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Discussion Starter #1 (Edited)
I'm looking into a new battery pack for my Polo soon. Same voltage as now (500V) or maybe a bit higher. About 30kWh to give me 250km relaxed driving range. It seems 18650 is the way to go in terms of availability and cell price.
As the Polo has a max power of 45kW I would draw 1.5C max. Much less continuous. Any cell should do that.

Found this offer on dhgate: https://de.dhgate.com/product/ultrafire-18650-4200mah-3-7v-li-ion-rechargeable/393296842.html#cppd-1-5|null:103:r0002516581

First of all, 4200mAh?? Never seen anything like it. Plausible?
Then the price $0.69 - a scam?
Weight: 37g - what?

That would be a 31kWh pack for $1380 and would weigh 74kg

Too good to be true, right?

EDIT: yes, too good to be true: https://lightsngear.com/beware-fake-ultrafire-18650-batteries/
 

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Definitely fake. One of the best cells available are the LG MJ1 and those are 3500 mah. They claim they are 3400 mah nominal but I bought one and tested it and got 2900 mah.

As they say, if it sounds too good to be true, it probably is.
 

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There are several "good" 18650s, depending on your prime requirements.
IE, max output, max capacity, max life cycle , etc etc
The Panasonic 18650 BD is a solid performer (and very similar to the cell Tesla use), whilst the Sanyo /Panasonic GA has more capacity (3500mAh) , good discharge (10 A cont) , and is earning a good life cycle reputation.
http://www.dampfakkus.de/akku_liste-nach-groesse.php?size=18650
But quality and reliability doesnt come cheap,..expect $4+ per cell. ($400 /kWh)
Best value packs for DIY EV use are still salvaged Volt, or LEAF, packs
And much simpler to work with than thousands of 18650s !
 

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Discussion Starter #5
Best deal I could find on what looks like Panasonic was this:
https://www.aliexpress.com/store/product/1pcs-2017-liitokala-lii-34B-New-Original-NCR18650-3400-34B-Rechargeable-Li-ion-battery-for-panasonic/217753_32807076413.html?spm=2114.12010612.0.0.76ae745bn07bHn

$2.73 for 3400mAh or $0.80/Ah. So in the ball park that prensel states.

I know salvaged packs are a good option for a one-off but I'm also looking into a more reproducible solution. So far I haven't found a single used pack in Germany.
 

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Johannes,

I have build custom sized modules from 18650 cells in different setups and buy all my cells from Arjen at www.nkon.nl, he's a good guy to deal with for bigger qty's and his stock is already in The Netherlands, EU, so no import hassle and duties. I have been doing some of the cell welding for his customers also.
 

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$2.73 for 3400mAh or $0.80/Ah. So in the ball park that prensel states.
I paid 1000 Euros for my Tesla P100 modules which is 1.94 Euros ($2.40 USD) per cell... if you factor in the design/build time and cost to package the cells then Tesla modules are much cheaper than DIY... and that's before you consider heating/cooling the battery (which I note some people are just ignoring) :rolleyes:
 

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I have built a test cell from 48P 18650 Panasonic ncr18650pf. They are considered consumer cells, but they show good performanse and good compromise between current and thermal stability.

I made one cell and put it in series with my Kokam 85Ah cells to measure performanse. Mind you 48P is more than 130Ah as a common cell.
In truth this cell is still in series with my pack and it holds it capacity - obviously. I measured its performanse however and it was worse than my Kokam cells.

Voltage drop was 13% in all current draw up to 200A, more i didnt check due to self destruct nature of Kokams.
Kokam had cca 8% voltage drop.

Surprisingly thermal stability was better than Kokam. Complete cell didnt show signs of higher temperature during long 150km drive with hard (10kW) charging in the end. Kokam had temperature of 37deg, NCRs only 32deg!

During charging NCR cells have higher Ri obviously and cell voltage rides higher then Kokam. This is evident in the end of charge when NCR BMS triggers first and then holds this cell clamped for longer. Result is that NCR full voltage will allways somewhat lower than Kokam.

My conclusion is Kokam LiPo are still better in every way except impact safety. But energy is energy and Johannes wil not notice voltage drop due to his inverter voltage correction.
I only notice torque drop at high RPM when motor is forced to drop slip so it wouldnt damage Kokam cells.

Have you consider Volt/Ampera cells? 2x battery packs would give you 30kW.
Would have to take them apart probably.

EDIT: I found some photos of design and built. First is the design for 6S 13P i considered good for e-bike. Second is my experimental cell being built. You have to have 100W iron, solder paste and 0.5mm wire to have 25A fuse rating. You have to use little solder paste on battery surface in order to prepare surface for quicker soldering. Do not heat-up + terminal too much! - terminal can handle some repairs, but + terminal is more sensitive.

If you have the time you can build battery up to your wishes, however according to price it is a better deal to just buy used tesla modules and modify them. They have cooling/heating system built in, same for BMS connection and module you can just put in a car. It is already made touch proof.
 

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Is it possible to modify Tesla packs for higher voltage?
.
This is confusing ...what voltage exactly do you need ?

Tesla "packs" are 384v (96s).nominal..(16 x 6s modules)
Tesla "modules" are 24v, (6s)
You can use multiple "modules" in series for higher voltages...48v, 72v, 96v, etc
Voltages below 24v require some specialised modification to modules.
 

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Discussion Starter #14
This is confusing ...what voltage exactly do you need ?
In the end I need 500V and a 25kWh pack. So each parallel cell assembly must be 50Ah.
With 3Ah cells it would be a 17P135S configuration

I really like what Arber has got going on. I could use a much smaller bus bar as max current draw is <100A.
 

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In the end I need 500V and a 25kWh pack. So each parallel cell assembly must be 50Ah.
With 3Ah cells it would be a 17P135S configuration

I really like what Arber has got going on. I could use a much smaller bus bar as max current draw is <100A.
Well i dont want to dissapoint you, but i wont pursue this branch. I think it is a dead end since cells are 2.4€ apiece at 4000pcs. They still have to be connected. You still have to buy plastic sockets. You have to buy copper or brass for busbars and in the end you dont have any temp management.

Tesla modules modified to 12s are more finalized and in the end calculate how much you pay if you join 444 cells to get 48V out of it. Compare that and see you are better off with Tesla modules.

BUT! There are also Volt cells like Damien uses. For your application i would recommend you take 2x Volt/Ampera used cell packs that have 15Ah pouch cells in 3P96S config and make 4P135S pack. That leaves 36 cells spare :). That would leave 29kW in a car. Lets say 26KW useful energy. Since you will have low current demand cells wont be under thermal shock like in a Volt.
Prices of Volt cells are quite low, you just have to find a scrapyard.

A
 

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Yes I think Arber is right, think we all have the idea of 18650's pack

all those ultrafire/trustfire type are know to be fake cells.

Its not not cost effective to use new cells.

When I was seriously thought about doing this with used cells but the recommendation was not to charge/discharge more than 0.5C.

Think there alot theads over at

https://endless-sphere.com/forums/

This youtuber has made a big home solar setup using 18650

https://www.youtube.com/user/nocrf50here/videos
 

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OK anyone, how would you rate Tesla cell modules vs Volt modules. I mean performance from experience. Please comment on their behaviour, capacity and power.

A
 

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OK anyone, how would you rate Tesla cell modules vs Volt modules. I mean performance from experience. Please comment on their behaviour, capacity and power.

A
This is a thread about building a pack on out of 18650 cells. Not really the place to ask a comparison question between two different OEM packs. I think you will have better luck asking this some where appropriate.
 

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Yes I think Arber is right, think we all have the idea of 18650's pack

all those ultrafire/trustfire type are know to be fake cells.

Its not not cost effective to use new cells.

When I was seriously thought about doing this with used cells but the recommendation was not to charge/discharge more than 0.5C.

Think there alot theads over at

https://endless-sphere.com/forums/

This youtuber has made a big home solar setup using 18650

https://www.youtube.com/user/nocrf50here/videos
I reconsidered some about those DIY battery modules. They may make sense in low voltage high current specs where you cant get usefull vendor batteries.

1. Very high current rating. In case of low voltage high current you could custom build battery module on your specs.

2. Strange shapes. In case of low space or strange position for battery box you could conform to the space with a custom battery.
 
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