2000w 48v Battery Needs

[MaroonChris]

I have a Velocifero 48v 2000w. The older version with straight board. It currently has 4x 12v lead and I want to change these for a custom built pack. I like the extra ah I can get with 21700’s over 18650’s and I understand how to achieve the 72v (20s) and how the P gives me the ah but how do I figure out if the pack will run a 2000w motor?

I see a few packs at 72v but will only run 1000w motor? I assume this is the amps? I am not sure how to calculate what I need for this but and also what downfalls will I have choosing 21700?

many thanks all

[D.808]

It goes something like volts x amps=watts. So you could run a 72v 27.7 amh battery on your 2000w motor full speed for 1hour.

[MaroonChris]

I think, that’s the watt hours calculation. That gives me the rough range of the bike. The bit I don’t understand is how I know if my 72v pack will run a 2000w motor. Some packs for sale on eBay, even 72v will only run a 1000w motor? How do they calculate that?

[DaHose]

In order to match battery and motor specs, you also need to know the specs on your controller, because the maximum current directly affects your calculations.

Battery Voltage X Max controller current capacity = Maximum possible wattage to run your motor

So let's assume you are dealing with a controller that runs at 48V, but you have options as to maximum current it can flow.

48V X 20A = Max output possible is 960W
48V X 25A = Max output possible is 1200W
48V X 30A = Max output possible is 1440W

If someone is selling you a battery and they tell you it can only operate a given wattage, then the battery has a current limit because ....

Max possible wattage = Voltage X Max possible current

You say you looked at a 72V battery that can only run a 1000W motor? Then that means ....

1000 = 72V X Amperage
Amperage = 1000/72
Amperage = 13.8

That would be a really low amperage battery. Most EV batteries can support 30 or more continuous amps.

In my case, I am building a 70V battery which will be able to run at max of 60A. At full power it could run a 4000W motor. However, my controller maxes out at 40A, so output will be limited to 2800W. Hence my kit runs a 3000W motor.

Jose

[MaroonChris]

Jose that is excellent. Thank you it explains a lot. Can I ask what actual battery model you are using to build your pack?

[BigJon]

The limiting factor in most battery packs is actually the BMS Circuit, It can only allow a certain output amperage. SO even if yo have a 48v 20 ah Battery it would unhindered produce 960 watts but...it may be limited to 15amp by a BMS so it would only be good for a 720 watt system which most builders will under rate for a 500watt system for battery safety.

[BigJon]

So you want 72v 2000 watt you need minimum 27.77 actual amps draw.

A LiFePo4 32650 cell is capable of 15 amp draw,
So for minimum you would need 2 in parallel But these cells are only 5ah so it would only be a 10ah battery.
In series to achieve 72 volts you would need 23 batteries in series in your pack.
Peak voltage would then be 85.2 Discharged would be 57.5.

At 85.2v with 30a draw you can run 2556 watts

I would recommend a 32650 pack running 23s3p which would be 15ah Minimum and would allow optimum amperage at 45amps continuous (33% over spec) But you would need 23x3 cells 69 (Giggity)

[Defjr333]

Just over build it and don't stress. I run dual 14s5p in parallel. Each capable of continuous 50a and peak 100a. My bbshd even with a ludi controller won't over tax either pack.

[MaroonChris]

So my main concern then, from what you can see on here is the continuous and maximum voltage charge of the individual batteries? So if I go with batteries that have a high discharge rate I should be good?

[Defjr333]

In my set up, even the long range non high current output cells would work fine, as none need to output their full potential. It keeps any single cell from hitting it's thermal or physical maximums. Thereby extending the life of each pack

[DaHose]

To answer your question above, I built my pack with LG M26 18650 batteries rated at 2600mAh, 10A continuous current. With my 6P build I can run at 60A continuous.

BigJohn - Agreed the BMS is where you enforce the the limitation on a pack, but the paralleling of the batteries informs you as to which BMS/limit you build with. A single battery might be rated at 10A max continuous discharge, but in a 3P build it all adds up to 30A continuous. If that were the case, you either build with a 30A max BMS, or (better yet) get something bigger like a 60A BMS that can be configured to limit at 30A. A BMS that is more programmable will also give you other features like adjustable minimum cutoff and adjustable max charge.

Understanding that parallelling aggregates current is the important thing. Shoot, even a high capacity battery with a low current rating of 5A continuous adds up to 30A in 6P. I think that unless you buy REALLY low current batteries, just about anything at 6P or better will be able to handle anything you throw at it.

If you really can run at 2000W/48V right now, that means the controller can handle 41.6A. IF the controller can run higher voltage, then you need less amps. We really need to know your controller and motor specs. to calculate/recommend anything with confidence.

Jose

[MaroonChris]

Hi Jose,

here are the details of what I want to run:

About Motor:

Model:MOTOR MY1020
Motor Type:High-Speed BLDC brushless Motor
Out put /W:3000W
Rated Speed:4900r/min 5800RPM(MAX)
Weight:4.8KGS
Diameter:95mm
Rated Torque/N.m:5.4N.m
Applicable:Electric Scooter,Ebike,Folding Bike,Small E-Moto,machine,MIni Electric Car ,DIY
Installation: Center,MID DRIVE
Application Chain:T8F Sprockt /Chain


About Controller:
Power:3000w
Voltage:48-72V DC
Current:50A
Mosfet:24WF
Under Voltage turn the 1.1-3.7V
Brake Low Level

Looking at what people have said, my intention is to run a 20s5p using Samsun 50e 21700’s. Reading what people have commented that will give me:

72v and 50amps and 25ah?

[Defjr333]

While they will wind up being a bit more costly per usable watt vs 18650s, they should last a bit longer due to their better handling of heat and high current drain. That should be a fun project

[DaHose]

Yep, 21700's have huge current and capacity compared to 18650's. If you controller peaks at 72V, you don't ever want to exceed that. A 20S pack will charge up to 84V, so I would not build that unless your goal is to NEVER use it at full voltage. Not so bad an idea, as charging to only 80% extends battery life tremendously, but you must be absolutely sure you have safeguards so you never exceed that 72V and fry your controller.

At 72V you need 41.6A to drive the full 3000W. Sounds like building with those Samsung 21700's in a 5P is a great choice. Are you building with on-board BMS, or balancing externally?

Jose

[D.808]

I agree. Dont go with 20s, you could fry controller. Most maybe 17s.