Hello!
After weeks of scouring this amazing website soaking up as much information as possible, I have decided the take the plunge with my first post.
I am currently designing a lightweight electric motorcycle/moped for use in the UK. The aim is for it to be a commuter vehicle for use in cities, retro-styled, with a removable battery. As such the minimum performance stats are as follows:
Max speed: 40 mph
Range: 50 miles
Battery maximum weight: 10 kg
Target vehicle weight (including battery): 50 kg
It can&#;t be slower than that, can&#;t have a lower range, and the battery can&#;t be any heavier than that. If the vehicle ended up being heavier than 50 kg, so be it, but I would rather sacrifice any performance stats above those already listed in order to achieve a low weight. In designing it I am taking inspiration from:
Meijs Motorman - https://www.google.com/search?q=meijs+moto&rlz=1C1CHBF_en-GBGB779GB779&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiBlsftzL7iAhWyXRUIHajhAWMQ_AUIDygC&biw=&bih=969#imgrc=YZhZQI25Qmb2BM:
Munro Motor 2.0 - https://www.google.com/search?q=munro+motor+2.0&rlz=1C1CHBF_en-GBGB779GB779&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjyx4v4zL7iAhU9QxUIHdx3Cz8Q_AUIDygC&biw=&bih=969#imgrc=lpIsZF982AU8jM:
I started this project with very little design or electrical experience but a) this site is incredibly useful and b) isn&#;t that half the fun!?
However, I have reached a stage where I could use some specific help. Each of these issues could probably use its own thread, but because of how interconnected they all are I have decided to do it on one thread and hope some people have the time and inclination to read the whole thing.
Battery
As it is the truly fixed input, it makes sense to start with the battery. I am almost certainly using cells, though am looking at a range given the trade off of high capacity vs high discharge rate. By my calculations, depending on the cell and depending on the weight of the other battery components, I will be able to get 200 cells into the battery and keep it below 10 kg. This means I have 200 to split into either series or parallel, and thus prioritise voltage or current/capacity. So this is where my lack of electrical knowledge, and therefore the first question comes in&#;
Given my desired top speed of 40 mph, and the low weight of the bike, what battery voltage should I be looking at? I realise of course that controller and hub motor play a major part in this, but I can&#;t progress choosing those that much until I have decided what voltage battery I should be working from. If say I was looking at a QS V3 watt motor, 17 inch rims and a Sabvoton controller, do I need to go with 72 volts or would 52 or even 48 volts suffice? Being able to stick to 48 volts would free up plenty of cells to have in parallel, upping current and capacity, which (as far as I understand) would improve torque and range respectively.
Linked to this, do volts need go up in multiples of 12? I understand that this is a hangover from lead acid batteries, but do I need to build the battery in this way from a compatibility perspective? For example if I built a 62 volt battery, would that work with a variety of controllers or only if there was a 62 volt controller? Phrased another way, what does a controller/motor&#;s voltage mean? Is that maximum voltage, minimum voltage, or the only voltage at which that it will work?
Finally, when choosing cells, if I choose cells with high max continuous output but lower capacity, am I right in thinking I will be able to output higher current to the controller and then motor, resulting in more torque? What should be the minimum &#;maximum continuous current&#; for the battery? By my calculations, if I use LG HB6 I can get 330A max continuous current with 72 volt but only have capacity of 16.5Ah capacity (1.19kWh), whereas if I use LG MJ1 cells I can only get 90A max continuous current with 72 volt, but capacity is huge at 31.5Ah (2.27kWh). Would 90A max continuous current feel sluggish given my parameters or is that adequate?
Motor
I am currently planning for a hub motor, predominantly for weight reasons, but also to avoid having the additional moving parts or having to think about chain servicing. I could be persuaded on this, but given the relatively low performance aspirations it&#;s where I am currently heading. Within this, I am currently expecting to need a w &#; w motor. Again, I realise that the bike&#;s ability to reach this speed will heavily depend on the controller and battery, but will w suffice? If not, then will w? According to this chart (http://www.cnqsmotor.com/en/article_read/QS%20Motor%%H%20V3%20Motor%W%20Electric%20High%20Power%20Bike%20Spoke%20Hub%20Motor/259.html), a QS V3 w motor with 48V and 70A of current will do 65 kmph, which is 40 mph, but is this reliable? Can anyone in general tell me about the trade-off of motor sizes in the context of the battery discussion? Finally, can anyone recommend any good hub motor brands? I would like to avoid Chinese suppliers such as QS if at all possible, but there don&#;t seem to be that many others to choose from (especially relative to mid drive system).
Controller
As above, my unsureness stems from a lack of true understanding of the fundamentals. So to phrase the question very simply &#; given the above, and let&#;s say I went for a 48v 150A, 53 Ah battery and a QS v3 motor, what voltage/amperage controller do I need to go for to achieve my target max speed of 40mph? My understanding is the more current the controller can draw the better the torque/acceleration, if I am trying to optimise for price within a given max speed constraint, what is the minimum amperage of the controller I need to be going for, and is there a maximum? Finally (back to my voltage confusion and the earlier question, does it need to be specifically rated for 48v, or if it&#;s rated for 72v but my battery is 48v is that fine? For example, I would love to get the Mobipus , but would that only work with a 72V battery?
And I think that is it for now. So to summarise the questions for easier answering now context has been given:
1) Can a 48 volt battery make a lightweight moped go 40mph if it has the right current/controller/moped? Is this a bad idea
2) Do battery voltages need to correspond to controllers/motors, and therefor move up in fixed numbers of series (48V, 52V, 72V), or can you make up a voltage as long as it fits within a controller&#;s/motor&#;s range
3) Is there a minimum or maximum &#;max continuous current&#; for my bike&#;s performance purposes that I should be aware of when designing my battery, or can I just totally prioritise capacity?
4) Will a watt motor get me to 40 mph, and if not will a watt motor (assuming adequate battery/controller)?
5) Any hub motor brands other than QS that anyone can recommend?
6) What amperage controller do I need to go for at a minimum to achieve 40mph?
7) Do I need to think about any controller brands other than Kelly, Sabvoton, Mobipus, Adapto?
Thanks in advance for all of your help!
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