Charging a 27s LiPo

[quattro]

Hi there,

i am reading quite a long time in this forum and i think it is relly great. A lot of useful information for anyone qho want to build his own ebike.

Actually i am using a 27s LiPo for my bike. The cells only have 4 AH and i am charging the cells with a common 6s LiPo charger one after another. So i have to go every hour to the charger and connect the next battery.

The target is to charge the battery pack without disconnecting and connecting it every hour. The charging time ist not very important, so overnight charging is ok.

I see 3 possible ways to charge the pack:

1. Using a 4x 6s charger like this one and install 4 separate 12 volt power supplys beacause of the common ground.
http://www.hobbyking.com/hobbyking/store/__56173__Turnigy_4x6S_400W_Lithium_Polymer_Battery_Charger_EU_Warehouse_.html

2. Using a 27s charger with 113,4 volt like this one.
http://de.aliexpress.com/item/lithium-lipo-battery-charger-e-scooter-chargers-27s-li-on-chargers-113-4v-5a-with-fan/32320350292.html?ws_ab_test=searchweb201556_2_79_78_77_91_80,searchweb201644_5,searchweb201560_9
In this solution i have to balance the packe with 5 Balancing units like this:
http://www.hobbyking.com/hobbyking/store/__10328__HobbyKing_8482_Battery_Medic_System_2S_6S_.html

3. Using a Radiolink CB-86 Plus charger that charges one pack afer another even when they are connected in serial
http://orlandoshop.info/radiolink-cb86-plus-6a-210w-lipo-balance-charger-discharger/
Have anyone ever tried to charge a serial connected pack with this charger? The manufacturer says that the charger can NOT charge a battery pack that is connected in serial, but i geuss they dont understood the question.

What do you think which way is good to charge the battery pack, when you can charge overnight and dont want to check the pack every hour or two?

Thank you very much for your replies.

Best regards

Jens Bultmann

 

[dogman dan]

Bulk charging can work for you, especially if you use the packs gently enough to not need to balance every cycle. If any packs get out of balance a lot constantly, get rid of that pack. Bulk charge only with packs you trust.

But the idea of putting them on a bulk charger and going to sleep is scary. If you do that, you MUST have them outside, in a place they could burn and not be any problem. Lots of people do the bbq grill, but still that grill must be located in a safe place. The balcony of an apartment is not good enough.

The key thing is to get enough wattage to not have to wait so long. Your pack is only 500wh, so a 5 amps bulk charger would do it in one hour.

Most likely that charger on ali express is a 250w charger, but that would still do it in a reasonable 2 hours.

 

[Ykick]

You can go something like this:

http://bestechpower.com/27Sto32Spcmbmspcbforli-ionli-polymerbatterypack/

4Ah cells/groups? Should be okay with the 35A version - they rate conservatively.

Or, perhaps a 13S and 14S BMS series wired to achieve your desired cell count protection?

 

[BVH]

Why not simply parallel charge them on a 2S-8S parallel (with balance feature and connectors) board such as this one? They are fully fused (main and balance circuits) protected.

http://www.revolectrix.com/MPA_XH.htm

I use two of them frequently.

 

[DrkAngel]

Test For Bulk Charge Feasibility

• Test all cells for:
• Self-discharge
• Comparative IR (Internal Resistance)
• Comparative Capacity

1. Carefully balance charge all packs
2. Confirm all cells of equal voltage, test after removed from charger for 1 hour (multi-meter at balance plugs)
label each cell with precise voltage - .01 needed .001 preferred
tape and felt tip marker works
3. Let set several days ... then re-test the voltage of each cell and compare to 1st measure
voltage loss is the Self-Discharge that must be (eventually) eliminated (some minor loss is to be expected, excessive discharging cells must be eliminated)
4. Connect cells in series ~24s-30s
5. Discharging gently through 2 - 120V 60w light bulbs should provide a 4 hour 1 time evaluation test.
6. At some time into test (1 hour?), measure and note the voltage of each cell.
This is the Comparative IR (Internal Resistance)
Higher voltage sag indicates poor IR
Exceptionally poor IR cells should be (eventually) eliminated
7. Continue discharge while testing voltage of every cell at intervals
Intervals should become closer as cells near "empty"
("empty" varies with battery brand-model and discharge rate)
Pay closest attention lowest voltage cell and watch for accelerated voltage loss = discontinue test
8. Let set several minutes
9. Measure and note cell voltages
This indicates Comparative Capacity
E.G. - (3 hours) 3000mAh + 3.725V (residual V)
Any notably lower cells should be eliminated-replaced - they diminish entire pack capacity
10. Recharge and balance all cells precisely ... again
Run a typical eBike discharge till your considered "empty"
Test each cell and compare voltages >> as a confirmation via higher discharge rate of cells of similar condition-capacity
11. If there are no notably self discharging cells, no cells of deviant IR and all of similar capacity ...
12. Test a bulk charge at ≤.5C (≤2A for 4Ah pack)
13. If cells return to equal beginning voltages at full charge ...
Congratulations!
Your pack is a good candidate for bulk charging (monitoring and occasional balance charges recommended as needed!)

If not ...
Replacing
#1 self-discharging cells
#2 poor IR cell
#3 poor capacity cells
can put you into good condition for bulk charging!