Don Foreman wrote:
On Fri, 23 Sep 2005 22:42:14 +0000 (UTC), Christopher Tidy
wrote:


Geoff M wrote:

Use a water pump, and a valve to adjust the flow. For a proper job, mount
the pump on bearings so it can rotate, restrained by a spring balance,
which is the basis for a Heenan and Froude water brake engine dyno.
Geoff

Thanks for the suggestion. I don't have a water pump, but I've been
offered a 2 hp hydraulic pump/motor unit free. I don't see a problem
with using this, do you?


Hydraulic pump should work well. Most hydraulic pumps have some
"drag" even with no hydraulic load -- which is OK because most loads
you'll have on your converter will also have some minimum drag.

You probably know that the fluid will get hot with extended testing.
Your "brake" power is being converted to heat. No problem for short
tests or with plenty of fluid.

I was thinking of 5 to 10 gallons of oil, which I reckon should be okay
for short tests.

snip
Jerry Martes once built an eddycurrent dyno for studying RPC's. It
worked extremely well, with torque easily adjustable from near zero to
about 5 HP worth at 1725 RPM. It used a thick aluminum disc and four
electromagnets made from alternator field coils. Torque was measured
by means of a torque arm and straingage loadcell, speed with an
inductive pickup. Both were recorded on a P.C. datalogger.

This is another interesting idea. It sounds very like the
electromagnetic retarders used on buses and trucks. I'd wondered about
something like this, but I reckon the parts will be harder for me to
acquire than the hydraulic parts. I might do a few simple tests before
building a nice convertor, then do more thorough tests afterwards, or I
might do it the other way round. I haven't decided yet.

Best wishes,

Chris