5 Feb
2015
5 Feb
'15
9:22 p.m.
On 2/5/2015 8:45 PM, Brent Hilpert wrote:
On 2015-Feb-05, at 8:16 PM, Josh Dersch wrote:
OK: Confirmed two things: There's 240V between the two HOT terminals
at the outlet, and the ground appears to be grounded (I get continuity
between the ground on the nearby 120V outlet (which I know is properly
grounded) and the neutral terminal of the 240V outlet.)
So it looks like I should be good to go here. One last question -- does
it matter which hot wire goes to which terminal in this case?
On 2/5/2015 8:00 PM, Brent Hilpert wrote:
If you are convinced it's wired for 240 then yes, you should be able to wire
the hots as you say.
You MUST somehow GND the chassis however, either:
- confirm the dryer receptacle neutral is adequately tied to ground, or
- if the dryer receptacle is wired with armored/BX cable that may be the ground, or
- waterpipe confirmed as adequate ground, or
- connect to a confirmed ground on a normal 120V outlet, although there is a warning
involved in such a scenario,
if the ground conductor is much smaller than the hot conductor, a fault can blow the
ground conductor open,
at which point you have no ground and a live chassis. In theory the circuit breaker
should open before the ground blows, but that's theory. On 2015-Feb-05, at 7:28 PM, Josh Dersch wrote:
Yes, there's high resistance between both line
inputs and chassis ground, higher than my DVM can measure.
And, let's face it, I'm spoiled and I
demand instant gratification and I'd like to know as soon as possible if this machine
is a basket case or not.
So: since all this stuff is in the basement, I'm just about 15 feet away from the
dryer, which at first glance runs off an outlet that meets my needs. I even have a NEMA
10-30p plug here that I could wire up to the existing power cable for the computer. But
looking into it I have doubts that it's actually that simple; in particular since this
house was built well before 1996 and so the outlet is not grounded; there's a neutral
lug and two hot lugs (I assume two 120V A/C lines out of phase?) and I'm guessing that
might not sit well with the power supply in this computer.
Yes, the two hots are
120VAC to neutral each, 180 degrees out of phase, giving 240 between the two hots.
Yes, you should be able to use those two hots to power the target machine, as long as the
240 input lines for the target are isolated from ground. Normally this will be the case, I
just mention it in case there is some strange circumstance where one side of the target
input is connected to ground. Measure the R between chassis and the two line inputs, it
should be very high R on both. Is the existing plug/line input to the the target
3-wire (2 hot + GND) or 4-wire (2 hot + neutral + GND)?
And have you confirmed that one wire IS GND/chassis? (it could conceivably be 2 hot +
neutral).
The existing plug is a 3-wire affair, white/black for hot and green
ground using a NEMA 6-20P plug. I have confirmed that ground is wired to the chassis
(with the DVM.)
So is it as simple as wiring the white/black wires up to the HOT terminals on the NEMA
connector and leaving the ground disconnected (from the "netural" pole on the
NEMA... or should that be connected as well)? Anything else I should watch out for?
Alternatively, if you'd like to examine rewiring the machine for 120, we could look
at that, via photos, etc.
(First question would be what are the target power/VA requirements, to consider whether
it's worthwhile on 120).
I have taken one photo (I probably should have taken more since it's a
PITA to get to, but I wasn't planning on rewiring things at the time).
You can find it at:
http://yahozna.dyndns.org/scratch/dap/supply.jpg
According to the panel on the front of the machine, the power draw is
rated at 120V/10A or 240V/5A. So it should run fine on a normal 120V
outlet. But there's a lot to reconfigure, it looks like, and the fans
are all 240V AC units as well...
- Josh
