How much over-wattage can one usually get away with putting into geared hubs?

[abagofcells]

I have 2 converted MTB's, both have 250 watt rear geared hub motors. Neither of the hub motors have any useful information written on the, except 36v 250w and some numbers that don't give any google results. All I know is they are about the same size as all the other 250 watt motors, commonly seen on EU ebikes.

The first one I built have a locked down controller and 36 volt battery integrated in the rear rack. Measuring the wattage with an external shunt, it would peak at 320 watts on a full battery. I have shunt modded it to peak at 400 watts, and it has run fine like that for a long time, but still speed limited.

My second conversion uses a Kunteng 17a sinewave controller and KT-LCD3, paired with a 48 volt battery. I have a lot more possibilities to tune power levels on this bike, but have so far I have also limited it to peak at 400 watts. This bike is much lighter and agile, and for my commute to work, I can run it at 200 watts, and still maintain 30-35 km/h, only running it at 400 watts for climbing a couple of hills without loosing speed.

On the other end of the spectrum, I have a Sondors fat bike, that peaks at 800 watts on a full battery, while the motor has 350 watts stamped on it. It has run this way for years, but I'm not completely sure if the controller has been replaced before I got it.

But how much power is really safe to put into these, if I still want them to last a long time? What are your experiences? It seems some people run them at ridiculous amount of power, and other add a bit extra, and instantly fry the motor by breaking without cutting motor power, but I have found very little data on longevity with just a modest power increase.

 

[spinningmagnets]

If you add a temperature sensor to the stator, that can provide important data when adding more amps.

 

[abagofcells]

I just read through the sticky thread about that, and yes, it certainly seems like a good idea. It seems getting the sensor in there is the easy part, and getting the wires out of the motor is much more challenging.

 

[TuomasK]

Some mods and you can pump quite alot of watts into geared hub. This is my G062.1000.DC that peaks >6000w peak (60v battery). Stock can take maybe half.

 

[TuomasK]

 

[richj8990]

My impression is that both mid-drives and gear hub drives can max out at about twice their rated power, assuming the controller can handle that amount of amps going through. So if your 2nd motor is rated at 250W and maxes out at 800W that's a bit more than 2x but it's in the range of max watts. It's also about how cheap your wires are, the plastic coating them, the max amps the controller can handle, and most importantly how long you are going above the rated watts with the outside temperature being hot or not.

This is just a guideline, can't 100% promise this, but for example if your motor is rated at 350W and you did 400W for 20 minutes straight, outside temperature was 50F, it would probably be fine to do that every day for hundreds of times.

If on the other hand a 350W motor was run at 600W for 20 minutes straight, outside temp was 90F, you are probably going to start melting your controller wires and may not even be able to run it for the full 20 minutes before the electrical system dies.

250W even for a geared hub drive is not really going to cut it for long steep inclines unless you really go slow, like not more than 5-6 mph at the most. I like to climb steeper, as in 8%+ grades with around 400W in PAS and 500W throttle for a geared hub drive, and that would not be good if it was rated only at 250W. There are some good 500W geared hub drives out there. Unless you are in a relatively flat area, then 250W is fine.

 

[abagofcells]

Thanks. That is really useful information. Luckily, it's pretty flat where I live. I'm currently waiting for a second controller, and want to try out the opensource firmware on that. That will give me even better control over how much power is delivered at each pas level.

 

[AHicks]

You can add way more than the motor is rated for easily. The rub comes in when you talk reliability, or just how long the motor can tolerate that kind of power without cooling down. 500w motors are routinely run up to 1000w or so. Just realize they can only be run like that for a few seconds, then they start overheating. That will all be on you for staying on the power too long. A few seconds won't hurt a thing....

 

[m3vuv]

i once experimented with a few geared hub motors,these were all 250w uk units,first one started out as a 36v battery powered with an 11amp controller so 396w may,this i upped too 48v with the same controller so 528w,after about 5 miles the motor jammed up,the magnets had flung outwards from the motor(inrunner type) jamming the wheel and destroying its self next was a geared outrunner motor ran with 2 36v packs in series so 72v x 11=792w,this lasted about 30 seconds,it reached about 45mph then the windings shorted and killed the fets in the controller,next was another outrunner geared motor running a 500w controller with a 48v battery,did about 3oo miles ok untill ripping the teeth from the gears,replaced those but same results about 3oo miles later,,theres a lot of variables to concider.

 

[slaphappygamer]

Another variable to consider, is your phase wire make up coming from the motor to your controller. I’ve been using this guide as my base.

For example, I have 16AWG wire and have max 25 amps (chart shows 22, but according to descriptions, this value is very conservative) set at my KT controller. The phase wires were getting hot, but I can still touch them for more than 20 seconds, so not too hot. I replaced the standard bullet connectors (rated at 15 amps), with MT60 connectors (rated at 90 amps) and shortened up my phase wires. Dressed the wires all nice with no kinks or hard bends. My phase wires don’t get nearly as hot. Melted phase wires are less of a concern now.

For reference, the motor is a Shengyi rear hub rated at 48 volts, 22 amps. The manufacturer locked the controller at 18 amps. I now run 25 amps, comfortably from my same, stock, 48 volt battery.

 

[TuomasK]

This version of G062.1000
DC runs 60v 114A peak (DC). Well over 200A phase.

 

[edgefx1]

Some mods and you can pump quite alot of watts into geared hub. This is my G062.1000.DC that peaks >6000w peak (60v battery). Stock can take maybe half.

View attachment 335105

thats 2 sets of leads for the same phases? is this for higherr current loads so the stock wires dont get too hot?

 

[AGS]

I’m a lot more conservative and have run an SWX02 at 52v 30amps for 800 miles and oil cooled it. So around 1750 watts hot off the charger. It’s holding up fine so far. I have some oil leaching through the motor cable but I managed to seal up the case and axle using Loctite 574 and that works just fine.

I also fitted a LM35 temperature sensor using the white speed sensor wire to keep an eye on it and it runs quite happily at around 80 degrees centigrade for extended periods flat out.

And for belt and braces I also fitted an alarm at 100 degrees and a motor trip at 110 degrees.

The temperature reading is only accurate when I am off the throttle and PAS because there is too much interference when the motor is running for it to be accurate.

The photo shows a little bit of ATF on the motor cable connector, where the oil has travelled along the inside of the cable. But the brake disc is nice and dry.

I can’t run it any higher without upgrading the wiring to handle more current.



Temperature gauge is a 3 1/2 digit 2 volt led meter.

 

[TuomasK]

thats 2 sets of leads for the same phases? is this for higherr current loads so the stock wires dont get too hot?

Yes, two sets of phase wires (~8awg combined) + L10 & MT60 motor connectors. Additional higo mini b for winding temperature probe. for I have upgraded the motor and wiring so not much stock.

 

[rhubarb]

I bought a job lot of puma geared motors in 2007, nominally 350/500w. Usually run them at 54V/60A, so around 3000W but have had them up to 6000w. I maximize the size of the phase wires by using stripped 10awg wires and running them in heat shrink through the axle.
Power loss/heat generated is proportional to current squared, so higher voltage is more efficient than higher current, as long as you don’t exceed the controllers limits.

 

[addertooth]

The nylon gears are an issue as your power goes up. This is why both Wired Freedom and eCells are using metal-edged Nylon gears to make them more mechanically robust. They had to do this for their 2k to 2.6k motors

 

[abagofcells]

Since this thread is still active, I'll add my experience with the latter of my two converted bikes, mentioned in the first post. I have used the bike for commuting for the last year, for a total of 6500 km. For the first 3500 km, I used a generic unbranded 250 watt rated rear hub. It ran fine, but was mounted in a 27" in a 29" bike. Changed the wheel, to one using a unknown Shengiy motor. also reted 250 watt, and that has been going for the remaining 3000 km. Usually I use around 300 watts, but on days with strong wind, it may run at 400 watts for an hour. Neither motor has had any kind of problems.

The Sondors fat bike still runs just fine at 850 watts. I recently took the motor apart and changed the very worn out bearings. The nylon gears are still in perfect shape, and I actually reused them, and just pressed new bearings into them. It always runs at max wattage, but newer more than half an hour at a time.