meepmeepmayer

[one more GOTWAY WARNING] ACM died on a hill (it was bad cabling + high stress, final update pg 16)

486 posts in this topic

Posted (edited)

16 hours ago, Hunka Hunka Burning Love said:

I'd be curious to see what @esaj thinks of my arcing theory.

Well, again my first reaction would be "not likely", but who knows? I know that motors/coils can produce very high voltages in spikes when a coil turns off, still, to strike through the cable sheaths, it would likely need to be somewhere in the kilovolts (thousands of volts) range...  Then again, I've seen a small DC-motor run with 9V kick back around -100V in short spike with the scope, so... :P

At least it cannot be common, otherwise stuff like this would be happening all the time. "Just" heating would seem more plausible (or a combination, where the sheaths first start melting, and once the cables got close together with the sheaths melting away from between them, at some point the isolation was thin enough for a strike-through to happen). But it's all speculation.

Edited by esaj
3

Share this post


Link to post
Share on other sites

Posted (edited)

4 hours ago, KingSong69 said:

As i have heard the 67 Volt machine boards are more or less limited to about 120 Amps, while the 84 Volt Powerhorses are about 180amps.

Even if all the three phases share this "180A" maximum value equally, then we have 180 / 3 = 60 A on each wire. Do we have 3.6 mm diameter motor wires? No.

In reality each wire should be able to carry even more because the current has to return to a controller board somehow.

Сечение проводов.JPG

Plus we need gilded wires because of the skin-effect.

Edited by Radislav
1

Share this post


Link to post
Share on other sites
5 minutes ago, Radislav said:

Even if all the three phases share this "180A" maximum value equally, then we have 180 / 3 = 60 A on each wire. Do we have 3.6 mm diameter motor wires? No.

In reality each wire should be able to carry even more because the current has to return to a controller board somehow.

Сечение проводов.JPG

Plus we need gilded wires because of the skin-effect.

Only two of the phases are carrying current at a time, the third is "floating". The same current goes "in" through one phase and "out" the other, so two of the wires carry the same current at the same time, it's not "distributed"/"shared" between them.

Here's an old post of mine about the basics of 3-phase BLDC-motor drive, although there are probably better sources in the internet and people who know more about them in these forums too:

 

3

Share this post


Link to post
Share on other sites

Posted (edited)

14 minutes ago, Radislav said:

Great article, thanks! It reminds me what I've learned in Moscow radio-electronics university :) 

The worst case - each wire must be ready to carry 180A if duty ratio is 100%. I even fear to imagine the diameter of wires for this current. The starter in a car eats ≈100A and we all remember how thick the battery wires are!

I've used this table in many occasions to pick (minimum) wire-sizes:

http://www.powerstream.com/Wire_Size.htm

It also lists the maximum frequencies for the 100% skin depths, but one thing to keep in mind is that the wiring usually hasn't got only a single conductor, but multiple smaller ones (multiple strands/conductors per wire), so for the skin-effect, you'd need to take into account the amount and thickness of each conductor.

conductor_solidstranded.jpg

 

Also, the skin depth frequency is for AC (single sine-wave) frequencies, the square(ish) wave used with PWM is different, since square-wave is actually a sum of multiple (theoretically infinite amount of) harmonic sine-waves, and of course, as usual, there are many more factors in play (stray capacitance and inductance of the wiring and circuits, back-EMF, electrical noise, the complex magnetic and electrical field effects in the motor etc.)

fftImage.png

So I guess the safest bet would be to use thick cables made of multiple smaller conductors..?

Edited by esaj
2

Share this post


Link to post
Share on other sites
16 minutes ago, esaj said:

So I guess the safest bet would be to use thick cables made of multiple smaller conductors..?

Higher sine-waves are weaker than the first one... And the motor coils give an inductive load, so when we feed it with a squared voltage, the current will take some time to rise to its maximum and I suspect at this frequency it will look more like 1-st sine-wave :)

Due to thermal issues I would bet on 10-15 strands in a 5mm wire and each of them should be gilded. But the axis of the wheel is not wide enough for it.

So if I had a GW, I would never let the temperature go higher than 68°C (at this temp my Ninebot doesn't let me do anything else than to slow down and stop). At this stage the wires temperature can be even twice as high but the maximum for the isolation is 200°C which is written on it.

2

Share this post


Link to post
Share on other sites

Posted (edited)

I peeled back the shrink wrap of the wire connectors and compared them to the picture Linnea from Gotway posted. They appear similar  My connectors will be completely eliminated as I proceed with my modifications and the wires will be soldered together followed by aviation shrink tubing.

Edited by Rehab1
2

Share this post


Link to post
Share on other sites

Posted (edited)

28 minutes ago, Xima Lhotz said:

I think this has little to do with skineffekt and all to do with to small wire for the current (and heat). It might contribute a bit but its all about the amps.

 

I totally agree. Transitioning from a 14 awg wire initiating from the PCB down to a 16 awg wire coming from the motor is just asking for trouble. The 14 awg is rated at 200 degrees C but the 16 awg wire has no visible temperature rating.

Once I open up the metal housing allowing me direct access to the motor I am hoping there is room to increase the wire size.

@meepmeepmayer we will gets this figured out sooner or later:)

 

Edited by Rehab1
3

Share this post


Link to post
Share on other sites

Posted (edited)

12 minutes ago, Rehab1 said:

I totally agree. Transitioning from a 14 awg wire initiating from the PCB down to a 16 awg wire coming from the motor is just asking for trouble. The 14 awg is rated at 200 degrees C but the 16 awg wire has no visible temperature rating.

The important thing here is that 200 degrees is not the surrounding temp, its the temp of the conductor in the cable. And this is the maximum temp and should never be used for design.

@Rehab1 Its really fun looking at the dismantling of your wheel :) Do you have a photo of the engine cable markings? It would be fun to find the specs of that cable.

 

A single, silicon, 16 AWG cable, in free air, at 30 degrees C, with a current of 30A has a conductor temp of 200 degrees. (according to this specific table but its all about the same (silicon insulation with copper conductor)  http://catalog.connectronicscorp.com/Asset/WIREMAX-conductor-CURRENT--2-.pdf

Adding 3 cables, bundled, overheat alarm with surrounding temp of 70+C = Not fantastic.

Edited by Xima Lhotz
2

Share this post


Link to post
Share on other sites
14 minutes ago, Xima Lhotz said:

Rehab1 Its really fun looking at the dismantling of your wheel :) Do you have a photo of the engine cable markings? It would be fun to find the specs of that cable

No markings on the engine ( motor) wires.

I need to start my own thread as I move into further disassembly and modifications so I don't muddy the waters any further here. What stated out as an inquiry into @meepmeepmayer's issue has turned into a full blown autopsy.

 

3

Share this post


Link to post
Share on other sites

Vee's old "I plan to test"-topic has a ton of pictures of his mods, including replacing/adding the motor wiring with thicker ones:

But I think that at that point he also had custom-made his own "sleeve nut" or whatever it's called for the motor, as the original had broken or something, so the extra wiring might not fit with the original (plus that was an MSuper V2, the newer ones are probably different).

2

Share this post


Link to post
Share on other sites
1 hour ago, Rehab1 said:

I need to start my own thread 

Great idea

0

Share this post


Link to post
Share on other sites

@Rehab1 Just be careful not to make the insides of the motor (coils?) the weakest point, because if you ever stress the wheel enough to break that.... you're ******.

That's really how a wheel should be designed. Design your electronics so there's a clear weakest point, and monitor that.

offtopic: How big is the actual diameter of the motor? I was wondering how much "easier" (less current/voltage etc) and possibly more efficient (use of battery capacity) it would be if the motor was designed to utilize the full tire diameter.

1

Share this post


Link to post
Share on other sites
6 hours ago, Marty Backe said:

Great idea

Hey Marty,

i just wanted to write you a PM...

"Marty" kann not receive personal message....

Is your Inbox full? 

1

Share this post


Link to post
Share on other sites
46 minutes ago, KingSong69 said:

Hey Marty,

i just wanted to write you a PM...

"Marty" kann not receive personal message....

Is your Inbox full? 

Yeah, it was full - I deleled a bunch of messages

 

0

Share this post


Link to post
Share on other sites

yip...now it worked ;-)

0

Share this post


Link to post
Share on other sites
1 hour ago, meepmeepmayer said:

@Rehab1 Just be careful not to make the insides of the motor (coils?) the weakest point, because if you ever stress the wheel enough to break that.... you're ******.

That's really how a wheel should be designed. Design your electronics so there's a clear weakest point, and monitor that.

offtopic: How big is the actual diameter of the motor? I was wondering how much "easier" (less current/voltage etc) and possibly more efficient (use of battery capacity) it would be if the motor was designed to utilize the full tire diameter.

I will be careful but if something happens you will be one of the first to find out!:P The biggest issue will be feeding 3 larger AWG wires up through the axle. 

Here is a photo of the motor.

 

3

Share this post


Link to post
Share on other sites

Oh wow, just realized you opened the motor cover. Cool!

More in your topic:

 

1

Share this post


Link to post
Share on other sites
13 hours ago, esaj said:

Here's an old post of mine about the basics of 3-phase BLDC-motor drive, although there are probably better sources in the internet and people who know more about them in these forums too:

Your superbly written EUC Motor Drive post should be proudly positioned front and center under (your) the Electric Unicycle Terminology topic! I am so impressed with your knowledge!:thumbup:

 

2

Share this post


Link to post
Share on other sites
On 3/19/2017 at 3:23 PM, Marty Backe said:

That's why I was disappointed to learn that the Monster has two fans. I hope they don't break. I was riding my Monster in the mountains yesterday (low 25c's temperature) and the internal temperature climbed as high as 65c.  I have a feeling the Monster is not going to do so well when I start riding it in the mid-30's.

My ACM, with no fans, rarely gets in the 60's even when I'm riding at it's 33c outside.

Oh wow I had no idea your Monster got that warm.  If it gets that hot with two fans, damn.  I have never seen the temp on my Msuper out of the 40's but flat Florida helps me there.

1

Share this post


Link to post
Share on other sites
20 minutes ago, Duf said:

Oh wow I had no idea your Monster got that warm.  If it gets that hot with two fans, damn.  I have never seen the temp on my Msuper out of the 40's but flat Florida helps me there.

The fan's on the Monster are more or less useless and totally misdesigned. These  weak Standard  fans with small Diameter do nothing more than shifting  the warm air in the closed chamber a bit around ....

That is not only my opininon, one of the French sellers said their repair-specialists are loughing about  that fans and titled them useless as well..

2

Share this post


Link to post
Share on other sites
28 minutes ago, Duf said:

Oh wow I had no idea your Monster got that warm.  If it gets that hot with two fans, damn.  I have never seen the temp on my Msuper out of the 40's but flat Florida helps me there.

Yep, it definitely consistently runs hotter than my other wheels. What I'm curious about is whether it'll actually overheat, but I'll have to wait for the summer months to find out.

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now