Stick Balancer for Nimh battery packs

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boelle

Member
Hi

i have tried to hack together a charger/discharger or balancer for a batterypack that has 20 strings of 6 nimh cells

the charger is build so that each string has it own module and each module sends data to a master module

the schematic: http://tina-og-bo.dk/stickbalancer.pdf
vsm design file: http://tina-og-bo.dk/stickbalancer.DSN
picaxe code: http://tina-og-bo.dk/v1stickbalancer.TXT

so far i'm stuck with an error.. i have tried to read as much about the picaxe but so far no luck, any the error is:

Code: 
symbol PreviousAmperage  = w7
                           ^

Error: Unknown symbol - w7
the picaxe code is taken from a design by peter perkins all credits for his work should still go to him

now feel free to comment and laugh at this danish fool :D
 
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BCJKiwi

Senior Member
08M has w0 through w6 available - no w7! you would need a bigger Picaxe for that (20x2, 28/40 x1 and above) - see Manual 2 Page 10
 
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boelle

Member
i do use a 20M.. also i have set that in options in the programmer software.... will read that page
 
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boelle

Member
read section one of the manual... so far i can understand i need to tell what is inputs and what are outputs... but the fool writing this post did not get it

i have written down what i want the 20x2 to do... but the programming seems to be over my head... at least until i understand it better
 
hippy

hippy

Ex-Staff (retired)
http://tina-og-bo.dk/v1stickbalancer.TXT

Unfortunately it looks like that code is a work in progress, incomplete and with a number of syntax errors within it. It would probably be worth contacting the author directly to see if they have complete working code or an explanation as to what the code is meant to be doing and why and write your own version.

The problem with correcting errors in incomplete code is that unless one knows what it is intended to do and how it is meant to work one cannot be confident of having 'corrected' it in a right or suitable manner. In a case such as this - where the code indicates it is for use in a vehicle, uses "potentially lethal battery systems and high voltages" - it is essential to get it right.
 
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boelle

Member
what i intend to do is a charger/balancer for 20 7,2V sticks...
i have build it to be in form of modules so that each module is only charging a 7,2 stick made of 6 1,2V cells welded together

what each module should do is to start messuring the voltage and send it to a master module, if it's below or equal to it should start charing turning on Q1.. while charging it should at a regular basis send voltage and amperage data to the master module so that amperagehours can be calculated to detect a stick that has gone bad or need extra cycles to be usefull... if the stick does not get within a preset Ah range then it should be marked as bad

as for the charing it should stop when the voltage has dropped 5 or 20 mv pr cell in the stick... of course if the top is not within a range the stick could also be marked bad if extra cycles does not help it

as for discharge that is done by turning Q1 off and Q2 on to pull the relay.. again voltage and amp's should be messured and send to the master module

as i have calculated the dummyload and charge current a cycle of charge and discharge should take 2 hours.. the spec for the cells are 1,2 V and 6,5 ah.... 6 cycles should be doable in about 12 hours

so the ultimate aim is to charge and discharge unattended with logging along the way... so far i have 3 leds to indicate charge, discharge and trickle charge

trickle charge should be started if the stick are ok after the 6 cycles to keep it at the top point, but before trickle charge there should be a 2 hour period where self discharge is messured. maybe the periods could be changed but the goal is to have all sticks tested and marked bad/ok plus trickle charged within 15 hours

the schematic should of course have added opto's so that the modules can be chained and 2 extra LEDs to indicate bad/ok

hope this helps a bit on clearing up on what my goal is

http://tina-og-bo.dk/v2stickbalancer.TXT should be my latest attempt but sure i figured out i was a bit on the wrong track
 
fernando_g

fernando_g

Senior Member
boelle;
don't be afraid of cleaning the schematic...it is actually a good excercise and will allow you to spot not-so-obvious-mistakes,

The schematic as is, is quite confusing. The problem with computer-generated routing signals, is that to a computer, a node is node, For instance, take a look at the top portion of resistor R6. A human would have connected it to U3's "adj" terminal, which would have made it very clear that this is used to control the charging current. However, the computer decided to loop the wire down.

There are other similar issues; the bottom of R9 looping around, instad of a straight connection, etc.
So yes, it would help if you tidy up the schematic.
 
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