Two 24V Batteries for 48V eBike?

[thetimmy]

Can I use Two 24V Lithium Batteries in place of a single 48V battery? College taught my I can wire them in series and it will work, however real life is rarely as simple as exams questions.

I currently use the http://lunacycle.com/batteries/packs/48v/48v-panasonic-11-5ah-or-13-5ah-dolphin/ 48V Dolphin Battery.
I plan to rewire the cells and replace the BMS with a 24V version like this. http://www.aliexpress.com/item/bott...ic-bikes-with-BMS-2A-charger/32440666627.html
The batteries will drive a 48V controller http://lunacycle.com/motors/bafang-...fang-bbs02-750w-48v-upgraded-controller-3077/

I have a few questions for those experianced.
Can the BMS of the dolphin battery accept being connected in series?
Will both batteries drain at the same rate (assuming the ideal conditions and both batteries are identical)
Any other issues with this system?

See the next post for more details on why I want this.

 

[999zip999]

Why just use the pack you have as it is. Why make problems ? Yes problems.

 

[thetimmy]

I'm transitioning from a sticks & bricks house to a Tiffin Allego Bus (RV). I plan to travel the country off the grid with 1000W of solar and a massive bank of lithium ion batteries. The first generation of programmable solar controllers built for lithium ion batteries are just coming out to market. From the point of view of the batteries, the solar controller is their charger, it can be set to slow or fast charging (.1C thru .5C) and to optimize voltage for capacity or longevity.

The massive bank of lithium ion batteries will be composed of eight 24V lithium ion batteries like this http://www.aliexpress.com/item/bott...ic-bikes-with-BMS-2A-charger/32440666627.html.
The first generation programmable solar controller supports batteries up to 32V http://electrodacus.com/SBMS100/manual/SBMSmanual.pdf
So I will need to use two 24V (actually 25.9v) to power my 48v eBike.

I could not locate any DC to DC smart chargers for a 48V lithium battery.
The current system takes the solar power DC and steps it down to 12VDC and stores it in 12V SLA batteries then it gets inverted to 115VAC which is connected to my 48v smart charger that converts it to 48-55VDC. This is totally inefficient and thus why I am asking the question.

 

[Hwy89]

Let me see if I understand correctly. You are replacing the lead acid "house" batteries in a motor home with 24v lithium bike battery packs and you want to know if you can run two of the 24 V packs in series for your 48 volt bike. Is this correct?
How are you converting the 24 volts to 12 volts for the motor home systems?
There are lots of choices of RC hobby chargers that run directly from 12 V and will charge up to 14 s lithium. (Mine only goes up to 6s but there have been others mentioned here tha will do 14.)
I'm pretty sure that you could put two of the dolphin packs in series to run the bike then separate them for charging. Be careful if you have several packs fully charged on the "house" bank and try to connect a depleted battery off the bike as there will be a large rush of current from the full batteries to the depleted battery.

 

[dogman dan]

I'd definitely lean towards some kind of setup that kept the pack 48v, kept it on the current bms for discharging. That would also allow opportunity charging when you happen to be at an AC plug.

But you can change to a better plug for the bms, allowing the pack to split into two 24v packs for charging purposes. When you charge 24v, you'd just have two naked packs, with the bms disconnected. Then an 8s RC charger that runs on 24v can balance it if needed, or generally, just do a bulk charge. Use a higher quality plug for the bms disconnect, so it doesn't wear out.

 

[Hwy89]

Do you have one of those Electrodacus solar charge controllers? I would be interested in finding out how it works for you.

I've been traveling around for the last year with a 185 watt solar panel to charge the 12V house batteries in my rig. I use a Quatro balance charger (4 channels 6S each) to charge two bike packs at a time (16 p 6s 18650 cells) which are linked in series on the bike. The Quatro charger is powered directly from the 12V house batteries.

I have been toying with the idea of converting to a large 18650 pack to replace the lead house battery but have not found a system that would allow solar charging and also be able to charge through the converter from the 110V land line.
I would build a 4s 50p pack which would fit nicely in the battery box that came with the rig.