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Author Topic: Battery storage charge  (Read 1625 times)
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Manne
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« on: November 01, 2014, 06:56:51 AM »

How long can a battery be stored with the original factory storage charge?
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Konrad
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« Reply #1 on: November 01, 2014, 11:25:24 AM »

What type of battery chemistry?

I assume you are asking about Lipo's. They generally have a shelf life of 2 years when stored at 3.85V (storage voltage) (AKA, changed to half capacity).

The 2 year shelf life refers to the ability of the battery to discharge (dump) 80% of its original capacity.

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Konrad
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tom arnold
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« Reply #2 on: November 01, 2014, 12:38:49 PM »

Konrad, That is interesting news about a LiPo. So does that mean a 4 year old battery discharges less than 80% of its capacity still at the original voltage/amperage but just for a lessened time? Sort of like less gas in the tank? If so, how do you know how long the supplier has held the battery before you bought it? or don't you?
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Konrad
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« Reply #3 on: November 01, 2014, 01:26:51 PM »

I think the electrolyte  breaks down the anode and cathodes. Keeping the battery half charged "balances" the deterioration on both.

Unfortunately the amperage is also deteriorated Again the anodes and cathodes can't carry as much current in their deteriorated state.

So it is a one two punch. Both the amount of  'Gas' and the 'size of the fuel lines' are restricted!

Yes, high end manufactures list the manufacturing date on their cells. As to the battery manufacture (assemblers), I know Thunder Power labeled their batteries ( For example 08-18-05).

I think that there is pressure not to date label the batteries. So ask your supplier how old are the cells. Now if looking at places like Hobby King please be aware that the yield during the manufacturing of lipos cell is around 66% to 70%. So where do the cells that don't make the cut (fail test specification) go?

Remember the issues with the 787 batteries? The manufacture was showing 90+% yields yet there was no documented improvement in the manufacturing process. Just for the record the issue wasn't with the manufacture but rather the method(s) used to certify the cells.

Friends don't let friends fly nickel,
Konrad

P.S.
And no that is not a serviceable battery.
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Re: Battery storage charge
« Last Edit: November 01, 2014, 01:40:22 PM by Konrad » Logged

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mjmccarron
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« Reply #4 on: November 01, 2014, 04:50:54 PM »

The original question asked how long with the "factory charge" Most manufacturers have a chemical coating in the battery that protects against the deterioration. It breaks down over the first few charge/discharge cycles. So, I would then assume that a new battery left at factory charge would have a longer shelf life than one that has been used stored at the recommended storage charge. Does anyone know any details on this?
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Konrad
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« Reply #5 on: November 01, 2014, 05:58:17 PM »

Well, not that I've been made aware of with regard to lipos. The issue is the internal deterioration of the structure from its own electrolyte. From my experience I wouldn't want anything to contaminate the matrix. The storage charge is what keeps the ion exchange in check, well minimizes it. That is why the batteries from the factory and when not in use should be stored at 3.85V (some other matrix dopings might have the optimum storage Voltage differ 0.03V).

So the statement is still valid that you don't want cells that are more than 2 years old. They will hold a voltage charge for a lot longer. But subsequent charges and current draw will be degraded.  Now the impedance of the cell is what drives a lot of this. So you want a cell with the lowest impedance.  

Now breaking in lipos has to do with the surface of the copper plated being roughened (microscopically) giving the battery more surface area to produce more power. But it has no appreciable impact of storage life

Again this is with Lipos. I don't know if the OP has lipos or other battery chemistries in mind.

Friends don't let friends fly nickel,
Konrad

Disclaimer,
I'm no chemist, My understanding comes from the use of lipos for the last 15 years, and as an aviation field service engineer with electrical power responsibility ( but with no responsibility for batteries)
« Last Edit: November 01, 2014, 06:08:33 PM by Konrad » Logged

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mjmccarron
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« Reply #6 on: November 01, 2014, 06:50:44 PM »

Thanks Konrad,
That makes sense. I don't remember where I saw something about the initial doping and how it breaks down but I have found no evidence that this is true. (I've been looking since my last post) Keeping the ion exchange in balance makes the most sense of anything so far. I've been an electrical engineer specifically involved in power conversion and magnetics for 28 years but LiPo technology is not something I have had much experience with other than in RC. My biggest problem is my need to know "WHY". That need ends when the answer lies too deeply rooted in chemistry. I am no chemist.
Thanks,
Mike
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Konrad
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« Reply #7 on: November 01, 2014, 08:00:19 PM »

Thanks Konrad,
… My biggest problem is my need to know "WHY". That need ends when the answer lies too deeply rooted in chemistry. …
You and me both! Unfortunately for me my curiosity is often stifled by most other disciplines, not just chemistry! Huh

Friends don't let friends fly nickel,
Konrad

BTW; That nickel  in my sign off is the nickel one finds in Nicads or NIMHs batteries. I jokingly used it to bring to light the power of lithium back in the early days of Lipos. You might recall when a 5C discharge rate was a high power set up!

P.S.
There is no standard or measurable characteristic that defines "C" rating. It is just sales hype.
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mjmccarron
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« Reply #8 on: November 01, 2014, 09:12:20 PM »

Quote
There is no standard or measurable characteristic that defines "C" rating. It is just sales hype.

So much of the information we see is just that. It's like CCA ratings for lead acid batteries. They both have to do with the impedance of the battery which is a dynamic property. But cool buzz words and big numbers sell products. Don't even get me started on kV ratings...

Mike
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USch
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« Reply #9 on: November 02, 2014, 06:39:54 AM »

Now the impedance of the cell is what drives a lot of this. So you want a cell with the lowest impedance.

There is no standard or measurable characteristic that defines "C" rating. It is just sales hype.

I am not a chemist either, have only "statistical" experience starting from NiCd's to LiPo's.

The "C" rating SHOULD have to do with impedance, as lower it is as more you can charge/discharge a batterie. But impedance will vary during the life of the cells, going higher and higher on every charge. And this may be worse than the loose of capacity, at least for some categories of models. But happily (for the producers), most modellers dont measure the impedance of there batteries.

But now to the main point. The batteries sold to the modellers aim at having the most capacity possible at the least weight and the lowest impedance. That means that the separators are getting thinner and thinner to get low weights, low impedance per energy output. This separators are deteriorating faster than thicker ones. The story repeats itself as happened to the NiMH batteriers. Trying to put more and more capacity into the cells the quality and working life diminuished rapidly. As happened to the last NiMH (4600mAh) cells sold where 50% of the cells arrived already with 0 V tension and had to be put into the bin befor ever used.

This is demonstrated by the fact that a LiPo cell from a serious producer has low C rating, is heavier than counterparts, higher impedance than others but
LAST MUCH LONGER WITHOUT SERIOUS DETERIORATION ON CAPACITY AND IMPEDANCE!

Going back to the initial question, if you buy high C rated, high capacity batteries usually sold to modellers try to put your hands on fresh ones. But how to control that???

Urs
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Konrad
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« Reply #10 on: November 02, 2014, 10:59:08 AM »

Both those quotes should be attributed to me, Mjmccarron should not be blamed.

What you say about the  separators is true for the Nimh and Nicad cells. Also the construction is very different between instrument grade (low current high capacity long life) and power cells (higher currents less capacity).

In the old days we use to 'ZAP" these cells to increase their current abilities. Zapping would expand the cell against the case lowering the resistance of cathode to case junction. Unfortunately the cells would sometimes fail the vent seal or rupture.  Shocked This would lower one yield of useful cells  Angry

With lipos the diminutional (Volume) characteristics follow the 'C' rating. Nothing magical here, higher 'C' rated cell have thicker anodes and cathodes ( lower impedance) . Now higher capacity cells in the same volume will have more surface area for the anodes and cathodes. This means anodes and cathodes are thinner and that there are more folds. Both of these characteristics result in higher impedance (kind of like a coil in a motor or choke). Also these thinner plate are subject to physical damage and chemical attack that limit their electrical characteristics.

I have not noticed any thinning of the separator in the cells from 2000 and those of today 2015. I forget the thickness of the mylar but I did measure some failed cells thinking that what was mentioned with the Nicads and Nimh was happening in the manufacture of lipos.

Most high end Lipo hobby charger will measure impedance. But it is a difficult characteristic to measure accurately, as charge state, temperature, leads and connectors effect the readings.
http://www.thunderpowerrc.com/Products/Chargers_2/TP1430C

Friends don't let friends fly nickel,
Konrad
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USch
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« Reply #11 on: November 02, 2014, 06:04:56 PM »

Sorry to mjmccarron, but I did not want to blame anybody, it's just a talk about batteries  Wink
I to have still a zapper for NiCd's, actually if somebody needs one, it's for free!

Your remarks, Konrad, are certainly right and my assumption about thinning of the separator wrong. But remains the fact that the cell are deteriorating at a fast rate nowadays. For example a high capacity cell (6400mAh), rated 40C, used this year in an application which uses 90% of the charge during 6 minutes (10C), looses 50mAh capacity every cycle and goes up on impedance by about 1-2mΩ per cycle. Impedance measured with always the same charger, leads, connectors and temperatur and protocolled, so the trend is easy to detect even if it may not be absolute in values.

Urs
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mjmccarron
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« Reply #12 on: November 02, 2014, 08:27:55 PM »

Quote
Sorry to mjmccarron, but I did not want to blame anybody, it's just a talk about batteries  Wink

No apology necessary USch. It is just talk about batteries. I am still learning about LiPo's. I find it interesting that there a quite a few similarities between them and Lead Acid as far as capacity vs. impedance is concerned. I don't take offense if someone disagrees with me or even if they misquote me. Especially if I agree with the person whose quote was tagged to me. LOL This is a forum of ideas and I'm on here to learn first and impart my little bit of knowledge where applicable. Thanks for the apology though.
Mike
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Konrad
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« Reply #13 on: November 02, 2014, 10:53:00 PM »

Both those quotes should be attributed to me, Mjmccarron should not be blamed. …
Sorry, I was trying to be funny. I know this a dangerous thing on the internet! Roll Eyes
I should have used an emoticon.

Its all good I don't think anybody here is taking offense. We are all trying to learn and help. 

I'd still like to know what chemistry MANNE (the OP) had in mind.
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lincoln
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« Reply #14 on: November 04, 2014, 08:56:41 PM »

Quote
There is no standard or measurable characteristic that defines "C" rating. It is just sales hype.

So much of the information we see is just that. It's like CCA ratings for lead acid batteries. They both have to do with the impedance of the battery which is a dynamic property. But cool buzz words and big numbers sell products. Don't even get me started on kV ratings...

Mike

What's wrong with kv? If it's measured accurately, it can help you pick the right prop or decide whether or not the  motor is suitable for your purposes. A high number isn't always bad, and a low number isn't always good.
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Konrad
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« Reply #15 on: November 04, 2014, 09:35:06 PM »

Wrong "KV".

Kv and Kt are motor constants. RPM= Kv x Volts, Torque= Kt x Amp. For our motors (in the USA) we think of inch ounces per amp. And for that the relationship is Kv x Kt =1355.

For rational metric units the values for the relationships are 0.97432 for kg-m or 97432 for g-cm

This is all off topic.

Friends don't let friends fly nickel, or measure in inches,
Konrad

Edited;
To add rational units
« Last Edit: November 04, 2014, 10:02:36 PM by Konrad » Logged

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Bill G
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« Reply #16 on: November 21, 2014, 12:49:07 PM »

Now the impedance of the cell is what drives a lot of this. So you want a cell with the lowest impedance.

There is no standard or measurable characteristic that defines "C" rating. It is just sales hype.

I am not a chemist either, have only "statistical" experience starting from NiCd's to LiPo's.

The "C" rating SHOULD have to do with impedance, as lower it is as more you can charge/discharge a batterie. But impedance will vary during the life of the cells, going higher and higher on every charge. And this may be worse than the loose of capacity, at least for some categories of models. But happily (for the producers), most modellers dont measure the impedance of there batteries.

But now to the main point. The batteries sold to the modellers aim at having the most capacity possible at the least weight and the lowest impedance. That means that the separators are getting thinner and thinner to get low weights, low impedance per energy output. This separators are deteriorating faster than thicker ones. The story repeats itself as happened to the NiMH batteriers. Trying to put more and more capacity into the cells the quality and working life diminuished rapidly. As happened to the last NiMH (4600mAh) cells sold where 50% of the cells arrived already with 0 V tension and had to be put into the bin befor ever used.

This is demonstrated by the fact that a LiPo cell from a serious producer has low C rating, is heavier than counterparts, higher impedance than others but
LAST MUCH LONGER WITHOUT SERIOUS DETERIORATION ON CAPACITY AND IMPEDANCE!

Going back to the initial question, if you buy high C rated, high capacity batteries usually sold to modellers try to put your hands on fresh ones. But how to control that???

Urs
I'll go with that.  I've found that some lipos last much longer than others.  When manufacturers started really bumping the C ratings, there were numerous complaints about rapid deterioration and low number of cycles.  

I have some lipos that have lasted for years, while being stored with more than a light charge.  What I've found is a happy medium between storing such that I can fairly readily charge for a flight, while not killing my lipos from storing overcharged.  Storing with an initial voltage of over 4V per cell seems to be the point I've found that will rapidly reduce lifespan, determined from a number of examples.  Storing at slightly below has not seemed to readily destroy them, while I can charge one, or several for that matter, for flights in a reasonable time frame one year later.  I also rarely charge lipos beyond 4V per cell, as we don't always fly on a battery that we charged and planned to fly on the following day.  At that level, I have more than ample flight time for pretty much everything other than demanding EDFs.
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Manne
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« Reply #17 on: December 11, 2014, 05:11:31 AM »

Hi Konrad, (and others) the batteries are LiPo's (18V 5400mAh) --- what else works?
Sorry that I have taken a while to reply, but life, in the form of a beautiful trip to Indonesia got in the way Smiley
The specific item I am referring to was purchased a year ago, and I suddenly realized that it had been sitting on the shelf for far too long. If it is kaput that is my problem. I measured the voltages and they were all at +/-3.85v per cell. I must admit I was a little apprehensive and measured twice.
What should the impedence be, or is it an infinite variable and no one knows?
Regards
 Manne
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Konrad
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« Reply #18 on: December 11, 2014, 11:48:32 AM »

3.85v looks like a safe storage voltage for most lipo chemistries.  But if you have a plus or minus swing of 3.85v between the highest and lowest cell the battery is junk!

Impedance is a property best tracked. If you notice a sudden change it is time to investigate what is going on.

The best test of a battery is to do a load test and measure the capacity you extract from the cells.

".. what else works?" I hope that was a joke!

All the best,
Konrad
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Manne
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« Reply #19 on: December 11, 2014, 11:01:04 PM »

Konrad,
The cells are all 3.85 (+_ 0.02v)
Regards
Manne
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Konrad
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« Reply #20 on: December 11, 2014, 11:30:03 PM »

That sounds a lot better!
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Manne
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« Reply #21 on: December 12, 2014, 06:54:24 AM »

Konrad, I measured them this afternoon and the readings are: 3.82, 3.818, 3,82, 3.811 and 3.82.
The total voltage is 19.1 and Impedence, if I measured correctly (Ohms across 2 terminals) 0 ohms
Regards,
Manne
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Konrad
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« Reply #22 on: December 12, 2014, 10:05:42 AM »

Zero ohms? Are you saying you have an open circuit ? I don't follow your 19.1 voltage and Impedence statement. Impedence Is measured in milli-ohms (0.00x).
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Manne
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« Reply #23 on: December 13, 2014, 08:08:17 PM »

Hi Konrad,
Measuring the resistance is another story Huh My electronic/electrical knowledge is nil, so I could end up with a flash and a bang!
My son is studying engineering at University so I will pass the task on to him. In the mean time I will continue with what I know best and that is building aeroplanes:)
Regards
Manne.
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Konrad
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« Reply #24 on: December 13, 2014, 08:20:29 PM »

Zero ohms? Are you saying you have an open circuit ? I don't follow your 19.1 voltage and Impedence statement. Impedence Is measured in milli-ohms (0.00x).
Sorry, I mis read your post.  I now see your measured voltage is 19.1v.  And measured zero ohms across 2 terminals.

My response should have been zero ohms? Are you saying you have a shorted circuit. As I said earlier, Impedance is difficult to measure

Good to hear there are some that will carry on with engineering. But "Engineering" is a very wide field of study. Don't hold your son to the fire if he isn't studying how electrons move.

It's all about having fun. I too am constantly learning about our airplanes. Not just the airframes but also their systems.

All the best,
Konrad
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