Anyone interested in designing a µC-based NiCd/NiMH battery charger?

[Odysseas]

Hi there,

i've just been browsing through my favourite electronics store, looking for a decent battery charger for my NiMH batteries. The only one that would really fit, however, costs 150 Euros - too much. All the cheaper ones strike me as being close to useless, so I thought why don't I do this myself?

I've been thinking: With all our expertise put together, we could develop a battery charger with, say, four battery slots, all independant, controlled by a microcontroller (I'd propose an atmega16 or 32, the integrated ADCs should come in very handy), with an LCD and a few buttons to control every feature. If possible, the capacity of each battery should be automatically sensed, and according to the state of charge, the charger pushes only as many electrons in as necessary. It would be nice, if the charger could support both standard charge and fast charge.

It would be cool if we could then make all the specs and schematics for this project available to the public, or at least to this forum.

What do you think, anyone interested?

 

[Nigel Goodwin]

Have a look at https://www.angelfire.com/electronic/hayles/charge1.html, which, although quite old, should give you a few ideas. Obviously a more modern FLASH PIC would be more useful for it these days.

 

[bryan1]

Hiya Odysseas,
Here's a microchip App note on doing just what you want
**broken link removed**

It uses a 16hv785 pic micro and looks like a neat project.

Hope this helps mate

Cheers Bryan

 

[Odysseas]

I cannot seem to view the second link, but that is probably because I am at work right now. I will check it once I am back home. I am sure these links will prove quite helpful. I will also check what specific tasks need to be accomplished in this project - I do want this to be a team collaboration.

 

[Odysseas]

Alright, after being in stasis for a while, I will revive this project now.

I think we will need the following expertise, and of course the people that have it

- Someone who is experienced at designing a PCB - I am not.
- Some who can program the microcontroller - I think I can take care of that.
- The schematic itself would surely be a collaboration of this entire forum.

But on top of it all, we will need to establish the very basics of the operation of the charger. I'll just propose the following:

The charger can charge four NiCd/NiMH batteries (can be mixed), each channel will be monitored independantly. There could be four different modes, again, individually selectable: Normal charge (say, 14 hrs), fast charge (say, 4 hrs), save discharge (and do nothing afterwards), and save discharge and charge afterwards (either fast or normal, wait for 10 minutes or so after discharging to let the battery cool down.) Surely, after charging to 100%C, the charger would perform trickle charge (say at 4%C, or user selectable)

For simpleness' sake I think we should let the user control the charger with three buttons or so and a 2x16 line LCD. Default language for the controlls would surely be english, but it would be cool if we could also make other languages available. I could provide german

If I really put my mind to it, I think I could do this project myself. But I do not want that. I want this all to be a collaboration of us all. Post your ideas now, don't think too much about it, just post it. Just about anything could be useful.

 

[audioguru]

Why not use a Ni-Cad/Ni-MH battery charger IC? Or copy one?

 

[Odysseas]

Huh, now that you mention it, could be worth considering. However, what ICs would you recommend? I only found the UC 3906 N, which is only useful for lead acid. Can they do things like save discharging, etc.?

 

[audioguru]

I think all semiconductor manufacturers have modern battery charger ICs. I know that Maxim, National Semiconductor and Texas Instruments have them but I haven't used them.

 

[HiTech]

thanks but I already have a $1000 charger that also analyzes, and restores rechargeables.

 

[TekNoir]

There are two different projects for Intelligent NiCd/NiMH chargers/cyclers based on PIC microcontrollers at OshonSoft's project page. Maybe they'll lend you a few new ideas.

https://www.oshonsoft.com/picprojects.html

 

[Odysseas]

Thanks for the links TekNoir, I see that I am not the first one to have a similar idea.

But one thing I think I would make clear: I am not looking for a professional, high quality charger that can decuple a batteries lifetime, but costs 1000 $. It should be a charger for everyone, but it should still be a decent charger, that charges the battery without torturing it, having it ready for the user at any time. It is not a charger for a laboratory. Just a decent charger alright.

 

[justDIY]

texas inst has several nice (and easy) 8 pin dip based charge controllers, for single or series cell nimh/nicd ... use one for each channel and then your microcontroller can play an overall supervisory roll, like collecting statistics, managing the display and user interface, etc.

 

[audioguru]

There are plenty of modern chargers that do the job well and are inexpensive.
Are you going to compete?

 

[Odysseas]

I will check all major part manufacturers and see what they can offer.

But now, I wish to be candid: I think there is not very much enthusiasm for such a project in everyone in here, is that correct? If so, I will resume the project myself and seek your advice whenever needed. But if somebody is really interested in helping me, that would be greatly appreciated, just send me a message.

@audioguru: In a way, yes. Surely not on the open market, but once the design is all ready to go, I intent to make it openly available to everyone (commercial use excluded, of course) who wants to built it themselves. As I said, the 'cheapest' charger that I find appropriate would cost 150 Euros, a bit too much for my tastes - and in that very moment my idea of doing it myself was born. Besides, it is a nice challenge, and, as with any DIY project, the fun is also a concern.

 

[Nigel Goodwin]

But now, I wish to be candid: I think there is not very much enthusiasm for such a project in everyone in here, is that correct? If so, I will resume the project myself and seek your advice whenever needed. But if somebody is really interested in helping me, that would be greatly appreciated, just send me a message.

Why reinvent the wheel?, I posted a link near the beginning of this thread which does what you're asking - you should be able to easily modify it to your exact requirements - bearing in mind you would have to write your own software anyway.

 

[Odysseas]

Yes, I saw these links and I will all use them. I have no intention of reinventing the wheel. But as you said: I have to write the software, and adapt all the stuff around it. But surely these links will provide useful information.

 

[picasm]

I think there is not much enthusiasm now for making one because as well as making the charging circuit, you also need a nice case with spring loaded battery clips etc. and provide a good power supply for high current charging.

A quick google search found products such as the "Ansmann Energy 8" which appears to have all those features for less than £50 in the UK.

 

[audioguru]

About 10 years ago, this would have been a nice project.

 

[Odysseas]

note to self: audioguru and picasm are not interested.

 

[audioguru]

All my rechargeable products already have a good charger.
All the circuits I built that are powered with rechargeable batteries already have a good charger.

When I shop for replacements for my old Ni-Cads I find that Energizer doesn't make them anymore, just less hazardous Ni-MH cells which have a much higher capacity. Then my products run 5 times longer and take 5 times longer to fully charge.

I have some extra Lithium rechargeable batteries that I might make a charger for. I'll use an IC that is made to do it.