1974 Vespa 125 Primavera conversion, 5kw hub motor

Voltspa

100 mW
Joined
May 2, 2021
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40
I have started to convert my 1974 Vespa Primavera to electric! The plan is to use a 5kw hub motor with hydraulic disc brake from QS motors, and a Kelly controller. I plan to make a 20s12p battery from 18650 cells (which is why I am on this forum specifically, thanks for your help!)

This is not going to be a pretty restoration. I like the aesthetics of well-used old vehicles, so I'll do no more than is necessary to make a clean installation of all the new components, and of course for safety.

I've had this since 1990 or so (I am old) and haven't ridden it since probably 2001. It's time to get it back on the road. This might go in fits and starts as I have the time or money. I have the battery materials already but haven't ordered the motor or controller and other components yet. Also have only made a cardboard mockup of the swingarm, necessary since the original motor and gearbox was itself the "swingarm".
 

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I'm seemingly in almost the exact same place you are, with a Stella 2t scooter. Batteries on hand, waiting for the next bit of money... Looking forward to your progress! Better patina on your scoot, though... that's beautiful. I might actually be forcing mine into more rust. Electro-rat rod?

following!
 
Thanks MrWorks and SlowCo!

Yeah the patina in that photo is very superficial and just wiped off with a rag, but agree, I like that photo. Otherwise the scooter does have a lot of chips and scuffs in the bad strip and paint job that I did on it in maybe 1998 or so. I regret doing that. It was orange originally, not pristine when I got it, but in pretty good shape.
 
My plan for the battery is for it to be a fake spare tire, so it has to fit into a circle shape. So far I have hot-glued the parallel groups of cells together and am wrapping them in kapton tape to further isolate them. I may keep the groups unglued and figure out another way to secure them together, in case of a cell failure and the need to take the pack apart, but then again it may be safer to just glue them all up. It will all be put into a pan that is mounted like a spare tire behind the leg shield and covered with a spare tire cover. Super-stealth!
 

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Cool. Where does the spare tyre go? Is it out back or under the side cover? How much is seen if it? Seems you could fit much more cells in if simply fitting them behind the panel in a bigger arrangement.

cheers
Tyler

 
I dig it!
Since the shroud that covered the engine will no longer have that task, is that where you're locating it?
 
The battery will be in a pan mounted like this spare tire, but with a vinyl spare tire cover on it. I'll run the cables through the center cavity to the controller under the seat probably. I'll need to drill a hole/holes for this. Hopefully I can keep the cables somewhat concealed...
 

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Ooh not to bad mouth your idea, it would make a great second battery location for extra range. But it is high and will be unbalanced. You are much better for space and handling and safety to put the battery under the side cover of the engine. Do you know what I mean? This will work but I suggest it is not the best solution. And that looks like a small battery capacity also.

cheers
Tyler

 
Thanks for the feedback Tyler. It's actually not much higher than the under-seat placement that is typical of Vespa conversions. And this model is a small frame, which means that the side covers don't come entirely off like they do on the larger frames, so it is tricky getting anything in there. Mine is also a model that had a 6v battery, which means it has an additional divider on the left side under the door. Initially I thought that would be useful as a mounting surface for some components, but unfortunately I discovered it will need to be partially cut to make room for the axle and motion of the wheel.

I tried at first to fit as many cells as possible where the gas tank was. That means a triangle shape and it maxed out at about 180 cells, and the space will not fit 21700 cells, it is that small. So what I ended up getting will give me 30Ah and 240A if I need it. Not a long range but fast and a decent top speed of around 55-60mph is what I'm expecting.

But I have thought of having two batteries, so maybe I will do my best to leave as much space as possible under the seat and be able to fit a smaller one under there. That's above my skill level right now, understanding how that would work, but I'm here to learn!

Eddy did a small frame conversion, but one without the 6v battery panel and no door on that side. He was an early inspiration of mine. https://endless-sphere.com/forums/viewtopic.php?t=89582
 
Oh that makes a lot of sense. I hadn't realised the scale of your battery diagram was 21700 cells either, 30Ah is a decent pack for bombing round town a few miles at a time.

I'm looking forward to seeing it progress. If you've got some more photos of the frame etc that'd be great, and the motor and swingarm setup you are planning.
Thanks

cheers
Tyler

 
Pause for life events, work, etc.....

I have ordered the motor and controller from Robert at QS, now waiting on that.

I decided to make my own swingarm because I'm like that. I got some 1"x2" stainless tube and will learn how to stick weld (or get someone to help me), following JVB's design.

To finish building the battery I need to choose a BMS. I am using cells that have a 20A continuous output, in a 20s12p configuration. By my understanding that will allow for a 240A continuous draw, yes? Is it best to get a 250A BMS, then, or should I go for a 300A, expecting that I will have much higher peak moments during acceleration? They start getting really large at that size, and of course I need to keep things as small as possible, but I don't want to end up with a BMS that is undersized for my battery and causing problems.

BMS: 250A or 300A???

Thanks!
 
If you are planning to use the 240A continuous rating at 20s pushing 17kW(!) into the hub motor until it melts you should get the 300A BMS.
If you like to stay on the safe side the 250A BMS will be sufficient :wink:
 
I don't have anything against overbuilding, its a very good way to keep things safe. But 250A is still far more power than you need. So if space allows, then by all means go 250, but your 5kw motor even peaking to 10kw, will only draw a max of 135 amps.

Do with this information what you will. The end decision is of course up to you.
 
craciunptr said:
Cool Build!!

Why did you choose a kelly controller?

Most of the other vespa conversions have used the Kelly and some have posted detailed programing notes so it seemed the way to go.

Millhouse_5 said:
I don't have anything against overbuilding, its a very good way to keep things safe. But 250A is still far more power than you need. So if space allows, then by all means go 250, but your 5kw motor even peaking to 10kw, will only draw a max of 135 amps.

Do with this information what you will. The end decision is of course up to you.

The battery specs are not going to change (bought and paid for), the BMS is the question. With this 5kw motor and 240A continuous at hand from the battery, what size BMS is wise to go with?
 
Voltspa said:
With this 5kw motor and 240A continuous at hand from the battery, what size BMS is wise to go with?

With 240A continous you are going to need one of the biggest BMS available...
In the course of my serach for a replacement to the shitty BMS built in by the manufacturer of my battery,
I have learnt that there are not many which can handle such currents.
 
Whelps! I looked up the specs of the 5kw motor I'm getting and it specifies max amps as 150A. So I plan to limit this with the controller and get a 200A BMS for now. IF at some point in the future I have another project with a larger motor I can use this battery with a larger bms and build a battery with lower amps (and more Ah) for this scoot.

I went with these cells because they were a trusted source and fairly inexpensive, but lower continuous amps and higher Ah would have been better....live and learn.
 
Voltspa said:
Whelps! I looked up the specs of the 5kw motor I'm getting and it specifies max amps as 150A.

Which exact version of motor do you have? If it's a QS205 50H it can take up to 250A continuous battery amps without cooling mods depending on circumstances (outside temps, etc.). See this thread for more info: https://endless-sphere.com/forums/viewtopic.php?f=2&t=109130

I would get a 250A BMS and set up the controller for 200A continuous and 250A peak amps. Your Vespa will be seriously quick then without maxing out anything.
 
Probably yes.
Not much experience yet where the limit of that motor is. What are your top speed and acceleration goals? An what size wheel/rim/tire is it?
 
The motor is a 10" rim, tire about 16". I'm sure the acceleration will more than impress me, and I was hoping to go for a mile or two at a time at 55mph, with top speed of 65 or so. I work 11 miles from home with minimal hills but a couple fast stretches. I plan to onboard the charger so I can charge at work.


I think the motor I chose tops out at 1368 rpm.
 
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