BTW one HP is 746 watts. At 14 volts with the alternator

running

that is 53 amps. In theory it does not take much HP to pump

water

at this flow rate and pressure. This is a stock Mazda
13B water pump. Any reduction in this flow rate risks
damaging the engine.


Paul Lamar

American Flyer wrote:

Has anyone tried measuring the current to the motor as an

indication

of HP? It might be easier than a mechanical measurement because
imbalance and vibration would probably not show up in the

readings.

The meter (assuming something like a digital clamp-on) would
naturally integrate out fast variations.

Harrison Young

With alternting current this is a loser, because of phase shift. If

you

can score a real wattmeter it then becomes a viable concept - Vance

American Flyer wrote:

Vance,

I agree that power factor is a problem, but if that motor is working
as hard as it sounds, it would begin to look fairly resistive
(i.e. little phase shift). I'd bet that you still get at least
as accurate a reading measuring current as with a mechanical device.
I wish I lived close to you guys, I'd bring over a power-meter
(AKA digital oscilloscope, current shunt, and software).

Harrison Young

Hi! Harrison! - My contention is that with my set up (now with Paul) was
using relatively little power - well under 1 hp with my 3hp motor. After
witnessing some runs, both Paul and I wonder why he an Bill were
blowing breakers. It would be nice to have a good DC motor
and we could dial up rpm and read power pretty directly. I have
some surplus perm mag DC motors of unknown origin, maybe I
will try some experiments with them - Vance

I am not sure I agree with Vance on that HP estimate yet. I need to balance that
motor around the pivot/shaft axis. Also we are still running the pump at a
modest 4500 RPM. It may start blowing the breakers when I get it
up to 6000 RPM using a larger pulley on the motor. Right now I am focused
on getting the NC mill to work and finishing the engine dyno. It will
be awhile before I can fool with the water pump dyno again. There is only
one of me.

Paul Lamar

American Flyer wrote:

Hi Vance,

It does seem strange that you are blowing breakers at 1HP. Even accounting 
for motor efficiency, that should only be around 10 amps
at 117v. I am using a 10HP motor as a 220v phase converter on
 my CNC mill. The idle current for this motor is only 4.4 amps, despite
running it in the inefficient single-phase configuration. Are you 
tripping the breakers at power-up, or when you load the motor for
a while? I think I read earlier that you were using a 220v motor on 
117v. In that case the startup circuit probably wouldn't be
tuned properly, and would cause slow starts (during which time 
relatively very high current is being drawn). I also run my 3HP air
compressor on 117v 15a circuits all day long without tripping the breaker.

I was at the junk yard today, and saw some nice 1.5HP 90VDC motors. 
They would work very nicely with a variac and a rectifier
bridge. I didn't get a price because I was in a hurry.

Harrison

It was not Vance. It was Bill Schertz and I. We both used single phase
110 volt motors.

Vance is using a 3 HP 220 volt motor.

Paul lamar

The AirCraft Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2003 All world wide rights reserved.