mneary

The requirements keep coming, one at a time, every few days.....

I gather you want mains shutoff when the battery is charged.

To shut off the mains, you can detect the current consumed by the charger. When it falls below a set threshold, you can cut off the mains (presumably to avoid wasting the standby current?)

hardcore misery

sorry for that sir

i'll be back soon, if my group wants to pursue with this project... so how can we do your idea sir?

mcs51mc

1) Read some theory about charging principles (Cypress app note for example)
2) Monitor battery current and voltage during some charge cycles
3) Analyse that data using your brain(s)
4) Translate your idea(s) into an electronic drawning
5) Submit it to this forum

Then, and only then advice will follow... ...

hardcore misery

folks...

Our group decided to use voltage comparators, one of my friend advised me to use an LM2901 quad comparator... but my problem is i can't understand how will i work on this component...

based from this site: http://home.cogeco.ca/~rpaisley4/Comparators.html

where can i put the 3V to 4V supply of the charger to the comparator? how can the comparator measure the voltage of a charging battery to know when to shut-off?
can someone explain to me the basic concept for this comparator? or any can
give some sample circuits?

Requirements:

>Supply Voltage for the cellphone battery is 3.7V
>the Load Current of the supply must be 1A or greater to accommodate 3 or more cellphones to charge.

here is the features of LM2901, let me know if it fits the requirements of the battery charger...

Features
• Single or Dual Supply Operation
• Wide Range of Supply Voltage
LM2901,LM339/LM339A,LM239/LM239A: 2 ~ 36V
(or ±1 ~ ±18V)
LM3302: 2 ~ 28V (or ±1 ~ ±14V)
• Low Supply Current Drain 800μA Typ.
• Open Collector Outputs for Wired and Connectors
• Low Input Bias Current 25nA Typ.
• Low Input Offset Current ±2.3nA Typ.
• Low Input Offset Voltage ±1.4mV Typ.
• Input Common Mode Voltage Range Includes Ground.
• Low Output Saturation Voltage
• Output Compatible With TTL, DTL and MOS Logic

mneary

I didn't think you could find another major change to throw at us, but suddenly you've decided to charge three or more batteries (phones?) at a time. I don't think that anyone could have guessed that.

Now you're charging cellphones instead of standalone batteries? That's good, actually, because cellphones usually have a complete battery charger, well matched to their own battery. (The "charger" for cellphones is usually just a semi-regulated supply at around 120% to 150% of the battery voltage.)

But if you do it this way, you only need a simple power source. My cellphone (with a 3.7V 900mAH battery) uses a 4.8V 0.9A power supply. The power source doesn't need to be switched off; the phone knows and does everything.

One amp for three or more phones? My phone uses a 0.9A supply.

hardcore misery

yes sir, this is our main design project...

just a few questions sir, to be able to supply 3 cellphone batteries with
3.7V/900mAH, do we need a 3A ac-dc transformer? as for the output voltage, we can only choose a value, greater than or equal to 3.7V, to accommodate 3 cellphone batteries?

seveprim

Ok i get what he wants to do...

He wants to stop the charger from consuming standby power once the phone is charged he trying to make a "greenie product". Mmmm nice idea now to steal it !

seveprim

mneary

Well, actually it would be safest to use the same voltage that the original wall-warts supplied. You might still be in danger unless you know if the wall-wart was current limited.

hardcore misery

[quote]just a few questions sir, to be able to supply 3 cellphone batteries with
3.7V/900mAH, do we need a 3A ac-dc transformer?[/QUOTE

sir how about this idea? is this ok?

ezpcb

comparator is the simplest solution...a more complicated solution is using a uC and ADC, it controls the current at different stage of the charging.

Mike

hardcore misery

^^ yes sir, and we will be working on that...

hardcore misery

up for this

hardcore misery

Supposedly, the Vref of the Voltage comparator is 4.2V ( voltage of a fully charged cellphone battery )

The rule of the comparator is to TURN ON when the –V is lower than the Vref (+V)
And TURNS OFF when the –V reached the voltage of the Vref…

On the circuit provided, the –V of the comparator is tapped at the +V of the cellphone battery (this is intended to monitor the battery voltage)

The LED before the transistor (C828/npn was used) indicates the status of the comparator.

Our main problem is this… at NO LOAD condition, the relay tends to turn ON/OFF at rapid motion(repeating process,on/off/on/off/on/off…..)
I’ve understand this because, at no load, the comparator senses the charging voltage instead of the battery voltage which turns OFF the relay (charger voltage is 4.2V and Vref is also 4.2V which turns OFF the comparator). So if the relay is OFF, the comparator senses a ZERO voltage since there is no load… BUT

When we’ve placed a cellphone battery which has 3.8V, again, the relay turns ON/OFF at rapid motion.. this is not expected, because If theres a 3.8V battery load, the comparator will sense a lower voltage than 4.2V Vref, which turns ON the comparator, but why does the relay turns OFF? We also tried to use a variable DC supply as a BATTERY TO BE CHARGE.. we’ve set its voltage to approx 3V, again the relay behaves as is..

What seems to be the problem? On our circuit, we did’nt put a Diode in parallel to the relay. And we did’nt set a hysteysis for the comparator… are there wrong connections on the circuit provided?

Are there any wrong connections on grounding? We’ve also observed that when the ground of the battery charger is not connected at the ground of the Power supply of RELAYS and COMPARATORS, the ON/OFF switching of RELAY is very fast, but when we connect both grounds of the charger and the power supply, the ON/OFF motion of relay was decreased

NOTE: when we pulled out the relay, the comparator behaves as what we have expected.

i hope that all i've said is clear...

thank you and godbless to all.

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ericgibbs

hi,
Some obvious changes I would suggest.
There maybe others.

Whats the Vref at the junction of 1K/470R, inp to Comp supposed to be?

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"Good enough is Perfect"

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