How can I test Amps?

I have uploaded a video to youtube of my circuit.

It's basically a laptop battery taken apart. All I'm trying to learn is how would I test for amps from these batteries? The battery should last over 2 hours on my laptop but it's barely lasting 15 minutes so I'm trying to work out why, while also learning along the way as I'm just starting to learn about electronics.

Cheers guys, Jake

by jakehazelwood
August 24, 2018

Batteries do go down over time, so if this battery is over three years old it is probably lifed out and needs replacement, alas at rather high cost. Alternatively buy a new laptop or chromebook and transfer your dara.

For information only:

The circuit board managing the battery is quite complex. It protects the battery against overvoltage, overcurrent, and sets up the correct charging conditions. It is possible but unlikely that it has developed a fault.

Be very careful. Those cells carry a lot of energy and can go bang or catch fire. Okay when properly packaged but unsafe when dismantled.

Nice vid.

by mikerogerswsm
August 24, 2018

ps - Here is a date code check:

I get October 2010 for your batteries, which is very old. It really is time for a new battery pack. Sorry to be the bearer of bad news. mike

by mikerogerswsm
August 24, 2018

Correction June 2010 - not a lot different, slightly worse.

by mikerogerswsm
August 24, 2018

Just a quick check, each set of three cells should be 4.2V when fully charged, and each should drop roughly the same amount after running the laptop for a time. If not, then you have a dud.

by mikerogerswsm
August 24, 2018

Replacement battery pack should be £50 for a first class one or £25 for a lower grade type.

by mikerogerswsm
August 24, 2018

In this era when the screen of the mobile phone is large and the performance of the mobile phone is getting higher and higher, the mobile phone becomes thinner and thinner at the same time, and our battery life is getting worse and worse. Some people's mobile phone power is not used every day, the battery power We can't change it, but we can change him to make his battery life more durable; the video reference is as follows:

In fact, the culprit is the mobile APP, yes, it is, many software will quietly start up on their own. ! Not only will they consume our mobile phone power but they will also consume our valuable traffic.

by deskely
August 31, 2018

3 Answers

Answer by jakehazelwood

Thanks for your replies. A new battery is £17 on ebay so I'm not too worried about replacing. Now I'm interested in learning more than anything. Each set of 3 batteries is reading around 4 volts with the total being 12 volts. So that seems okay. When I said this too my dad he said but the amperage could be low and that's why they don't last very long.

How can I test this circuit for amps? From what I understand I would need to connect a test load like a lamp with the multimeter in series on the positive lead. If i de-solder the circuit board away from the battery and instead connect my multimeter in line with a lamp and then back to the negative side of the battery will this work? Is it safe for me to be soldering onto a live circuit that I can't turn off because it's a battery? Diagram of my proposed circuit

+1 vote
by jakehazelwood
August 25, 2018

No, no, no! Your proposed circuit shorts out the top three batteries and the bottom three. Bang times six!!!!!! Followed by major fire.

You need to put your load across top and bottom. Just delete the two innermost connections. Then measure the three voltages over time. They should drop equal amounts down to about three volts.

If you wish to measure the battery capacity, measure the current and the time to discharge from 13.2V (3x4.2V) to, say, 9V (3x3.0V)and then multiply the two together. This gives you the capacity in amp-hours. Should be 2.8, probably is in the region of 0.35

This may be of use to you if you don't already know it:

by mikerogerswsm
August 25, 2018

Correction 3x4.2V = 12.6V

by mikerogerswsm
August 25, 2018

So if I know the voltage is 12 volts. Could I measure the resistance across all 9 batteries and get a reading in ohms. Then just 12 / resistance gives me the amps?

Here is how I would think you measure resistance? Though I don't know if I've shorted the batteries again.

by jakehazelwood
August 25, 2018

How do I include an image? I've tried using image tags and putting my link to my picture in between like below. I've read the formatting guide but still not working.

img /img (I've removed the [] brackets from the img tags so you can see)

by jakehazelwood
August 25, 2018

No. Don't do that, you'll wreck your meter.

I don't know your age or background. I included the link to ohm's law so you got some basic electrical education, if necessary. You are tackling a difficult and dangerous area. Please don't try to run before you can walk.

Take a course in basic electricity.

by mikerogerswsm
August 25, 2018

On reflection I think your father is confusing you. He says measure current when he means Amp-Hours and he says measure resistance when he means internal resistance. This is measured in a very different way and in this case is irrelevant. You need to learn about electricity from someone who understands it, such as a college lecturer or a ham radio enthusiast. Beware of false prophets and pub sages.

by mikerogerswsm
August 25, 2018

Thanks for your input. I know I'm running before I can even put one foot in front of the other. I've given up on the battery after I put it back together and the laptop recognized it but doesn't hold any charge anymore. I've ordered a new one for £11 now. I will look into doing some projects that I can follow along with out of a book so I can get the basics down. I may consider doing a little after hours course or something but I don't really want to go back to a course as I didn't like my 2 years at college doing joinery.

by jakehazelwood
August 26, 2018

Answer by mikerogerswsm

Fifty years ago I'd have said subscribe to one of the many magazines but there's only one left and that's Everyday Practical Electronics. They occasionally run a beginner series, well worth a monthly read.

+1 vote
by mikerogerswsm
August 28, 2018

Answer by Gazingstock

Using Ammeter.

Current is the flow of electrons and according to Ohm's Law you can also find it by measuring voltage and resistance and use the law to obtain the current.

+1 vote
by Gazingstock
September 07, 2018

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