One of the more common questions I get asked is whether people should buy a 48v or 52v battery to drive their ebike mid drive kit. How much power you use on your builds is a choice everyone has to make for themselves, and many people seem happy with lower voltage while others want as high voltage as they can get away with, so they can eek out a slightly higher top speed. The BBS02 and BBSHD drive unit controllers can take a range of voltages from a low of 39v to a high of 60v, but there is no question that these units perform much better at the higher end of that range. A 52v battery fresh off the charger at 59v is a peppy wheelie machine, while on a 48v battery when the voltage drops below about 44v starts to feel pretty anemic. What are the long-term consequences of reliability from driving these units with a 52v battery versus the industry standard 48v battery?
First, you should figure out what battery you have, as you might think you have a 48v battery that is really a 52v battery. When your battery pack is fresh off the charger just hook it up to a volt meter. If it reads around 54v then it is a true 48v battery, if it reads 58v or 59v then you have a 52v battery. LifePo4 batteries often come in a 16S (a string of 16 cells in series) configuration which equals about 52v volts nominal, although these batteries for whatever reason are often sold on the Chinese ebike market as 48v batteries. If you are running LifePo4 a ‘real’ 48v pack will only be a 15S configuration. 18650 cells that are 52v run in a 14S pack configuration although some Chinese vendors (like Paul) call these 50v packs for whatever reason, further adding to the confusion. ‘Real’ 48v 18650 packs are sold in a 13S configuration with a BMS that will be around 54.4v fresh off the charger. If you are running HK lipos they are about the same voltage as the 18650 cells, although there are people who run their BBS02 systems off a 12S system (44v nominal) , I really do not recommend it.
Why would you want to use a more powerful battery pack than what the controller was designed for? That’s really the million-dollar question, and it is my belief that these mid drives were actually designed from the ground up to work with 52v packs. In China, it is not uncommon to buy a 48v labeled pack that is really a 52v pack, so the folks at Bafang had to design for that contingency. Since they had no idea what battery people were going to use with their drives, they made it work with the most powerful one that people would buy that they would expect to work with their drive unit. Now that Bafang has upgraded the controller mosfets, the weak point on both the BBS02 and the BBSHD is the nylon primary reduction gear . When the BBSHD was hooked up to a 65 Amp Lyen controller the nylon gear was the first thing to melt. Luckily the nylon gear is only about $20 to replace and it takes about an hour for a BBS veteran to swap out.
Do you really feel a difference when riding with a 52v battery instead of a 48v battery? I have spent hundreds of hours riding the BBS02 & the BBSHD with both 52v and 48v batteries from a variety of vendors. Honestly, right off the charger both the 48v and the 52v batteries feel about the same even though the 52v battery is about 4v more. I have not noticed any difference in the top RPM range of the unit, although it might be slightly higher with a 52v pack. The real differences come when your ride is about 1/2 over. With a 48v battery, once your battery is about half depleted you can feel the power drop off slightly. As the battery gets down to about 1/4 of its charge left, the difference becomes even more noticeable with both throttle lag and a noticeable lack of power. With a 52v battery this never really happens as the voltage never sags into the ‘ho-hum’ zone. With a 52v battery the BBSxx drive units run quite powerfully right up until the battery BMS cuts out.
What about the long-term reliability of the drive unit based on battery usage? Unfortudently I am not the best one to consult on this because I have swapped batteries around on drive units pretty haphazardly and it’s hard for me to remember what battery I had on which drive unit at the time of failure. I know that on the BBS02 both nylon gear failures I suffered were with 52v packs hooked up at nearly a full charge. I also know that the one controller failure I had was with a 52v battery at nearly a full charge. In general, I have had enough problems with the BBS02 that I still hesitate to recommend it to people for singletrack riding. Those statements alone might be enough to keep you away from using a 52v pack with a BBS02, but also be aware that I’ve beat on my BBS02’s without remorse for over 500 hours with a 52v battery on brutal singletrack. That being said the BBSHD is an animal of another color.
The BBSHD seems to run just fine all day long at 30 Amps and with a 52v pack. This motor system was so overbuilt that I honestly have a hard time believing that you are going to have any problems with this unit using a 52v battery over a 48v battery. The controller has 12 mosfets instead of 9 with the 750W BBS02 and there are large cooling fins on both the motor and the controller. I’ve hooked up a temperature probe on my BBSHD and the thing barely gets hot even when climbing extended hills at full throttle. Try that on a BBS02 and you will most likely have a serious problem.
Overall the voltage of the battery you’re using is not as important as having the right sized chainring for the application. If you are trail riding, you will not want to use the large 46T steel chainring with the BBSHD or the 48T chainring with the BBS02. I find that the 42T Luna eclipse or the 42T Lekkie Bling Ring work pretty well for both trail riding and commuting. If you have a cargo bike or a tandem then a 30T Luna Mighty Mini is a decent choice, but I think it produces a little too much torque for the trails. On the BBS02 for trail riding, you will want a 38T or smaller chainring, I highly recommend the 30T Luna Mighty Mini for the BBS02. This is by far my favorite BBS02 chainring and it will help save your plastic gear and your controller when you are running with a 52v battery. The average size of chainring on my BBS02 builds is 34T and I have had great luck with both the 34T and the 36T Raceface rings with an adapter.
Be aware when you buy your BBS02\BBSHD that there are a LOT of ebike kit resellers out there who will NOT warranty your drive unit with anyone else’s battery (regardless of the voltage). You should be aware of this before you plan to buy the drive unit and the battery from different sources. I recommend that you buy your drive unit and your battery from the same dealer so you are guaranteed that it will work and that you will have connectors that will match. When in doubt about whether your ebike controller will take a 52v battery without hitting the high voltage cutoff, you should contact your controller dealer before you purchase a 52v battery and ensure the controller will not cut out at 60 volts.
If you are running a hub motor and want to decide between a 48v and 52v battery I’d say just go with the 52v battery. Most quality controllers will be able to take the extra power and it should give you a few more mph of top speed. In general, if you want more torque you add amps, if you want a higher top speed then you add volts. When you add amps you have to make sure that your phase wires are thick enough and that the controllers have enough solder on the boards to carry the loads. When you add volts you really only have to worry about frying your mosfets in the controller. There are some newer 60v and 72v 18650 packs that are hitting the market, but as of right now I believe that the 52v packs offer the best reliability for the price and are also the safest choice.
I’ve used a lot of batteries over the years but the only two that have impressed me enough to write about are the 52v 14Ah NCRb shark pack (750W BBS02 only) and the 48v 21Ah 30q pack. I’m convinced that the next big thing is going to be the NCR18650GA cells and I’m hoping to get my paws on a 52v GA shark pack in the not to distant future for a review. When in doubt, the 25R cells are always a really safe bet, they are also getting pretty cheap in bulk (about $4.40 each).
Use a more powerful battery, you should. – Yoda