Help on LM358/UV741 based autocutt off 12v battery circuit problem.

[codemaster11]

this is an autocutt off 12v battery circuit based on LM358 ic. set the upper cutoff threshold of the circuit is 13.7vdc

lower turn on threshold is 12.2vdc with bench power supply. output voltage of my smps battery charger circuit is 14vdc.

when i connect the charger, the battery voltage instantly goes to 13.7vdc and relay turn on stop charging process

by removing the charger terminal from battery, the battery terminal voltage shows 12.8vdc on DMM.

why the battery voltage goes to 13.7vdc instantly by connecting the charger? not actually charging the battery to 13.7vdc/13.6vdc.

 

[BradtheRad]

why the battery voltage goes to 13.7vdc instantly by connecting the charger? not actually charging the battery to 13.7vdc/13.6vdc.

A battery takes time to convert incoming current into electrochemical energy. Thus it
puts up a kind of impedance that is hard to measure by itself. It's a gradual process and it cannot be rushed.

A capacitor on the other hand charges quickly in the same situation. It maintains voltage after the charger is disconnected.

The battery also has its innate (idle) voltage, which the charger must overcome by applying an even higher voltage, or else it pushes no current into the battery.

 

[danadakk]

Post schematic .....

Regards, Dana.

 

[codemaster11]

i don't have the schematic diagram of this circuit that's why put the pcb layout.

i tried this circuit with a new 12v/65Ah battery, is 13.7v or 12.7v is a stable full voltage for 12v lead acid battery?

battery voltage is not stabilizing at 13.7v and decreasing slowly to 12.7-12.6v without load by disconnecting

charger, continuous turning on/off of cutoff circuit is a problem.

 

[danadakk]

Might help forum to help you if you do a hand draw of schematic off layout, just a thought.
Otherwise just a whole lot of guessing would ensue.

To see if circuit designed properly.

Regards, Dana.

 

[codemaster11]

that's rough schematic drawn for the pcb layout.

 

[crutschow]

i tried this circuit with a new 12v/65Ah battery, is 13.7v or 12.7v is a stable full voltage for 12v lead acid battery?

The normal resting voltage of a fully-charged 12V lead-acid battery is 12.6V.
13.7V is typically used as the float charge voltage.
14.4V is typically used as the maximum charge voltage.
If you try to charge a fully-charge battery, it's voltage will immediately rise to the charger voltage (as long as it's below about 15V).

some information on lead-acid batteries and how to charge them.

 

[Audioguru]

The wires all over the place, dots and <TEXT> <TEXT> <TEXT> on the schematic look like Multisim.
I guess it is an old fashioned lead-acid car battery. Cars charge them at 14.4V to 15V.
There is nothing in this circuit to limit the charging current.

 

[codemaster11]

the schematic drawn in Proteus v7.0.
it's an smps based battery charger decreasing charging
current as battery goes from absorption stage to float stage.

is the charger keep the battery float voltage this why if to do the following method?

"to keep the battery at floating voltage 13.7v i have to eliminate the hysteresis gap which in
my circuit is from 13.7v(high threshold) to 12.5v(low threshold), only keeping high threshold 13.7v
with battery charging voltage 14vdc."

 

[Easy peasy]

C4 is redundant, as is R3, C3, - the whole design is not completely well thought out ...

 

[codemaster11]

the circuit works by setting high-low threshold values of battery voltage also adjusting the hysteresis
gap, but what should do to keep battery voltage at floating voltage 13.7vdc.
prevent to discharge battery below that voltage without load?

 

[BradtheRad]

I made a home-brew charge controller for my lead-acid batteries. It worked on a similar hysteresis principle as your schematic. It charged until the battery reached 14.4 V, then stopped, to resume again when the battery dropped to 13.4 or so.

The switch-On-and-Off action seemed efficient and equally effective as tapering the charge rate. The idea was to prevent battery voltage from rising to 15 or 16 V (which resulted in acid bubbling), yet the battery gets fully charged.

Since I used a single op amp it took a lot of time adjusting the potentiometers until I got the proper amount of hysteresis. I had to wait a few minutes each time while the battery settled down to 13.4 V. Still I thought I was being clever.

I think an easier alternative is to use two op amps in a window comparator, with resistors and/or diodes to create two individual setpoints. In other words, to do without hysteresis.

 

[codemaster11]

it took a lot of time adjusting the hysteresis gap that's why here i put 55k/0.25R from Opam O/P to non inverting pin.
i think to keep the battery voltage a floating charge voltage we have to remove the hysteresis gap.

"low threshold voltage = high threshold voltage."

so that battery my not discharge below 13.7vdc in no load condition.
however using 12vdc/10ampere relay for switching may cause welding of relay points.
i think it will be better to use 75nf75/80nf70 N-channel mosfet in low side configuration on O/P side
to avoid this problem.