Ni-MH variable current supply charger

HI
Just bought 4X 2700mHa Ni-MH AA battery's my old charger is not up to
charging these in a reasonable time C/10 so im looking to build my own
charger.
I have a 1.5 amp power supply what I need is a variable current
circuit add-on- about 150-800 mA but cant find anything Simple! as in
DIY simple.
Any thoughts, suggestions?
Reply to
Phil Gardner
Yes, get a decent 'intelligent' charger ready made unless you want to build one yourself for the educational side of it. If you want to DIY then get a chip that provides the 'intelligence'.
Maha make quite good chargers (among others), see:-
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Reply to
tinnews
When you look at the spec for this one from La Crosse, it would be hard to beat as a DIY project.
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machine. The capability to Refresh cells is very useful. The only DIY worth doing is an adaptor so that you can charge C and D size cells.
Rob
Reply to
robgraham
LM317 voltage regulator IC set up for constant current.
Googling on "LM317 constant current" produced this:
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to mount the regulator on a heatsink - a square of 1/8 inch aluminium a couple of inches square should do the job
Reply to
Jim Backus
... but it won't do nearly such a good job (as in treating the cells well so they last well) as a proper NiCd/NiMh battery charging chip.
You can buy the chips or beg a couple free off the manufacturer as I did, problem is I can't rememeber the manufacturer's name now.
Reply to
tinnews
No need, the circuit is in the data sheet where you'll also find useful info like package choices and thermal data.
MBQ
Reply to
manatbandq
But a fast charger only costs a few quid.
You canhave my old one f you like. Ex model car racing charger. Does 4-8 cells at about 3A fast, dropping back to trickle when the delta peak is detected. Runs off 12v or the mains. Can';t sell em for love nor money.
Reply to
The Natural Philosopher
Thanks but the problem with the 317T and also the L200 is R=1.25/I Fine for a fixed current but hard to achieve a variable one.
Reply to
Phil Gardner
On Tue, 16 Oct 2007 11:24:39 +0100, The Natural Philosopher wrote:
£35 ? Were is the fun and DIY in that
Thanks but I don't want or need a quick/fast/Gadget lovers DREAM charger. also what I failed to say was I will also be using this for AAA,D,C,and subC cells.
Reply to
Phil Gardner
Due to the low value R not available as a variable one? How many different currents do you want? Just switch in different resistors.
Alternatively use a simple transistor as a current source.
MBQ
Reply to
manatbandq
Yes that's how I do it now with fixed value resistors But I would like to build a completely variable supply as per the original post !
Great can you point me to a circuit that works and I can build. Electronics is just a diy hobby I am not a design engineer.
Reply to
Phil Gardner
Google "transistor as current source" gives the first hit as
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which has a circuit for an NPN transitor that will sink current from the load (battery). Not sure if you can charge like that. A similar circuit can be made with a PNP to source current.
Basically you control the base voltage and assume the Vbe to be 0.6 V which gives you the voltage across the emitter resistor. That sets the current through the emitter resistor. The same current (to a first approximation) flows through the load.
MBQ
Reply to
manatbandq
You just know that one is going to be copied and be available from all good local Grocers & DIY stores before long ...
Next addition will be some Flash memory and a USB interface, so you can view the charge rate and the condition of the cells graphically.
And now that I've mentioned it, the odds of anyone placing a restrictive patent on the idea should be zero.
Reply to
Adrian C
Yes, that's the one, you can (or could) ask for sample chips on their web site. I got a couple of their deltaV charger chips this way, along with loads of documentation.
Reply to
tinnews

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