Could that cells work great at 1.5C rate ?

http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1643


Here you are - specification:

Product Specifications

Capacity* Nominal 2200 mAh, Minimum 2150 mAh

Dimensions:
Diameter 18+/- 0.2 mm
Height 68+/- 0.2mm

Weight (Typical) Approx. 46 g yes

Nominal Voltage: Average 3.7V

Cut-off Voltage: 3.0V

Internal Impedance: less or equal to 180 milliohm (with PTC)

Cycle Performance: 90% of initial capacity at 400 cycles

Cycle life: > 500 cycles

Charge: Current = 0.5C mA Voltage = 4.2 V End Current = 0.01 mA

Discharge: Current = 0.5C mA End Voltage = 3.0V

Max. Charging current: 1.5C ma

Max. Discharging current 1.5C ma (for continuous discharge)

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At 1.5C discharge rate the sag at each cell will be around 600 mV within specification.

Are they able to work great at such rate ?
Is it the right choice for e-bikes supply ?

Is the cycles number competitive for that price ?

Is the voltage sag within fair range ?
Are you ready accept such voltage sag for your e-bike supply ?

I can't see the point in the poll. If you look at Xyster's posts you'll see that the he only discharges them at 1C so the sag is only a few volts.

I think the idea of using a large number of high resistance batteries is a good one. Keep the discharge rate low and there isn't a problem.

NickF23 said:

I can't see the point in the poll. If you look at Xyster's posts you'll see that the he only discharges them at 1C so the sag is only a few volts.

I think the idea of using a large number of high resistance batteries is a good one. Keep the discharge rate low and there isn't a problem.

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So they work great or not ?
What is their life at 1C or above ?

Isn't a problem to throw out once a year $1000 for such kind battery pack if you can get twice longer life pack for $700 ?

Is they work great or not ?
Or you have no idea yet ?

I don't think anyone argues that these kind of batteries are not good for over 1C discharge.

They do have the highest energy density of commonly available batteries, just not a good power density.

If you have a low powered system and a really large battery capacity, they should work fine for a few years. There's a reason they're popular for laptop computers.

For a high powered system, they could explode or live a very short life.

I just got a bunch of similar cells from pull-outs. I haven't figured out what to do with them yet, but they were free.

fechter said:

I don't think anyone argues that these kind of batteries are not good for over 1C discharge.

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Burst or continuous over 1C discharge rate ?

fechter said:

For a high powered system, they could explode or live a very short life.

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At what C rate ?

fechter said:

I just got a bunch of similar cells from pull-outs. I haven't figured out what to do with them yet, but they were free.

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If they are for free they are almost always great -until they start to burn at least.

I think it depends on the quality of the cells, but my understanding was that they could take 1C continuous and survive OK.

1.5C burst discharge, limited by temperature rise.

They probably explode around 2C or less if allowed to heat significantly.

The BMS is supposed to prevent the cells from exceeding their limitations.

Xyster and others are using these type of batteries with acceptable results so far. There is a risk of fire or explosion if you crash the bike and dent one of the cells or if you severely overcharge or overdischarge them.

If the batteries are under your seat, wear Nomex underwear

fechter said:

I think it depends on the quality of the cells, but my understanding was that they could take 1C continuous and survive OK.

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Survive but at what the cost ?
At how much voltage sag ?
At how much life cycles decrease ?

fechter said:

1.5C burst discharge, limited by temperature rise.

They probably explode around 2C or less if allowed to heat significantly.

The BMS is supposed to prevent the cells from exceeding their limitations.

Xyster and others are using these type of batteries with acceptable results so far. There is a risk of fire or explosion if you crash the bike and dent one of the cells or if you severely overcharge or overdischarge them.

If the batteries are under your seat, wear Nomex underwear

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Acceptable results for me is far far away from working great.
And for You ?

eP said:

Acceptable results for me is far far away from working great.
And for You ?

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Exactly. - Personal Preference.

Ep - have you been hijacked by Randy or something lately ? geez man.. :wink:

These 18650 cells are a good buy if you know what you are doing, they come on sale at really good discount prices at times...

Me.. well.. it was either

1- Buy a pile of Kokam RC helicopter packs, multiple chargers, ballancing units.. etc.... have a minimal AH capacity at high-rate and cross my fingers they last for 300 cycles..

2- Buy a ready made pack, with built in BMS , and Plug-n-play charger, and just go have fun...

I chose option 2 with my LiMn packs, but went with 20ah anyways so that in worst case situation i still keep below 1C discharge and have a better chance at 500+ cycles.. hopefully 4 years of service is my goal regardless of cycle count..

So far, i don't yet regret my purchase, i did not go with the 18650's simply because of the daunting number of cells required to install/build/maintain... but for some situations they are just fine.. no need to knock something that's proven to work as expected.

Ypedal said:

eP said:

Acceptable results for me is far far away from working great.
And for You ?

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Exactly. - Personal Preference.

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No, it is not personal preference it is matter of money.

Ypedal said:

Ep - have you been hijacked by Randy or something lately ? geez man.. :wink:

These 18650 cells are a good buy if you know what you are doing, they come on sale at really good discount prices at times...

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But - if you know what you are doing.

If somebody telling me they work great at 1C-1.5C continuous discharge rate it is obvious sign for me that he/she definitely doesn't know what is doing.

Ypedal said:

Me.. well.. it was either

1- Buy a pile of Kokam RC helicopter packs, multiple chargers, ballancing units.. etc.... have a minimal AH capacity at high-rate and cross my fingers they last for 300 cycles..

2- Buy a ready made pack, with built in BMS , and Plug-n-play charger, and just go have fun...

I chose option 2 with my LiMn packs, but went with 20ah anyways so that in worst case situation i still keep below 1C discharge and have a better chance at 500+ cycles.. hopefully 4 years of service is my goal regardless of cycle count..

Click to expand...

If you will keep below 1C the rate and your target is 500+ , so you have a chance to reach your target.

If regulary will use them at 1C rate or above you have no chance.

If you buy the cells at $0.36/Wh and your cells reach 300 cycles so the effective cost is $1.20/kWh/all_cycles.

If you will keep discharge rate below 1C you can get $0.70/kWh or even below.

If you buy cheap and durable Power cells at $0.60/Wh you can get $0.60-$0.55/kWh at the end at discharge rate above 1C.
So you simply need half the cells at once (for half the money) and they are working great this way.

If you buy inefficient cells at $0.80/Wh they definitely couldn't work great if you compare them to cheap and efficient power cells.

Ypedal said:

So far, i don't yet regret my purchase, i did not go with the 18650's simply because of the daunting number of cells required to install/build/maintain... but for some situations they are just fine.. no need to knock something that's proven to work as expected.

Click to expand...

So far you was unable to buy more powerful and cheaper cells, so you dont have the reason to regret.

Keep in mind: everything is change and what was acceptable yesterday will not work great tomorrow.

Regards

I'm using the exact same cells as those listed. I discharge mine at an average 0.7C, peak typical use is 1.1C - the highest draw that I have ever used is 1.2C which I rarely see show up on my ammeter.

My voltage sag the average discharge rate is 3.37V (at 50V), which compares to the voltage sag at typical discharge of 2.8V (at 40V) using 12Ah SLAs. Which is 6.7% sag for 18650's vs. 7% sag for 12Ah SLAs - with measurement inaccuracy factored in, call it a draw.

I have seen nothing to indicate that the cells would be substantially worse at 1.5C than they do at about 1.1C. They barely even rise 3 Celsius in 30 minutes in use when I'm riding and pulling ~13A out of them - and they are wrapped in almost 1cm of bubble wrap on all sides... which not an ideal thermal dissipation system.

My pack:
http://endless-sphere.com/forums/viewtopic.php?t=826

I did capacity measurements after about 100 cycles, 10 months of use a few weeks ago, and measured that they hold ~8% less capacity than when I bought them - when discharged at a C/20 rate. I measured 18210mAh (C/20) when I bought them - a bit more than the 2200mAh per cell they were rated for, I measured 16700mAh last week... but then realized that I'd left them balancing (in discharge balancing mode) all night long after I'd taken them off the charger which probably pulled a couple of % off of them. I meant to redo the measurement with the packs fully charged, but it's been busy... and I can't ride the pack for a day while I do the measurement... plus I like to be nearby.



eP, I don't understand your point entirely. The cells clearly work fine for a couple of us. I have a 44V 17Ah pack that weighs 4.75kg in it's case (with a thermal monitor built in). I ride it almost daily. It has given me no trouble at all since the day that I bought it. It cost $302 (not incl. shipping, case or charging/BMS system). That's US$1.43/Ah. And the cells are 3.7V:2.2Ah and weigh 46g each. Those are pretty good numbers.

I have a feeling that this discussion is a bit like my response to Randy. I like my x5304 hub motor. I like my 18650 lithium ion (cobalt) pack. The cells work fine for me. Although I'm proud of my pack and like to talk about it, I have never once ever recommended that anyone else go down the route that I did. In fact, at several points, I've said that if I was going to do it again, I'd probably choose A123's instead, or perhaps C-LiFePO4 cells. But I couldn't find a great way to charge A123's (or a great way to buy them) a year ago, and I don't recall anyone selling LiFePO4 cells in quantity last summer at any kind of reasonable price... if they were, they didn't show up in my research.

But your point about them being "dumb" doesn't make sense to me. The cells are not good high power output cells, they are kind of scary to charge and use - but they are working great, they are lightweight, and they were cheap to buy - and I would argue that based on my usage, they are cheap even with lifetime calculations included. Even if I lost 8% over the last year - and I think it's more like 6-7% - I'll still likely get 4 years and 400 cycles out of this that cost me ~$300 and I get the joy of carrying 4.75kg into restaurants and stores when I don't want to leave the pack on the bike. If someone wants to pull 50Ah, this is not a good cell type. If someone is planning on using the cells a lot - like more than 5 cycles per week - then this is not a good cell type. But if your power output requirements are modest and you have a moderate level of usage, then these cells are not a horrible choice (aside from the risk of your house burning down).

In summary, if I was going to do it again now - a year later - I probably wouldn't use lithium (cobalt) ion cells. I definitely do not recommend them to anyone who isn't well aware of the safety issues, and would generally steer people towards NiMH, A123's or LiFePO4 cells instead - and even SLA if cost is a concern and weight isn't. But that doesn't mean that my pack is dumb... it works great for me... I'm very pleased with it and I don't plan on replacing it any time soon.

I voted that these cells are not "dumb" for use at 1.5C.

eP, like Randy, seems zealously religious in his convictions. Mountains of quality evidence contrary to his personal dogma will not sway him; marginal evidence in his favor solidifies his certainty; leading him to become ever-more evangelical, prostelytizing, and prosecutorial.

In short, he's a perfect candidate to be the next U.S. president. :wink: