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Re: [TCML] Variac
There's no need to try to "make" a current tansformer
as they are quite available for a pretty reasonable price,
especially when they show up on ebay. One thing to keep
in mind is that they are nearly always rated at X:5, meaning
that most AC ammeters that have a full scale deflection
of more than 0 - 50 will require a MATCHING current
transformer in order to give the correct current mea-
surement - i.e. a 50:5 current transformer would be
required for a 0 - 50 amp ammeter to give a correct
measurement, a 150:5 current transformer for a 0 -
150 amp scaled meter, ect. Many higher current scaled
AC ammeters will come with a matching current trans-
former when purchased new and as far as I know, all
AC ammeters that measure over 50 amps will have a
5 amp full scale deflection and therefore requre a cur-
rent transformer to give a correct current measurement.
----- Original Message -----
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, October 24, 2008 10:30:32 AM GMT -06:00 US/Canada Central
Subject: Re: [TCML] Variac
Sweet thanks for the help. I guess my question is really how do I determin how much power such a meter would be able to handle. all the web sites i found just list what voltage its good for and not what current or power.
Like if if got a regular old volt meter 0-150 AC what current could I use it with. the one i was going to get on ebay i found out from the seller to be rated for 150v but only in the ma level. well thats no good for my TC variac.
I do like what you said about the ""circular" transformer" thing . Is that like a toroid core type set up.
anyone try to make one of these before.
-------------- Original message --------------
From: bunnykiller <bunnikillr@xxxxxxx>
> Hey Jay...
> Analog volt meters are pleantiful, Check out your local industrial
> supply center, if you do online shopping, check out Digikey,Mouser,
> Depending on face size, expect to spend between 15 - 50$
> As far as the amp meter, there are 2 methods of measuring amperage. 1
> way is to have a meter with a shunt rated for the voltage and amperage
> range. The shunt is a precision "resistor" which attaches to the meter
> and reduces the voltage going to the meter. Shunts are rated for
> specific amounts of current, for example 0-5A, 0-20A, 0-50A....
> The second way to consider is the current transformer type. This uses a
> "circular" transformer which sends voltage to the amp meter. How it
> works is that the hot lead is placed thru the transformer and when
> current runs thru that wire the transformer picks up the current and
> creates a voltage in the outputs of the transformer thus sending the
> voltage to the amp meter. Altho this method is a bit more accurate and
> less prone to damage as compared to the shunt type, they are a bit more
> expensive... C.T. type meters are rated in a ratio value, meaning
> that the current transformer is matched to the amp meter for the
> intended amperage range.
> Scot D
> jhowson4@xxxxxxxxxxx wrote:
> >Hey guys anyone know where i could get a analog panel mount volt meter and an
> ammeter that would work well with my 0-140 20 amp variac
> >looked all over the web and i cant really find any rated for a high power like
> >Jay H.
> >Tesla mailing list
> Tesla mailing list
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