Doubt about 48V + 20AH bateries

[jorgerosa]

Hello all,
My first post here, nice to see that there is a huge community interested in EVs

My question:
- I intent to mount my own bike that will run at 45Km/h (maximum speed by law) and make ~60Km distance (if more, better, of course...)
- I have 4 (lead-acid) batteries, each one with 12V 20A, their connection outputs 48V 20A (I can´t escape from this, since I already have them from my brother "old" crashed bike, and that is all that is left for me)
So, I´m interest in one of these motors (in my case they must be BLDC motors only - to fit right in the middle of the bike frame - "mid-drive" motor)

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So with the above batteries output specifications, what could went wrong with these motors, merely as examples?...

Motor N.1) 350W (36V/48V) 12.5A ...
Motor N.2) 1200W (48V) 32A ...

1 - Nothing, all depends from the controller?... (The amps and watts from the controller must have an exact match with the motor ones?)
2 - In the 350W the motor (with only 12.5A) will be overpowered and could be fried?...
3 - In the 1200W the motor (with 32A) will be underpowered... but it will run?...
4 - I really have to find and exact macth for my 24V 20AH batteries?...

Thanks in advance for all suggestions/tips/ideas!

 

[cycborg]

A "36 V" motor will be fine with a 48 V battery; the thing you need to pay attention to is the 350 W rating. Use some sort of power meter and make sure you aren't exceeding this for any length of time. Unfortunately, your 45 km/h target will make this challenging.

Conversely, the 1200 W motor will perform fine below its power rating.

So the motor doesn't have to be perfectly matched to the battery, but you should take some care in choosing a controller. It should be a 48 V controller with a current limit that will protect your battery. I don't really know lead acid so I don't know what the current limit should be.

 

[kdog]

A motor will draw whatever it needs for the given load and rpm it's at. This could be minimal amps or huge. The W rating is generally what it can take for extended periods at optimal rpm. Your controller dishes out the power according to, well a few factors, but how much you are asking for through the throttle.
So both motors will work but if you run the 350w motor at 600w for too long it will die. This could be uphill, high speed etc. two options to prevent this.
Get a 350w controller. So it is more matched to the size of the motor. (You can stil melt either) it's just harder to do.
Get a bigger motor.
At 45kph you'll be sucking back about 700-800w continuously. The 350wmotor will do this with difficulty for a little while then die.
To run the 1200w motor well look at getting a 48v 1500w controller. Then you won't have any problems....except your lead anchor batteries.
These are going to die soon no matter what you do so plan on moving to lithium as soon as they go. (First time- don't buy more)
At 45kph ~800w and at 50v you'll be drawing 16amps roughly. At almost 1c for they will deliver, er I dunno, maybe 12-14ah depends...
So you might get 20kms range out of them for a few months, then less and less then...buy lithium!
All off the top of my head but the concepts are there....
Which motors are they?

 

[jorgerosa]

Thakyou guys! You are very helpfull, I´m going to read all your tips and ideas carefully and digg (as I could) around it.
I´m not rich, so I´m trying to mess as little as possible. Any more ideas, suggestions, etc... are welmome!

EDIT: kdog (...) "Which motors are they?" (...) - Probably (only according my own "ideal" idea for it, of course) something like these:

MOTOR: https://www.aliexpress.com/item/750w-Dc-48v-brushless-motor-electric-bicycle-motor-BLDC-BM1418ZXF-02/1800681635.html?spm=2114.01010208.3.60.AHBQio&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10068_10501_10503_433_10136_10137_10138_10060_10062_20501_20503_10056_10055_10054_302_10059_10099_10103_10102_10096_10052_10053_10050_10107_10051_10106_20517_20515_10084_10083_10119_10080_10082_10081_10110_10111_10112_10113_10114_10078_10079_10073_10070_10122_10123_10120_10126_10124-20503_20501_10503_10501_20517_20515_10120,searchweb201603_2,afswitch_1_afChannel,ppcSwitch_4,single_sort_0_default&btsid=341b4b04-8fd4-4224-bf97-cc7fb7570afd&algo_expid=ee83fe74-1675-430f-aed8-6d4b9c8c7f15-7&algo_pvid=ee83fe74-1675-430f-aed8-6d4b9c8c7f15
CONTROLLER: https://www.aliexpress.com/store/product/750W-48V-60V-DC-15-MOFSET-brushless-motor-speed-controller-BLDC-motor-controller-Ebike-E-scooter/1209624_1794324454.html?spm=2114.10010108.1000023.1.aEcI54
BUT... MY batteries are output 20A, and the motor says 9.4A (Mostly is all about Amp that is my bigger concern... Because I have no idea...)

 

[amberwolf]

No, your batteries are 20Ah, which is a different thing.


I recommend going to the ES Wiki http://endless-sphere.com/w and looking thru the various articles; there is one that explains a number of the terms like that, directly and thru links to other articles/threads.
https://endless-sphere.com/w/index.php/Terminology_and_Explanations_of_Common_Misconceptions

It'll help your understanding of some of the things you see in markings on stuff, and maybe why they are marked that way.

 

[jorgerosa]

Thanks for the urls ans explanation!
I see lots of "mid-drives" motors (the motor that I want to) in the web, aliexpess, ebay, etc...
But they all come directly from China, there are any brands (or dealers/factories/shops) in Europe, to buy engines from?... (To avoid huge import fees)