14S performance

[E-HP]

Background: I've been experimenting with different voltages on my rear hub motor ebike, by running different combinations of lipos in series with my 14S UPP triangle pack (cheap cells), mainly for deciding on my future battery upgrade. My main pack is limited to 30A continuous, so I've limited battery current to 30A to avoid abusing it too much. I've gone as high as 22S (90V), which was fun, but not what I'm looking for for my main pack. I'm landing at 18S as being a good combination for my riding, giving decent speed with field weakening, on my slow wind motor, to keep up with traffic when needed (something over 30mph, but haven't tested the top speed). It also climbs better, since I can maintain a higher speed too. I did two 1 mile climbs in a row the other day, 800 ft elevation so around 15%, and the motor was barely warm.

I've started to come full circle with respect to my main pack replacement. When I started this endeavor, someone on this forum suggested that I just keep 14S and upgrade the cells, so I'm starting to see the light. I have a feeling that the extra lipos/voltage are helping with my performance due to the extra power provided at the same 30A current limit, and that if my main pack had greater current capability, I could replicate the same performance (climbing), with 14S. I don't really need the extra speed, although fun to play with, for my normal riding, but having the extra current on tap makes a difference. So, I'm going to do a couple more tests to see.

I want to use the same hard cased UPP pack style for the upgrade, and 14S seems to provide space for the most parallel groups (8P). Going to 16S would have the same cell count, but fewer parallel groups, and 13S wouldn't allow anything greater than 8P either. UPP has a 14S8P option using Sanyo cells and a 40A BMS, 100A peak.

Question: So here's the question: If I use my CA to limit current to 40A, and connect lipos for 14S (no main pack), will that provide a good proxy for 14S performance of a battery pack with quality 18650 cells?

I'm going to still be using my series lipos for fun, but my main goal when starting my experiments is to find the best voltage and cell combination before I commit to the upgrade.

 

[999zip999]

More info on motor and controller.

 

[E-HP]

More info on motor and controller.

7kW Powervelocity Bluetooth, Sine Wave 36V-100V
Generic eBay 1000W motor kit, MXUS direct drive rear hub
52V 14S8P main pack w/generic Chinese cells
4 x 5Ah 4S lipos, paralleled and in series with main pack

Will be testing with 3 x 5Ah 4S and 1 x 5Ah 2S in series for 14S, 20C rated, but limited to 40A via the CA.

 

[goatman]

14s8p=112 cells
16s7p=112 cells

same watt hours available

i run 17s but am dropping to 16s because of the luna sur ron 10 amp charger.

14s just seems too weak with a low battery

 

[E-HP]

14s8p=112 cells
16s7p=112 cells

same watt hours available

i run 17s but am dropping to 16s because of the luna sur ron 10 amp charger.

14s just seems too weak with a low battery

Yup, I have an email to UPP asking if they would configure to 16S7P but have t heard back. They have that configuration with Samsung 2900 cells but no Sanyo 3500. That would still provide 40A continuous, which will meet my needs.


Sent from my iPhone using Tapatalk

 

[999zip999]

I'm buying a battery from these guys it should be here in the next couple days.
https://bicyclemotorworks.com/product/52v-16ah-samsung-40t-high-output-lithium-ion-e-bike-battery/
It's a custom 20s of Samsung 40t 6p

 

[E-HP]

I finally got around to testing with lipos in different series combinations, limiting current via the Cycle Analyst. 14S at 40A was pretty good, with decent acceleration and climbing hills nicely. 14S at 60A was much better though. Current makes a big difference. The UPP 14S8P pack with Samsung or Sanyo cells comes with a 40A BMS, but can put 100A out peaks, so I'm hoping it will perform similarly.

I made the harness to put up to 5 packs in series, using the female half of the XT60's, shorted, for the unused plugs.


16S at 50A is really nice, riding around the neighborhood, which is mainly 6%-15% rolling hills, is pretty effortless (I pedal). The motor stayed lukewarm during testing. It felt similar to 14S at 60A, the difference in feel being subjective. It seems like as long as I can pump 3000W into the motor without hurting the battery, that's perfect for most of the riding I do.

I think I'll end up going with the same 14S8P pack configuration I currently have, but with the Samsung/Sanyo 3500 cells. Rated current will go up by a third, and capacity goes up 40% to 28Ah. Then my series battery packs can be added as needed for a proportional increase in speed, power or capacity (and fun).

 

[E-HP]

I tried several more tests yesterday, running 16S lipo only, setting different current limits and checking the readings I'm seeing on my Cycle Analyst, and the seat of the pants feel. I set the power limit to 6kW, so there was plenty of headroom for testing the different battery current limits. Testing was done on flat ground, observing acceleration from dead stop, and throttle roll on from a ~5mph rolling start.

The highest power reading from a dead stop was 3280W, with my battery current limited to 50A. I tested battery current limits from 40A to 80A, but raising the limits didn't increase the peak power hit before power tapers off as the bike accelerates. That's what the data shows. However, the CA power display has a slight lag, so I suspect the peak watts are higher when the throttle if first applied. This shows up in the seat of the pants feel, since setting the battery current limit to 70A vs 50A definitely feels stronger off the line and for the first 10-20 feet or so. 50A to 60A is less noticeable, as is the difference between 60A and 70A, but you can feel increases of 20A+ more easily. 40A to 70A is a pretty noticeable difference in feel. However, rolling start acceleration differences weren't noticeably different for current limits above 50A.

My thoughts are that for this cheap MXUS 1000W motor, 3500W is about all it's going to take advantage of for riding around town, so 55A or so is all I need from my battery. It would potentially pull more on hills, but I'm not going to want to put that much power through it anyway or experience a meltdown. I also realized that I won't be able to get that much current out of my UPP 114 cell pack, even configured with the best cells, so I'm looking into other options, which are:

• I've found that a 20S7P triangle pack just fits within my triangle (I see lots of packs with this configuration, with pretty consistent dimensions). That means I can get 140 cells, in some configuration, to fit (14S10P or 16S?)

• Move to lipos, likely 18S, using 6S 10Ah bricks in series (two sets in parallel for 20Ah

I'm going to do more testing today, but right now I think for this motor, I won't see many advantages of having current available above 60A or so, so going with a bigger motor would likely be the solution if I want more performance (since neither power/current from the controller or battery are limiting it in any way).