my group and i decided to use trickle charging to our 4 AAA NI MH batteries .
but we need a basic (and simple!) configuration of the batteries. I want to know how to build a circuit that can supply a constant amount of CURRENT flowing into my batteries. how do i regulate current?
the other sites were kind of confusing and I don't have the given parts such as a LM 317

also, where/how do i attatch the DAQ in my circuit?

 

hi wheetnee
parts are usually the easy bit, they usually arrive next day and are as cheap as chips.no pun intended,
confessing my ignorance here but whats a DAQ is this a computer program.

 

my prof expects us to use the parts we have
is there any alternative way to build a constant current supply?
i want 85 mA to flow into each battry while its being trickle charged

a DAQ is a data acqtuisition board -- we use it to connect to the computer so we can program matlab on it and have a chart showing voltage vs current

 

 

'my prof expects us to use the parts we have'
what parts have you got, apart from the power supply and daq

have you any info on the daq could be useful.

 

the 1k resister can be connected to pos

 

the transister will need to drop from at least 12 volts to around 5/6 volts
so will need a good heatsink.

 

help. if wheetnnee has few parts could he take something like the carbon rod out ofa battery and tap for 6 volts?

 

Hi
First of all You and your group have to change the way you are working. As it is now nobydy knows what to do. And everybody is pulling in the oppesite direction. If you keep doing this kind of work. You will fail big time in this project. An engineer must be able to navigate safe in unknown water. As a starter you should post the document describing your assignment. Without this we can not give you any advice. But have in mind that is you and your gruop that must do the work. This forum can only give you some adiveces, or a push in the correct direction.
Also in the future please do not post questions like "also, where/how do i attatch the DAQ in my circuit? " Questions like this can not be answered as we have absolutely no idea which daq unit you have. They only reduce the amount of people willing to help you. Because it gives the impression that you are to lazy to find it out by yourself, and find it much more convinient to just toss in a quick question. But I found a video on You Tube that may be of some help. http://www.youtube.com/watch?v=L0A9Gvk2cUk

 

WHEETNEE
im leaving it to the experts now, good luck on your project,
will you keep us informed on your progress?
regards
dougal

 

Something you might consider, the spec sheet offered a tantalizing spec on the first page,

AC Impedance (no load):​

The impedance of the charged cell varies with frequency, as follows:

There may be something you can use to sense when the unit if fully charge.

There is another specification that you might use (but not at the same time as the above) is the

Internal Resistance:​

The internal resistance of the cell varies with state of charge, as follows:

Just a suggestion, draw a block diagram, include everything you want to do here. Then simplify.

Don't over complicate it, it is easy to do.

A nearly discharged battery rated for 850ma/hrs discharge at 170ma (from the data sheet) to 1 volt will take 100ma for 8.5 hours, this is another approach to use. The amp/hour spec gives you a firm handle on the upper limit, the other specs tell you how you can sense the state of charge.

 

Then I was in the National Guard my commanding officer had two phrases that he like to mention. He used them in military meaning, but I think they also apply well in electronic. The first one "keep it simple stupid" or KISS. I do not say you are stupid Wheetnee, but a complex plan or (or circuit) is more likely not to succeed, than a more simple and robust plan or circuit. The second phrase was "attention to details". Then working with electronic circuits, you must be sure that everything is correct. Like is the diode correct placed in the circuit board, or do all circuits have the correct operating voltage. I could mention a lot more, but I think you get the picture

 

Energizer has a Ni-MH Applications Manual on their website. It tells how to charge and discharge Ni-MH cells.

IC manufacturers like Maxim-IC have battery charger ICs with full descriptions about what they do and how they do it.
Make your own battery charger circuit by copying their IC.

 

Using Panasonic's hand book,refferenced earlier, I picked dooable items, delta temp & V not included. Using only trickle charging will get you a D. Fast charging @ 1C with trickle finishing = C.
If your DAC can supply timing & comparator functions-great. Cutting to the chace: Q9-constant current generator,800 mA, is turned on by switch Q8 if, battery not discharged below 3.2V[.8V/cell]. by Q6. Q8 turned off by Q7 if fault causes more than 1.8 V/cell.[Could be eliminated to simplify ] Thermister monitors temp. At 50 deg. C, Q8 turned off by Q5. An 85 min. timer turns Q8 off also. With Q8 off, trickle charging continues via Q1,Q2 untill 20 h timer turns them off. All sensor outputs should be stored in memory, like flip-flops, or DAQ to prevent operational oscillations. It's a start.

 

The 2.5V reff. got lost from Q7+ to ground, 2.5V zener or IC LM336. R10 is pot to adj temp trip. Q9 will charge 1 to 5 cells @ 800 mA. V sensors would need to be changed for different no. of cells. Thermister must be atteched to an active cell. Q9 heat dissipation was covered in another post. R13 just for current monitoring.

 

It uses a hell of a lot of parts to replace a battery charger IC.
So why not use a battery charger IC?