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Heatsink on the ACM


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Have you seen the picture of the heatsink on the new ACM they posted on Facebook?

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That shows how much current the new motor requests which results in heat at the MOSFETs.

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We all demand more powerful motors, but it seems that comes at the cost of added risk to strain on the control board. KS designed the 16a with active cooling in the form of a fan that turns on when the heat sink can't dissipate enough heat. ACM initial units were overheating so they had to beef up the heat sink. Hopefully both companies find solutions that eliminate the risk of frying the boards altogether.

Anyone in-the-know have anything to add about the methods they're using?

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58 minutes ago, Linneaunicycles said:

ACM heat sink, we test the wheel until the temperature goes to 90℃ more (Gotway wheels will alarm when the temperature goes up to 80℃), at this moment the main board didn't get any problem, we knocked an egg on the heat sink, it seems the egg is ok to have. What a pity, I didn't have a taste. :D

Hi GotWay, you sure get that extra point for creative cooking - but your food photography leaves room for improvement ... :P

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58 minutes ago, Linneaunicycles said:

ACM heat sink, we test the wheel until the temperature goes to 90℃ more (Gotway wheels will alarm when the temperature goes up to 80℃), at this moment the main board didn't get any problem, we knocked an egg on the heat sink, it seems the egg is ok to have. What a pity, I didn't have a taste. :D

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Mainboard is still functional after that burn test ? :huh:

Ha Ha, an egg. I remebered Horst Fuchs and his car protectors - he cooked eggs on car hood :D

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45 minutes ago, Tilmann said:

Hi GotWay, you sure get that extra point for creative cooking - but your food photography leaves room for improvement ... :P

I will keep the egg for your tasting next time you come to visit us.:D

There is no problem with the main board after the high temperature test. 

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27 minutes ago, Linneaunicycles said:

I will keep the egg for your tasting next time you come to visit us.:D

There is no problem with the main board after the high temperature test. 

Now we can safely say that the ACM can withstand egg cooking temperatures. :lol:

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41 minutes ago, lizardmech said:

Does it have any airflow though? There's a big difference between ideal conditions and a heavy rider using it on a 30 degree day.

90c is 90c with or without ventilation.

 

Ventilation will only effect how fast it gets to 90c.

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The temperature of the heatsink is defined by the Mosfet power dissipation(heat source), all the thermal resistances (junction-case, case-heatsink, heatsink itself) and the ambient temperature. The simplified heatsink calculations are quite easy calculations *) - the heatsink temperature is defined by all these values. If the ambient temperature changes, the heatsink temperature changes. Often the heatsink thermal resistance is given for free convection (assuming the hot air rises and is replaced fresh cool air at a given ambient temperature. For use with a fan and a given volumina of airflow (which again has to deliver fresh air at an defined ambient temperature) different thermal resistances are provided. (These defined ambient temperature is normaly used in the calculation as a worst case maximum ambient temperature which if exceeded will lead to overheating of the heat source(mosfet))

So both airflow and ambient temperature have an direct impact on the heatsink temperature (and the mosfet junction temperature of course).

*) For the heatsink everything happens in 3D and calculating a heatsink is just a simplified model. For this also finite model software exists for exact simulations.

For example http://www.ti.com.cn/cn/lit/an/slva462/slva462.pdf shows the simplified heatsink calculation in more detail.

Edit: PS.: In an closed and perfeclty insulated compartment @chriscalandrois right - if there the heatsink temperature comes to 90°C the air will reach  90°C, too (everything in this compartment will then get to this "equilibrium") and any airflow will change nothing - it just moves 90°C air around and 90°C heatsink. But this is imho an quite theoretical thought - also no heatsink would be needed in this case (just to heat up the air in this closed compartment a bit quicker...)

Edited by Chriull
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Air flow with fresh air is a contradiction to IP55/ IPX4. It would be possible to use the inner side to the wheel to get the heat transferred away. But it shouldn't burn the tyre, plastic case or increase battery temperature.

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42 minutes ago, OliverH said:

Air flow with fresh air is a contradiction to IP55/ IPX4.

I haven't seen or heard of any wheel that would classify for IP55. :( As here are quite some threads for diy glueing/siliconing... Maybe the new models (will) fullfil the standards better?

I assume some of the wheels just need some vents to not overheat too soon/often. Would be interesting how much the diy glueing/siliconing influenced overheat tendencies...

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It would be possible to use the inner side to the wheel to get the heat transferred away.

That is done with some wheels like the ninebots. But they also fail IP55 - which could imho be reached more easily with this approach...

at the ninebot.com website they started stating IP65, changed it to some statement like "rideable in all weather situations", now canceled this completely - i wonder when they take the last step and remove the picture of the ninebot in the rain. ?

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But it shouldn't burn the tyre, plastic case or increase battery temperature.

Imho the "massive" metal part/mount between the axle and pedal could be a nice heatsink - but would maybe force one to drive uphill one-legged ?

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On 5/3/2016 at 1:33 AM, Jeffrey Scott Will said:

We all demand more powerful motors, but it seems that comes at the cost of added risk to strain on the control board. KS designed the 16a with active cooling in the form of a fan that turns on when the heat sink can't dissipate enough heat. ACM initial units were overheating so they had to beef up the heat sink. Hopefully both companies find solutions that eliminate the risk of frying the boards altogether.

Anyone in-the-know have anything to add about the methods they're using?

The only reason the control boards are under strain is cost cutting only 6 MOSFETs and poor cooling, in the bicycle world when you buy a ebike kit you get a control board that's under stress however you are free to buy one with 18 or 24 MOSFETs that will not be under any stress even with a 5kw motor. Even if we had quality control boards then we would claim the motor is under stress, in practice for safety reasons we do not want any parts to be under stress, in a far future there will be control boards aluminum enclosed with 18 or 24 MOSFETs, and 2 to 3kw motors. I would gladly pay a little more and not have parts under strain or stress, but the electric unicycle market is currently too small, little by little there will be better components available. Eventually a day will come when you will be able to replace the control board by one of your choice and the motor by one of your choice having nice options available. Year by year I see unicycles getting better it is a matter of time before this happens. But on today's market yes the larger motor causes the control board to strain and other than try to improve cooling there is little that can be done. The main reason you need lots of power on a unicycle is safety, the power needed to avoid a faceplant, speed does not provide you safety but power does, strained components provided a safety hazard, components will get better over time specially if there is a market for better components.

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6 hours ago, koto said:

I'll receive my ACM very soon, probably this week. I'm in France. How can I know if I'll have the new heat sink ?

new heatsink began to put from the 6 May, it is unlikely that you wheel released after this date

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1 hour ago, Дмитрий Дмитрий said:

new heatsink began to put from the 6 May, it is unlikely that you wheel released after this date

So, what will be the real risk for having the old heat sink. How dangerous is it ? If it is considered not really secure, should gotway upgrade all previously packaged machines ?

 

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On 7.5.2016 at 11:38 AM, Дмитрий Дмитрий said:

before and after

 

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New motor connector

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How secure is the fastening of this plugs? I can't understand that this yellow plugs are still in use for batteries and now with 3 wires for the motor.

1 hour ago, koto said:

So, what will be the real risk for having the old heat sink. How dangerous is it ? If it is considered not really secure, should gotway upgrade all previously packaged machines ?

 

Overheat warning comes faster if in a higher temp environment or if you stress the ACM on uphill tracks. Keep in mind: Gotway still manage to have the EU without active fan cooling.

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22 minutes ago, OliverH said:

How secure is the fastening of this plugs? I can't understand that this yellow plugs are still in use for batteries and now with 3 wires for the motor.

Overheat warning comes faster if in a higher temp environment or if you stress the ACM on uphill tracks. Keep in mind: Gotway still manage to have the EU without active fan cooling.

I don't know if the small fan make sense as the room for the main board is small and likely closed. Just like when you feel it is too hot in summer, will you feel better when you face to a fan in a closed rooms and works for several hours? But it is just my thought.

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7 minutes ago, Linnea Lin Gotway said:

I don't know if the small fan make sense as the room for the main board is small and likely closed. Just like when you feel it is too hot in summer, will you feel better when you face to a fan in a closed rooms and works for several hours? But it is just my thought.

Correct. Heat needs to be transported away from the hot spot. If you can't transport heat and a fan in closed environment makes no sense. A fan needs maybe maintenance or to be replaced by time.

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1 hour ago, OliverH said:

Correct. Heat needs to be transported away from the hot spot. If you can't transport heat and a fan in closed environment makes no sense. A fan needs maybe maintenance or to be replaced by time.

I can't say that a cooling fan is the perfect solution, but I don't think its life expectancy is really that much of an issue. It should easily last the length of the batteries at the very least. Ks16, for example only runs when temps reach 50C, which is not often- likely not even for a moment daily, just occasionally for brief periods when needed. Compare this to a PC which have active cooling fans that last years and years running constantly throughout the day. If your CPU quits for even a few moments it can fry, but we trust heatsink+fan to protect it. The quality of the fan has to be considered especially with vibrations from riding, but I'm just saying many such critical solutions for electronics exist already. 

And I totally agree ventilation from the inner chamber should be part of the solution - I also love the idea of copper cooling pipes like you see on higher end graphics cards. 

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