# Determine mAh

Discussion in 'Electronic Design' started by Andy K, Nov 11, 2013.

1. ### Andy KGuest

Is there a way to determine if a camera battery that ouputs 7.4 V really has a 1900 mAh rating instead of a 1000 mAh ?

Thanks.

2. ### Andy KGuest

Is the 7.7 Wh on the battery Watts/hr ?

How would the rated load be applied ?

I have a Sunwa YX-360TR but it does not have that feature.

Thanks.

3. ### Anthony StewartGuest

I doubt if there is an accurate non-destructive method.

You can however measure the charge transfer, Q in a number of ways. integrating I*t=Q

1) power the camera using a very large capacitor charged externally from the battery, Monitor the charging current with a 100R in series and measure time to fully charge.

2) Use a tiny shunt resistor and scope the current pulse ( harder)

3) Measure the charge voltage on the battery remaining after each photo and lens adjustment. You may be able to extrapolate a very flat curve to estimate the current state of charge for that chemistry using the OEM specs. from 100 to 10%

You can also measure the quality of the battery by it's ESR which rises with with reduced capacity and rapidly near end of life. If you are looking for statistical data, it may be a good metric for SOC using historical data.

4. ### misoGuest

You need to know the "official" termination voltage of the battery pack.
That is, 7.4V is a nominal fully charged pack, but what is the voltage
when it is considered discharged. For NiMH and nicad, 1V per cell is a
fair estimate. Some people take them down to 0.9V per cell.

Your 7.4V pack COULD be 6 cells. Usually it is 1.2V per cell, but it all
depends on how things are rounded. So pull the expected load current out
of the fully charged pack and see how long it takes to reach 6V under
load.. If you pulled 1000ma for one hour and 54 minutes, the pack would
be 1900mAh.

It helps to know the load current used by the battery manufacturer in
their datasheet. That is, to verify a datasheet specification, you need
to know the exact test conditions. [You don't know the number of fucking
idiots that call manufacturers complaining parts don't work to spec, but
don't test them as stated in the datasheet.]

Needless to say, you will need to use an electronic load. There are
plenty of circuits floating around the internet on how to do this. For a
battery test, the electronic load design is basically a DC circuit, so
it isn't all that hard to build. [Transient load testing is difficult.]
For battery capacity testing on the cheap, it can be done with analog
alarm clocks for timers. I've seen battery capacity testing projects
that look like bomb factories.

Some people have used the current limit in a bench power supply to do
capacity testing. I don't like the technique, but it should be written
up on the internet somewhere. [Note that battery might lift the supply
voltage since regulation expects current sourcing, not sinking.]

Another scheme is to use a power supply "under" the battery voltage.
That is, the positive output of the power supply goes to the ground of
the battery. You use a resistive load going from the positive pin of the
battery to the negative output of the power supply. The idea is to make
the change in voltage across the battery be small percentage wise so it
looks like a current source. [Obviously Ohms law is used to pick the
resistor.] If the supply was 20V, that mean the voltage across the
resistor varied from 27.4V to 26V, with a median voltage of 26.7V. That
implies the error in the current is +/- 0.7V/26.7V or 2.6%. All
presuming I made no math errors. Be sure to check the power rating on
the resistor.

Yes.

6. ### Guest

No, it's 7.7 watts * hours. One watt for 7.7 hours or 7.7 watts for 1
hour. In reality, your battery is something else. Reality matters.
If you want to test the batter to the manufacturer's specifications,
than you test the way the manufacturer specifies.
What feature?

7. ### Phil AllisonGuest

"miso" = moron

** Hardy matters at all.

One the cell voltage drops below 1.1V it then drops rapidly to 1.0V or 0.9V.

Digital cameras auto shut off at about 1.1V per cell anyhow - and INCREASE
the current draw as the terminal voltage falls.

** Horse poo.

A 10W resistor of 6.8 ohms will do fine.

Monitor the actual current and plot it against time every 10 minutes.

Use the simple average.

.... Phil

8. ### Guest

10 ohms??? Are you outta your mind, that would be almost 0.8A. Just about every battery, regardless of technology, specs the capacity, C, at load current of 0.1C. He needs to load it with 1900 mAH/10=190 mA. For 7.4V terminal voltage, which as Miso stated is realy 6x 1.2=7.2V, he needs 7.2V/0.19A= 37.89473684 ohms! That's 36-39 ohm nominal resistance to you. Then Prating=0.19 x 7.2= 1.368W = 5W nominal to you.

9. ### Phil AllisonGuest

** My post says 6.8 ohms at 10Watts.
** You must certainly be.
** Horrors...........

Just about every battery, regardless of technology, specs the capacity, C,

** So fucking what ?

NiCd and NiMH cells can easily do a 1 hour discharge with barely any loss of
capacity.

Plus a digital camera draws at least that much.

Bet anything a bullshitter like you has NEVER tested a NiCd or NiMH cell or
pack in you whole life.

** ROTFLMAO !!!!!!!!!!!!!!

Wot a pedantic IDIOT !!!!!!!!!

**** off - you fucking, tenth wit MORON

.... Phil

10. ### Guest

On Monday, November 11, 2013 8:40:37 PM UTC-5, Phil Allison wrote:

Your subhuman intelligence is coming through. Care to explain how he's going to verify the rated capacity if he discharges the battery at an inordinately high discharge rate at which the apparent capacity is significantly less???? Like probably 50% less at your dumb suggestion.

11. ### Bill BowdenGuest

I did it once using the camera as a load. The camera had a 'slide show' mode that continuously displayed pictures on the memory card. I think the camera drew about 600mA and the show lasted about 2 hours, so the battery capacity was around 1200mAH.

-Bill

12. ### mpmGuest

Thanks.

You would think the 1900 would last a lot longer. If you have both varieties, just time them in actual use.

The mAh rating is a guide, but becomes much more meaningful when you know the discharge, recharge and temperate curves for the battery chemistry. Youcould rig up a discharge test while monitoring cell voltage, amperage and temperature and then test/compare each battery.

It won't hold perfectly true for a different battery chemistry, but it may give you some rough ideas about how to approach the problem. If both batteries are the same basic chemistry, (Li-ion, for example) I'm wondering out loud whether you could just weigh each battery - and assume the energy-to-weight ratios for both camera batteries are at least in the same ballpark.

14. ### Andy KGuest

Thanks for the positive responses.

My question was because someone is selling Vivitar batteries at 1900 Mah.

Vivitar's own site has no such battery. Only a 1000 Mah battery.

I can see another company making a higher capacity battery, but why is Vivitar's name on it?

15. ### Guest

That's because 9 is next to 0 on the qwerty and it's a typo in the ad. They probably mean 1000mAH .

16. ### misoGuest

Horse shit yourself.

When you measure a spec, you do it accurately. You sound like the kind
of fucking idiot that calls up manufacturers and tells them the part
doesn't meet spec when in reality it is your own stupidity.

17. ### mikeGuest

It's amazing the amount of useless posturing you get from such a simple
question.

that you're sure matches the instance of battery that you have.
If the RATING is not on the label, there's not much you can do to determine
the RATING.

If you want to determine the ACTUAL capacity of the battery you're holding
in your hand, you just load it with the test current you want and
discharge it to the terminal voltage you want and see how long it takes.

But the devil is in the details.
If 7.4V is the voltage RATING it's probably a two-cell lithium.
If 7.4V is the MEASURED voltage, could be anything.
While the battery technology doesn't really matter when you multiply
the current and time, it might affect the test parameters.

I've done considerable automated battery testing. I've got a box full
of laptop batteries that still have most of their RATED capacity when tested
at low current, but won't boot the laptop at all.
mAh is not always the problem.
High ESR is often the issue for high-current applications.

What are you going to do with the answer? Acquiring info that doesn't
change your future is wasted effort.

Which gets us right back to determining the problem you're trying to
solve that will make your future better.

18. ### Phil AllisonGuest

"miso" = moron
** Go **** you mother - ASSHOLE
** But that is NOT the case here with the OP's question.

YOU are just another nut case, autistic, pedantic

FUCKING IDIOT that causes all the trouble on earth.

FOAD and take all the other trolls with you.

19. ### misoGuest

I don't recall the OP asking "Is there some fucking stupid way to
measure battery capacity." If the OP stated it that way, I would have
simply waited for you to answer the question.

20. ### misoGuest

That makes a lot of sense. Sometimes they put in higher capacity
batteries as chemistry progresses, but a pack the same physical size
probably wouldn't have a nearly 2x improvement. A typo is much more likely.