From: noel shelley (noel@shelley1722.freeserve.co.uk)
Date: Sat Nov 08 2003 - 03:01:14 PST
Dear Jim and list,
Having just built a 20Kva 415v 3ph diesel genny I
will share some of my experiences .
The simple answer to the question is " there isn`t one "{ a formula } it
could only be found by test .
With very little info my comments are general in nature , select those that
apply . You say alternator , for the machine to
produce rated voltage and power it MUST be spun at the correct CONSTANT
speed , any variation will cause large damaging and potentially dangerous
surges . For some applications frequency is also important , this is
directly related to speed .
Most diesel governors used on vehicles are not suited to constant speed
governing , they limit the top end and prevent stall , rebuilding the
injection pump for this application may be
possible but may also be costly , gasoline engines { vehicle } are not
suitable unless equiped with a governor { most unusual }.
For normal electrics most alternators will spin at 1500 or 3000 for 50 cps
or 1800 or 3600 for 60 cps
At engine idle there is very little power , only enough to over come
friction Etc, listen to the revs fall when the lights or aircon come on .
Needing about 30Hp I run a 1.9 L {116 C"}diesel at 1950 rpm belted to 1500
rpm alternator . The best way to set speed is to use a frequency meter {45 -
65 cps } wired to the alternator , this will allow speed set to 15rpm or
better . For lighting 5% under voltage will dramatically increase bulb life
, the converse is also true .
For 5Hp you will get about 2-2.5 Kva . Small engines are rated at 3000rpm
engine speed { honda , briggs Etc } remember Hp = revs X torque .
When looking at POWER don`t forget the power factor often 0.8 , derate the
output by this for real power .
Hope this helps , for more detailed info on building genny`s call me off
list .
NOEL
This archive was generated by hypermail 2.1.4 : Sat May 07 2005 - 20:26:26 PDT