Need help understanding battery "math"

[R84]

Hi guys I'm a newbie in the ebike world, I have some electrical knowledge (mechanic) I have a few questions. I am looking at purchasing from thunderstruck Ev the budget screamer kit 72 v brushed. 160amp continues and 400amp peek. This has the altrax SPM 72400 controller. Ok my question is I want to use 18650 3.7v 3100mah battery's. I'm thinking I will need at least 100ah and 72volts. Is there anyone who built a battery of this size ? I'm kinda stuck on the "math" part of this. How do I set them up, how many do I need ect. If anyone can help me out I would appreciate it. I have done some research with confusing conclusions. Made in China.com and the manufacturer is Wama they sell these battery's for5-8 cents a cell min order is 100 some are a 1000

Any info is a great help

Richard

 

[FluxZoom]

https://youtu.be/cxkVxi9P0EA

Cells are the individual pieces that go together to make a battery. A battery is a collection of things, like a bunch of single 18650 cells.

100(Ah) x 72(V) = 7200(Wh)

So you want a 7200 watt hour battery (or pack).

Each of the cells you noted is 3.7(V) x 3100mAh (or 3.1Ah), which means 11.47Wh (assuming ideal variables).

7200Wh / 11.47Wh = 627.73 cells. You'll probably want something like a battery configuration of 20S32P or 20 in series by 32 in parallel.

 

[spinningmagnets]

If you truly want 400A peak, get the Samsung 25R cell, which is factory rated at 20A per cell.

400A divided by the 20A per cell using the 25R is 20P. That is a big battery. A nominal 20S (20 cells in series) is 3.6V X 20 = 72V, when fully-charged to 4.2V per cell, it will be 4.2V X 20S = 84V

20 cell in series X 20 cells in parallel is 20S X 20P = 400 of the 18650 cells. I know many people will say this cell can put out more amps as a peak, but if you do that they will get hot, so...I cannot recommend any amp-draw above 20A per cell, due to a dramatic reduction of life-cycle due to heat degradation. Can they put out more? (and can you reach 400A with fewer cells?) Yes. But...if it gets hot, it will have a short life.

 

[Hillhater]

If you are struggling with the maths, wait till you have to assemble those 600+ cells into a reliable pack !
That is no task for someone with no prior experience of pack builds.!
Also, forget that 5-8c/cell, anything decent will cost $2-$5 per cell.
There are many fake cells with false capacity and performance claims so be aware and buy from reputable or established sources.
There are many threads on here about how to build a pack from 18650, and may others suggesting alternative cells for these larger packs to make DIY pack builds easier.
Search for recycled Leaf or Volt cell pack builds.

 

[Hwy89]

I looked up the Thunderstruck Budget Screamer and noticed that the motor is "*Motenergy ME1003 Permanent Magnet brushed motor". I'm no expert on motors but the way I understand it motors are either permanent magnet type or brushed type. Is this motor using brushes to energize the coils in place of a controller and hall sensors?
My second comment is that $1,300 is a lot of money for a kit that doesn't include the bike or the battery.
And third, Chinese 18650 cells for 5-8 cents per cell ??? Good luck with that.

 

[R84]

I think I'm going to do more homework with this bike. thank you for everyones input.

 

[R84]

There is a ton of information to go through and trying to understand what will work for me is becoming more difficult. I'm fighting the odd hill, if I should go with a hub motor, mid drive, and batteries. I want to make my first Ebike a decent one, with some distance and speed. most of all cost effective, i don't want to get ripped off with crappy stuff. If anyone knows a decent combo thats managble for someone getting into this sport it would be much appreciated.

Im not to worried about a bike I have an complete XR 80 frame, welders and access to a machine lathe so modding the frame to fit suff is not an issue


something like this :https://youtu.be/_RElmQ4Xn70 but no description on battery type and chemistry

 

[Hillhater]

You could start by clearly setting out your requirements and Expectations,..range , speed, weight, cost, etc
That will help define what motor, controller, battery etc you would need.
But be realistic, 100 mole range at 100 mph is unlikely to be possible, and having range or speed that you dont need or cannot use, is simply going to mean extra weight and a waste of money.

 

[amberwolf]

Ok my question is I want to use 18650 3.7v 3100mah battery's. I'm thinking I will need at least 100ah and 72volts. Is there anyone who built a battery of this size ? I'm kinda stuck on the "math" part of this. How do I set them up, how many do I need ect.

Lots of threads on 18650 builds, most here in this battery tech section. I highly recommend reading as many build threads about these packs as you can, and about all the spot welding/etc threads you can find. It's a lot of reading, but you will learn answers to questions you haven't even considered yet.

Made in China.com and the manufacturer is Wama they sell these battery's for5-8 cents a cell min order is 100 some are a 1000

Those are probably recycled garbage (like ultrafire, surefire, etc) (no matter what those vendors might say, real cells are going to cost more than that just to put heatshrink on, much less to manufacture.

You're probably looking at at least a couple dollars to several dollars *per cell* for something brand new that won't waste your time or catch fire the first time you try to charge or discharge them, etc.

Less if you don't mind them used (like old tesla packs, etc).

Look around the forum in the battery and items wanted sections for other people's threads about where to buy good 18650s for recommendations on where to get them (and some to avoid).

There are also sellers in the items for sale new and used sections, with some feedback in those threads (and elsewhere on the forums in people's pack builds).

 

[amberwolf]

First, just so you have some idea what you're looking at building, then some questions.

Hi guys I'm a newbie in the ebike world,
<snip>
thunderstruck Ev the budget screamer kit 72 v brushed. 160amp continues and 400amp peek. This has the altrax SPM 72400 controller.

FWIW, you're talking about a motorcycle, not an ebike, at least as most people call them. Unless your'e doing something like me, and hauling around St Bernards and heavy cargo (sometimes at the same time) in city traffic.

Part of it is the weight, because between the motor and hte battery, it's probably going to weigh as much as my CrazyBike2, which is over 200lbs without anything on it. (see link in signature; it's a long semirecumbent cargo bike capable of pulling an automotive-style-hitch trailer full of dog or cargo or both).

It probably wont' weigh as much as my SB Cruiser trike, but you'll probably want to build it as a trike so you can have space for the giant battery.

100Ah at 72v is a very very large battery, for an ebike.

SB Cruiser has just a 40Ah "52v" battery on it right now, and that pack is heavy enough I have trouble lifting it out of the seatbox compartment it's in, and I can't carry it any distance (a few feet at best). If I put the full 120Ah (3 of those) in there, it'd almost fill up the seatbox compartment, which is over a foot tall, and over a foot front to back, and around 3 feet side to side (basically like a bench seat, as a box). See the SB Cruiser thread linked in my sig, near the end of the thread, for the present configuration showing that.

If it were a 72v system, otherwise the same, it would more than fill that whole box, and I don't knwo what it would weigh, but I'm pretty sure my biggest St Bernard, Yogi, would be lighter.

If you want to put 100Ah 72v on a bicycle frame, I think you might want a trailer, or a trike you can fill the cargo area up with.

If you do it with a motorcycle sized/shaped frame, replacing hte engine area with batteries, that's a different story.



Ok, so....all that said, you should look at this thread
https://endless-sphere.com/forums/viewtopic.php?f=3&t=66302
and then copy the first posts's questions to a reply in your thread here, along with your answers to those questions.

That will help us help you figure out what you *really* need, and get you building and riding what you actually would enjoy riding.

 

[dogman dan]

Fwiw,, this is a motorcycle kit. http://www.thunderstruck-ev.com/budget-screamer-72v-brushed.html

Looks like lifepo4 bricks in the picture.

Brushed permanent magnet motors definitely exist. They just don't run them on bikes no more. Chances are your cordless drill has one.

To get 400 amps peak, you need to know your battery specs. If they list c rate, that number will be the Max discharge rate for the cell.

For example, a 10 amp hour cell,, if listed as 1c, can put out 10 amps max. A 10 ah listed 2c,, 20 amps. A 20 ah at 1c, 20 amps.

Or it may list a certain size,, and a max amps. You can back out the math to get back to c rate. But again for example, lets just say such and such a cell, a large one, can put out 100 amps. Then you would need to parallel 4 of them to get to 400 amps capable. Then the groups of 4 in parallel would get series connected to make the voltage higher. likely about 20 groups to get 72v. More if you choose lifepo4 prismatic cells.

 

[kevbo]

I looked up the Thunderstruck Budget Screamer and noticed that the motor is "*Motenergy ME1003 Permanent Magnet brushed motor". I'm no expert on motors but the way I understand it motors are either permanent magnet type or brushed type.

OK, I'm a Newb to EV, but not to motors:

There is no contradiction there.

A DC motor can be brushed or unbrushed. That determines how the armature coils are commutated. "Permanent Magnet" (PM)Refers to the field, not the armature. This would distinguish it from a wound field motor, where non-commutated windings provide the magnetic field for the armature to react with. A wound field requires power, but makes it possible to vary the Kv of the motor, so you could trade torque for speed. But EVs usually go for the efficiency of PM field. A wound field also carries the risk of overspeeding the motor if the field winding or supply fails. Many older automotive starter motors were wound field...PM geared starters are now becoming popular, at least for smaller engines.

Now some people will read the above and start arguing because there is plenty of variation in how the terms field and armature are used. Some people always mean the rotating member when they use the word armature. MY usage is that the magnetic poles of the armature change polarity as the motor turns, and those of the field don't...so the armature could be fixed or rotating. This allows the terminology to stay consistent with respect to the electrical elements, though the mechanical elements will then vary with the motor design.

Your confusion may be related to the fact that A brushed motor will nearly always have a rotating armature...that is pretty much required for the mechanical commutation to work. A stationary armature would require slip rings and a second set of brushes to supply the normal brushes carried by the rotating field construction...nobody does that. A brushless motor will normally have the armature stationary and the (permanent) field magnets rotating, otherwise you'd need brushes and slip rings, and that would be silly! So a brushless motor will be permanent magnet in almost every case, and a wound field motor will almost always include brushes.

To further add confusion, induction motors are also have no brushes, but they also have no permanent magnets. It is now practical to use these on battery power, an inverter to drive them is only a bit more complex than the ESC for a brushless motor. To avoid confusion, these should be referred to as induction motors, not brushless, even though the latter is technically correct if interpreted as a discription rather than a lable.

 

[Hwy89]

Thanks Dan and Kevbo for the motor info. I'm so used to seeing "brushless PM motor" that at first I thought that was a typo.