Would me allow me to use my existing 48V battery
The battery, even if it is brand new, may be part of the system limitation, especially if it sags in voltage much under load.
This is usually what causes system cutouts--the voltage drops below the controller's LVC, so the controller stops operating the motor, but leaves the system "on", display, etc. When the display/etc also shuts off, the battery's BMS is actually shutting off output to protect the cells against overdischarge damage, usually because of unbalanced cells (which usually means the battery is aged or damaged or wasn't built well to begin with).
If you haven't checked that, you may want to measure sytem voltage sag, between battery and controller. Using a wattmeter (as cheap as $10-20 on Amazon, etc like this one https://www.amazon.com/dp/B013PKYILS?psc=1&ref=ppx_yo2ov_dt_b_product_details ) is easiest, as they typically hold the min/max readings for a ride, where a voltmeter you have to be looking at constantly and it has to have a high screen refresh rate to catch some sag under short loads.
The wattmeter will also tell you the "real" power usage; they track Watts and Amps, and also count Ah (and often Wh), along with Volts. That way you will have a better idea of how much power you really need to do the job you need it to (in case the controller's readings are not correct, it's a double-check).
Torque sensor you can add, if you want one. If the controller you have now doesn't support one (most don't support one directly), you can add the Cycle Analyst v3.x to take all your inputs (PAS, torque sensor, throttle if any, etc) and process them to create a throttle signal to run the controller with. If the controller has no throttle input, or requires PAS signal to be present first to operate, then you may need a different controller that is throttle-only for this to work as designed without creating workarounds.
The good part about using the CA to interpret all sensor input is that you can get a controller that supports whatever features you want at whatever power you want without worrying whether it supports the sensor inputs you want to control it with (since the CA does that part). You can use the CA as a display screen (wattmeter / battery meter, speedometer, etc) on the handlebars, or you can put it in your system enclosure (bag, box, etc) since you don't need access to it for anything. If you need to change presets on it, or have an adjustable parameter, you can use remote handlebar buttons to access that even if you can't see the CA itself.
If you have to get a new controller anyway, you could go for one of the KT controllers that supports a torque sensor (using the Open Source Firmware (OSFW) created here on ES by Casainho, Stancecoke, et. al.; IIRC there are now preprogrammed OSFW controllers available from some places so you don't have to do this part yourself). IIRC these can use a display for changing assist levels, settings, etc., if you want one.
There are also some controller kits available that use a version of the Erider torque sensor directly, but you'd want to check that they support the power level you need and any other features you want; I don't recall much about them (only saw a couple of them a while back, both on Aliexpress from random sellers).
If you prefer to replace the whole powertrain (controller, motor, etc) with a middrive (like BBSHD, etc) that goes thru the bike's gears, it would be more efficient, but you will *have* to properly change gears for each situation every time, for this to be more efficient. If you don't shift gears it will still take more power than otherwise just like the hubmotor, because it won't be in it's efficient RPM range for the speed/torque you are after at that moment.
A new hubmotor, of whatever kind, is likely to be roughly the same efficiency as what you have now, within a few percentage points, unless the one you have is damaged in some way, or is not nearly the right winding for the speed/torque you need vs the wheel size it's in vs the battery voltage/etc it's being run at.
The simulator at http://ebikes.ca/tools/simulator.html may help you figure this part out (but measuring actual usage you see now with a wattmeter will help you see what you have, vs what you need).
For instance, with a Gmac 8T in 26" wheel, 20A controller, 48v battery,
https://ebikes.ca/tools/simulator.html?motor=GMAC8T&batt=B4816_GA&hp=0
then on the flats at full throttle it'll go almost 45kmh, but it takes almost 1000w from the battery to do it, and almost 800w from the motor (over 200w wasted power as heat in the system). It might go faster with a bigger controller (because it will take more power); you can play with the settings to see what else you can do with it.
Wheel Torq 21.2Nm
Mtr Power 786W
Load 788W
Efficiency 83.4%
RPM 354.8 rpm
Electrical Syst A
Mtr Amps 24.9A
Batt Power 942W
Batt Amps 20.0A
Batt Volts 47.2V
Performance Syst A
Acceleration -0.01 kph/s
Consumption 21.3 Wh/km
Range 36 km
Overheat In never
Final Temp 99 °C
So to do what you want, easily, a system that can do 1000w at least for as long as you need to go that speed would be needed. That includes the battery; if has to be able to support that without sagging very much (or else it won't be able to do it for it's entire capacity, as the sag would then cause either controller or BMS to shut off under the load). If your present battery can't do that, you would need to replace it or parallel a second one with it that can support the load.
A Gmac 10T, same controller/battery/wheelsize/etc
https://ebikes.ca/tools/simulator.html?motor=GMAC10T&batt=B4816_GA&hp=0
takes significantly less power at full throttle, so it has a lot more range for the same battery size, but it can't reach the speed you want.
Wheel Torq 18.0Nm
Mtr Power 607W
Load 609W
Efficiency 84.1%
RPM 322.9 rpm
Electrical Syst A
Mtr Amps 17.0A
Batt Power 722W
Batt Amps 15.1A
Batt Volts 47.8V
Performance Syst A
Acceleration -0.01 kph/s
Consumption 18.0 Wh/km
Range 43 km
Overheat In never
Final Temp 89 °C
turesnuur said:
I purchased it secondhand 5 years ago when it was 5 years old, making it 10 years old now. I have put around 8000 km on it myself. I have had to replace the frame battery with a luggage rack battery as it died and was not sourcable anymore.
It has a Bafang 8Fun 500W rear hub motor, operating off a 48v, 960Wh no-name battery
<snip>
- If I forget to gear down (traffic light), it is very hard to get away (as there is no torque sensor, so it has to move first)
- The LCD tells me I am exceeding 500w a lot. It may even get over 1000W during acceleration and when I have achieved speed it may still be above 500 despite me adding ample power myself
- The system will cut out at times, I got used to not go above power level 7 out of 9 to prevent cutouts and preserve range
But as the frame itself is solid; is there a replacement power train that:
Would me allow me to use my existing 48V battery
- Would run more efficiently (as in getting to 45 without needing a 1000W input / getting better range)
- Equipped with torque sensor
I.e. what alternative rear hub motor, controller combination wou;d you all recommend (given that there has been 10 years of development since)? I am interested in range primarily and don't need to do 45+ all the time (but need it sometimes). I am from a falt (but windy) country (Holland).
Thanks!
