Rear rack battery evaluation

[seebol]

I am considering buying a cargo bike, and it only comes with a rear rack battery option. The videos I found about batteries always examine the Hailong style downtube batteries. Does anyone have videos explaining the construction of rear rack batteries?

Below is a photo the vendor sent me of a 36V battery. Am I looking at 4 parallel packs of batteries in series of 10? Beyond the worse handling of a higher mounted rear rack battery, are there technical disadvantages of this setup vs Hailong/shark batteries which usually are a series of 10 packs of 4 parallel batteries? (E.g. is one style safer or more tolerant of misbalanced cells? )

I noticed that EM3EV doesn't sell rear rack batteries, which is a shame. Wondering if there was a reason for that...

 

[amberwolf]

There are numerous styles of "rear rack batteries", both in casing designs and materials, sizes, and cell types used.

Regarding "safety" that entirely depends on the specific pack builder and the materials and design and construction they used. Until you actually have it in your hands and can test the pack you get you won't really know how well it works or it's quality, etc., or whether it is capable of what the seller claims.


To figure out how many cells are in parallel for a pack, you take the total number of cells and divide by the number of series cells needed for that voltage a pack. For 36v, that's 10s for typical Li-Ion. The pack you show looks like it's 4 stacks of 5 wide and 2 high, which is 4 x 5 x 2 = 40 cells. 40 / 10s = 4, so 4p.

The cells have Samsung 26J printed on them (whether they actually are those cells or not would require testing and comparison to the spec sheet), which should mean they can do what has been tested here:

Test of Samsung ICR18650-26J 2600mAh (Pink)

 

[999zip999]

Show us a picture and style of the bike you're talking about let us know what you're going to use it for are there a lot of hills trails ect .

 

[seebol]

It'd be a long John cargo bike. With bikes near 100lb, I don't care as much where the battery weight is located. I just want ideal battery reliability. I've read that having 10 series packs of 4 parallel batteries is easier for a bms to balance. Since parallel batteries balance each other, you only need to balance between the ten groups in series. If you have four parallel groups of 10 batteries in series, the bms would need wires to each individual cell to do effective balancing. batteries connection series-parallel vs parallel-series

 

[999zip999]

Quality quality quality. That's what keeps the battery in balance not bms quality to say. These BMS can just help to balance a battery a battery shouldn't really be going out of balance. Mismatched cells of low quality need constant assistance because they're not matched.
Once again we need to know your weight what type of riding you're doing hills and how much are you going to carry on this cargo bike this are the answers we need to help you. And please give us a picture of what you think a Long John cargo bike is as there are many many different types.
Some with 20-in tires some with 24 some with 26-in tires

 

[999zip999]

What kind of setup are you thinking about front motor rear motor mid drive. I see you say 36 volt well that's pretty slow for a front motor or rear motor some mid drives work well but I'd still go 48 v. Talk to text at the beach so bear with it

 

[eMark]

I am considering buying a cargo bike, and it only comes with a rear rack battery option.

The rear rack of a true cargo ebike isn't for the battery. The battery is attached to the seat post or frame ...

https://www.addmotor.com/u_file/2212/photo/m81-ebike-accessoriesgif_1672132052.gif

https://cdn.shopify.com/s/files/1/1144/6508/products/Skycap2_black_800x.png?v=1668533789

https://u7q2x7c9.stackpathcdn.com/photos/25/11/372648_24600_XL.webp

Does anyone have videos explaining the construction of rear rack batteries?

About the only thing special about a rear rack battery is a protective enclosue to dampen bumps and vibration. You should be ok with a rear rack battery with protective enclosure in case of an accident.

 

[eMark]

It'd be a long John cargo bike. With bikes near 100lb, I don't care as much where the battery weight is located. I just want ideal battery reliability.

Agree with previous post that a 48V battery is better ooption with heavier cargo bike; even moreso with some moderate hill terrain. Here's one with rear rack battery auxilliary backup battery and a seat post mount for the primary (e.g. 10s5p 36V) battery ...

Battery reliability is as much or more the responsibility of the owner as it is the BMS and A-grade battery. For example only 90% charge most of the time (41.0V instead of a 42.0V full charge), and discharging no lower than 34.0V t0 33.0V instead of 32.0V to 30.0V. Best to use moderate speed and top speed only when needed. Also don't store for any lenght of time at FULL Charge. Get a DMM so you can check bounce back voltage after 1-2 hr rest (e.g. 34.0V to 35.0V resting volts with 10S battery). With 10S the 10 BMS wires are connencted to each of the ten parallel groups.

 

[Chalo]

Rack mounted battery is fine for a long wheelbase bike like that. Don't fret about unfounded generalizations regarding pack voltage or battery location. If the pack you're looking at has good construction quality, and the bike can get satisfactory performance at the relevant voltage, then it's fine.

 

[seebol]

Thanks for your advice. I've attached a screenshot of the cargo bike in question. The application would be carrying one or two children, so no need for incredible speed, just mostly flat paved paths with an occasional bridge crossing with ~25% incline. The bike has a net weight of 45kg. The motor is a 250W Bafang M410 middrive with torque sensor. Unfortunately there are not many reviews of this motor, but the integrated frame battery that Bafang recommends is 36V, 17.5 Ah.

 

[999zip999]

Great bike I love that style I guess the Danish have a couple like that. 8 years ago I saw someone at a e-bike event with a Crystal light motor in a big controller going 35 miles an hour around the track on it with a guy up front it was hilarious. You can get away with 36 volt on a mid-drive.

 

[tomjasz]

I've had EM3ev Dolphin and Polly cases (Reention) mounted on two longer wheelbase Townie and Townie style frames. Even the 120lb Mrs doesn't feel the bike is tippy. I also have an older Crystalyte rack pack with a shrink-wrap 24Ah battery with protective "plates". All good. Sadly they were discontinued before I could grab two more!

There's nothing wrong with a soft pack that's sensibly protected.

 

[999zip999]

As long as you're talking battery here you want to buy a quality battery the vendor will tell you the brand name and model of the cell he's going to use this will help you to get a high enough rate itself for your needs.
It's been known some popular battery manufacturers make a BMS without the balancing mode well that means LvC and hvc only.
There's a good battery book out there you need to read. Micah toll or something close to that name.

 

[eMark]

I noticed that EM3EV doesn't sell rear rack batteries, which is a shame. Wondering if there was a reason for that...

Chinese manufacturers (e.g. UPP) have captured the market for rear rack Li-ion batteries. I have 2-UPP rear rack 36v 10s4p & 10s5p batteries. The 5p is over 3 years old with 340 cycles so far (cost $256 with A=grade Chinese cells).

With your easy going biking with heavier load you should still get at least 12-15 miles round trip with motor assist (and some pedaling)

UPP also offers customized builds to your specifiaction ...
Custom Battery-Lithium Battery factory-UPP Battery ... scroll down to R006 - 36V 10S5P 17.5A

 

[tomjasz]

that UPP battery will have a featureless BMS and pack with steel connections rather than pure nickel. Typically over rated and for some a poor value.

 

[eMark]

UPP R007 AliExpress - 36V 20Ah - 21700 Samsung 50e (Nickel Bus Bars) - $400 (battery only) ...

https://www.aliexpress.us/item/3256803874029031.html?spm=a2g0o.productlist.main.9.4d4f2e37q6YslO&algo_pvid=81795f66-067e-49a0-952a-9d08deb2e7ea&aem_p4p_detail=2023052607285110547837622959010005174329&algo_exp_id=81795f66-067e-49a0-952a-9d08deb2e7ea-4&pdp_npi=3%40dis%21USD%21749.0%21516.81%21%21%21%21%21%40211be72e16851113315968366d079b%2112000027899989210%21sea%21US%210&curPageLogUid=h5DqIhpcpffE&p4p_pvid=2023052607285110547837622959010005174329_5

Only el-chepo Chinese 36V rear rack batteries might still use steel bus bars instead of nickel, but doubtful. Fires are more likely caused by cheap chargers that overcharge and a cheap BMS with faulty overcharge protection.

Overall UPP has as good of a rear rack battery as any Chinese rear rack 36V Li-ion battery. Personally don't believe it's worth the extra cost and labor to build your own spot-welded rear rack battery. Many members have used AliExpress with few complaints.

Again the overall cyclelife of a Li-ion battery is as much or more the responsibilty of the owner

 

[999zip999]

UPP sells battery packs without cell balancing. You must ask. Must.

 

[eMark]

Does anyone have videos explaining the construction of rear rack batteries?

Micah Toll's 5 videos. Here's 5of5 - Importance of a Good Reliable Charger ...

The other 4 videos 1/5-4/5 are listed on the youtube side bar.

First a couple photos of my own rear rack 10s3p design using 18650 Samsung 33G cells. Prefer using Vruzend Kit for experimental testing (nickel plated copper bus bars) in my Cargo Trike. Cycled 10 c/d times without a BMS. I'm my own best BMS when it comes to first experimental testing of a battery design. All 30 cells when tested individually were still within 8mV of each other after 10 c/d cycles. Charged to 41.0V and discharged to approx 33V. The BH cells cost $2x30=$60 (batteryhookup.com).

The other two photos are with 21700 5000mAh cells (actual capacity 4500mAh) to show spacing between cells. Total dimension 3" x 13.5" with just blue protective shrink wrap - before adding cushioning and protective enclosure.The DALY BMS shown is only 20A, and isn't enuf for 10s3p 18650 33G rear rack design and for sure not enuf the 21700 rear rack design. Would need a 30A DALY for 18650 33G 10s3p (19.5A MCD). and a 40A DALY for the 21700 rear rack design if the Controller has 25A to 30A cut-off.

Actually you'll rarely get the rated Ah range when charging to 41.0V and discharging to 33.0V to 32.0V (to optimize cyclelife longevity). That's why it's a good idea to build a 17.5Ah or 20Ah rated rear rack battery due to loss of Ah capacity as battery ages with more c/d cycles.

 

[eMark]

UPP sells battery packs without cell balancing. You must ask. Must. x

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Bus bars are nickel plated. Solid nickel bus bars increase cost a few more dollars. Brand of balancing BMS unknown (not Daly).

Another 10s DIY option is: The Barncat Battery- No weld/no solder ... The Barncat Battery- No weld/no solder ... 10s4p/5p 21700 50e - 3"H x 5.5"W x 15"L (approx enclosure od)

Another option is paralleling 4 of these ($160) ... Model 3 Cells 21700 36V lithium ion Battery 210wh 5000 mAh 10 cells XT60 . Remove shrik wrap, redo both power wiring, BMS wiring and add balancing Daly BMS.

 

[tomjasz]

UPP sells battery packs without cell balancing. You must ask. Must.

I have 10 or more UPP BMS. I'll post some photos and maybe someone can sort the maker.

 

[batteryGOLD]

I have 10 or more UPP BMS. I'll post some photos and maybe someone can sort the maker.

Looks like a store showroom (window shopper) no humor

Those bms need to be tested to know if full working and safe
The right corner bms w/ chinese text is used at some citycoco scooter, pushing 30A peaks. this bms works low and high level cut, but it gets a bit hot. maybe rated for 20A.. and some of those go faulty , maybe because used at 30A citycoco. some go crazy hot after faulty. some output mosfets burned? and current goes only at the rest of mosfets, generating lot of heat..

to test a bms, you need to do a full charge and discharge test methods.
the real bms cuts at low 2,7V or 3V and high cut level is at 4,2V-4,25V
if none of those protections happens or just one, than U could be on trouble or goin at fire risk level!

a quick way to test a bms is to put battery under a load, and simulate voltage at some B and B-1 number pin voltage samples.
the way to do this is to disconnect from cells 2 wires ,example B5 and B4 terminal and connect to a variable supply to variate from 2,5V to 5V and see if bms cut at low and high level..

write tha results at a paper!
if bms ok just do a check mark with edding 3000 pen at top of bms

have a nice time testing bms's

 

[999zip999]

Tomjasz did you buy all those bms's or they come off a old packs. They look brand new ? What size battery are they for mainly what do you know about them. And how much they cost ?
Looks like you have a heavy duty one on the far right you didn't buy that from UPP did you ?

 

[eMark]

write tha results at a paper!
if bms ok just do a check mark with edding 3000 pen at top of bms

have a nice time testing bms's

Maybe one of you would be so kind as to direct Seebol to one of the ES "BMS testing" threads
Otherwise here are some BMS testing youtubes ... battery bms testing youtube - Google Search

Now tha US minimum wage is $15 hr is there any American company can build a quality rear rack battery to compete with China ?

 

[batteryGOLD]

Otherwise here are some BMS testing youtubes ... battery bms testing youtube - Google Search

Are you serious? MATLAB bms´s testing? sure, before build a product need to be designed from scratch and circuit simulation,produce and testing..
butt after product out to final consumer, the only way to test is to simulate voltage inputs and expect output results..

too much matlab, will drive U crazy!

 

[eMark]

Apparently you didn't watch this DALY testing BMS youtube ...

... explains why a "balancing" BMS is close to useless. If your DIY build is with salvaged cells consider a "smart" active balancing BMS ... if you're not smart enuf to be your own best BMS

That's why all one really needs is a good BMS with overvoltage protection and undervoltage protection. As far as inexpensive BMS' the DALY seems to be the most popular.

Have an enjoyable MD weekend