Looking for good source of 21700 LiFePO4 batteries

[chaosdsm]

Other than amazon, alibaba, aliexpress, banggood etc... is there a good source for good 21700 LiFePO4 batteries that ship to the US? I'm wanting to replace some single cells in 4 solar lights that currently have 18650 1000mAh LiFePO4 cells. The battery space will fit a 21700 flat-top cell and the lights are currently fully charged in about 3-4 hours clear sunlight / 4-6 hours partly cloudy sunlight so it shouldn't be a problem with the extra capacity. They run about 8 hours at night then step down to about 50% brightness. On the longer nights of the year, they are barely lit at dawn, I'd guess about 10% of initial brightness.

Only 21700 LiFePO4's I've found are from Selian Energy (never heard of them) labeled as Hakadi (never heard of them either) & show 3.0Ah on them.

$20 for 4 cells with free shipping - seems to good to be true.... but if there are no other options, I'll give them a try.

 

[chaosdsm]

No replies.... I guess I'll be the guinea pig then.

 

[hamhanded]

I've been looking too. I haven't even stumbled upon those. Where did you buy them?

 

[chaosdsm]

I've been looking too. I haven't even stumbled upon those. Where did you buy them?

Just purchased this morning. I found them on "Selian Energy" and they have PayPal checkout available.

 

[chaosdsm]

Those batteries just arrived today:



I KNOW.... the charger does not support LiFePO4, just making sure the charger works like it's supposed to.... 4 batteries charging at 1A removed from charger about a minute after taking the photo.

I'll actually test these with my Imax B6 chargers to ensure they live up to the spec's.

Manufacturers specs say:
Nominal voltage: 3.2V
Standard capacity: 3000mAh
Min capacity: 2800mah
Size: 71.8*21.5mm
Weight: 65±5g
Charge voltage: 3.65V
Cut-off voltage: 2.0V
Internal resistance: ≤30mΩ
Standard charge current: 0.5C
Standard discharge current: 1C
Max charge current: 1C
Max. continuous discharge current: 3C
Max. Pulse Discharge Current: 5C

A bit oversized I would say, and if capacity is based on a 3.65V charge & 2.0V discharge cut-off, this might be a bit disappointing....

Most of the 21700 flat top spec's I've seen (regular Li-ion, not LiFePO4) are 20.4mm to 21.2mm diameter x 69.5mm to 71mm long. All 4 of the one's I received measure 21.72mm x 72.03mm +/- 0.005mm, but on the diameter, I measured at the widest point, i.e. with the wire that runs up the side.

 

[hamhanded]

Wait, there's a wire up the side? They're protected? I wonder why.

 

[chaosdsm]

Wait, there's a wire up the side? They're protected? I wonder why.

Not protected... I just couldn't think straight last night, it's the seam where the outer steel case overlaps slightly.

 

[chaosdsm]

Been testing these for the last several days.... I'm not impressed... I'm seeing capacity readings all over the board... from a low of 2461mAh to a high of 3119mAh

I decided to get the Tenergy T180 hobby charger which supports 5A discharge / 10A charge, most of the testing was done on it. None of the charge / discharge cycles exceeded the maximum (1C charge / 3C discharge) listed by the manufacturer of the batteries. All discharge cycles were run down to 2.80V and all charge cycles were run up to 3.60V All battery voltage was tested with Klein DMM720 digital multi-meter 30 minutes after cycle finish. Battery holders were individually marked to make sure batteries did not get mixed up. All mAh readings were taken off the charger displays at end of cycle.

@4.5A discharge:
C1 = 2580mAh @ 3.189v
C2 = 2568mAh @ 3.226v
C3 = 2581mAh @ 3.232v
C4 = 2578mAh - voltage not recorded due to sleep

@3A charge:
C1 = 2725mAh @ 3.407v
C2 = 2689mAh @ 3.415v
C3 = 2581mAh @ 3.450v
C4 = 2461mAh @ 3.395v

@3A discharge:
C1 = 2714mAh @ 3.222v
C2 = 2701mAh @ 3.217v
C3 = 2717mAh @ 3.217v
C4 = 2716mAh - voltage not recorded due to sleep

@2A charge:
C1 = 2672mAh @ 3.407v
C2 = 2670mAh @ 3.430v
C3 = 2581mAh @ 3.450v
C4 = 2658mAh - forgot to check voltage on this one

Added the SkyRC Imax B6 AC V2 charger at this point to speed things along cells charged / discharged marked with * were done on the Imax.
@1.5A discharge
C1 = 2806mAh @ 3.221v*
C2 = 2691mAh @ 3.218v
C3 = 2792mAh @ 3.208v
C4 = 2795mAh @ 3.187v*

@1.5A charge
C1 = 2753mAh @ 3.436v
C2 = 2635mAh @ 3.426v*
C3 = 2807mAh @ 3401v
C4 = 2806mAh @ 3.414v*

@1A discharge
C1 = 3099mAh @ 3.033v
C2 = 2823mAh @ 3.127v*
C3 = 3119mAh @ 3.010v*
C4 = 3099mAh @ 2.970v

@1A charge
C1 = 2835mAh @ 3.429v*
C2 = 2751mAh @ 3.448v
C3 = 2879mAh @ 3.398v*
C4 = 2862mAh @ 3.431v

@0.5A discharge
C1 = 2973mAh @ 2.988v
C2 = 2847mAh @ 3.037v*
C3 = 3011mAh @ voltage not recorded due to sleep
C4 = 2862mAh @ 2.998v*

@0.5A charge
C1 = 2679mAh @ 3.451v
C2 = 2716mAh @ 3.415v*
C3 = 2755mAh @ 3.379v
C4 = 2733mAh @ 3.395v*

Definite capacity improvement over 18650 LiFePO4 options, which was the main thing I was looking for out of the 21700 format, but to get such mixed results out of the cycles...

 

[chaosdsm]

Wanted to add a follow-up. I recently bought the SkyRC MC3000 charger and custom programmed a discharge > charge > discharge > charge cycle for these batteries. BTW... these batteries just BARELY fit in the charger, I had to wiggle them in just right.

First discharge cycle ended with all batteries at about 2,950mAh discharge capacity at 1A discharge down to 2.8V. First charge cycle (1A charging) just ending with all batteries at or over 2927mAh. So definitely better results than my other testing.


I might also run a cycle 2A discharge / 0.5A charge & see what those results might be....

I picked up some protection circuits from battery space for 2S operation and 5A discharge cut-off

 

[ebuchner]

Wanted to add a follow-up. I recently bought the SkyRC MC3000 charger and custom programmed a discharge > charge > discharge > charge cycle for these batteries.

With this charger, can you specify custom charge termination voltages?

 

[chaosdsm]

With this charger, can you specify custom charge termination voltages?

It's expensive, but it's well rounded:
3 UI modes: 'dummy', 'simple', 'advanced'
4 independent slots that can handle 4 different chemistries at the same time
handles most modern chemistries even ones I had never heard of like RAM & LTO
30 programmable memory locations
50mAh capacity setting increments up to 50,000mAh
0.01A charge / discharge increments (NOTE: corrected from 0.1A)
0.01V charge / discharge increments (must be careful: you can over-charge or over-discharge with this charger)
0 - 240 minute resting phase between cycles
USB > Computer for PC Link software recording
Bluetooth (old 4.0 standard)

 

[chaosdsm]

These batteries ended up being about 0.2mm too long for the MC3000 charger... the base of all 4 batteries have a little indentation where I pushed them into place in the charger.