Headway Battery sag

[riba2233]

Rated for only 8C, I don't consider any of those as high rate cells. I use 20C rated rc lipo and don't even consider that high rate.
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

That's because lipo rates don't have anything to do with real life, they are just some imaginary numbers. Unlike 18650 cells where there's a reputable manufacturer responsible for that nubmers, and also you get a datasheet (yeah, imagine that for lipo cells ) with cycle life at those claimed max ratings (both charge and discharge). I would really like to see cycle life graph for your "20C" lipo cells at 20C discharge cycles. It would probably be around 20-30 cycles before their quick death :lol:

Also, they are caller high rate because it's realtive to other 18650 cells. Of course that there are other special or industrial high rate cells, with real 50C and up rates, but they don't even come close to energy density of 18650 cells, which is crucial for e-bike users. Not to mention safety, quality, and consistency and really close tolerances. You can't find any of those in hobby grade lipo.

 

[johnnyz]

..... . When the highest cell is fully charged (around 3.7 volts), the lowest is around 3.45 volts and most others around 3.5-3.6 volts..

This is the root cause of your problems....unbalanced cells.
those Headways have such a flat discharge voltage curve profile, that the difference between a 3.7v cell and a 3.45v cell could be 80% of capacity. !
..IF they come back to life, ...try top balance for a change . :wink:

Yes, im going to top balance...right now most cells using the Imax are coming up just fine, except one...seems to be bucking the charge a bit...on the imax after the cell got to 2.5 vlts I put a 5 amp charge on it but the Imax is onl giving it 2.5 amps...currently at 3.3 volts..hopefully none are damaged.

John

 

[johnnyz]

Forget about lipo now that NCA costs very close, and it's like million times safer. No need to risk your house, EV, whatever. NCA costs slightly more, but lasts more so it's effectively not much more expensive.

Give me an example of this chemestry....a link?

John

High rate:

http://eu.nkon.nl/rechargeable/18650-size/samsung-18650-inr18650-25r.html

http://eu.nkon.nl/rechargeable/18650-size/samsung-inr-18650-30q-3000mah.html

http://eu.nkon.nl/rechargeable/18650-size/lg-18650-hg2-3000mah-20a.html

3C:

http://eu.nkon.nl/rechargeable/18650-size/panasonic-ncr18650pf-3-7v-2900mah.html


Topic about high rate cells:

https://endless-sphere.com/forums/viewtopic.php?f=14&t=57291


As far as these 18650 cells go, first they are expensive...in order to make up an equivilant pack (92 volt 15 ah) I would need 5 P x 25=125 cells..at $4 pounds each thats (8 bucks canadian)=$1000.00 ...lol..no thanks..


John

NOTE - sony vtc5 and lg he2 are NMC chemistry, not NCA

 

[riba2233]

Isn't lipo also around 500 usd? I checked price for turnigy 20c soft case and it costs even more... LOL

 

[johnnyz]

Isn't lipo also around 500 usd? I checked price for turnigy 20c soft case and it costs even more... LOL

Exactly...so here I go again charging up the cells only this time top balancing...when a cell starts getting too ambitious I attach some heatsinks and keep it in line untill they are all around 3.5 volts...untill I get a good BMS this will have to do...I will stick wih the headways as they have proven to be robust and reliable.

John

 

[amberwolf]

when a cell starts getting too ambitious I attach some heatsinks and keep it in line untill they are all around 3.5 volts

"heatsinks"? Do you mean you let the cell overcharge enough to get hot?

That's not a good idea. It may not cause a fire or other dramatic failure, but it's gonna damage the cell(s).

You'd be much better off to individually charge each cell that is not at the same voltage as the others, until they all match at the highest voltage you want them at, using a current-limited power supply (like a lab PSU, etc) set to the voltage you want.

Otherwise you should discharge the high cells down first, to match the low cells, using paralleled car headlights or similar loads.

This will take a while, but it will get you a reasonably balanced starting point to then do your bulk charges.

 

[riba2233]

You wouldn't have any of these problems with good 18650 cells Just charge, drive, repeat

 

[johnnyz]

when a cell starts getting too ambitious I attach some heatsinks and keep it in line untill they are all around 3.5 volts

"heatsinks"? Do you mean you let the cell overcharge enough to get hot?

That's not a good idea. It may not cause a fire or other dramatic failure, but it's gonna damage the cell(s).

You'd be much better off to individually charge each cell that is not at the same voltage as the others, until they all match at the highest voltage you want them at, using a current-limited power supply (like a lab PSU, etc) set to the voltage you want.

Otherwise you should discharge the high cells down first, to match the low cells, using paralleled car headlights or similar loads.

This will take a while, but it will get you a reasonably balanced starting point to then do your bulk charges.

LOL>...no I dont let them overcharge...I have 5 50 watt resistors all soldered up and that I what I use to drain the cell( it equates to a 7.5 amp draw)..thats what I meant by "heatsink"..lol...Ive charged them all up and all have balanced quite nicely...i think maybe one cell is perhaps damaged but we will see when I take it out...

The other writer regarding the 18650 cells...they are simply too expensive and since they are Lithium, they still need some sort of balancing system or they too wiould get out of whack.


John

 

[wesnewell]

Rated for only 8C, I don't consider any of those as high rate cells. I use 20C rated rc lipo and don't even consider that high rate.
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

That's because lipo rates don't have anything to do with real life, they are just some imaginary numbers. Unlike 18650 cells where there's a reputable manufacturer responsible for that nubmers, and also you get a datasheet (yeah, imagine that for lipo cells ) with cycle life at those claimed max ratings (both charge and discharge). I would really like to see cycle life graph for your "20C" lipo cells at 20C discharge cycles. It would probably be around 20-30 cycles before their quick death :lol:

Also, they are caller high rate because it's realtive to other 18650 cells. Of course that there are other special or industrial high rate cells, with real 50C and up rates, but they don't even come close to energy density of 18650 cells, which is crucial for e-bike users. Not to mention safety, quality, and consistency and really close tolerances. You can't find any of those in hobby grade lipo.

All one has to do to see how crappy those 8C rated flashlight batteries are is to look at the discharge curves. Under an 8C load they sag .6-.7V per cell. On my 24s pack, that means the sag would be from 100.8V down to 86.4V. That's more than double the sag of 20C rc lipo under the same 8C load. Now I don't know how many cycles I've got on my 24s 20C rc lipo pack, but I've got over 3 years and 13K miles on it, it it still won't sag as much as those flashlight batteries. Now you can feed all the crap you want to to some people and they'll eat it up, but those that know better will throw it back in your face. As for cost, I paid 30 cents per wh on my original pack. The last 10ah 10c pack I bought was 20 cents per wh. To be equal, that means you'd have to get those cell for $1.85 each. Go luck with that.

 

[johnnyz]

Rated for only 8C, I don't consider any of those as high rate cells. I use 20C rated rc lipo and don't even consider that high rate.
http://lygte-info.dk/review/batteries2012/Common18650comparator.php

That's because lipo rates don't have anything to do with real life, they are just some imaginary numbers. Unlike 18650 cells where there's a reputable manufacturer responsible for that nubmers, and also you get a datasheet (yeah, imagine that for lipo cells ) with cycle life at those claimed max ratings (both charge and discharge). I would really like to see cycle life graph for your "20C" lipo cells at 20C discharge cycles. It would probably be around 20-30 cycles before their quick death :lol:

Also, they are caller high rate because it's realtive to other 18650 cells. Of course that there are other special or industrial high rate cells, with real 50C and up rates, but they don't even come close to energy density of 18650 cells, which is crucial for e-bike users. Not to mention safety, quality, and consistency and really close tolerances. You can't find any of those in hobby grade lipo.

All one has to do to see how crappy those 8C rated flashlight batteries are is to look at the discharge curves. Under an 8C load they sag .6-.7V per cell. On my 24s pack, that means the sag would be from 100.8V down to 86.4V. That's more than double the sag of 20C rc lipo under the same 8C load. Now I don't know how many cycles I've got on my 24s 20C rc lipo pack, but I've got over 3 years and 13K miles on it, it it still won't sag as much as those flashlight batteries. Now you can feed all the crap you want to to some people and they'll eat it up, but those that know better will throw it back in your face. As for cost, I paid 30 cents per wh on my original pack. The last 10ah 10c pack I bought was 20 cents per wh. To be equal, that means you'd have to get those cell for $1.85 each. Go luck with that.

Even though I have only dealt with Lifepo4 cells, 18650 and headway, I can only go from my own experience..and the lousiest thing about the Lifepo4 cells, and YES all forms of 18650 cells to my knowledge are Lithium ion derivatives, they sag much more than the manufactures claims under specific loads. Even cruising at 10 amps and they go from 89 volts (27 cells S) to 85 to 85.5...at 40 amps(2.5 C) their down to 80 volts and at 60 amps(4 C) there are hitting 74-75 volts. This is a FACT with these cells. Also, they end up always less than claimed Ah rating. My first 18650 cells rated at 1480 mah or 1.5 Ah tested out between 1000 and 1200 mah...my headways tested out between 13.5 ah and 14.2ah which isnt bad but if it isnt a 15ah cell then dont call it a 15 ah cell!. The good is that they are robust, they last forever, and are safe.

John

 

[wesnewell]

10A on my 3+ year old 10ah 24s rc lipo pack sags a total of <1V. And 10A gets me ~30 mph.

 

[johnnyz]

10A on my 3+ year old 10ah 24s rc lipo pack sags a total of <1V. And 10A gets me ~30 mph.

On the whole pack?....wow...more and more im leaning to try these...its just the idea of them catching fire..I have seen videos of them apparently spontaneously combusting and then videos where a guy is hammering on them completely discharging and then way over charging them and nothing happens. If I did make a pack out of them, I would have to make an enclosure to contain any possible unfortunate events. Supposedly they las only 3-400 charges but I see alot of guys say they have over 10000 miles on them...pretty amazing..

John

 

[riba2233]

We already seen that lipo costs almost the same as better, safer 18650 option, so why are you still considering it? I mean 18650 should last much longer. He uses it on pretty low C rates, so his results are nothing extraordinary.

 

[Ykick]

We already seen that lipo costs almost the same as better, safer 18650 option, so why are you still considering it? I mean 18650 should last much longer. He uses it on pretty low C rates, so his results are nothing extraordinary.

Sorry bro, I know you’re on an honorable “crusade” but that’s simply bullshit.

They’re not almost the same cost to acquire and any proof they (18650) will last several years longer has yet to be demonstrated.

Only source I can find (thanks to you) is outside the USA and 2.5Ah HR Samsung running about $5/cell plus any welding and of course international lithium shipping.

So, for 10Ah pack I must send at least $320-$400 to somebody in another country and hope the spot welding turns out how I will need it? And I better not change my mind about ultimate configuration…

For the same capacity and more flexibility in regard to configuration, I buy 10Ah of 20C Turnigy hardcase shipped in USA for $216. 4mm bullets series up easy, a few JST extensions to connect to BMS and I’m rolling.

I really, really, really wanna buy and use 18650’s. Honestly, I do and I’m almost ready to pay double. But until I can make a simple USA order/transaction and get what I need/want configured to reasonable satisfaction, hobby shit will continue to power my eBike.

 

[wesnewell]

And if you sold dog harnesses you'd be saying they have more power and speed than a horse. Could it be you're a little biased since you sell spot welders to build a pack made from 18650 cells.

 

[MadRhino]

Some just can't use RC lipo.

To have a powerful bike that is light weight and charges quickly, one has to accept the cons of using an aggressive chemistry. Once you decide for RC lipo, either for cheap or power reasons, you need to follow the rules methodically. They can cost a lot of trouble and money to negligent people, we have seen that happening many times.

Not saying that some might not be foolish enough to set fire to round cells. Yet they are much safer and cost less on the long term, when you can manage to keep them long enough.

 

[johnnyz]

We already seen that lipo costs almost the same as better, safer 18650 option, so why are you still considering it? I mean 18650 should last much longer. He uses it on pretty low C rates, so his results are nothing extraordinary.

Sorry bro, I know you’re on an honorable “crusade” but that’s simply bullshit.

They’re not almost the same cost to acquire and any proof they (18650) will last several years longer has yet to be demonstrated.

Only source I can find (thanks to you) is outside the USA and 2.5Ah HR Samsung running about $5/cell plus any welding and of course international lithium shipping.

So, for 10Ah pack I must send at least $320-$400 to somebody in another country and hope the spot welding turns out how I will need it? And I better not change my mind about ultimate configuration…

For the same capacity and more flexibility in regard to configuration, I buy 10Ah of 20C Turnigy hardcase shipped in USA for $216. 4mm bullets series up easy, a few JST extensions to connect to BMS and I’m rolling.

I really, really, really wanna buy and use 18650’s. Honestly, I do and I’m almost ready to pay double. But until I can make a simple USA order/transaction and get what I need/want configured to reasonable satisfaction, hobby shit will continue to power my eBike.

Ok so lets get ino some specifics...

SHow me how and demonstrate a price for buying a 15 ah 92 volt LIPO pack to replace my headway pack which ultimately cost me $840.00 plus $75.00 to ship and no BMS. Total price was $915. Most of the cells were in the range of about 14 ah's.

John

 

[Ykick]

That’s an extreme voltage and large capacity compared to what I’m used to assembling. I normally construct little 5-10Ah 16S packs.

But, if your 92V is “nominal” then 24S3P RC Lipo should fit enough to the requirement with much less sag than Headways. Hot off the charger would be about 100V. Nominal voltage around 89V.

24S3P (15Ah) can be assembled using 18qty of these Turnigy 20C 5Ah hardcase bricks.

http://www.hobbyking.com/hobbyking/store/__58976__Turnigy_5000mAh_4S1P_14_8v_20C_Hardcase_Pack_AR_Warehouse_.html

The price will be lower if you’re logged into HK account or if you wait on the page as a visitor it will popup a special price discount.

FWIW - I’ve been buying these from USA East warehouse for $27 ea. shipped to NY. That would be $486 for 18qty if similar shipping charges. You might have to split up the order for that amount of RC Lipo? Potential weight restriction.

Anyway, I’d advise rounding it up to 20qty just in case of a duff brick/cell or two.

Next, you’ll still need some cabling and connectors. I use the stock bullets for series stringing and then convert to Andersons for parallel grouping the main power using 12a silicone wire.

If you wanna add BMS for bulk charging you’ll wanna source some 4S JST extensions (HK or RC Buddy) and whatever housings needed to mate to the chosen BMS, if any. I ran naked for along time but bulk charging is a good use for BMS and it's alerted me to a failing cell during discharge on a couple of occasions.

I normally use 4S extensions and then populate housings needed for BMS in the proper order of the series string for parallel cell group level monitoring. I try not to molest the bricks in the event I need to ever seek warranty replacement. So far so good on that account.

 

[wesnewell]

Ok so lets get ino some specifics...
SHow me how and demonstrate a price for buying a 15 ah 92 volt LIPO pack to replace my headway pack which ultimately cost me $840.00 plus $75.00 to ship and no BMS. Total price was $915. Most of the cells were in the range of about 14 ah's.
John

I also use the 4s hardcase packs, configured as 24s2p for 88.8V nominal that fully charges to 100.8V. I've never used a bms on them although I bought a couple and a bulk charger to charge them a few months back. I've been splitting them into 20ah 12s to charge with a 12s rc balance charger. I'm now thinking I'll just use the 24s bms as an external charger, rather than mounting it on the pack, but haven't made up my mind yet. IIRC I paid ~$22 each for the 13 I bought over 3 years ago. I think you can get them now for ~$25 each, so 20 of them would be ~$500 plus shipping, and that would leave you a couple of spares.