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'[EE] Lead Acid battery charging'
2008\11\04@025035 by Luis.Moreira

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Hi Guys,
I need to charge some 12V 1.2Ah batteries and unfortunately someone as
"relieved" me of my battery charger over night, so I was wandering if I
could just use a current limited bench power supply.
The charger was charging the battery at a 135mA rate but I can not
remember the voltage level, I think it was around 16V. Is this correct
and what is the maximum rate of current I can safely use?
Any draw backs or things I should look out for?
Thanks
               Luis


2008\11\04@041547 by Clint Sharp

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In message
<spam_OUTD6F368154C2B1043938B495AE13F245B0533821DTakeThisOuTspamntsrv-exch01.jetnet.jet.efda.or> g>, Luis Moreira <.....Luis.MoreiraKILLspamspam@spam@jet.uk> writes
>Hi Guys,
>I need to charge some 12V 1.2Ah batteries and unfortunately someone as
>"relieved" me of my battery charger over night, so I was wandering if I
>could just use a current limited bench power supply.
>The charger was charging the battery at a 135mA rate but I can not
>remember the voltage level, I think it was around 16V. Is this correct
>and what is the maximum rate of current I can safely use?
>Any draw backs or things I should look out for?
>Thanks
>               Luis
>
>
I used to use a current limited bench PSU for charging salvaged UPS
batteries many years ago, it worked very well but was rather expensive
for a 'simple' battery charger.

SLA batteries usually have charge recommendations printed on the side.

The current drawn is a function of battery charge state, battery
temperature and charge voltage, but for temperatures under 25C I'd
consider 135mA somewhere about right for your 1.2AH battery, charge
voltage should be 14.4v so you'll probably find the measured current a
little lower.
--
Clint Sharp

2008\11\04@051803 by apptech

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flavicon
face
> I need to charge some 12V 1.2Ah batteries and unfortunately someone as
> "relieved" me of my battery charger over night, so I was wandering if I
> could just use a current limited bench power supply.
> The charger was charging the battery at a 135mA rate but I can not
> remember the voltage level, I think it was around 16V. Is this correct
> and what is the maximum rate of current I can safely use?
> Any draw backs or things I should look out for?

Best to use proper charger for ongoing use, but for one offs ...

If your supply has constant current and voltage settoings as many bench
supplies do.

- Set supply to 14v
- Set current limit to C/10 (120 mA here). Rough is OK.
- Apply to battery. Current will start at 120 mA and then back off as
vopltage rises, depending on the supply. This is a moderately gentle
approach.

Alternative is to set Vout to say 20V and Ilim to 120 mA and it will charge
at 120 mA indefinitely.
Notional float value for wet plate LA is about 13.8V but SLA vary and there
is a whole arcane art lurking for the keen to discover.



  Russell McMahon

2008\11\05@025304 by cllow2020

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I've made one of this and works (but some components value need change)

http://www.talkingelectronics.com/projects/BatteryCharger-12vSLA/BatteryCharger-12vSLA.html

--------------------------------------------------
From: "Clint Sharp" <piclistspamKILLspamMIT.EDU>
Sent: Tuesday, November 04, 2008 5:15 PM
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam.....MIT.EDU>
Subject: Re: [EE] Lead Acid battery charging

{Quote hidden}

> --

2008\11\05@160216 by Clint Sharp
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In message <EE051D0C369E478BAFB034FB9F7DC9A0@userdc51bee4b6>, cllow2020
<@spam@cllow2020KILLspamspamgmail.com> writes
>I've made one of this and works (but some components value need change)
>
>www.talkingelectronics.com/projects/BatteryCharger-12vSLA/Battery
>Charger-12vSLA.html
>
The 'standard' LM317 circuit works just fine and is easy to add
temperature compensation to if you really feel the need (I live in the
UK, for the number of times ambient is over 25c I can save the cost of a
few 1n4148 diodes). Google for lm317 sla charger.
--
Clint Sharp

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