Picaxe based Li-Ion charger

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Pauly1980

New Member
Hi everyone, im new to these forums and am really excited about them already.

I am thinking about trying to construct a Li-Ion battery charger based on a picaxe chip. I have done some searching in these forums but have been unable to find any projects like this. My questions are
a)has anyone done this already?? no point going through the whole design phase if its been done already.

b)can anyone give me any advice if the answer to question a is no?

I look forward to getting really involved in these forums.

Paul
 
slimplynth

slimplynth

Senior Member
Hi Paul welcome to the forum, a Li-Ion charger sounds like it might be a dangerous first project. My status says senior member but in reality I still consider myself a complete newb, maybe explains my nervous feeling when thinking about attempting a Li-Ion charger and apologies if you're well versed in electronics... is this your first project? The other forum members will no doubt also ask this before offering advice.
 
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Pauly1980

New Member
This was going to be my first picaxe project, and to be honest I didnt think it would be that complicated... But I will take advice from you both and maybe try some simpler things first.

I am making my own LED scuba diving lights now and am getting sick of having to buy buck drivers to run them when the drivers never seem to be exactly what I want. I may have a go at one of those first.

I have some experience in electronics but I wouldnt say a lot. Most of it is outdated now but I am always happy to learn new things.

Paul
 
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BeanieBots

Moderator
Have to be honest that I'm stunned that you can't find an ideal constant current LED buck driver and at a price lower than you could ever build one yourself.
Plenty to choose from at both RS and Farnel for <£10.
 
hippy

hippy

Ex-Staff (retired)
I think as a first project it's overly ambitious, too many things which could go wrong and with potentially dangerous results.

There's quite a lot to learn with battery charging, theory and implementation. I had lots of fun and learned at lot as well from just charging a single AA NiCd from a PICAXE I/O line limited to 20mA charge. Something simpler, perhaps along those lines, would be a good prerequisite to somthing more complicated.
 
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Pauly1980

New Member
BeanieBots said:
Have to be honest that I'm stunned that you can't find an ideal constant current LED buck driver and at a price lower than you could ever build one yourself.
Plenty to choose from at both RS and Farnel for <£10.
Click to expand...
You are right, there are plenty of drivers out there, but I need one that is simply designed to my specs. ie if you want to buy a 3 stage dimmable one then you seem to always get the SOS function and a whole heap of other stuff. I dont want that. All I want is 3 dimming stages, and low battery cutout. Oh and a few other features for the new torches I am making but I dont want to go into these yet until I get my patent through for them. Needless to say that the cost to build is not really a problem. I can safely say that I am willing to spend about $70AUD to build one to do what I want. I am a tinkerer and I cant help but want to make things myself. Also most of the premade drivers are sized physically inappropriately for what I need.

Paul
 
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Haku

Senior Member
If you're only charging a single lithium cell it's is easy with the cheap MAX1555 IC.

As pointed out, multiple cell charging gets tricky, but if you can isolate the cells when charging you could use a MAX1555 for every cell, which would have the benefit of making sure each cell is individually fully charged..
 
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papaof2

Senior Member
I agree on the MAX1555 for a single Li cell. It's about $4US, plus an SOT-23 to DIP adapter board (uness you can make your own boards for surface mount components).

John
 
slimplynth

slimplynth

Senior Member
hippy said:
I think as a first project it's overly ambitious, too many things which could go wrong and with potentially dangerous results.

There's quite a lot to learn with battery charging, theory and implementation. I had lots of fun and learned at lot as well from just charging a single AA NiCd from a PICAXE I/O line limited to 20mA charge. Something simpler, perhaps along those lines, would be a good prerequisite to somthing more complicated.
Click to expand...
That's a brilliant, 'first charger' project, cheers Hippy. Am lookin forward to seein Stocky's work with the solar too... sounds like a good combo, with summer coming soon (with any luck). Have got a 5" x 3" solar panel from a caravan toilet light.
 
hippy

hippy

Ex-Staff (retired)
I think the bulk of what I did was described in -

http://www.picaxeforum.co.uk/showthread.php?t=7878

Basically, PICAXE at 5V, discharged battery, add an R to an I/O set high to charge. You can see charging happen and the charge finished peak on a meter. Add ADC to read the voltage and detect the peak and that's really it. Not perfect as not constant current but it does work.

You can then add auto-detect to start charging a battery when it's inserted, fail-safe for if battery already charged, not charging, too discharged to charge, cut-out timer, delta-T protection, PC logging etc, discharge ( just set the pin low ). You can give 'battery quality' indication.

The good thing is that you get to see what the battery is actually doing, understand what the documents and guides actually mean in practice, and all relatively safely. You also get to see where your PICAXE program is weak, where theory doesn't match with practice. Put the charging pin on a PWMOUT and/or add a second R to another pin and you can experiment with pulse charging and so on. You see where changing things messes up things that were working and it's all incremental development so you are mainly going forward, always improving, always learning.

It was one of the most enjoyable PICAXE experiments I've done.
 
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