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Old 13th September 2020, 19:50   #1
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Default Charging a car battery using a laptop charger!

Necessity is the mother of jugaad !!!

This is what I realised during the lockdown.

The following story gives an account of how I went about charging a battery at home using a rather unconventional procedure with whatever I had on hand.

This technique will work brilliantly in crunch situations when charging centers are closed ( weekends/ holidays) or one doesn't have a battery charger.

The Problem

A car was parked at a remote parking inside a gated community on March 21st 2020 thinking that we could get the car back in operation around March 25th but that never happened.

The car remained there all of April, and the first time one could move out with restrictions was in the first week of May 2020.

After about 50 days, when we went to the car, its 85Ah battery, which was already 3.5 years old had expectedly run down.

The idle voltage was surprisingly 11.6V but there wasn't enough juice to crank the car.

Jump starting also didn't work, leading us to believe that one cell in the battery must be terribly weak.

I dismantled the battery and brought it home, and enroute found that no battery center or auto electric center was open.

The Idea

I came home and was thinking of what to do when my eyes fell on my laptop charger.

It suddenly dawned on me that this is an AC - DC converter and might be useful.

I examined the name plate which read output 19V DC 3.42A.

Charging a car battery using a laptop charger!-p_20200913_160218_1.jpg

What next? I went about figuring a way out to use this as my battery charger.

The apparatus used was

1. Laptop charger
2. A 21W bulb
3. few cables
4. some insulation tape
5. two clothesline clips
6. Multimeter

Preparations

1. Opened all vent plugs on the battery
2. Ensured that the job was performed in a well ventilated area

The Execution

The inner pin of the laptop charger is the positive and the outer metal covering is the negative.

Charging a car battery using a laptop charger!-plusminus.jpg

Since the rated amps of the charger is 3.42A, I didn't want to just connect some cables and end up blowing the charger due to high current, hence used a current limiter in the form of a 21W bulb.

At the rated voltage of 19V, this would ensure that the current flow would be no more than 1.1A

1. Prepared a wiring for the +ve side with the bulb in series ; a bulb holder would have been lovely but I didn't have one and so made do with some insulation tape

2. Connected the +ve cable green to the +ve pin of the charger, and then the pink cable from the bulb to the +ve of the battery using a clothesline clip

So the +ve end line up was:

Charger -> green cable -> bulb -> pink cable -> battery +ve terminal

Charging a car battery using a laptop charger!-bulbnwires.jpg

Charging a car battery using a laptop charger!-positive.jpg

3. Connected the -ve cable grey black to the -ve of the charger using insulation tape

Warning : It is very important to ensure that the
+ve and -ve cables don't touch


4. Connected the -ve cable to the -ve of the battery using a clothesline clip

The -ve line up was thus:

Charger -ve -> grey black cable -> battery -ve

Charging a car battery using a laptop charger!-completewiring.jpg

5. After ensuring that the connections were secure and proper, switched the charger on

6. The bulb was seen glowing and after a few minutes, measured the voltage on the battery to be 12.5V

Name:  Charging85Ah.jpg
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7. Measured the voltage on the battery every 30 minutes, and at the end of 6 hours it was approx 13.1V

8. Suspended charging in the night and resumed the next morning at 7

9. When the battery voltage read 13.5V, I could notice bubbles, to indicate first signs of success, and as the battery charged, the bulb glow became dimmer

10. Continued to charge till the battery voltage read 15V ( I didn't want to go beyond this since I know that the typical voltage a 12V battery sees with car running is no more than 14.2V)

11. At around 15V on the battery, I unscrewed the charge indicator sight glass and dipped it into each cell to measure the state of charge.
It would move between white and green indicating that the charge was adequate.

However, cell no.4 showed next to no bubbles plus the charge indicator was in white, and this had me thinking.

12. Eventually stopped the charging at approx 4pm to take the total charging time to approx 15hrs

13. Approx. 30 mins after stopping charging and disconnecting the cables from the battery, measured the voltage to be 12.4V, which, in my view, was good enough to start the car.

Moment of Truth

We took the battery the next day to the remote car, and it started in a flash.

I was concerned about cell no.4, but there was some life left in that cell, I believe.

The battery eventually packed up in end June because cell no.4 went totally dead, but this effort of reviving a battery from dead using a laptop charger worked quite well.

The only "consumable" was the bulb, which went kaput after this marathon operation.

I repeated this on a weak 65Ah battery and it worked very well.

Charging a car battery using a laptop charger!-charging65ah.jpg

We may have battery charging centers, we may have battery chargers, but when we have neither, we still have ideas that can be executed successfully !!!

Note : I've tried this method out at my risk after conducting risk assessments, and have seen success twice with no damage to the charger or the battery.

Last edited by Sheel : 14th September 2020 at 09:37. Reason: As requested.
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Old 14th September 2020, 09:06   #2
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Default re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by vigsom View Post
The Idea
I came home and was thinking of what to do when my eyes fell on my laptop charger.
It suddenly dawned on me that this is an AC - DC converter and might be useful.
I examined the name plate which read output 19V DC 3.42A.
Hi Vigsom
The method you have used is damaging to battery, laptop charger and Dangerous ! no more than 14.5 volts should be applied across 6 cell lead acid battery, and you are using a 19 plus volts high current source to charge !
you should have applied voltage regulation at least by using few high current rectifier Diodes in series to drop the Voltage before they are applied across battery terminals. Bulb is a Resistor, and drops the voltage by varying amount.
At start of charging the charging current is high and voltage dropped across battery terminal might have been safe. As the battery charges after some time, its potential ( voltage ) increases and Charging current becomes Low. At that time voltage dropped across Bulb is much less and much higher voltage than recommended 14.x will be applied as your power source is 19 volts. This can lead to batter heating, gassing and can even explode if left applied for long time.
Procedure you used must be applied only if some one is having urgency to move out and start his car which is having discharged battery.
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Last edited by Aditya : 14th September 2020 at 16:36. Reason: Quote tag fixed
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Old 15th September 2020, 08:09   #3
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Default Re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by Lightning2 View Post
The method you have used is damaging to battery, laptop charger and Dangerous ! no more than 14.5 volts should be applied across 6 cell lead acid battery,

you should have applied voltage regulation at least by using few high current rectifier Diodes in series to drop the Voltage

Bulb is a Resistor, and drops the voltage by varying amount.

This can lead to battery heating, gassing and can even explode if left applied for long time.

Procedure you used must be applied only if some one is having urgency to move out and start his car which is having discharged battery.
Very valid points by the book, but I'd just like to say here that I evaluated the risks and performed this under very close supervision.

My post above has details on all precautions, but here are a few more points for the benefit of all :

1. charging was performed in a ventilated area

2. the charger temperature and the battery temperature were monitored every 15 minutes and were always normal

3. You'd have noticed that it took 15 hours in all - the rate of charging was extremely slow

4. The charging was stopped overnight because I wanted to do it under my eyes only

4. This was done in the lockdown and I obviously didn't have any diodes or any other devices to help drop the voltage to 14.5V

5. Before performing this, I consulted an expert electrician who works on cars, plus has charged batteries for over 30 years

6. This procedure requires a lot of patience and won't work for someone who has an urgency to move out

For me, safety is paramount always !!!!

Last edited by vigsom : 15th September 2020 at 08:11.
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Old 15th September 2020, 08:26   #4
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Default Re: Charging a car battery using a laptop charger!

Here's a tip: most external USB hard drives, not the portable variety, use a 12V DC adapter rated at about 2-4A depending on the model. And if you have a redundant Tata Sky set top box, which quite a few do having given up their connection in favour of streaming services, those too have a 12V 4A adapter which can be safely used for this purpose. These will act like dumb chargers and the process will need to be monitored.
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Old 15th September 2020, 08:28   #5
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Default Re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by R2D2 View Post
Here's a tip: most external USB hard drives, not the portable variety, use a 12V DC adapter rated at about 2-4A depending on the model. And if you have a redundant Tata Sky set top box, which quite a few do having given up their connection in favour of streaming services, those too have a 12V 4A adapter which can be safely used for this purpose. These will act like dumb chargers and the process will need to be monitored.
However the OC voltage would never exceed 12V as that is the voltage where the adaptors are regulated internally, typically a TL431 device being used. Also when the battery is deep discharged, the adaptor will run in "hiccup" mode as it encounters constant over current due to absence of a constant current limit. It may be actually detrimental for the adaptor! Given lack of a proper CVCC charger, I would highly recommend Vigsomji's method!!!

Last edited by lapis_lazuli : 15th September 2020 at 08:32.
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Old 15th September 2020, 08:43   #6
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Default Re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by lapis_lazuli View Post
However the OC voltage would never exceed 12V as that where they are regulated. Also when the battery is deep discharged, the adaptor will run in "hiccup" mode as it encounters constant over current due to absence of a constant current limit. It may be actually detrimental for the adaptor!
Yes, you have a point there. At 12 V OC the battery is only approx 15-20% charged. I'd prefer to under volt than over volt (strictly IMHO) whilst charging because batteries are dangerous. In the absence of a proper car battery charger any jugaad requires constant monitoring. Also, this method of using a 12V DC source is good for smaller batteries of <50 AH which generally use a standard C10 charging amps i.e. up to about 5A. It may not work for large batteries.

Given the experience post COVID in 2020 it is best if car owners invest in a battery charger even if it is a simple manual one.
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Old 15th September 2020, 14:13   #7
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Default Re: Charging a car battery using a laptop charger!

Thanks for sharing! This is the best Jugaad to charge dead car batteries during emergencies, All of the above inputs are equally important. I'd never risk it indoors though! I see OP keeping the battery in the balcony which is a good idea. Things like these are very risky for amateurs / newbies, many things can go wrong and I request everyone to check their voltage and amperage output of their laptop chargers and other adapters before trying to pull this off. My two laptops have different Amperage and Wattage ratings. As R2D2 said, I'd prefer under volt than over volt and 12 to 12.3V will be just enough to crank an engine, even for older diesel engine cars.



Quote:
Originally Posted by R2D2 View Post
Yes, you have a point there. At 12 V OC the battery is only approx 15-20% charged. I'd prefer to under volt than over volt (strictly IMHO) whilst charging because batteries are dangerous.
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Old 15th September 2020, 16:44   #8
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Default Re: Charging a car battery using a laptop charger!

I use a APC 700VA ups to charge the batteries and it works brilliant.

Have charged even suv batteries with this, I just discarded the dead battery inside this and extended the positive and negative leads with crocodile clips at the end. Here is a picture of the same.

[ATTACH=16001683218658520094275520419323.jpg][/ATTACH]
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Charging a car battery using a laptop charger!-16001683218658520094275520419323.jpg  

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Old 15th September 2020, 17:22   #9
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Default Re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by vigsom View Post
3. You'd have noticed that it took 15 hours in all - the rate of charging was extremely slow
Try replacing the bulb with a lower wattage bulb as most power is dissipated in the bulb leaving smaller power to charge the battery. Lesser charging current = higher charging time.
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Old 15th September 2020, 20:15   #10
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Default Re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by srini1785 View Post
Try replacing the bulb with a lower wattage bulb as most power is dissipated in the bulb leaving smaller power to charge the battery. Lesser charging current = higher charging time.
The bulb is in series. A lower wattage bulb has a higher DC resistance, thus pushing even lesser current into the battery!
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Old 15th September 2020, 23:19   #11
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Default Re: Charging a car battery using a laptop charger!

When I read title of this thread, I thought it was about charging an EV with laptop charger. I was wondering how someone would attempt such a thing with the most expensive thing in an EV. Only realized we are talking about a normal car battery when I saw the pictures and realized how foolish I was. Anyway one thing we all should appreciate are these small shops that provide us services like battery services. We tend to take these services for granted and situations like these make us value them.

Wanted to share one small experience. In places like Mumbai we tend to take puncture shops that provide 24/7 services for granted. We had been to Goa on a bike ride and one of friends RE Thunderbird suffered a puncture at night in Calangute. Someone gave us number for a tire shop but we learnt he would not be available till next morning. We tried offering him three times the money but the guy just flatly refused to open his shop. He said he won't even open if we gave him a thousand bucks.

I just hope once things are back to normal, we start showing these small businesses some more respect and gratitude.

Coming back to the thread, really loved the idea. Indians have always been known for Jugaad, the concept of Indian ingenuity.
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Old 17th September 2020, 12:32   #12
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Default Re: Charging a car battery using a laptop charger!

Quote:
Originally Posted by lapis_lazuli View Post
The bulb is in series. A lower wattage bulb has a higher DC resistance, thus pushing even lesser current into the battery!



Yes. I saw that the bulb was in series. The idea was , as you mentioned, to get the resistance lowered so that there is more current for charging. By wattage i meant losses due to heat. Two resisters can have the same resistance but different wattage. Total power delivered to circuit is sum of all power , including losses.
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