# [Solved]Measure a battery amps

How can i get to know the maximum amps of a battery?
Is it possible to measure that with a multimeter or something?

You can measure the amps being drawn - put your meter in Amp mode, or mA mode for lower currents.
Red probe connects to + of battery, black probe to where the battery + would have gone, so your meter is in series with the current flow.

Start off in Amp mode.

tsunamy_boy:
How can i get to know the maximum amps of a battery?
Is it possible to measure that with a multimeter or something?

While a simple question there is not a simple answer. The maximum current a battery can supply at a given terminal voltage mostly depends on it's built in internal resistance. This is a specification that most battery manufacture don't publish or make easily available, but if it's a 'name brand' battery you might be able to find a datasheet published somewhere.

Note that where this is a very important specification as in radio controlled electric motor powered aircraft or the such where current demand can be very high and total flight time is measured is mins rather then hours. A battery's total charge capacity is measured in amp/hours or millamp/hours, but that doesn't tell you the maximum current you can draw for a short time. The newer specification for max current draw is so called C rating as specified in some Li-Po cells where they might say it can support a 10C or 20C or even higher value. What that says is that a cell that is say rated as a 1 amp/hour can supply (for a very short time) 10 amps or 20 amps peak current. I've only seen those ratings on some Li-po cells, although auto 12volt batteries often give a short time high current capability as 'peak cranking amps' which is effectively the same kind of spec.

Don't know if that helps, and if you can give us more information about what you require in current demand, duration, and what specific battery you are considering maybe a better answer can surface.

You can measure the amps being drawn - put your meter in Amp mode, or mA mode for lower currents.
Red probe connects to + of battery, black probe to where the battery + would have gone, so your meter is in series with the current flow.

Start off in Amp mode.

I did that and i just discharged a Lipo Battery completely (0v now)
Maybe i can't do that with lipo batteries.

Don't know if that helps, and if you can give us more information about what you require in current demand, duration, and what specific battery you are considering maybe a better answer can surface.

It's a chinese (from ebay) nokia battery but it looks like it's not 750mA because when i charge it with my charger (TP4056 - with a resistor of 1.6k) the final voltage is 4.1v. But when i use the Nokia itself i get 4.2v.
I look up online and those Chinese batteries can stand more than one type of amps

Charge control chips can be set to different voltage levels to finish at.
MAX1811 for instance, a pin high or low determines what level is used.

MAX1811.pdf (271 KB)

tsunamy_boy:

You can measure the amps being drawn - put your meter in Amp mode, or mA mode for lower currents.
Red probe connects to + of battery, black probe to where the battery + would have gone, so your meter is in series with the current flow.

Start off in Amp mode.

I did that and i just discharged a Lipo Battery completely (0v now)
Maybe i can’t do that with lipo batteries.

Correct and you most likely destroyed the battery cell. Li-po cells should never be allowed to discharge below 3.0 volts.

Don’t know if that helps, and if you can give us more information about what you require in current demand, duration, and what specific battery you are considering maybe a better answer can surface.

It’s a chinese (from ebay) nokia battery but it looks like it’s not 750mA because when i charge it with my charger (TP4056 - with a resistor of 1.6k) the final voltage is 4.1v. But when i use the Nokia itself i get 4.2v.
I look up online and those Chinese batteries can stand more than one type of amps

I think you should research more about li-po batteries before you do anymore ‘experimentation’. Li-pos have very specific charging and discharging rules and one can easily destroy them and even cause fires.

Ok, so after a lipo battery charging, if the battery is low than 4.2V, this means that the battery is not fully charged right? So in other words, it will not overcharge if i keep charge it the same way over and over?

4.1, 4.2 - depends on the charger.
4.1 is going to be pretty charged.

4.1, 4.2 - depends on the charger.
4.1 is going to be pretty charged.

Cool, so it looks to you that there would be no problem? If i got 4.4 for example, this would be a problem (is this what it's called over charging?)?

4.4 would be a problem.

4.4 would be a problem.

Understood, thank you and thank you all.
Have a nice day guys

tsunamy_boy:
Understood, thank you and thank you all.
Have a nice day guys

What I'm going to write here may seem a little terse and rude, but I'm trying to get your ATTENTION! Please don't take it personally but this is your life and/or your family's life were talking about.

No, not 'understood' at all. I don't know if realise the implications of '4.4 - would be a problem.' A lipo burns a 2000F and shoots flames up to 6'. Anything within reach that is potentially combustable instantly combusts. That includes your face.

Back in the day lipos got a very bad reputation for causing fires, generally caused by crappy chargers. Lately, most fires are caused by overcharging, or trying to keep using damaged batteries.

How can i get to know the maximum amps of a battery?

The mere fact that you ask question says that you are not an engineer, and are therefore not qualified to 'know' (measure) the A of a battery.

The mAh of a battery is a shell game. It is essentially determined by how many potential -cycles- a battery will have.

The cycles are determined partly by how hard you draw the current, and how far down you run the voltage.

A lipo is fully charged at 4.2V. Notice though that when you buy one brand new it's at 3.65-3.75V. That's the nominal voltage, the 3.7 that's printed on the label. That's what the factory charges the battery to to give the longest life when sitting on a retail store shelf for a year or two.

When they say that 4.2 is the maximum, they mean that anything beyond that risks fire/explosion. (OK 4.25 or whatever but who wants to risk it.)

Beyond 4.2 the battery doesn't necessarily immediately go 'poof.' It starts to get warm, probably it puffs, the chemicals degrade, it gets hotter, there's a thermal runaway and -then- it goes poof. The only lipo fire I ever saw personally was a 'moderate impact' helicopter crash. walking over to it, and then looking for a bit, it had to be somewhere between 1 and 2 minutes before it actually caught fire, 3' flames. A multicell battery fire can -appear- to go out, then catch fire a minute later as another cell catches.

These numbers aren't cast in stone either. Manufacturers vary, chemistries vary, production processes vary. Stay on the safe side of all the numbers and you'll have the best chance of not suffering a disaster. But the reason I'm being LOUD about all this is that so far you're playing on ALL the UNSAFE sides of the numbers.

The point being that once you go past 4.2x, or give it a severe shock/impact, you're holding a grenade in your hand, the pin is pulled, you just haven't released the yet. But the the detonator is not under your -control-, it's a chemical reaction that will light up sooner or later.

...i just discharged a Lipo Battery completely (0v now)

BTW you just destroyed the lipo. Yes there're potentially ways to 'revive' them but it is severly damage, will have a drastically shortened lifespan, and every time you charge it you're playing 'pull the pin on the grenade and see if it lights up this time.'

Ok, so after a lipo battery charging, if the battery is low than 4.2V, this means that the battery is not fully charged right? So in other words, it will not overcharge if i keep charge it the same way over and over?

Not necessarily, and probably not, because you haven't mentioned what you're charging it with, also given some of the treatment you give them such as discharging down to 0V. A damaged battery -may- not have the ability to be fully recharged to 4.2. The fact that it won't go to 4.2 -may- be a sign of damage. A reputable charger, first, won't let a battery charge past 4.2, and if it doesn't reach 4.2 won't let it charge past a certain time limit.

The C rating of a battery is not cut and dried. Again, it is a shell game number picked by the manufacturer to get an 'OK' number of cycles from the battery by the average consumer. 100 cycles is generally assumed to the target cycles. (As was mentioned, manufacturers don't publish -real- specs.) You can, for instance, discharge a 10C battery at 20/30/40/whatever rate you want, but it may work only 20 or 5 times, or only once. OTOH I've heard of rare instances of mocel aircraft catching fire in flight because they pushed a battery too hard.

Battery usage isn't supposed to be measured by mA, it's supposed to be measured by V. The 'ABSOLUTE maximum discharge' is -generally- touted at 80% or about 3.4V. But, that will give you the fewest usable cycles. One fellow I read about, whose -job- it is to manage battery systems, said he got -600- cycles by dischargong to the nominal 3.7 / 50%.

Regardless the topic really was about charging. You didn't mention what size batteries you're using. Common consumer toys come with a charger, and shouldn't be messed with by either using a different charger or using the charger on other batteris unless you KNOW what you're doing. Here's a good reference about overcharging and the 4056. RC Groups - View Single Post - Syma S107 battery upgrade

One more BTW. NEVER leave a charger unattended. There was a story this past Xmas about a new toy, got used a few times in the morning, and was left on the charger while the family went out. They came home and the house was burned down. It was -probably- a 10-15 minute charger, that -probably- had a warning label on it that said 'do NOT leave on charge for more than one hour.' Misuse = 'poof.' Junky charger = 'poof'

I ended up building my own lithium ion charger circuit using simply 5v, arduino powered.

I think there was a misunderstanding and the OP connected his meter set on Amps directly across the battery.

jbarchuk:
The point being that once you go past 4.2x, or give it a severe shock/impact, you're holding a grenade in your hand, the pin is pulled, you just haven't released the yet. But the the detonator is not under your -control-, it's a chemical reaction that will light up sooner or later.

Ok, i'm scared now!!
So by this, tell me what's the best way to charge a lipo battery.
I've followed this topic: Battery charger - General Electronics - Arduino Forum
Do you think i'm ok with that?

cjdelphi:
I ended up building my own lithium ion charger circuit using simply 5v, arduino powered.

It looks scary for me do you have a schematic and the source that you can share with this community?
It would be awesome.
Also tell me, can you charge any kind of lipo battery (i have an idea that each mA need a different situation)?

polymorph:
I think there was a misunderstanding and the OP connected his meter set on Amps directly across the battery.

Well, yeh

tsunamy_boy:
So by this, tell me what's the best way to charge a lipo battery.

The way the -battery- -manufacturer- says to, for the part number printed on the battery. Wikipedia lists 24 different 'lithium' chemistries. Lithium is the family name -lithium ion and lithium polymer are not necessarily synonyms. Voltages and charge/discharge characteristics vary DRASTICALLY.

I've followed this topic: Battery charger - General Electronics - Arduino Forum
Do you think i'm ok with that?

That looks like the straight dope.

MAX1811 is easy to use for a LiPo.
Here I used one to charge a 1000mAH LiPo in my RF remote control.
I used 3AA battery pack for development, then connected the LiPo when I get the other parts in.
Has been running since ~Jan 2011.

jbarchuk:

I've followed this topic: Battery charger - General Electronics - Arduino Forum
Do you think i'm ok with that?

That looks like the straight dope.

Why

MAX1811 is easy to use for a LiPo.
Here I used one to charge a 1000mAH LiPo in my RF remote control.
I used 3AA battery pack for development, then connected the LiPo when I get the other parts in.
Has been running since ~Jan 2011.

Do you have the need to setup resistors based on the amps that your batteries have?

No. Lower left resistor is there to set Enable High or Low depending on whether external power is available. Upper right resistor is there to limit current to the charge indicator LED for brightness control.
Pins 1 & 2 determine whether it charges to 4.1V or 4.2V, and at 100mA rate or 500mA rate.