What could I do in the predicament?

General Discussion about electric bicycles.
john61ct   100 GW

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Re: What could I do in the predicament?

Post by john61ct » Mar 14 2020 9:05am


MadRhino wrote:The 15C discharge rate of the Graphene Pro bricks is very conservative. The big bricks are under rated deliberately, because the bigger the bricks the higher the risk of overheating.

If you are building with 4 bricks only, I recommend higher discharge C-rate. The Graphene Panther are best, but you will need 8 bricks for the same capacity. Anyway, 8 Ah is not enough IMO when you are building performance. The range will be very short. Most of the time I use 12 bricks Graphene Pro for 24s 3p= 24 Ah. Then I never risk feeding above the 15C (15 X 24= 360A)

If you have only 8 Ah capacity, you will need at least 40C discharge rate. Otherwise you risk heat build up.
Maybe it's me, but this is very confusing syntax.

Heat buildup is prevented in all cases by keeping the C-rate low.

If the amps rate is a given, then building the total pack bigger, increasing Ah capacity is one way to lower the C-rate.

If the component modules being themselves bigger means the C-rate must be kept lower, then better to use a higher number of smaller Ah capacity modules.

There is no scenario I can think of where a higher C-rate keeps the pack cooler.


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MadRhino   100 GW

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Re: What could I do in the predicament?

Post by MadRhino » Mar 14 2020 9:25am

john61ct wrote:
Mar 14 2020 9:05am
MadRhino wrote:The 15C discharge rate of the Graphene Pro bricks is very conservative. The big bricks are under rated deliberately, because the bigger the bricks the higher the risk of overheating.

If you are building with 4 bricks only, I recommend higher discharge C-rate. The Graphene Panther are best, but you will need 8 bricks for the same capacity. Anyway, 8 Ah is not enough IMO when you are building performance. The range will be very short. Most of the time I use 12 bricks Graphene Pro for 24s 3p= 24 Ah. Then I never risk feeding above the 15C (15 X 24= 360A)

If you have only 8 Ah capacity, you will need at least 40C discharge rate. Otherwise you risk heat build up.
Maybe it's me, but this is very confusing syntax.

Heat buildup is prevented in all cases by keeping the C-rate low.

If the amps rate is a given, then building the total pack bigger, increasing Ah capacity is one way to lower the C-rate.

If the component modules being themselves bigger means the C-rate must be kept lower, then better to use a higher number of smaller Ah capacity modules.

There is no scenario I can think of where a higher C-rate keeps the pack cooler.
Sure, building with smaller bricks does make the cells easier to shed the heat. Big bricks are more prone to keep the heat, that is why the same cells assembled in bigger bricks are ofter rated lower. There is some confusion with brick C-rate, and cell C-rate, for bricks rating does vary with size even when they are made of the same cells.

Higher C-rate cells though, are definitely running cooler supplying equal Amps, simply because they are lower IR. When building with a small battery and needing high power, the only solution is higher C-rate cells. I have used some 100 C cells that were running very cool under hard, repeated high current bursts. Good when you want to optimize weight/power ratio, but expansive solution. High C-rate cells also have the advantage to stand the cold better, they are not suffering as much power and capacity loss in extreme winter days. In the summer, even with high C-rate batteries, it is important to provide proper air flow, and to build batteries such as to let air flow circulate between the bricks.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

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Re: What could I do in the predicament?

Post by john61ct » Mar 14 2020 10:16am

Aha, you meant to buy higher C-rated packs!

Yes absolutely

I interpreted that you were recommending running at an actually higher C-rate

8-D

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Re: What could I do in the predicament?

Post by ebike11 » Mar 14 2020 10:03pm

MadRhino wrote:
Mar 14 2020 8:49am
Yep. Three series of four, each in a bag: front fork mounted bag, top tube bag, and down tube bag. The frame triangle is clear, but for a big shock. Modular batteries are letting you ride with 8,16, or 24 Ah easily. Useful when you don’t have the same commuting distance all the time, and you don’t need the same performance either. Many bikes built, all with the same connectors and mounts, are making it easy to swap battery bags. I have some that are much higher C-rate, for those times racing short distances in mountain trails. Or, I can fit 4 battery bags for 32 Ah if required for a long ride. And, the connections can be reassembled pretty quickly to make 18s series, mostly winter configuration when high top speed is not required.
Great info thanks!!

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Re: What could I do in the predicament?

Post by ebike11 » Mar 15 2020 7:44am

john61ct wrote:
Mar 14 2020 10:16am
Aha, you meant to buy higher C-rated packs!

Yes absolutely

I interpreted that you were recommending running at an actually higher C-rate

8-D
But his packs arent high C rate, correct?
Thr packs he is using the 15C 8000mah ones

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Re: What could I do in the predicament?

Post by john61ct » Mar 15 2020 8:06am

Well everything is relative. He says that rating is not accurate, or rather oriented more toward continuous rather than short bursts.

As always need to go by trusted user test results over vendor ratings.

Does this seem enough for your use case?
MadRhino wrote:Mine are assembled 24s and could supply 500A if required. Of course I don’t feed that much, but +250A bursts in acceleration is frequent.

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Re: What could I do in the predicament?

Post by ebike11 » Mar 15 2020 8:24am

john61ct wrote:
Mar 15 2020 8:06am
Well everything is relative. He says that rating is not accurate, or rather oriented more toward continuous rather than short bursts.

As always need to go by trusted user test results over vendor ratings.

Does this seem enough for your use case?
MadRhino wrote:Mine are assembled 24s and could supply 500A if required. Of course I don’t feed that much, but +250A bursts in acceleration is frequent.
Sure...the info from you guys is much more reliable and real compared to product pages

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Re: What could I do in the predicament?

Post by DogDipstick » Mar 15 2020 8:54am

Ebikes are fine with 15C.

The 75C are for the helicopeters that drain a pair of those 5000mAh in series in three min at 44v.... 250 Wh in three min.. Kill any lipo if it is not a good one. You will have a hard time killing the 15c ones on a ebike. Like I said, I have flown them ( on my small, 5 foot, 4Kw contin, 6Kw peak, single pack heli.. ) and they good. Stiff voltage till the end.

250Wh in three min..flight. ....

Hell, I dont use 25Wh on my ebike in three min.

Ebike? Less than 8.5Wh/min.... Like going ten miles @ 25Wh/mile.... 15-20mph cruise.

Helis?... the helis use ~85Wh / MIN.... ... 10x the energy consumption.
83.1v of Ironhorse XC.. :) :bolt: by Chevy :bolt: :D Broke 10 horsies :twisted: (..about 80% healed..).. :? Anybody.. what equals √3 times the line to neutral voltage? Asking for a friend.. :| (gottenymoem4115thangs?Yall?) :confused: Fabricator @ BSECo. Inc.

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Re: What could I do in the predicament?

Post by ebike11 » Mar 15 2020 9:04am


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Re: What could I do in the predicament?

Post by john61ct » Mar 15 2020 9:43am

make your own custom to suit

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Re: What could I do in the predicament?

Post by ebike11 » Mar 15 2020 9:58am

john61ct wrote:
Mar 15 2020 9:43am
make your own custom to suit
Yes but those premade ones look simple and easy. If i put many bricks in the same back then i wouldnt need long wire connections in between bricks.

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Re: What could I do in the predicament?

Post by HK12K » Mar 15 2020 10:38am

Nothing wrong with using the pre-made ones if they'll suit your needs, especially if they can assemble them with a higher level of quality than you can accomplish yourself. It'll likely just end up being more expensive. Imho anyway.

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Re: What could I do in the predicament?

Post by markz » Mar 15 2020 1:01pm

XT90's are easy to solder, but the key is to use the extra piece to cover the solder joints. I like to use heat shrink and I can't use the extra solder joint piece most times because I use too much solder, so I triple up on heat shrink. Sometimes there isnt enough room to use heatshrink so then you can use liquid electrical tape which is a gooey mess to apply. Then use electrical tape. Recently, I found Mastic Epoxy, like playdoh, I used it and its holding up strong. I put a piece in the middle of the XT90 bowls for solder, and wrap it around. Then more around the outside. Form to suit. Works great.....until I need to t/s.

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Re: What could I do in the predicament?

Post by MadRhino » Mar 15 2020 1:15pm

DogDipstick wrote:
Mar 15 2020 8:54am
Ebikes are fine with 15C.
This is relative to power usage and battery capacity. When building with a small 8Ah battery, 15C will safely deliver 120A which is more than enough for most. But what if one has a big motor/controller that are able to pull 250A in acceleration? Every hard start will build some heat and wear the battery very fast, likely puffing them lipo bricks the first day of use. Bigger capacity would then be required to make those 15C adequate and lasting.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

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Re: What could I do in the predicament?

Post by john61ct » Mar 15 2020 1:50pm

MadRhino wrote:
DogDipstick wrote:
Mar 15 2020 8:54am
Ebikes are fine with 15C.
This is relative to power usage and battery capacity. When building with a small 8Ah battery, 15C will safely deliver 120A which is more than enough for most. But what if one has a big motor/controller that are able to pull 250A in acceleration? Every hard start will build some heat and wear the battery very fast, likely puffing them lipo bricks the first day of use. Bigger capacity would then be required to make those 15C adequate and lasting.
Confusion again for me.

I interpreted DD's post to mean

**not** that a 15C pack is always fine no matter what C-rate is drawn from them, obviously that would be silly.

But that a pack sized so that the amps rate never goes higher than what a (properly rated) 15C pack will support well will be OK for that use case.

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Re: What could I do in the predicament?

Post by HK12K » Mar 15 2020 2:33pm

Image
I stand corrected. Removed so I don't confuse anyone else.
Last edited by HK12K on Mar 16 2020 12:56pm, edited 1 time in total.

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Re: What could I do in the predicament?

Post by john61ct » Mar 15 2020 3:42pm


HK12K wrote:My understanding is that if you parallel packs it effectively increases the c rate by roughly the rated amount for each additional pack you add. So two 15c packs in parallel would be rated at approximately 30c.
No just wrong.

C-rate (amps capacity) is by definition already proportional to Ah capacity.

So a pack composed of 15C modules stays 15C no matter what.

If 8Ah means can output 120A

if 80Ah then 1200A, still 15C.


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Re: What could I do in the predicament?

Post by HK12K » Mar 15 2020 5:41pm

Thanks for the clarification. I'm still getting used to thinking in terms of c rate. My mind was still stuck on continuous discharge rating, which would increase proportionally with additional packs in parallel.

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Re: What could I do in the predicament?

Post by john61ct » Mar 15 2020 8:39pm

Nope, same thing.

C-rate is just **a unit** of measurement.

The acceptable "peak output" might be 5C, while highest continuous is 1.5C.

Of course the **vendor ratings** are pure fiction.

And you may not agree with what one forum tester accepts as OK, it really is a judgment call how much you prioritize longevity, adjust the maximum temperature rise effect or the voltage sag effect to below what **you** consider abusive in your use case.

How long do you define "a brief peak" session of very high discharge rate?

Same with charging, if I'm not in a big hurry, I consider anything over 0.4C too high a rate.

While others are fine with routinely going to 2C or even higher!

Depends on the weather too of course. . .

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Re: What could I do in the predicament?

Post by DogDipstick » Mar 15 2020 9:49pm

john61ct wrote:
Mar 15 2020 8:39pm
Nope, same thing.

C-rate is just **a unit** of measurement.

The acceptable "peak output" might be 5C, while highest continuous is 1.5C.

Of course the **vendor ratings** are pure fiction.


Same with charging, if I'm not in a big hurry, I consider anything over 0.4C too high a rate.

While others are fine with routinely going to 2C or even higher!

Depends on the weather too of course. . .
I agree with John with all of these point absolutely. Generally, I have a 6.6C discharge rate for my pack for an instant.. less than3 seconds... less than one even...

Most of the time discharge between 2-3C.. on my 15Ah pack, this is 30-45A.
83.1v of Ironhorse XC.. :) :bolt: by Chevy :bolt: :D Broke 10 horsies :twisted: (..about 80% healed..).. :? Anybody.. what equals √3 times the line to neutral voltage? Asking for a friend.. :| (gottenymoem4115thangs?Yall?) :confused: Fabricator @ BSECo. Inc.

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Re: What could I do in the predicament?

Post by HK12K » Mar 15 2020 11:05pm

john61ct wrote:
Mar 15 2020 8:39pm
Nope, same thing.

C-rate is just **a unit** of measurement.

The acceptable "peak output" might be 5C, while highest continuous is 1.5C.

Of course the **vendor ratings** are pure fiction.

And you may not agree with what one forum tester accepts as OK, it really is a judgment call how much you prioritize longevity, adjust the maximum temperature rise effect or the voltage sag effect to below what **you** consider abusive in your use case.

How long do you define "a brief peak" session of very high discharge rate?

Same with charging, if I'm not in a big hurry, I consider anything over 0.4C too high a rate.

While others are fine with routinely going to 2C or even higher!

Depends on the weather too of course. . .
Essentially what I was alluding in my subsequent post.

Just for discussions sake, if we can agree that a single Samsung 25R has a maximum continuous discharge rating of 20 amps (because attempting to continuously discharge at over that rate would allow the cell temperature to reach more than 80 Celsius where cell damage is presumed to occur) then adding a second 25R in parallel would allow you to discharge at a maximum of 40amps while maintaining the same temperature as a single cell at 20 amps. The 40amp load would be spread between the two cells. Double cells, double the continuous discharge rating of the group. You were absolutely right though, the c rate would remain unchanged. (I was clearly wrong initially.)

Of course attempting to use those cells continuously at their mutually accepted maximum would negatively effect cycle life. It would not however be unsafe in the sense of risking thermal runaway.

That said, if the highest load ever put on that pair of cells was 40 amps and the duration of that 40 amp load were only a few seconds at most before dropping to say 5 amps continuous, I wouldn't expect to see much reduction in cycle life as the cell would never get the chance to accumulate any real amount of heat. Of course if we had 2 more cells in parallel bringing the CDR of the group to 80a, and were only asking 40a for a few seconds here and there it would be all the better. The more the merrier to share the load.

As you noted though, vendor ratings are fiction and some manufacturer ratings aren't necessarily much more accurate. Combine that with the fact that finding 2 people with the same opinion or standard is neigh impossible and there's no wonder a consensus is difficult to reach.

Fwiw, I outright ignore any sort of pulse or burst rating thrown around by sellers as there is no standard that I'm aware of which defines the duration of a pulse or burst. Could be 5ms, could be 5 min. Pure marketing malarkey without qualification.
Last edited by HK12K on Mar 15 2020 11:19pm, edited 1 time in total.

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Re: What could I do in the predicament?

Post by markz » Mar 15 2020 11:09pm

You need to get the specification sheet from the manufacturer, also there are plenty of people out there testing 18650's.
Lyte something or other is a website.
Lemme see what pops up with serch term "lyte 18650 test"
Boom there we go, https://lygte-info.dk/review/batteries2 ... %20UK.html
Cheesy website but informative non the less.


As previously mentioned
Hobbyking loves to over exaggerate their C_rating to get sales. Not sure what our man Icecube57 stated, probably half the # Hking states.
Here lemme frocking find it for you.
Warm - viewtopic.php?f=14&t=61672&p=948499&hil ... te#p948499
In my verdict Turnigy 20C was still the best bang for the buck and for some reason always over delivered when ran at 1/4 of the stated C rating.
Bingo was his name oh

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Re: What could I do in the predicament?

Post by john61ct » Mar 15 2020 11:37pm


HK12K wrote:Of course attempting to use those cells continuously at their mutually accepted maximum would negatively effect cycle life. It would not however be unsafe in the sense of risking thermal runaway.

That said, if the highest load ever put on that pair of cells was 40 amps and the duration of that 40 amp load were only a few seconds at most before dropping to say 5 amps continuous, I wouldn't expect to see much reduction in cycle life as the cell would never get the chance to accumulate any real amount of heat.
In a gentler use case like House banks, or say high capacity solar storage,

you definitely will see lower cycle longevity for a bank frequently discharging at say 1.5C, as opposed to 0.5C

maybe even half the number of cycles.

It is only at even C lower rates that the life-extending effect reaches diminishing returns.

Of course in mobile / propulsion use cases where pack space and weight becomes an issue, 2C may be considered very low, and 5C normal

but this facts is still relevant in a general battery discussion.

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Re: What could I do in the predicament?

Post by HK12K » Mar 16 2020 12:07am

john61ct wrote:
Mar 15 2020 11:37pm
In a gentler use case like House banks, or say high capacity solar storage,

you definitely will see lower cycle longevity for a bank frequently discharging at say 1.5C, as opposed to 0.5C

maybe even half the number of cycles.

It is only at even C lower rates that the life-extending effect reaches diminishing returns.
You would expect a significant decrease in cycle life even if that 1.5c load was, say, just a periodic brief inrush current before falling to .5c nominal?

Low and slow. Good for batteries, bbq, and to prevent your batteries from becoming a bbq. :mrgreen:

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Re: What could I do in the predicament?

Post by john61ct » Mar 16 2020 12:21am

No of course the less time spent at a given C-rate (do please capitalize it)

the less stressful.

But note, all these issues vary widely by chemistry, and even from one cell mfg / line / model to the next.

And are very inter-related with the temperature factor, and in some cases with the cells' stage in its lifespan, cycle count different from calendar aging.

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