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Auto Cut Off Battery Charger with LM317 & BD139

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Irfan
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Auto Cut Off Battery Charger with LM317 & BD139

I am looking for a battery charger circuit with auto cut off functionality,

 

Transformer : 18-0-18 1.5Amp

 

Battery Lead Acid 12v 7.2AH

 

I wish to use majorly two components namely :

LM317

&

BD139

 

Circuit posted by D MohanKumar is not working.

 

AJISH ALFRED
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Hi Irfan,

Please post the link from where you find the circuit.

Irfan
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http://www.engineersgarage.com/contribution/inverter-battery-charger-wit...

 

This is where I found the circuit

 

Transformer used is a 18-0-18 1.5 Amp

 

Battery is an Artheon Make 12v 7.2Ah

 

Irfan
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http://www.engineersgarage.com/contribution/inverter-battery-charger-wit...

Irfan
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The Circuit

 

Transformer I have used is a 18-0-18 1.5Amp

Battery is 12v 7.2 Ah

Irfan
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Transformer I have used is a 18-0-18 1.5Amp

Battery is 12v 7.2 Ah

AJISH ALFRED
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What is the status of RED and GREEN leds? What is the voltage with refernce to ground at the point just before D3 and after D3?

Make sure that you connected the zener diode in the reverse bias direction itself.

Irfan
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The LED's (both) are always lit!!!!

 

Zener is connected as depicted

 

Vario used is 5K and not 10K

 

I have also tried removing the resistance R4, but nothing happens

 

Voltage measurements that you require are with

1. the battery connected and transformer on, 

or, 

2. with battery connected and transformer off, 

or, 

3. with transformer on and battery not connected.

 

you may mark a mail to my gmail that would be irfanalavi at gmail

AJISH ALFRED
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Hi Irfan,

Sorry for the delayed response,

I need the volatge readings with the battery connected and transformer ON.

Irfan
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Thanks for the response

 

Volatge is

 

Before diode 14.95 & 14.65 after diode

 

Please be updated that all diodes used are 5402 & not 4107

 

please if u can mail me

Savio
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Just wondering! won't the zener be in breakdown condition  @ 8V causing red LED to be always lit up.

Pete Braven
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I don't know if you already solved this problem, but a quick look at the schematic shows that the zener diode is shown the WRONG side of the resistor R4.

 

That R4 value is stated as 100 Ohms, I would think that should be nearer 10 Ohms with the zener diode connected to a point closest to the battery lead. This connection then picks up the voltage drop across R4 and when the battery is charged, the diode conducts and switches on TR1. Where the original schematic shows this as connected to the side of the resistor that will always be the 'fully charged' voltage, which of course it isn't, is it!

 

In the way this is shown, the green LED is merely connected from the output of the LM317 to 0 volts and is an indicator that the circuit is powered, not neccesarily charging, you should not connect the charger to the mains until AFTER you have connected the battery. Sparks look pretty but not in this circuit.

As any silicon device is the 'fastest fuse on the planet' I would suggest adding a fuse in the output lead rated at the maximum value for an LM317 which according to the datasheet is 2 Amps but not for very long! A 2 amp slo-blo fuse is cheaper than new chips in the event of a short circuit or a seriously dead battery.

 

The red LED should be on when T1 is switched on as the battery terminal voltage reaches the required potential. If you are charging a lead-acid battery to full capacity, this would be 14 volts approx depending on the battery charging requirements. if you wish to retain a 'float' charge, that voltage should be reduced to 13.2 volts

 

That voltage is set by VR1 with TR1 on the off state. To set this situation up, simply disconnect the zener diode and adjust VR1 for 14.2 volts at the junction of D3 - R4 (or 13.2 for float charging), then reconnect the zener diode (to the juncton ot R4 - battery terminal !) and with no load, TR1 will immediately turn on, the red LED will light and the output voltage will drop. Because there is little or no current flowing through R4, both sides will be at the same potential.

 

Now if you charge a battery, it will work correctly and indicate the state of charge.

 

I should point out that this charger is capable of 1.5 Amps and as a LA battery should be charged at 1/10 of the Ah rated, this charger will work for batteries up to 15 Ah if they are used in cyclic mode (heavy discharge) OR as a float charge for any LA battery.

Irfan
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I have not yet been able to solve this freaking issue, all i seek is an auto cut off charger

Pete Braven
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Hi Irfan,

 

I am actually building a few SLA chargers at the moment, both with LM317 and also a 5 amp version with LM338T which works in a very similar way. I have adjusted the schematic to show more clearly what it should look like in order to work correctly.

LM317 Auto-off charger SLA Auto-off Charger

 

 

 

 

 

 

 

 

 

 

For clarity, the green LED connection is shown not connected to the base of T1 as some people have mistaken that in the original.

R4 has been made 10 Ohms and ZD is now connected via a link to the battery side of R4 where it will sense the voltage on the battery terminal as is required. I notice that R2 is maybe a little low compared to the datasheet and I would increase it to the 240 Ohms suggested as original spec.

Setting up is now a matter of having the whole circuit powered up with no load and adjusting VR1 to give 14.2 volts (or what is suggested on the datasheet for your particular battery) at the positive battery terminal. To check the cut-off works, simply connect the LINK and if a fuly charged battery is now connected, TR1 will pull the adjustment pin low and the output from the regulator will fall.

With a battery under charge, the current flowing through R4 will give a voltage drop, as the battery becomes charged, so the voltage across the resistor is less and ZD will eventually conduct, switching off the charge current. The red LED will stay lit because it is being fed by the current from the adjustment pin but the drain on the battery is really tiny.

I have not actually built this circuit yet but have a few very similar that work well.

As Savio has noticed, the 8.2 volt value for ZD does seem a little low to get a switch-off at 14.2 as shown here. You may need to increase that and a quick guess would be 1.2 volt across the LED then another volt base-emmitter on T1 is only going to give you a little more than 10 volts at best before the zener kicks in and shuts the thing down. You may find it needs to be 12 volts to work to a full charge but as I say, I haven't tested this yet.

Let me know how you get on with these changes.

Irfan
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Thanks for the response,  Please guide as to where the negative bus is running and I intent to be usig a 18-0-18 transformer for the 12V7.6Ah SLA battery, in the above circuit the negative bus is not very clear to me.<br> I shall be building this in the coming week starting from scratch and since this is a busy week of festivities may be delayed, however I appreciate your efforts and promise to update you on the status of the circuit.

Irfan
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Hi & thanks for the response, in the circuit provided by you I do not understand the negative bus, kindly guide, I shall be building this circuit shortly

Pete Braven
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Ah,.. oops! Sorry, I forgot to check that side of the schematic didn't I?

The centre-tap of the transformer connects to the 0 volt line and I would suggest that the charger (low volts) circuit is ISOLATED from the case entirely. This ensures that accidentally dropping the live lead on the box does not burn something out or frighten the life out of you with the spark.

Certainly connect an earth point to the case to prevent any mains failure from making the case live.

So, the circuit should now look like this,... with your 18-0-18 transformer you should then have a positive line of 25 volts DC, in which case C1 should have a working voltage higher than that and I tend to allow for transients 10 volts above so it would be 470uF, 35 volt working at least.

 

SLA Auto-off [2] SLA Auto-off [2]

 

Pete Braven
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Ah,..  Sorry, I forgot to check that side of the schematic didn't I?

The centre-tap of the transformer connects to the 0 volt line and I would suggest that the charger (low volts) circuit is ISOLATED from the case entirely. This ensures that accidentally dropping the live lead on the box does not burn something out or frighten the life out of you with the spark.

Certainly connect an earth point to the case to prevent any mains failure from making the case live.

So, the circuit should now look like this,... with your 18-0-18 transformer you should then have a positive line of 25 volts DC, in which case C1 should have a working voltage higher than that and I tend to allow for transients 10 volts above so it would be 470uF, 35 volt working at least.

 

SLA Auto-off [2] SLA Auto-off [2]

 

Pete Braven
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Ah,..  Sorry, I forgot to check that side of the schematic didn't I?

The centre-tap of the transformer connects to the 0 volt line and I would suggest that the charger (low volts) circuit is ISOLATED from the case entirely. This ensures that accidentally dropping the live lead on the box does not burn something out.

Certainly connect an earth point to the case to prevent any mains failure from making the case live.

So, the circuit should now look like this,... with your 18-0-18 transformer you should then have a positive line of 25 volts DC, in which case C1 should have a working voltage higher than that and I tend to allow for transients 10 volts above so it would be 470uF, 35 volt working at least.

 

SLA Auto-off [2] SLA Auto-off [2]

 

Irfan
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hey Pete thanks for your response and the corrections, I shall be implementing this circuit shortly and update on the functionality, I just hope that it trips the way I want it to.Thanks again

Irfan
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Thanks for your circuit Pete, I shall be implementing the same shortly and updating you accordingly, I am sure this will work, but again wish to check it

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will this ckt work............

how will it work

whats flowchart

Irfan
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Hi Pete, have tried pout this circuit and sob sob sob sob, it doesnt work, I have made it exactly the way you denoted but the RED Led comes on and cuts off the charging, the charger voltage is set to 13.8v without the zener connected,  and the moment the zener is connected it drops off!!!! what do I do now, also the funny part that I noticed is if the zener is not connected and I touch it with my finger the RED Led comes on and stops charging, funny but true, so what is it that you can please help me with now, the circuit for sure did look very promising but hasnt yet worked, also some points I would like to tell you the batter used was a AMPTEK 12V7.6 SLA and transformer was 18-0-18 1.5 Amp, the battery post discharge showed voltage as 12.42 and on full charge generally shows around 13.10. Please guide your help is utmost required.

Pete Braven
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Hi Irfan. Ah,.. oops!

I did say that I thought the voltage of the zener used here might be wrong as it looks like the original schematic was generated by a computer program. In my long experience (40 years), I have found that all the theory in the world develops some very strange habits when we let it lose in the wild.

I have a looked at this schematic again and as the forward voltage drop on a red LED is approx 1.6 volts and the voltage drop from base to emitter on the transistor will be 0.6 volts, (due to the minute current the resistor is not doing much) then the zener then should be,.. 13.8 - 0.6 - 1.6 = 11.6 volts. Now that is a very odd value and I suggest making the zener 10 volts with  the resistor R4 a 5K preset potentiometer, then adjust it till the circuit shuts off at the suggested 'float charge' level of 13.6 volts which is standard for all lead-acid bateries, or just a little higher than that. It is possible to charge to a higher voltage but that may also cause the battery to heat up and shorten its working life-span. I'm not saying that the circuit goes into a float state, it shuts off completely at the max value you set.

You also mention that putting your finger on the end of the zener causes the circuit to switch off. Yes it will.

This is because our bodies operate with electrical impules in the nerves that are actually a lot higher than some might think. Add to that the fact that we also pick up any mains interference like an aerial, thus what is happening is that our bodies generate quite enough voltage to interfere with a simple base junction in a transistor! This is the buzzing noise you get if you touch the input lead to an audio amplifier. It is also why sensitive electronic components are packaged in anti-static bags and foam.

If there is a lot of electrical noise in the envoronment (remember there is a mains transformer very close), adding a capacitor of around 100nF from the bottom of the zener to 0 volts should dump that noise and stop EMI (electro magnetic interference) from triggering the transistor at random.

Just to be certain, as I have just had a delivery of 10 x LM317 chips, I will dig out some bits tomorrow and actually put this circuit together myself to pinpoint where the computer that originally designed it, got it so wrong. I will update the schematic accordingly.

Irfan
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Sob Sob, Pete tried everything you had guided, changed zener to 10V and then 13V and also R4 to 5K Vario, but alas seems lady luck aint happy with me at all, now if I connect the 10V zener voltage drops down to 11.96, and with the 13V zener nothing happens, if I change the preset(adjust) then nothing for 13v zener but in 10V zener fluctuates only a bit from 11.88 to 11.96, which I guess is not suffice. What do I do now and is there any other way to contact you via mail or somethng

Irfan
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  Circuit Circuit With Amendments  

Pete Braven
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Hi Irfan.

I notice your comment here, ".. but in 10V zener fluctuates only a bit from 11.88 to 11.96" so if we look at that result, then the voltage drop across the transistor and LED is 1.88 volts isn't it? That's the voltage with R4 at a zero value or close as make no difference.

As we are aiming at getting a cut-off at 13.6 volts than we need to arrive at a value for the zener/resistor combination of 11.72 volts.

As we have found that making R4 a 5K variable and that gives just over 1 volt adjustment, we could then make up the right voltage drop from a 10 volt zener by adding two diodes (1N4001,.. anything silicon really) in series. Each diode has a forward voltage drop of 0.6 volts (actually between 0.6 and 0.7 but always give as the 'worst case') and that would then make the effective zener+diodes a value of 11.2 volts, the 5K can then be used to trim the extra 0.7 volts and you should be in business.

In every case such as these where circuits don't work quite as expected, it is neccessary to take a step back and look at what causes the error, then tweak the smallest number of component values till it does work. Adding series diodes to a zener reference is quite common practice because it gets expensive for equipment manufacturers to specify odd values which are not produced in such large numbers.

I would also add the 100nF capacitor from the junction of the diodes and R4 to 0 volts to be certain you will not get random variations due to noise. Zener diodes are electronically very noisy devices as they approach the point where they start to operate.

Oh yeah, if you were to search the internet for my name (this is my real name too), there is only one of me and you will find the website with contact details, and all kinds of other stuff I get up to!

Pete Braven
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The circuit should now look more like this with the diodes added to a 10.0 volt zener and the capacitor added to eliminate spurious triggering.

Ah,.. just re-reading your comments again, that 5K isn't doing much is it?! This is because the zener 'can' handle 1 Watt but in this case it's nowhere near that, so the actual current flowing is very small. That means that where I have suggested a 5K preset, to get enough adjustment it maybe should be increased to as much as 50K or more, or it's still going to be pretty ineffective.

I think maybe I should get to bed earlier so that my brain is actually awake when I post replies in here! Haha.

 

SLA AUTO-OFF (rev:4) SLA AUTO-OFF (rev:4)

Irfan
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Dear Pete , lady luck sure aint happy with me, this is what I have made, tested and failed, somehow am just doubtful on the preset value, shouldnt it be lower rather than so high, please lemme know if you have been able to make and implement tthis circuit

Pete Braven
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I'm putting this on the bench,.. give me a day to sort this one out. we will get there!

Irfan
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Hey Pete thanks for all your efforts, this aint yet worked for me, so waiting for whats coming up, anyways searched for you on net and downloaded a lot of your music but could not find any contact info like a mail address

Irfan
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Hey Pete, best of luck, I await thy response, and yes I did search for you online but got a lot of nice music but no mail ids for you, and I sure do hope what you build solves thgis long running mystery

Pete Braven
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There's the 'pbsong(dot)com' website and  there's a contact link on the left side of the page.

Or you can just add 'pete(at)' before the domain name and you should get through.

Irfan
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hey good morning Pete, I havent had any luck on this yet, kindly lemme know if you have met Ms Success

Irfan
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some modifications that I did to no excellent luck are demonstrated

Irfan
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Whoops sorry, in the above diagram VR1 is 100K and not 200K.

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