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UL transformer?
- Thread starter DTSFA
- Start date
Max power source nameplate rating for Class 2 AC supply with that voltage output rating is 100 VA - See Table 11(A) in the NEC.
xnuke
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xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
The definition of a Class 2 transformer per UL-1585 (which preceded 5085) is limited to 100VA and under 30V. I don't have a copy of the new standard, but I'm pretty sure that part remains the same. So if it is 2000VA then by definition it cannot be Class 2 regardless of the voltage.
"Will work for (the memory of) salami"
"Will work for (the memory of) salami"
jraef and xnuke are correct. I deal with Class 2 stuff regularly.
As for your 27V out -- if that's the full load rating, you are definitely in for a search. May I ask why 27V? I'm just curious. Common 24V transformers that size will deliver 27+V at no load.
Best to you,
Goober Dave
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As for your 27V out -- if that's the full load rating, you are definitely in for a search. May I ask why 27V? I'm just curious. Common 24V transformers that size will deliver 27+V at no load.
Best to you,
Goober Dave
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- Thread starter
- #6
DRWeig & jraef, thanks for your helpful answers,
27V ac is a bit strange I agree, it feeds into one of our bespoke PCB control boards, where, it is rectified for 24v DC.
I can only guess that the original designer wanted to bump up the output from tx to account for volt drop.
( as the cable run into the PCB is quite a few metres)
what say, if we used a Rockwell 1606 PSU, where it states it is a regulated Class 2 supply ?
( obviously we will need to modify our PCB to take in the DC directly from new PSU)
thanks in advance
27V ac is a bit strange I agree, it feeds into one of our bespoke PCB control boards, where, it is rectified for 24v DC.
I can only guess that the original designer wanted to bump up the output from tx to account for volt drop.
( as the cable run into the PCB is quite a few metres)
what say, if we used a Rockwell 1606 PSU, where it states it is a regulated Class 2 supply ?
( obviously we will need to modify our PCB to take in the DC directly from new PSU)
thanks in advance
Sure, DTSFA, as long as your power supply is listed and labeled as Class 2 you'll be fine. That's a good solution as long as you need <= 100 VA on the DC output. Your initial transformer design may have been oversized to accommodate linear power supply losses maybe?
By the way, it's the NEC that defines Class 1, 2, 3, etc... UL 5085 just specifies construction and testing methods to ensure that they meet the NEC rules.
Best to you,
Goober Dave
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By the way, it's the NEC that defines Class 1, 2, 3, etc... UL 5085 just specifies construction and testing methods to ensure that they meet the NEC rules.
Best to you,
Goober Dave
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- Thread starter
- #8
Yes. 100 VA max. But if your power supply is listed and labeled Class 2, that's already been taken care of for you. I suspect that the output of the original DC supply was less than 100 VA (or Watts since it's DC). Check that out. But don't parallel Class 2 supplies if you need more. That would nullify your product's exemption from scrutiny.
The advantage of Class 2 circuits is that in most circumstances, stuff on the downstream side of a Class 2 power supply is not subject to investigation by UL or even an AHJ (unless the AHJ decides to).
Best to you,
Goober Dave
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The advantage of Class 2 circuits is that in most circumstances, stuff on the downstream side of a Class 2 power supply is not subject to investigation by UL or even an AHJ (unless the AHJ decides to).
Best to you,
Goober Dave
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- Thread starter
- #10
Good luck with it!
Best to you,
Goober Dave
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Best to you,
Goober Dave
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Trick to the control circuit.
If you have large consumers in the controls and a higher voltage level available, use the higher voltage for them and use interposing relays in the controls. Costs more in components, but gets around the limitations, which can end up costing less in the long run.
For example if you have contactors switching 230V power, but we're going to use 24V coils, use the 230V for the coils, switched by a small relay that operates at 24V. Some contactor mfrs even have clip-on interposing accessories that do this right at the contactor.
"Will work for (the memory of) salami"
If you have large consumers in the controls and a higher voltage level available, use the higher voltage for them and use interposing relays in the controls. Costs more in components, but gets around the limitations, which can end up costing less in the long run.
For example if you have contactors switching 230V power, but we're going to use 24V coils, use the 230V for the coils, switched by a small relay that operates at 24V. Some contactor mfrs even have clip-on interposing accessories that do this right at the contactor.
"Will work for (the memory of) salami"
I have no idea if this is what you're looking for, but we use similar drivers for our LEDs.
NES-350-27
NES-350-27
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