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240-208v transformer, increasing output voltage?

SND

Diamond
Joined
Jan 12, 2003
Location
Canada
My transformer is a 240D-208Y/120V , right now it has about 247v going in ,factory taped for at 240V in but still putting it out bang on 208V. If I wanted to raise that 208 up a bit, would changing the primary tap to 234 or 228V do anything to raise the 208V side?
Mostly just curious.
thanks.
 
If you feed your 240 into the 234 tap you will get 213 volts. 228 will get you 219. It's possible the transformer could run hotter, but not by much.
 
Thanks, I may try it on 228v tap.
The transformer is only gonna see about 1/3 of its KVA rating, so heat/efficiency probably won't be affected.
Machines all call for 220v so getting it closer to that might be good.
 
If you have these taps on the 240 V side, you could set it up as an autotransformer and get close to the exact voltage you want.

Bill
 
Yeah, the 5 taps are on the incoming voltage side in 2.5% increments I think.
I just have to carefully remove the varnish off the loops, its copper wound thankfully.
 
Thanks, I may try it on 228v tap.
The transformer is only gonna see about 1/3 of its KVA rating, so heat/efficiency probably won't be affected.
Machines all call for 220v so getting it closer to that might be good.

I haven't done it here, yet. I need to find a home for the old Delta-Delta 15 KVA first.

But IF I can find older, used-but-good nominal 220 VAC- 208, or even 230- 208, the 246 VAC I have off present-day mains --> RPC or --> Phase-Perfect will be good enough, Wye-side with no need of taps. I can already run the 208 Wye off the MEP-803a gen set to 220 VAC with a panel knob twist. Running off Diesel smoke is just not in the longer term plan.

CAVEAT; One gets a handy re-derived local Neutral off that Wye side. But it will no longer be 120 V any-leg to Neutral, it will be a skosh higher.

1-P leg at 130++ VAC is not a big deal if one is running 12V LED worklights off a wide-input-range world-market wall-wart.

Might want some care and attention of one is running older CNC gear - or even just power-traverse add-ons to a manual mill - that might not have as flexible-input choice of PSU as Pee Cee's and such use. DRO are actually more likely to have "eat whatever's there" world-market PSU, much as laptop pee cees do.

2CW
 
Thankfully I don't need the 120V/neutral on the Wye output, its only got 3ph breakers in the panel that is fed from the transformer. Anything needing 1ph goes into the regular outlets in the shop.
 
Thankfully I don't need the 120V/neutral on the Wye output, its only got 3ph breakers in the panel that is fed from the transformer. Anything needing 1ph goes into the regular outlets in the shop.

That "was" my plan as well. Simple, but.. what with nuisance and trip-hazard, I'll do it on-machine instead, even if I have to pop for the odd multi-tap control transformer and come off 220 VAC for lack of a Neutral of any kind.

So far, the machine tool builder has been there already fifty and more years ahead of ME..so no spend needed.

Cheap enough if/as/when. Only need to do it the one time, and only for a couple of the machines, anyway.
 
I ended up tapping it on the 228 #5 taps, which brought the output to 222V.
Might just my ears, but it seems to me like it might be humming a tiny bit more than it was on the 240v taps.
 
I ended up tapping it on the 228 #5 taps, which brought the output to 222V.
Might just my ears, but it seems to me like it might be humming a tiny bit more than it was on the 240v taps.

It will because it is drawing more idle current. A perfect core material would draw the same current until it hit the saturation point, then draw a large current. The silicon steel in most common transformers will start an increasing current as it approaches saturation and the current will rise increasingly rapidly as the voltage goes higher. I normally figure a transformer to handle a 15% over voltage. You have moved 5% up that curve.

Bill
 
I ended up putting it back to factory 240V tap #3. It quiet a very tiny bit I think.
I checked the amp draw at idle on either one and it was about 5Amp on the 1ph side into the PP.
I'll leave it there for now, maybe try the 234v tap sometime.
 








 
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