Battery power dependent on level of charge?

E

EVDan

New Member
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USA
A new e bike rider with 400 miles on my Propella 9S Pro V2. I'm very happy with the bike and ride mostly in analog mode using the battery mostly for some of Seattle's challenging hills.
I have not run my battery below a 30% charge, and normally keep it at 60% - 80% charge. I am planning some longer rides and am wondering if the battery power output remains constant despite its state of charge till it finally poops out at zero. Thanks!
 
As the battery drains the voltage drops so less power at constant amps, and the amps delivered depends on your controller. There are low voltage cut-outs on the controller and the battery's BMS. It would be nice to know what your controller's low voltage cut-out is set for. You would need to operate above that limit due to inherent voltage sag in your system.
 
EVDan said:
A new e bike rider with 400 miles on my Propella 9S Pro V2. I'm very happy with the bike and ride mostly in analog mode using the battery mostly for some of Seattle's challenging hills.
I have not run my battery below a 30% charge, and normally keep it at 60% - 80% charge. I am planning some longer rides and am wondering if the battery power output remains constant despite its state of charge till it finally poops out at zero. Thanks!
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There is some difference but not enough for average riding concern. If you fully charge you will notice a more peppy response when compared to a battery near empty. Just keep in mind that the rate a loaded battery near empty will deplete is more quickly than when full.
Your battery quality and overall size (Ah) play a roll as well
 
If youre down to the last bar then you will notice a difference while climbing or into the wind.
In fact it may be as large as a power setting drop.
As mentioned cell condition, quality of battery and controller architecture play a part.
My tired Haibike when down to one bar can barely pull like eco on a hill even in Turbo.
 
This has always been a pet peeve of mine. This voltage drop issue is easily corrected by using a motor rated at a lower voltage than the battery. IE: a 36 volt motor with a 48 or 52V battery. A DC to DC buck converter could then be used to maintain constant voltage & current to the motor as the battery voltage drops. It would only add a few $$ to the cost of the bike but most manufacturers just ignore the problem.

I saw somewhere that there are a few e-bikes on the market that use this principle but I don't know the brands.
 
It is really down to the implementation.

My hub-drive e-bike seems to have a very weak battery protection. I could ride it with no significant power loss until the battery was almost empty, then an avalanche of warning signals appeared.
A 36 V Vado 6.0 can produce the whole power until 10% battery level then the assistance is slightly reduced; at 5% the assistance is cut off totally.
A 48 V Vado SL has a little bit less power below 20% battery charge, then the system drastically reduces the assistance below 10%, and the cut off happens: Range Extender at 8%, and the main battery at 5%.
A 36 V Giant Trance E+ works with the full power over the whole battery charge range down to 3% but the battery charge drops down the cliff below 20%.

There is no general answer to the question asked.
 
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I would test the ebike at under 30% power on Seattle hills to see if you have reduced performance. My old 16 Radrover will provide max power available until the battery dies. Example: I need 350w and Radrover can only output 300w in PAS 3 at low battery %; but, the Radrover will give me the full 175w if I only need that in PAS 2 at the same battery %. My Himiway seems to ramp down the power once I start to get below the 30% range in any PAS level.
 
Chargeride said:
It would constantly waste power though, unless it was physically removed till needed?
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And if you only use it to increase the voltage when the battery is low, it will draw even more current from the battery, increasing the voltage sag. Then the battery cuts out even sooner, so you still have to reduce your level of assistance and/or your throttle level.

EDIT: That's not right.

@6zfshdb suggests using 48V or 52V batteries to power 36V motors, so the buck converter would always be needed to reduce the voltage for the motor.

Buck converters are generally about 85% efficient and are less efficient when the input and output voltage difference is greater.

A high quality buck converter can be more efficient, but they all come with a large heat sink or even a fan to deal with the energy wasted as heat.
 
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mrgold35 said:
My Himiway seems to ramp down the power once I start to get below the 30% range in any PAS level.
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My ebike will go 43 kph with a fully charged battery (54.6 volts), then the top speed drops to less than 30 kph before the controller kicks out at ~40 volts.
All while drawing the same 21 amps from the battery.
 
mrgold35 said:
I would test the ebike at under 30% power on Seattle hills to see if you have reduced performance.
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I agree.
Testing it will help you get a feel for how quickly the power drops from 30%-0% so you have a better idea what your maximum range is.
 
" if the battery power output remains constant "
No Dan, Volts ( the unit of measurement ) are power and if you continue undercharging ( not balancing your pack ) and then discharging to some 0% of what?
(B.M.S. voltage Min? or actually an unknown value ) you may create a poopalla.
Sincerely
M.V.
 
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