Battery configuration / Requirements Help

[ElijahTheConqueror]

Hi Everyone,
First time poster so forgive anything unconventional. Also feel free to link threads that can answer these questions.

I’m build an e-bike. 2 mid drive motors running parallel chains to the rear wheel, each will have a freewheel to account for if they l are not running in sync, however will be identical motors (36v 250w hoverboard motors) and one front hub motor (also 36v 250w). Each motor will have its own controller (identical for mid drives) and here’s where my question arises.

Should I run 3 seperate 36v batteries to each accordingly?
Should I run 3 in series and split them accordingly?
(will this divert the power evenly across them and draw it evenly from the batteries?)

Also side question, can I run a throttle rated for 36v seeming as it is only sending feedback to the controllers and not actually drawing 36v through it?

Happy to answer any and all questions and will post the build at completion.

 

[amberwolf]

Should I run 3 seperate 36v batteries to each accordingly?

For best redundancy, yes. But it depends on the reason for using three separate systems--if it's not for redundancy then there's not much reason to separate their power supply either.

Should I run 3 in series and split them accordingly?

You can't run them in series, or the voltage would be far too high for your 36v controllers and almost certainly would blow them up.

It also presents challenges to the BMS in the packs; if any turns off while in operation, you can end up with the entire pack voltage across the now-off FETs and if they aren't designed for that voltage, they'll fail. That could turn the system off, or it could just cause the BMS to be unable to ever turn the FETs off to protect the pack against any out-of-limits conditinos.

You can run them in parallel, however. If they all use common-port BMSes (only one C- or P- pad for all input and output on the BMS) then they can be left in parallel all the time for charge and discharge. If they're separate port (C- for charge and P- for discharge) you'd have to disconnect the charge ports while riding and disconnect the discharge ports while charging.

Given the behaviors people have reported, I recommend against any of the battery combiners, and would ust use commmon-port BMS on all and then charge them individually up to full, then directly parallel them and then leave them that way.


But if you're doing that, just get one bigger capacity and higher current-capability battery that can handle the entire system load. Simplifies everything.

(will this divert the power evenly across them and draw it evenly from the batteries?)

In parallel, each battery will contribute as needed/possible depending on it's internal condition.

In series...if you had a 100V+ system to run off them, then all batteries must work equally to provide the current, and any that can't will degrade performance or shutdown the system.

Also side question, can I run a throttle rated for 36v seeming as it is only sending feedback to the controllers and not actually drawing 36v through it?

I don't understand the question. If you're running a 36v system then a 36v throttle has no conflicts.

But anyway the throttle voltage rating is only for the voltmeter that's on it, for those that have one.

If they don't have a battery meter, they won't have a voltage rating. (other than the 5v that almost all of them use to power themselves, which is provided by the controller, not the battery).

Personally, I recommend against throttles with integrated battery meters or switches or anything else--if anything goes wrong in the wiring, crash damage, gets wet, etc., you can get battery voltage fed into the 5v or throttle signals back to the controller and blow up not just the throttle but the controller and anything else that was connected to the 5v (like motor hallls, PAS sensors, etc).

Same thing can happen if motor cables get damaged, if they have anything other than the three phase wires in them--phase voltages are battery level, and it's VERY common for people to damage the motor cable at the axle and blow up the motor halls, the controller, throttle, PAS, etc.

 

[DaLanMan]

Ermagurd, the idiot child that apparently is involved in impulse control just went nuts...

Ok, I gotta ask, how exactly are you putting 2 electric motors in the middle of the vehicle that is like 6" wide? I am kind of in awe and slightly terrified on what this answer is gonna be.

 

[ElijahTheConqueror]

Ermagurd, the idiot child that apparently is involved in impulse control just went nuts...

Ok, I gotta ask, how exactly are you putting 2 electric motors in the middle of the vehicle that is like 6" wide? I am kind of in awe and slightly terrified on what this answer is gonna be.

modifying the original crankshaft to house motor axel mounts and attaching the freewheels via custom fabricated parts that bolt through the motor casing, won’t be any wider than the pedals would’ve stuck out No pedals, and ofc no pedal assist.

 

[ElijahTheConqueror]

For best redundancy, yes. But it depends on the reason for using three separate systems--if it's not for redundancy then there's not much reason to separate their power supply either.




You can't run them in series, or the voltage would be far too high for your 36v controllers and almost certainly would blow them up.

It also presents challenges to the BMS in the packs; if any turns off while in operation, you can end up with the entire pack voltage across the now-off FETs and if they aren't designed for that voltage, they'll fail. That could turn the system off, or it could just cause the BMS to be unable to ever turn the FETs off to protect the pack against any out-of-limits conditinos.

You can run them in parallel, however. If they all use common-port BMSes (only one C- or P- pad for all input and output on the BMS) then they can be left in parallel all the time for charge and discharge. If they're separate port (C- for charge and P- for discharge) you'd have to disconnect the charge ports while riding and disconnect the discharge ports while charging.

Given the behaviors people have reported, I recommend against any of the battery combiners, and would ust use commmon-port BMS on all and then charge them individually up to full, then directly parallel them and then leave them that way.


But if you're doing that, just get one bigger capacity and higher current-capability battery that can handle the entire system load. Simplifies everything.




In parallel, each battery will contribute as needed/possible depending on it's internal condition.

In series...if you had a 100V+ system to run off them, then all batteries must work equally to provide the current, and any that can't will degrade performance or shutdown the system.



I don't understand the question. If you're running a 36v system then a 36v throttle has no conflicts.

But anyway the throttle voltage rating is only for the voltmeter that's on it, for those that have one.

If they don't have a battery meter, they won't have a voltage rating. (other than the 5v that almost all of them use to power themselves, which is provided by the controller, not the battery).

Personally, I recommend against throttles with integrated battery meters or switches or anything else--if anything goes wrong in the wiring, crash damage, gets wet, etc., you can get battery voltage fed into the 5v or throttle signals back to the controller and blow up not just the throttle but the controller and anything else that was connected to the 5v (like motor hallls, PAS sensors, etc).

Same thing can happen if motor cables get damaged, if they have anything other than the three phase wires in them--phase voltages are battery level, and it's VERY common for people to damage the motor cable at the axle and blow up the motor halls, the controller, throttle, PAS, etc.

Thanks a lot, now for more reasearch

 

[999zip999]

Can you draw this up and post this so we can see it.

 

[glennb]

Happy to answer any and all questions and will post the build at completion.

Good attitude.

What prompted this design?

 

[ElijahTheConqueror]

Can you draw this up and post this so we can see it.

Sure, I’ll upload a digital mockup in a couple hours,

edit.. mockup is in the thread

 

[ElijahTheConqueror]

Good attitude.

What prompted this design?

Initially I was hoping because I already had the hoverboard motors and bmx I could just splice them together, the more I planned the more complicated it became, the mechanical side is not a problem as I’ve been building and 3d modelling all sorts of things for 4+ years now, and learning new things (the electrical side) is a good way to stay sane.

I could’ve made it easier for myself, rebuilt a second hand ebike I bought for parts, or saved money by buying one prebuilt, but I like the challenge and I’ll end up with a 1 of 1 ebike.

 

[ElijahTheConqueror]

Super Basic mockup, took files from other people who have generously uploaded them onto grab cad for free, quite obviously missing components like the whole electronic setup, sprockets, actual chain size, freewheels on mid drives, etc etc. Batteries and controllers I may cram into a false fuel tank.. idk yet. But this thread was originally to help me decide on battery stuff so forgive the lack of effort. Hope this helps you visualise.

 

[DaLanMan]

Uhm, where ya gonna put yer feet?

 

[ElijahTheConqueror]

Uhm, where ya gonna put yer feet?

Like I mentioned, basic mockup, missing components, might just run front pegs or mount some.

 

[DaLanMan]

fair enough, it was just the first thing that popped into my mind.