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RE: Suggestion for current limiting

Subject: RE: Suggestion for current limiting
  Date:  Tue, 27 May 1997 21:12:13 +-100
  From:  Robert Davis <RE.Davis-at-btinternet-dot-com>
    To:  "'Tesla List'" <tesla-at-pupman-dot-com>


>
>

>
>Subject:  Re: Suggestion for current limiting
>  Date:  Mon, 26 May 1997 02:07:30 -0400 (EDT)
>  From:  Jeremy Bair <pwac-at-flinet-dot-com>
>    To:  Tesla List <tesla-at-pupman-dot-com>
>
>
>On Sun, 25 May 1997, Tesla List wrote:
>
>> Subject:  Suggestion for current limiting
>>   Date:   Sat, 24 May 1997 17:03:33 +1000 (EST)
>>   From:   Rodney Davies <rgd872-at-anu.edu.au>
>>     To:   tesla-at-pupman-dot-com
>> 
>> 
>> Hi all,
>> 
>> Ever thought of current-limiting that 10KVA pig-pole transformer with
>> water?
>> 
>> Since water in it's pure (distilled) form is a perfect insulator, since
>> there are no impurities or free ions to conduct electrons.
>> 
>> I built a resistor out of 1" diam PVC pipe, about 6 feet in length, 
>> plugged at each end with feed-thru conductors, where I filled the pipe
>> with distilled water, then added tap water to give it conduction.
>> While adding the tap water, I was continuously measuring the >resistance. 
>> Once I reached the required resistance, I plugged it up.
>> 
>> The beauty of this resistor is that it can dissipate heat very well, so
>> it's ideal for current limiting and I haven't had any problems at all
>> with
>> operation.
>> 
>> The costs was < $10 as I mostly had all the parts lying around the
>> house...
>> 
>> Well, there's a cheap solution if you don't have an arc-welder! :-)
>> 
>> My suggestions for the day...
>> 
>> Catchya!
>> Rod
>Hey Rod,
>   
>    Sounds real nice, but LONG! It sounds like transportation of a PVC
>pipe 1" x 72" would be difficult, especially if you want to take it to
>some place in a car. 
>
>    One Question, since most arc welders allow you regulate the power,
>is
>there a way to design this type of resistor with some sort of regulation
>control? Maybe two small pumps (Maybe the cheap Windshield wiper >fluid
>pumps that you can get from Auto Magazines for 5-10$) to add both of >the
>separate waters (Tap and distilled).
>
>    Put a pump on one end to control distilled water being entered and a
>pump (or a solenoid valve) to control the tap water going in. Stick some
>sort of valve on the other end to let the water mixture out. Sounds like
>a
>cool idea. It actually may work really well, the only problem I see with
>it
>is that the distilled water may not mix quick enough and may actually
>start
>to lower the resistance after the pump has been shut off, same with the
>tap water. But it would produce a cool smooth effect when showing it off
>to people. 
>
>    Or how about making a bunch off water resistors, like 10 or more, or
>however you may need. And measure them out from high resistance to >low
>resistance, and use something like jumper cables to quickly switch the
>resistors, this would probably work the best, especially if you have
>them
>all sitting in the same area where you can easily just changed the
>resistors. 
>
>    I'm going to stick with my neons for now, but at one time in the
>future I think it would be great to get into pigs, but the money I'm
>going
>to use for the pig will definitely not leave me enough to purchase an
>arc
>welder :)
>
>Thanks for posting this helpful info!
>
>--------------------------------------------------------------------------
>|Jeremy Bair IRC:DeadBatry chat.talkcity-dot-com #Tesla
>|Email: mailto:pwac-at-flinet-dot-com mailto:deadbatry-at-hotmail-dot-com
>|Web page: http://www.flinet-dot-com/~pwac
>|Phone: 561-585-4165

I think a similar setup was used at one time in stage lighting.  If
memory serves a long tube containing water (I think) with two metal
plates immersed in it.  The current was then controlled by lifting one
of the plates gradualy out of the water to limit the surface area
immersed.  You could do a similar thing, maybe using a threaded rod
screwed in and out of the tube at one end, sealed with a suitable 'O'
ring or whatever. 

If this works you could then adjust it with a motor, remotely.  This may
also be useful if there is a problem of thermal runaway, you could
attatch a thermistor to the pipe and use it to control the motor so that
as it becomes hot it pulls the plate/rod out slightly automatically
giving you a fully self regulating resistance!

If the setup is to long to transport you could use a few shorter lengths
and 'U' bends at the ends.

I hope this is useful.


Rob Davis