36v/500W motor upgrade

radvi

1 mW
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Oct 9, 2020
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I would like to upgrade the motor - from the Bafang rear 36V/250W to the Bafang rear 36v/500W, while powering it with a silverfish 21Ah battery and a brushless motor controller (max. current 17A/rated current 8A).

I have posted a similar question (https://endless-sphere.com/forums/viewtopic.php?f=3&t=108619&p=1589353#p1589353) last year but have not received any relevant answer. So I am trying to rephrase my question:

The current bike setup (36V/250W) is really slow at climbing, sometimes the motor overheats.

Does the planned upgrade (36v/500W, same battery, same conroller) remedy this issue?

I mean does the upgrade avoid overheating and the bike would climb more faster?

Thanks for any help.
 
You did receive some replies, but what they told you wasn't the simple answer you wanted.
The first prob. was your post lacked specifics. You wrote;
. I would like to upgrade the motor - from the 36v/250W to the 36v/500W....
Depending on who's rating the motor, you could find the same basic motor rated from to 250 Watts to 500 Watts.
Or, you could find another Bafang model rated from 350 to 750 Watts.
You need to tell us exactly which models you are talking about and what they weigh. What the mass tells one is how much power they can absorb as heat and although they are part of the Power SYSTEM, motor size, windings, etc don't dictate how much power the ebike produces. They are not like little gas motorcycles, where you can just put in a bigger engine and expect a proportional increase in power. it's most likely that just putting in a larger motor won't change anything.
The first step to understanding this is to understand Ohm's law.
A simplfication is;
Higher Amps will produce more power avail. for climbing.
Higher Volts relates to top speed.
They are related though (Watts) and must be considered together.
From a practical standpoint, asking how you can can make your ebike climb stronger, the first thoughts are;
How many Watts can the motor take over a reasonable amount of time? A true Bafang is usually honest and one can double, maybe treble, the rated amount if the motor is not other-wise abused.
How many Amps will the batt discharge continiously?
Is it strong enough to warrant buying a larger motor and controller?
What about the controller, is there room for a bigger one and will the wires handle the extra Current?
There are basicly three sizes of sm. geared hub motors;
Mini-up to 2.9 Kg.s - up to 900 Watts
Mid.- 3 to 4 Kg.s
Large - around 5 Kg.s
My bike in the sig runs 1000 Watts thru a 500 Watt rated 3.5 Kg. motor.
Give us some specifics and we can tell you what's worked for us.
 
Frankly, I do not what other specification should I add about those motors.

This is the one I have now:

IMG-7200.jpg


and this is the one I am thinking about:

HTB1-HVTz-OXXXXXX3ap-XXq6x-XFXXX8.jpg


The controller: yes, there is room for a bigger one.

The wires: I guess they will work fine. But just a guess based on what I have read in various forums.
 
Ok, the Sliverfish batt. maxs out at 30 Amps continuous, but I would pull that back to 25 Amps, so that is what you have to work with.
The Motor in the pic has a code that doesn't relate to anything, but I'm pretty sure it's a Bafang or Bafang copy (A larger overall pic would help ID it), but as far as I know, the smallest Bafang geared is 3 Kg.s, plenty big enough to take 25 Amps @ 36 Volts. So you don't need a bigger motor which would be a lot of cost and work.
Some controllers are weak for their rating, others have more punch. Can you show us some good overall pics of the controller and tell us what features it has and you want to keep.
Stout controllers in the 20 to 25 Amp range are a little hard to find.
Something like this might be an option;
https://ebikes.ca/shop/electric-bicycle-parts/controllers/c4820-gr-higo.html
But you would have modify the connectors. You could talk to Grin.
Also, Lyen makes great controllers;
Lyen.com
He put me a 22 Amp Mini-Monster together some years back and it was a little hot rod.
You could talk to him too and tell him what you want to do.
It could be that other cheap Chinese controllers in the same power range would pull harder. Hard to tell without trying them.
I know I said Volts is speed, but higher Volts adds to the total (Watts) and adds performance all around. A 48 V, or even better, a 52 Volt system would make your bike feel like a whole different bike, but since you are invested in the Sliverfish, I would imagine you wouldn't want to shell out for a new Batt.
 
Thank you for your time and comments motomech.

Let’s close this topic.
 
The main thing that answers your question was not discussed. What is your weight, including the bike, the battery, and the cargo you will carry, or tow. 300 pounds or below is ideal. Above that, mid drives would be a better idea, or just big power such as 2000w or more in big heavy direct drive motors.

As a general rule, you won't have much trouble climbing hills up to 10% with a 500w rated geared motor. This is the larger type discussed above. Overheating will only be a problem if you weigh more than 250 pounds yourself.


With the battery you plan on using, a controller in the 20-25 amps would be ideal. With a stronger battery, you could do 30 amps, about 1000w of power. (1500 with 48v) But for now, just upgrade the motor. Next battery, get 48v, and then get a 25 amps controller. Upping the volts will get you the speed, but later, when funding permits.

With the same battery and controller, the bike won't be noticeably faster on the flat. But it will lug less and overheat less on the hill. It will take less effort from pedaling to maintain 15 mph up the hill, which is the speed you need to go to avoid that overheating issue. Your current motor is overloaded with 250 pounds, it would not overheat so much if you only weighed about 120. (plus 70 or so for the bike).
 
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