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VK3ABK > TECHNI 09.08.04 07:21l 45 Lines 2436 Bytes #999 (0) @ WW
BID : 31659_VK3KAY
Read: GUEST OE7FMI
Subj: Re: Charging Batteries.
Path: DB0FHN<DB0RGB<OK0PPL<OK0NAG<9A0BBS<PP5AQ<ZL2TZE<VK3KAY
Sent: 040809/0605Z @:VK3KAY.#WEV.VIC.AUS.OC #:31659 [Wendouree] $:31659_VK3KAY
From: VK3ABK@VK3KAY.#WEV.VIC.AUS.OC
To : TECHNI@WW
Hello again all Techies.
There has been a good response to my query about possible dangers when using
an external car battery charger. Anecdotal evidence suggests that care is
required to limit the charge current, but otherwise charging is simply a
matter of connecting a charger with the right polarity.
My concern comes from charging batteries in two 'old' cars, both 1981 models
with electronics limited to a clock and radio, and the integral voltage
regulator in the alternator. No fussy computer or engine management, just
bipolar transistors and the alternator diodes. I changed a faulty voltage
regulator and alternator diodes, before I started to disconnect the battery
before charging it. Our shops and supermarket are about 1km away and in
winter the battery gets very little 'normal' recharging.
I had assumed I was introducing high voltage 'spikes' along with the 12 volt
charger, and this had destroyed the transistors and diodes. Sten, ZS6CFC,
has given some support in this thinking and his VDRs to clip the spikes is
something I had intended to do 'someday'! But since I started disconnecting
the battery before charging, many years ago, I have not had a problem.
My experience, plus an occasional comment, heard or read, and the suppressed
battery charger leads available, caused me some surprise when I saw the
Silicon Chip denial of potential problems.
The battery chargers I have used are simple $20 (Aus) transformer and ammeter
in a box types, which usually start off delivering 3 amp and tapering down to
less than 1 amp overnight. Constant voltage, with slight loading variations,
and virtually harmless to the battery from overcharging. The only harm that
might come is from voltages that could exceed the safe transistor ratings,
or the PIV of the alternator diodes. Sten warns against 'static charge', a
particular enemy of mine in a dry Australian summer. This is worth a mention,
as cars, as well as aircraft, can create high static voltages. Maybe, with
modern cars and modern solid state electronics, these are no longer a problem.
Anyway, thanks for the comments, I have a battery charger delivering 2 amp
into a resistive load on the bench beside me, but I haven't seen any high
voltage spikes yet! Just to be sure, I will fit some of Sten's VDRs and get
some steel studded boots and try to be statically neutral in future!
73. Dick. VK3ABK.
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