Charging Batteries

[Millenniumman]

Looking a this site, there is a diagram of a circuit for checking battery charge level, but I can't find one for actually charging batteries. I'd like for them to charge in my robot from a 12VDC power supply. In what I am doing right now, I am planning on 10 NIMH AA batteries in series, maybe in the future 2 sets of those in parallel. Any tips/links on how to charge that from such a power supply? Should they get 12V or 1.2V ?

[airman00]

Welcome to the forum


Here is a helpful link
http://www.powerstream.com/NiMH.htm

Also, since you have 10 identical NiMH batteries in series , practically speaking it is one battery and not 10 batteries. So treat it like its one 12V battery.

,Eric

[Millenniumman]

That information is very useful, but it seems to be more oriented towards choosing a normal battery charger and there don't appear to be any circuit diagrams.

[AndrewM]

Texas Instruments makes what appears to be a rather nice IC for handling battery recharge.  I picked one up, but haven't had a chance to integate it into a circuit yet.  Here's the link:  http://focus.ti.com/docs/prod/folders/print/bq2000.html

The PDF datasheet on the page includes sample schematics.  MAXIM-IC also has some charging circuit diagrams on their website.

[Admin]

I am planning on 10 NIMH AA batteries in series, maybe in the future 2 sets of those in parallel.

How many mAh? Might be better to just buy a $40 charger (cheaper than your batteries, anyway!)

As for a circuit, just attach it directly to your charger. No circuit needed. You can also use a desktop power supply to control the current. Just make sure you don't go above the rated current or overcharge (you need to time it), and lower the current to trickle towards the end.

edit: Forgot to mention, you must charge at above the battery voltage, like 14V or something like that. Use a diode to make sure the current only flows into your battery.

[Millenniumman]

How many mAh? Might be better to just buy a $40 charger (cheaper than your batteries, anyway!)

2000 mAh. They cost less than $30, which is just a little more than the equivalent (voltage and mAh, figuring in how I am setting up the AAs) lead acid battery at Frys and a lot lighter and more versatile. But also a little more complicated.

As for a circuit, just attach it directly to your charger. No circuit needed. You can also use a desktop power supply to control the current. Just make sure you don't go above the rated current or overcharge (you need to time it), and lower the current to trickle towards the end.

It seems more elegant to just plug in a DC power supply into the robot, but maybe a charger would be the best way to go.

[Millenniumman]

Also, I am wondering if there is any information available on how many amps a given battery can supply? Like a AA NIHM vs. a little lead acid vs. a salvaged laptop battery. When I try to look for it, I just get amp hours, but I would think that a battery could only supply so many amps at a time, and a quick test with a motor, a wheel, and my ability to stop it seems to show that AAs provide can't provide as much as my desktop power supply.

[Admin]

It will/should be in the datasheet:

Discharge rate: 3amps

(or something like that)

[benji]

can a dc regulator be used as a charger to the batteries?without any circuit in between? as it is a constant voltage source

[Admin]

can a dc regulator be used as a charger to the batteries?without any circuit in between? as it is a constant voltage source

you don't want to use a voltage regulator, or even a regulated voltage . . . and its still not the power source

[benji]

i mean by voltage regulator a trans , power>trans>6 volt dc regualted

if i connect this directly into a battery ,whats gonna happen?
as the voltage is the same nothing i guess is gonna happen ... just to be sure

anyone can post a battery charger circuit?

[ed1380]

i've noticed that batery chargers charge at about 133% the batery voltage rating.
and yes you could use a wall wart as a charger. thats what cheap chargers are