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Re: [TCML] Variac

Hi Jay, 

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. 

David Rieben 

----- Original Message ----- 
From: jhowson4@xxxxxxxxxxx 
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, 
> Newark... 
> 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 
> that. 
> > 
> >thanks 
> >Jay H. 
> >_______________________________________________ 
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> > 
> > 
> > 
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