Variac

[Marvin]

I have just bid for this variac its rated at 2a 220v.
Output 0 - 250V

[[XC] gomeler]

Grats :)

[Marvin]

Ok. sorry my ignorance as i am not good in mat and phys.
I need a cartrige rated at 220v
so W = V * A
amperage is fixed at 2A
How can i meansure the wattage ?

[Tonic]

Ok. sorry my ignorance as i am not good in mat and phys.
I need a cartrige rated at 220v
so W = V * A
amperage is fixed at 2A
How can i meansure the wattage ?

One notice, how many ampers will be drawn from variac, it depends on what you are powering.

I'm not sure what you mean, but if you want know wattage at load, you have to measure voltage and amper draw, then multiply them, as you said.

BTW, congratulations, this toy might be very handy :-)

[Marvin]

thanks tonic. Should a amperimeter check it ?
I have one laying here.

[tim-]

the easiest way to measure it to get a "killawatt".

those are rather cheap.

as far as I se the variac you got is rated for maximal 0,5kVA, which means maximal 500w,

[DetroitAC]

Hi Marvin,
Amperage will not be fixed it will depend on the impedance (resistance) of the load. you should buy cartridge heater(s) that have an output of the power you want @220V.

Cartidges are specified by their power and voltage, so as long as you don't go above the rating of your variac (500W or 440W depending on which column you believe :shrug: ) you will be OK.

If you get for example a 600W cartidge(s), it will draw too much current, and probably blow the fuse.

[Tonic]

Hi Marvin,
Amperage will not be fixed it will depend on the impedance (resistance) of the load. you should buy cartridge heater(s) that have an output of the power you want @220V.

Cartidges are specified by their power and voltage, so as long as you don't go above the rating of your variac (500W or 440W depending on which column you believe :shrug: ) you will be OK.

If you get for example a 600W cartidge(s), it will draw too much current, and probably blow the fuse.

500W is a nominal power, I believe that it's different term than working power.

If I'm not wrong, it means that you can pump at most 500W, with a little overload.

This variac probably doesn't have fuse. 600W is possible, but for certain time. In datasheet there's a table which describes how long variac can work at specific load. 600W is a 35% overload (600W - 440W = 160W. 160W/440W*100% = ~35%) and according to table, it can work maximum 30 minutes.

[kayl]

that variac is similar to mine.

k formulas

P=Vx I [power(W)= Voltage x current]
I=V/R

So P=v^2 /R

So if you want 280w using 250v you need a 225 ohm resistor, i use 3x 75 resistors.

P=V^2/R
R=V^2/P
R=(250x250)/280
R=223ohms

i did up an Xsl sheet to work it all out. I cant host it, but if you pm me your email address i can email it to you.
ALso anyone else that wants it can pml me

I use a watt meter these days as its easier and looks good for pics ;)
The wat meter reads the same wattage as V^2/R though :up:

[Marvin]

500W is a nominal power, I believe that it's different term than working power.

If I'm not wrong, it means that you can pump at most 500W, with a little overload.

This variac probably doesn't have fuse. 600W is possible, but for certain time. In datasheet there's a table which describes how long variac can work at specific load. 600W is a 35% overload (600W - 440W = 160W. 160W/440W*100% = ~35%) and according to table, it can work maximum 30 minutes.
Thank you guys a lot.
But, if i remember correctly
500VA is not 500 W
500VAx0.8=400W max
overload 480w no more than 30 min
maybe the variac is up to date until upcome ¨hot¨ Intel processor.

[kayl]

mines a 500VA and its yet to trip/switch off overhead etc running 312w load for hours at a time.

http://img441.imageshack.us/my.php?image=dsc09624bi6.jpg

http://img178.imageshack.us/my.php?image=dsc09626nu4.jpg

[SexyMF]

VA rating are for transformers. I it is 500VA and you are changing to an output of say 100V then you can draw 5A. If your output is 200V then you draw 2.5A etc. Variac is actually a brand name (like Philips screwdriver or Monkey wrench). These are auto-transformers.

Also, you can only get a maximum of what you put into the variac. So your power is probably 230V. Hence you can have a maximum of 230V.

All you have to do is purchase a cartridge heater rated around 400W. Then you can vary the voltage to obtain a load of anything up to 400W. As many have found, using a kill-o-watt meter is the easiest way to see this - given the voltage indicators on the variac are usually analog needle guages.

[kayl]

[QUOTE=SexyMF;2555396]
Also, you can only get a maximum of what you put into the variac. So your power is probably 230V. Hence you can have a maximum of 230V. [\QUOTE]

SexyMF mine is 240v input, it does output 260v though

[jinu117]

Variable transformer... can be up or down... doesn't really matter does it? I am sure there are some that only goes down stepping while some can do upstepping too. (well, I have few around but not variable... gotta love in laws who keeps brining wierd stuff from out of country)
In all honesty, as long as it is rated for more than your cartridge is rated for given voltage, you are good to go ;)

(WITH A THERMAL CUT OUT SWITCH :))
There is more than one reason thermal cut out switch should be there.

[killermiller]

Can you recommend a cut off switch? I am not sure why but I think I need one...:)

[jinu117]

Thermal cut off swtich :) Mouser has few/surplus electronics store has few, etc, etc. Just search by that. I think around 75c cut off temp would be good enough for our use typically :) (which I use). Could be lower too of course. Just keep an eye out for voltage rating and amperage rating to be able to handle what you are going to subject it to :) There was more than one person that burnt load tester this month alone from what I know and I've done it few times myself as well..
(and anyone who has done it knows what a pain it is to clean off the smell, clean off the system, etc, etc) not to mention being dangerous. Go for it :)

[[XC] gomeler]

I typically use my loadtester to warm up the TIM before I start my final loadtesting so 75C would be the "coldest" i'd get a cutout for. I typically warm up the evap/loadtester to 60-70C to get the TIM nice and fluid then I do a final torquing of all my nuts to get everything secure and let the assembly gradually cool down to ambient temperatures. Find this technique makes for some crazy contact patches when I have to later rip the thing apart, literally a strength test :D

[Marvin]

Man that thing is bigger thank i thought......
:D

[tim-]

that one was a cutie.

[Marvin]

thanks, but is a little big:D

[kayl]

marvin you will like it, makes tunning a system very easy.
Good to check load and idle conditions ;)

[jinu117]

Just don't forget thermal cut off... I've seen too many things burnt...
I feel like nagging parent... heh.

[Marvin]

marvin you will like it, makes tunning a system very easy.
Good to check load and idle conditions ;)
right kayl, nice to play with.

[Marvin]

I was searching the cartridge heater, but i only found one that is 3/8, but is too long.
I need to search the power one.
Regards,
Marvin

[tim-]

use two smaller then?

[Marvin]

no chance. the smaller one was that i mentioned.

[SexyMF]

ahhh the higher line voltage measured comes from the crappy multimeter used. It is not a true RMS measurement.

[Marvin]

i bought a true rms multimeter;)