[Waverley ARS] PROJECT: Building a battery charger

[Adam Carmichael]

Hi Texx,

Thanks for the tips about the DMM :)

To reveal more details... I picked up a battery at a club meeting about 
a week ago for $1! It's a 12v 1.2ah lead acid battery. I'm wanting to 
build a charger for it, and because I had a broken halogen lamp with a 
working transformer in it I decided that would be a great start.

The PIC (in another post) was for a separate project - I'm building a 
timer in another project (all very hush hush because it will end up 
being an xmas present for someone, but here's a taste: it has gyroscopes 
and inclinometers in the plans!). I was at one point thinking about 
putting a PIC in the charger with 5-10 LEDs and a test button to 
indicate the charge capacity of the battery. It should also be possible 
to use the PIC to control the charge rate too.

I really need to go back and read in my books some more on the charge 
cycle of lead acid batteries before continuing.

Thanks again,

73 VK2JSI... Adam

Texx wrote:
> 1st of all, builing hardware instead of being an "appliance operator"
> GOOD FOR YOU !!!
>
> About DMM;
> Unless they are absolutely the top of the line, they get confused when 
> measuring AC.  Last time I was in Sydney, my FLUKE told me wall voltage was
> 265 VAC !  Further, it claimed the output of my travel adapter was 134 instead 
> of 120.
>
> Sorry, forgot to warn you, Im a yank.
>
> Now about that "peak hold" feature.  Its a bit of a misnomer.  (Laughter)
> Peak, in this case, means "highest value on the display".
> It does NOT mean peak voltage.
>
> Im intriqued about your project.
> PIC chips and batteries, sounds very fun.
> Sounds like an intelligent battery charger.
>
> Im making the assumption that the battery in question is 12 volts.
> It sounds like you are starting with 18V at the filter cap.
> How will you lose the 5 volts so as not to cook your battery?
>
> (I just about melted a nice 12v 20ah gell battery a few months back
> because I didnt notice that the current flow hade suddenly jumped from
> 1/20 if the ah rating to about 10 times the ah rating.  Sadly its "toast". )
>
> evdw at iprimus.com.au wrote:
>   
>> Hi Adam,
>>
>> The reading you are getting will be RMS unless the meter specifies it as
>> Peak, which would eb very unusual. The paek value will be 13.3 x 1.414 =
>> 18.8V so if you use a fuk wave rectifier with a capacitor input filter you
>> should have about 18.8V on the capacitor under no load. 
>>
>> Not sure what sort of battery you are thinking of charging but that should
>> be adequate for most of them, it'll just have a lower current capability.
>>
>> 73....Eric.
>>> -- Original Message --
>>> Date: Mon, 23 Jun 2008 12:16:38 +1000
>>> From: Adam Carmichael <carneeki at carneeki.net>
>>> To: "W.A.R.S. Members List" <members at vk2bv.org>
>>> Subject: [Waverley ARS] PROJECT: Building a battery charger
>>>
>>>
>>> Hi List,
>>>
>>> I'm measuring the voltage on transformer that steps down from mains to 
>>> about 13V AC (I pulled it from a broken halogen desk lamp - I'm really 
>>> getting into the spirit of the "ham thing" now!). I measured it with a 
>>> DMM - on the AC setting and it reads 13.3V. I was wondering, if I want 
>>> to use this as a power supply in a battery charger - would this 13.3V 
>>> setting be RMS or it's peak voltage and I'll need to calculate the RMS?
>>>       
>>> (The meter is a Tes 2360 - there is a "Peak Hold" feature - perhaps what
>>>
>>> I read on screen is the RMS value?).
>>>
>>> The other question I have is... Most of the charger circuits I'm looking
>>>
>>> have chargers for anywhere between 3-10A. Is it possible to build one if
>>>
>>> my transformer is 25W (about 1.6A at 12V)? I figure it might be, but it
>>>       
>>> will just take longer to charge the battery.
>>>       
-- 
Adam "carneeki" Carmichael - VK2JSI, ex VK2FNRD
p: +61 415 37 1990
w: http://bigneek.com (personal); http://carneeki.net (business)
e: carneeki at carneeki.net
i: 2207644