Lead Acid Battery Charging

Jessica Shaw · 2012-07-19T18:03:30+00:00

Hi,Battery:Charger:Circuit: I am trying to power up my circuit using the above mentioned batteryand the circuit. My load works fine. It requires 300mA at +5V. Theproblem comes when I tried to charge up the battery with the charger.The charger tries to charge the battery and than gives the error afterhalf an hour of charging.I replace the Load with the charger. So, in the schematic the point Ais connected to positive of the charger and Ground is connected thecharger's ground.Any suggestions!ThanksJess

I

Ian Field 14 years ago

Many (most) integrated regulators don't like being backdriven.

***the reverse protection diode would take care of that - but only if each regulator had its own diode, and in any case I agreed with whoever said a single 5V reg would do. ***Phil already pointed out the forward conduction diode knocks 0.6V off the output - If the OP really does feel the need to include that diode, then the correct output can be restored by grounding the reference pin via a compensating diode with a bias resistor to force a forward volt drop.

Vote

K

krw 14 years ago

The question wasn't answered but it looked to me that the intermediate voltages were being used.

Vote

F

Fred Abse 14 years ago

I think that might have been me ;-)

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Vote

F

Fred Abse 14 years ago

That wasn't what she drew.

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Vote

K

krw 14 years ago

You're right. I was remembering that the arrows form the regulators were just that, not grounds.

Vote

D

David Eather 14 years ago

formatting link

connector on one end and solder it to the output of the 7805 ( positive terminal) and the ground of the battery.

solve the problem.

The 'real' solution is to design a custom battery charger - because that diode stuffs it up for off the self chargers. Normally the state of voltage tells a lot about the amount of charge but in this case there is an extra .7 that isn't taken into account.

As a suggestion you could replace it (IIRC D2) with a 1 amp 30 volt schottky diode (1N5818 or 1N5818 would be OK) - this will *reduce* the problem introduced by the diode.

But the best solution is to customize the charger (there is an ugly hack that might be possible - similar to using the diode to jack up the output voltage of the 7805)

Vote

J

jsscshaw88 13 years ago

Hi,

Will 1N5819R will work instead of 1N5818. The digikey link is given below

formatting link

I have few 1N5819 already in stock. I have to place order for 1N5818.

Thanks

jess

Vote

I

Ian Field 13 years ago

Hi,

Will 1N5819R will work instead of 1N5818. The digikey link is given below

formatting link

I have few 1N5819 already in stock. I have to place order for 1N5818.

***1N5817=20V, 1N5818=30V & 1N5819=40V.

Apart from those differences; all 3 are pretty much the same - The "R" suffix may be an artefact of their stock number, or posibly an encapsulation variant.

Vote

J

jsscshaw88 13 years ago

I am unable to understand that why a zener will work better than a diode

Vote

F

Fred Abse 13 years ago

1N5818, etc are not zener, they are schottky.

Lower forward voltage than a junction diode, at the expense of (usually) higher leakage.

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Vote

I

Ian Field 13 years ago

I am unable to understand that why a zener will work better than a diode

***A zener is a diode with the difference that its doped in such a way as to have a closely defined by voltage, reverse leakage and a sharp knee curve in the reverse current - strictly speaking; anything less than 7V is a zener and anything over 7V is an avalanch diode.

***I've found by experiment that I can usually identify zeners with a DMM diode check range because they read almost exactly 0.7V, regular (for mains frequency) diodes usually come in between 0.55 & 0.65V, fast diodes usually have Vf down to about 0.4V. SB diodes are quite variable from as much as

0.4V for a small signal type, to as low as 0.1V for a thumping great metal stud rectifier.

***SB diodes with your application will give the lowest Vf loss, with a 12V SLA battery; any common SB diode will have adequate reverse voltage rating - provided there's no large inductors to produce back emf. SB diodes do have measurable reverse leakage, but that shouldn't be a problem.

Vote

I

Ian Field 13 years ago

1N5818, etc are not zener, they are schottky. ***Back in the days when I repaired monitors for a living, I found that some manufacturers used either a 1N5817 or a BYV10 20 SB diode to clamp the connection between the UC3842 & the MOSFET gate, it was fairly usual for the source current sensing resistor to fail O/C if the MOSFET punched through. The SB diodes were much better at failing S/C under such extreme conditions than a zener - sometimes they even protected the UC3842!

Vote

Lead Acid Battery Charging

Join the Discussion

Didn't find your answer?