500w vs 1000w hub motor for city driving?

[CUDAcores89]

I am a teenager and I Recently got a job at mcdonalds, but I only live a couple of miles away, so I decided instead of burning gas up every day in a car I decided I am going to embark on building an ebike. I have just purchased the bike. It is a cheap Giant brand Bike I bought at a garage sale for $50 and it has almost everything I am looking for. It has all steel construction, has standard 26" wheels and is 21-speed. Now the only question is what hub motor should I buy. Should I get a 500w or 1000w hub motor? The riding I will be doing is mostly flat. If I do encounter a hill I can pedal (duh, it's a bike) and most of the hills on the way to work will be only a few degrees uphill anyway. FYI, I weigh 140lbs and my battery weighs 20lbs. So what wattage hub motor should I get, 500W or 1000w?

EDIT: The reason I am leaning towards a 500w motor is because I can get away with a 10lb battery instead of a 20lb battery. A 500w motor may not be as powerful but it will allow my to use a much lighter battery.

 

[wesnewell]

I wouldn't even get a motor for just 2 miles flat. That said, you can get a 1000W kit for about the same price as a 500W kit. More power, more top speed for those times you may need/want it. Why is your battery pack so heavy?

 

[CUDAcores89]

It's because the battery is built from lithium cells from dead laptop batteries. And no I wasn't an idiot and just took apart a bunch of laptop batteries and threw it together. I went to a scrapyard and picked up 30lbs of laptop batteries for 50 dollars. Over the next several weeks I spent the time tearing apart each laptop battery, charging, discharging and internal resistance testing every single individual cell. The problem with doing this is the lithium cobalt chemistry found in laptops cannot discharge over 1C. Therefore I had to build a battery pack that was at least 1000w, (I assumed at the time I would be buying a 1000w hub motor). The battery is 1.45KWh and I had to overbuild the battery like that to prevent it from discharging over 1C under load. I have already load tested the battery at 1200w using some power resistors so I know it is capable of driving a 1000w hub motor. Sincwe old laptop cells tend to drift out of balance more easily, I purchased a turnigy accucel 8150 to balance charge the cells so I am not using a BMS on the battery. Although I am protecting the battery from over-discharge in the form of cell loggers that sound an alarm when the battery get's too low, and I have the battery fused for protection from over-current. This video is also one of the reasons I chose not to use a BMS:

https://www.youtube.com/watch?v=pljSZcEwc8Q

I should've mentioned this earler but my budget for the entire ebike is $300. Using used parts I believe I can get it just barely within that budget. Total costs so far:

Bike: $55
Battery: $50
turnigy charger: $55
Hacked computer power supply to charge the battery: $0
wires and balance cables: $10
Cell loggers: $5
Fuses: $3

 

[wesnewell]

The only problem is your thinking that a 1000W motor only draws 1000W from the battery. When it really doesn't draw anything from the battery. The controller does all that and most 500W and 1000W kits both draw the same amount from the battery pack. The ones I see most range from 26-30A max draw. And the max amp draw of the controller is what you need to match your battery pack to, not the motor. Motor size doesn't matter one bit for brushless systems. Look at it this way. 30A drawn from a 50V battery is 1500W. From a 100V battery it's 3000W. Same amperage, but see what I mean. VA=W. So if you want to limit the battery pack to 1C, that means you can't draw more than 20A from a 20ah battery. This also means the motor size you buy doesn't matter one bit as far as the battery is concerned. Only the controller max amps matters. Still, if you built a decent pack, it will probably work fine with a 30A controller as long as you don't get heavy handed on the throttle from a stop or steep hill.

 

[dogman dan]

Well obviously with that budget you are looking at the cheaper kits on amazon, or ebay.

The main thing is what is your battery voltage? The 1000w kits run on 48v batteries. The 750w kits run on 36v batteries. buy whichever one matches your voltage.

Any of them will get you a couple miles to work, quick enough to not freeze in winter, or sweat a lot in summer and arrive stinky.

Given the cells you have,, not great stuff, I'd say make the battery as big as you can comfortably carry on the bike,, about 15 pounds is the max for rear racks.

And lastly,, you can always limit your watts, by not using full throttle,, but I never could do that for long myself. I might cruise slow, but from the stop, I want it all.

 

[kdog]

Firstly, bloody good on ya! Good to see some young ones getting into it- and building your own battery. I'd say a good 500w motor would be heaps. My 9C (8x8 winding) will handle >1500w continuous which will drive me at >50kph no problem ( I'm on 84v). I have done some cooling mods but stock it'll probly handle 1000w cont. Given you don't want to hammer your cells too much a 500w motor with a 30amp controller will have you charging.
Remember most of the time you won't be drawing your max only at start up/low speed. At speed BEMF usually keeps amp draw down. A bit of restraint on the throttle will help as DD said.
Just be careful letting your less than co-ordinated mates on it( we've all got them!) or put a three speed switch on it and stick it on low for them :? You don't want all your hard work pranged into the closest tree/wall.

 

[MadRhino]

Congrads on recycling and making your own battery. A 500W motor will do, it can pull a lot more on a start. It is not important anyway, for most kits 500w or 1000w do have the same motor. The controller makes the difference and I suggest that you buy a programmable controller. I have do doubt that you will soon find out the optimal parameters to match your battery and, when you mod or build another one, you can adjust your controller to take the best advantage of a different battery voltage and/or capacity.

Forget about the 21 spd, you will need a freewheel and don't buy it before the motor is fitted on the bike, unless you have the exact dimensions, including torque arm(s). With a motor you will not need many speeds to shift anyway, and the extra space gained from a shorter freewheel is usefull to make a better stronger fit in the bike's dropouts.

 

[wesnewell]

A 500W motor will do, it can pull a lot more on a start. It is not important anyway, for most kits 500w or 1000w do have the same motor.

I wish people would stop saying this. It's simply not true. It's a crime to sell a 500W motor as a 1000W motor in every country I know of. It's called fraud. And I can assure you, it's not the case where I bought both kits. The motors may look identical, but they are far from the same.

 

[amberwolf]

It's a crime to sell a 500W motor as a 1000W motor in every country I know of. It's called fraud.

Doesnt' stop all the Ultrafire cell vendors from what must be pretty successful businesses. So I dont' think it would stop kit or motor sellers, either--just cuz some of them don't do it doesn't mean that no one lies about their motors. I seriously doubt that most of their customers could tell even if they knew they should try to check. Most people here on ES wouldn't even know to check, or how.


@CUDAcores89
That said, with "mostly flat" roads for a short trip of only a couple of miles, even with a lot of stops and starts in city traffic, you could use much less than 500w....a small 250-350w geared hubmotor would probably work just fine, using an 8-12A controller at 36v (48v if you already have it setup that way, then it uses less current for the same wattage).


You can probably find something at the right price in the ES used for sale section, if you poke around, or are patient if it isnt' there at the moment.


That's pretty much the kind of setup I started out with on DayGlo Avenger when I put the first hubmotor on there (a little Fusin unit from Dogman). It did waht I wanted at the time, and even more eventually (until I setup bigger controllers on it and eventually overdrove it hard enough to break it's clutch abusing it beyond it's limits).

Nowadays, I use much more powerful stuff, but I"m doing a lot more with it, and for what you're wanting to do you don't need that. (yet, anyway).

 

[wesnewell]

The actual cost between actual 500W and 1000W rated motors is maybe a couple of bucks, if that. It just makes no sense to commit fraud for that amount. I doubt if there or any large volume dealers in the US that do it. Although I know several dealers that fudge on the specs by calling them peak watts for the motors.

 

[Cephalotus]

Ride your bike without motor!!! You need to learn where the old bike needs maintenance and replacement parts. This is 100x times easier to realize when you ride on your own power.

Big hub motors are not without disadvantages:

- You will have a heavy ebike that is no fun to ride without motor.
- the heavy load may kill your battery quickly
- high torque may kill your dropouts
- you need a larger more heavyweight controller
- you may need to compromise on your gears, could make the bike unrideable without motor.

At your low weight and just some moinor hills imho a geared hub motor is big enough.

A typical 36V or 48V 14A controller will give you more power than you need. Imho!

This is my commuter bike. Also bought used for little money. Weights 15kg incl. battery. Tiny 36V Cute 85 motor, controller even limieted to 11A at 36V. This is plenty of power for my needs.Very easy to ride on little or no motor power.

Battery is a 10s3p Sanyo UR18650E from early 2011. Still around 90% of original capacity after ca. 400 charging cycles (not full cycles) and 5,5 years. No balancer. Every cell is in balance within 0,01V at 4,2V/cell end and at 0,05V at 2,7V/cell after 5,5 years!

Keep it simple.

 

[emco5]

...... I only live a couple of miles away.... A 500w motor may not be as powerful but it will allow my to use a much lighter battery.

Consider the Clean Republic 350 watt 36 volt system. It doesn't weigh a lot and has plenty of assist muscle for hills, and pedaling would be optional on other roadways. Keep it simple. http://tinyurl.com/7ccg5cz

If you must have 500 watts, checkout the Leed package http://tinyurl.com/z67waq8

 

[dogman dan]

Well, a 350w rated motor will be plenty for his short ride and light weight. But the kits actual peak wattage can be much higher, even as high as 1000w. If it has a 20 amps controller, then the kit will put out about 750w with 36v, 1000w with 48v, if the controller can stand 48v. The smaller geared motors used in those "350 w" kits can handle 750w pretty easy, but pushing them to 1000w is not a great idea if the ride is long and the load heavy. ( yours is short and light though).

In your price range, you may find some of the lower wattage, smaller motor kits.

Again,, the only thing that really matters is your battery voltage,, if you have a 48v battery now,, you should look at the 48v kits, which usually will be the 1000w direct drive kits, in your price range.