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Old Jun 24, 2011, 10:18 AM
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I'm sorry, but we don't accept any documents unless they have been funded by non-profit organizations and have appeared in at least 3 peer-reviewed journals.

I
Indeed, any ipse dixit will do!
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Old Jun 24, 2011, 10:22 AM
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Originally Posted by Julez View Post
This method is built up on the theory, that a cell can be divided into the charge storage (galvanic cell), and a resistor (the inner resistance).
This "inner resistor" is not even similar to a resistor.

Do you mean just an ohmic resistance or a serial connection of ohmic resistance and Warburg impedance?

At what frequency do you expect to measure correctly "inner resistance"?
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Old Jun 24, 2011, 10:46 AM
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To bring this back to the iChargers, I have no idea what they do, but I suspect "nothing" as we already know they have issues reading cell voltages because they don't compensate for the voltage drop of the wires.
Perhaps not 100% correct as they do use the balancing leads (if they are connected) to read the individual cell voltages. hese are used because they are not carrying much current and in theory have extremely low voltage drop. Problem is that often balancing connectors make very poor contact and also often extensions,PCBs with poor connectors and extremely small traces are used and at times even multi extensions and adapters are used.

The tech support at Hyperion have always advised not using long balancing leads and in fact even advised ensuring that all balancing leads on a battery were the same length.

Some chargers are much better at taking sample reading and adjusting accordingly.

Charles
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Old Jun 24, 2011, 11:01 AM
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Originally Posted by Julez View Post
During charge, the total cell voltage is allowed to go up to 4.35V (LiPo), but only, if the "resting voltage" (without current) of the cell stays at or below 4.20V.
It is said, that this considerably reduces charge time, while not compromising the batterys cycle life.
With a cell of very high internal resistance, yes, it could dramatically reduce charge times. It could also create safety issues when charging cells in series unless the algorithm was very carefully thought out. We all know that all cells with a series pack do not necessarily have the same internal resistance. The algorithm would obviously need to consider this to avoid dangerous overcharge of cells with lower internal resistance.

Might be beneficial to reduce charge times of some of my older 18650's that I use in my flashlights.

Since today's lipolys have extremely low internal resistance and charge times are in the minutes, I see it providing negligible benefit for lipoly flight packs.

Mark
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Old Jun 24, 2011, 11:02 AM
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I don't think the suggestion was to measure the "resistance" but simply to pause the charge current so that any series impedance would no longer be affecting the cell voltage measurements.

iChargers at the moment do not do this, they apply the charge current continuously. That means the cell voltage measured is the applied voltage across each cell, not the rest voltage.

Using the rest voltage would reduce the sag that we see in the cell voltages at the end of charging but I am not sure by how much given that charging terminates at a small fraction of the initial charge current. I guess for high-C charging it would make a more significant difference than for 1C charging.

It is worth considering that, for example, turning the charge current off for 1 second after each 10s operation would lengthen the charge time by 10%. Whether the overall charge time would end up shorter due to a small extension to the CC-phase that would result from the cutoff being measured on idle cells is far from clear to me. I would be happy to do some tests with beta software to find out.
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Old Jun 24, 2011, 11:05 AM
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Good points Mark. Certainly for those of us already charging at 3C and above a small percentage reduction in the charge time would make little practical difference.
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Old Jun 24, 2011, 11:38 AM
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During discharging, interrupting the current to measure the voltage should be beneficial, especially for high internal resistance batteries - even if it is not done not during charging (assuming unbalanced operation). The Robbe Powerpeak does that during discharge.

While charging that might be less of a problem, because the current is tapering to a minimum in the CV phase; but during discharging the process is stopped at a voltage that is the determined cutoff voltage plus the voltage drop on the inner resistance. If the inner resistance can be compensated for by the charger, this might not be an issue.

This is one reason why I keep using the Robbe Powerpeak with Nicads, instead of the icharger.

Bulent
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Old Jun 24, 2011, 01:24 PM
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Here is a translation of postings of people having actual experience with a fast mode:

http://translate.google.com/translat...n&hl=&ie=UTF-8

Even the most reputable charger/battery expert in Germany, Gerd Giese, says that the fast mode works very well.

Here is a test from a guy who programmed a fast mode in his selfbuilt charger.

http://www.rclineforum.de/forum/boar...e_2#post823778

Most interesting excerpt from a test with an older battery pack:

Quote:
9. laden FastMode 3A (charging in fast mode)
22min 45sec, 1075mAh temp ca 35C

10. entladen 3A (discharge)
21min 50sec, 1053mAh temp ca 45C

11. laden Standart 3A (charging in standard mode)
47min 35sec, 1085mAh, temp ca 20C

12. entladen 3A (discharging)
1089 mAh
In this case, his fast charge algorithm cut the charge time in half.

Nowhere in any postings people reported negative experiences with a fast charge mode.

I think this method offers too much potential to casually dismiss it.

By making the CV phase more efficient, smaller Charging rates could be applied during the CC phase. Thus, to achieve the same charging time, less initial current is needed, which is good for any battery.
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Old Jun 24, 2011, 01:55 PM
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Originally Posted by Julez View Post
Hi!
<snip>

- Cut-off (they mean input voltage here): 1-1.3V lower than what you power supply's voltage rating is. 12V when using a starter battery in a car, 11v when using another 12V PB battery.

<snip>

That was it. Hope you find it helpful at least a little.

Cheers,

Julez
Thank you for this nice write up Julez

Just set it up, I'm ready to do my 1st charge on my new 306B

The above setting I'm not sure about. I use a Meanwell SP-750-24 PSU, so do I set the cut-off voltage to 23 (default is 4.5V)?

Thanks in advance,


-Patriek
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Old Jun 24, 2011, 04:36 PM
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Originally Posted by Julez View Post
By making the CV phase more efficient, smaller Charging rates could be applied during the CC phase. Thus, to achieve the same charging time, less initial current is needed, which is good for any battery.
If you choose a charging rate small enough maybe CV phase can magically disappear at all?
I don't get it. When I charge my lipos @1C from storage mode CC takes 40 minutes and CV eats additional 5. What do you want to achieve? When do you expect a balancer to find time for operation?
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Old Jun 24, 2011, 05:13 PM
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There has been plenty of debate on the use of a charge method for lipos that takes into account pack resistance to allow a higher than 4.20V/cell voltage, with the goal being a rebound or resting voltage voltage of 4.20V. Instead of a CC stage terminated by a C/x value, the charge stops as soon as the final cell voltage limit is reached.

In the end, the debate is really on whether or not lipos like to be quickly "topped off" or slowly filled near the top, and if the temporary subjection of the cells to higher voltage causes measurable damage.

I'm not sure anyone in this hobby knows the answer, and the industrial applicants of this technology in many industries still hold to the C/x charge termination method (as far as I am aware). Another potential issue or concept I don't understand is how imbalance is affected/handled in this "fast mode" due to variations in cell capacity matching, initial charge state, and cell internal resistance. That said, I do believe this concept has merit and I'm sure folks with significant R&D have or are exploring this.

- David
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Old Jun 24, 2011, 05:21 PM
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I charge at 3 to 12C and the only time it takes more than 20 min. to charge a LiPoly is the first few cycles of a new one which I do at 1 or 2C depending on the quality of the LiPoly.

I have not posted this in some while but here I go again.

I very much dislike any changes which really server no practicle purpose. Every firmware change is yet another opportunity for qnother Bug to creap into the firmware and said bugs can cause major problems for many and be difficult to find and eliminate. After many years the iChargers are at last fairly stable and I for one would like them to remain so.
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Old Jun 24, 2011, 06:40 PM
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Originally Posted by everydayflyer View Post
I very much dislike any changes which really server no practicle purpose.
Precisely why my three 106B's are still running 3.09 firmware circa 2008. After months of watching users brick their chargers by beta (at best) firmware, I decided that mine were just fine. While some of the new features were niceties that I wouldn't mind having, there were none that were necessities. Now that 3.14 seems to be quite stable, I might flash 'em at some point if I get the itch.

Mark
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Old Jun 25, 2011, 03:49 AM
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Quote from the datasheet of the bq2057 charger IC from Texas Instruments.
Quote:
To reduce charging time, the bq2057 uses the proprietary AutoComp technique to compensate safely for internal impedance of the battery pack.
http://focus.ti.com/lit/ds/symlink/bq2057.pdf
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Old Jun 25, 2011, 05:42 AM
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And you think the iCharger doesn't compensate?
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