Re: Transformers

On Fri, 9 Feb 1996 tesla-at-grendel.objinc-dot-com wrote:

>         I've got an Atlas Device Corporation 6500W Arc Lamp starter that I
> have been trying to determine the output current on. It is a shunt limited
> transformer with a core 6.25" long, 3.75" high and 1.25" X 1.25" cross
> section. It's name plate rates it a 220v 50A, but the 50A MUST be a surge
> rating, nothing inside is that heavy! With 110Vac applied to the primary I
> measure 7.28Kv out. I find this reasonalble for a 220v transformer run on
> 110v.

With the core-dimensions mentioned I'd guess that it won't handle
more than about 1 kW.. That 6500W and 220V 50A most propably means
the specs of the power going to the lamp when it is lit - not the
starting xformer.. In fact, that xformer might not even be designed
for continuous use as I think that the arc-lamp will sustain the
arc once triggered.. 

btw: those zenon etc. lamps used at projectors etc. are at a high-pressure
and when they break they will explode violently with glass flying to the
surroundings.. Those are not something to play with.. The xformers running
the lights are interesting as well - I've got a unit with three 24V 40A
xformers and rectifying diodes for that.. 

>         Now for the confusing part. When I connect an ampeure meter to the
> secondary I measure NO current! Even on the 250uA scale! When I use a load
> resistor 1 ohm = 0uV. 250 ohm = 5v => 20ma, 2100 ohm = 43v => 20.5ma. Am I
> missing some fact about shunt limited transformers? This transformer is
> massive compared to the 30ma neons I've seen. Does halving the input voltage
> more than halve the output current? Does the load effect the output current?

Apparently it won't supply current to a short circuit (ampere meter) but
to a load it supplies 20ma.. Sounds reasonable - it propably won't take 
much current to trigger the lamp and it's shunting is designed for that 
application. Neons behave like that too : connect leds to the hv-side and 
they will just be lit..

I hope this helps,

  Kristian Ukkonen.