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Q on Variac Specs from Catalog

N

Norm Dresner

Jan 1, 1970
0
Okay, I admit it, I'm a physicist, not an EE, but still ...

An unnamed company in their printed catalog lists the following 2 Variacs

110VAC in, 0-125Vout

Model Capacity (KVA) Max Output Current
#1 .5 2A
#2 2 8A

Now, according to my detailed calculations, 8A x 125V = 1000VA and 2A x 125V
= 250VA

I admit, I never really felt that I understood "power factor" fully, but,
hey, aren't their numbers off by a factor of 2?

Thanks for helping an old fart

Norm
 
T

Tim Wescott

Jan 1, 1970
0
Norm Dresner said:
Okay, I admit it, I'm a physicist, not an EE, but still ...

An unnamed company in their printed catalog lists the following 2 Variacs

110VAC in, 0-125Vout

Model Capacity (KVA) Max Output Current
#1 .5 2A
#2 2 8A

Now, according to my detailed calculations, 8A x 125V = 1000VA and 2A x 125V
= 250VA

I admit, I never really felt that I understood "power factor" fully, but,
hey, aren't their numbers off by a factor of 2?

Thanks for helping an old fart

Norm

They're trying to tell you that you can run 8A at 0V (0kVA, but lots of amps
heating the wire), or 4A at 125V, but not 2000A at 1V (hey, it's 2kVA,
right?), or 8A at 125V, etc.
 
R

Rene Tschaggelar

Jan 1, 1970
0
Norm said:
Okay, I admit it, I'm a physicist, not an EE, but still ...

An unnamed company in their printed catalog lists the following 2 Variacs

110VAC in, 0-125Vout

Model Capacity (KVA) Max Output Current
#1 .5 2A
#2 2 8A

Now, according to my detailed calculations, 8A x 125V = 1000VA and 2A x 125V
= 250VA

I admit, I never really felt that I understood "power factor" fully, but,
hey, aren't their numbers off by a factor of 2?


As you said, VA is different to Watt. The first including blind
(reactance) power from capacitors or inductivities such your
transformer here.

Since the current throuh an inductivity(capcitor) is phase
shifted against the voltage, there is power going in both ways,
to and from the load.

Select the variac from the current you need.

Rene
 
C

Chris Carlen

Jan 1, 1970
0
Tim said:
They're trying to tell you that you can run 8A at 0V (0kVA, but lots of amps
heating the wire), or 4A at 125V, but not 2000A at 1V (hey, it's 2kVA,
right?), or 8A at 125V, etc.


That still doesn't make sense. The maximum current is the maximum
current, which at 8A leads to 1kVA at 125V out. There is no way to get
2kVA without having 16A go through the wire, which violates the max
current spec. The specs. can't be inconsistent in this manner, if they
are to be credible.

My variac says "output 0-140V 10A 1.4kVA"

I'd find another Variac manufacturer, like Staco Energy, whose numbers
make sense.

Good day!
 
T

Tim Wescott

Jan 1, 1970
0
Chris Carlen said:
That still doesn't make sense. The maximum current is the maximum
current, which at 8A leads to 1kVA at 125V out. There is no way to get
2kVA without having 16A go through the wire, which violates the max
current spec. The specs. can't be inconsistent in this manner, if they
are to be credible.

My variac says "output 0-140V 10A 1.4kVA"

I'd find another Variac manufacturer, like Staco Energy, whose numbers
make sense.

Good day!




--
_____________________
Christopher R. Carlen
[email protected]
Suse 8.1 Linux 2.4.19

Mmphd, mmpffftd -- POP! OK, I've pulled my head out of my ass, now.

Yes, they're off by a power of two, and not in the direction I was thinking.
In the immortal words of Rosana Rosanadana -- "never mind".
 
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