Question about the C5 setting on the KT-LCD3?

[mike killay]

[QUOTE="d8veh, post: 427404,

If you're sub-80kg, most 36v geared motors should be able to give you all the power you need.[/QUOTE]

If only!
my problem is that besides weighing 108 kg, my old legs have not got power in them at all.
I don't want speed, 15 mph is more than enough but I do want more bottom end grunt, even on my mid motor.
I have looked at shunt soldering, but frankly am too nervous to try.

 

[Deleted member 4366]

my problem is that besides weighing 108 kg, my old legs have not got power in them at all.
I don't want speed, 15 mph is more than enough but I do want more bottom end grunt, even on my mid motor.
I have looked at shunt soldering, but frankly am too nervous to try.

201 rpm 48v Q128H with a 20A controller should sort you out.

 

[Blunderbuss]

Any opinions on this motor would be welcome, from the description it will work a treat with my 48v battery - is there any way to determine what the torque is compared to a 1000w DD?

https://ampedebikes.myshopify.com/collections/motors/products/built-wheel-bafang-8fun-cst-geared-500w-electric-rear-hub-motor-cassette-disc-brake-fit?variant=34186122438

 

[anotherkiwi]

Good choice. It will have more grunt than you DD motor with controller at 22 Amps.

 

[Blunderbuss]

I still can't get my head around some of this!

If a motor sold as 500w can be run happily at 1000w, does it produce the same power as the 1000w rated motor being run at 1000w (all other things being equal)? And if so does it consume the same amount of power to achieve that same output?

I can see that with a direct physical comparison the 1000w is bigger that the 500w, so maybe a bit heavier, but why bother with 1000w if you get the same power from a 500w - I am now going for a lie down

 

[Deleted member 4366]

I still can't get my head around some of this!

If a motor sold as 500w can be run happily at 1000w, does it produce the same power as the 1000w rated motor being run at 1000w (all other things being equal)? And if so does it consume the same amount of power to achieve that same output?

I can see that with a direct physical comparison the 1000w is bigger that the 500w, so maybe a bit heavier, but why bother with 1000w if you get the same power from a 500w - I am now going for a lie down

I keep telling you that you can completely disregard power ratings. they have no bearing on how much power you get. The power comes from the battery and is regulated by the controller. The only thing you need to worry about is whether the motor will smoke when the controller gives it maximum power.

I've used that 500w CST motor in a few bikes. One was run with 64v and 30 amps, which is roughly 2kw. I used one as my main commuter for a year that I ran at 36v and 30 amps, which was plenty of power for a bicycle. You only need higher volts if you want more speed. The one in your link is 285 rpm, which will max out at about 28mph in a 26" wheel and cruise happily round about 22 mph.

I would summarise by saying that that motor is suitable for hauling very heavy loads at medium speed, or run it at 48v and 25A for cruising at 25mph plus. If you weigh less than 80kg, it's overkill for a bicycle. The Q128C is much lighter and still gives good power in the mid-range.

 

[anotherkiwi]

One more time:

- the motor has a certain rating, this is the power output which it is guaranteed to deliver by the manufacturer for a specified period of time without getting hot and melting
- a 250 W road legal motor must run for 2 hours without getting 2° K warmer at that output - it requires 7 A current from a 36 v battery to make 250 W
- in fact it requires a little more than that to compensate for mechanical and electrical losses so the controller you get is a 15 A one which can give 630 W when the battery is fully charged to 42v.
- a 250 W road legal rear hub motor* can often take much more (see d8veh's post above), let's just say that usually the nylon gears will get soft and be stripped before anything else bad happens to the motor (the insulation melts at about 130°C the gears go before then) but you can, if you are careful, run a road legal 250 W rear hub motor at up to 1kW

Your DD 1000 W motor can produce up to that limit before over heating
A 500 W geared hub motor is guaranteed to produce 500 W but is usually good for well over 1 kW
A 250 W road legal motor can produce 750 W without much risk of failing

*I mention rear hub motors because they are generally larger than front hub motors and have more copper in them.

 

[Deleted member 4366]

One more time:

- the motor has a certain rating, this is the power output which it is guaranteed to deliver by the manufacturer for a specified period of time without getting hot and melting
- a 250 W road legal motor must run for 2 hours without getting 2° K warmer at that output - it requires 7 A current from a 36 v battery to make 250 W

It's nowhere near as simple as that - unfortunately.

Before they can do a power rating test, they have to find the rpm of optimum efficiency and the rating test has to be done at that RPM.

You can burn any hub-motor by running it below optimal RPM, which is the main danger with the big 1000W DD motors, especially when they're two fast for the power supplied by the battery.

The most important criterion when selecting a motor is to find one that will spin at maximum efficiency at your modal or desired cycling speed. When running at that speed, it needs to be provided with enough power to maintain that speed. In the case of a crank-drive, its most efficient RPM should match your modal cadence.