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 Automatic 12V Lead Battery Charger

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drilon Posted - Mar 11 2007 : 12:00:48 AM
Moderator pls help me. How does this circuit work, especially the function of the SCR and TRIAC? please help me. Your Answer will be very much aprreciated.
15   L A T E S T    R E P L I E S    (Newest First)
Tharanga Posted - Apr 12 2019 : 12:29:51 PM
In fact I set the charger at 28.5 volts.

Even a higher voltage around 30 volts is possible with this configuration.
Tharanga Posted - Apr 11 2019 : 10:59:30 AM
For a 24 volt version of the charger, the following changes found to be effective.

28 Volt, 4 or 5 Ampere Transformer

R1 & R3 - 1k/1W Resistors

R2 - about 750 Ohm Preset (I used a 250 Ohm preset with a 560
Ohm Resistor in series with center pin)

13.1 volt/1W Zener Diode

I used a 28v/5A Transformer with above changes & a Voltage of 28.5 was obtained.
Tharanga Posted - Oct 22 2018 : 11:13:34 AM
I have made two 12V chargers of this circuit & they work great.

Now I want make a 24V charger from this circuit & change only following components

1. Two 1k / 1W Resistors for the Voltage divider
2. 24.1V / 1W Zener

Will it work with the rest of components.
ravens1970 Posted - Dec 06 2015 : 9:56:07 PM
I've got another circuit that the SCR is a BT169D and the voltage on this one will go past 15v and the LED never comes on. The other circuit uses a X0402MF 0AA2 for the scr and this one never goes above 13.6V.

Thanks for the help.
Aaron Cake Posted - Dec 06 2015 : 10:36:44 AM
It sounds as though the charger is operating as it should. The voltage rises to the cut point when the LED begins to flicker. Left alone it will eventually turn solid. The difference of 0.1V is negligible.

If you can't get a voltage higher than 13.6V, then try another 12V transformer.
ravens1970 Posted - Nov 30 2015 : 1:39:22 PM
I've got 12.6V 3A transformer that I'm now using. I set the pot to half way turn on the charger and connect the battery. The LED is on and when I turn the pot the LED turns off and the voltage rises to around 13.6V and the LED flickers. I'll keep it connected for 20 to 30 minutes and the voltage drops down to 13.5V.

R1 and R3 are 330 ohm and R2 is a 100 ohm pot. D3 is a 1N4734A 5.6V 1 watt zener diode and it's connected the same way as in the schematic.

Thanks for the help.
Aaron Cake Posted - Nov 15 2015 : 10:43:59 AM
Don't connect transformers in parallel unless they are exactly the same. Using only a 2A transformer is fine.

If your LED is on it means Q2 is conducting. Correct values for R1 - R3? D3 connected properly in reverse bias and proper value?
ravens1970 Posted - Nov 07 2015 : 7:26:14 PM
I thought the voltage rose up to 14.8v but today I hooked the battery up and the voltage kept going up to almost 16V. Today I used a 12.6V 3A transformer. I just can't seem to get it working.
ravens1970 Posted - Nov 04 2015 : 6:40:30 PM
I've built this circuit but it looks like I'm having a problem. When I hook it to a battery the voltage rises to around 14.8V. The only time the LED is on is when the battery is not connected.

Does the terminal 2 on the triac connect to D1?

Also I don't have a 12V 4A transformer so I'm using 2 12.6V 2A transformers in parallel.
Tharanga Posted - Nov 23 2014 : 08:31:41 AM
Hi Aaron. Thank you for the great Circuit. My LED goes off at about every 10 seconds.Is it the normal state of operation ? Do I need to adjust the Pot ?
kaycee Posted - Mar 18 2014 : 12:21:28 AM
Originally posted by drilon

yup it's working, im just wondering why the output is only around 7-9V

thanks again it helped me a lot =)

i have also constructed this circuit, the output voltage is only 8V. Is it okay? How can i make it 12V?
Aaron Cake Posted - Mar 02 2014 : 10:29:08 AM
The circuit can be modified to charge nearly any voltage by just changing the value of the voltage divider. You'll of course have to uprate component voltage/power ratings if you do this.
kivdenn Posted - Feb 28 2014 : 02:51:42 AM
Hi Aaron , I want to modify this circuit to charge a 48 Volt Battery bank, how should I alter the parts and their values? Thanks
mnasim31 Posted - Jun 18 2013 : 03:18:19 AM
Hi moderator. At last leg of my making the circuit I need expertsí help, a request across the Atlantic from Greece, please. Transformer T1 outputs 13v. On BT136 triac (Q1) left leg T1 to R1&bat+; center leg T2 to D1(P600) & gate as usual to D2. Now for SCR could not find BRX49(Q2) & used equiv. BT169 where right leg anode to R7&8 & left leg K to bat- & center leg as usual gate to R9&D3 (these connections are doubtful ones). Led on flashing mode battery is slowly discharging. I do not know what I am missing. Please help. Thanks
Aaron Cake Posted - Mar 31 2012 : 10:18:54 AM
You can use that transformer.

There is no PCB available. If there was a PCB pattern, it would already be on the page with the circuit.

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