Add a mid-drive motor to a 1000w hub-drive

[Lectriceye]

I confess that I am a newby with a strong electronic background. I have a very good 1000w hub drive ebike with a 48 volt 21ah battery. I don't care about speed and usually motor around on PAS 2 of 5 going about 12 mph pedaling with a cadence of about 70-75 RPMs, which is plenty fast most of the time. I like to go distances of 25-40 miles, and I ride a lot of forest service roads which often times have inclines in excess of 5% that can run 4 or more miles. In the last 3 months I have burned out 2 controllers on those long hills and I am coming to the conclusion that I purchased the wrong bike for my kind of riding. Without getting into a lot of detail about the circumstances of the demise of the controllers, I will say that I have ran the simulations and can see how and why they were zapped by too much current and the ensuing heat. Power is my friend heat is my enemy. Thus, I am now contemplating going to a mid-drive that gives me the advantage of combining the power of the motor with the gears of a mountain bike. I ran the simulation of a bafang BBS02B 750w on the same bike, and it indicated that I could ride any of those long hills up to 9-10% without running out of gas/juice. Using what little knowledge I gained in the last few months, I would like to add the BBS02B to my existing bike, which would be the most economical approach, I can get the get from Amazon for about $450 and do the work myself. I don't care if they run together or seprately and independantly. I have 2 batteries currently in use on my ebike with a blender, and a switch to turn them on or off as desired. they are there primarily for extended range. The downtube OEM battery is 48v 21ah with 30A BMS. the second battery is 52v 20ah with 40a BMS. Using both together is how I blew my second controller, obvious to me now, that I had about 40 amps available to my controller going up that 4 mile 7% grade.

So, the real question I have when running them separately, at different times, with the mid-drive switched off, what happens to the bub drive pedal assist? I need help from someone with more experience here.

 

[hillslayer@]

I just posted a thread about combining hubs with mid-drives . I added a BBSO2 to a 1500 watt DD hub, pretty happy with the results on pavement. I use the hub on throttle only and the mid-drive takes care of pedal assist

 

[Lectriceye]

Thanks for the reply, I had come to the same conclusion about using the hub on throttle only, hoping there was another solution, but clearly the hub PAS sensor comes right out of the hub where the motor will go. I may just use the hub as a backup if I get tired of pedaling on an extra long ride or if I have some sort of problem with the mid drive. I will look at your post.

 

[hillslayer@]

Thanks for the reply, I had come to the same conclusion about using the hub on throttle only, hoping there was another solution, but clearly the hub PAS sensor comes right out of the hub where the motor will go. I may just use the hub as a backup if I get tired of pedaling on an extra long ride or if I have some sort of problem with the mid drive. I will look at your post.

If you're hub is a geared hub it will freewheel while pedaling if direct drive hub it will have a little drag when not on.

 

[hillslayer@]

If you're hub is a geared hub it will freewheel while pedaling if direct drive hub it will have a little drag when not on.

I should add I did mine for uphill speed if your not needing that I would just build a trail bike with only a mid drive.

 

[neptronix]

Yeah big problem you'd have with the DD is that it constantly has some drag and the mid drive will be fighting it.
You'd want a very small and efficient DD that has low drag as a prerequisite.

If you don't need mega hill climbing power, it'd be better to just run a big DD and keep things simple, in most cases this will be lighter.

 

[Lectriceye]

Thanks for the reply, I had come to the same conclusion about using the hub on throttle only, hoping there was another solution, but clearly the hub PAS sensor comes right out of the hub where the motor will go. I may just use the hub as a backup if I get tired of pedaling on an extra long ride or if I have some sort of problem with the mid drive. I will look at your post.

I have a factory built 1000w gear drive hub. I almost exclusively ride forest service roads on the Oregon coast with a lot of long (3-5 mile 5-7+ degree hills). I blew 2 1500w controllers in the last 3 months, trying to grind up a 5 mile hill of 6 degrees. me and my bike weigh 300 lbs, and I didn't get past 2 miles up when it went out. fortunately I had 2 miles back down hill on the brakes and then 5 miles back to my car on shallow rolling hills pedaling withput power at 8-9 mph, but I made it fine. Thus my need for a mid drive, I don't have to speed up the hills, just get to the top and head back down the other side. The simulator says i should be able to do that and adding the bbs02 seems to be the most economical way to get to where I want to get, costing lest than $500 for the kit.

 

[Lectriceye]

Does anybody know if it is possible to interupt power to 2 motors with 1 set of brake levers; i.e., Like spice the 2 sensor wires together at the lever?

 

[neptronix]

If you have an on/off switch type brake lever, i could see paralleling the brake lines working out w/o complications. You'd probably want duplicate controllers, as the voltage coming off that line will vary from controller to controller ( a big difference could = major problems )

You can get a wimpy front motor kit for $200-$300. You can get a rear DD hub with 2x the climbing capability for ~$300. Anything would be cheaper and less complicated than a mid drive, if that's your priority.

Controllers would only blow because they're underrated, tuned for too many amps, or not getting enough passive cooling. If your main problem is blowing controllers, and you don't actually need more power, the solution is even cheaper and could be simply a matter of buying a high quality controller that lives up to it's rating.

Controllers determine the flow current, not batteries, BTW. Battery blenders probably have funky/choppy output ( as typical with cheap DC-DC devices ), and this might also be bad for controllers TBH.

 

[Lectriceye]

Thanks for your feedback. Both controllers are already defined; the rear hub controller is 30 amp for BLDC Geared 1000W, and mid drive is Bafang BBSHD 1000w. I will look into the electrical characteristics of the brake sensor for both. I am a newby with ebikes but have a strong electrical background to figure things out.

The hub controller was originally in a sealed plastic container mounted to the back of the down tube - a poor design with no heat sinking. I removed it from the "heat box" and mounted it on a 4"x9"x1/4" aluminum plate in the same location. I also placed a heat sensor on the controller, with a LCD readout on the handlebars so I could continuously monitor the suface temp. of the controller, I think the controller is unterrated for the bike and if this fix doesn't work I will replace it with a better and higher rated controller. Going from a gerad driven hub to a DD isn't an option for me at this point.

One of the fun things about being a newby on anything, is that I get to experience the joy of learning new things, sadly some learning experiences are expensive. I could use some additional advice on where to find information on the electrical characteristics of the brake sensor and what it does in the controller to cut off the current/voltage to the motor. Possibly it is as simple as interupting the voltage to the throttle? Also, the voltage and function of the throttle, which I assume is potentiometer varying a voltage input to the controller that biases the FETS?

Thanks for your help

 

[G8trwood]

Grin has a video on this a few years ago I believe. He talks about how to set up controllers for mid combined with DD or gear drive

 

[hillslayer@]

Thanks for your feedback. Both controllers are already defined; the rear hub controller is 30 amp for BLDC Geared 1000W, and mid drive is Bafang BBSHD 1000w. I will look into the electrical characteristics of the brake sensor for both. I am a newby with ebikes but have a strong electrical background to figure things out.

The hub controller was originally in a sealed plastic container mounted to the back of the down tube - a poor design with no heat sinking. I removed it from the "heat box" and mounted it on a 4"x9"x1/4" aluminum plate in the same location. I also placed a heat sensor on the controller, with a LCD readout on the handlebars so I could continuously monitor the suface temp. of the controller, I think the controller is unterrated for the bike and if this fix doesn't work I will replace it with a better and higher rated controller. Going from a gerad driven hub to a DD isn't an option for me at this point.

ouOne of the fun things about being a newby on anything, is that I get to experience the joy of learning new things, sadly some learning experiences are expensive. I could use some additional advice on where to find information on the electrical characteristics of the brake sensor and what it does in the controller to cut off the current/voltage to the motor. Possibly it is as simple as interupting the voltage to the throttle? Also, the voltage and function of the throttle, which I assume is potentiometer varying a voltage input to the controller that biases the FETS?

Thanks for your help

I would think you could just splice the mid drive into your current brake cut offs so it kills both motors. To setup your motors since you have a geared hub just make that throttle only, and pedal assist on the BBSHD when you want to go a little faster uphill just give it some throttle.

 

[Lectriceye]

I would think you could just splice the mid drive into your current brake cut offs so it kills both motors. To setup your motors since you have a geared hub just make that throttle only, and pedal assist on the BBSHD when you want to go a little faster uphill just give it some throttle.

Yes, thanks for the info. I have determined that both motors use similar magnetic switches, so splicing together should be easier than running another set of wires and magnets up to the handle bars. I have been playing around witht the hub throttle and your advice is what seems to work best; my econo mode limits the throttle to 12.8 mph, which is fine for casually motoring around town. I can generally pedal at that speed in gear 3 without power, so I leave the throttle off unless I am going up a hill, good exercise that way. The next power level up makes full throttle available. Since most of my riding is in the mountains, I will primarily use the Mid for that. I have yet to figure out the best way to use both at the same time or if I will ever need to.

 

[Lectriceye]

Has anyone connected 2 batteries simultaneously with 2 motors? A picture attached. Both batteries would have on/off switches so I could draw from eother or both at the same time.

 

[neptronix]

keep in mind that the voltages have to match fairly closely when you switch from single to parallel, otherwise you're charging one of the batteries in a way that doesn't limit current, and that current can be magnitudes higher than what the battery is rated for ( the larger the distance between voltages, the more current )

Battery blenders can overcome the problem, but they don't work with regen, and some of our battery's energy is lost in the conversion.

I would recommend keeping things simple!

 

[Lectriceye]

keep in mind that the voltages have to match fairly closely when you switch from single to parallel, otherwise you're charging one of the batteries in a way that doesn't limit current, and that current can be magnitudes higher than what the battery is rated for ( the larger the distance between voltages, the more current )

Battery blenders can overcome the problem, but they don't work with regen, and some of our battery's energy is lost in the conversion.

I would recommend keeping things simple!

Thanks for the input, I am currently running 2 batteries with a blender and 1 motor (no regen) and I am cognizant of the limitation of keeping the batteries withing about 4-5 volts of each other. When I have them both active at the blender, I start with full charge at 58v and 56.4. I can ride for about an hour before the 58v is discharged enough to equal the 56.4. I always check my battery voltage and log it after a ride so I know how each battery is performing. I am thinking of a devloping a voltage control loop that will monitor the voltage differential of both batteries and auto shutoff the lower voltage battery if the differential exceeds a certain level. Conceptually it doesn't sound hard to do and I am hoping someone has already developed the circuitry for it, and has it available in a nice inexpensive package. more on that later.

 

[bengxe]

I'm not seeing what advantage that could provide over the normal LVC in each BMS. Since it sounds like you have 2 batteries and 2 motors, is there a reason you don't just run 1 battery to each controller? If you cant discharge them evenly you could make the plugs/ wiring interchangeable so you can swap them mid ride. Battery blenders and mixing voltages are inherently risky, 2 motors gives you an opportunity to avoid that.

 

[2old]

It sounds (to me) as though you're making everything more complicated than it needs to be. Why not have two dedicated systems, use the brake cut off for one or the other (I don't use them since the BBS02 cuts out when I stop pedaling and my hub is throttle only) and climb with the mid using the hub as needed (actually if needed)?

 

[neptronix]

I just run a big battery here on my DD and enjoy regen a lot.
I don't even use hall sensors.

Less stuff to break = more reliability

 

[Lectriceye]

It sounds (to me) as though you're making everything more complicated than it needs to be. Why not have two dedicated systems, use the brake cut off for one or the other (I don't use them since the BBS02 cuts out when I stop pedaling and my hub is throttle only) and climb with the mid using the hub as needed (actually if needed)?

It sound like you have pretty well figured it out, and that is how ai plan to use the batteries and motors. I do have my connectors set up up so I can isolate a battery to a motor/controller or quickly quickly swap them if need be. Thanks for all the feedback.

 

[Lectriceye]

It sound like you have pretty well figured it out, and that is how ai plan to use the batteries and motors. I do have my connectors set up up so I can isolate a battery to a motor/controller or quickly quickly swap them if need be. Thanks for all the feedback.

This is exactly why I registered with Endless Sphere. I love the idea that there is such a wealth of knowledge in one place to be drawn from. I especially like that there is so much willingness to share that knowledge, thank you. I consider myself a techie without much experience with ebikes. I am always looking for technical solutions to solve problems, but sometimes the technical solution isn't the most practical.

 

[hillslayer@]

Yes, thanks for the info. I have determined that both motors use similar magnetic switches, so splicing together should be easier than running another set of wires and magnets up to the handle bars. I have been playing around witht the hub throttle and your advice is what seems to work best; my econo mode limits the throttle to 12.8 mph, which is fine for casually motoring around town. I can generally pedal at that speed in gear 3 without power, so I leave the throttle off unless I am going up a hill, good exercise that way. The next power level up makes full throttle available. Since most of my riding is in the mountains, I will primarily use the Mid for that. I have yet to figure out the best way to use both at the same time or if I will ever need to.

On my BBSHD hub combo I don't even have the throttle installed for the BBSHD just pedal assist, only throttle is for the hub motor, when I want a little more speed up hill I use the throttle. Also when taking off from a stop the hub throttle keeps you from having to worry about downshifts of the mid drive.

 

[Lectriceye]

On my BBSHD hub combo I don't even have the throttle installed for the BBSHD just pedal assist, only throttle is for the hub motor, when I want a little more speed up hill I use the throttle. Also when taking off from a stop the hub throttle keeps you from having to worry about downshifts of the mid drive.

I agree on how you use the hub motor. I won't have my BBSHD installed untill this weekend but, I anticipate using the hub tthrottle to start from a dead stop and use mid PAS in a mid gear to accellerate from there and in the hills. I will probably use the hub most of the time when casually riding around town. I have been practicing using the hub in econ mode (good to 12.7 mph) while pedaling, and only use throttle when going up shallow hills and can't maintain at least 11 mph pedaling. How did you handle the brake cutouts for both motors. I read some use left and right some only use on 1 motor, what do you handle that.?

 

[Lectriceye]

I agree on how you use the hub motor. I won't have my BBSHD installed untill this weekend but, I anticipate using the hub tthrottle to start from a dead stop and use mid PAS in a mid gear to accellerate from there and in the hills. I will probably use the hub most of the time when casually riding around town. I have been practicing using the hub in econ mode (good to 12.7 mph) while pedaling, and only use throttle when going up shallow hills and can't maintain at least 11 mph pedaling. How did you handle the brake cutouts for both motors. I read some use left and right some only use on 1 motor, what do you handle that.?

I am thinking I won't install the throttle or the brake cutout on the BBSHD, and maintain the option to add later if I find any reason to change that later.

 

[hillslayer@]

I agree on how you use the hub motor. I won't have my BBSHD installed untill this weekend but, I anticipate using the hub tthrottle to start from a dead stop and use mid PAS in a mid gear to accellerate from there and in the hills. I will probably use the hub most of the time when casually riding around town. I have been practicing using the hub in econ mode (good to 12.7 mph) while pedaling, and only use throttle when going up shallow hills and can't maintain at least 11 mph pedaling. How did you handle the brake cutouts for both motors. I read some use left and right some only use on 1 motor, what do you handle that.?

I don't use brake cut outs on any of my bikes . I just make sure to have really good brakes.