Hi to all
Has nobody heard of "Current equalising resistors", but I guess this
principle is only used in the domain of solid state amplifier construction
:)
One suggestion is to place a low value resistor (couple of ohms - use ohms
law) in series with one secondary line from each transformer with a suitable
wattage rating. Sometimes a resistor is placed in each line to lower the
wattage rating required. The principle is that as the current increases in
one transformer (the higher voltage one as it tries to push up the lower
voltage one) the voltage drop across the resistor will equalise the load
between them. Using ohms law you can work out what a suitable resistance
will need to be at full load for each. Note the wattage rating of the
resistors can be quite low as at full load you are only trying to drop a few
volts at around half an amp.
The overlooked fact is that there is a big difference between the "no load"
voltage that you measured and the "fully loaded" voltage out of each
transformer which is the rating that you stated. As current is drawn the
output voltage drops on the secondary so the equalising resistors don't have
to work as hard as what you would think. If it was two regulated supplies at
different voltages then that would be a different story trying to match
them.
You are going to generate a bit of heat (in the resistors - few watts) to
equalise them because of the difference in voltages, but it won't be too
serious and then you have a ~2000VA transformer (stacked)
Cheers
Noel
PS> Power in resistors = current squared by resistance
Yeah I know power factor and all that but lets KISS (keep it simple stupid)
And resistance = voltage (drop) divided by current
You don't need to drop 60V (the no load difference between 1950 and 1890) at
0.6A, you would need only need to drop the difference between the full load
voltages (1880V to 1870V). I would check the full load voltages of each
transformer first though!
Assuming this 10V as 0.6A = 16 ohms
and power = 0.6 x 0.6 x 16 = 6 watts
So the simplest case is one 15ohm 10watt wire-wound resistor in one
secondary lead of the higher voltage transformer.
IMPORTANT: Although the voltage across the resistor is low the resistor is
floating at nearly 2000V so take proper HV precautions and mounting
----- Original Message -----
From: "Firson Maryutenli" <firson@hotmail.com>
To: <amps@contesting.com>
Sent: Wednesday, January 17, 2001 8:03 PM
Subject: [AMPS] Two XFMR in parallel
>
> I have two unit transformer with different manufacturer, one of them are
> 1880 volt and 0.6A RMS secunder, and another are 1870 volt and 0.4A RMS
> secunder. Actual voltage when connected to AC line are 1950 volt and 1890
> volt, measuring by HV Voltmeter.
>
> I want to connect both of them in parallel in order to have 1A RMS Output.
> What will be happen when I Connected this two transformer in parallel with
> little bit different in output voltage ???.
>
> Thanks for your suggestion,
>
> de Firson - YD1BIH
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