If you have dire need to measure current and cant get a CT. In a pinch, I once used a short segment of #10 solid core wire to measure 35 or so amps of current, which was outside the range of my measuring device at the time.
I measured the resistance along the length and found a length that corresponded to .1ohms. (like a foot or wire or so) then i soldered 2 loops of smaller wire at those locations so i could clip on my multimeter. Solder some ring connectors a little further down. Measure the millivolts and you can easily determine the current.Calibrated it by using my meter and verifying it was accurate at lower currents. Of course it gets less accurate when it starts getting warm and its dangerous, but its still reasonably close at currents around the wires standard rating.
Worked great in a pinch!Probably not ideal for what your trying to do, but figured i'd offer the concept for inquiring minds anyway.
Cheers, Jay
On a side note, i really hate how my phones email app wont reply to tcml directly. It used to -.- so sorry for the message Jim.
------ Original message------From: Jim Lux Date: Thu, Sep 3, 2015 8:27 AMTo: tesla@xxxxxxxxxx;Cc: Subject:Re: [TCML] Power factor correction
On 9/2/15 9:13 PM, David Speck wrote:> John,>> Check out eBay for a current transformer. A 50:5 unit will multiply> your DMM readings by factor of 10. They should be available for under> $20 with some diligent looking.>> Something like the following would work. (no connection to seller.)>> http://www.ebay.com/itm/130895906892>> Just be careful to never put current through the transformer (CT)> without having a load, like your DMM on its amperes setting, across the> CT terminals. When unloaded, a CT tries to put out infinite voltage> which may break down its internal windings.You can put a resistor or back to back zener diodes across the winding to prevent this. WHen you do hook up the ammeter, it's so much lower resistance that the current flows through it, rather than the protection resistor.>> Then, you can investigate which arrangement of PFC caps works best for you.>> Dave> ----------------------------->> I'm at the point I need to add some motor run caps, I'm thinking the> same that go on your ac units in the 40-50uf 330-440v variety unless> someone has a better suggestion. Looks like I will need around 150uf> per transformer I have 3 12/60 NST. Biggest question is do I run all 9> parallel or run about 3 strings of 3 to each? Would before or after the> EMI filters make a difference. Blowing 20 amp fuses on variac, don't> have a clamp meter and my dmm is only good to 10 amps inline. I was> going to add some and then start measuring the current? John Cooper>> _______________________________________________> Tesla mailing list> Tesla@xxxxxxxxxx> http://www.pupman.com/mailman/listinfo/tesla>_______________________________________________Tesla mailing listTesla@pupman.comhttp://www.pupman.com/mailman/listinfo/tesla
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