[Flatstone]

Hi,

This is my first post, so sorry if this has been covered. I have searched and I'm going around in circles.

So I'm getting close to converting my 1972 VW Bus. I'll be using a conversion kit from EV West, with AC-50 motor and Curtis controller. I'm fairly happy with the system, it's just the batteries I'm having issues with.


My first option would be 30 x 3.2 Lifepo04 100ah (30s1p) wired up to a BMS. This seems to be a safe option and looking at other project should get me 30-40 mile range. If I have the room I would ideally like to get it too 200AH so 32s2p.

The second option, which I'm just a bit jittery about, is going the 18650 option. I have no intention of using old laptop batteries, all cells would be new. I could make 48v 50Ah battery pack myself, or buy the same spec E-Bike batteries (from Aliexpress etc heres one on eBay http://www.ebay.co.uk/itm/48V-50AH-rechargeable-Battery-Pack-Lithium-li-ion-ebike-EVs-BMS-20A-max-charge-/263205445934?hash=item3d4844612e:g:BKsAAOSw42dZN2XG ) and then connect them together, 2s2p, or budget willing 2s4p giving me 200Ah. They would all have there own charger, and have BMS's Would the premade E-Bike batteries standup to be using in this way. The gauge of the wire seems quite small, and would it be pushing to many amps through the batteries in series?

This area is such a black hole to me, and I'm very aware of how much of a fire risk it is, so I'd like to get it right. Not to mention the money involved!

Any ideas?

 

[john61ct]

Buy big prismatics.

You already have enough to worry about, DIY at that level is nuts to me if you can afford CALB or Winston cells.

 

[aquabiologist]

Hi
Excellent!!! Got a vw 1971 bus i like to convert, so i am super interested in your project.

I was looking at bike batteries as well: http://www.diyelectriccar.com/forums/showthread.php?t=188106

Those bike batteries are much lighter and way cheaper than lifepo4.

Does not seem to me to be more diy than lifepo4. Especially as they come packaged with bms already.

So from paper specs seems a good choice. Or not?

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[john61ct]

You need many hundreds of AH, a 4.4AH pack is irrelevant.

There are some chemistries lighter per AH than LFP but they're more costly not cheaper, and much more dangerous.

 

[Duncan]

Those are all very expensive and relatively low performance options
These days the best option is a battery pack from a wrecked EV
Chevy Volt (I use one of these)
Nissan Leaf
Tesla

Much cheaper and much higher quality

 

[Flatstone]

There doesn’t seem to be much of a secondhand market in the UK yet for salvage EV’s. Most EV cars (Zoe,Leaf) are sold with battery leases so I guess these remain property of the manufacture.

I’ve done some (back of a fag packet) calculations and the E-Bike packs are coming out too good to be true in terms of size, price, and weight.

So just as a base line I’ve speced up a 96v 100ah pack (ultimately I’d like a 200 or 300ah pack)

Prismatic 3.2v 100ah Cells

30 cells (@ £115 per cell) needed (s30p1) Total cost with BMS = Approx £3,500
Total weight = 110kg
Total Volume = 0.07m3


DIY 18650 3.7v 3ah Cells

884 cells (@ £4 per cell) needed (s26p34) Total cost with BMS = Approx £4000
Total weight = 44kg
Total Volume = 0.02m3

E-Bike 48v 50ah Pack using 26650 Cells inside built in BMS

4 cells (@ £540 per cell) needed (s2p2) Total = Approx £2160
Total weight = 52kg
Total Volume = 0.027m3


This is the spec of the E-Bike battery. Am I missing something really import as they seem spot on.

Battery Model
48v 50ah
Nominal Voltage (V)
48v
Nominal Capacity (AH)
50ah
Source Resistance (mΩ)
about 40
Cell Specification
3.7V 5.0AH
Cell Combination
10-parallel 13-series
Cell Size
3.7v 5.0ah 26650
Cell Quantity (parallel*series)
130pcs
Discharge Cutoff Voltage (V)
41+/- 1V
Charge Cutoff Voltage (V)
54.6v
Rated Discharge Current (A)
50A
instantaneous Maximum Discharge Current (A)
150A
Maximum Continuous Discharge Current (A)
50A
Maximum Continuous Charge Current (A)
5A
Charge Mode
CC-CV
Standard Charge Current (A)
2A
Charge Time under Standard Charge Current
12hours
Fast Charge Current (A)
5A
Charge Time under Fast Charge Current
6hours
Charge Temperature Range
-20-55°C
Cell Size (L*W*T )
360*270*70mm
Battery Weight
About 13KG
Battery Power
2000W

 

[Duncan]

Look a bit further - there are over 20,000 leafs and over 100,000 EV's in the UK

Something in the order of 1 in 80 will be written off - They will be there! - you just got to find them

 

[Flatstone]

I've just had a look (have to admit never occurred to me to look before), and there are 2 Leaf batteries packs for sale on Ebay uk, for £3500-£4000.

That works out a little bit more money to make the 96v 100am pack and weights more than the Prismatic option. Plus you have to take it apart, put it back together, etc etc. Secondhand batteries doesn't look that good to me. Might as well go down the Prismatic route.

 

[john61ct]

Not to mention dealing with voltages, complex electronics, signaling, all proprietary.

Buy a Leaf and tow it as a battery pack maybe. . .

 

[Flatstone]

Might as well tow a generator.

But good point, digging about in Nissan or Renaults electronics doesn't appeal, especially in a car thats written off in some way.

So that brings me back to the E-bike battery. What am I missing as they seem ideal, cheap(er), light, and much smaller.

Prismatic seems to be the first step away from lead acid, but still bulky and expensive, I can't imagine having 90 of them in the van to get to 300ah (and still have room for 3 kids in the back). And I'm not keen on creating my own "Tesla" style battery.

 

[john61ct]

Might as well tow a generator.

Hybrids actually work well as both, seen a big Expedition rig dolly a Prius.

 

[john61ct]

Might as well tow a generator.

But good point, digging about in Nissan or Renaults electronics doesn't appeal, especially in a car thats written off in some way.

So that brings me back to the E-bike battery. What am I missing as they seem ideal, cheap(er), light, and much smaller.

Prismatic seems to be the first step away from lead acid, but still bulky and expensive, I can't imagine having 90 of them in the van to get to 300ah (and still have room for 3 kids in the back). And I'm not keen on creating my own "Tesla" style battery.

Let's see, 300AH cells * 90, you really need 288V?

There are 12V units available, but lower AH, and you don't want drop-in with built-in BMS.

Unfortunately the physics doesn't go away, AH per kg vs fire risk.

The smaller the cell the more of them you need, hassles of interconnect, more points of failure.

I'd say lower your voltage requirement, you're going to need the AH if you want to go farther than around the block.

 

[Flatstone]

Sorry that was my fault, I should of specified 90 prismatic would be in s30p3, so the volts would remain at 96v but I would have 300ah.

But practically 90 prismatic cell just wouldn't work. It would just be one VW Bus shaped battery on wheels.

Hence, if the 48v 50ah e-bike batteries aren't going to create a massive Nov 5th (read July 4th in the US) display, I could get to the goal of 96v 300AH with 2s6p each pack with it's own BMS and charger.

 

[john61ct]

My first option would be 30 x 3.2 Lifepo04 100ah (30s1p) wired up to a BMS. This seems to be a safe option and looking at other project should get me 30-40 mile range. If I have the room I would ideally like to get it too 200AH so 32s2p.

I thought you were just talking 300AH cells?

The above implies you only need 96-102V.

2P does give some redundancy, but I don't think 150AH is available.

I'd start with a string of 200AH, then later double that for good range.

 

[Flatstone]

I think something getting lost in translation. I'm happy with the prismatic setup, it's a well trodden route.

My question is around the E-bike packs (48v 50h), and connecting them in s2p2 to make a 96v 100ah system (and then later adding more s2sp2's to increase the AH). See post 6 for the details.

 

[john61ct]

Hence, if the 48v 50ah e-bike batteries aren't going to create a massive Nov 5th (read July 4th in the US) display, I could get to the goal of 96v 300AH with 2s6p each pack with it's own BMS and charger.

Fewer parallel fewer problems, if true LiFePO4 little fire risk, but I've seen pretty authoritative sources say don't go past 3 maybe 4P, which implies go with at least 100AH cells.

IMO
30*200AH, later doubled, or 30*300AH

Advantage of standard 3.2V cells is you can always drop in a good BMS if one you like later comes on the market.

Plus CALB, Sinopoly, GBS or Winston known good quality. . .

 

[john61ct]

Just build a special bench seat for the kids, under-dimensions just right for 30-32 cells.

Weight will be between the axles, maybe toward the back.

Or maybe even (mostly) fit with the motor in the very back, you'll be messing with the "frame" there anyway.

 

[rmay635703]

Ebike packs are notoriously unreliable

 

[john61ct]

LiCo02? greater fire risk?

FYI, maybe be worth talking to this seller

Look at this on eBay http://www.ebay.com/itm/112562977502

 

[aquabiologist]

Did some digging on the fire/safety issue
Here's a link that explains the different chemistries in detail:
http://batteryuniversity.com/learn/article/types_of_lithium_ion

And here's is one with the battery codes for the 18650 battery cells*often used in e-bike packs:
https://batterybro.com/blogs/18650-wholesale-battery-reviews/18880255-battery-chemistry-finally-explained

So it seems that the 'cheap' e-bike packs use LiCo chemistry = the fire risk chemistry

Leaf and volt batteries use NMC chemistry = safe with bms

Tesla uses NCA chemistry = safe with bms

Diy ev builders recommend LFP = lifepo4 = safe even without bms, no fire risk whatsoever

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