Help With Circuit Information??

R

Randy Gross

Guest
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!
 
Randy Gross wrote:
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
Click to expand...
Something wrong here.

(Primary volts x primary current) should be approx equal to (secondary volts x secondary current).
How did you measure it?

There is only about 8 watts ( 8V x 1A)being dissipated in the resistors. I wouldn't expect them to get hot.

--
--

Beginners and Intermediate Electronics
http://homepage.ntlworld.com/g.knott/index.htm
 
"Randy Gross" <rgwg99@acsplus.com> wrote in message
news:01c368e1$1f7816c0$442525d8@dialup...
grahamk <g.knott@ntlworld.com> wrote in article
0Ut1b.1072$MS5.18804@newsfep4-glfd.server.ntli.net>...
Randy Gross wrote:
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

Something wrong here.

(Primary volts x primary current) should be approx equal to (secondary
volts x secondary current).
How did you measure it?

There is only about 8 watts ( 8V x 1A)being dissipated in the resistors. I
wouldn't expect them to get hot.

--
--

Beginners and Intermediate Electronics
http://homepage.ntlworld.com/g.knott/index.htm


----------
The load was intended to limit the current as it did. My problem is
translating the information from the load into values that will balance
out
the circuit. This transformer is simply a test case, the load is a
homebuilt dummy load. I'm looking for a formula to use with this load in a
variety of current test.

Thanks for answering!
---------
Click to expand...
The problem is that as a test case, the data is strange and it is hard to
get any meaningful information from it. .
8.1V open circuit and 8.5 ohms plus internal impedance of the transformer
leads to something less than 1A (V/R) out and 8/120 or 67ma input. Even
allowing for magnetising current 8A input is very strange -83ma maybe?
In addition the 50/7 turns ratio doesn't match the apparent voltage ratio of
120/8 (closer to 120/17).
Either some of the data given is wrong or the transformer is extremely poor
and the magnetising current and primary impedance are horribly bad.
If you are using the load at a given voltage range and have measured its
resistance under these conditions (V and I at the same time) then, as long
as you operate at a low voltage, that value will be OK.
--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer
 
Randy Gross <rgwg99@acsplus.com> wrote in article
<01c368e1$1f7816c0$442525d8@dialup>...
:
:
: grahamk <g.knott@ntlworld.com> wrote in article
: <0Ut1b.1072$MS5.18804@newsfep4-glfd.server.ntli.net>...

<Snip>

: > 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
:
: Something wrong here.
:
: (Primary volts x primary current) should be approx equal to (secondary
: volts x secondary current).
: How did you measure it?
:
: There is only about 8 watts ( 8V x 1A)being dissipated in the resistors.
I
: wouldn't expect them to get hot.
:
: --
: --
:
: Beginners and Intermediate Electronics
: http://homepage.ntlworld.com/g.knott/index.htm
:
:
: ----------
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
load the secondary measures 8 volts, 1 Amp at 8.5 ohms. How do I convert
the 8VA to reflect the actual 720VA to balance the tranny?

Randy Gross
 
I appreciate the concern you have for my safety. It sounds genuine as
others using this site.
I'm an old fart that started out in high school building radios in the
electronics class. I studied Electronics in the USAF before digital made
its debut. I was an Avionics Instrument Systems Technician. I worked as an
assistant to engineers (Electronic and Mechanical) until I started welding
20 years ago. Use it or lose it ring a bell? I'm so rusty the threads are
gone. I find myself having to relearn and Learn, new technology and all
but, the one thing I will never lose is my respect for the juice.

I built this load hoping to reduce the high currents I want to work with.
Then use the reduced values measured at a safe load, to tell me high
current that I am actually working with. For instance, I know this tranny
is producing 90 amps at 7 turns. Instead of burning up stuff trying to get
that measurment, I want to take a percentage of the 90 amps as a
measurement, then calculate the actual. Is this still garbled?

Randy Gross

John G <greentestatoptusnet.com.au> wrote in article
<3f47f9fa$0$28118$afc38c87@news.optusnet.com.au>...
: Randy,
: First I think you should be very careful playing with things connected to
: the mains as your understanding of electricity seems to very very small.
:
: Your transformer needs a load resistance of something like 1 tenth of one
: ohm to deliver 90 amps.
: 90 amps or 720va is a lot of power to be playing with if you do not
: understand the basic principles of Ohms LAW.
: This is welding type current and you could easily get an arc or fire just
by
: having connections that are too small for the job.
: I have no idea what you mean by "How do I convert the 8VA to reflect the
: actual 720VA to balance the tranny?"
: --
: John G
:
: Wot's Your Real Problem?
:
:
: "Randy Gross" <rgwg99@acsplus.com> wrote in message
: news:01c36989$785b6f00$422525d8@dialup...
: >
: >>
: > : > 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
: > :
: > : Something wrong here.
: > :
: > : (Primary volts x primary current) should be approx equal to
(secondary
: > : volts x secondary current).
: > : How did you measure it?
: > :
: > : There is only about 8 watts ( 8V x 1A)being dissipated in the
resistors.
: > I
: > : wouldn't expect them to get hot.
: > :
: > : --
: > : --
: > :
: > : Beginners and Intermediate Electronics
: > : http://homepage.ntlworld.com/g.knott/index.htm
: > :
: > :
: > : ----------
: > 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
: > load the secondary measures 8 volts, 1 Amp at 8.5 ohms. How do I
convert
: > the 8VA to reflect the actual 720VA to balance the tranny?
: >
: > Randy Gross
:
:
:
 
At first this Idea seemed feasible and, not trying to change Ohms law, I
sought to apply it from a different angle but, I see where the group has
been trying to lead me on this:

There are no short-cuts. There are no tricks. You have to take the law at
face value. It is written in stone!

The collective nature of this group is commendable. When the group homes in
on a goal, it is achieved. That builds confidence and trust. You've
certainly saved me a lot of wasted time trying to snare an apparition.
Thanks to all.

Now it's time to turn the page.

Randy Gross
:
:
:
 
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