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Often Tripping ON & OFF the Relay

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Junior Member level 3
Feb 10, 2010
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Hi Friends..

I am doing the project of Charging circuit with Auto cutoff. The charging circuit designed from AC-DC converter. The problem is while the battery is charging sometime the relay tripping ON & OFF state.When i try to measure the voltage across the battery, whenever i touch the battery terminal with my multi meter probe, it generates tripping changes and produces noise.
meanwhile the the both LED's are ON and produces NOISE. Here i attached my circuit diagram. Please Help me out friends. Circuit Wizard - auto cutoff.cwz_001.jpg


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in your charging ckt , what is the battery spec?

you are generating 14v supply.
but where is the battery under charge testing pin?
some more info is reqd.

Your schematic does not show a battery and does not show a battery charger circuit.

A 555 is supposed to have a supply bypass capacitor.
A 555 is not supposed to have a zener diode at its pin 2 or at its pin 6.

Why is your electricity 155VAC? Then the transformer output is 155/7= 22VAC which has a peak voltage of 31V reduced by the bridge rectifier to 29V which is too high for the 7815.
Maybe your electricity is 110VAC with a peak of 155V??

Re: Often Tripping ON & OFF the Relay

The battery is charging on the cathode of zener, which is connected on pin 2 of IC555. Check out my battery spec. by image20150826_103402.jpg

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Why we not supposed to use the zener on IC555?

Re: Often Tripping ON & OFF the Relay

The battery is charging on the cathode of zener, which is connected on pin 2 of IC555.

pin no2 is trigger . it cannot be for charging battery.

your circuit is to be heavily changed as it contains lot of unusual connections.
or take a standard 555 based charger circuit and modify to your requirement.

The datasheet of a 555 shows that its pin 2 is the input of a comparator, not an output. The pin 2 input voltage is compared to the voltage set by three resistors inside the 555 that sets its trigger voltage at one-third of the supply voltage of the 555. Pin 6 is shown to be the input of another comparator set to two-thirds of the supply voltage. Your zener diodes leave pins 2 and 6 floating with no set voltage. Because the inputs are floating then the 555 output is erratic.

The label on your tiny lead-acid battery says that its initial charging current is less than 2.1A but does not say if the battery limits this current or if your charging circuit must limit the current.
It looks like R1 (1k ohms) in series with D6 on your circuit charges the battery with a very low current.

You do not understand how to charge a lead-acid battery. It is fully charged only when its voltage reaches a certain voltage and its charging current has dropped to a certain low current.
Go to to learn about it.
Then you should read about battery charging circuits for lead-acid batteries and about comparators.

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