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Re: NEON- Building a loading meter

Welcome back Tom.  Looking forward to the photos.

The transformer loading technique is often used with an ammeter 
on the primary side (always in in series) but the test is most direct 
on the secondary. In either case we are looking for a ratio between 
the loaded circuit current and  short circuit current of between 
78-80%. 

Let's say you  have an ammeter in series with your neon tube 
connected to the transformer in a normal neon circuit. A typical 
reading for a properly loaded tube would be 24mA. Now use a jumper 
wire across the tube.  This short circuit current will be 
(hopefully) around 30mA.  The ratio of 24mA to 30mA is 80% which 
is in the  acceptable range.

All that this means is that the transformer is designed 
(theoretically) to handle the short circuit current.  Our preferred  
normal operating load is less.

Side note: It's a general practice in any electrical circuit to run a 
smaller load than  the overall rating - but beyond that, keep in mind 
that neon's current (and voltage) fluctuates. The voltage rises and 
current is low, it reaches breakover level and the current rapidly 
rises while the voltage is now steady.  At the same time at the 
instant the current flow surges, feedback is 'leaked' back to the 
primary to reduce it's output, thereby limiting the secondary 
current.

It's fairly complex when you think about it.  Even more if you  
leave impurities in the tube - which is why an o-scope is the 
way to go. 

The kV test is a nice addition, because it tells you roughly the 
actual voltage of the circuit which you want to be certain is within 
the transformer's spec as well.


Kenny



> Okay folks, from the "No Question is Too Basic to Ask" files comes
> the following:
> 
> I'm interested in building a unit for determining "proper"
> transformer loading.  The units I saw being used in Holland (every
> shop had one, some nicely built by you-know-who) all had both a kV
> and mA meter as part of the unit.  I understood the demos I got at
> the time and the general concept, but I think it got lost in one of
> those water canals over there.
> 
> In a recent post, Morgan referred to determining loading with a mA
> meter. So, is a kV and an mA meter required to do this or can it
> just be determined with a mA meter?  I understand the mA meter is
> connected in series with the unit, but how do I interpret the
> reading?  Say I connect a unit to the mA meter and get a reading of
> 20 mA, now what exactly does that tell me?
> 
> I recently "acquired" (hmm, wonder from whom) such a mA meter
> ranging from 0 to 60 and some hardware to start with, but I'm a
> little unclear still on how this whole process is done.  A usual,
> all help will be appreciated.
> 
> (Yes, Dirk, here's evidence that I indeed came back with more
> questions than I came over with!)
> 
> Tom U.
> 
> 
> 
Kenny Greenberg --  Neon - Scenic and Environmental Art  
                    Internet Site Consultant and Author   
KRYPTON NEON 34-43 Vernon Blvd Long Island City, NY 11106
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