Battery and controller pairing question

Hi all,

I’m not too sure where to start. I’ve been reading a lot recently for my conversion project.
Even though I have broader decisions to make (still hesitating between eZee and MXUS kits from ebikes.ca), I also had specific technical questions.

So I’m pretty much set on going with a Grin kit. Let’s assume I am going with the MXUS rear kit. My initial thought was to go with the C7240-GR controller (36-72V 40A) even though I probably would not need such power demanding levels initially. Just to be futureproof. Upon further reading the Controller Selection section at http://www.ebikes.ca/product-info/grin-kits.html I gather that it may not be such a good idea. That if I select this controller, I better have a battery that can push out 40A or more (continuous, I assume). It wouldn’t be recommended to use a battery that’s only rated 30A continuous. I suppose it’s not recommended as in, it’s not good for the battery to draw current from it at its rated limit. Am I understanding this correctly? Should I aim for a controller that’s rated just a bit under the battery rating, i.e. get a 25A controller for a 30A battery?

I would recommend getting more capacity than you think you'll need for every component; battery, motor, controller, etc. If you are like the rest of us, you will quickly find yourself wanting to have just a little (or a lot) more of everything; range, acceleration, top speed, etc.

The nice thing about the Grin kits is that you can tell the controller (through the Cycle Analyst) to only pull a certain number of amps from the battery. Hope this helps.

Get a battery that's rated for 10/20C or higher discharge and then not worry about it.

If your controller can do 30a continuous, you should have a battery at least 30a continuous. Chances are you won't be needing 30a continuous unless you have a long hill go go up.

The newest 18650 cells are getting better with their discharge rates.

My bike and I roll around at about 275lbs. I run on 30a. Around here I only need 30a. If you have hills you might want more.
If you can afford it, go with a battery that can handle your 40a controller.

Wesnewell makes a good point that rc lipo is a high drain battery with a lot of energy for the price. Handled property you can use RC Lipo without problem. Misuse them and they can burn your house down.

Wolfeman said:

I would recommend getting more capacity than you think you'll need for every component;

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That's what I'm doing by going with 40A. I think that 25A should be enough, especially I plan on pedaling. So I'm tempted to go with a 40A controller because yes I'm pretty sure I will find myself wanting more.

It certainly helps knowing that I can limit the pulled current using the CA. Thanks for your fast reply

Honestly though, I've been poking around the simulator on ebikes.ca and I'm at a loss deciding between combinations of e.g. the MXUS fast or slow winding, 25A or 40A controller and 36V or 48V battery. I can well see the effect of the parameters, but the acceleration is hard to imagine. Like in how much time am I reaching a given speed (on given terrain).

About 'between slow or fast winding' (3006 or 3005), I'm not sure I am seeing the disadvantage of the fast one, if only ever so slightly slightly less torque initially. I must be missing something. I'm especially wondering because I have 700c wheels and they don't seem to recommend fast windings for those...

For MXUS:
http://www.ebikes.ca/tools/simulator.html?motor=MX3006&wheel=700c&cont=C25&bopen=true&cont_b=C25&motor_b=MX3005&wheel_b=700c&batt=B3623_GA&throt_b=100&throt=100&batt_b=B3623_GA&grade_b=0

But if I look at it for a geared hub, it's a different story. It becomes clear that I trade max speed for initial torque
http://www.ebikes.ca/tools/simulator.html?motor=MEZEE250&wheel=700c&cont=C25&bopen=true&cont_b=C25&motor_b=MEZEE350&wheel_b=700c&batt=B3623_GA&throt_b=100&throt=100&batt_b=B3623_GA&grade_b=0

First of all, I would not run that motor myself at more than 2000w. So 48v 40 amps, or about 30 amps for 72v. I would say the 48v 35 amps controller would do if you want the power. Its still possible to get the 40 mph bike with this motor, but you NEED to limit the time you run that hard, to about 10 miles max. It most likely will overheat running 40 mph continuous. If you want that kind of performance, got with the big crystalyte motor.

So if you do invest in the expensive grin 40 amps controller, you really would be smart to also invest the the DP Cycle analyst to go with it. Then you set the amps to your needs. You'll need a wattmeter anyway, if you don't buy a bms protected battery.

But if you do go for 40 amps controller, then it goes without saying that you really need a battery that can at least put out 40 amps briefly. This would be a very large pack of 18650 cells, or the lipo that has a much higher c rate.

Though dangerous, and not a great choice for the average moderately smart but careless guy, the lipo is the only way to go if your goal is a small, lightweight bike that hauls ass. Just be prepared for the learning curve with lipo, and don't let them in the house. You don't have to be a genius to use the lipo, but you do have to pay attention to how deep you discharge, and be careful hooking up when you assemble the pack.

If its going to be a cargo bike, or tow trailers, then you can lug along 30 ah of the less than the best 18650's.


A 48v , 15-20 ah, 18650 cell battery, and limit amps to 25 with this kit will work excellent. I'd rather have two bikes, one 25 amps, and start over for 72v, than rebuild. Or just go for the big ass motor right away. It depends on your needs, what you want.

If you want a bike, 48v 25 amps is more than plenty. It will haul ass compared to bikes. But if you want a motorcycle, then get the big motor and the big controller, and the lipo.

dogman dan said:

So if you do invest in the expensive grin 40 amps controller, you really would be smart to also invest the the DP Cycle analyst to go with it.

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Well, my reason for going with the Grin is actually the CA, so that's not a problem. (Also it's a Canadian company so it makes things simple) I like the openness, the fine tuning and tweaking, the data analysis. I'm also likely going DD just to have regen braking, and not even for the regen "savings", but just because it's something more (and it helps save brake pads).

I'm not hauling a lot. I mean I think the bike will be about 50 lbs max in the end, and I'm about 135. Add a backpack to get to 200 lbs. VERY occasionally i could be transporting something sensibly more heavy.

dogman dan said:

Just be prepared for the learning curve with lipo, and don't let them in the house.

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Oh I'm convinced that this is not for me yet I don't have the time to put into the learning curve at the moment.

dogman dan said:

I would say the 48v 35 amps controller would do if you want the power.

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I think it would be either the 25A or 40A controller. I don't find the 35A interesting as it's the same size as the 40A, with lower quality FETs (allegedly).

Now because I will do quite a bit of stop-and-go on my daily commute, I would like something that will accelerate appreciably fast. With the numbers I'm looking at now with a 25A controller/48V batt, I see starts of 60 N-m. I don't know if it's a lot. Compare this with 90 N-m with the 40A controller (and appropriate 48V battery). Let me put it another way: I'm stopped at a traffic light with a car next to/behind me, right at the stop line. It's a road limited to 40 km/h. Broadly speaking, can I start fast enough so that the car driver does not have to wonder too long if he should attempt to pass me?