Volts or mAh...which is more important?

[Marduke]

Believe me I understand exactly what you are saying. I am just confused about the milliamp ratings. Isn't the M reading the amount of current being put out? If two cells have about the same ma (current)rating (according to the meter) then are they not "matched" CURRENT WISE.
I know you can have a rated 2000mah (discharged= 1900) and another rated 2000mah (discharged= 1500) and they are NOT matched. But for argument sake they both have a 1500 (charged)milliamp rating. If they are both putting out the same amount of current isn't that "good".
Consequently can it go the other way too.
i.e. 2 exactly charged mah readouts of 1900 and one has a milliamp rating of 1500 and the other 1350.

Note: I am not suggesting that the milliamp rating and the mah ratings are supposed to be the same...

Since I am a novice, I am just trying to understand what the meter is telling me.
Also trying to decide if I need a ZTS tester or just use a meter. (I know the ZTS put a load on it).

I think you still do not understand the difference between current and capacity.

To put it simply and plainly, you cannot match "current". There is no such thing as "current matching". Cells do not have a "mA" rating, which is current. They have a "mAh" rating, which is capacity. Trying to measure the "current" of a cell with a multimeter doesn't give you a measure of ANYTHING, it just does one of 3 things (or some multiple thereof):

1) blows the fuse of your multimeter
2) blows the multimeter itself if it is unfused
3) causes the cell to vent/explode because you are short circuiting it

The ZTS puts a cell under load, and measures voltage.

Since you have the Maha, why try to use the meter at all? You can test a cell's capacity, and match them accordingly for use in various devices. This only needs done infrequently to spot check cell health.

 

[fireguy]

I know you can have a rated 2000mah (discharged= 1900) and another rated 2000mah (discharged= 1500) and they are NOT matched. But for argument sake they both have a 1500 (charged)milliamp rating. If they are both putting out the same amount of current isn't that "good".

Dang! Had typed a response but must have hit "back" by mistake. :sigh: Let me try again.

If I understand correctly (being a newbie, it's quite possible that I don't) the case above does not show they both have a 1500 mAh rating. They both have at least a 1500 mAh rating, though. If you were to use these two cells in a device, the 1500 mAh cell would discharge first since it has less capacity. The 1900 mAh cell would still have available energy at this point. If you continue to use this, you could have a cell reversal. As the cells are connected in series, the + of one connects to the - of the other. As the one cell still has deliverable energy and the other doesn't, the one will start to charge the lower one. As they are connected in reverse to each other, the one gains a charge but a negative charge. By using matched cells, they both have close to the same capacity and they will both run out of energy close to the same time. This way, one cell cannot end up charging the lesser-capacity cell. Also, the device will last longer because you don't have one cell running empty quickly, resulting in the entire "group" of cells or "battery" of cells going below the minimum voltage required to power the device.

The capacity of the cell can only be measured after draining it, to see how much energy it can deliver. I can take a 2000 mAh cell and put 2000 mAh into it (say .5C or 1000 mA for 2 hours), or I can put 3200 mAh into it (0.1C or 200 mA for 16 hours). The cell will only retain what it is capable of retaining. The extra energy will be lost to heat, but the cell can't retain it. The only way to actually tell how much it did retain is to drain it and measure the amount removed.

Perhaps I'm stating the obvious or talking gibberish, just thinking out loud here and more asking a question than trying to state fact. :rolleyes:

 

[fireguy]

...

 

[TakeTheActive]

A Basic Understanding of Electricity is MORE Important!

I apologize if I'm not being clear in my questions... ...On my multimeter, in the VDC area, I have ranges of 20, 200,600, but also there is a range for 200m and 2000m. That is what I am questioning. Is that the milliamps rating?

Pardon me for being blunt, but, IMHO, you are being VERY CLEAR in demonstrating your lack of knowledge in basic electronics and would benefit greatly from reading a few hours of theory.

If you're in the VDC (Voltage Direct Current) area on your DMM, why would there be a selection for current? Current selections are in the ADC (Amps Direct Current) area; Resistance selections are in the OHM area. AC voltage selections are in the VAC (Voltage Alternating Current) area. Did you happen to read the DMM manual?

I'm sorry but I get very concerned when someone is doing something (possibly dangerous) that they have no basic knowledge of. For example, I get very nervous watching folks giving advice to newbies on installing three-way switches that have no clue what Hot/Neutral/Ground means. :poof:

...Perhaps what is confusing you is the difference between milliamps (mA) and milliamp-hours (mAh)...

I STRONGLY disagree! IMO, what's confusing the OP is the difference between VOLTS and AMPS. :o

He's not going to understand your answers until he understand the basics - i.e. he don't know the 'language' you're speaking yet... :sigh:

... And can you use THAT reading to determine the matching of cells?

NO! You can't even GET a capacity reading using your logic.

 

[TakeTheActive]

Where's the LOAD?

...But isn't matching the current (ma) via a multi meter still an indication of the "life" or at least for matching?

Sure!

The current THROUGH A LOAD (ma), measured via a multi meter can be an indication of the "life". But, I don't see where you mentioned the value of the LOAD? If you connect your DMM, set to read 'something' in ADC, directly to a battery, your DMM will be *BOTH* the LOAD and, for a short time, the MEASURING DEVICE. Then, either the fuse or the DMM will blow, and your experiment will be over. :oops:

 

[TakeTheActive]

Just the FAQs, Mam...

What about internal resistance? Can you use a DMM to measure the resistance within a cell?

Sure!

There are two methods listed in my Sig Line LINKs. :)

 

[TakeTheActive]

Believe me I understand exactly what you are saying...

Believe me I understand exactly what you are saying. I am just confused about the milliamp ratings. Isn't the M reading the amount of current being put out?

What's M? :confused:

...
Also trying to decide if I need a ZTS tester or just use a meter. (I know the ZTS put a load on it).

Just use your new C9000. That's all you need... :thumbsup:

 

[TakeTheActive]

The Tale of George and John...

I'd suspect it was millivolts...

:thumbsup:

...let's take a fictional pair of batteries. We'll call them George and John.

Both start off fresh; George is labeled 2700 and so is John.
John gets a knock at some point and starts deteriorating.
Now, unless you've tested it... how are you going to know?

for example. 1A load, 2700mAh --> 2.7 /1 should mean 2.7h IF the battery gets drained to 0 (which is not good). It might be that John charges great but can't hold the charge and discharges faster due to lower internal resistance - he becomes more of a sprinter, where George is a marathon runner. It may be he still has the same capacity, but because of the chemical changes (also caused by use), it's not necessarily deliverable in the same way...

I understand what you're trying to explain, but, I believe that you have a few things reversed:

...Higher internal resistance - can't hold the charge and can only discharge slower...

Due to the damage (higher internal resistance), John might still be able to supply 2700mAh total, but only at the rate of 100mA. Any faster / higher and his voltage drops (and he stops moving). John can still finish the race, but, it will take him a longer amount of time (Turtle).

Without the 'speed governor', George can sprint to the finish line at 'full speed' (let's say 500mAh), arriving in much less time (Hare).

If George and John are harnessed to the same wagon (in series), George will be limited by John's capacity. When John "drops dead", George is stuck... :(

 

[fireguy]

Re: The Tale of George and John...

Due to the damage (higher internal resistance), John might still be able to supply 2700mAh total, but only at the rate of 100mAh. Any faster / higher and his voltage drops (and he stops moving). John can still finish the race, but, it will take him a longer amount of time (Turtle).

Without the 'speed governor', George can sprint to the finish line at 'full speed' (let's say 500mAh), arriving in much less time (Hare).

In this case, the damaged cell with high internal resistance would work well in a low-current device such as a tv remote control? If we assume that the damaged cell could still retain as much capacity as a cell in good condition, and that there was no self-discharge, then both would work equally as well in this application. Of course, these two conditions never exist.

John (but no relation to George's brother mentioned previously in this thread)

:popcorn:

 

[TakeTheActive]

*FINALLY*, getting to the original question:

...However, I do have a noob question reagrding volts/mAh.

Is it more important to match your batteries according to their charged volts or mAh?

My quess is mAh?

Wrong! :eek: As narrated by bretti_kivi in the 'Tale of George and John', it's BOTH! :twothumbs

But, not CHARGED Volts - UNDER LOAD Volts (which are affected by INTERNAL RESISTANCE).

That's why you'll see folks posting different capacities for the same Make/Model cell (i.e. 2000mAh AA Eneloops) and questioning their cells, their new C9000, etc... If you want to compare, you have to follow the standards - discharge at the 'Standard Discharge Rate' of 0.2C. Discharge at 1.0C and the capacity reported will be lower; discharge at 0.05C and the capacity will be higher. When the voltage reaches 0.9VDC, the test ends - even if the 'Open Circuit Voltage' climbs back up. That's why you can perform a 0.5C discharge AFTER a 1.0C discharge and get more current out of a cell - less effort is required. It's like you doing 10 reps of 100 lbs and can't do #11. Rest a bit and then try 50lbs - maybe you can do 4 more. When you can no longer lift 50 lbs, rest a bit and try 25lbs - maybe you can do 2.

SilverFox has explained this MANY times in the CPF Archives - several of his posts are referenced in my Sig Line LINKs.

 

[TakeTheActive]

Re: The Tale of George and John...

In this case, the damaged cell with high internal resistance would work well in a low-current device such as a tv remote control? If we assume that the damaged cell could still retain as much capacity as a cell in good condition, and that there was no self-discharge, then both would work equally as well in this application...

Well, that's the KEY isn't it, i.e. no (or low) self-discharge?

Just like the situation with your (and my) remote outdoor temperature sensors and my slew of indoor temperature / humidity displays, I'm looking to wring the last droplets of life from my <80% Crap Cells in these VERY LOW current draw applications (where self-discharge will deplete the capacity before the device does).

I recently moved several of my chargers up to the HEATED den from the UNHEATED basement where I can, for the FIRST TIME, watch them fairly continuously (at least while I'm surfing the web ;) ). I can actually see the discharge voltage turn around and jump back up a bit when I discharge at 100ma on the BC-900 and, hopefully, the large crystals are breaking up.

I've had health problems the past few years, so I've neglected MANY things. For example, MANY of my alkaline devices leaked and I'm now in the process of cleaning them. With the chargers down the basement, I would just do a 1000/500 or 700/350 Refresh on the BC-900 with a fan running and use the batteries 'as-is' (unless the capacity was REALLY low). Now, with my *NEW* C9000, I'm running 100mA discharges and 0.5C (or higher) charges. Even with the OLD BC-900, I'm now interrupting the 200/100 Refresh after the discharge and restarting it at 1000 or 700. The cells that don't hit around 75% then head over to the OLD Sakar 150mA 2-cell series untimed charger for a ~0.1C for ~16hours.

I knew NOTHING about this (Voltage Depression / Crystalline Formation) before arriving here and reading the CPF 'Batteries Included' Archives DAILY since ~Thanksgiving 2008. Great stuff! :)

 

[SilverFox]

Re: The Tale of George and John...

Hello Chase2b,

Matching cells is a multi stage process...

First you run a standard charge (charging at 0.1C for 16 hours), then note the capacity in mAh during a standard discharge (discharging at 0.2C). At this time you are matching cells according to capacity.

Next you figure out the load your cells will be operating at and decide on what rate you will be using to charge at. Now you charge at your pre-determined rate, and discharge at a rate that is representitive of the load you will be operating at. Once again the matching is done on capacity.

Finally, you observe the voltage during the discharge, and in this case you match on voltage under load.

The voltage under load is directly related to the internal resistance of the cell, and closely related to the health of the cell.

The tighter you set your tolerances, the closer matched the cells will be.

Tom

 

[Chase2b]

I thank everyone for all the advice and to state the obvious... Yes I am very new to all of this. I am weak in this area, but learning; just like everyone had too at one point.
The meter I have (Ideal 61-360) is a high end meter that was given to me as a gift. The manual is not geared towards novices, so it is difficult for me to understnad some things.
On the VDC dial it shows the settings of 20, 200, 600 , 200m and 2000m.
It's the 200m and 2000m that I am asking the questions about. This is a milliamps setting correct?
If I put the dial on 20 and take a reading of a battery it will show say, 1.42 which is the volts. When you put the dial on 2000m it will show 1420 which I am assuming is the milliamps? My only other question was if you have two batteries that have very close milliamps, again 1420 as an example, aren't these two batteries putting out about the same amount of current?

 

[SilverFox]

Hello Chase2b,

In the case you illustrated, 1.42 is volts, 1420 is milli volts. Neither is current.

Tom

 

[Marduke]

I thank everyone for all the advice and to state the obvious... Yes I am very new to all of this. I am weak in this area, but learning; just like everyone had too at one point.
The meter I have (Ideal 61-360) is a high end meter that was given to me as a gift. The manual is not geared towards novices, so it is difficult for me to understnad some things.
On the VDC dial it shows the settings of 20, 200, 600 , 200m and 2000m.
It's the 200m and 2000m that I am asking the questions about. This is a milliamps setting correct?
If I put the dial on 20 and take a reading of a battery it will show say, 1.42 which is the volts. When you put the dial on 2000m it will show 1420 which I am assuming is the milliamps? My only other question was if you have two batteries that have very close milliamps, again 1420 as an example, aren't these two batteries putting out about the same amount of current?

As stated several times, VDC is DC voltage, NOT current. 200m and 2000m is mV. Your meter is NOT measuring current or capacity.

The current scale is ADC, but again, do NOT try to measure your batteries on any of those settings. They will not measure anything, and you'll just destroy either your cells, or the meter, or both.

 

[TakeTheActive]

NO!, NO!!, NO!!!, NO!!!!, NO!!!!!

I thank everyone for all the advice and to state the obvious... Yes I am very new to all of this. I am weak in this area, but learning; just like everyone had too at one point...

...The meter I have (Ideal 61-360) is a high end meter that was given to me as a gift. The manual is not geared towards novices, so it is difficult for me to understnad some things.

On the VDC dial it shows the settings of 20, 200, 600 , 200m and 2000m.
It's the 200m and 2000m that I am asking the questions about. This is a milliamps setting correct?

:hairpull:NO!!!!!:hairpull:

SEVERAL folks have already told you it's MILLIVOLTS, *NOT* MILLIAMPS!
:dedhorse:​

As someone who openly ADMITS to being a Newbie, you CERTAINLY DO NOT easily accept the advice of those more experienced. ***PLEASE*** GOOGLE for (and READ!) some 'Basic Electricity' theory... :sigh:

At this point, I will stop replying to Chase2b until he demonstrates that he has READ AND UNDERSTOOD some 'Basic Electricity' theory... :(

IMHO, he has refused to accept the sound advice of SEVERAL experienced members and insists on continuing with his own, INCORRECT beliefs... :confused:

What more can we do? :shrug: :sigh:

 

[Chase2b]

"TakeThe Active" I take offense to your reply that I am refusing to accept your answers. Unlike you, I was brought up to ask and keep asking until you understand.

I figured out where the misunderstanding was. After my original post, people were telling me NOT to measure currents. I took that to mean that putting the dial on 2000m (which I now understand means milliVOLTS not milliAMPS) is wrong and can damage the MM.
Naturally I'm shaking my head because it doesn't.
Then in my post #8, I INCORRECTLY stated that I put the meter on MA. That is what is throwing everyone off. I know that is current and can't measure that way. I meant putting the dial on 2000M.
Someone than asked what M was? My meter does not say MV which would have cleared everything up.
And as I mentioned, the manual says NOTHING about this at all.

In post #16 I again ask about putting the dial on 2000M and the next reply was that I was measuring current and that you can't go by MA. People kept telling me I was on ADC trying to measure current when I was NEVER on that.

Posts after that kept telling me you can't measure by MA. Until post #20. THAT WAS THE FIRST TIME MILLIVOLTS was mentioned.

Where I was wrong was I kep using the words MILLIAMP when it should have been MILLIVOLTS. That's where all the confusion is.

"TakeThe Active" mentioned if I had the dial on VDC then why is there a selection for current? Again more confusion. You can see being a novice how I am REALLY confused now.
So I keep asking and eventually the misunderstanding has been cleard up.

Trying to understand through typing on forums is difficult at times since you cannot get the one-on-one attention like a classroom. Sometimes people have a difficult time trying to comprehend what you are trying to say.
If my original question was presented to someone in person, it would have been answered and cleared up in 1 minute since they would have seen exactly where on the MM dial I was referring to.

But... I'll say again. "TakeTheActive" clearly demonstrates his impatience at a novice and relies on condescending remarks with his illustrating the beating of a dead horse. Were you an EXPERT when you were first learning about this? There are guys like you in every forum. If you are trying to help someone, then at least have the patience and more importantly, the understanding that people sometimes just don't get it and need additional explanations. NO MATTER HOW MANY TIMES THEY ASK.

 

[-LightOn-]

Charged capacity?

I guess this thread is good for asking this. I have a Bantam bc5 for charging my Li-ion cells. The charger dispays the 'charged' capacity in mAh, but since the figure is substancially higher than the nominal capacity of the cells, I'm guessing that the number is just the integral of the charge current over time and doesn't reflect the actual charge that 'sticks' to the cells. I'm right?

If so, what is the charged capacity figure good for??

 

[Marduke]

"TakeThe Active" I take offense to your reply that I am refusing to accept your answers. Unlike you, I was brought up to ask and keep asking until you understand.

I figured out where the misunderstanding was. After my original post, people were telling me NOT to measure currents. I took that to mean that putting the dial on 2000m (which I now understand means milliVOLTS not milliAMPS) is wrong and can damage the MM.
Naturally I'm shaking my head because it doesn't.
Then in my post #8, I INCORRECTLY stated that I put the meter on MA. That is what is throwing everyone off. I know that is current and can't measure that way. I meant putting the dial on 2000M.
Someone than asked what M was? My meter does not say MV which would have cleared everything up.
And as I mentioned, the manual says NOTHING about this at all.

In post #16 I again ask about putting the dial on 2000M and the next reply was that I was measuring current and that you can't go by MA. People kept telling me I was on ADC trying to measure current when I was NEVER on that.

Posts after that kept telling me you can't measure by MA. Until post #20. THAT WAS THE FIRST TIME MILLIVOLTS was mentioned.

Where I was wrong was I kep using the words MILLIAMP when it should have been MILLIVOLTS. That's where all the confusion is.

"TakeThe Active" mentioned if I had the dial on VDC then why is there a selection for current? Again more confusion. You can see being a novice how I am REALLY confused now.
So I keep asking and eventually the misunderstanding has been cleard up.

Trying to understand through typing on forums is difficult at times since you cannot get the one-on-one attention like a classroom. Sometimes people have a difficult time trying to comprehend what you are trying to say.
If my original question was presented to someone in person, it would have been answered and cleared up in 1 minute since they would have seen exactly where on the MM dial I was referring to.

But... I'll say again. "TakeTheActive" clearly demonstrates his impatience at a novice and relies on condescending remarks with his illustrating the beating of a dead horse. Were you an EXPERT when you were first learning about this? There are guys like you in every forum. If you are trying to help someone, then at least have the patience and more importantly, the understanding that people sometimes just don't get it and need additional explanations. NO MATTER HOW MANY TIMES THEY ASK.

And you are still getting it wrong. Your meter doesn't have 2000M (mega), it has 2000m (milla) in the VDC section.

And your manual does state about that scale being millivolts, not milliamps.
http://www.testequipmentdepot.com/ideal/pdf/61-360_manu.pdf
Page 3 has your unit of measure multipliers. Page 4/5 explains how to measure VDC and where on the dial that is. Page 11 tells you how to measure DCA, and where on the dial that is, not that current is what you wanted to measure to begin with (despite several people telling you that).

Is it perfectly clear now, that you do NOT under ANY CIRCUMSTANCES try to measure ADC (current) of batteries directly with your multimeter??

 

[SilverFox]

Hello -LightOn-,

You are correct. The charger is telling you the capacity put into the cell(s). To determine the actual capacity of the cell, you have to do a discharge test.

With NiCd and NiMh chemistry, there can be quite a difference between the charged and discharged capacities, but with Li-Ion chemistry it is usually pretty close. I think you get out around 98-99% of what you put in, or something very close to that.

Tom