SWX02 36V vs 48V

[Waspy]

So what would be the advantages/disadvantages of a SWX02 48V based kit over a SWX02 36V kit please?

Rear hub kit.

This would be on a 700c hybrid, 85 kilo rider (with backpack for work) 15 mile commute (one way), some small hills.

Thanks in advance.

 

[Nealh]

Generally the main parameters increase by 33%, so speed, power/acceleration/torque. Also to match the same watts output as a 36v system one can use a controller with less current. 48v therefore is better for a heavier rider.
Battery capacity ah can be less for the same wh capacity as a 36v battery, for instance 8ah/48v = 384wh a similar 36v battery would be 10.6ah. So a 48v battery will be a bit lighter, theoretically depending on cells used one could get away with 13s 2p, easily enough for a 15mile one way commute.



On one of my bikes I have replaced the heavy 36v/14.5ah (522WH) battery with a 12 2p 44v/6ah ( 264wh) battery, it manages 25-30 miles in low PAS. Cells used are genuine LG hg2 3000mah/20a cells.

 

[vfr400]

So what would be the advantages/disadvantages of a SWX02 48V based kit over a SWX02 36V kit please?

Rear hub kit.

This would be on a 700c hybrid, 85 kilo rider (with backpack for work) 15 mile commute (one way), some small hills.

Thanks in advance.

There are no disadvantages of running at 48v, only advantages, so if there's a choice, only a fool would choose 36v, unless you were using the lower voltage to get the correct speed.

The only imprtant things are that you choose a motor that can handle the power you need for the speed and conditions that you want to travel, and you choose a motor that has a maximum speed of about 1.3 times your desired modal speed. Bear in mind that the same motor will run 30% faster with 48v compared with 36v, which can be a disadvantage if it doesn't march the conditions just stated.

As very general rules, the small motors can handle upt to 18 amps at 36v and 15A at 48v, the middle-sized ones can go 30% higher and the large ones (original Bafang BPM and CST size) another 20% as long as the max speed isn't too high.

 

[Waspy]

Generally the main parameters increase by 33%, so speed, power/acceleration/torque. Also to match the same watts output as a 36v system one can use a controller with less current. 48v therefore is better for a heavier rider.
Battery capacity ah can be less for the same wh capacity as a 36v battery, for instance 8ah/48v = 384wh a similar 36v battery would be 10.6ah. So a 48v battery will be a bit lighter, theoretically depending on cells used one could get away with 13s 2p, easily enough for a 15mile one way commute.



On one of my bikes I have replaced the heavy 36v/14.5ah (522WH) battery with a 12 2p 44v/6ah ( 264wh) battery, it manages 25-30 miles in low PAS. Cells used are genuine LG hg2 3000mah/20a cells.

Thank you Nealh. Interesting, the main thing I'm getting from your reply is 33% more everything plus smaller battery. Very good, but I would hesitate at 6ah LOL. When I say one way commute, I do have to get home again, hoping I could blag a free battery charge at work, also low PAS all the way sounds like un-fun. This commute would only be on dry, warm-ish days.

I don't really understand all the battery chemistry and what cells are in the actual battery pack does not seem to be an option. I'm assuming you make your own battery packs? That would be a steep learning curve for me.

Thanks for answering.

 

[Waspy]

There are no disadvantages of running at 48v, only advantages, so if there's a choice, only a fool would choose 36v, unless you were using the lower voltage to get the correct speed.

The only imprtant things are that you choose a motor that can handle the power you need for the speed and conditions that you want to travel, and you choose a motor that has a maximum speed of about 1.3 times your desired modal speed. Bear in mind that the same motor will run 30% faster with 48v compared with 36v, which can be a disadvantage if it doesn't march the conditions just stated.

As very general rules, the small motors can handle upt to 18 amps at 36v and 15A at 48v, the middle-sized ones can go 30% higher and the large ones (original Bafang BPM and CST size) another 20% as long as the max speed isn't too high.

Thank you vfr400. Your first sentence says it all really. So 48v it is then!

Not sure I understand everything you've said.

I'm thinking of a SWX02 48V motor and staying within the law at 15mph.

I guess the advantage of 48v is not so much top speed but power to get up hills?

But like I said above, 48v it is.

Thanks for answering.

 

[vfr400]

Thank you vfr400. Your first sentence says it all really. So 48v it is then!

Not sure I understand everything you've said.

I'm thinking of a SWX02 48V motor and staying within the law at 15mph.

I guess the advantage of 48v is not so much top speed but power to get up hills?

But like I said above, 48v it is.

Thanks for answering.

Each motor has it's own inherent top speed, which is designed into it. You can't make a motor go faster by giving it more power. The motor's actual speed depends on the volts applied to it, so the same motor will go 30% faster with 48v than with 36v, which is not necessarily a good thing becaiuse it affects efficiency, and efficiency affects heat. You can get 36v and 48v versions of the same motor, which are designed to go the same speed as each other, so they're different inside. The two motors might have the same speed, but at 48v you'll get 30% more torque than at 36v.

The particular design characteristic that decides the motor speed is the Kv, which you need to know before you buy any ebike motor, though sellers never list it. Instead, they might say something like max speed 20 mph at 36v. 20 mph is 260 rpm for a 26" wheel. Translating that: 36v gives a max speed of 260 rpm, therefore the Kv is 260/36v rpm per volt = 7.22rpm/v

Remember I said you need a motor speed of 1.3 times your modal riding speed, so if you want to ride at 15mph with a 36v battery, you need a motor with a Kv of 7.22 and at 48v, you need a motor with a Kv of 260/48 = 5.42. If you want to ride at 20 mph at 36v, you need a Kv of about 9, at at 48v, a Kv of about 7.

 

[Waspy]

vfr400, I really, really appreciate your comprehensive answer, but I have to admit it's all a bit out of my depth.

"The particular design characteristic that decides the motor speed is the Kv, which you need to know before you buy any ebike motor, though sellers never list it. "

So this information is pretty redundant? I mean, if they don't tell you the kv.

Mate, I just want to know if I should buy the 36v or 48v version of the SWX02 from Woosh (I've also been looking at Greenergy)

I'm a simple man, if someone with your knowledge recommends 48v, that will do for me.

Thanks again

 

[vfr400]

So this information is pretty redundant? I mean, if they don't tell you the kv.

I showed you how to figure it out when they don't tell you.

You can ask Woosh about the max speed of their motors. you need to compare that with your desired modal riding speed. As I said, ideal is 1.3 times your desired modal speed.

 

[Waspy]

I showed you how to figure it out when they don't tell you.

You can ask Woosh about the max speed of their motors. you need to compare that with your desired modal riding speed. As I said, ideal is 1.3 times your desired modal speed.

Yes you did, I apologise.

I guess my modal speed (on an open road) is going to be 15.5mph. That is if I understand 'modal speed' correctly.

Thank you for your help.

 

[vfr400]

For 15 mph modal speed, you need around 260 rpm for big wheels, 330 rpm for 20" and 400 rpm for 16".

 

[Waspy]

So, after all that I managed to miss the part where it says SWX02 (36 and 48V) are for freewheels.

So looks like I'll go for the 85SX or the XF08C or the DWG22C-48V which all take cassettes.