Sat Apr 10, 2021 9:33 pm

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
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Posts: 273
Location: Undisclosed
Sat Apr 10, 2021 9:33 pm linkquote
recently acquired a smallframe with a lot of rust in the floorboards

no engine, no gas tank, no problem!

planning on converting it to use a 10" electric hub motor and batteries - calling it Lucciola (Italian for firefly/lightning bug)

purchased replacement floor/legshield from SIP

https://www.sip-scootershop.com/en/product/repair-sheet-legshield-floor-board-sip_PV153485

dumb question: what do I do about the horncast? can I just remove it from the original legshield and splice it in?

I also ordered the metal engine-side door and will need to figure out the elusive battery-side door (anyone have one they are willing to lend me so I can copy it?)

going to use an aluminum tubeless front rim to match the new rear motor and convert the front to disc brake with better suspension

pretty enthusiastic about this project. hoping I can come up with an inexpensive system and either sell kits or do full conversions on new reproduction vespa frames after this prototype.

the plan is to swap all lighting to LEDs (12v) and eliminate the foot pedal to move to a completely automatic layout (both levers functioning as brake levers) with hydraulic disc front and rear.

4kw or better motor and plenty of juice - hoping for 55+ mph and 50-70 mile range! will custom-fabricate a battery to fit in the unibody.

another thought is remote-mounted master cylinders for the brakes (and hiding them in an ET3 Faco glovebox)















Sun Apr 11, 2021 4:21 am

Hooked
1966 Sprint 150 & px200 and a shed full o shit
Joined: 15 Aug 2016
Posts: 132
Location: New Zealand
 
Hooked
1966 Sprint 150 & px200 and a shed full o shit
Joined: 15 Aug 2016
Posts: 132
Location: New Zealand
Sun Apr 11, 2021 4:21 am linkquote
Great idea. I'd prefer the rear brake on the floor though (consistency). Would trade range for acceleration, if that is a thing, as these gonna be city bikes. Hope this feedback helps
Sun Apr 11, 2021 5:24 am

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Sun Apr 11, 2021 5:24 am linkquote
This should be fun. One change I would have made to mine is to completely replace the legshield like you did. Looking forward to the results!
Sun Apr 11, 2021 5:43 am

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
Sun Apr 11, 2021 5:43 am linkquote
If you're using the same motor Jim did contact the company. I was looking and they have a higher voltage Kelly controller you can use on the same motor. Higher voltage battery means higher top speed and more torque.
Sun Apr 11, 2021 6:42 pm

Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 2410
Location: california
 
Ossessionato
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 2410
Location: california
Sun Apr 11, 2021 6:42 pm linkquote
They also have a drum brake I believe.
Not sure there is any real advantage of a disc on the back - the drum will happily lock up the rear wheel - and you keep the foot pedal brake.
Just a consideration - disc is cool too - just not a must in my view.
Sun Apr 11, 2021 7:12 pm

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Sun Apr 11, 2021 7:12 pm linkquote
charlieman22 wrote:
They also have a drum brake I believe.
Not sure there is any real advantage of a disc on the back - the drum will happily lock up the rear wheel - and you keep the foot pedal brake.
Just a consideration - disc is cool too - just not a must in my view.
Though I have the disc rear brake on my VespaLectric, I can't say whether or not the QS drum is as good as the Vespa drum in the rear. I can say that the Vespa front drum is not up to the task of 50mph plus stopping power.
Sun Apr 11, 2021 7:45 pm

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
Sun Apr 11, 2021 7:45 pm linkquote
I would personally opt for rear drum as that's obviously a direct swap, but I agree: no idea if their drum brake is any good, and I would want to swap the front to disc (probably a grimeca kit or similar). seems more consistent to just do disc brakes front and rear.

as for brake lever on the floor... the automatic Stellas ditched the brake lever on the floor and most automatic scooters use hand levers for front/rear - so it's more consistent to an automatic bike (plus easier/cleaner to plug a hole in the floor than it is to find a way to eliminate a handlebar lever). I want to avoid modifying the handlebars if possible.

I definitely want to focus on speed and torque over range. there'd be no way to get 200+ miles as there simply isn't room in a smallframe even if you stuffed it with the best cells - you need room for the other components. I'm sure this will change with time as batteries get better and better. planning to use the same cells they use in Tesla cars (Panasonic 18650).

something I did in an old VBB was a modern 4.5" headlight using a Harley style "fog light" with high/low. it's a few mm too small but it can be made to fit by 3d printing an adapter to mimic the 3 mounting tabs on the stock headlight. here's a pretty cheap one I grabbed: https://www.amazon.com/gp/product/B07VV9LBSR

the frame was also missing the US DOT spec "tractor" tail light and license plate bracket. I always thought they looked insanely huge, and even the "Ducati" style one is pretty big. I got a cheap bobber style thing from ebay. https://www.ebay.com/itm/133558168256









Last edited by saturn on Mon Apr 26, 2021 6:53 am; edited 1 time in total
Mon Apr 12, 2021 6:33 am

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Mon Apr 12, 2021 6:33 am linkquote
For the rear brake, and front, there is a way to cable operate the master cylinders, mounted in the glovebox or under the seat, or even in unused cowl space. You can also remote operate your throttle with one of these: https://www.aliexpress.com/item/32954909008.html?spm=a2g0s.9042311.0.0.4b7c4c4dVKTIWn By doing all this you could keep your handlebars stock, and have disc brakes. Or, just go drum rear and stock front. It may be enough.

As for range, current battery technology will allow a lot of speed, or a lot of range, but not both. At heavy throttle and high speeds, with my 280 pounds on it, I can get about 28 miles. IF I can ride more sedately I am confident 40+ could be had, or if you are significantly lighter than me. You may even beat my current top speed of 62mph.

That rear tail light looks like it will be perfect for your bike. I like the headlight as well.

Nice progression so far!
Mon Apr 12, 2021 9:03 am

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
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Posts: 273
Location: Undisclosed
Mon Apr 12, 2021 9:03 am linkquote
JimVonBaden wrote:
Nice progression so far!
thanks!

and as for remote master, I'm considering it as I think it'll be easier than cutting the handlebars or trying to do some crazy linkages.

do you know if the "kelly" controller is any better than the less expensive one?

https://www.alibaba.com/product-detail/Kelly-Controller-KLS7250D-24V-72V-400A_60832387498.html?spm=a2700.wholesale.0.0.2c6c350ctVlhmu

less expensive one:

https://www.alibaba.com/product-detail/6000W-7000W-8000W-SineWave-FOC-BLDC_1600172023336.html?spm=a2700.wholesale.0.0.19036a449yjjtM

thanks for the tip on the throttle controller! I was going to fabricate one myself but this is too cheap to not use.
Mon Apr 12, 2021 11:39 am

Member
2003 Stella (2T) 4kW Electric Conversion
Joined: 31 Aug 2020
Posts: 22
Location: Salt Lake City, UT
 
Member
2003 Stella (2T) 4kW Electric Conversion
Joined: 31 Aug 2020
Posts: 22
Location: Salt Lake City, UT
Mon Apr 12, 2021 11:39 am linkquote
Rear master cylinder
I am finishing my project up and opted for a master cylinder under the scooter by the rear pedal. It was plug and play on my large frame. Pricey though.

https://www.sip-scootershop.com/en/product/brake-pedal-crimaz-disc-brake-hydraulic_30004200?tab=tab_germany
Mon Apr 12, 2021 1:51 pm

Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3331
Location: Staten Island, NY
 
Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3331
Location: Staten Island, NY
Mon Apr 12, 2021 2:38 pm

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
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Posts: 273
Location: Undisclosed
Mon Apr 12, 2021 2:38 pm linkquote
swiss1939 wrote:
https://miami.craigslist.org/pbc/mpo/d/wellington-electric-scooter-hub-motor/7305842810.html
whoa! going to see if he'll ship... not ideally the pieces I want but great price. thanks!
Mon Apr 12, 2021 4:51 pm

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Mon Apr 12, 2021 4:51 pm linkquote
saturn wrote:
JimVonBaden wrote:
Nice progression so far!
thanks!

and as for remote master, I'm considering it as I think it'll be easier than cutting the handlebars or trying to do some crazy linkages.

do you know if the "kelly" controller is any better than the less expensive one?

https://www.alibaba.com/product-detail/Kelly-Controller-KLS7250D-24V-72V-400A_60832387498.html?spm=a2700.wholesale.0.0.2c6c350ctVlhmu

less expensive one:

https://www.alibaba.com/product-detail/6000W-7000W-8000W-SineWave-FOC-BLDC_1600172023336.html?spm=a2700.wholesale.0.0.19036a449yjjtM

thanks for the tip on the throttle controller! I was going to fabricate one myself but this is too cheap to not use.
I strongly recommend you contact Robert at QS motors: He can set you up with a motor/controller that works well together. info@qs-motor.com

With that said, three of us have the same controller and it was cheaper than your price when combined with the motor, and even the throttle and disc brake kit. My total for all was $710. Plus shipping.
Mon Apr 12, 2021 8:21 pm

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
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Posts: 273
Location: Undisclosed
Mon Apr 12, 2021 8:21 pm linkquote
FYI, Robert emailed me back and said:

- 10 inch 4kw (7kw peak) hub with disc rotor: USD290
- rear brake caliper and bracket: USD20
- controller and wiring(Kelly KLS7245N): USD230
Tue Apr 13, 2021 7:04 am

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Tue Apr 13, 2021 7:04 am linkquote
saturn wrote:
FYI, Robert emailed me back and said:

- 10 inch 4kw (7kw peak) hub with disc rotor: USD290
- rear brake caliper and bracket: USD20
- controller and wiring(Kelly KLS7245N): USD230
Sounds quite reasonable, and what I have. Make sure they include the Bluetooth interface with the Kelly Controller.
Tue Apr 13, 2021 7:16 am

Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3331
Location: Staten Island, NY
 
Ossessionato
VSX, Stella 177, Stella 150, VNX1T, V9B1T
Joined: 20 Jul 2018
Posts: 3331
Location: Staten Island, NY
Tue Apr 13, 2021 7:16 am linkquote
Basically same price as that guys craigslist motor.. but new so no questionable condition!
Wed Apr 14, 2021 6:55 am

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
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Location: Undisclosed
Wed Apr 14, 2021 6:55 am linkquote
JimVonBaden wrote:
Sounds quite reasonable, and what I have. Make sure they include the Bluetooth interface with the Kelly Controller.
they included the bluetooth
Fri Apr 16, 2021 10:00 am

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
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Hooked
AmeriBodge
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Fri Apr 16, 2021 10:00 am linkquote
can someone better with electronics than me help with some calculations?

I want to do a battery pack of 40 cells (20 + 20) at ~72v

how do I do calculations to figure out amps and how do I know which battery management system and which charger?

my (possibly wrong) calculations seem off:

each battery cell is 3.7v at 3400mah (3.4ah)
total should be at ~250 watts
total current should be ~6.8 amps? so anything rated at 7 or 8 amps would work?
Fri Apr 16, 2021 10:10 am

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
Fri Apr 16, 2021 10:10 am linkquote
saturn wrote:
can someone better with electronics than me help with some calculations?

I want to do a battery pack of 40 cells (20 + 20) at ~72v

how do I do calculations to figure out amps and how do I know which battery management system and which charger?

my (possibly wrong) calculations seem off:

each battery cell is 3.7v at 3400mah (3.4ah)
total should be at ~250 watts
total current should be ~6.8 amps? so anything rated at 7 or 8 amps would work?
20 batteries in series would be 3.7*20 = 74 volts, current would be the same at 3.4 AH. Battery voltage adds in series, current stays the same.

A second set in parallel would double the current capability to 6.8 amps, voltage would stay the same.

So you would have a 74 volt, 6.8 amp hour battery.

Watts = Volts x amps

74 volts * 6.8 amps = 503.2 watts



I think your going to need a bigger battery, Jim ended up with something around 40 amp hour battery. Your going to need something like 11 sets of cells in parallel. So 20 in series to get 74 volts. Then 11 sets of those in parallel to get more current. I think some of those BMS allows for 100 amps of current.


A 4000 watt motor can draw 55 amps at 72 volts. So when you initially accelerate from a stop you could easily be pulling 55 amps, depends if that number is peak or continuous. Peak you may draw around 100 amps.

4000 watts @ 72 volts = 55 amps,

Last edited by Christopher_55934 on Fri Apr 16, 2021 12:17 pm; edited 3 times in total
Fri Apr 16, 2021 10:24 am

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
Location: Undisclosed
 
Hooked
AmeriBodge
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Fri Apr 16, 2021 10:24 am linkquote
oh so my math was right except the watts!
Fri Apr 16, 2021 10:41 am

Hooked
AmeriBodge
Joined: 01 Sep 2010
Posts: 273
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Hooked
AmeriBodge
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Posts: 273
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Fri Apr 16, 2021 10:41 am linkquote
I ordered this BMS:

https://www.aliexpress.com/item/4001015122052.html

and these cells:

https://www.aliexpress.com/item/32771532107.html

amazon carries the same chargers for the same prices when you include shipping from China (and I'd receive them faster)

I assume something like this would work? https://www.amazon.com/Battery-Charger-Lithium-Electric-Bicycle/dp/B07PT6ZL87/
Fri Apr 16, 2021 12:27 pm

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
Fri Apr 16, 2021 12:27 pm linkquote
saturn wrote:
I ordered this BMS:

https://www.aliexpress.com/item/4001015122052.html

and these cells:

https://www.aliexpress.com/item/32771532107.html

amazon carries the same chargers for the same prices when you include shipping from China (and I'd receive them faster)

I assume something like this would work? https://www.amazon.com/Battery-Charger-Lithium-Electric-Bicycle/dp/B07PT6ZL87/
If I'm understanding how that BMS works it supplies power to the controller. I think it maybe a bit underrated for current at 60 amps maximum, added a few more lines of math to the the previous calculations.
Fri Apr 16, 2021 2:39 pm

Enthusiast
Piaggio P125X
Joined: 05 Jul 2017
Posts: 60
Location: Finland
 
Enthusiast
Piaggio P125X
Joined: 05 Jul 2017
Posts: 60
Location: Finland
Fri Apr 16, 2021 2:39 pm linkquote
Christopher_55934 wrote:
saturn wrote:
can someone better with electronics than me help with some calculations?

I want to do a battery pack of 40 cells (20 + 20) at ~72v

how do I do calculations to figure out amps and how do I know which battery management system and which charger?

my (possibly wrong) calculations seem off:

each battery cell is 3.7v at 3400mah (3.4ah)
total should be at ~250 watts
total current should be ~6.8 amps? so anything rated at 7 or 8 amps would work?
20 batteries in series would be 3.7*20 = 74 volts, current would be the same at 3.4 AH. Battery voltage adds in series, current stays the same.

A second set in parallel would double the current capability to 6.8 amps, voltage would stay the same.

So you would have a 74 volt, 6.8 amp hour battery.

Watts = Volts x amps

74 volts * 6.8 amps = 503.2 watts



I think your going to need a bigger battery, Jim ended up with something around 40 amp hour battery. Your going to need something like 11 sets of cells in parallel. So 20 in series to get 74 volts. Then 11 sets of those in parallel to get more current. I think some of those BMS allows for 100 amps of current.


A 4000 watt motor can draw 55 amps at 72 volts. So when you initially accelerate from a stop you could easily be pulling 55 amps, depends if that number is peak or continuous. Peak you may draw around 100 amps.

4000 watts @ 72 volts = 55 amps,
Your current calculation is a bit off, the battery max current needs to be calculated using the maximum discharge of the cells, not the capacity, so if the cell can discharge at say 10 A, then the max current for that battery pack is 20 Amps.

This of course is very dependant on battery chemistry, Li-Ion is probably the best bet for this application as LiFePo or LTO are too bulky at any reasonable amperage.

Check the specs on the 18650s, a single 18650 can have a discharge current of 5A, 10A, 20A or 30A. There's a tradeoff between discharge current/cost and capacity, so it's something you want to look into.

But, if we take this battery: https://eu.nkon.nl/rechargeable/li-ion/18650-size/lg-inr18650-mj1-buttontop.html

It has a voltage of 3.6V nominal, 3500mAh capacity and a discharge current of 10A.

If you start with 20 cells in series, aka a 20S battery, you get 3500mAh at 72V nominal. Then you can stack say 4 of these in parallell, that I'll give you a 20S4P battery, with 14Ah at 72V. This pack has 4 parallell strings of 10A batteries, so the maximum discharge current is 40A, aka 72V * 40A = 2880 Watts.
You usually don't want to exceed the rated discharge current of the cells under any conditions, so a 20S6P or 20S8P battery would be better, as they could theoretically support a 4320W or 5760W motor respectively. Of course, if you went for 20A cells, you could cut the parallell strings in half, but that would also cut your battery capacity in half (or even less, as you'd be hard pressed to find 3500mAh cells at that discharge current).

Also make sure that your chosen BMS has balancing leads for every cell in series, aka. a 20S BMS, it's important for these larger battery packs if you want to have long life from the cells. The BMS only cares about how many cells you have in series, and the maximum battery current, so size accordingly.

This is of course from a guy with just an electrical background, not someone with any experience with DIY EVs, so real world experience may dictate otherwise.
Fri Apr 16, 2021 3:20 pm

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Fri Apr 16, 2021 3:20 pm linkquote
Just an FYI, I have a Daly BMS https://www.aliexpress.com/item/32924399920.html?spm=2114.12010612.8148356.1.383e4078Iv6gS8 150 amp, and regularly push 220 amps.

My battery is a 72V 38 ah, 20s, 8p.

This can help: https://www.ebikeschool.com/how-to-build-a-diy-electric-bicycle-lithium-battery-from-18650-cells/
Fri Apr 16, 2021 3:24 pm

Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
 
Hooked
P125x (4KW Hub Motor)
Joined: 06 May 2019
Posts: 406
Location: Alexandria, VA
Fri Apr 16, 2021 3:24 pm linkquote
Stuggi wrote:
Christopher_55934 wrote:
saturn wrote:
can someone better with electronics than me help with some calculations?

I want to do a battery pack of 40 cells (20 + 20) at ~72v

how do I do calculations to figure out amps and how do I know which battery management system and which charger?

my (possibly wrong) calculations seem off:

each battery cell is 3.7v at 3400mah (3.4ah)
total should be at ~250 watts
total current should be ~6.8 amps? so anything rated at 7 or 8 amps would work?
20 batteries in series would be 3.7*20 = 74 volts, current would be the same at 3.4 AH. Battery voltage adds in series, current stays the same.

A second set in parallel would double the current capability to 6.8 amps, voltage would stay the same.

So you would have a 74 volt, 6.8 amp hour battery.

Watts = Volts x amps

74 volts * 6.8 amps = 503.2 watts



I think your going to need a bigger battery, Jim ended up with something around 40 amp hour battery. Your going to need something like 11 sets of cells in parallel. So 20 in series to get 74 volts. Then 11 sets of those in parallel to get more current. I think some of those BMS allows for 100 amps of current.


A 4000 watt motor can draw 55 amps at 72 volts. So when you initially accelerate from a stop you could easily be pulling 55 amps, depends if that number is peak or continuous. Peak you may draw around 100 amps.

4000 watts @ 72 volts = 55 amps,
Your current calculation is a bit off, the battery max current needs to be calculated using the maximum discharge of the cells, not the capacity, so if the cell can discharge at say 10 A, then the max current for that battery pack is 20 Amps.

This of course is very dependant on battery chemistry, Li-Ion is probably the best bet for this application as LiFePo or LTO are too bulky at any reasonable amperage.

Check the specs on the 18650s, a single 18650 can have a discharge current of 5A, 10A, 20A or 30A. There's a tradeoff between discharge current/cost and capacity, so it's something you want to look into.

But, if we take this battery: https://eu.nkon.nl/rechargeable/li-ion/18650-size/lg-inr18650-mj1-buttontop.html

It has a voltage of 3.6V nominal, 3500mAh capacity and a discharge current of 10A.

If you start with 20 cells in series, aka a 20S battery, you get 3500mAh at 72V nominal. Then you can stack say 4 of these in parallell, that I'll give you a 20S4P battery, with 14Ah at 72V. This pack has 4 parallell strings of 10A batteries, so the maximum discharge current is 40A, aka 72V * 40A = 2880 Watts.
You usually don't want to exceed the rated discharge current of the cells under any conditions, so a 20S6P or 20S8P battery would be better, as they could theoretically support a 4320W or 5760W motor respectively. Of course, if you went for 20A cells, you could cut the parallell strings in half, but that would also cut your battery capacity in half (or even less, as you'd be hard pressed to find 3500mAh cells at that discharge current).

Also make sure that your chosen BMS has balancing leads for every cell in series, aka. a 20S BMS, it's important for these larger battery packs if you want to have long life from the cells. The BMS only cares about how many cells you have in series, and the maximum battery current, so size accordingly.

This is of course from a guy with just an electrical background, not someone with any experience with DIY EVs, so real world experience may dictate otherwise.
Very good advice.
Fri Apr 16, 2021 3:44 pm

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
Fri Apr 16, 2021 3:44 pm linkquote
Stuggi wrote:
Christopher_55934 wrote:
saturn wrote:
can someone better with electronics than me help with some calculations?

I want to do a battery pack of 40 cells (20 + 20) at ~72v

how do I do calculations to figure out amps and how do I know which battery management system and which charger?

my (possibly wrong) calculations seem off:

each battery cell is 3.7v at 3400mah (3.4ah)
total should be at ~250 watts
total current should be ~6.8 amps? so anything rated at 7 or 8 amps would work?
20 batteries in series would be 3.7*20 = 74 volts, current would be the same at 3.4 AH. Battery voltage adds in series, current stays the same.

A second set in parallel would double the current capability to 6.8 amps, voltage would stay the same.

So you would have a 74 volt, 6.8 amp hour battery.

Watts = Volts x amps

74 volts * 6.8 amps = 503.2 watts



I think your going to need a bigger battery, Jim ended up with something around 40 amp hour battery. Your going to need something like 11 sets of cells in parallel. So 20 in series to get 74 volts. Then 11 sets of those in parallel to get more current. I think some of those BMS allows for 100 amps of current.


A 4000 watt motor can draw 55 amps at 72 volts. So when you initially accelerate from a stop you could easily be pulling 55 amps, depends if that number is peak or continuous. Peak you may draw around 100 amps.

4000 watts @ 72 volts = 55 amps,
Your current calculation is a bit off, the battery max current needs to be calculated using the maximum discharge of the cells, not the capacity, so if the cell can discharge at say 10 A, then the max current for that battery pack is 20 Amps.

This of course is very dependant on battery chemistry, Li-Ion is probably the best bet for this application as LiFePo or LTO are too bulky at any reasonable amperage.

Check the specs on the 18650s, a single 18650 can have a discharge current of 5A, 10A, 20A or 30A. There's a tradeoff between discharge current/cost and capacity, so it's something you want to look into.

But, if we take this battery: https://eu.nkon.nl/rechargeable/li-ion/18650-size/lg-inr18650-mj1-buttontop.html

It has a voltage of 3.6V nominal, 3500mAh capacity and a discharge current of 10A.

If you start with 20 cells in series, aka a 20S battery, you get 3500mAh at 72V nominal. Then you can stack say 4 of these in parallell, that I'll give you a 20S4P battery, with 14Ah at 72V. This pack has 4 parallell strings of 10A batteries, so the maximum discharge current is 40A, aka 72V * 40A = 2880 Watts.
You usually don't want to exceed the rated discharge current of the cells under any conditions, so a 20S6P or 20S8P battery would be better, as they could theoretically support a 4320W or 5760W motor respectively. Of course, if you went for 20A cells, you could cut the parallell strings in half, but that would also cut your battery capacity in half (or even less, as you'd be hard pressed to find 3500mAh cells at that discharge current).

Also make sure that your chosen BMS has balancing leads for every cell in series, aka. a 20S BMS, it's important for these larger battery packs if you want to have long life from the cells. The BMS only cares about how many cells you have in series, and the maximum battery current, so size accordingly.

This is of course from a guy with just an electrical background, not someone with any experience with DIY EVs, so real world experience may dictate otherwise.
I would say you are correct.

From what I can find those are Panasonic cells capable of 2CA or 6.8 amps maximum.

https://www.orbtronic.com/batteries-chargers/panasonic-3400mah-18650-li-ion-battery-cell-ncr18650b

That motor is 7000 watts peak.

P=ExI

7000/72 = 97.2 amps

97.2 / 6.8 would be a 20S15P battery, minimum.


Charge current says 1625 mah per cell so that would be 1625 x 15P in the above example something less than 72 volt 24 amp should work. You just have to decide on charge time and battery life.

I would look into better cells,

https://www.orbtronic.com/18650-battery-3500mah-li-ion-high-drain-panasonic-sanyo

These allow for a 10 amp discharge, so

97.2 / 10 = 9.72 or 10 in parallel with no safety margin built in.

https://www.18650batterystore.com/products/sony-vtc5a

These are better yet 25 amp maximum

200 / 25 = 8P

NCR18650B-Datasheet-Panasonic-Specifications.pdf
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Last edited by Christopher_55934 on Fri Apr 16, 2021 4:09 pm; edited 1 time in total
Fri Apr 16, 2021 4:00 pm

Molto Verboso
2007 Stella 225
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Molto Verboso
2007 Stella 225
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Posts: 1879
Location: Rochester, Minnesota
Fri Apr 16, 2021 4:00 pm linkquote
JimVonBaden wrote:
What did your battery build say max current draw for the pack is?
150 amps / 8 sets in parallel = 18.75 amps per parallel cell
220 /8 = 27.5 amps
Fri Apr 16, 2021 7:29 pm

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Fri Apr 16, 2021 7:29 pm linkquote
To deal with peak power draw couldn't I just build a super capacitor and shove it under the seat or something?

And couldn't I bypass the BMS for discharge and only use it for charging and regen?

I'd just have to build a safety cutoff to stop discharge below a certain low voltage right?
Fri Apr 16, 2021 8:23 pm

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Location: Alexandria, VA
Fri Apr 16, 2021 8:23 pm linkquote
Christopher_55934 wrote:
JimVonBaden wrote:
What did your battery build say max current draw for the pack is?
150 amps / 8 sets in parallel = 18.75 amps per parallel cell
220 /8 = 27.5 amps
I honestly don't remember, but that is what my gauges say when pushing it hard. Cruise amps are about 40 amps at 35-40 mph.
Fri Apr 16, 2021 8:23 pm

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Location: Alexandria, VA
Fri Apr 16, 2021 8:23 pm linkquote
Christopher_55934 wrote:
JimVonBaden wrote:
What did your battery build say max current draw for the pack is?
150 amps / 8 sets in parallel = 18.75 amps per parallel cell
220 /8 = 27.5 amps
I honestly don't remember, but that is what my gauges say when pushing it hard. Cruise amps are about 40 amps at 35-40 mph.

Sat Apr 17, 2021 5:37 am

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
Sat Apr 17, 2021 5:37 am linkquote
saturn wrote:
To deal with peak power draw couldn't I just build a super capacitor and shove it under the seat or something?

And couldn't I bypass the BMS for discharge and only use it for charging and regen?

I'd just have to build a safety cutoff to stop discharge below a certain low voltage right?
I'll start this with I'm not an Electrical Engineer, I'm a Electronics Technician by trade who has been working on electronics for too many years. I only design stuff for my own small projects.

If you go the bypass route your going to lose the cell protection of a BMS, a BMS monitors overall voltage and cell to cell voltage. If one of the parallel cells goes below the cell cut off voltage you will continue to run it and possibly destroy the entire parallel cell. An example could be one of the single cells in the entire row of 20 cells goes bad. Lithium batteries are not as forgiving as lead acid when mistreated.

Yes, you could use a ultra capacitor. Those are going to take up a lot of room from my limited experience and not add anything to the range. I have a motor dyno from a hobby of mine, I use a 12 volt 1 farad capacitor for this exact purpose. That single capacitor for a 7.4 volt RC car motor, is as big, maybe bigger than a 16oz beer can. That only limits my voltage sag, it's not big enough to stop it. You would need 6 or 7 in parallel to handle 84 volts. For people doing the math, a 72 volt nominal battery can charge to 4.2 volts per cell or 84 volts peak.

I hate myself for saying this, as I'm usually all for experimenting and trying new things. In my opinion your straying from, keeping it simple into getting complicated with more parts. Every extra part adds complications and does nothing for range. Every dollar you spend on an extra part could go towards purchasing an extra parallel cell. Every extra parallel cell is a larger capacity battery which is more range. With a good battery and correct BMS you won't need the extra parts and will increase your range. Jim did a good job with his and I would try to emulate that, its a great recipe to get you pointed in the correct direction.
Sat Apr 17, 2021 8:27 am

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Sat Apr 17, 2021 8:27 am linkquote
The big issue is there isn't a lot of room inside of a smallframe.

I have to measure and figure it out.

As for room for a capacitor, I think I could build a seat that is just an upholstered box full of them...
Sat Apr 17, 2021 12:44 pm

Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
 
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1879
Location: Rochester, Minnesota
Sat Apr 17, 2021 12:44 pm linkquote
saturn wrote:
The big issue is there isn't a lot of room inside of a smallframe.

I have to measure and figure it out.

As for room for a capacitor, I think I could build a seat that is just an upholstered box full of them...
Personally if I had space for capacitors I would make a cell of 20 batteries instead. Nothing says all the cells have to be in one place. With the cells being in parallel you can run a larger set of main wires to a single junction point. The BMS wires are the same thing, the smaller wires are for balancing when charging. They don't carry much current. You just have to wire them in order so the BMS can read the cells correctly. You could have three separate areas for battery storage and the BMS will see them as one battery as long as you wire them correctly. Off the top of my head can't think of a reason that wouldn't work. You could have a 20S15P battery with 15 separate cells of 20 each hidden wherever you can fit them.
Sat Apr 17, 2021 10:16 pm

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Sat Apr 17, 2021 10:16 pm linkquote
I have to measure but I hope to fit as many as I can inside the gas tank / carburetor area, then the controller and inverter and other items in left cowl. My idea for a super capacitor is to help with dips and spikes.

See this:
Mon Apr 19, 2021 9:38 am

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Mon Apr 19, 2021 9:38 am linkquote
need to figure out how to mount this.

spot/passing light from a harley, but it has high and low and a "halo"

does anyone know where to buy the smallframe style headlight ring with the space for the block nuts at 9 and 3? I can't find them anywhere. I ordered one from scooterwest years ago and it had chipped chrome so they sent me another. I stupidly tossed the imperfect one. I'd love to have a rusty one to paint black!





Mon Apr 19, 2021 12:54 pm

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P125x (4KW Hub Motor)
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Hooked
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Location: Alexandria, VA
Mon Apr 19, 2021 12:54 pm linkquote
I know yours is different than mine, but I used the original bulb bracket and used epoxy to hold it in.





Mon Apr 19, 2021 1:42 pm

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AmeriBodge
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AmeriBodge
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Mon Apr 19, 2021 1:42 pm linkquote
That's a good hack! You could have used the Stella/PX parts which allow you to mount a stock motorcycle headlight (or LED version).

Mine is different - unfortunately, the smallframe/sprint/etc lights are slightly smaller. I know how to make the adapter (I'm going to 3d print a ring that snaps around the outside to make it the ~5" instead of 4.75") but the decorative ring which mounts to the handlebars to hide the headlight mounting hardware is what I can't find anywhere. (edit: found one on ebay)

here's a photo of the Stella/PX adapter ring for a regular 5-3/4" headlight:





Last edited by saturn on Mon Apr 26, 2021 6:54 am; edited 3 times in total
Thu Apr 22, 2021 10:05 pm

Addicted
Too Many piles of Junk that need too much work and too much money
Joined: 06 May 2019
Posts: 795
Location: PNW from LBC
 
Addicted
Too Many piles of Junk that need too much work and too much money
Joined: 06 May 2019
Posts: 795
Location: PNW from LBC
Thu Apr 22, 2021 10:05 pm linkquote
saturn wrote:
That's a good hack! You could have used the Stella/PX parts which allow you to mount a stock motorcycle headlight (or LED version).

Mine is different - unfortunately, the smallframe/sprint/etc lights are slightly smaller. I know how to make the adapter (I'm going to 3d print a ring that snaps around the outside to make it the ~5" instead of 4.75") but the decorative ring which mounts to the handlebars to hide the headlight mounting hardware is what I can't find anywhere.

Best I found is the entire fixture. https://www.scooterwest.com/usa-head-light-for-vespa-rally-sprint-super-small-frame-114345.html

here's a photo of the Stella/PX adapter ring for a regular 5-3/4" headlight:
I did a brief search, and didnt come up with the ring by itself. Someone has it for sure.... OR, you can post a want add for an original; # 10973 chrome ring.

If you do need to get the entire assembly, I recommend the version from Scooter Mercato; NOT the Scooterwest version.
SM headlight glass is unmarked, while SW glass has molded in 'INNOCENTI'
*Some Lambretta's of the same eara used the same type of headlight glass. It fits, but obviously a Vespa is not Innocenti. lol!

http://www.scootermercato.com/Scooter-Parts/Headlight-Assemblies/114435
Fri Apr 23, 2021 5:19 am

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AmeriBodge
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Fri Apr 23, 2021 5:19 am linkquote
I was able to find one

Since I ordered two LED fixtures (they come as a pair) I plan to put the other one in my Lambretta
Sat Apr 24, 2021 6:31 am

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Joined: 05 Sep 2019
Posts: 160
Location: Brooklyn, New York
 
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Posts: 160
Location: Brooklyn, New York
Sat Apr 24, 2021 6:31 am linkquote
Looking forward to following this project, as this is my old rusted out v90 frame. Plans are looking good Saturn!
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