Hagar69

I'm thinking of building a charger that can charge multiple packs in series. I have a programmable micro controller with several digital inputs and outputs as well as a few analog inputs. I also have a cheap NIMH charger that outputs 0.5 or 1.0 A and it has selections for number of cells. I do not thrust the peak detection in this charger and would try to make my own logic for this in the micro controller.

I know how to program the controller and know a little bit about electronics. But tips and ideas would be greatly appreciated.

Can I control/change the charge current by using relays to switch between different resistors? Or is there a better way?
How can I use the A/D to measure battery voltage while charging? How to avoid measuring the charger voltage?

Does anyone have a link to a page that describes how an intelligent charger works?

Plan to use it for charging 7 and 8 cell packs for my F-27 Stryker, but also for charging NiCd packs for my power drill.

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Hagar

CFIMEI

Hi,

Several years back, before virtually all assembly language programming of 8 bit microcontrollers went to the Third World, I designed several projects for use in building control, energy management & fire alarm systems. I was therefore able to justify the purchase of an Intel development system which I used a lot over the years. One project for my own consumption was a NiCd charger, primarily for field charging my Tx & Rx packs. I used an Intel 8051 as the core processor & several outboard chips for sensing voltage over the range that 1 to 12 cell packs would exhibit. The unit had two channels so that I could charge two separate packs simultaneously. It had an LCD display which multiplexed the charge level of each channel plus the voltage of the incoming supply. The actual voltage sensing was done by a Motorola single-slope A to D converter under the control of the MPU. I built in a keypad so that I could set the battery C capacity & then could select full C rate charge or .1C for slow charging. After a fast charge cycle it would display the peak that had been reached for that battery & the elapsed time & then revert to a trickle charge rate. I used this charger for years & often powered it by a solar cell which I took to the field. It currently needs a new LCD & now having gone to Li Polys for everything but my Txs, I haven't found the will to fix it. I may still have a schematic for it somewhere & possibly a source file listing for the code.

There was an article 10 or 12 years ago in one of the major model magazines about a microprocessor peak detector which could be used with an early Astro timed field charger (before Astro had its current line of peak detecting units.) I got several of my ideas from that article but included features which it didn't have.

It took a full 4K of assembler code to make it do all of its tricks & I had to experiment with program changes to find the ideal parameters for reliable peak detection & cutoff. It did not have a switching converter built in as do the current Astros, Apaches & all the rest of them. I needed an input voltage slightly higher than the maximum peak voltage of the packs under charge so I sometimes used a separate converter for old Tx batteries that sometimes reached almost 15 volts at peak. It turned out to be impractical as a commercial venture as the world became flooded with cheap & effective chargers, but I enjoyed the development process & got a lot of use out of the resulting charger. I always planned to include a discharge feature with selectable rates of discharge & readout of capacity but never did tackle that improvement. Now my development system is pretty creaky & Intel no longer supports it so I don't start long projects using it for fear that it may die in the middle, leaving me with no way to salvage my effort to that point. New development systems that run under Windows start around $3,000 & go a lot higher! So unless I find a paying project that would justify a new system I likely will not develop any more 8051 based firmware.

Anyway, good luck with your project. I think in light of all the stuff easily available it will be more of a learning exercise, but that's a good thing!

Richard

Hagar69

Richard,
Thanks for a long and informative post. The micro-controller I have is a little higher level. It is programmable in "C", has flash memory, a 2 line LCD display and a 10 key keypad. I was hoping to be able to use it in this charger project (I have no other use for it), but I am uncertain about what other electronics I would need to acomplish this task? I know a lot about programming, but not enough about the electronics.

I'm probably better off just buying a good charger, but it would be more fun to create something.
I also think it would be nice to have a charger where I could hook up several battery packs, turn on the charger and then just forget it until I want to fly with all my packs fully charged.

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Hagar

Glacier Girl

My Feedback: (4)

Hanger,
Keep an eye on the PARK FLYERS forum,under the STRYKER posts.
Cadetman has built a "cascade" charger, does up to 10 packs at a time,charges first battery,switches to 2nd when 1st is charged,and applys trickle charge to 1st when switches over to 2nd for fast charge, and so on, automaticly. Very simple system. He's in the process of trying out a new system now, maybe you could check with him on some suggestions. As he is an electrical engineer and you're a programmer[sm=idea.gif]
Just a thought.
BJ