Hung Chang os615s Battery

[spec]

Just one point, it may be best to go for five LiIon batteries in series to give a nominal voltage of 5 * 3.6V = 18V, a charge voltage of 5 * 4V =20V, and a cut off voltage of 5 * 3V = 15V. The determining factor will be the lowest voltage that the scope will operate from. The external range, from your figures is 11V to 30V, so presumably the permissible battery voltage will be the same.

The battery charging arrangements need further detailing, but we can sort that further down the line. Best not to cover too much ground in one go.

spec

 

[KeepItSimpleStupid]

Pleas re-think the Li-ION power source: **broken link removed**

 

[Tony Stewart]

If I charge 6 li-ion cells Which I believe would be 22.2v with a constant 18v would that be ok do you think?

Vbat =3.7 to 3.5 ,maybe 3.3 for heavy load BUT at 3V it is dead AND getting damaged so 6*3=18V is n.g.

only 22.2 +/-0.5 is ok unless it is a smart charger or you dont mind shorter capacity or shorter lifespan

 

[spec]

Vbat =3.7 to 3.5 ,maybe 3.3 for heavy load BUT at 3V it is dead AND getting damaged so 6*3=18V is n.g.

only 22.2 +/-0.5 is ok unless it is a smart charger or you dont mind shorter capacity or shorter lifespan

Where do you get your figures from Tony. A LiIon battery is certainly not dead at 3V.

In fact, a cut off voltage of 3V is on the conservative side.

spec

 

[Tony Stewart]

My references are many datasheets from many std LiPo cells OEM datasheets not at my finger tips

the capacity below 3.2C is far less than 20% and risks chemical degradation at 3V (depending on cell temp)

it's dead due to high ESR with voltage dropping quickly here the cut-off is 3.2V but worse it's Ah capacity declines quickly when "over-discharged"

 

[spec]

Not sure what that graph is showing Tony.

For some reason you keep referring to LiPo cells, which are not recommended for this application. Genuine LiPo cells have a nominal voltage of 3.4V rather than 3.6V for LiIon cells. That is a full 200mV difference.

(Panasonic NCR18650B datasheet attached to post #24)

spec

Charging Non-cobalt-blended Li-ion
While the traditional lithium-ion has a nominal cell voltage of 3.60V, Li-phosphate (LiFePO) makes an exception with a nominal cell voltage of 3.20V and charging to 3.65V. ... (See **broken link removed**.)

**broken link removed**

Most mobile phones, laptops and other portable devices turn off when the lithium-ion battery reaches 3.00V/cell on discharge. At this point the battery has about 5 percent capacity left. Manufacturers choose this voltage threshold to preserve some energy for housekeeping, as well as to reduce battery stress and allow for some self-discharge if the battery is not immediately recharged. This grace period in empty state can last several months until self-discharge lowers the voltage of Li-ion to about 2.50V/cell, at which point the protection circuit opens and most packs become unserviceable with a regular charger. ( **broken link removed** )

**broken link removed**

 

[Dudley]

OK I 'm a bit slow but finally I understand what I need to do and how to do it so I have ordered the bits and will let you know how I get on.
Many thanks to everyone
Dudley

 

[Tony Stewart]

My graph shows that if you allow float charge to 3.9V and only run down the battery charge 50%SoC you get 5x more Ah* cycles delivered.

Your graph shows if you use the batteries at -20'C the ESR rises so that Voltage drops by 0.5V
Here: I show your spec by Panasonic and the earlier one I read which used a slightly higher CV charge rate ( both Dated 2012 )
The extra capacity in ORANGE I coloured to show what is left below 3V when the rate of voltage drop speeds up rapidly. ( Read declines quickly .. ok almost dead

 

[spec]

Still not sure what you are demonstrating Tony. The issue is that at 3V LiIon batteries will not be dead, unless you mean by dead, discharged to 5% of their capacity rather than destroyed.

The normal regime for LiIon batteries used in billions of consumer equipment throughout the world is, charge to 4.2V, with smart control from 4V to 4.2V, and discharge to 3V.

In many equipments, if the cell voltage then drops to 2.5V due to self discharge over a period of time, the battery will be disconnected and will no longer be able to be charged by a standard charger (you need to apply about 9V upwards to reset the protection circuit).

spec

 

[Tony Stewart]

I'm sure you can understand what I am demonstrating.. I forgot "dead" battery in cars means no useful charge left to startup , while "dead" can have two connotations.

I doubt the scope would even start up at 3V *6 =18V due to high ESR. and load impedance of DC -DC converter on power up.

 

[audioguru]

The receivers in my radio controlled model airplanes pulse the motor when the Li-Po battery has dropped to 3.15V per cell as a low voltage warning and cuts off the motor when it drops to 3.05V per cell, then there is enough power to steer it during a landing. The manufacturer says and we all agree that such low voltages reduce the life of the battery.

 

[spec]

The receivers in my radio controlled model airplanes pulse the motor when the Li-Po battery has dropped to 3.15V per cell as a low voltage warning and cuts off the motor when it drops to 3.05V per cell, then there is enough power to steer it during a landing. The manufacturer says and we all agree that such low voltages reduce the life of the battery.

A Lipo battery is not being used A standard LiIon battery is being suggested. how many times has that got to be repeated

The use of any battery reduces its life!

The next thing you will be saying is that the batteries will explode and everybody will be killed

spec

 

[Tony Stewart]

spec as far as I know Lithium Polymer and LiPo and Lithium Ion Polymer mean the same value thing today, as what you are thinking of never became mainstream,. https://scottiestech.info/2015/06/21/lithium-polymer-vs-lithium-ion-batteries-whats-the-deal/

 

[spec]

Tony it is quite true that many batteries that are described as LiPo have the same characteristics as LiIon, but there are also genuine LiPo batteries which have a lower terminal voltage nominally 3.4V versus the common 3.6V. Many battery chargers are either designed to handle LiPo batteries only or have a switch to select either chemistry.

I really can't understand all this angst about LiIon batteries, As I said before, they are used by the billion throughout the world and most people walk around with around three LiIon batteries in their pockets (in their cell phone battery packs).

Neither do I see the reason for all this focus on the battery minimum voltage. Quite honestly, it is not in the order of things and there are much bigger issues to be sorted in the OP's application (if I read him correctly he has got fed up with all the flack on this thread and gone elsewhere). So lets agree on a voltage that keeps everybody happy. Shall we say 3.1V; it makes absolutely no difference to me.

I use all sorts of charge discharge regimes, depending on the application: extremely conservative for rechargeable battery backing to very aggressive for high power applications as in power tools where the batteries are caned to death as they are in laptops. I am on my second set now in three years.

Over and out.

spec

 

[audioguru]

My single cell Li-Po batteries have 3.7V printed on them and are fully charged at 4.20V exactly like a Li-Ion cell. The 2-cells batteries are marked 7.4V. These voltages (3.7V per cell) were chosen because it is halfway from minimum (3.2V) to maximum (4.2V).
They are 3.7V per cell when purchased and I store them at 3.7V.

 

[spec]

My single cell Li-Po batteries have 3.7V printed on them and are fully charged at 4.20V exactly like a Li-Ion cell. The 2-cells batteries are marked 7.4V. These voltages (3.7V per cell) were chosen because it is halfway from minimum (3.2V) to maximum (4.2V).
They are 3.7V per cell when purchased and I store them at 3.7V.

Thanks for that AG. 4.2V is a heavy charge voltage and will shorten the battery life- one thing LiIon/Lipo cannot take is over-charge. The 3.2V minimum voltage is good from a battery life point of view. For a conservative regime, ease of charging, and long battery life 3.2V low to 4V charge is a good choice. 3,7V nominal, normally corresponds to a battery that has had a high charge (4.2V). 3.6V is the nominal voltage for the average LiIon battery- see battery university.

Anyway, I think we are all talking the same language about LiIon now, which is good news as far as I am concerned.

spec

 

[Tony Stewart]

I recall NASA discovered that Li-ions above 4.10V/cell tend to decompose due to electrolyte oxidation on the cathode (+), while those charged to lower voltages lose capacity due to the solid electrolyte interface (SEI) building up on the anode (-) with Lithium Oxide and Lithium Carbonate.

This was verified by Dalhousie University by Dr. Dahn who proved battery death is accelerated for the duration above 4.1V, while NASA knew that capacity was reduced to 60% with this method of reducing Vcv charge to 3.9V MAX. This enabled them to use Lithium Ion batteries for > 8yrs.

I later show how one major brand total lifetime Ah*cycle delivered was increased by 5x over the typical 500 cycle Ah rating.

The Depth of Discharge also affects aging rating. If you are familiar with how Mil-Std_HDBK 217 works with MTBF , they model the accelerated failure rate with formula based on stress factors. They may have a model now for LiPo's that uses factors for %DoD and CV voltage.

I would expect time, t becomes an exponential MTBF accelerator for both of these factors outside certain thresholds and varies with chemistry and quality of contaminants in the electrodes and electrolyte.

I once plotted the lifetime Ah capacity for one brand based on 50% min. DoD and CV max with available Ah for each cycle and number of cycles in life time, which I will show below, but I lost the source data.

Charging at ANY rate consists of measure Voc, measure V at pulse load , measure initial ESR and final ESR with CC to Vcv then Vcv to 10%CC then shuttdown. The risk here is that one cell reaches 100% SoC before the others and the balancer cannot bypass enough current during CC mode when current is reduced. i.e. Balancers may not be able to dissipate enough heat for a 0.5C rate if this implies 5400mA*0.5*4.2V = 11.34 watts !! per cell balancer.

FWIW below with little explanation...

If battery capacity is Ah=C , left vertical axis above is number of C cycles of battery life achieved vs slow CV charge voltage and 50% MIN DoD. but discharged at any rate like 0.5C to 2C depending on DoD rating from 10% to 25% to 50% to 100%. ( I will try to find source info) Note longest lifespan is 50% DoD for recharge threshold. (Lenova has a smart charge algorithm using these parameters)

The solution as I see it is to get a better charger with the following characteristics;

• programmable CV, CC and %%CC for shutoff levels,
• measures Rs or ESR imbalance throughout the charge cycle ( very important for self-heating) ( OR )
• Commutates bypass current with flying inductors ( like a SMPS) ( flyback half-bridge between cells, rather than passive TVS or active zeners with excess ESR )
• Computes actual Ah supplied to each cell and compares with estimated %DoD based on initial tests above (Voc, ESR) rather than to whole array or simply just ESR at end of charge.

Consider that in Car batteries with 850 A crank capacity at 7.5V each cell ESR must be balanced within 1% when new and when this mismatch rises , acid boiling in the weakest cell due to ESR*I^2 accelerates battery death quickly. Same holds true for LiPo's. The greater the ESR mismatch with a a passive balancer, the greater risk to cell death can occur due to one cell reaching full charge while others still in CC mode.

FYI https://www.dal.ca/diff/dahn/publications.html

 

[audioguru]

In addition to my Li-Po model airplane and drone batteries I use 18650 Li-Ion batteries harvested from old laptops. I charge and discharge them the same:

 

[Tony Stewart]

 

[Dudley]

Hi everybody and thanks for all your help. I know its been a while but at last I have achieved my aim after a few teething problems and would again like t thank you all for your assistance
Dudley