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When is a Watt, not a Watt... and Other Stupid Questions.

JimD

1 µW
Joined
Apr 15, 2024
Messages
4
Location
Kansas City Mo
Hi all,
new member here. How many times have y'all seen a thread start with those words... ;) About me first, the condensed version. I'm a retired aircraft mechanic. Also spent time as an avionics tech. Retired air Force, retired teacher. I've also dabbled in cars and motorcycles my whole life and have spent the first 10 yrs of retirement restoring old motorcycles. So yeah, fully versed in wrenches and VOM's, not much of a clue about 'lectric scooters though. Moving right along....

I have a Razor Ecosmart that I picked up a few yrs ago. Bone stock. First dumb question:

Are a 700 watt hub motor and a 700 watt shaft and sprocket motor (I'm sure there's a better name for 'em) as strong as each other? I know that roughly 750 watts equals one horsepower and, technically they should be equal as far as power output... but I've heard and read that the hub motors are typically "over" rated. In other words, a 700w hub is about as strong as a 500w shaft motor. Any truth to that?

Cheers,
Jim.

Edit: I looked around this forum and didn't really see where this was asked before. At least not in it's own thread. Apologies if I'm floggin' a dead horse here.


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In a perfect world where everyone agreed to you know, use truth.. It would be equal.

However the reality is....

Every frigging one of the companies is lying one way or the other, in the EU with most locales requiring a max power limit, they are all lying to be under that max. (which doesn't exactly work, electric motors respond to how much juice ya give them, up to the point where they overheat, or find the weak spot)

If you have an offset motor like you show on that scooter, while the volt/amp level may be the same as a hub motor, being further mechanically seperated it will have a bit of inevitable work loss due to Murphy being a total ::ducks:: Ok, don't joke about physics when your bestie is in the house (he has a degree in that field and is very ::ducks again:: Happy about it..)

Generally the output of hub motors is less mechanically challenged, but then you have the fact that your motor is attached to a wheel, and yhou can't do anything about issues with maximum tork. If the resistance is too high, the motor will do a lot of things that act and sound unhappy, or just flat out refuse to motor at all.

I mean not that my 6'4 280 pound retired Ranger Arse has ever challenged a motor to a dual and kicked it in the ding ding or anything..

Long and shor is that you are looking at apples to apples comparisons, but some of these apples are Fuji which are technically pears, others are them lil sour bastards, and occasionally you get one of big beautiful red ones that tastes like chalk and sadness...

I hope that cleared up your questions for ya!
 
Most Razor scooters have a knock-off version of Currie-Tech motors. Currie-Tech motors are powerful little motors that utilizes rare earth magnets. My wife's Schwinn S750 is running at 48v 35a 1600w +25mph. 0-25mph in 4-5 seconds

SChwinn stealth pink.jpg


Check the bolt patterns to ensure it fits.
750w motor

900w motor

1000w motor
 
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Thanks guys for the replies. I get that chain and sprocket comes with it own set of power eater issues and all that. So I guess when it comes down to manufacturer claims... it's a crap shoot. I guess I already sorta knew that... jus' was hopin' for... well, not sure what I was hopin' for. Thanks... I think. ;)

The batteries in this thing are 6ah. First step is some 10 or 12ah... and get 4 of 'em. Bumped to 48v, I'll look for a suitable controller. That'll bring me back to the motor. Would like to get an 800 to 1000w motor... still scratchin' my head on which one. So, after a bit more research I'll throw some names out here and get some thoughts.

Stand by for the next stupid question. :mrgreen:

Cheers.
 
Are a 700 watt hub motor and a 700 watt shaft and sprocket motor (I'm sure there's a better name for 'em) as strong as each other? I know that roughly 750 watts equals one horsepower and, technically they should be equal as far as power output... but I've heard and read that the hub motors are typically "over" rated. In other words, a 700w hub is about as strong as a 500w shaft motor. Any truth to that?
Power doesn't really mean anything as far as motor performance in a specific application for being able to compare two dissimilar motors applying power in different ways. See the simulators at ebikes.ca to learn how motors, controllers, batteries, and drivetrains and riding conditions all interact and affect each other.

Power ratings for motors don't really mean much either, because there are no applied testing standards by those that give the ratings (the sellers, sometimes the manufacturers, etc). See the Futility of motor power ratings article by Justin_LE on ebikes.ca and other discussions about that here on ES.


Below are a couple of snippets with questions to point you at things to find out, so that you get what you really need, and don't spend either money on stuff you don't need, or money on stuff that won't do the job you need it to do, and have to buy parts over again.

The ebikes.ca simulators can help you guesstimate the answers to them.

Would like to get an 800 to 1000w motor.
How much power do you actually need to achieve your specific goals, under the riding conditions you have, including being able to accelerate as quickly as you need to?

The batteries in this thing are 6ah. First step is some 10 or 12ah... and get 4 of 'em. Bumped to 48v,
How much range do you need, under the riding conditions you have, and the power usage you'll have under those conditions?

That, and the average power usage, will help you guesstimate the capacity in Wh required.
 
How much power do you actually need to achieve your specific goals, under the riding conditions you have, including being able to accelerate as quickly as you need to?

How much range do you need, under the riding conditions you have, and the power usage you'll have under those conditions?

That, and the average power usage, will help you guesstimate the capacity in Wh required.
Yeah, I'm coming at this sorta backwards... normally I (we) would set the conditions or goals and figure out what we'd need to get there. In this case, I'm just tinkerin' Don't really have any set goals other than speed. Not worried about range, recharge times or carrying heavy loads... not even really "speed" as a goal, just want to find out how much I can improve the top end without breaking the bank or slowing to a crawl uphill. You know... tinkerin'.
 
How much power do you actually need to achieve your specific goals, under the riding conditions you have, including being able to accelerate as quickly as you need to?

Hey AW, my understanding is power delivery permits a speed - that is, if the motor doesn't dole out the power needed to match a given friction+air resistance+geometric gravity input I won't maintain that speed.

But torque permits an acceleration. Or not.
 
Yes, and power is torque x speed, so if you ensure you have sufficient torque for the speed you want, you have sufficient power.

The problem is, power (watts) depends on where you measure it. There is mechanical watts at the ground from the wheel, and electrical wats into the motor, and electrical watts into the controller out of the battery, and they are all different because none of them is 100% efficient, so there's less and less of it as you get closer to the ground, and more of it wasted as heat in the system.

So, yes, a certain amount of power will give you a certain speed under those conditions, which is why I asked the question you quoted. ;)

But really, it's a guesstimate, as conditions vary, system efficiencies vary, etc., so having more than you need is probably safer, but no point in paying for way more than you need if you know you'll never use it (like getting a 1kw system instead of a 500w system), unless you're like me and just prefer huge margins.
 
Power is the ability/rate of doing work. Regardless of power rating, if the motor is not able to spin due to being over loaded,, it's not making any power and therefore not able to do any work. Torque is the twisting/turning force trying to make the motor spin. Not enough torque to over come the motor loading, then your motor become a glorified heater. Given enough time, out comes all your. magic smoke
 
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