thats what i have on one of my designs ALAN one reason i designed my battery charger to handle up too about 100 amp battery at 24 volts ,or 12 or 6 or any voltage of a battery

so a battery like yours would need about 5 amp charging rate at 3.4 hours and thats mostly a fast charging rate,idea rate would be 2.5 amps at 6.8 hours,but mostly depends on what the charging rate that the company says to charge it at

TO measure voltage on a bettery is not really the best way to go,but it can work ,but checking each cell voltage

what most company who designs battery chargers ,they use a simple current monitor ,using a low ohm resistor or a hall effect design with analog output

thats what we use at work since all our test equiment mostly use batteries one of the big test equipment company we bought is AMPROBE ,factory not in new york any more,looking at next to buy FLUKE

But i think FLUKE wont sell yet

Alan, ill post the voltage divider schematic later too, its simple enough and measuring voltage on adc has been 100% accurate for me so far.

Robotmaker and Rich, thanks both. I'll research Hall Effect (I have seen it mentioned here before) although for this purpose I too think voltage measurement will be sufficient. Just want to get home while there is enough juice to run the motors. Everything else is lower voltage so should keep running long after the motors can't go.

For the charger, I am set already. I have an electric wheelchair charger designed for this specific battery.

Alan

I like wheelchair motors great for large robots that weigh about 200 lbs or more mine about 150 lbs may more once i get my arms done,i have my macnine done with every machine needed ,lathe and a mill are the best for it ,next is to buy a very good 3d printer .i saw a nice one for $4800,so for me its easy for me to buy it,just need to do more reseach on it and make room for it might add another room on to my hose i need it

ALAN you adding arms to it, also on chargers i hate buying them,mostly made for the battery it made for .or not higher in current or voltage,witch meens every robot a person makes you need to buy a charger for it

Now on LI-POLY battery,i may or may not buy it,it does take CC and CV to charge a battery and the circuit not hard,plus you need a cell switching board,depending on the cell count

ALAN you making a wheelchair setup ,when you said about getting home without the batteries doing out,if yes that very cool i seen a few and one is controlled by EEG headset ,witch i bought 2 types to use on EZB its done with using arduino,so should be easy to port to EZB it uses you mind to move and control the robot

A basic voltage divider, set up for 1/4 of the battery voltage to ADC0

If you only need half then replace R1 for a 10k resistor, if you need 1/8th then replace R1 for 70k... basically, equal resistance either side of the signal wire will halve the voltage, increasing one over the other will vary the ratio. For less voltage to ADC increase R1, for more increase R2. I don't run mine with R3 connected as I didn't have enough resistors but it's apparently advisable to add in a 10K as R3.

Then you can monitor the voltage on the ADC port by running the GetADC(ADC0) command in EZ-Script.

My actual script I use to monitor my current projects 7.2v 2S LiPo is;

# Read voltage level of battery and report to software.
# Set variables
# Change $vmin to low level alert value
# Change $vmax to battery full charge
# Change $multiplyer if using voltage divider
# Factor is 5/255 for adc value conversion to volts
$vmin = 3.6
$vmax = 4.5
$multiplier = 2
$factor = 0.019607843

:ReadCells
# Get ADC values
$vc1 = GetADC(ADC0)
$vc2 = GetADC(ADC1)

# Convert values to voltage
$cell1 = $vc1 * $factor
$cell2 = $vc2 * $factor * $multiplier
$cell2 = $cell2 - $cell1
$batteryv = $cell1 + $cell2

# Check for errors on connections
IF ($cell1 > $vmax or $cell2 > $vmax)
  Print("Battery Connection Error")
  
  # Check for errors on cells
ELSEIF ($cell1 <= 0 or $cell2 <= 0)
  Print ("Battery Error")
  
  # Check if below recommended levels
  # Cell 1
ELSEIF ($cell1 < $vmin)
  # Do sometihing if voltage low
  Print("Cell 1 Low")
  
  # Cell 2
ELSEIF ($cell2 < $vmin)
  # Do sometihing if voltage low
  Print("Cell 2 Low")
ELSE 
  # Wait 5 seconds
  Print("C1 Round($cell1,2)V")
  Print("C2 Round($cell2,2)V")
  Print("To Round($batteryv,2)V")
  Sleep(5000)
  # Go back to the start
  Goto(ReadCells)
ENDIF 
  # Go back to the start
Goto(ReadCells)

If there is an error connecting to the battery it will report it, this is determined by an ADC value of over the maximum voltage of the battery, as my batteries cannot get above 4.2v when fully charged I've added a slight tolerance and set the $vmax to 4.5v. With the battery monitor cables disconnected the ADC value returned is 255 so will report a 5v level and output the error message or run the error command.

Again, if the ADC is low, as in 0v, it will report a battery error and, if required, run another script or other functions if needed.

Then the monitoring script checks the current voltage against the preset minimum voltage. Once the minimum voltage is met it reports it as low and can run another script or other functions if needed.

While the voltage is OK the script just loops around reporting the voltages for information.

I did plan to include an LCD screen but the one I got was I2C and no datasheet so couldn't get it to work correctly, but that could be added in easily. As could additional cells/batteries, less cells/batteries, setting it to illuminate an LED for low power, shutting down for power saving or most importantly, running the find home script to get to the dock to charge.

I'm still developing the script but as it stands it works so feel free to use it, modify it, have fun with it. Hopefully the comments and the above descriptions will aid in adjusting for your specific requirements.

P.S. I believe all of the in the code are just closed brackets )

Rich, thanks very much for the data. That looks like it should be easy to implement and meet the needs.

Robotmaker, I am using wheelchair motors for the weight carrying, and in some cases for the speed. The bot will actually be sort of dog shaped (think k9 from Dr who, but with steampunk decoration when it is done), but will also have fold down foot stands (like motorcycle passenger foot pegs) and an attachable handle with a joystick so I can ride it standing up, sort of seqway like.

I want it to be under 50 pounds so I can take it on Amtrak as luggage, but I think it will wind up 60-70, but since I am an employee, I can probably get away with telling them it is for personal conveyance and exceed the weight limit. I am 225 lbs (although trying to get down to 200) so I need the power of the wheelchair motors to get me around, but they themselves, and the battery are almost 50 pounds before I add the robot body and other parts. Motors are rated for 300 lbs, so should be OK carrying me.

Most of the time though, it will be autonomous and one of its jobs is guard dog, which is why I want the speed ability of the high power motors. I want it to be able to go fast enough to scare the cr-p out of any intruder in my home.

Alan