Questions about batteries and dual motors.

[Joe EE]

Some questions for the community;

I have a question about running 2 motors off 1 battery simultaneously. I am running a 48 Volt 1000 Watt Direct Drive motor front hub, powered by a 48 Volt 10 AH Lifepo4 battery. Not sure what the max discharge current is. I am toying with the idea of adding the same motor in the rear. Will it be safe to double the current draw off of 1 battery? Don’t want an accident.
Additionally, I am awaiting delivery on a 48 Volt Lithium Ion pack. Can I safely run them in parallel with the chemistries being different? Would I need to have 2 identical cells to do this? Would I be better off running each motor to its own dedicated battery? Lots of questions and different configurations possible. Just wondering what would be optimal, what would be dangerous and I’ll advised etc. should I decide to add the second motor. Thanks to all.

 

[Ann M.]

@Joe EE, it's unlikely that the BMS of that particular battery will allow that much current draw. I know that the Golden Motor 48V 10Ah LiFePO4 battery has a max rating of 50 amps output. Just one 1000 watt hub motor can draw as much as 25amps continuously, so 2 - 1000 watt motors will be at the edge of what that battery can handle. You certainly will have a shorter battery life and range and may experience power cutouts when the BMS is maxed.

If you had a 48V 12 to 30Ah battery you would be less likely to max out the BMS, since those have a max rating of 60+ amps, dependent upon the specs of the battery. Also, if this is a Golden Motor system, then using a battery larger than 48V could fry the FETS of the motor controller according to the manufacturer's website info.

As for running 2 batteries in parallel, that is risky since it is possible to have one battery dump directly into the other if they are not at exactly equal charge. That's a potential instant fire hazard. You would need to wire a Schottky diode in between the batteries to prevent the voltage dump.

And for more specific info on that setup, I ask @Rick Speicher, to elaborate, please

 

[Joe EE]

Thanks Ann, I am leaning toward running both motors with independent power supplies. It just seems less risky and achieves the same end result. Thanks for the reply.

 

[harryS]

You should never run batteries of different chemistry in parallel because they have different voltages at full charge. A LiFePO4 cell is 3.6V, while an 18650 is 4.2 V. A nominal 48V battery made from these two types of cells will not be equal. If you equalized them in voltage when connected, they have different discharge curves. Kaboom.

Even if they were the same chemistry, run two separate batteries. It's always safer and keeps one from making a sleepy headed connection error.

Many 10AH batteries don't have enough capacity to run 1000W very long. You could start with two as an experiment to test the wiring, and maybe on a fresh charge you might be able to pull both throttles easy. I would expect two full throttle pulls would either sag the battery below LVC of the controller or reset the BMS. That would be a bummer when trying to beat a train at the crossing.

Incidentally, I did make a two motor fatbike two years go. Used two batteries. Everything separate. A throttle on each side of the handlebars. It did pull me thru deep snow very well. Pulled me into a bad case of bronchitis too. The meds would have paid for a third hub motor. I took it all apart in the Spring. The Spruce Goose of ebikes for me.

 

[Joe EE]

Hi@harryS
I am thinking about running both motors off of two different batteries and on one throttle, that should be a blast. Thank you for your input as well.

 

[rich c]

Hi@harryS
I am thinking about running both motors off of two different batteries and on one throttle, that should be a blast. Thank you for your input as well.

Two batteries, one throttle? How many controllers? What kind of controller? Not an easy home shop hack to do what you are talking about.
Easy Motion, Evo Big Bud AWD, runs two motors, but one of everything else.

 

[Joe EE]

Hey Rich, I haven’t actually done this yet but it seems possible at first glance. I am running a Golden Motor with an integrated controller and governing the system using a Cycle Analyst. Micah Toll has an interesting video here
https://electrek.co/2018/04/30/all-wheel-drive-electric-bicycles/
About how to run 2 motors on 1 throttle. Using dual batteries may be a wrinkle but I have not fleshed out the idea completely yet. Work and other things have a way of interfering with my DIY bicycle pursuits. In theory, at this point, I think it might be possible. I believe Micah’s setup is using only 1 battery but both motors are running on the same throttle.

 

[Joe EE]

Hey Rich C. You ask a lot of really good questions. Remember when you asked if if I was looking for a moped lol?
Did you get a chance to follow up on my response? Did you look at Micah’s video? I think that I might possibly be onto something here. It may violate the 20 mph rule.. lol but with a new motor in the back...I won’t have to worry about the gauge of the spokes, don’t you agree?
Hope all is well for you my friend.

Just getting a little bit lonely for a response on this end ... in my “home shop” where I “hack”.

 

[harryS]

Sure, I think I could run two controllers off one throttle. The grounds on the two controllers has to be common. Only use the throttle power lead from one controller, and run the throttle signal to the other unit. Maybe I will try it.

Your Cycle Analyst may complicate things. I have never seen one. Doesn't it modulate the motor current? WOuldn't seem to work if you had two motors.

 

[Joe EE]

Hey @harryS, take a look at the video in the link I posted above. He pretty much spells it out ABC. I probably won’t be trying that until next summer as I am going to use the rig I have set up this summer for the rest of the season. It is just a tantalizing idea.

 

[tomjasz]

https://www.scribd.com/document/354778065/2WD-Wiring-Diamgram-for-EBike

 

[Joe EE]

How cool is that?!!! Thanks so much @Thomas Jaszewski
Nothing else like seeing it in print! I’m going to use independent batteries at full power. I can hardly wait to start scratching my head lol.

 

[Andrii]

Hi. Just working on electric tricycle with two rear motor-wheels 1500w each. I'm planning to use two motors together and each separately as well to save a battery. Just have a question: when using the first motor is that good enough to switch off the ignition of second motor's controller or I have to switch off relay (power supply to second controller) as well?

 

[JES2020]

Not sure about the 1st motor switching off the ignition of the 2nd. But it seems clear that if you switch off the power supply to the 2nd , that would certainly turn off the 2nd motor.
I'm sure you realize you will need to use geared hub motors , otherwise you will have an unbalanced drag issue when only one in use.

 

[harryS]

If you use this controller, you can use a single PAS and throttle, and it runs off one battery. I think it's two 17A max units, so that would be 500W-700W, so it wouldn't do for 1500W x 2.

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Unless you get a controller with no display, you need two displays to set up similar PAS levels and sometimes the throttle response is cued with PAS level,

The simple ones without displays, (I've never used one but have looked at how they power up) will have an "ignition" wire that connects to battery power to turn on the unit. You can just rig up a pair of switches to turn on one or both controllers. This can be a low current switch, as it's just turning on a transistor inside the controller. The controllers will already be connected to your battery via their thicker power leads.

 

[jangles]

I have two motors set up on one battery , one controller and one display . Same thing as Evo Big Bud AWD .
I took them off and put a mid drive in it . I'm still thinking of putting a motor in the front to compliment the mid drive .