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IN BRIEF:

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Some battery chargers perform erratically, or suffer damag e, when run from portable petrol g enerators

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This is due to poor waveform quality from small portable generators, particularly when lig htly loaded.

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Either apply an ad ditional load to the generators when running battery chargers, or get a better generator set.

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The generator VA rating should be at least FOUR times the battery voltage multiplied by the charger current.

THE PROBLEM - MORE DETAIL

In recent years, WOODS Battery Chargers have been seeing an increasing number 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 most likely to be used with

small gen-sets.
Power from gen-sets of 7kVA and higher seems to be of good quality. No problems have been reported from using chargers
with these larg er gen-sets.

Similarly, few problems have been noted in WOODS ELECTRIC “Automatic”, “BETAcharge” and “Neptune” chargers, simply
because these are not generally used with small gen-sets.

Although most appliances are not affected by the poor waveform quality from smaller gen-sets, those appliances which use
“Phase Power Control” are particularly affected. “Phase Power Control” is used in WOODS ELECTRIC battery chargers, in speed
controls for p ower tools, and in domestic lighting dimmers.

THE CAUSE – MORE DETAIL:

The generators in many small gen-sets produce highly distorted waveforms.
Although meters are readily available to measure generator output voltage

and frequency

, it is rare to see meters for output

distortion

measurement. The easiest way to view a generators’ output is to use an oscilloscope. This will not directly measure

distortion, but it will give a good visual indication of the degree of distortion.

Here is the (simulated) waveform of a typical “cheap and nasty”
generator, shown against a pure 240V 50Hz sinewave:
This particular waveform exhibits a distortion of around 25%.

Ideally, mains power (and gen-set output power) would be a pure
sine-wave. In fact, mains power may have up to 5% distortion.

This level of distortion does not create any misb ehaviour in
Dialomatic chargers.

Some gen-sets, however, produce p ower with more than 20%
distortion (sometimes as high as 25%!).

The distortion is due to the design of the generator. The engine
driving the generator is not responsible.

The phase-control circuits in Woods Dialomatic chargers
manufactured before 2001 cannot cope with more than 8%

distortion. The circuits in new Dialomatic chargers can cope with
up to 15% distortion.

Woods Dialomatic battery chargers are generally quite tolerant of
the variations in frequency and voltage produced by gen-sets, but

they don’t cope with high distortion levels.

SOLUTIONS – MORE DETAIL:

We have found that the distortion produced by gen-sets may be

reduced to useable levels by loading the generator with a resistive
load, in addition to the battery charger.

Loads of between 500 watts and 1500 watts will g enerally reduce
the generators’ distortion sufficiently. The load must be resistive,

and it must be constant. Good examp les include 500W
incandescent floodlights, and bar-element rad iators.

Fluorescent lighting, refrigerators and stoves are unsuitable –
either because they are not resistive, or because they are

thermostatically controlled and 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 distortion reduction is immediately apparent – it is

now down to 12%.
This “resistive loading” technique works well - but the operator must locate suitable loads (and remember to use them each
time!), and the engines’ fuel consumption will increase.

It may be viable to up grade your generator set, instead.

PORTABLE GENERATOR SETS:

16m

24m

32m

40m

48m

-600

-400

-200

200

400