Running 1000W Controller on 350W Hub

[Braddudya]

I have been offered an old Nakto Super Cruiser fat tire 350w.

I have gotten accustomed to 750W+ bikes so 350 seems quite boring but I think I can get it for like $50 due to it's condition.

If I throw a new battery and a 1000W controller on there what is likely to happen? I know you can over drive electric motors by a good margin but I don't know if 3X is realistic or if I am just going to fry it immediately.

Thoughts?

Otherwise I guess I can just replace the hub. I figured if it's got a chance I might as well burn this one up before changing it out!

 

[calab]

1000w =
24v x 40a
or
36v x 28a
or
48v x 21a

With that 350w motor you could probably do 500w continuously under light load. With short stints up to 750w, if your throttle hand is so keen to pick all that info up. Probably not tuned in and it frys so why bother with low power setups, but for $25-50 I'd say go for it.

 

[dogman dan]

Its going to depend on the actual size of the motor. Wattage of the original set up could be a 500w rated motor running on 350w or a 250 w rated motor running on 350w controller. The tiny motor will look tiny, it won't be 7 inches in diameter, more like 5, maybe 6 inches.

If its the small motor, I've run them on 1000w, 48v, in destruction tests, and melted them. But that happened with me weighing 200 pounds, and finding a nice steep hill to ride up for a long time. Like 5 mile long hill.

What EBK decided, was to try not to sell the smallest motor to the guy over 150 pounds, to avoid motor warranty replacements. Later, he just stopped selling the tiny motors entirely.

Look at your weight, and how you will use it. If its a fat bike, and you weigh 200 pounds, and you ride it at 48v on a beach with deep sand, its going to melt. It may melt in deep sand if you weigh 150 pounds. Same goes for if you try to ride horse trails in the national forests. Too steep and grades too long.

Rather than replace the motor right away, I'd just ride it on 750w, which is well within the wattage capability of smaller motors, and replace it if it melts. So 48v 15 amps controller. or 36v 20.

 

[amberwolf]

Is it a 350w geared hubmotor?

If so, it will probably feel a lot better on startup from a stop than you expect if what you had was a 750w DD hub before. If it was a 750w geared hub before, well, this will feel like half of that, most likely, with the stock 350w controller.

However, it will take a bigger controller less well, if you are using the higher power a lot, because there are more layers to the motor to hold in heat, and you can easily kill the hall sensors or melt the gears.

Another problem is the clutches (one-way bearings, really): they don't like the higher torque of the bigger controllers, and you can physically break the clutch. I did this on a Fusin 350w geared hub using a "monster" Lyen 6FET. If it's a "softstart" controller (that ramps the throttle up slowly) it's not as big a deal, but the "instant start" ones will hammer that clutch if you don't slowly roll throttle up yourself. When it breaks you'll hear the motor running, but you don't go anywhere anymore.


If it's a 350w DD hubmotor...it'll likely feel pretty wimpy compared to either of the others. But it will take the bigger controller better, as far as heat dissipation goes. You can still damage it, so you'd need to keep an eye (hand ) out for overheating.

 

[AHicks]

The 350w motor will handle the 1000w controller fine - until it doesn't. That's what's going to happen if you feed it 1000w for more than a minute or 2 with no cool down period. Assuming the gears and clutch hold up (mechanically), from an electrical stand point, you'll be fine for crossing a busy road, climbing a short hill, or catching up with a riding buddy.

NOT OK for fighting a stiff headwind in the wrong gear (trying to go too fast) for extended periods of time, and NOT OK for climbing a way too long/tall hill.

 

[jimmyhackers]

if its direct drive, stick some oil in it for cooling....

that will up that heat limit a fair bit.

 

[Braddudya]

Thanks all for the Opinnions. I have attached pictures just for fun. It's a burning man bike haha I live in Reno.

I think I am going to replace the hub. The bike is also missing the crank set so I may just ditch all peddling and go for a high power hub motor "electric motorcycle" style build! I specifically would like to be able to ride it on my short commute to and from work but it is a big hill the whole way. So I am considering a 1500-2000W hub motor and 72v battery. Gotta figure out controller etc but I am hoping I can pull off 40mph up a hill?!? That is crucial for my commute.

 

[999zip999]

Put a 3,000 watt mxus 4t or a 1,500 leaf fat bike kit and what voltage you can afford. Do you want in the battery same place ? And hang the controller. It looks like a iron man left over. Make sure the frame is not cracked.

 

[amberwolf]

I specifically would like to be able to ride it on my short commute to and from work but it is a big hill the whole way.
<snip>
Gotta figure out controller etc but I am hoping I can pull off 40mph up a hill?!? That is crucial for my commute.

That's unlikely to happen even once with that little motor, so you'll need to replace it.

I recommend you go to http://ebikes.ca/tools/simulator.html and play with systems like what you have and/or want, and see what they will handle before meltdown, and what power levels it is going to take to do what you want to do.

Since you don't specify the actual hill attributes, I used 10% (which is pretty steep) and a stokemonkey geared hubmotor that's probably similar enough to the one you have for this basic "test", and the 72v battery and 40A controller, 27.5" tires that might be close to common fat tire diameter,
https://ebikes.ca/tools/simulator.html?motor=M4209&batt=B7223_AC&cont=C40&hp=0&wheel=27.5i&mass=110&grade=10&axis=mph
and it only gets 24mph max, pulling almost 3000w out of the battery, 1800w at the motor, at such a low efficiency that if this motor had thermal modelling available in it it's probably show meltdown in a minute or few.

Using the same setup but with a 100A battery / 250A phase controller, and the HS3548 DD hubmotor, it does make 40mph, using over 6000w battery power to make almost 4300w motor power
https://ebikes.ca/tools/simulator.html?motor=M3548_SA&batt=B7223_AC&cont=cust_100_250_0.03_V&hp=0&wheel=27.5i&mass=110&grade=10&axis=mph
before the motor melts in a couple of minutes.

Since the last one lets you reach the necessary speed, you can start from there. If your hill really is 10% slope, you can figure you'll need a hefty big powerful battery so it isn't damaged by supplying the high current required, and if you use a hubmotor it'll need to be a big heavy one, like the QS205 50H (call it almost 40lbs of just motor, not counting the wheel around it!).

Power usage on the simulated hill is over 150wh/mile, so with a 72v battery, 150/72 is about 2, so it will take about 2Ah per mile or more at that voltage.

In the simulation, the bike would also do 48mph on the flats (until your tires explode from the heat, anyway, and you smear across the pavement in the crash ), with power usage dropping to only 100wh/mile (meaning a battery needs sizing to around 1.5Ah/mile or so, maybe a bit less).

However, most batteries (cheaper ones especially) will need high Ah capacities to be able to create high currents without damaging the cells. So you may need a huge battery just to handle the power requirements even if you don't need the capacity, unless you're willing to spend money on a really good battery made of cells that can handle a high C-rate without significant voltage sag and internal heating. (meaning, probably not made of 18650 cells)


Note that none of this includes headwinds, or adverse road conditions, all of which can add significantly to the power needs.

 

[999zip999]

The battery is the heart of a electric bike.

 

[Braddudya]

I've built batteries so that was my plan. I have a few hundred 2600mah LG cells sitting around. But your simulations have brought me back to earth. That is a lot of power. I'll have to look into the actual grade of the hill. Any idea on how to determine this? Measure manually I assume?

I can say it is quite steep but it is only about 1/2 mile of hill. I live part way up the base of a mountain and my business is down in the valley. It's a 1.5 mile total commute but it's damn steep.

 

[amberwolf]

But your simulations have brought me back to earth. That is a lot of power.

They *are* just simulations, so they're only as accurate as the input data. But most of the ones Iv'e run on stuff I've actually got under conditions I ride in are pretty close to my actual results, so I tend to trust most of what I see in it's output as a general picture.

I'll have to look into the actual grade of the hill. Any idea on how to determine this? Measure manually I assume?

I can say it is quite steep but it is only about 1/2 mile of hill. I live part way up the base of a mountain and my business is down in the valley. It's a 1.5 mile total commute but it's damn steep.

If you have a smartphone, most of them have sensors that measure tilt, and there are apps out there that use them to give you slope in various ways. Can't remember if Strava does it, but some will give you the slope continously as data you can graph, or the average over a distance, etc.

One way to use this function is just lay the phone flat on the ground at as many points along the path as you can, note down the readings, and take the average. The slope on any particular spot on the ground could be very different from the slope as a whole, so the more points you measure the more likely you are to get a realistically usable number for the entire thing.

If you can mount it on the bike so it is perfectly parallel to the ground ant won't wiggle around, then you can ride up the hill and use one of the continuously-recording apps to do it instead.

ONce you know what it is, you can click any of my simulation links and change the grade there to what you measured, and rerun the simulation to see what it would take to go the speed you want. There is an autothrottle checkbox that will set the throttle for you to the level needed to maintian the speed you drag the slider rule to on the graph.

1/2 mile at 40miles an hour means 1/80th of an hour to go up, so less than a minute. If your selected motor, controller, and battery can handle the load reliably for several minutes then they would probably survive repeated climbs of the slope if they have time to cool off and recover afterwards.

If the whole 1.5-mile commute is "damn steep" then it would be perhaps a bit over a mnute at 40mph....

 

[calab]

Human nature for self limiting of the throttle is non existant.

The 350w motor will handle the 1000w controller fine - until it doesn't. That's what's going to happen if you feed it 1000w for more than a minute or 2 with no cool down period. Assuming the gears and clutch hold up (mechanically), from an electrical stand point, you'll be fine for crossing a busy road, climbing a short hill, or catching up with a riding buddy.

NOT OK for fighting a stiff headwind in the wrong gear (trying to go too fast) for extended periods of time, and NOT OK for climbing a way too long/tall hill.

 

[dogman dan]

definitely the 350w rated motor type.

40 mph up the hill will take quite a bit more than 1000w of course. I would not consider a fat tire bike for a commute anyway, unless it was a fun shortcut commute in the dirt.

However, a fat frame like that will fit a much larger moped or even motorcycle rim and tire nicely! Good starting point for a homemade, illegal ( assuming 40 mph mopeds are illegal for you), motorcycle with pedals, or pedals removed.

Once you build it up, you will never look legal going 40 mph around town. But these days, do cops even care in the USA? Lot of places no, till the ambulance comes.

For now though, why not run it on 1000w till it fries? 2000w no, but again if you don't weigh 300 pounds, it will last awhile on 1000w. Or at least till you climb a hill long enough.

 

[E-HP]

I'll have to look into the actual grade of the hill. Any idea on how to determine this? Measure manually I assume?

can you provide the street and city?

 

[AHicks]

For now though, why not run it on 1000w till it fries? 2000w no, but again if you don't weigh 300 pounds, it will last awhile on 1000w. Or at least till you climb a hill long enough.

Might last long enough to allow you to save up for a motor that will last a while too?

ANY geared hub motor is going to require a certain amount of discipline on the part of the rider if fed enough power for a long enough period. Properly matched, they do really well, but they do have their limits....

 

[Braddudya]

Thanks again for all the advice! I do have multiple ebikes already so this doesn't actually NEED to make that commute. I just thought it would be fun. I may just run the 750W controller and avoid long hills. That is a good suggestion!

As for it's future form I am now looking into the big standard form factor brushless motors running a gokart chain. I can weld and fabricate pretty well so that doesn't seem to be a too difficult option that is probably both more economical and powerful. Are steal frames heat treated? I know you don't want to weld aluminum frames but I am unsure if the steal ones.

Maybe the 350W motor running 750W will last long enough for me to get this figured out and the parts ordered!

 

[Braddudya]

So a lot has changed and now I am building this bike up for a friend. He has has tried my bikes and wants in on the fun!

I have another idea. What if I buy another 350W geared hub motor for the front and run 48v with 2x500W controllers?

I don't think I can find this exact hub motor so would a slightly different motor be a problem? of course I want it to be as close as possible.

I like the get up and go of the geared hubs and its probably cheaper to just get an additional run of the mill 350W one and two controllers than the new 1000W bafang geared hub. I know my friend is looking to cruise around for fun and not set a land speed record so acceleration would be preferred.

This bike does have a steel front fork no front suspension.

 

[electric_nz]

If it’s a Bafang hub they can be run a lot higher than nominal ratings; some of the factory ebikes run a 500W one at 1000w (52V 20A) with no issues at all