1980 Yamaha SR250 with 75-7

[dozentrio]

I'm hoping to get some comments on whether my plan for this conversion makes sense or if I'm way off-base on anything.

Goals:

• capable of sustaining ~140 kph
• ~120 km range (at average speed more like 110 kph)
• comfortable ride to enjoy some electric cruising with a passenger

Components I have or plan to get:

• 75-7 motor, secondhand from Steveo (is this a 75-7 or maybe a 75-7R? anyone know how to find out?)
• Sevcon Gen4 Size6 with harness and domino throttle
• 10t 520 chain drive sprocket
• stock 45t rear sprocket on bike
• 12.5 kwh battery using Samsung EV modules from batteryhookup. 24s Li-ion, 88.8v nominal, 3c continuous capable

What I'm not so sure about:

• what rpm will the motor run with my specced battery? 88.8v sevcon gen4? what is the kv of this motor? Does kv matter so much when talking about these motors and controllers?
• what will the efficiency of the motor be running 100+ kph?

based on Zero's specs on this page: https://www.zeromotorcycles.com/en-gb/fleet/police/specs I think I am in the right ballpark, but I'm concerned about the rpm numbers they're giving. The 4300 max continuous rpm is lower than I'm anticipating and I'm already having to change my rear sprocket because I can't find a 14t front sprocket for 520 chain. I have a 14t but it's for 530 chain, which means I should change the rear sprocket to match the wider chain. And that means a custom sprocket, because they don't make 530 sprockets for the SR250 sprocket bolt pattern.

Any input, comments, or suggestions very welcome. I know there is some experience with these motor/controller combinations but I can't find a lot of information from google searching yet.

 

[SafeDiscDancing]

10t 520 chain drive sprocket
stock 45t rear sprocket on bike

....because I can't find a 14t front sprocket for 520 chain.

Not clear if you want 10t or 14t.

I will say that at 10t you are going to need a roller very near the sprocket (underneath... after power pull) to be certain you get a full contact.

14t would be better.

Then get a custom made 85 tooth rear sprocket.

Most people want to gear it low enough to be able to get the torque they need.

You need more teeth or you could switch to a smaller chain size like #219.

But at the power levels you are looking at the #219 might not survive.

I use a #219 but it's at under three horsepower.

 

[dozentrio]

Thanks for the suggestion about higher tooth count front sprocket. I wasn't aware that I might need a roller.

So if I do my gearing with 14t front 45t rear I should hit 167 kph at 5000 rpm. Do you think I won't have enough torque with that gearing? The motor peaks at 55 kw...

I just don't want to find myself gear limited to a top speed of 130 kph and then end up running inefficiently at that speed for long periods of time on the highway.

 

[TysonScott]

I'm hoping to get some comments on whether my plan for this conversion makes sense or if I'm way off-base on anything.

Goals:

• capable of sustaining ~140 kph
• ~120 km range (at average speed more like 110 kph)
• comfortable ride to enjoy some electric cruising with a passenger

Components I have or plan to get:

• 75-7 motor, secondhand from Steveo (is this a 75-7 or maybe a 75-7R? anyone know how to find out?)
• Sevcon Gen4 Size6 with harness and domino throttle
• 10t 520 chain drive sprocket
• stock 45t rear sprocket on bike
• 12.5 kwh battery using Samsung EV modules from batteryhookup. 24s Li-ion, 88.8v nominal, 3c continuous capable

What I'm not so sure about:

• what rpm will the motor run with my specced battery? 88.8v sevcon gen4? what is the kv of this motor? Does kv matter so much when talking about these motors and controllers?
• what will the efficiency of the motor be running 100+ kph?

based on Zero's specs on this page: https://www.zeromotorcycles.com/en-gb/fleet/police/specs I think I am in the right ballpark, but I'm concerned about the rpm numbers they're giving. The 4300 max continuous rpm is lower than I'm anticipating and I'm already having to change my rear sprocket because I can't find a 14t front sprocket for 520 chain. I have a 14t but it's for 530 chain, which means I should change the rear sprocket to match the wider chain. And that means a custom sprocket, because they don't make 530 sprockets for the SR250 sprocket bolt pattern.

Any input, comments, or suggestions very welcome. I know there is some experience with these motor/controller combinations but I can't find a lot of information from google searching yet.

20220205_180508.jpg

20220130_171646.jpg

Im using the same parts (75-7, sevcon gen4 size6 and domino throttle) what harness and contactor are you using for your build? is it a old zero harness?