lead acid battery charger

[theslayer]

Hi guys!!
I am trying to make a lead acid battery charger from this circuit diagram but the output voltage is 9.2V instead of 14.5V

I found out that this was because of negative resistance of BC548 which was around 9V
I want a charger with current limiting of 1.5A and which goes to 13.65V after full charge using lm317 and other part which are locally available.

Can anybody help me??

 

[ronv]

Seems like it should work. The transistor shouldn't turn on until the current is over 1.2 amps.

Your schematic doesn't say what the input voltage to the circuit is. It needs to be above 17 volts for the regulator to have enough voltage to regulate. My guess is that either your input voltage is not high enough or the filter capacitor at the output of the bridge rectifier is not large enough to keep the "ripple" from going below 17 volts.
I would also add the protection diodes shown in figure 3 of this data sheet.

https://www.electro-tech-online.com/custompdfs/2011/05/LM117-1.pdf

 

[theslayer]

Thanks for reply
I think u didn't understood my question !!
Its the collector-emitter break down of transistor Bc548 which is not letting voltage rise above 9volts
And I have 24 volts input and a 2200uf filter capacitor on both ends
there is no tickle charger in this circuit, I want those too .
Can anybody provide another circuit diagram working with lm317??

 

[crutschow]

The BC 548 has a Vce rating of 30V so I don't think that's your problem.

That circuit schematic looks good. Are you sure everything is wired correctly? Is the transistor perhaps upside-down (emitter and collector interchanged). That would account for a breakdown of 9V or so (the max. reverse Vbe is 5V).

 

[mvs sarma]

With input voltage at 24 and output expected to be 14.xV load current of 1.5 amps is possible with a 3V in/ out differential, but not 10V. The thermal shut down must be acting and pulling down output to 9V. Perhaps the input can be reduced to say 17V or so.

 

[ronv]

Do you have 24 volts DC at the input or do you have a 24 volt transformer? If you have a 24 volt transformer your input voltage will be higher which means the regulator must dissipate more power. Do you have a BIG heat sink?
Which package do you have (TO3, TO220)? Either way you can't get 1.2 amps with such a large voltage across the regulator.
If you can't get 14 volts with no load something else is wrong.
Setting the output voltage should be able to give you a trickle charge current when the battery is fully charged.

Here is a datasheet:

https://www.electro-tech-online.com/custompdfs/2011/05/LM117-2.pdf

 

[colin55]

Here is a very simple automatic charger that will solve your problems. You can use any plug pack. The full write-up of how the circuit works in on my website.
**broken link removed**

 

[crutschow]

Here is a very simple automatic charger that will solve your problems. You can use any plug pack. The full write-up of how the circuit works in on my website.
**broken link removed**

Suggest you add a diode across the relay coil to avoid blowing the transistor.

 

[colin55]

A diode is not needed across the relay.
The transistor is turned off very slowly so no back EMF is produced by the relay

 

[theslayer]

thanks for your help guys !!
The transistor was upside-down so I was getting 9v across the output terminal I planned to use my circuit with the automatic charger that colin55 provide.
I am using a 3"Computer fan to cool lm137.
And colin55 can u provide your web-address.

 

[shreddy]

just use 5k pot at Location R5.