question

rspott avatar image
rspott asked

Isolation transformer high output voltage

I have an automatic isolation transformer that I am supplying with 120VAC input.

I’ve set the output voltage to 230VAC via the jumper settings provided in the manual but I am seeing 260VAC output.

What am I missing?

voltageIsolation Tranformer
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3 Answers
wkirby avatar image
wkirby answered ·

What is your exact input Voltage at that time?
Remember, the output is 1:1.05 higher than the input Voltage within tolerance. It will be 1.2.1 higher when stepping up like you are.
So, an input Voltage if 123.8V will result in 260V at the output when there is no load. Under load, the output Voltage will reduce.

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rspott avatar image
rspott answered ·

Thank you, this was exactly the case. We turned on several AC units and the voltage dropped with the use.

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Rod avatar image
Rod answered ·

Thanks very much for your posts, they are very helpful:


“ This (Automatic isolation transformer 3600 VA), model will automatically switch to 115V or 230V supply, depending on input voltage.

  • Supply 88 V ~ 130 V: switches to 115 V supply.
  • Supply 185 ~ 250 V: switches to 230 V supply range.
  • Note: The AC input voltage is raised by 1:1.05 ratio at the AC output.”

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A.

The transformer should not give any output on the following input voltage intervals:

0V ~ 87 V

131 V ~ 184 V

250 V ~ 380 V


Why a transformer with input 123,8 V plus 7.5% to about 133 V, will supply 260 V; instead stop supplying ?

… otherwise it will damage the end user’s devices rated at 115 V


But my transformer ( Which jumpers are set for 230 V) is receiving 252 V at input… would these “Intervals of no-supply” be a reason for the inverter not to kick- in supplying from batteries, when the AC input isn’t present?


Even if the input voltage is 250 V as specified, plus the 1,05 increase built in, will result in 262.5 V…. Enough to damage any equipment in the US rated for 220 V with a 20 % tolerance.

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B. WHEN JUMPERS CONNECTED FOR 115 V

If tolerance is + 18.25%: 115 x (1.1825 / 1.05) % 129.51 V

If tolerance is - 18.25%: 115 x (.8175 / 1.05) % = 89..5% V

Been 1.05 the built-in output design

===========================

This calculation seems odd to me because:

115 x 1.1825 ( ≈ +18.25% ≈ +20.98 V) = 135.98 V

115 x 0.8175 (≈ -18.25% ≈ -20.98 V) = 94.01 V.


Even with a 13% variation / tolerance:

115 x 1.13 (≈ +13% ≈ +14.95 V) = 129.95. V

115 x 0.87 (≈ -13% ≈ -14.95 V) = 100.05 V


Please … what am I missing ?


======================

Your comments, will be appreciated:

Rod

Whatsapp 786 239 1329

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