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how do i get more juice from ba6209

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pkshima

Member
hi all,

i am using ba6209 to control 6v(100 ma) dc motor in my new robot.
the motor is a normal tape deck motor.

my problem is ... when i connect the motor directly to the supply voltage
(9v 500 ma), the motor runs great and is literaly unstoppable by any weight. but when i drive it through the ba6209, it just cant take much load
and my robot has a tough time turning left and right. (it turn great if powered directly by the suply voltage)

i used the ba6209 as per the schematics shown in its datasheet but it just give out much juice. i tried keeping its 'reference voltage' pin open for max Vout but in vain.

a simple 6 transistor H-Bridge (using SL100s and SK 100s)gives out far more power than this IC. but i cant use H-bridges cos i have 4 motors
so 4 h-bridges will make the circuit very bulky.

can i possibly do anything bout this problem. i want real power.
the ba6209 gets its control siglans from CD4555BE (which in turn gets its inputs from a dtmf decoder i.e. cm8870). its a wireless robot controlled by a PC.
i dont have a multimeter so cant take any readings.
 

bogdanfirst

New Member
from what i see from the datasheet and a graphinc, you cant squeze ,ore than 7v out of it for a voltage of 10 to 18 volts.
also, you say that instead of a zenner diode you conected the pin to Vcc?
well i think that it might not be that stable on this case.
for a 9v suly use a 8 and something volts zenner(8.5), maybe you would get more power that way.
try that
 

pkshima

Member
thx bogdanfirst for replying. :D
i didnt connect the Vref pin to the Vcc. i left it open as mentioned in the datasheet. the sheet says its ought to give max Vout in that configuration but it didnt actually.

btw which IC/method do u prefer for max torque. for a dc motor from a tape deck ? does lm298 or others have significantly more power than the ba6209.

thx again for replying,
bye
 

bogdanfirst

New Member
i dont know...
connect pin 8 directly to vcc.
but have you thought of something...
when you drive the 6V motor to 9V, it gives a power much greater than the power it is intended for(at the voltage of 6V).
no, i read again, DO NOT connect pin 8 to Vcc, connect it trough a resistor(but not smaller than 3 ohm-what it sayd in the datasheet)
from what i see from the charts, i have read the datasheet 3 times by now, for Vcc=12 V, RL=60 ohm, VZd=7.4 you should have a voltage of minimum 6.6 and a typical value of 7.2
mersure that, if its in limits, it should work. but consider if you have more than one motor, because in this case, tha suply voltage might drop with the load increasing.
also consieder this, for the Vref pin left open, tha voltage is Vcc=1.8, but for a zenner connected to it it is Vzd-0.2 so for some values of zenner diodes you might get a highter value
im out of ideas now.
 

pkshima

Member
well i plugged the IC off the robot and breadboarded the exact circuit
shown in the datasheet and well it gives reasonable torque !!!
i tried pulling the 7.4 V (7.5V exactly) zener in and out but it doesnt seem
to make much difference. but who cares, i get good enuff torque (considering the size and price of the IC).

but thats only on the breadboard. so my ciruits got to have some problem elsewhere. i suspect only two problems.

1) as u said the power supply is wasting power elsewhere. but i have 4
motors of which only 2 (max) run at a time. also no part of the circuit
gets hot ever even in about half an hour.

2) i suspect the IC just before the ba6209 i.e. CD4555BE gives out too
low output voltages to b able to saturate the ba6209. but the the inputs
of ba6209 r supposed to b logical and not analogue. so either the the
motor shud run at full torque or not at all. not at less torque.
what do u say ?

i guess to pinpoint the exact problem i need a multimeter. and i dont have one. so the new question is what type of multimeter i buy. what to look for. what features to look for (like inbuilt capacitance meter, transistor tester etc). i m basically a software engg. so dont have much experience with multimeters.

thx again for taking interest,
Pradeep K. Shima
 

bogdanfirst

New Member
from whar i understand you are using cd4555 to decode into 8 bits, because you have 4 motors?
so here is what i think it is happening, the motor is acually turning on and of because the signal that comes out of the demultiplexer, it is logical, nut not continous.
thats because for ecah decoder you cant have more than one output HIGH, and you have 2 motors for each decoder. so the one is is controlled, then another, but fast. so you might try this...
connect a capacitor to the ba... input and the ground of a few micros(2.2, 4.7, 10) try more values and see wich works.
from what i understand about the breadbouard, you connected the input if the ba... tu the Vcc for testing and the motor worked well?
 

pkshima

Member
i m using cd4555be to decode 4 bits to 8 bits out of which TWO can be HIGH at a time. (cd4555 is a dual 2X4 decoder). so two motors can run at a time simultaneously. so the loss of power cant b due to accidental PWM.

instead the good news is that i have bought a multimeter and taken some readings ...

Vout of the ba... -------- 14.* V (* = something)
Iout of the ba... -------- 0.38 A

i read the Iout by putting he multimeter directly across the Vout pins with no motors in between. i heard this is wrong but dont know exactly why and how to do it cleanly.

anyway, the Iout read 0.38 A which is nowhere near 1.6A as mentioned in the datasheet. so i took some measurments of the source power supply which is a wall adaptor of 12V 500mA rating. the actual readings came out to be 19.*V and 0.78A !!!!!!!! dont know whos crazy, me, the multimeter manufaturer or the one who rated the adaptor.
i took the current reading in the same (crazy ?) manner.

so my friends is this the problem ? that i m expecting high currents at the destination starting with a weak power supply at the source ?

but isnt the ba... ought to convert the high volatge of 12V (as in the datasheet) to a lower voltage of about 6V but of high amperage ?

here is the list of major components on my circuit to help u get an idea of the power consumption ...

one L7805 (5V regulator )
one LM386 ( audio amp )
one CM8870 (dtmf decoder)
one 74LS04 (hex NOT gate)
one CD4555BE(dual 2X4 decoder)
two ba6209 (motor driver)
one ba6238 (same as 6209 but with two drivers operable one at a time)
four 6V tapedeck motors(max 2 run at a time) dont know current rating.
one 3Ohm 2 Watts speaker.

and now i realise as i write that my robot will perhaps never be able to run on its own battery.
so guys is this the problem ??? is too much load ailing my sweety PI.
was i wrong in thinking that the ba6209 would convert the excess voltage to current. same is the case with 7805. doesnt it convert the excess (min 3V) to current ???
am i right or i just messed up my whole degree ?
 

bogdanfirst

New Member
lets starrt with the beginning.
when you mesure the current you dont connect the multimeter like that!!!
you need to conect it in series with the load. like you connected it, you connected the internal resistor of the ampermeter(VM) as a load, and that
resistance is very low, usually 0.1Ohm, so its like a short circuit, so what you mesured is the short circuit current. DONT connect tha multimeter as an ampermeter in paralel like that!!!!!!!!!!!!!!!!!!!!!!!!!
now. o.38 amps is the short circuit current, but it doesnt have to do anything to the 1.6A in the datasheet. what it says there is that the maximum cureent that the motor can draw from the ic is 1.6 amps, but for your motors i dont think that might be greater than 200mA.
next, for the adaptor. the voltage you mesured is the voltage without the load, so it is usually larger than the voltage mentioned. when you have a load to the adaptor, the voltage you will mesure would be smaller.
now, the current you mesured is the short circuit current, wich is greater than the one it is specified on the adaptor. the cureent written(500mA) is the maximum current that you should use the adaptor for.
and something i forgot to mentio, curent depends on the voltage aplied to the resistor(or whatever load you got) and its resistance, as Ohm's Law says: I=U/R(cureent = voltage/resistance).
now, from what i understand, you have a 7805 to get a 5V suply for the ICs, exept the ba...(and maybe the audio amp), so the cd4555 driver is connected to 5V and it drives the ba.. wich is connected to 12V am i right?
then this could be the problem, because the ba...needs a CMOS input andthis could be the broblem....
now a useful thing would be the schematic. it could really help. so please atach it to the message or email it to me.
and another thing to the 7805 regulator, waht it does is like you have a variable resistor connected in series with a load, and you adjust the variable resistor so that you get 5v on the load. this is what the ic does. the 3v you are talking about reffer to the fact that the iput voltage of the 7805 must be minimum 8V to get 5v TO THE OUTPUT.
 

pkshima

Member
u r right a schematic wud help but i havnt drwan it yet :oops: . and was supposed to b my next question. how do i draw a schematic ?
can anyone suggest a good free software for that.

in the meantime i measured the output voltage from both the ba6209s
plugged IN the actual circuit. and it does give out 7.4*V.
however the voltage across the zener diaode was 0.22V.
sorry to ask that without the schematic but shudnt the zener be showing its rated value. i have it connected between the Vref pin (pin 4) and the ground with the band towards the IC just as shown in the datasheet.

too bad dont have the drawing. it would have helped a LOT and would have fetched other suggestions and improvement ideas.

thx for the time being,
Shima
 

kinjalgp

Active Member
I can suggest you one thing, for getting very very high starting torque from Tape Deck motors, carefully open the back lid of the motor and then bypass the 12V regulator circuit by connecting the supply wires directly to the copper brushes. Believe me I have done this with all my motors and now the speed is not limited to mere 3200 RPM. I have measured 15,400 RPM at around 24V. Isn't it amazing. It is not a good practice to run these motors at such high speeds/voltages because it will destroy its copper brushes in no time. But at 12V these motors runs very well with good starting torque.
 

bogdanfirst

New Member
that, i forgot about it.....
the tape deck motors have a regulator circuit inside, so you might have noticed that the mototrs go faster in one direction. so opent the back of the motors and connect the brushes directly to the input pins of the motorl like kinjal said. , i forgot about that because i remember that i bought special deck motors that dont have a regulator circuit inside.
 

pkshima

Member
before i tear up my motors, i have the following doubts.

1) i m quite pleased with the speed/torque even with the regulator inside.
but only when i apply the power supply to it but not when i drive it thru
the ba6209 IC. i doubt whether the bloodshed :) would do the trick.

2) when reverse biased, the inbuilt regulator gets bypassed automaticaly.
in that case the motor gives slightly more power but still not enuff.
(i.e when driving thru the ba... )

3) wont soldering the wires directly to the motor terminals (i.e bypassing
the regulator) spoil the regulator as this method would power up the
regulator too but from the wrong place ? is there a way to do this
peacefully ? i.e bypassing it but still letting the tiny reg. pcb live there
physicaly since it provides mechanical support to the motor's back lid ?

4) :lol: i knew the ohms law bogdanfirst. what i meant by the voltage and
current story was that to b able to draw more current (~ 400 mA per
motor), wont i need a power supply with that capability ?
or is the power supply i m using (i.e. wall adaptor 12V 500mA) enuff ?

i measured the current that way to know the max current drawable from the ba... and wasnt that supposed to be ~1.6A ?
i also measured the current the motor draws when stalled( :twisted: crazy again ?) and it read some 0.4 Amps.

i m in the process of drawing the schematic (still in the proc of getting used to Eagle). will b done in a few hrs. thx kinjal for that link :D

what would be the current capability of a battery pack of eight AA (UM-3) size cells ? better or worse.

thx again for taking interest and bearing me :)
Shima.
 

pkshima

Member
whats up guys !
no response to my previous post ?

neway heres the schematic ...

http://www.geocities.com/netguruin/

hope it sheds some light.
please read the previous post as well :)

bye
 

bogdanfirst

New Member
hey, i had some hard days in school, so i couldnt reply.
to sttart, if you bypass the regulator, wich is usually a series one, it wouldnt be any problem leaving it inside, but dont remove it because from what i know, it hods the rotor...
and let it run for some time, after th modification, make sure it doesntt heat....something int there...
and something i observed....when you use the motor with the regulator( this i tries with a 6v motor)i observed that for a voltage interval, the speed remains the same, but after you get passed by that value it starts getting more power and increases the turation. i think that the voltage drop on the ba... makes the voltage applied to the motor be under the value that i spoke about.
and you shouldnt get 1.6A in short circuit of the ba...because the the suply cant handle that much power. the 1.6 amps means that whatever motor you connect to the ba... it shouldnt draw more than 1.6A.
ok, got to go now. ill check for replies later.
 

pkshima

Member
got it !!!!!!!

it WAS the power supply.
i tried powering the robot from the computer, and it rocks.
it sort of flutters as if saying "load me lead me" :lol:

the power supply i used from the computer is 12V 9A !!!

now the problem is where do i get a battery of that size ????
maybe 12V 2A would be enuff but even that seems too much.

so what do i do now ?
will post this as another topic too. pple get scared by the name of ba6209 it seems :lol:

neway,
thx again,
bye !
 

bogdanfirst

New Member
so it works. the problem is not to get the power from a battery, but to be small enough.
i think i say some 12V 2Ah batts, they were about the sizi of 5 x 8 x 15 cm and about 1-2kg, so it could be good for you
 

pkshima

Member
cool !!!!

where did u c them.
were they lead acid accumulater types, NiCd or what ?

bye,
Shima
 

bogdanfirst

New Member
no, lead acid. i saw them in a shop from bosh, all kind of batteries, used for portable drills. you might find them in a shop for drills.
 

pkshima

Member
oh i m afraid. no hand held drill shops here.
even otherwise i guess two battery packs of 4 AA size cells each
would look great on the robot. i.e. a pack of 4 cells on each side.
but what wud be the amperage of this pack (i.e. all 8 cells in series) ?

also i m talking bout the simple AA cells cos i wont be running the robot
all year long and wouldnt mind even if they last 5 days.
also i want the robot to be cheap. its already run to almost Rs. 300 (US$ 6). it looks cheap already but belive me i have the will to do a lot better 8)

bye,
 
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