Help With Circuit Information??

[Randy Gross]

Please view in a fixed-width font such as Courier.

________________
| _____|_____
______ | | | R1 and R2 used as a
)|| __| | |
120vac )||(8vac R1 R2 test load to
)||(7 Turns 14 Ohms 21 Ohms
6A )||(__ | | determine output amps.
______)|| | | |
| |___________|
50 Turns |________________|


This schematic depicts a transformer under load for testing purposes. I
scoured the web in search of a high current dummy load, no luck! I came up
with the Idea of using 2 heating elements (R1 and R2) wired in parallel to
reduce the total load resistance.

The result was surprising. I expected a good deal of heat but, the elements
didn't even warm. The drawback is, how do I use the resulting data to
determine the actual circuit amperage. These are the figures:

OCV: 8.1v
Total secondary load resistance: 8.5 ohms
Secondary current (clamp-on meter): 1.02 Amps
Primary current under load: 8.3 Amps

SOS

 

[John Crighton]

Please view in a fixed-width font such as Courier.

________________
| _____|_____
______ | | | R1 and R2 used as a
)|| __| | |
120vac )||(8vac R1 R2 test load to
)||(7 Turns 14 Ohms 21 Ohms
6A )||(__ | | determine output amps.
______)|| | | |
| |___________|
50 Turns |________________|


This schematic depicts a transformer under load for testing purposes. I
scoured the web in search of a high current dummy load, no luck! I came up
with the Idea of using 2 heating elements (R1 and R2) wired in parallel to
reduce the total load resistance.

The result was surprising. I expected a good deal of heat but, the elements
didn't even warm. The drawback is, how do I use the resulting data to
determine the actual circuit amperage. These are the figures:

OCV: 8.1v
Total secondary load resistance: 8.5 ohms
Secondary current (clamp-on meter): 1.02 Amps
Primary current under load: 8.3 Amps

SOS

Hello Randy,
with the load removed from the secondary,
what is the measured primary current?
If it is several amps then something is wrong.
Maybe your transformer has some shorted turns
in the primary and it is just not working properly

Just looking at your turns ratio.
secondary is 7 turns for 8 volts.
call it 1 turn per volt for easy maths.
Primary is 50 turns, so maybe roughly 50V
should be used instead of 120V.
Try reducing the primary volts with a variac
and measure the primary current with no load
on the secondary. If you are still measuring
amps of primary current then your transformer
is suspect. A 400Hz aircraft type maybe?

Regards,
John Crighton
Sydney

 

[Randy Gross]

<[email protected]>...
: On Fri, 22 Aug 2003 03:55:35 +0000 (UTC), "Randy Gross"
:
: > Please view in a fixed-width font such as Courier.
: >
: > ________________
: > | _____|_____
: > ______ | | | R1 and R2 used as a
: > )|| __| | |
: > 120vac )||(8vac R1 R2 test load to
: > )||(7 Turns 14 Ohms 21 Ohms
: > 6A )||(__ | | determine output amps.
: > ______)|| | | |
: > | |___________|
: > 50 Turns |________________|
: >
: >
: >This schematic depicts a transformer under load for testing purposes. I
: >scoured the web in search of a high current dummy load, no luck! I came
up
: >with the Idea of using 2 heating elements (R1 and R2) wired in parallel
to
: >reduce the total load resistance.
: >
: >The result was surprising. I expected a good deal of heat but, the
elements
: >didn't even warm. The drawback is, how do I use the resulting data to
: >determine the actual circuit amperage. These are the figures:
: >
: >OCV: 8.1v
: >Total secondary load resistance: 8.5 ohms
: >Secondary current (clamp-on meter): 1.02 Amps
: >Primary current under load: 8.3 Amps
: >
: >SOS
: >
: >--
: >
: >An Inquiring Mind
: >Randy Gross
: >----------------------------------------------------------
: ><') >< Homebuilt Arc Welders >< ('>
: >http://www.gomedia.ca/~aaawelder/
: >Chance favors the prepared mind whose hands do the work!
: >
: Hello Randy,
: with the load removed from the secondary,
: what is the measured primary current?
: If it is several amps then something is wrong.
: Maybe your transformer has some shorted turns
: in the primary and it is just not working properly
:
: Just looking at your turns ratio.
: secondary is 7 turns for 8 volts.
: call it 1 turn per volt for easy maths.
: Primary is 50 turns, so maybe roughly 50V
: should be used instead of 120V.
: Try reducing the primary volts with a variac
: and measure the primary current with no load
: on the secondary. If you are still measuring
: amps of primary current then your transformer
: is suspect. A 400Hz aircraft type maybe?
:
: Regards,
: John Crighton
: Sydney
:
Yes, the transformer is junk. It was only used here to test the performance
of the homebuilt high current load. The load worked (2 heating elements
wired in parallel) too good. I limited the secondary current to 1 amp and I
am not sure how to translate the test data into values that would balance
the primary and secondary volt/amps.

Randy Gross
:

 

[Phil Allison]

I limited the secondary current to 1 amp and I
am not sure how to translate the test data into values that would balance
the primary and secondary volt/amps.

** Huh ? Since when do primary and secondary VAs need to be in balance
???

Primary magnetising current can easily dominate - it does with plug
packs.




............... Phil

 

[Rheilly Phoull]

Like John has mentioned the primary current should be nowhere near 8 amps.
Must be something amiss there.

 

[Randy Gross]

<[email protected]>...
:
: "Randy Gross" <[email protected]>
:
:
: > I limited the secondary current to 1 amp and I
: > am not sure how to translate the test data into values that would
balance
: > the primary and secondary volt/amps.
:
:
: ** Huh ? Since when do primary and secondary VAs need to be in
balance
: ???
:
: Primary magnetising current can easily dominate - it does with
plug
: packs.
:
:
:
:
: .............. Phil
:


The load was intended to limit the current as it did.

This transformer is simply a test case (primary turns 105, sorry).

The load is a homebuilt dummy load, the focus of this post.

To help clarify my question, I'll cut to the chase:

This is a 720VA tranny, secondary should measure 90 Amps, 8 volts. Under
this dummy load, the secondary measures 8 volts, 1 Amp at 8.5 ohms. How do
I convert the 8VA to reflect the actual 720VA of the secondary?

Randy Gross