Hi Dave,
> Date: Thu, 1 May 2003 16:59:27 -0500
> From: "Dave Sawatzky" <[email protected]>
> To: <[email protected]>
> Subject: CS>Current Limitation Please check my math
> Hi Mike
[...]
> That is a neat graphic Mike. I agree with your point about
> polarity, I should have explained what I meant with shock
> protection. Shock hazard has little to do with voltage and
> everything to do with current.
The last time I checked Ohms law, I = E / R. According to OSHA, 6 mA
is the pain level. When the ratio E / R >= 0.006, you hurt.
> If you consider the circuit I described with the bridge rectifiers
> and current limiting resisters, with a 15k ohm bleeder resister
> the open circuit voltage will be 55 volts. You can take both
> silver rods in your hands (even wet hands) and not get any shock
> when handling because of the current limiting resisters. The
> maximum current flow through your body is likely less than 1ma.
Reducing the bleed resistor reduces the output voltage. But high
voltage is needed to overcome the resistance of pure distilled
water, and reducing the output voltage negates the reason for
building the device in the first place.
I just uploaded a cs generator you might be interested in
critiquing. It uses an inexpensive 24V doorbell transformer and
voltage doublers to generate 130VDC:
http://www3.sympatico.ca/add.automation/misc/130vdc.htm
> Now take a worsed case scenario; I have seen many diodes short
> circuit when exposed to lightning or line voltage surges. Imagine
> then the diode in one AC line shorting to the B+ side of the
> bridge.
> Another diode on the other side is shorting to the minus side of
> the bridge, the other two diodes are open. You now have 115 volts
> AC on the DC side of the bridge. This is where the polarity
> reversal becomes an issue. If a person was to hold one rod in one
> hand and touch a water pipe or any other type of ground, he would
> be exposed to approx. 40 volts AC with one polarity and about 80
> volts AC the reverse polarity.
> However, if you consider the body resistance to be 100k ohms, your
> maximum current that can flow is limited to 1ma. This is very
> safe.
The resistance of human skin has many variables. If it were 100k
ohms, then nobody could get electrocuted by touching 110VAC. But
hundreds die each year. According to many sources, it can get as low
as 500 ohms. Your figure of 100k is incorrect. Try it in the summer
when you are hot and sweating.
> I have in fact grabbed the rods and played around with conceivable
> scenario's, in the shorted diode case you will get a slight shock
> if you take the 80 volt rod in one hand and the other hand on a
> natural ground, but even here the current will still be so low
> that it cannot harm you. With the bridge rectifiers in tact, I did
> not get any shocks until I increased the bleeder resistor to 27K
> ohms. Even then just a little tickle.
> So I repeat, This circuit is very safe although not as safe as
> when you use an isolation transformer.
What is acceptable to you and your skin condition may be different
for others. Your circuit is safe in that it probably won't kill
anyone, but it could deliver a nasty shock as I stated before.
You also have not addressed the issue of extremely poor regulation
due to the 3k resistors in series with the bridge. This means the
output current is dependent on the load, which makes it difficult to
get repeatable results.
> I should mention that I make all of my CS with 25 kv HVAC, and
> have been doing this for three years. Talk about a shock hazard.
> My reason for playing around with this circuit is because I enjoy
> experimenting with LVDC. I have been intrigued by Ole Bob's
> experiments and try to copy some of his experiments. I am also
> looking for a very inexpensive circuit that can I can afford to
> give away to people in poverty situations.
Why not use two 9V batteries? This works fine, but you have to watch
the current rise at the end. Since the working current is so low,
batteries that will not work in radios still work fine, so there is
an infinite supply for use in making colloidal silver:)
Best Regards,
Mike Monett
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