Re: [TCML] Variac

[bunnykiller <bunnikillr@xxxxxxx>]

Volt meters dont care what the amperage usage is , they measure voltage 
only. What got you confused is that volt meters have a "rating" mA wise 
that will be used to go to full swing measurement. Normally volt meters 
have a face value ( 0 -150V for example) and will have built into them a 
resistor that will limit the current going to the movement coil for said 
voltage.  If you wanted to, you could add a resistor in series to the 
meter and decrease the swing amount which in effect would give you the 
capacity to read higher voltages ( but you would have to replace the 
meter scale for proper "readout"). So, in effect, you could add a series 
resistor of the "proper" value and make a 0-150 meter capable of reading 
0 -300V ( you would either have to remember to double the face plate 
value by 2 or replace the face plate with a 0 -300V range.  The mA value 
gives one the opportunity to "custom" design a volt meter to voltages up 
to several thousand volts depending on the resistors used.

winding ones own current transformer is a bit more technical than it 
seems, purchasing one is alot less time consuming than trying to 
engineer/design and build one.

Another though to consider, Volt meters hook up to the Hot and neutral 
leads, shunt type Amp meters are hooked up in series in the hot lead, 
current transformers types just have the hot lead pass thru the core of 
the "circular" transformer ( not physically hooked up to the lead as in 
shunt types).

Scot D


jhowson4@xxxxxxxxxxx wrote:

> 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.  
>
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