hardcore misery

the Vref should be 2.1V ( 2 x 2.1V = 4.2V )my apologies on the wrong values of resistors, because i did the schematic quickly... on the actual circuit, the ratio of resistors on +V of comparator is 1k/270 ohms, and the Voltage of the power supply is variable, on the circuit, we've came up with a 9.7V making the vref=2.06V (4.12V)

if you don't mind sir, what is the reason why should an 8mA be chosen to flow on the LED?(on our circuit, 9.7 / 2k = 4.85V.... 4.85V/1k = 4.83mA, which drives the LED and the NPN transistor)

on the hysteysis side, my friend suggest me to add a series diode(1n4148) after the RH, for one direction flow of current.is it correct?

what capacitive value should we use in parallel to the power supply on your edited schematic?what is the purpose of that sir?

ericgibbs

Does that answer you questions?

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"Good enough is Perfect"

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hardcore misery

i had a different understanding on the concept of Hysterysis, based on what my friend told me, and you can give me sir some clarification about this...

if the resistor ratio is 1k / 270, and the input voltage is 9,7V, the Vref will be 2.06

if i will add an Rh equivalent to 2k ohms, the Vref will change AFTER the comparator turns OFF, which is equal to 1.86V (3.73V)

so if theres an hysterysis, the RH would only parallel to 270 ohms if the comparator shuts down, but in ON state of the comparator, only 1k and 270 ohms are used by the comparator..

i think what you mean by 0.3V hysteryssis is 2.1V (4.2V) - .3V is equal to 1.8V (3.6V) is this it? i'll report back soon, after we tried those suggestions of yours..

so is it the voltage spikes which is the culprit of our problem?

godbless and thank you sir.

ericgibbs

hi,
Look at this drawing.

It should give you an idea what the hysteresis is doing.

Remember to calculate the Vref for a almost 'discharged' battery and the hysteresis to ensure a fully charged battery before charger shut off.

Is this clear?

Attached Images

Hyst1.gif (2.5 KB, 11 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

hardcore misery

can't understand it fully (on the Vref=1.5V, this should be 2.1V?)

ok sir, we tried all your suggestions ( shunting a 47uF and 0.1uF capacitor across the supply voltage for RELAY and COMPARATOR, and shunting a Diode across Relay, and finaly, putting a 2.2kohms as hysterysis to the circuit)

we did some measurements on the circuit.

1. Power supply voltage for Relay and comparator ( so as the voltage input for Vref ) is equal to 9.484V and the Vref is equal to 2.033V ( ideally it should be 2.1V )

2. The charging voltage is 4.02V ( 2.01V as a result from 1k/1k ratio for -V of the comparator )

as i've stated on the previous post(s), at no load condition
( if the Charging voltage is 4.2V while the Vref is equal or less than the charging voltage(2.1V), the Relay switches on/off rapidly )

after putting those capacitors and diode as you've suggested on our circuit, the problem didn't removed.....

3. We observed the effects of adding hysterysis on the circuit.

at the +V of the comparator, the ratio of resistors are 1k / 270 ohms.. the supply voltage is 9.484V and it gives a Vref of 2.033V (without RH
but when the 2.2k was connected between the output and 1k/270, the Vref increased from 2.033V to 2.33V and when the comparator is off, the decreased from 2.33V to 1.895V
i don't know the computation for the Vref at ON state of the comparator, but on the OFF state of the comparator, the 2.2k was first paralleled to 270 (which is equal to 240.49ohms) and the ratio was 1k/240.49 then the Vref becomes 1.84, ** the resistors has tolerances, we didn't measure its actual resistances and 1.84 is close to 1.89V(actual Vref at OFF state)

so if the Vref increases due to 2.2k added resistor for hysteresis at ON state(2.33V) therefore the voltage required to turn off the comparator is greater than 2.33V?(4.66V, which should be 4.2V)

so this is another problem? the Vref should not be changed whether there is a hysteresis on the circuit(except for the Vref at OFF state of the comparator)

ok we used the circuit with added components as you've suggested, with a Vref of 2.33V, we tried to increase the charging voltage until it exceeds the Vref, AGAIN the Relay switches back and forth, rapidly, hence there's still a problem.

hope that all i've mentioned here is clear to you sir...

will for the reply... thanks and godbless..

ericgibbs

hi,

can't understand it fully (on the Vref=1.5V, this should be 2.1V?)

I will study your last post and reply later.

Do you understand the diagram?

EDIT: Adding revised drawing.

I would suggest that you add a variable resistor in the junction of R3/4, this will give you some control while testing.

Look at this drawing, hope it explains OK.

Attached Images

Chrg3.gif (34.1 KB, 30 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

hardcore misery

i had a wrong understanding about hysterysis, on our actual circuit.

we used 1k/270 ratio of resistors for the +feedback, and to configure the Vref to 2.1V... i was wondering why the Vref increases as the RH is added on the circuit... i realized that, we should include the RH to configure the ratio of resistors for Vref... i'll reply soon as after we revised our circuit.

thank you and godbless sir.

hardcore misery

i'm having a hard time on setting the Vref(ON state) to 2.05V and Vref(OFF state)=3.6V

ericgibbs

WHY are you trying to set the Vref at these voltages?

Look at the drawing I posted explaining the Vref and hysteresis.

Are you using a variable resistor, to set the Vb/2 or Vref as I have suggested?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

hardcore misery

oops, it's a typoerror it should be
Vref(ON state) to 2.05V and Vref(OFF state)=1.8V

quick question sir, how can we properly discharge a li-ion battery? our problem is we need to discharge the batteries at approx 2.8V or lower than 3.7V.. if we can't achieve that, we have a problem on the Vref at OFF state(1.5V as you've suggested, or 1.8V)

i haven't tried those potentiometer on vb/2, i'm trying to get fixed values of resistors.. thanks sir

hardcore misery

sir i think theres no problem on the ratio of resistors for vb/2, (1k/1k) the problem is on setting the Vref of ON/OFF states with the correct values of resistors

ericgibbs

hi, hcm,
Tell me the type of opa/comparator you are using?

The quickest solution is going to be if I make a working version of the project,
so that I can tell you the resistor values.

Is the power supply still at +10Vdc?

Is the charger voltage still set for +4.2V?

EDIT: also give me details of the battery type, voltage, AHr,,,etc.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

hardcore misery

thats great sir!!! we are 6 members on a group, and i'm the only one who works for our prototype..

we are using LM339 as a comparator, our supply is variable, but on my calculations we use 9.7V as a supply, and 4.2V as the charger voltage.

i think i got the correct resistors to be used.

R1=1k
R2=270
Rh=2200
RL=100k (r5 on the given schematic on previous post, is it ok to use this? previously 1k)

i got a vref(on state)=2.078V and a vref(off state)=1.8907V ( so we can charge batteries with voltage lower than 3.7V or 3.8V )

btw sir, how can we safely discharge li-ion batteries? on our sample batteries we can only got 3.7V.

quick question, our charging voltage is 4.2V and the limitting resistor is 10ohms, and we charge at least 3.7V, the charging current is only 50mAh, is this ok? or is it advisable to charge batteries with constant current? at least 300mah?

EDIT: Original Nokia Li-ion Battery BLC-2

950 mAh LI-ION / 3.6V
Weight: 108g
Talk time: 2h 40 min - 4 h 45 min
Standby time: 55 - 260 h
Variation in operation times will occur depending on SIM card, network settings and usage. Talk times is increased by up to 30% if Half Rate is active, and reduced by 5% if Enhanced Full Rate is active
Picture for reference only

Compatability:
3310/3330, 3410, 3510/3510i, 5510, 6650, 6800, 6810

ericgibbs

Hi,
I'll build a prototype of your circuit, give me 24hrs.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

hardcore misery

ok sir, that would be nice... so i can verify the status of our prototype (mainly the status at NO LOAD condition, which the the charging voltage is 4.2V and the Vref is lower than 4.2V (2.1V or 2.05V)