Woods Dialocharge D1230 - Portable Generator Sets and DIALOcharge; Power Quality Issues; Solutions for Distortion

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IN BRIEF:

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Some battery chargers perform erratically, or suffer damage, when run from portable petrol generators

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This is due to poor waveform quality from small port able generators, particu larly when lig htly loaded.

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Either apply an ad ditional load to the generators when running battery chargers, or get a bet ter 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-s ets of 7kVA and higher seems to be of good quality. No problems have been reported from using chargers

with these larger 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 power tools, and in domestic lighting dimmers.

T HE CAUS E – M OR E D ET AIL:

The generators in many small gen-set s produce highly dis torted waveforms.

Although meters ar e readily available to measure generat or output voltage

and frequenc y , 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 distortion.

Here is the (simulated) waveform of a typical “cheap and nasty”

generator, shown against a pure 24 0V 50Hz sinewave:

Thi s 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.

Thi s level of distortion does not create any misb ehaviour in

Dialomatic chargers.

Some gen-sets, however, produce power with more than 20%

di stortion (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 ci rcuit s in Woods Dialomatic chargers

manufactured before 2001 cannot cope with more than 8%

di stortion. The circuits in n ew Dialomatic charger s can cope wit h

up to 15 % dis tortion.

Woods Dialomatic battery chargers are generally quite tolerant of

the variation s 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 produc ed 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 15 00 watts will g eneral ly reduce

the generators’ distortion sufficiently. The load must be resistive,

and it must be constant . G ood examp les include 500W

incandescent floodlights, and bar-element rad iators.

Fluores cent lighting, refrigerators and stoves are unsuitable –

either because they are not resistive, or because they are

t hermostatically controlled an d may cut out at any ti me.

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%.

Thi s “resistive loading” technique works well - but the operator must locate suitabl e loads (and remember to use them each

time!), and the engines’ fuel cons umpt ion will increase.

It may be viable to upgrade your generator set, instead.

PORTABLE GENERATOR SETS: PORTABLE GENERATOR SETS:

0 8m 16m 24m 32m 40m 48m

-600

-400

-200

200

400

600

Xa: 48.00mXb: 0.000

Yc: 337.8 Yd:-340.0

a-b: 48.00m

c-d: 677.8

freq: 20.83

Ref=Ground X=8m/Div Y=voltage

b a