Lithium battery question

[eMark]

The motor rating is irrelevant in this case. It only determines whether the motor will get hot or not. The controller current limit is what counts.

For something like that I would be looking for a 45A or more BMS. They are quite inexpensive if you avoid the Bluetooth ones. Under $20 shipped.

FWIW, I am running a 45A BMS on my Sur-ron secondary pack at nearly double the current rating. I beefed up the copper in spots and modified the current shunt, but otherwise the stock unit.

So, maybe this 50A $22.50 BMS ... https://www.aliexpress.com/item/32879269241.html?spm=a2g0o.detail.1000014.9.18752c52XtxN3D&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.128125.0&scm_id=1007.13338.128125.0&scm-url=1007.13338.128125.0&pvid=4210cce2-8dae-4041-b27a-c7705b4050ce ... for 7S 24V protection to power Currie Technologies 24v 500w 28A motor xyd-6b via 3A Controller. Do you have a better "best" BMS in mind under $20 shipped ?

Then if he decides to upgrade to a Sur-ron may not need to get another BMS unless bluetooth ...

 

[twilloug]

Thanks for all the great information. Looking at the 45 or 50 amp bms. I assume i need the seperate port configuration in lieu of common port. Does seperate port mean i get a 3 wire configuration with P-, C- and B-?

 

[twilloug]

Again thank you everyone for your comments. I did some research and the 18650 cells in my battery have a max continuous discharge current of 7650mA each. So with 4 in parallel, that would be a max of 30.6. So my 28amp motor and 30amp controller should be fine right. Note the cells are eve ICR18650 26V cells.

 

[fechter]

Thanks for all the great information. Looking at the 45 or 50 amp bms. I assume i need the seperate port configuration in lieu of common port. Does seperate port mean i get a 3 wire configuration with P-, C- and B-?

You could use either kind but the separate port style will make less heat. I saw an ad for one where they called it "split mouth", which I assume is a literal translation from chinese.

 

[eMark]

Older scooter with a 7S 24V battery, possibly an overrated 500W motor (China origin?), possibly an overrated 30A Chinese controller. My 20 amp reliable BMS suggestion was based on twilloug's first post followed by obcd's post. That's right i previously said "reliable" 20A BMS (see last pasted quote). Oh my how he does exaggerate ... "Dead wrong!" ... he's definitely no expert, but neither am me.

I have an older Scoot-e scooter. 24v scooter. I wad having issues with motor so i decided to buy a new 500w motor off of ebay as well as a controller. Now for the question...the battery is a 7s4p 24v battery from china. It measures 27.5 volts, so it is charged. However when i connect directly to motor, nothing happens. Is my battery not big enough for motor?

And ...

A 20 Amps BMS will limit the current to 20 Amps.

Isn't that a good thing considering twilloug's 7S4P 24V battery? What if it's a cheap Chinese overrated 500W motor? 12mph (on level terrain) may be top speed for twilloug's e-scooter ... does it really require a 40-50A BMS?

It's also important that you check if it's safe to draw 20 - 30 amps from your battery. The fact the BMS was only rated 4 15A could mean you shouldn't load your cell much higher. Just check the brand and type of your battery cells and see how many cells are connected in parallel. Check the datasheet of your cells and you know what your safe discharge rate is. Multiply this with your number of parallel cells and you have your total allowed discharge rate.

Wouldnt i want a 30 amp bms to match the 28 amp rated motor and 30 amp controller?
I see a lot of 20 amp bms but wouldnt that put me in the same boat?

Not if you have a reliable 20A BMS and healthy battery.
Are you sure your battery is AOK?
BMS and controller don't need to be rated at more than your 28A 500W motor.

My own "reliable 20A BMS" with 20A controller and 750W hub motor draws at most 350W at 12mph up a grade with my 10S5P 36V 10A capacity battery. Agree that we don't know how efficient is twilloug's 500W motor. Thus, some justificaton for a 20A BMS and a 20A controller. Do you want to burn up both battery and motor with a 40-50A BMS and 30A controller? According to obcd's post ... "A 20 Amps BMS will limit the current to 20 Amps" ... and ... "is it safe to draw 20-30 amps from your battery" ... implies a reliable 20A controller was sufficient enough for a 7S4P 24V Chinese battery and 500W motor (China origin?).

As far as another battery is there even enuf room on twilloug's older e-scooter? Not a good idea unless both batteries have Grade A cells with same capacity and amp rating? Adding another battery borders on overkill (even if room) unless twilloug's plan is using the e-scooter for commuting some distance or a few hours of recreational enjoyment without taking a break at McDs to recharge.

Bottomline: All twilloug really needed was a reliable 20A BMS to protect his 7S4P 24V battery with hopefully an overrated 30A controller an what may be an overrated 500W motor. fechter is Right On when he says you don't need to pay more than $20 for a BMS including shipping. Whereas john61ct is grossly over exaggerating when he says i'm "Dead wrong!"

fechter (if you're still here) glad you didn't belittle me for my comment that twilloug could use that 50A (7S 24V) BMS if he ever upgrades to a sporty Sur-ron dirt ebike. Maybe, you didn't catch my tongue-in-cheek ... unless you thought someday he might add another 7S 24V for balance charging when split and then joining together again into a 14S 48V battery for his Sur-ron dirt ebike, but then he wouldn't need a 7S BMS. But not using any BMS is for another thread :wink:

As Wernher von Braun said, “One good test is worth a thousand expert opinions.”

If only we were all experts then there would only be 1,000 opinions ... assuming it was a 'good' test :wink:

 

[john61ct]

Dead wrong, again.

A BMS does not limit current.

Best case it isolates the pack, worst case it burns.

Limiting current is the controllers job, or a CAv3 if so equipped, if not then the rider must exercise self control.

So if one states "I never allow more than 16A", then a 20A BMS would be fine.

And just like that safety overhead margin, the controller should also be **rated capable** of handling a fair bit higher V&A than the maximums it will ever see.

Same again for the C-rate of the battery, if you're pulling 25A for more than a few seconds on a regular basis, the pack should **be capable** of putting out that much for many minutes at a time.

If you want reliability and longevity.

These components being a lot more robust that what is required, is what **makes** them well suited to the task.

Yes, one element will be a weaker link than the others, but the normal usage should not get even close to its limits.

 

[fechter]

The BMS (and the battery cells) need to be rated for somewhat higher than the current limit of the controller. The current is not regulated by the BMS, that is done by the controller. The BMS is like a circuit breaker that just trips if the current goes too high. You don't want it to ever trip unless something failed, or the cell voltages get too low.

If the battery cells are underrated or weak, the voltage might sag a lot under full load and make the low voltage protect kick in way before the pack is really discharged. This might be a good thing as it is protecting the cells from abuse.

 

[twilloug]

Just to clarify, i bought the 500w motor and controller off ebay to replace the stock 300w motor/ controller combo that came on the unit. When tested the controller. Motor and new throttle with my battery it didnt work. I just bypassed the bms on battery because i was thinking the motor/ controller were just trying to pull more than the bms was rated for. Now i think the bms is just bad...burned up or something. Based on my last post, if my battery is rated for 30.6 amps continuous draw, am i ok with 7s4p battery or do i need to go with different battery. If so what size? Everything else is new why not another battery.

 

[fechter]

The battery is probably at the limit but should be OK if you don't abuse it too much. A bigger battery is always nice if you have room.
I'd try the one you have and see how it does. If it gets hot or trips prematurely during discharge, you would know it's too small. If you don't need much range, you could use high rate cells, but those tend to have short cycle life. I prefer a lower rate cell but have enough capacity so you can get the desired amps.

 

[john61ct]

Do you have space to double up the existing battery?

The second one can be higher quality cells, would then give a huge boost both to power (amps) and range (Ah) when running both in parallel.

Or can choose to run just one at a time to lighten the load.

 

[eMark]

Just to clarify, i bought the 500w motor and controller off ebay to replace the stock 300w motor/ controller combo that came on the unit. When tested the controller. Motor and new throttle with my battery it didnt work. I just bypassed the bms on battery because i was thinking the motor/ controller were just trying to pull more than the bms was rated for. Now i think the bms is just bad...burned up or something. Based on my last post, if my battery is rated for 30.6 amps continuous draw, am i ok with 7s4p battery or do i need to go with different battery. If so what size? Everything else is new why not another battery.

OK, as a review assume your older Scoot is similar to a newer E3 (if not post a photo) ...


Most likey burned out the 15A BMS when you changed over to higher rated 30A controller and 500W motor from what was a lower rated controller and 300W motor. Now the weak link is your current battery. This Ali 7S4P may've been suitable replacement if you hadn't decided to upgrade to 30A controller and 500W motor ... https://www.aliexpress.com/item/33057373759.html . It's doubtful Ali has a 7S4P configuration with the right cell rating an BMS for your 30A controller. With a 500W motor you didn't need more than a 20A controller for your older Scoot e-scooter. Even then is there any 7S4P scooter configuration for your Scoot with even a 20A BMS available from Ali or any source ??

Your current 7S4P Chinese battery (with dead 15A BMS) probably has Grade-B 2500mAh cells. They now may be closer to 2200mAh capacity. Your Chinese 7S4P cell rating may be no more than 5A. Do you have any idea the cell rating of your 7S4P battery and its specs ...

• Rated discharge current ___ ?
  Instantaneous maximum discharge current ___ ?
  Maximum continuous discharge current ___ ?

Your 30A controller and 500W motor will make quick work of that battery with a 40A BMS. You or someone needs to build a DIY battery with name brand cells spec'd for your 40A BMS, 30A controller and 500W motor.

Is there even enough space under your older Scoot to parallel modify to a 7S8P battery? Besides it can be "tricky" even for an expert assuming you could find comparable cells. Doubt even Ali can supply a 7S4P (or 6P) to marry with a 40A BMS, let alone a 30A BMS for your 30A controller and 500W motor. You really didn't need more than a 20A controller for that older Scoot and even then you'd need a better battery with 30A BMS.

Perhaps the best option is a DIY build of a 7S (4-6P) 24V battery with 10A rated cells(6P) or 15A rated cells(5P) or 20A rated cells(4P). If you decide on modifying to a 7S8P with 40A BMS (assuming you can find compatible cells) you may need to add two sturdy protective wings on each side to extend the width of your older Scoot e-scooter

 

[fechter]

One more thought;

You could possibly modify your new controller for a lower current limit. Some you can do this with software, others you need to take apart and do something with the current measuring shunt. In most cases it's not too hard.

But this is ES, and we usually try to make things more powerful than stock.

 

[eMark]

Even if twilloug would have used a 20A controller with 30A BMS the problem is finding a compatible scooter battery to supply the power at maximum continuous discharge or maximum burst. It's not easy to find out the cell amp rating of these Chinese 18650 packs at Ali or Amazon. For example the cells in this 7S5P have 3000mAh capacity, but no way of knowing the actual cell rating ... https://www.amazon.com/25-9V-Li-ion-Battery-electric-bicycle/dp/B07VR54DHR/ref=sr_1_1?keywords=Seilylanka+7S5P+li-ion+battery&qid=1582244198&sr=8-1 . FWIW the majority of 3000mAh 18650 cells have at least 10A cell rating if not 15A or higher. Perfect for a 30A controller 40A BMS battery.

This 7S4P 12AH scooter battery also has 3000mAh cells ... https://www.amazon.com/dp/B07VSTQ99H/ref=psdc_552354_t2_B07VNXJVMP ...

Possibly same rated cells in both packs with at least 10A rating if not 15A. If only 10A cell rating go with a 40A BMS and the 7S5P. If you can be assured that the cells in the 7S4P are at least 12A or better yet 15A then the 7S4P battery would be sufficient. More likely same 3000mAh cell in both the 7S4P and 7S5P with same cell amp rating. Sure be nice if cell amp rating were published.

Maybe you can find similar scooter 7S4P or 7S5P at AliExpress with 3000mAh cell capacity and cell rating of 10A (7S5P) or 15A cell rating (7S4P) for less money.

 

[john61ct]

I doubt I would ever buy a pack without knowing exactly what cells it's composed of, and getting in writing **through the selling platform** an assurance they are genuine, new and factory fresh Grade A.

If not a top-shelf model thoroughly tested here and known good, then stress-test a couple cells myself before ordering the pack.

Or get a trusted member here to do so if I couldn't myself.

 

[eMark]

Those that own a $1,700 Boosted Rev (the Tesla of Electric Scooters, 24mph built like a tank) would have to know an insider to fnd out what brand of cells, whether Grade A or Grade B and the cell discharge rating? Same with owners of the $670 Xiaomia Mi PRO or $380 Xiaomia Mi (250W motor top speed 15.5mph).

Is there any electric scooter that will list the cell discharge rate of their battery?? Will Harley Davidson or BMW make available the cell discharge rating of their electric scooter?? Will Harley Davidson make available the brand name and cell discharge rate of their $30,000 LiveWire electric motorcycle?

The original distributor of those two 7S batteries listed above is through Seilylanka, but when you go to seilylanka.com it says the domain is for sale for $990. When googling Seilylanka they specialized in power tool batteries still available through ebay. It's probably safe to assume that that 7S4P and 7S5P scooter battery use higher discharge cells (10A, 15A) ... most likely rebranded Grade B seconds ... you get what you pay ... there's Grade B and Grade B ... if you follow my drift.

When in doubt do your own DIY battery build :thumb:

 

[twilloug]

Guys, so attached is a picture of my cells. Look to be 2.55 ah cells. Max dicharge current of 7650 mamps per cell. Not sure if grade b or a. I will snap a photo of scooter when i get home. I have more space in the battery compartment which i will show in photo.

 

[eMark]

... https://secondlifestorage.com/showthread.php?tid=6952 ... interesting, ??? realistic capacity
... https://www.endrich.com/sixcms/media.php/2474/ICR18650%20IN%20STABLE%20STEEL%20CASE%20WITH%20PROTECTION%20DEVICES.pdf ... 9.65 max continuous discharge rating
... http://xuqybattery.com/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=19&virtuemart_category_id=42&Itemid=371 ... 30milliohm IR
... https://szkeshee.en.alibaba.com/product/60747049539-806324222/Great_Power_ICR18650_Battery_Rechargeable_2600mAh_Lithium_for_Electric_Vehicles.html ... 1000 cycle life specification
... https://linksunhk.en.made-in-china.com/product/gBWJhcoUYPRI/China-Eve-26V-Icr-18650-Dry-Cell-Rechargeable-Battery-for-Power-Tool-with-Super-Good-Prices.html ... for great power :wink:
... https://www.batteryspace.com/prod-specs/ICR18650-26F.pdf ... possible Grade A substitute ?

 

[HK12K]

At least they labeled them ICR as fair warning.

 

[john61ct]

ICR got used for both LCO and NMC chemistries, so not that specifically meaningful?

 

[eMark]

At least they labeled them ICR as fair warning.

Earlier ICR cells weren't as safe as current NMC cell construction. A 20A controller and reliable 20A BMS was sufficient ... even if paralleling another 7S4P pack is such a good idea?? Maximum continuous discharge cell rating of only 7.65A. What's the risk when paralleling two ICR EVE 7S4P packs (one older/one newer) with a 40A BMS and 30A controller without increasing the risk of FIRE ??

Is the cell capacity of the older 7S4P pack the same as the new cell capacity of a 7S4P pack? How unbalanced is the older pack?

ICR got used for both LCO and NMC chemistries, so not that specifically meaningful?

Supposedly stands for Lithium-Ion Cobalt Rechargeable. NCA and NMC cell technology with newer venting caps are less likely to explode (fire) than were early ICR cell caps. These EVE ICR cells hopefully use newer venting caps to reduce chance of fire.

Removed three of above links in previous post and replaced with three others. EVE 2.22A, 2550mAh cells with max continuous discharge of 7.65A and IR of 30mV (when new). Chinese supplier thought this 2.22A cell with max continuous discharge of 7.65A was suitable for Power Tools ?? ... https://linksunhk.en.made-in-china.com/product/gBWJhcoUYPRI/China-Eve-26V-Icr-18650-Dry-Cell-Rechargeable-Battery-for-Power-Tool-with-Super-Good-Prices.html ... this link also posted above.

At $1.45 a cell it's understandable why scooter manufacturers would choose this cell for a 7S4P 24V battery for 250W motor. With non-abusive scootering, conservative charging and conservative discharging this battery was good for 1000 cycles (70% capacity with all 28 cells being Grade A cells).

 

[eMark]

At least they labeled them ICR as fair warning.

Earlier ICR cells weren't as safe as current NMC cell construction. A 20A controller and reliable 20A BMS was sufficient ... even if paralleling another 7S4P pack is such a good idea?? Maximum continuous discharge cell rating of only 7.65A. What's the risk when paralleling two ICR EVE 7S4P packs (one older/one newer) with a 40A BMS and 30A controller without increasing risk of FIRE ??
Then if that isn't enough concern for an increased risk is replacing the 250W motor with a 500W motor.

Is cell capacity of the older EVE 7S4P pack the same as the cell capacity of a new EVE 7S4P pack? How unbalanced is the older pack?

ICR got used for both LCO and NMC chemistries, so not that specifically meaningful?

Supposedly stands for Lithium-Ion Cobalt Rechargeable. Latest NMC cell technology, with newer venting caps, are less likely to explode (fire) than were early ICR cell caps. These EVE ICR cells hopefully use newer venting caps to reduce chance of fire.

Removed three of above links in previous post and replaced with three others. Those EVE 2.22A, 2550mAh cells with max continuous discharge of 7.65A and IR of 30mV when new. Chinese supplier thought this 2.22A cell with max continuous discharge of 7.65A was suitable for Power Tools ?? ... https://linksunhk.en.made-in-china.com/product/gBWJhcoUYPRI/China-Eve-26V-Ic-18650-Dry-Cell-Rechargeable-Battery-for-Power-Tool-with-Super-Good-Prices.html ... this link also posted above.

At $1.45 a cell it's understandable why scooter manufacturers would choose this cell for a 7S4P 24V battery for 250W motor. With non-abusive scootering, conservative charging and conservative discharging this battery was good for 1000 cycles (70% capacity with all 28 cells being Grade A cells).

 

[HK12K]

Sometimes when we challenge what we think we know, we learn that we had been mislead.

https://youtu.be/Y0T5-a104p0

I stand corrected.

 

[john61ct]

Sorry, could you be more explicit about what you learned?

IMR I believe was only used for LMO

but yes INR can vary, mostly NMC & LCO

 

[eMark]

That brings up something that no one seems to know (for sure) the answer to when it comes to BMSs. Are they really just a BPS (Protection) as some claim? Or if they are capable of balancing (BMS) a battery how and to what extent?

Previously posted the following earlier in this thread with no reply. Will post again with the question being: Is the following claim bogus? If true how and when does cell balancing take place/occur ...

Getting back to this inexpensive BMS ... https://www.amazon.com/Protection-Charging-Controller-Balancing-Function/dp/B07DMTSZQ5 ... do you believe the following and if so does it require you to leave the charger plugged in after the green light (fully charged) comes on ... and if so for how long before unplugging your CCCV charger? ...

• BALANCING FUNCTION: This battery protection module has a equilibrium function to keep each cell in balance and can extend the service life of battery.

Is this individual cell balancing claim completely bogus or partially true? If somewhat true--how does it work and to what extent?

 

[eMark]

Sorry, could you be more explicit about what you learned?

IMR I believe was only used for LMO

but yes INR can vary, mostly NMC & LCO

He explained it already that acronyms like ICR and IMR are more general as they don't reference the inclusion of all the tangible ingredients (e.g. Lithium, Cobalt, Nickel, Manganese or Aluminum). For example ICR references only Cobalt. IMR is an acronym for Lithium-ion Manganese Rechargeable and ICR for Lithium-ion Cobalt Rechargeable. Did you not watch his youtube link?