Calculating amp hours on 13s x 8p packs

General Discussion about electric vehicles.
Post Reply
Bigfillly
1 mW
1 mW
Posts: 10
Joined: Sep 18, 2017 10:05 am
Location: Earth, U.K. Derby in a shed :-)

Calculating amp hours on 13s x 8p packs

Post by Bigfillly » Sep 19, 2017 2:28 am

Hi,
As you can see I'm new to this forum and not sure on a few things,
I'm building 13s x 8p packs and was wondering how to calculate what amp hours they would be?
Also do I need to get the capacity of every pack to be around the same?
Thanks very much again,
Phil.

User avatar
amberwolf
100 GW
100 GW
Posts: 23920
Joined: Aug 17, 2009 6:43 am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Calculating amp hours on 13s x 8p packs

Post by amberwolf » Sep 19, 2017 3:05 pm

This thread
https://endless-sphere.com/forums/viewt ... 7#p1320617
shows you're already building the packs.

But this new thread implies you don't know what you need to run your vehicle yet.

So before you build anything, you first have to know what your vehicle will need. And to know that, you have to know what *you* need the vehicle to do.

So to start with, you should go to this thread
https://endless-sphere.com/forums/viewt ... =3&t=66302
and copy all of the first post's questions, then paste them into the thread we're in now, along with your answers. That will help us help you figure out what voltage and capacity you need, as well as what C-rate, so you can build a battery that will provide the power your vehicle needs to do the things you need it to do.

It'll also help us help you make sure the other parts you have already bought (controller and motor from the implications of the other thread) will actually do what you want, or if you will need to return them and get different ones.

Without that information, you can't know what to build (and we can't know how to help you).

Bigfillly
1 mW
1 mW
Posts: 10
Joined: Sep 18, 2017 10:05 am
Location: Earth, U.K. Derby in a shed :-)

Re: Calculating amp hours on 13s x 8p packs

Post by Bigfillly » Sep 20, 2017 4:03 am

Hi,
Thanks for replying,
As you can so easily tell in very new to this, it it a steep learning curve for me but I am willing to listen to all the guru's out there,
My project is a go kart that my son drives, it's a 2 stroke at the moment but we are converting it to electric powered,
I have the motor and controls unit, they are:-
Montgomery ME0909 motor
Kelly KDZ Series Pm Motor Controller
Desired max speed on level ground. Around 45-50 mph and getting there as fast as possible
Desired max range at what cruising speed will be around 2-3 hours use every 2-3 weeks average speed 35-40 mph
wheel size is 5" but with the tyre, it's 10" (standard gokart wheels)
Brake type of wheels is rear disc (standard on karts) but I'm hoping to harvest braking with the motor to
Rider weight is 70kg
Terrain will be flat race tracks
Batteries I'm using are x500 18650 laptop batteries
Budget is what ever it needs to complete the project with the parts already bought
Hope that helps,
Thanks in advance,
Phil.
Last edited by Bigfillly on Sep 20, 2017 6:56 am, edited 1 time in total.

User avatar
amberwolf
100 GW
100 GW
Posts: 23920
Joined: Aug 17, 2009 6:43 am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Calculating amp hours on 13s x 8p packs

Post by amberwolf » Sep 20, 2017 5:09 am

Bigfillly wrote:My project is a go kart that my son drives, it's a 2 stroke at the moment but we are converting it to electric powered,
Desired max speed on level ground. Around 45-50 mph and getting there as fast as possible
Desired max range at what cruising speed will be around 2-3 hours use every 2-3 weeks average speed 35-40 mph
Ok, then with those numbers, you can use various online calculators (some are listed in the ES wiki and some of the calculator / simulator threads in the sticky index threads, others can be found via google) to take the weight you expect it plus him to be, and determine what wattage it will take to maintain that speed, so that's teh minimum watts the whole system has to maintain continously. kreuzotter.de might be a good start though it's for bicycles it could ge tyou a ballpark. (a quick check shows around 4-5kw for 50mph)

Then you can also determine how many watts it will take to reach that speed in a specific amount of time (standard physics math, though I'm afraid I don't know which formula to use, as me and math don't get along).

Alternately, you can look around at other e-karts here on ES or with google, and see what speeds and accelerations they get, for similar weight of kart+driver, and what watts their system requires to get there.

Then that would tell you how many watts you'll have to be able to sustain with your motor, controller, and batteries.


The batteries are the main key, because if they can't handle the current at the voltage you need without significant voltage sag, they don't produce the watts you need to reach the speed you're after, or else not as quickly as you want to get there.


Also, knowing how many watts continuous you'll need also means you'll know about how many wh/mile you'll use. That then tells you how many wh (watts per hour) your battery pack has to be to run for the period you need it to, before recharging.

Keep in mind you may want to make the pack bigger than that, so you can run longer if you have to, and also because a pack doesn't output as well as it gets emptier. voltage gets lower, too, so top speed drops.

I have the motor and controls unit, they are:-
Montgomery ME0909 motor
Kelly KDZ Series Pm Motor Controller
wheel size is 5" but with the tyre, it's 10" (standard gokart wheels)
Rider weight is 70kg
Terrain will be flat race tracks
Batteries I'm using are 500 8650 laptop batteries
I don't know the Montgomery series of motors. Are you sure it's not Motenergy?

There's quite a variation in the KDZ series. Which one is it?


For the laptop batteries, what kind are the actual cells? There will be markings on them that say what manufacturer and model each cell is. This is important because there's a lot of different kinds of cells. Some will provide high current, and some will provide high capacity. Most can't do both. Once you know who made the cells, you can look up that manufacturer's spec sheet for that specific cell. Many ofthem are already discussed in their own threads here on ES, or on candlepowerforums, etc., which can make it easy to find.

Are they brand new, or used? Used cells you'll have to test and sort to ensure you've got good ones, and then arrange them in the packs based on their remaining capabilities. DrkAngel has a good thread about building packs from used laptop batteries that will help you with this. If you're not absolutely certain of their origins, you'll need to test every cell to be sure you don't have problems later on (which are harder to troubleshoot once they're all in packs).


If new, are they "NOS" (new old stock)? This means they've been sitting around for probably years, and may or may not be any good. Lots of packs that sit liek that drain to nothing, and while they may revive, they are fire risks and are unlikely to deliver either capacity or current they way they were originallly rated.



Have they been disassembled into the individual cells, or left in the plastic laptop battery cases? They can be easier to use if you leave them in their groups, welded together, as long as they all test good.


How are you planning to assemble the cells into packs? There's a number of methods; I'd recommend reading around all the many 18650 threads here on ES if you havent' decided on a method yet.

Bigfillly
1 mW
1 mW
Posts: 10
Joined: Sep 18, 2017 10:05 am
Location: Earth, U.K. Derby in a shed :-)

Re: Calculating amp hours on 13s x 8p packs

Post by Bigfillly » Sep 20, 2017 5:48 am

WOW :shock:
You are a master,
The motor is Indeed a motenergy, its capable of:-
2000-4000w
2150-4250 rpm'
98A
24-48v
Torque 80lbs.N(9N.m)
But I'm guessing you already know this :)
The controller is capable of:-
24-48v
300A
It has j1 and j2 plugs, (M-) (B-) and (B+/M+) it also has the Rs232 plug to program with a laptop, It has the number KDZ48300
The laptop batteries are 18650's and various makes, I've stripped them from the plastics, they are being individually tested now (very long process)
I'm using the 4x5 plastic cell holders to make the packs,
I'll research a few more things where you mentioned (that will keep me busy for a bit) and get back with what I have worked out,
You have been most helpful so far,
Thanks for all the help,
Phil.

User avatar
amberwolf
100 GW
100 GW
Posts: 23920
Joined: Aug 17, 2009 6:43 am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Calculating amp hours on 13s x 8p packs

Post by amberwolf » Sep 20, 2017 11:31 am

Bigfillly wrote:The motor is Indeed a motenergy, its capable of:-
2000-4000w
You might have to add external cooling to it so it doesn't overheat, especially if you're running it at higher speeds a lot, and/or doing a lot of repeated accelerations. I think another member is using the more efficient (less waste heat) brushless version of this motor on his kart here on ES, and still working out sufficient cooling for it.

The wattage on that motor is actually a lot higher than that, according to their page here:
http://www.motenergy.com/me0909.html
Capable of 4.8 KW continuous and 12 KW for 30 seconds.
though a google search shows that different sellers make up their own numbers for it rather than using the actual manufacturer specs. :roll: (something you should keep in mind when looking up specs for parts you're going to use--sellers can lie and/or have no idea what they're talking about, so go to the manufacturer for specs).

KDZ48300
Looks like the controller is easily capable of burning up the motor if you don't either be careful with the throttle or program in a lower motor current limit to match the motor you have. ;)

The laptop batteries are 18650's and various makes,
You should note down which kinds you have, and find their spec sheets, then make a list of their important characteristics (capacity, C-rate (continuous amps), nominal voltage, internal resistance) so you can set aside all the types that don't meet your needs.

You'll need to know their factory specs anyway in order to do the testing, because you have to know if the cell still comes close to those specs--if it doesn't, you probably dont' want it in your pack.

If you just use all the random cells you have that test ok (compared to an arbitrary limit, rather than factory spec) for capacity/etc, you'll wind up having to build a bigger, heavier pack than necessary, which will affect acceleration (more mass is bad for quick acceleration, and also bad for good braking).

Let's assume you've got just one type of cell (to save time/confusion in discussion), and that they are 2Ah capacity, and a 1C/2C cell (2A continuous / 4A burst), 3.7v nominal voltage. And assume that all the cells you actually use still meet their factory specs.

13s x 3.7v is a common 48v pack voltage, so that's ok.

8p x 2Ah means 16Ah pack capacity.

8p x 2A means 16A pack current capability continuous.

8p x 4A means 32A pack current capability burst.

Let's assume you'd need a continous battery current (different from motor current, usually higher) of 100A to meet your speed needs.

100A / 16A (per pack capability) = 7 packs (have to round up ;)) in parallel.

If you need no more than 200A peak battery current, then that also meets the peak demand, but you might need more than that. You'll know best once you actually test the kart on the track, with a wattmeter between the battery and the controller (if you don't have one, you'll want one by that stage, if not before).

Keep in mind that these would be *minimum* requirements, and if you can get more parallel packs than that it'd decrease the load on each cell, making them last longer and they'd have less voltage sag, so you get more watts out of the pack, and so higher performance out of the system.


Now, for endurance, or Ah, you have to figure out how many watts are continously used. Until you determine that, let's just go with 4000W figure, since it's near the max the motor can do anyway.

4000W for an hour is 4000wh, (4kwh). if you need 3 hours of runtime, that's 12kwh.

At an average of 48v, 12kwh (12000 / 48) is 250Ah.

If each pack is 16Ah, then 250 / 16 = 16 packs.

If each pack is made of 13 * 8 cells, then 16 of those is 1664 cells total you'd need.

That's all assuming 2Ah 1C cells, and 4kW continuous power usage, none of which might be the case.

If the cells you're using are better than that, you'll need less cells.

If they're worse, you'll need more.

If the power usage is less, you'll need less cells.

If it's more, you'll need more (and a bigger motor, or two of the ones you have).


I'm using the 4x5 plastic cell holders to make the packs,
I'm not sure what holders you mean, as there are a lot of kinds. Pictures or links would be useful.

If you mean the spring-loaded ones like the type that hold AA or AAA cells (but for 18650), those may just melt (or at least deform) from the high-resistance connections they make, and you won't get the performance you need from the pack. There's other types of solderless/weldless holders out there but I don't know how well any of them perform at high currents. There's discussion about them in various no-weld pack threads around ES.

I'd recommend spotwelding the pack for best performance. There's other alternatives, but it's possible to damage the cells with some of them (like soldering) if you're not careful and work out your technique on dud cells beforehand. Lots of discussion on those in the various 18650 threads, some of which are in the lists below.
https://endless-sphere.com/forums/searc ... mit=Search

https://endless-sphere.com/forums/searc ... mit=Search

Bigfillly
1 mW
1 mW
Posts: 10
Joined: Sep 18, 2017 10:05 am
Location: Earth, U.K. Derby in a shed :-)

Re: Calculating amp hours on 13s x 8p packs

Post by Bigfillly » Sep 20, 2017 2:58 pm

Thanks yet again for a great reply,

I'm glad to hear that the motor can be pushed to higher than I thought, although that means I need more battery power, I'll do a search for some kart builds on here,

I found the cell manufacturers spec list, so I can check them all an figure out which ones are close and which ones are scrap,

Im also glad the controller is more than capable of coping with what I intend doing, I'll just make sure it's set low when I first test it all :wink:

I'm now a little worried about the battery pack needed to max the motor, I'll have to make what I can with what I have, try it and see what I think, I may have to get more laptop batteries,

The battery holder are these:-
https://www.ebay.co.uk/itm/391396521454
There the ones that fit together in groups of 4x5 cells, they are the type that go on the top and bottom, and I'll need to either solder or spot weld bus bars on,

I have to say a big thanks to you, you have been very, very helpful and I have a lot to go at now,
I'll update as and when I make progress,
Once again, thank massively, :wink:
Phil.

Bigfillly
1 mW
1 mW
Posts: 10
Joined: Sep 18, 2017 10:05 am
Location: Earth, U.K. Derby in a shed :-)

Re: Calculating amp hours on 13s x 8p packs

Post by Bigfillly » Oct 07, 2017 5:23 am

Hi again, Quick update,
I’m still in the process of battery reclaiming but I have decided to got with 5 packs of 13s x 12p
Am I right in thinking that these pack (assuming they are 2a) will give me:-

12 x 2ah = 24ah pack capacity
12 x 2a = 24a pack current capacity continuous
12 x 4a = 48a pack current capacity burst
5 packs in parallel = 120a/24a (more than the 98 needed for the motor)
5 packs in parallel = 240a/48a burst (safe for the motors 300a maximum)

Hopefully this will be enough for what I need,
Thanks,
Phil.
Last edited by Bigfillly on Oct 08, 2017 3:10 am, edited 2 times in total.

User avatar
amberwolf
100 GW
100 GW
Posts: 23920
Joined: Aug 17, 2009 6:43 am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Calculating amp hours on 13s x 8p packs

Post by amberwolf » Oct 07, 2017 7:06 pm

Bigfillly wrote:12 x 2a = 24ah pack capacity
12 x 2a = 24a pack capacity continuous
12 x 4a = 48a pack capacity burst
Keep in mind:
Ah is capacity
A is not, it's just Amps (current) and the word capacity can't be used with A, only Ah.

Ah and A are tied together via C-rate, in that C-rate is how many times the Ah that you can get A out of a pack.

Meaning, C-rate is a multiplier; usually written as 2C or 1C or 5C, etc; on low-current-capability packs it can be less than 1 like 0.5C.

C-rate (xC) * capacity (Ah) = current capability (A).

If you have 2C cells that are 1Ah each then you have cells that can do 2A max.


Most cells have a continuous C-rate and a higher burst C-rate, usually for a few seconds (have to check the spec sheet for that particular cell to find out).

Bigfillly
1 mW
1 mW
Posts: 10
Joined: Sep 18, 2017 10:05 am
Location: Earth, U.K. Derby in a shed :-)

Re: Calculating amp hours on 13s x 8p packs

Post by Bigfillly » Oct 08, 2017 3:16 am

Yes, I see what I did, I’ve corrected things now (hopefully :D )
I’m sure I would be ok with this setup but only one way to find out, and that’s to get it all together,
Thanks again for stepping in an helping,
:)

Post Reply