Aaron

Firstly I'm not an expert or even very knowledgeable on these matters but   
have been gaining information on chargers for Gavin scooters and lights.   
 Also, this is from memory, as my information is at home - ask for a data   
sheet from the battery supplier.

Secondly, do not use an auto battery charger on gel cells, you will kill   
them with too high a current.

You should be able to charge the batteries with your power supply running   
with constant voltage but best to get a dedicated charger as this will   
work automatically.

The cells used in the Spectrum 14 and the Gavin light are YUASA 12V 7 Ah,   
connected in parallel.  YUASA recommend a maximum charging current of   
0.25 times the Ah of the battery (Dry Fit recommend 0.5 times the Ah so   
this is manufacturer dependent).  For bulk charging a single 12V 7 Ah   
battery, the voltage should be 14.4-15V with 1.75 A maximum (i.e.   
limited) current.  When the current drops to a certain value the battery   
is about 90% charged and the voltage should be reduced to 13.8 V to   
complete the final charging in float mode.  The charger can be left on   
float charge indefinitely at this point.  YUASA state something like 20   
hours maximum charge time (excluding float charging) and an optimum   
charge time of about 9 hours.  The "certain value" of amps is determined   
by the battery I can't remember the values but they were something like   
but 100 mA for a 1 or 2 A charger and 800 mA for a 4 A charger.  My   
scooter batteries took about 8-9 mA on float when fully charged.

YUASA state that the charge time from full discharge can be approximated   
as:

(Ah * 1.6)/Max Charge Current

7*1.6/1.75 = 6.4 hours

A charger intended for these batteries (i.e. matched to the battery) will   
do the staged voltage switch automatically - the chargers I use are 3   
stage units.

Barry recommended that I buy a 1 to 1.5 A charger for the Gavin light.   
 Given that the batteries are used in parallel and never discharged   
separately, I rang YUASA to check if I could charge them at a rate   
suitable for 2*7Ah = 14Ah and they confirmed that this was the case.  I   
have therefore (bravely?) bought a 12V 3 A, 3 stage charger to do this.   
 As I am expecting my torch in the next day or so, we'll see what the   
currents are and whether I made the correct decision.

I hope this helps - but remember - get the data sheets and check my   
memory!  If you have specific questions I'll look them up if I can   
tonight - email me directly.

David Shimell
Project Manager, Sequent Computer Systems Ltd, Weybridge, UK
Email: shimell@se*.co*

 ----------
From:  owner-techdiver[SMTP:owner-techdiver@aquanaut.com]
Sent:  05 January 1998 11:47
To:  Tech Diver
Subject:  Charging batteries

I just got a used AUL light (Thanks Barry!) and I have some questions   
about
charging the batteries. I could just go get a cheap auto battery charger   
I
guess, but I already have a perfectly good 0 to 14V adjustable power   
supply
that can be limited on amperage as well.

What I want to do is set the power supply to a given voltage, and charge   
the
batteries. The power supply has a current (amp) meter as well as voltage,
and is infinitely (versus discrete) adjustable for volts, and infinitely
limitable (intermittent breaker) for amps. Can I get away with using   
this?
What is the desirable voltage to charge batteries? What should I expect   
in
current draw? How many amps should I put on the batteries? I realize that   
as
the batteries charge, the amps drawn should drop, will this allow me to
judge the level of charge?

So, if I have two 7 AH batteries in series for a total of 14 AH, what is   
a
good current (amps) to charge at? What voltage should I expect that to be
for fully discharged batteries? My power supply can sustain 20 amps, and
peak to 30 amps, so I'm sure I could cause something destructive to   
happen
if I'm not careful, what is an absolute limit in amps?

Thanks,
 -->Aaron
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