Cooling a Mac hub motor

I am intent on cooling my Mac, in some fashion. Yeah, I might be babying it, but at 87 C and only 94 F outside temps (we get to 110) without riding it hard, I feel I am right near the edge and want to take some precautions. I am running 1200watt peak btw, so not all that high power. Usually average 400-500watts over 10-20 minute trips. 18-22wh/mile.

I will start by asking, why can't you drill the drive side cover on a Mac? It's separate from the gear side.

I am experimenting with attaching custom heat sinks.

Other ideas are:
- Build a sun shade (very marginal help)
- Attach a fan to use when stopped at a light, or while parked etc.
- Water spraying system to use while moving

Does anyone have any data on the actual healthy limits of a Mac? Temperature next to the windings? (heat sensor installed). At one end, some members say 80 C is where magnets start losing power (I haven't noticed any drop in power). On the other end, members are saying 200 C is possible for short bursts (on a DD).

I recall that recently a poster said he had fried his MAC when he was using 60V and 45A on an uphill (2700W?), What turn-count do you have? I'm assuming you have the geared motor?...

Also factor in that you can air-cool or oil-cool a hub, several threads around here on that...

I have 2 mac 8t's that I am swapping parts back and forth trying to find the limits of this motor.

I ran 24S at 35amps Lifepo4 for a while watching the CA and trying to stay under 3k.

Now I run 18S lipo also babying the motor trying to stay under 2500k.

I know at some point something is going to fail and then I will just swap in parts from the other motor and back off somewhat.

Read where someone used oil to cool their mac , but it does sound messy to me.

Here is my preliminary custom "heatsink" for the hub motor:

It's held together by some speaker wire threaded through the holes I drilled out in each of the 50 pieces I cut from an aluminum channel. It was a lot of work, 2 hours straight, but I think will be worth it.

I don't expect a very good conduction of heat with just the bare metal touching, so I ordered some Arctic Alumina Thermal Adhesive. I will still keep the wire to prevent any chance of these heat sinks from flying off.

Has anyone ever done something like this? Am I the first?

Open up the motor and you will see where the heat is coming from - the disc brake side. where the stator is.

The place with the best heat shedding potential is on the sides.
Order one of these and you be able to confirm this with your own:

http://www.hobbyking.com/hobbyking/store/__12582__Turnigy_Infrared_Thermometer_33_220Celsius_.html

BTW, this motor is not overheated at 87C. It's 100C and beyond that you need to worry about. Can't imagine how hot mine gets climbing 8% grades out here with my fatass on it . Definitely hot on the cover... despite all the abuse and heat soak, mine has lived this long.

87 isn't too far from 100, when you are still 10-15 degrees F cooler outside than it will be. I was also not pushing it too hard.

I think you mean that the bike gear side is where the heat is coming from. The disk brake side is where the gear/clutch is. (At least on the old gray Mac)

But if you're right, then that's even easier to cool.

Duh, you are right about the freewheel side

Actually it is harder to cool because there is a freewheel sitting in the way of letting heat out on that side
I cut my tallest gear off. Did that help? i dunno :lol:

Guess i never really thought about heat on my MAC motor. Nowadays my expectations for it are rather low, now that i have tasted over triple the power

I'm going to eventually do a DD build, I do want to see what 4kw feels like, probably like the acceleration of my road bike in a sprint, but without the effort.

I think the Mac is fine, it's just this insane heat we get here, and the hotter it is, the less I want to pedal, and riding in the city is so ridiculously immpeding with stops every few blocks which really heat things up.

What if you made a plastic 2 liter soda bottle bottom that sealed against the side of the hub motor right at the axle. Drill holes in both side covers and plumb an air line to the 2 liter soda bottom and connect to an air pump.

veloman said:

I'm going to eventually do a DD build, I do want to see what 4kw feels like, probably like the acceleration of my road bike in a sprint, but without the effort.

I think the Mac is fine, it's just this insane heat we get here, and the hotter it is, the less I want to pedal, and riding in the city is so ridiculously immpeding with stops every few blocks which really heat things up.

Click to expand...

Yeah... it's your environment, dude .. you need a super oversized motor. As far as your ambient air 'cooling' anything, forget it

My MAC is struggling in the 80-90f heat out here on the super steep hills, after having noooo problem all winter running at 2-2.5kW ... so i got a preview of what you're dealing with.

I am sure the DDs out there are sucking too. I think a cromotor is in order.. stat..

I read somewhere that 2500W was the edge of the danger zone for an 8T MAC @ 48V...(no personal experience with this yet)

Theres nothing wrong with the heat-sinks you added to the hub shell, but I fairly certain they will only be a very small help. The captive air inside the hub (no inside-to-outside flow) is a very poor conductor. Simply cutting holes in the side plates will dramatically allow more ambient cooling.

Recent builders who have added an internal thermometer have noticed that even when they come to a stop at the top of a hill (no longer adding watts), the motor continues to heat up. This suggests to me that while the motor is moving, at least some of the growing heat is shed by the aluminum side-plates.

Since you haven't added oil or cut air-cooling holes, I highly recommend that you add an internal thermal probe, so you can start data-logging the temps when you are with heat sinks, and without the heat-sinks.

Clearly, if you cut large air-cooling holes, you would have to swap in new side-plates if you decided to try oil-cooling. So I'd recommend trying the oil-cooling first (Automatic Transmission Fluid, ATF)...and I suspect oil-cooling will work better than air. Its my opinion that the oil cooling effectively draws the heat from the coils, then efficiently transfers the heat to the aluminum body of the hub.

If someone is committed to air-cooling a geared hub, I am of the opinion that the most effective set-up would involve attaching a disc to the disc-brake flange, with vanes in-between the disc and the hub left side-plate. If you added holes near the axle of the left side, this would re-create the well-designed ventilated front disc brake of automobiles. Some rim holes on the right side would provide the best air-flow across the coils, with a minimum of dead spots.

It may seem counter-intuitive that the air would easily flow from the rim towards the center of the interior, and then flow outwards through the vanes of the impellor, but my study of Stirling engines and "cowl induction" on Trans-Am cars assures me that this will not be a problem at all.

Disassemble hub
Add a temp probe (even if you don't add a read-out until much later)
Upgrade phase wires, perhaps with Teflon insulation
Coat the inside with a conformal water-proofing spray
Re-assemble and collect wattage/heat data
Add oil or air-cooling...collect more wattage data

Thanks for the thoughts. Cellman already put a temp sensor in, that's where I'm getting my readings from. He says I have nothing to worry about. I am pretty certain I could get this motor to 100 C and that doesn't seem like a good recipe for longevity. Phase wires are already upgraded (doubled).

I know what you mean about the cooling fins doing very little, it's the air inside the hub that needs to be cooled.

I rode it this morning in about 83 F, pulling my trailer, with the cooling fins on. I don't think there is any difference. After 5 miles at 22-26mph, the temp was 66 C. On my way back I was pulling a 25lb plant I picked up, but I went really slow. Temps hit 74 C when I got home, but that was after some small hills, it was staying near 62 C.

I'm not going to jump into oil cooling just yet, will want to read more on it from the members who are trying it here. I've seen some have had some leakage issues on their HS clytes.

Drilling holes in the side cover freewheel side may be fine. What if you found some rubber plugs to plug in when it was wet (and you didn't need the additional cooling)? Then you wouldn't worry about water getting in. Dirt still possible though.

On my 6 turn Mac, the freewheel side cover is needing to be replaced sometime anyway due to a crack, so I may experiment drilling that one first to learn.

Drill some holes in the wire side cover just outside the bearing support. Then, with the motor out of the shell, drill steeply rearward at the top angled holes between the spoke flanges. That's where we'd put the exhaust holes in our DD motors if the magnets weren't in the way. Angle them rearward to deflect debris and water as well as avoid negative effects of the influence of outside airflow from your new centrifugal fan. Keep in mind that the fast spinning motor inside is spinning the opposite direction of the wheel, so that's the direction the air inside is probably spinning. If I was doing it, I'd take a sharp hobby knife and score the outside of the motor bell with deep scratches parallel with the axle to act somewhat like fan blades.

If you really want to get adventurous, and if there's room. Then you could bolt some small blades to the spoke side of the rotor bell to help suck air through the stator, but that would require actually taking the motor apart. I've never hand one of those motors in my hands, just Fusin's and Bafangs as far as geared hubbies go, so I'm not sure if it's practical on your motor, but just getting some fresh air flow in near the axle and out between the spoke flange should be a big help on cooling.

Oil cooling still has some bugs to be worked out with oil leaking on tires and brakes, and oil eating shrink wrap and who knows yet what else. I'm glad I didn't follow that herd. You might check MWKeefer's stuff though. He's been using oil in geared hubbies like yours with good effect for years, and did enough experimentation that I'd have no problem following his lead, so check his stuff before drilling holes.

John

This needs more research because the payoff will likely be very effective. I saved a thread on water-proofing the inside of a hub, and one of the suggestions was a urethane coating that just so happens to be ATF-resistant.

Might be worth experimenting on something cheap that wasn't a hub-motor?
http://endless-sphere.com/forums/viewtopic.php?f=30&t=36786

I also have a temp sensor on my mac. What do you use to read the temp?

Cellman installed the temp sensor which one is connected to one of the hall wires (I think) and the other wire comes out of the 6th unused slot in the hall plug. So using a voltmeter on these leads, you will get a readout of 1v = 100 deg Celsius. I have my bike setup with my multimeter strapped in my front basket, with leads connected. All I do is turn it on to check the temp. A smaller voltmeter would be nice, but I can't seem to find such a thing.The highest I've seen in .87. If I go over 80, I tend to try riding slower to let it cool. I'm pretty sure I'm babying the motor, but I like things to last. The controller is another story, I don't have a temp sensor and it can get quite hot too. Time will tell if it's an issue I guess.

This analog voltmeter is the smallest I've found to fit this requirement:

http://www.ebay.co.uk/itm/YS-50-DC-0-2V-Analogue-Needle-Panel-Meter-Voltmeter-/180906757521?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1ee20d91#ht_1290wt_789

Not the smallest but quite small and lightweight (57g), and should be way smaller than a multimeter.

It looks about 1/3 the size of my voltmeter.

I did a distance test just now, since I'm worried there is a problem with my battery. After 13 miles in 96 F deg heat, the motor temps hit 94 deg C. This is at 21wh/mile. This is ridiculous IMO. There is just no cooling happening, unless I go downhill at <200watts and over 25mph. It just saturates and saturates.

Looks like I need to ride a 9c when it's above 85 and I need to do more than 7 miles at any reasonable speed. Not that I am having motor issues, the power still feels fine. But at 94, things are getting very close to the danger zone IMO. Not all of us ride in 70 degree temps and have few stops to heat the motor. Riding in rush hour traffic, you can't baby it, and there's a lot of stop and go.

I'm surprised your mac motor get so hot so easily. Do you have the right calibration from your cycle analyst?

My little direct drive hub (24V 250W of 4.6kg) handle 2500W peak and 600W continuous without breaking a sweat. The motor is barely warm after 20-30 mn ride.

Have you tried to touch the motor to feel the temp?

What is your ambient temperature?


I don't have a CA hooked up. There is a temp sensor installed as described a few posts above.

It doesn't get hot right away, but it just keeps going up without cooling off. I was only running 1250w peak today too.

I do touch the motor and it feels hot when it's in the 70,80,90 deg range. Not hot enough to burn me, but hot.

I live in london, so the local temperature is quite low. Around 15-25C most of the time. And very often raining :lol:

Just wondering if one of the sensor doesn't read correctly, either in term of power usage or if the temp meter is wrong.

cwah said:

I live in london, so the local temperature is quite low. Around 15-25C most of the time. And very often raining :lol:

Just wondering if one of the sensor doesn't read correctly, either in term of power usage or if the temp meter is wrong.

Click to expand...

Well it sounds like it's a matter of ambient temperature. I didn't have such high temps when it was below 80 F here.

I'm certain my power usage is correct, it matches my controller settings and my performance calculations on hills.

Don't forget that the motor is seeing much higher than 90°F ambient temps. A foot above the road on a Texas summer day, I'd add 20 degrees and that might not be enough.

MWKeefer has been using oil for cooling and lubrication in his geared hubbies for years. Makes them more quiet too. Look up his discussion from a couple of years ago. FWIW, his testing came up with no significant benefit for DD's.

My mac motor 8T at 74V is really noisy with strident noise. Not very agreable. Is it normal? I have a very nice sound with my DD motor, but on the mac it seems different.

The new Macs with composite gears do make more noise than the older ones, and definitely more noise than a DD. Overall they are still very quiet compared to old Currie style motors with steel gears (think of a powerdrill).

I wouldn't call the Mac sound a bad sound. It's most noticeable if you get a tailwind on a hill. Maybe take a video of yours?