'm looking to get on one trafo 2x15VAC and the other 1x9VAC. I will certainly insulate the second pair of wires from each other and everything else for my safety.
I thought CT would be... green by itself, red and brown together, and then blue by itself.
Ok so then I don't want to wire my secondaries in parallel then? From Amveco's PDF, which is where I got their schematic (which is shown in both examples), they mention either wire things in parallel or series. I'm not looking to do center tap though. I'm looking to get on one trafo 2x15VAC and the other 1x9VAC. I will certainly insulate the second pair of wires from each other and everything else for my safety.
I thought CT would be... green by itself, red and brown together, and then blue by itself.
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yes, the red and brown connected together is your center tap, then the blue and green are your outer windings...you can check with a dmm to confirm that indeed the green to blue wires give you 30v ac with the red and brown tied together...
I'm still a bit confused. I'm not trying to do CT. I'm just trying to use both my secondaries on one transformer and only one secondary on the other. I can double check with the manufacturer of the power supply boards for what they recommend.
Thanks!
Thanks!
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