Need advice on a honda c70 passport build

[cyghorb]

I have a 1981 honda c70 passport that I want to convert to electric. Guess i'll start with my need case:
-55 mph top speed
-20-30 miles range
-i live in a decently hilly area
-i weight around 90kg, bike is also around that weight before modification.

realistically i only want to go 40 mph around town, maybe into the city on some days. But im trying to overpower the build just a little bit, especially since i live in a hilly area.

the original ICE engine has a max torque of somewhere around 6 Nm, and a power output of 4.5 kW. Might do some more research on the gearing and update later. I believe the gear ratio in first gear is somewhere around 1:3.3, so maybe 20 Nm of torque in first gear?

I need some advice on the following:

MOTOR
-QS 6kw hub spoke motor; 72v, 91A continuous, 180A peak. No load RPM ~1340 RPM.
-wheels on the cub are somewhere around 24" in diameter, meaning for a 55mph top speed the motor will need to spin around 750 RPM. I read somewhere that peak motor efficiency is around 80% of the no load RPM which is ~1k RPM for this motor. Not sure if running significantly lower than this number will have significant impact on the bikes range, say if im mostly riding at 30 mph at 500 rpm.
-I will need a custom swing arm as the motor is too wide.
-200 Nm advertised max torque

CONTROLLER
-kelly mini KLS7220NV; 72V 200A peak, sinusoidal.
havent thought too hard about this yet

BATTERY
This is where i need the most help. I want to DIY a pack with lithium cells and just not sure what I will need. I know thats kind of a hard question to answer. Using this vespa build as a reference because it seems like a similar use case: Vespa PX125 (Large Frame) Electric Conversion.
100 Wh per mile * 25 miles desired = 2.5 kWh battery. At 72 volts i need 34 Ah.

cell option 1: samsung Q30 18650: 3.6v, 3Ah, 15A continuous
means 20 in series, and 6 in parallel to get 72V, 90A continuous. but only 18 Ah. Would have to double up this battery to get 36 Ah, which would be 20 * 6 * 2 = 240 cells. That seems like a lot of cells.

option 2: go with something with a higher capacity like samsung 50s 21700
5Ah, 25A continuous, 3.7V
20 in series, 6 in parallel, gives me 72v, 30Ah, 150A continuous. ~ 2.1 kWh, which is fine with me. and thats 120 cells, which is somewhere around $650 and 8 kg.


Do these numbers look normal to anyone?

I saw a book on this forum by Micah Toll i wanted to read to learn more about DIY batteries, wonder if anyone else has read it?

sorry this is all over the place. Might update later.

 

[harrisonpatm]

I have a 1981 honda c70 passport that I want to convert to electric. Guess i'll start with my need case:
-55 mph top speed
-20-30 miles range
-i live in a decently hilly area
-i weight around 90kg, bike is also around that weight before modification.

realistically i only want to go 40 mph around town, maybe into the city on some days. But im trying to overpower the build just a little bit, especially since i live in a hilly area.

the original ICE engine has a max torque of somewhere around 6 Nm, and a power output of 4.5 kW. Might do some more research on the gearing and update later. I believe the gear ratio in first gear is somewhere around 1:3.3, so maybe 20 Nm of torque in first gear?

I need some advice on the following:

MOTOR
-QS 6kw hub spoke motor; 72v, 91A continuous, 180A peak. No load RPM ~1340 RPM.
-wheels on the cub are somewhere around 24" in diameter, meaning for a 55mph top speed the motor will need to spin around 750 RPM. I read somewhere that peak motor efficiency is around 80% of the no load RPM which is ~1k RPM for this motor. Not sure if running significantly lower than this number will have significant impact on the bikes range, say if im mostly riding at 30 mph at 500 rpm.
-I will need a custom swing arm as the motor is too wide.
-200 Nm advertised max torque

CONTROLLER
-kelly mini KLS7220NV; 72V 200A peak, sinusoidal.
havent thought too hard about this yet

BATTERY
This is where i need the most help. I want to DIY a pack with lithium cells and just not sure what I will need. I know thats kind of a hard question to answer. Using this vespa build as a reference because it seems like a similar use case: Vespa PX125 (Large Frame) Electric Conversion.
100 Wh per mile * 25 miles desired = 2.5 kWh battery. At 72 volts i need 34 Ah.

cell option 1: samsung Q30 18650: 3.6v, 3Ah, 15A continuous
means 20 in series, and 6 in parallel to get 72V, 90A continuous. but only 18 Ah. Would have to double up this battery to get 36 Ah, which would be 20 * 6 * 2 = 240 cells. That seems like a lot of cells.

option 2: go with something with a higher capacity like samsung 50s 21700
5Ah, 25A continuous, 3.7V
20 in series, 6 in parallel, gives me 72v, 30Ah, 150A continuous. ~ 2.1 kWh, which is fine with me. and thats 120 cells, which is somewhere around $650 and 8 kg.


Do these numbers look normal to anyone?

I saw a book on this forum by Micah Toll i wanted to read to learn more about DIY batteries, wonder if anyone else has read it?

sorry this is all over the place. Might update later.

In general, it looks like you have a lot of your variables under consideration. And in my opinion, your use case and requirements are realistic, which can't always be said about people planning their first build. So you're already off to a good start.

If I were you, I'd go with the 18650s, 240 cells. Not only will you appreciate the longer range, but 12 cells in parallel means they'll share the load better, you'll be going easier on each cell, they'll last longer. The weight added shouldn't be too much: 11.8ish kg, not too much heavier than the 8kg you worked out for option 2.

Downside: 240 cells is a lot, and it's a lot of interconnects, points of failure. If you're not comfortable with that amount of work, then don't do it. I just finished my pack of 840 cells, and I wouldn't do it again.

 

[cyghorb]

In general, it looks like you have a lot of your variables under consideration. And in my opinion, your use case and requirements are realistic, which can't always be said about people planning their first build. So you're already off to a good start.

If I were you, I'd go with the 18650s, 240 cells. Not only will you appreciate the longer range, but 12 cells in parallel means they'll share the load better, you'll be going easier on each cell, they'll last longer. The weight added shouldn't be too much: 11.8ish kg, not too much heavier than the 8kg you worked out for option 2.

Downside: 240 cells is a lot, and it's a lot of interconnects, points of failure. If you're not comfortable with that amount of work, then don't do it. I just finished my pack of 840 cells, and I wouldn't do it again.

Thanks

Did some crude measurements just to see how I would fit in the 240 cells and looks like it might fit where I want it to. My plan was to put the battery in the space where the engine currently sits since I will be going with a hub motor.

Thinking if I go with 240 cells I would split it into two packs of 120 to make it fit.

Some screenshots:







Ill have to tinker around with it some more, might try and make it look more like the original engine, add packaging, etc. But For now I think it could possibly work well with 240 cells.