Hot weather cooling for motor

[Gr8fun]

When the ambient temperature is below 70 it is difficult to overheat the motor. Putting 500 watts into motor for twenty miles barely gets motor to 120 degrees. Now at 95 the same ride temperature approaches 160. This is not good.
any body try cooling with mist, felt pad, evaporative cooling? Water bottle. Pressurized with mister in front of motor green scrub pad for water retention, evaporation??? Other than that a copper heat dissipation fin wrapped around motor...
Otherwise my 750 watt motor becomes a nominal 300 watt motor. Or new plastic gear.

[commuter ebikes]

What motor do you have?

[Gr8fun]

Bbs02 .. Tofayi drove pas 2 instead of 3. Very sparing use of throttle. Slightly lower gearing that was too fast to pedal. Used 2.5 ah compared to 4.2 yeaterday. Maybe 150 degrees on motor. Hotter ambient temp than yesterday.
it is strange that motor efficiency is higher when rpms are too fast to pedal. Almost self defeating to pedal. Pedaling range is ineffecient motor range. Then again migt be a bit exaggeration..

[moarpower]

You are accurate. A different motor gear reduction ratio would allow efficient pedal RPMs to match efficient motor RPMs. But then your bike would go no faster than you can peddle!

[commuter ebikes]

I limit motor heat by using the display to place a limit on the current. If I am not getting enough power with this limited current, then I install a larger motor (which I have actually done).

[Gr8fun]

Just waiting for the money. Even with the bbshd, more cooling may help on high ambient days and prolonged high amp draw.
For now trying some added heat sinks with thermal conducting epoxy.

[Gr8fun]

I can pedal easily to to 50mph
with my gearing. Sa hybrid drive with 52 ring 11 cog.. But the motor is a no go except with downhill and wind at my back. Which i never do. That would be illegal and dangerous. Top gear is not usable. But i stay out of the 11 13 fast wearing skipping cogs. At speeds above thirty using 1400 watts heats motor way fast, and only possible when it is too cold to ride. Cool the motor and get more usable watts for longer.
the 750 rating is only for cooler temps possibly standard temp of 20 degrees C. ( 71 F)
i say different motor ratio. Peak at 95 cadence not 130.? Just overthinking what i can not do.

[commuter ebikes]

This is why I prefer 72V systems for the higher street speeds that you mention. I also love huge chain rings and small rear cogs. Most 36-60V systems will perform well at lower speeds, but some people, myself included, like to cruise at 35+ mph. Is that possible with 48-60V systems together with the voltage sag and when the battery is nearly depleted?

[commuter ebikes]

In practice, I won't pedal at cadences above 100 RPM because it is so turbulent. Raising the voltage, running a huge chain ring and a small rear cog, having a motor that can supply a continuous 2200W or more without ever overheating, and then drawing enough current (e.g. 34A) to maintain 35+ mph and pedaling meaningfully with the tall gearing makes for a fun, fast ride that provides exercise.

[Gr8fun]

The 72 volt is interesting lower amps less heat. as well as getting the heat generating controller out of the motor. I can cruise as long as my battery lasts at 25. But 30 is not an option for more than 5 miles when it is cold. . 20 mph like today is tedious.
25 is good for me. I can sit back using the throttle drinking coffee in the am commute.
Wiring a bbshd to external 72 volt controller was my question here. Which motor are you using?

[commuter ebikes]

The 72 volt is interesting lower amps less heat. as well as getting the heat generating controller out of the motor. I can cruise as long as my battery lasts at 25. But 30 is not an option for more than 5 miles when it is cold. . 20 mph like today is tedious.
25 is good for me. I can sit back using the throttle drinking coffee in the am commute.
Wiring a bbshd to external 72 volt controller was my question here. Which motor are you using?

I use a Cromotor (almost identical to a QS Motor 205) and a 24 FET Lyen Mark 2 controller. I definitely want my controller to be away from the hot motor; I have never liked the idea of a controller mounted inside a motor. Having an external controller gives the builder the option to use extra FETs in order to handle the controller heat better.

I have my controller mounted on a large, thin aluminum heat sink which is attached to the steel frame with thermal pads sandwiched in so that the controller heat transfers to the heat sink and frame. Here is a video: https://www.youtube.com/watch?v=EmUPmt3noyA&t=185s. Since that video, I have made all of my heat sinks out of 1/8 aluminum because the 1/4" plate is needlessly heavy.

The idea to use an external controller for a mid drive seems like a great idea to handle heat. I look forward to seeing your results of running a BBS at 72V. How many Amps will you draw?

When I limit my current, the reduction in heat is significant. Remember the heat is proportional to the square of the current because P=(i^2))R, so tripling the current causes nine times the heat.

You can also try reducing mass in order to reduce heat.

One good thing about traveling more slowly is the reduced damage to your body in the case of an accident. From K.E. = (1/2)m(v^2), the kinetic energy is proportional to the square of the velocity, so tripling your speed is expected to cause nine times the damage to your body. Crash at 15 mph and I would bet that you continue on your ride; crash at 45 mph and I would bet that you do not finish that ride.

[Gr8fun]

Some good info and suggestions here. I have seen external controllers for bbshd mentioned and luna has their ludicrous . thes projects are outside my finanxial condition. I think the bbs02 would not take a 72 volt external controller. Might be able to wire with an external controller though. Scavenging aluminum heat sinks from nonworking electronics is not. Nether is jb weld.
Heat is proportional to the square of the current. Thanks for that.

[commuter ebikes]

How are other mid drive riders helping to cool the motor?

[moarpower]

I have a newly acquired BBS02 (30 miles) and always use a lower PAS setting and almost never use throttle. I mostly use PAS 1 (200-300 watts) but sometimes use PAS2 or 3. It hardly gets warm at 20 - 25 mph (500 watts) even in 90 degree F weather.

[Gr8fun]

Thanks moarpower. Ended uop Damaging nylongear. Probably controller is getting too hot. Same driving as you and motor is a hell of a lot hotter than warm.

[Gr8fun]

Although i did not take accurate temperature measurements, relubing the primary and secondary gear reduction areas in the bbs02 with copious amounts of synthetic grease has apparantly dropped temperature over 20 degrees under adverse conditions. Better heat transfer. The primary nylon gear freewheel had stopped working. The grease fixed that too.

[Zippy]

Although i did not take accurate temperature measurements, relubing the primary and secondary gear reduction areas in the bbs02 with copious amounts of synthetic grease has apparantly dropped temperature over 20 degrees under adverse conditions. Better heat transfer. The primary nylon gear freewheel had stopped working. The grease fixed that too.

What's the stuff to use when doing this? Synthetic Lithium grease?

[Gr8fun]

I used mobil 1. A red synthetic grease that has been reccomende by several people. And luna maintainence instructions. On both primary and secondary gear cases. The original white lithium and black moly greases as done by factory can mix with bad pinion seal and damage nylon gear. Also reports have been that factory did not use enough. I found very little grease in the primary. Suspect some bearing damage in primary. Discovered problem with mileage totalizer so it is closer to 10000 miles w/o a problem and no visible wear to motor or gears! Original grease. Small amount of moly grease got to primary (grey color) in primary.
The thing about lower temperatures needs to be verified. Just finished 30 mile. . trip. Motor good and warm. 85 degree ambient. 130 on motor. Before was running in excess of 150. Mostly uphill. No actual verifiable numbers on this. Would be helpful if someone actuall did before and after temps. Ambient. Before and after temps on same route exceeding 10 miles.

[Zippy]

Thanks Gr8fun, now you've got me wanting to crack my cases open and look how much grease is in there. Obviously the stuff is going to be warmer and thinner when it's 95 degrees out and the motor's pulling hills. Glad I read this thread.

[Gr8fun]

Get an impact screwdriver to loosen the lock tighted screws on clutch and primary gear covers. Mandatory do not strip out these phillips head screws. One quick tap with hammer and all the tension is removed.
it makes total sense to me that the heat transfer is more effective through a viscous liquid than air to metal. Plenty of lube.

[Gr8fun]

Over 90 degrees today. Temperature rise in bbs02 only 30 degrees, 10 miles 25 mph. This is after relubing with copious amounts of mobil synthetic grease. Before it was too hot to touch.
But on running at 750 watts for three miles at 90 degree ambient temp. Motor still too hot to touch. 500 is max safe wattage for temperature dissipation. My opinion

[Madjag]

Hey, it's 106-108F where I live when I head home after work now. Luckily much of my ride is downhill and I coast a lot. Still, the motor is damn hot when I get home after 12.5 miles. Never had heat problems in 7 years with my previous bike, a 350watt hub motor Bionx mounted on a Specialized mountain bike. 27 speeds helped I guess plus the fact that I had to pedal like crazy the whole ride to work which is 12.5 miles and a 1,600 foot climb.

[Gr8fun]

At 107 degrees you only have 33 degrees of cooling before you need to stop and cool down motor. 110 degrees is safe. At 120 be careful. 130 no more than 1/2 throttle. 140 stop and cool. At 70 degrees 750 watts is okay. At 107 you loose 37 degrees cooling ability. Do not even think of running at 750. Not even 500 watts. IMO (bbs02)
At 160 magnet damage begins to happen. At first reversible but can be permanent. Nylon gets soft. Varnish on motor windings can burn.
Cut power. No temp gauge? 120 degrees you can keep hand on motor for 20 seconds. 130 very short time. 140 feels burning.
Trying to add karl geisslins electric bike article on electric bike.com adding a temp. Gauge. but i am a clutz on remembering how to add link to article. Help.

[Gr8fun]

350 watts and you have a large surface area to help cooling. The bbs02 is 750 nominal and 1400 max watts. That is a lot more heat to remove with a smaller area to remove it from. As long as you keep your speed up operating above 50% rpms i can see that you have less of a problem. At temps above 100 i just limit the power and gear down to your level and am able to ride without worry. Using the throttle and pas above 2 is asking for trouble.