Dual Batteries on an eBike ... ????

[Over50]

Oh man I don't understand why some bike companies go with 2 small capacity battery packs...

I'm with Alaskan on this. I like the form factor and modularity of the separate packs. I can take one or I can take two dependent on need. Often one is all I need. My Riese and Muller has a convenient bag that fits into the second battery harness and I use that when only using one battery. The Bosch Powerpacks fit easily in a backpack. One 500wh pack is easy to remove from the bike, throw in my backpack and take to the office. Perhaps having separate but modular packs also provides some insurance in case of pack failure. If one of my packs fails then I still have one to ride with whilst I wait for a replacement.

 

[Dionigi]

For the last year my wife and I rode R&M Nevo bikes with 500 watt power packs. Our rides are between 30 to 50 miles. At the end of our rides my wife (80 pounds lighter) has more energy left in her battery. This coming January we purchased two new Nevo bikes one having the duel batteries and the second with just the power pack battery. Our logic is we can extend our range by 50% by exchanging the power pack batteries in mid ride.

 

[JRA]

@Ken M I was addressing this: "unless I went with an A/B switch. Thanks for any additional feedback"

I was addressing the possibilities of using differing voltage systems using an A/B function. If you are using batteries of the same voltage as noted by KenF and Feliz et. al. a parallel system is entirely possible.

 

[Ken M]

@Ken M I was addressing this: "unless I went with an A/B switch. Thanks for any additional feedback"

I was addressing the possibilities of using differing voltage systems using an A/B function. If you are using batteries of the same voltage as noted by KenF and Feliz et. al. a parallel system is entirely possible.

Thanks that is exactly what I was hoping was the case. I just wanted to be able to plug in the 2nd battery in parallel when I wanted the extra capacity. It's not that important to me if they'll charge simultaneously but that would actually be beneficial if they did (I would think the BMSs will prevent over-charging of the smaller battery. I just want the simplest way to add more battery capacity but I will be certain to match at least the voltage of the packs and probably even the cells so internal resistances are not a problem.

Ideally I was hoping the smaller capacity pack could be 18650 cells and the 2nd rack pack could have 21700 cells for maximum possible capacity because the rack volume will simply allow a much larger pack.

 

[JRA]

"Ideally I was hoping the smaller capacity pack could be 18650 cells and the 2nd rack pack could have 21700 cells for maximum possible capacity because the rack volume will simply allow a much larger pack."

If you have 2170 cells they can withstand a higher charge rate that may be useful at times so I would just plan on using 2170's for both, you know that is what it is coming to. I hope to have a 14s3p HL here to test soon.

 

[Mr. Coffee]

Oh man I don't understand why some bike companies go with 2 small capacity battery packs.

Juiced offers 21amp and 32amp batter packs instead of connecting two battery packs.
They even developed their own casing instead of using two Reention packs. (Plus probably the fact that they didn't make a pack for 52v)

It's more convenient when you're charging out of the bike because you don't need two chargers and you can just carry one pack and pretty sure it would avoid extra mechanical or electronical complexity.

You don't need two chargers with the Bosch dual-battery system unless you want to charge both batteries simultaneously.

Having two smaller batteries rather than one big one makes it easier to get good weight distribution on the bike.

Since the PowerPacks and PowerTubes are a standardized design, you get somewhat better economies of scale than you would with a much larger battery that is less widely distributed. My suspicion is that in the future there will be battery sharing services where you can exchange your (hopefully partially) depleted battery for a freshly charged one and be on your way -- and that approach would only make economic sense if there was a standard battery pack profile.

As others have noted, it is sometimes convenient to operate with just one battery.

 

[tompat]

Maybe Bosch has a more advanced BMS that R&M is taking advantage of on some of their dual pack ebikes.

It's not the BMS which is technically is the system for controlling charging of the battery.

The entire Bosch system is far more advanced that just a pack of cells that delivers voltage on a pair of terminals, that then can be connected in parallell or series and wired to the motor controller.
In the Bosch system all parts of the system (batteries, motor, display) communicate together with the CANbus-protocol, familiar from modern automobiles. This way the motor can know exactly how many % the batteries have left. After draining 5% from one battery it automatically requests power from the other one and switches over to it.
Charging is done in a similar way. If you have both batteries on the bike and connect your charger to it, it charges the first battery up 5% and then the second up 5%, alternating between them all the way until full.

When both power draw and charging is done alternating i 5% increments both batteries are always utilized most like to each other. Not one of them will be more worn than the other. It helps prolong the batteries life, for what it's worth.

 

[Norm Harrris]

If you anticipate having to recharge both batteries quicker than 9 hours, buy a second charger, remove one battery from the bike and charge them both simultaneously. Problem solved.

Alaskan- What is your experience removing the second battery and fully charging that battery and then remounting it on the bike? So, you would have a partially depleted battery and a fully charged battery. How would the Bosch controller deal with that scenario? Is it contraindicated to do this?
Thanks

 

[Mr. Coffee]

Alaskan- What is your experience removing the second battery and fully charging that battery and then remounting it on the bike? So, you would have a partially depleted battery and a fully charged battery. How would the Bosch controller deal with that scenario? Is it contraindicated to do this?
Thanks

I recently went on a multi-day bike tour with a dual-battery R&M Charger and one extra battery. There were many very long and strenuous days with 70-80 miles of riding and substantial elevation gain of 6000 feet or more. Much of the distance was traveled on atrocious roads.

Typically I'd start out the day with two fully charged battery and the backup battery charged to 60-80 percent. When the two batteries on the bike were down to 20 percent (one bar) I'd swap the backup battery in and finish the day's ride. There was never a problem with the Bosch system -- everything worked as expected.

So no, there is no requirement that the two batteries in a dual battery system be in the same charge state.

 

[Norm Harrris]

Thanks for the info, Mr. Coffee.

 

[Alaskan]

What @Mr. Coffee said.

 

[tomjasz]

3 positions. Front, Off, Rear packs. Works without matching packs. Several of these done in 2015 and still flawless. 48v and 52v, 10Ah through 23Ah packs. The switches are a bit hard to find but they are a post away if interested. Sorry about notdirectly postingbut I don’t have the file on my iPad.