Dual MP3 set up...

[Rollerbyke]

I will soon have (2) MP3 conversion kits and (one) 48v battery... and (one) Large Screen Cycle Analyst...

I plan on attaching them to a tandem bike...

Question is... How to set the system up... as for both motors to be on the Cycle Analyst... If, possible...

Second question... How to set both motors to be on maximum torque for hill climbing... Speed does not matter...

Third question... As the primary use, for the two motors... is to climb back up the very steep hill... at the end of the ride...

The battery will still be mostly fully charged... as we will be pedaling along the beach...during the ride...and not using the motors or battery much...

The question... Will the (one) battery be able, to fully power both motors... for the short but steep climb...( 1 mile / 700 feet )

Or will it take two batteries to fully power both motors for the climb... even if we are only talking about a 1 mile climb. on (one) full battery... or batteries...

I am hoping that the one battery can do the job... and just be drained twice as fast... while putting out maximum power, to meet maximum demand... for the two motors...

Any answers will be greatly appreciated...

[pirontas]

It really depends on the Ah and discharge rate of the battery pack. Many packs are unhappy running at 2C (Ah rating * 2) for more than a few seconds here and there. The MPIII specs say the controller pulls a max 35A continuous, so that's 70A combined for the two motors. With a heavier tandem bike and two riders, going up a very steep hill, I'd assume the motors would run at around the max amps, even at low speed.

So if you had a 40Ah battery that had a true max cont. discharge of 2C (according to independent research, not just a claim from the manufacturer) then it should be fine. But discharging faster than 1C will shorten the cycle life. The number of cycles advertised is usually based on testing at 1C and room temp., and sometimes 0.5C when they want to boast a higher cycle count.

As far as using the cycle analyst or controller software to limit the amps to the motors, this may be possible but seems risky to me. Electric motors should be allowed to run at a reasonable RPM when put under load. If they were to stall going up the hill, or accelerate very slowly, they would produce a lot of heat. In an extreme case the windings in the motor could melt, but more likely the internal controller would overheat.

If it were me, I would run each motor with its own battery pack, even if I had faith the one battery could do the job. At the very least a 2nd battery would take a lot of strain off your main 48v battery, and it would live longer for sure.

I haven't used a cycle analyst so I can't be much help with that.

Good luck with everything. If you could make a video of that climb it would be awesome. I would check it out for sure Have fun!

[Lollandster]

You might want to specify what chemistry your battery uses.
What I found out before I ordered my battery is that most LiFePO4 batteries can deliver 10C without problems and do 15C in shorter periods while a123 cells can do 30C continuously and 65C bursts. Sealed lead acids I found usualy had a maximum at about 2C (car batteries can often do 10C short term), but this varied from manufacture to manufacture, they where usually tested at c/8 or less. I never looked into other chemistries, but I think pirontas post might be covering Li-Ions. Most lefepo4 bike battery packs I've seen for sale has had a BMS that only delivers about 1 to 3C. I guess you can bypass the BMS if you can trust the cycle analyst to protect your batteries or you can rebuild your battery with a stronger BMS. If you can afford two batteries that would probably be best as heavy usage might shorten battery life as pirontas said. Don't take my word on any of this, I'm fairly new to non LiPo battery packs. I hope someone else can confirm what I say, or prove me wrong.

I can't help you with all the other questions you have since I'm new to hub motors, but surly someone else can.

Edit: In case someone decides to read this I though I might rectify a mistake I did. It turns out a lot of prebuilt battery packs uses cheaper LiFePO4 cells that can only deliver 2C. This means you might not be able to just bypass the BMS to get more power. My disclaimer still applies, don't take my word on any of this.

[Bikemad]

Question is... How to set the system up... as for both motors to be on the Cycle Analyst... If, possible...

Check out Gary's video showing how to connect the two kits to a single set of controls.

As far as the Cycle Analyst is concerned, it should be possible to connect this to monitor the current draw of both motors if you are using a single battery or two batteries connected in parallel. If you are using a separate battery for each wheel, it will only be possible to monitor one of the motors.

Here is an updated diagram for the Cycle Analyst wiring details:


The switch is optional, but it enables the Cycle Analyst throttle override to be connected or disconnected to quickly swap between restricted speed/power and unrestricted speed/power.

The original solution to the Cycle Analyst problem can be seen here.

Second question... How to set both motors to be on maximum torque for hill climbing... Speed does not matter...

The Factory default setting for My MPIII controller was pre-set for maximum current (maximum torque) so unless they are programmed differently nowadays, I presume this will still be the case with yours.

Third question... As the primary use, for the two motors... is to climb back up the very steep hill... at the end of the ride...

The battery will still be mostly fully charged... as we will be pedaling along the beach...during the ride...and not using the motors or battery much...

My only concern here is the amount of residual drag produced by two motors (which will require more pedal effort to overcome), you could find that you will need to use a bit of motor assistance to help overcome this drag if you're cycling along the beach at over 10mph.
The amount of assistance you use (if any) will ultimately depend upon how energetic you and your rear passenger are feeling.

The question... Will the (one) battery be able, to fully power both motors... for the short but steep climb...( 1 mile / 700 feet )

Or will it take two batteries to fully power both motors for the climb... even if we are only talking about a 1 mile climb. on (one) full battery... or batteries...

I am hoping that the one battery can do the job... and just be drained twice as fast... while putting out maximum power, to meet maximum demand... for the two motors...

As already mention by both Lollandster and Pirontas, the combined current draw from both motors is probably going to be too much for a single battery (assuming you have opted the GM 48V 10Ah battery) and this could result in the motors cutting out under continual high load.

They don't appear to have a maximum continuous power output for the 10Ah packs stated on the GM site, but the 12Ah packs are only rated as 20 Amps continuous and 35 Amps Max.
I suspect that the current rating of the BMS on the 10Ah pack will be pretty much the same as the 12Ah pack, but that's just a wild guess.

After watching Gary's dual drive torque test video I reckon that you could be pulling at least 55-60 Amps on parts of your steep climb home, but without knowing how quickly your going to climb the hill, it's difficult to estimate how much lower the average current draw will be.

Gary has come up with a solution to ensure he has enough Amps available to power his Dual Pie Machine:



Alan