Portable Generator Sets - Woods Dialocharge D1230 User Manual

PORTABLE GENERATOR SETS:

IN B RIEF:
•
Some bat tery chargers perform errat ically, or suffer damag e, when run from portable petrol g enerat ors
•
This is due to poor waveform quality from small port able generators, particu larly when lig htly loaded.
•
Either apply an ad ditional load to the generators when running battery chargers, or get a bet ter generator set.
•
The generator VA rating should be at least FOUR times the battery voltage multiplied by the charger c urrent .
THE PROBLEM - MORE DETAIL
In recent years, WOODS Battery Chargers have been seeing an increasin g nu mber of chargers which have been damaged by
poor power quality. In all cases, power has been supplied by portable generators ("Gen-sets") of less than 5kVA rating .
Almost all of the damaged chargers have been Woods "Dialomatic" types, since these are the style mos t likely to be used with
s mall gen-sets.
Power from gen-s ets of 7kVA and higher seems to be of good quality. No problems have been reported from u sing chargers
with these larg er gen-sets.
Similarly, few problems have been noted in WOODS ELECTRIC "Automatic", "BETAcharge" and "Neptun e" chargers, simply
because these are not generally used with small gen -sets.
Although most appliances are not affec ted by the poor waveform qualit y from smaller gen-sets, those appliances which use
"Phase Power Control" are particularly affec ted. "Phase Power Control" is used in WOODS ELECTRIC battery ch argers, in speed
c ontrols for p ower tools , and in domestic lighting dimmers.
THE CAUSE – MORE DETAIL:
The generators in many small gen-s et s produce highly dis torted waveforms.
Although meters are readily available to measure generat or output voltage and frequency , it is rare to see meters for output
distortion measurement. The easiest way to view a generators' output is to us e an oscilloscope. This will not direc tly measure
distortion, but it will give a good visual indication of the degree of dis tortion.
Here is the (simulated) waveform of a typical "cheap and nast y"
generator, shown against a pure 24 0V 50Hz sinewave:
This particular waveform exhibits a distortion of around 25%.
Ideally, mains power (and gen-set output power) would be a pure
s ine-wave. In fact, mains power may have up to 5% distortion.
This level of distortion does not create any misb ehaviour in
D ialomatic chargers .
Some gen-sets, however, produce p ower with more than 20%
distortion (sometimes as high as 25%!).
The dist ortion is due to the design of the generat or. The engine
driving the generator is not responsible.
The phase-control circuit s in Woods Dialomatic chargers
manufactured before 200 1 cannot cope with more than 8%
distortion. The circuits in n ew Dialomatic chargers can cope wit h
up to 15 % dis tortion.
Woods Dialomatic batt ery chargers are general ly quite t olerant of
t he variation s in frequency and voltage produc ed by gen-sets, but
t hey don't cope with high dist ortion levels.
SOLUTIONS – MORE DETAIL:
We have found that the distortion produc ed by gen-sets may be
reduced to useabl e levels by loading the generator with a resist ive
load, in addition to the battery charger.
Loads of between 5 00 watts and 15 00 watts will g enerally reduce
t he generators' distortion sufficiently. The load must be resistive,
and it must be const ant . Good examp les include 500W
incandes cent floodlights, and bar-element rad iat ors.
Fluores cent lighting, refrigerators and stoves are uns uitable –
eith er because t hey are not resistive, or because they are
t hermostatically controlled an d may cut out at any time.
Here is the (simulated) waveform of the same generator as before,
now loaded with a 1000 watt resistive load :
The degree of distort ion reduction is immediately apparent – it is
now down to 12 %.
This "resistive loading" technique works well - but the operator must locate suit able loads (and remember t o us e them each
t ime!), and the engines' fuel cons umpt ion will increase.
It may be viable to up grade your generator set, instead.
PORTABLE GENERATOR SETS:
Xa: 48.00mXb: 0.000 a-b: 48.00m freq: 20.83
Yc: 337.8 Yd:-340.0 c-d: 677.8
b
A 600
B
400
200
0
-200
-400
-600
0 8m 16m
Xa: 48.00mXb: 0.000 a-b: 48.00m freq: 20.83
Yc: 537.8 Yd:-140.0 c-d: 677.8
b
A 800
B
600
400
200
0
-200
-400
0 8m 16m
9
24m 32m 40m
Ref=Ground X=8m/Div Y=voltage
24m 32m 40m
Ref=Ground X=8m/Div Y=voltage
a
c
d
48m
a
c
d
48m