Multiple Batteries / Mixed Chemistry Q?

[MeanGene36542]

I currently have an ebike: 36v w/ 16Ah LiFEPO4 on a rear rack. Can I mix chemistries, e.g. add a frame mounted Li Ion 10S 6P, 29E cells, 36V, 16.5Ah? Can they be combined in parallel and/or used independently without issue? (I would isolate & charge each battery independently)

 

[dogman dan]

It's tricky to combine lifepo4 and lion, because they tend to have such different charge to voltage, and different stop discharging voltages. Your best approach will be to ride awhile on one, then switch to ride some more on the other.

 

[MeanGene36542]

Thanks for your feedback Dan... all agree?

 

[KINNINVIEKID]

I would not mix them ,simply run them as 2 seperate systems.
I have done it myself with a LiCoMn on a rear rack as some LiPos in a frame bag.
Even using the same chemistry but of different ages can cause problems.

 

[dogman dan]

Lets get into the details anyway. When I combined 14s lipo with 16s lifepo4, it was pretty awkward. They did start at about the same voltage, 58v.
But on the other end, I had to stop the lipo while there was still a fair bit of capacity in the lifepo4, or risk over discharging the lipo.

Running 36v, 10s and 12s for the lifepo4, you'd need to stop your discharge at about 3v per cell for the lifepo4. They will be able to start out the same voltage, provided your lifepo4 is at 3.5v per cell. So it will be like roll to the end of the driveway with just the lifepo4, then hook up.

In your case, I saw no pressing need to bother with combining them. When I was doing it, I was trying to eek just a few more cycles from a dying battery that could not run the bike by itself anymore. But I still wanted 5 ah more range, whatever it took to get it.

 

[dnmun]

can you show a picture of the lifepo4 pack that you have so we know what you need?

i run 21S of lipo in parallel with 24S of lifepo4. you can run 14S of lipo in parallel with the 16S of lifepo4 if you can wire it up properly and can purchase a specific balancing voltage for the lipo BMS and if you know how to adjust the charger output voltages.

just do not know your skill level and if you can do this.

to fully charge 16S of lifepo4 to 3.65V requires 58.4V on the output of the charger. full charge on 14S of lipo is 58.8V.

we know it is not good to charge the lifepo4 above the 3.60V/cell level and you do not wanna leave your lipo charged up to the full charge 4.20V level for long periods.

if you order a Bestechpower BMS such as the 16s lipo D167 then you can use the first 14 channels for the lipo and if you can order one with a 4.15V balancing voltage then you can charge the 14S of lipo to 58.1V and if you charge the lifepo4 from that same point then the cell voltage of the 16S will be 3.63V so almost full charge and just .03 over the balancing voltage of the lifepo4 BMS.

so you should be able to charge up both packs in parallel and discharge them in parallel with protection for both packs against short circuits on the output as well as protection against over discharge and over charging.

the advantage of doing this is that if you charge up to this level and do not use the batteries immediately, then the lifepo4 balancing network will drain voltage off of the lipo pack and reduce the voltage on the lipo cells back down to about 4.1V so the pack is not too too totally hot anymore.

but if you use the pack immediately after taking it off the charger you should be able to use that last 7% or so between the 4.15 and the 4.1V of the lipo. and instead of losing that charge to heating the balancing network on the lifepo4 then it will all be used to propel the ebike. so using the battery immediately when it reaches the 58.1V level and is balancing instead of letting it sit around overnight after removing from the charger should help keep about 8% of the charge over the lifepo4 balancing voltages.

plus by having the drains of the two BMSs in connection then the 16S lifepo4 pack voltage will be sustained up around the 14S lipo pack resting voltage too. so it will be a higher voltage to the controller at all times.

 

[MeanGene36542]

I'm just a newbie and my (first) bike is a stock Prodeco Phantom X3 with a LiFEPO4 36v /16Ah battery in a sealed unit which I must admit has served me well over the last 9 months and 3500 miles. After exchanging emails with Paul @EM3ev I've opted to buy his 16.5 (bottle style) frame pack which I'll use as a 2nd bank for my longer journeys of 35-50+ miles. I am planning my next bike already which will probably have another DD rear hub motor, but with a 48/50v battery system for just a little more speed and again long range. Thanks to all of you for your input!