GoldenMotor.com Forum
General Category => General Discussions => Topic started by: Just on October 07, 2012, 06:15:03 PM
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Hello All,
My question is "How to choose the right Charger?"
Actually there are many of them in the market... Prices are vary from several dollars to several hundreds.... There are "smart" chargers, there are "cleaver" ones, there are "intelligent" and so on... So, how to choose?
Actually I need 24V charger for my LiFePo4 10Ah pack. Hopefully it may have a battery internal resistance meter, but not for extra $100 price...
Any comments are welcome.
Thank you!
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Any responses? Comments?
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A you can guess; there's no 'right' charger out there, but for me, this one come close:
http://www.jun-si.com/EnProductShow.asp?ID=93 (http://www.jun-si.com/EnProductShow.asp?ID=93)
The price are around $200, and you have to be able to make your own connections for balance etc...
;)
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I charger :(
Hyperion ;D
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That kind of posting are not very helpful... :-\
I'm sure the Hyperion are good chargers, but the deciding issue for me was the iCharger's ability to show me the IR for all the cells individually; I couldn't find that in the Hyperion specs...
But nothing are perfect; not even the iCharger... ;D
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Yes they have!
Just download the manual en have a look :)
Hyperion support is great, firmware etc etc...
Also I own a lot of chargers, Icharger blows up after couple of charges.
My friend owns Icharger and he hate it when he switched to Hyperion.
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Thank you guys for your posts! And what's about all these terms like "smart", "cleaver" and "intelligent"? Are they just marketing term or technical meanings as well?
Actually I need a charger, which is able to determine whether the cells full or not, and if they are then stop the charging. I don't need a balance port in the charger since by battery has BMS, which balances of the cells during the charging.
As for the Internal Resistance measurements, just take a look at this device: http://www.ebay.com/itm/160504165351?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
What's your opinion on this charger: http://www.ebay.com/itm/271057048976?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 - it's cheap enough... What questions should I ask the manufacturer before purchasing this charger?
Thank you!
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The resistance looks fine to me!
The charger is dumb charger (no inetrnal bms).
But I prefer this kind of charger, because your battery back has an internal bms.
This charger has fixed output, so if you like to play with output (current) go for an intelligent charger.
But when you will buy Icharger etc etc.
You have too unhook the battery pack bms, soo...make your choice :P
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The resistance looks fine to me!
You will have to be very careful not to accidentally reverse the polarity or it will blow the meter.
Check out this review by Dr Bass on YouTube (http://www.youtube.com/watch?v=yohD2mtLYbQ) for more details.
Alan
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Haha that's bad!
So maybe looking for another model with reverse protection?
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Alan, thank you for your warning!
What about these devices:
http://www.hobbyking.com/hobbyking/store/__22631__Turnigy_7_in_1_Mega_Meter_.html
http://www.hobbyking.com/hobbyking/store/__22412__Turnigy_Mega_Checker_4_in_1_Battery_Checker_Monitor.html
Thank you
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And what about these device:
http://media.hyperion.hk/dn/sentry/
Interesting how does it able to measure a remaining battery capacity...
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I don't see any reference to LiFeP04 cells in the info - only LiPo. Do the different cell types have internal resistances in the same range?
With my limited knowledge of chemistry, i'm probably lucky to be alive :)
Jeff
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What about these devices:
http://www.hobbyking.com/hobbyking/store/__22631__Turnigy_7_in_1_Mega_Meter_.html
http://www.hobbyking.com/hobbyking/store/__22412__Turnigy_Mega_Checker_4_in_1_Battery_Checker_Monitor.html
7 in 1 video review (http://www.youtube.com/watch?v=47OcIdd-1Zw)
4 in 1 video review (http://www.youtube.com/watch?v=MMrBuCeeXv4)
I really don't like the idea of having a pair of male bullet connectors on the battery supply lead for the current measurement on the 7 in 1 meter, if the unit was accidentally pulled and the battery leads came out, a short circuit across the battery would most likely occur.
The reviews on HobbyKing's website do not inspire confidence either.
The 4 in 1 Mega Meter has suffered numerous failures due to an incorrect polarity on the USB charging lead ???, and the 7 in 1 Mega Meter apparently has a very inaccurate Internal Resistance meter:
The IR measurement is hopeless. Uses a roughly 0.5Amps load and two wire method which is useless for modern LiPos.
I got readings varying from 104mOhm to 41 mOhm per cell on a 4S 3700 mAh battery as I watched.
The actual IR per cell is between 3.96 mOhm and 4.20 measured with an ESR/IR meter!!
Perhaps my estimated internal resistance of 2.5 mOhms (http://goldenmotor.com/SMF/index.php?topic=4612.msg26626#msg26626) is about right for my almost new 5Ah pack.
And what about these device:
http://media.hyperion.hk/dn/sentry/
Interesting how does it able to measure a remaining battery capacity...
The estimated remaining battery capacity is presumably based on the actual battery voltage and would have to be measured with the battery under a no load condition.
Alan
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"The estimated remaining battery capacity is presumably based on the actual battery voltage and would have to be measured with the battery under a no load condition" - is dependency linear? What's the cell voltage be considered as 25% of capacity? 50% of capacity? 75% of capacity? 100% of capacity?
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The voltage drop during discharge is not linear:
(http://www.arhservices.co.uk/GoldenMotor/Batterycomparison.JPG)
I'm guessing that the software will contain a look up table containing a series of 100 measured cell voltages (and their corresponding remaining capacities as a percentage) compiled from cell testing, which the lowest cell voltage of the battery being monitored is then compared against in order to roughly estimate the remaining capacity of the battery pack.
Alan
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Okay, thank you!
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Is there a way to achieve/get such Look-Up-Table for LiFePo4 cells?
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If you can't find anything on the web, you would need to carry out your own discharge test at 0.1C discharge rate over a 10 hour period, using a suitable charger equipped with a discharge function and PC interface to monitor and record the entire discharge process, and then study the recorded data either during or after the complete test.
For example, a 5Ah cell would need to be discharged at a constant 500mA and the voltage readings noted at 50mAh or 6 minute intervals throughout the test.
Here is a typical graph to give you an idea of what the test results should look like:
(http://www.arhservices.co.uk/GoldenMotor/LiFePO4dischargecurve.JPG)
On the graph above, the voltage difference between 20% and 80% consumed capacity is only 0.1V, but the difference between the no load state and loaded state could possibly be greater than this, so maybe it's not worth all the hassle.
Alan
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yap... as for the Battery Checker http://media.hyperion.hk/dn/sentry/ (http://media.hyperion.hk/dn/sentry/), which I mentioned in the post, it's very interesting how does it calculate the remain battery capacity - based on the load or unload battery conditions...
Should battery discharge curves would be different for different discharge currents (from remaining capacity point of view)?
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Yes Dmitryl, the discharge curve does vary according to the current load:
(https://www.benergytech.com/style/js/plugin/editor/php/upload/39861420884145.jpg)
This is why Hyperion's EOS SENTRY Battery Checker is designed to be used on a disconnected pack, which would obviously be in a no load condition. With radio control electric models, the first thing you are supposed to do when retrieving your model is disconnect the battery (or turn off the power switch) for safety reasons. Therefore testing the remaining capacity at the end of each flight or race should automatically be done with the power turned off, so theoretically, the battery is always being checked under "no load" conditions.
Take a look at the EOS Sentry in action on YouTube (http://www.youtube.com/watch?v=MEdqXJ6ZYW0).
Even if safety guidelines were not being followed, with most of the typical R/C models, failing to turn the power off would only result in minimal standby current being drawn by the receiver and speed controller. So, the estimated remaining capacity should still be reasonably close if the throttle and servos were not being operated during the test. ;)
Alan
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This EOS SENTRY Battery Checker indicates only the remaining capacity of the battery without saying the actual capacity, right?
So, what's good for? 10Ah battery with edging loose a maximum capacity it's able to hold. So, as for the EOS SENTRY Battery Checker, what capacity does it refer when calculate the remaining capacity?
Thank you!
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The iCharger can tell you the capacity of the pack by discharging it at a set current. :)
I don't have a snapshot of that, but here's a logview of a charging cycle of a tired 36V, 16Ah LiMnPo4 battery from GM, which tells you much the same...:
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WattUp Meter could also do this job, but a full battery charge/discharge should be involved... Not always practically.... Probably having such Battery Checker could help solving some doubts regarding the battery ...
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The only way to get an absolute precise Ah capacity reading of a battery, are to charge it up and Discharge it with a 'normalized' current (the current the battery are discharged at on normal use) while timing the discharge process.
All other methods would be approximate.
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This EOS SENTRY Battery Checker indicates only the remaining capacity of the battery without saying the actual capacity, right?
So, what's good for? 10Ah battery with edging loose a maximum capacity it's able to hold. So, as for the EOS SENTRY Battery Checker, what capacity does it refer when calculate the remaining capacity?
If you have a well used 10Ah battery that is only able to deliver 5Ah before it is exhausted, I would expect the estimated remaining capacity to be a percentage of the battery's actual capacity rather than its rated capacity.
So if the battery checker estimates 40% remaining, I would expect to have approximately 2Ah remaining (40 / 100 x 5) for that particular battery.
Alan