On Fri, 30 Nov 2018 15:11:03 -0000, trader_4 wrote:

On Friday, November 30, 2018 at 7:35:51 AM UTC-5, Art Todesco wrote:
On 11/30/2018 6:51 AM, Muddymike wrote:
On 29/11/2018 20:30, Bruce Farquhar wrote:
Those cheap Chinese water heaters which are simply two plates of
metal, one on live and one on neutral, how can they work? Because the
resistivity of tap water apparently varies from 2 to 200 ohm metres.
That's a range of 100 fold in possible power output. I assume the
resistivity changes due to impurities like lime in hard water areas?

They work best with Chinese water which is full of crap:-)

Mike
When I was a kid, we had a vaporizer that used 2 carbon rods, which were
in a Bakelite tube, with the whole thing submerged in a large water
bowl. It worked, but, even though we had city water (Chicago area), the
carbon rods would get coated with minerals and would have to be cleaned
from time to time. Otherwise, the output would be very low.

They still make those AFAIK. I never saw ones with carbon rod, only steel.
I have one, it is a couple decades old.

I've never seen one of these Chinese water heaters they are talking about,
but obviously they work on the same principle. Typical water has enough
minerals that it will conduct. It also simplifies the design, you don't
need over temp limit cutoffs if it runs with no water and the like.
have one

But since the designer has no idea of the mineral composition of the water you're going to use, the output power could vary by a factor of 100. So you might buy one that's capable of 2kW and find you get a measly and utterly useless 20W.