Battery Charger

Page last updated 04 Jan 2011, by Harry Weston. 5 replies Battery, NiMH, pwm

NiMH Battery Charger

Stages in implementing a battery charger for a battery of eight NiMH cells in series, 2000 mAh capacity. Based on the design by Peter Hayles, and I acknowledge with gratitude that this design will be a close copy of that on his website, at:

http://www.angelfire.com/electronic/hayles/charge1.html

This is the first stage schematic I am using: /media/uploads/ColonelPewter/_scaled_batychgr005.jpg

Progress so far (at 03-Jan-2011)

1) Testing a Nokia diplay as an output device

2) Test program to display input voltage on an ADC pin

3) Need to have mbed using local time, three ways to get it a) typed in via Teraterm, program written and tested b) from a GPS module, not yet tried c) from the Internet, needs an ethernet socket on my PC - one on order as a PC card (PCMCIA card)

4) Checked that PWM can control the average output current of the charging circuit; this was successful, now waiting to buy a more suitable suitable power transformer, it needs a 12 V secondary to get about 16 V.d.c. at 1.25A. The LM317 maintains a constant 1.25 volts between its ADJ and OUT pins, so, with a 2 ohm sense resistor the load current is 615 mA or so, and this was kept for 0 to 15 or so ohms load, zero to about 10.7 V ( the sums aren't quite right because of regulation and tolerances).

(Thanks for the posts, I'll reply soon: double hyphen for a 'dash' did cause the strike through, thanks again)

5 comments on Battery Charger:

Hendrik Lipka
03 Jan 2011

For 3), you might want to check my TimeZone library. It allows using NTP for getting the current time and converts it to your local time (after some configuration).

Steve Ravet
04 Jan 2011

Harry, I'd like to build a battery charger as well, my kids go through tons of AA batteries. Where do you get a holder for 8 (or more batteries)?

Regarding the strikethrough, if you type a double dash "--" then it'll apply strikethrough. Click the "editing tips" link for formatting details.

Harry Weston
04 Jan 2011

Well, I posted a long reply to these, and when I clicked 'Post comment' I got a blank page headed "http://mbed.org/comments/post/", and the comment disappeared. Well I'm blowed, what happened?

Harry Weston
04 Jan 2011

Thanks all, I will answer these posts in turn

Hello Hendrik Lipka, thanks for the information, the TimeZone libray looks very useful, from it I followed up the link to NTP, and discovered that the time on my Windows XP PC is already set using that. In my case the old C time.h library is included in mbed.h and gave me the necessary definitions, and I am fortunate to live in time zone Z, so my time is just GMT = UTC near enough (with daylight saving when applicable).

And hello Steve Ravet. Mouser sell at least two types of eight AA cell battery holders, the reference is the Mouser part number in their UK list.

12BH382B-GR /media/uploads/ColonelPewter/inline8aa.jpg Four on top and four below.

12BH381-GR /media/uploads/ColonelPewter/eightaa.jpg There is also a ten cell version of this one.

And also hello Christian Lerche. Thanks for the posting, but as you'll see Steve Ravet's suggestion did the trick; thanks again, Steve. I looked in the "editing tips" and found it there, but what it doesn't say is how to put in a good dash that isn't a hyphen.

I will post a comment about current control, which this is, on your home page, Christian.

Harry Weston
04 Jan 2011

Aha! so it didn't just disappear, sorry. In my panic I clicked the 'Go Back' on the blank window, and up came the notebook page again with the new posting. I've obviously a lot to learn.

Please log in to post comments.