The Gotway Gods Destroyed My ACM

[lizardmech]

At low speed the motor can convert the higher battery voltage into low voltage with much higher currents. If the battery can supply 80V 40A it will easily be able to reach 100A+ on the phase wires. It's hard to know how much current is being used without knowing what the software settings are.

[Pingouin]

Hi Marty,

Ouch I feel very sorry for you again, thankfully not as dramatic as the last time ! This Gotway wire issue is becoming a pest, I hope they'll think this through, for now I will no longer try climbing moutains with my ACM (I reduced my moutain ride frequency with my ACM because I was always afraid this might happen) & Monster, it's a shame because the older Gotways do it just fine (MCM3 & MCM4), I've ridden for hourw up very steep moutain climbs (so steep I couldn't even ride anymore) with no issues...I think this might be due to the high power motor that pumps so much energy. There should be a warning beep for extreme heat inside our EUC, this would be a minimum.

Thanks again for sharing with us your adventures !

[Maximus]

Sorry about your fall @Marty Backe!

As I wait for my new ACM to arrive, I can't help but wonder what settings to pay attention to while riding up hills...I know that temperature and current are displayed in the Darkness Bot app.  I'd hate to think that I have to walk my new wheel up my street and driveway when I've been powering up these with ease on my V8...after all, the reputation of the ACM was that it was a "beast" on hills...right?  Now I'm lead to believe that I may want to consider walking it up?

If anyone has a temperature or current threshold that I should look for on the app, at least I could have a gauge for when things are approaching a problem zone...

Thanks again for bringing this topic to the group @Marty Backe!

[Marty Backe]

16 minutes ago, Maximus said:

Sorry about your fall @Marty Backe!

As I wait for my new ACM to arrive, I can't help but wonder what settings to pay attention to while riding up hills...I know that temperature and current are displayed in the Darkness Bot app.  I'd hate to think that I have to walk my new wheel up my street and driveway when I've been powering up these with ease on my V8...after all, the reputation of the ACM was that it was a "beast" on hills...right?  Now I'm lead to believe that I may want to consider walking it up?

If anyone has a temperature or current threshold that I should look for on the app, at least I could have a gauge for when things are approaching a problem zone...

Thanks again for bringing this topic to the group @Marty Backe!

Thanks 

I really do think this is only an issue with very steep hills. In a previous comment I posted the Google Earth track which includes the elevation profile. This happened when I was climbing a slope approaching 30% (~17 degrees). Is that your street or driveway 

I still have faith in the Gotway wheels to tackle hills without worrying about this kind of a failure.

[Marty Backe]

5 hours ago, KingSong69 said:

Isn't this inside the specification of the ACM-30%???

;-)

<snip>

Hey, let's not exaggerate things. It was only 27%  

[Maximus]

1 minute ago, Marty Backe said:

This happened when I was climbing a slope approaching 30% (~17 degrees). Is that your street or driveway

Great question.  I doubt the road is, but maybe the driveway...?  I'll have to try and figure out the grade somehow.  How did you get that information from Google Earth?

[Marty Backe]

10 minutes ago, Maximus said:

Great question.  I doubt the road is, but maybe the driveway...?  I'll have to try and figure out the grade somehow.  How did you get that information from Google Earth?

If you have Google Earth installed (why wouldn't you ) you can load my track. There is a menu item that will display the elevation profile for the entire track which shows the slope at any given point. It's very cool.

[Maximus]

2 minutes ago, Marty Backe said:

If you have Google Earth installed (why wouldn't you ) you can load my track. There is a menu item that will display the elevation profile for the entire track which shows the slope at any given point. It's very cool.

So when you are riding what is recording this "track" is it from the Gotway app or do you have Google Earth running while you ride or is there something else that records this track to eventually overlay onto Google Earth?

[Marty Backe]

Just now, Maximus said:

So when you are riding what is recording this "track" is it from the Gotway app or do you have Google Earth running while you ride or is there something else that records this track to eventually overlay onto Google Earth?

I carry a Garmin 60CS which records my rides. But if you have a phone you can do the same thing. If you get one of the riding apps (for runners or bicyclists) they will save your track and you can export the data into Google Earth. It's fun to record your rides, so give it shot.

[Maximus]

Just now, Marty Backe said:

I carry a Garmin 60CS which records my rides. But if you have a phone you can do the same thing. If you get one of the riding apps (for runners or bicyclists) they will save your track and you can export the data into Google Earth. It's fun to record your rides, so give it shot.

I use Cyclemeter, but have never tried exporting...I'll have to check it out, thanks again!

[Rehab1]

10 hours ago, Marty Backe said:

No, @Jason McNeil didn't get into town until today. I still might meet up with him later in the week, but one way or another I should have a new MSuper by the weekend. Until then I'm down to only one Gotway wheel (my Monster) 

Check to see if @Jason McNeil has any ACM plus control boards. If not I have a spare CB with all of the updates. Of course given GW's ongoing saga this 4 week old board may already be obsolete!

[Duf]

Very sorry to heard about the failure and subsequent internal findings.  It would make me nervous to use that particular wheel for any remotely strenuous riding unless you replace it's entire heart - motor, board, and wiring just because you don't know what other damage went down.  I know you had to be bummed out that it finally happened to you.

That hill looked incredibly steep.  I'm surprised it got as far as it did.

[DaveThomasPilot]

3 hours ago, Chriull said:

That's something imho noone really knows by now... or happened to calculate and design properly... 

The motor does not really "need battery power". 

The torque of the motor is proportional to the current. The "forward force" is proportional to the torque. The motor power is force time speed.

So there is fortionately no feedback loop with the battery voltage and battery power.

Just max speed is limited by lower battery voltage (due to high currents).

They could introduce line circuit breakers as used in our homes to secure the wires...

It's pretty simple--for a given power output, the current required is inversely proportional to the voltage.  So, yes, the lower the battery voltage (or increased voltage drop through series resistance) the more current is drawn. 

This is true for all electric motors.  That's why 240 volts is preferred for motors instead of 120 volts.  It's why higher voltage is always better for driving a motor (it has to be designed for it) than lower voltages.

Power = Volts * Amps.   Constant power, lower voltage requires more amps.

 

[Marty Backe]

22 minutes ago, Rehab1 said:

Check to see if @Jason McNeil has any ACM plus control boards. If not I have a spare CB with all of the updates. Of course given GW's ongoing saga this 4 week old board may already be obsolete!

I bought this ACM from Ian. I'm waiting to hear back from him. I'll get the parts from somewhere.

I actually thought of you and your spare board for a bit  Figured you might be willing to sell it to me. But I'm going through the proper channels right now. Ian just asked me for my motor code, so we'll see where that goes.

Very funny, but you're correct. That 4 week old board of yours is sooo yesterday 

[DaveThomasPilot]

I guess I would (naively?) expect that a wheel would be run under a load and at a speed for an advertised maximum power specification and at an elevated ambient temperature  Then, component case temperatures would be measured to make the chip junction temperatures don't exceed their maximum. 

Wire ampacity is also easily calculated.

If this isn't part of the design process, I'm not sure that the maximum power rating means.  Probably just the maximum output power the motor can deliver wrt what drives it.

[Chriull]

2 hours ago, lizardmech said:

At low speed the motor can convert the higher battery voltage into low voltage with much higher currents. If the battery can supply 80V 40A it will easily be able to reach 100A+ on the phase wires. It's hard to know how much current is being used without knowing what the software settings are.

Interesting - i once already got to the point, that the h-bridges and the motor coils somehow should/could work like a transformer (http://forum.electricunicycle.org/topic/7371-a-brief-word-on-batteries/?do=findComment&comment=97090)... But all the implications with phase shifts, coils , complex numbers, blind current, etc gives me headaches...

But since at the points in time the two mosfets connect a circuit over 2 phases of the motor with this both phases having a phase shift of 120° it starts out to get "spooky" - in combination of the average voltage at the motor has to be in a "small" range above the back-emf, so that just some "controlled" current is flowing while at the battery just some "normal" voltage sag is happening and no (real amount of) power is lost, i start getting lost...

@lizardmech- do you have links to sites with good explanations of what's exactly happening in regard to this topic?

Could/?should? be that my above statement/conclusion that EUCs at low speeds are inefficient (http://forum.electricunicycle.org/topic/7520-the-gotway-gods-destroyed-my-acm/?do=findComment&comment=99778) is just wrong and the high currents at the motor cables comes from this transformation: Ubatt 60V -> a little bit more than back emf, lets say 10V, so the current gets transformed up by the factor of 6. So with this example of 800W being 13A at the battery side this would result in a current of 78A at the motor side. And here the question how much is the current in the seperate coils, in the motor cables, how are the phase shifts, where flows how much blind current... But would be a nice explanation of the cable probs...
And a relativization of the ongoing opinion that higher battery voltage results in lower motor currents...
 

18 minutes ago, DaveThomasPilot said:

It's pretty simple

That's the big question....
... i am looking forward to @lizardmech's answer ...

[Marty Backe]

20 minutes ago, Duf said:

Very sorry to heard about the failure and subsequent internal findings.  It would make me nervous to use that particular wheel for any remotely strenuous riding unless you replace it's entire heart - motor, board, and wiring just because you don't know what other damage went down.  I know you had to be bummed out that it finally happened to you.

That hill looked incredibly steep.  I'm surprised it got as far as it did.

Thanks Duf. It's a disappointment for sure. I'm communicating with Ian now. I may get a new motor too. You living in flatland () should give you peace of mind.

[meepmeepmayer]

3 hours ago, Chriull said:

So this brought me to my conclusion "Seems like slow EUC driving (at least uphill) beeing very inefficient... ;("

I've noticed that too, sometimes going a bit faster produces a much lower current than going slow. Like 40A slow vs 25A bit faster. But the margins are very thin, a little more faster and you get even higher current.

[Duf]

3 minutes ago, Marty Backe said:

Thanks Duf. It's a disappointment for sure. I'm communicating with Ian now. I may get a new motor too. You living in flatland () should give you peace of mind.

Yep flat is good.  My only other thoughts on the failure beyond the obvious things you mentioned about the under-engineering of the cables is the lack of adequate monitoring by the wheel itself to not allow it to continue to run in such hot circumstances.  If a wheel is getting hot enough to melt wire there should be some mechanism in place that shuts it down before catastrophic heat damage can occur.  I think you have described your 14C doing exactly that. (shut down when it gets too hot)  Why Gotway would not be able to put at least a reasonable amount of buffer in place to prevent this scenario is baffling.

[DaveThomasPilot]

Ok, I was trying to keep it simple.  These motors are actually driven by multiple phases and aren't DC.  But, the same principals apply.  For a given output power, you need at least as much input power.  Higher input oltage means less current (and vice versa).

There are additional inefficiencies  due to switching power losses in the MOSFETs that could become significant relative to total power when you are going slow.  So, when measured as a percentage of output power, the wheel may be less efficient going very slow.

However, I'd think the main source of wasted power (power not used to turn the wheel and what causes heat and temperature rise) would be the "I squared R" losses in the motor windings. 

Resistive power dissipation is proportional to the square of the current.  So, at a give power output if the voltage is 1/2, the current is double, but the power dissipation is 4X!

[Marty Backe]

7 minutes ago, Duf said:

Yep flat is good.  My only other thoughts on the failure beyond the obvious things you mentioned about the under-engineering of the cables is the lack of adequate monitoring by the wheel itself to not allow it to continue to run in such hot circumstances.  If a wheel is getting hot enough to melt wire there should be some mechanism in place that shuts it down before catastrophic heat damage can occur.  I think you have described your 14C doing exactly that. (shut down when it gets too hot)  Why Gotway would not be able to put at least a reasonable amount of buffer in place to prevent this scenario is baffling.

Andy's Monster did tilt-back from overheat. And the ACM will too. But that's based on the temperature of the control board. They would have to have temperature monitors on the cabling. The best solution is to design a system that can't pass enough current to melt the insulation. Either use insulation that won't melt or use heavier gauge wires. Someday Gotway will probably get it right. They've only been making wheels for a few years 

[Duf]

Just now, Marty Backe said:

Andy's Monster did tilt-back from overheat. And the ACM will too. But that's based on the temperature of the control board. They would have to have temperature monitors on the cabling. The best solution is to design a system that can't pass enough current to melt the insulation. Either use insulation that won't melt or use heavier gauge wires. Someday Gotway will probably get it right. They've only been making wheels for a few years 

Yep I saw Andy's tilt back.  I assume you didn't have the Gotway app running so you don't know what the temp readings were when it died? I have a feeling they were way in the red.

[DaveThomasPilot]

But since at the points in time the two mosfets connect a circuit over 2 phases of the motor with this both phases having a phase shift of 120° it starts out to get "spooky" - in combination of the average voltage at the motor has to be in a "small" range above the back-emf, so that just some "controlled" current is flowing while at the battery just some "normal" voltage sag is happening and no (real amount of) power is lost, i start getting lost...

You don't really need to understand the specifics of how the motor driver works, back emf, etc to know that lower input voltage means higher current. 

Just draw a black box with an input voltage and input current.  Input power equals input current * input voltage.  So, to deliver the minimum power at a lower voltage, higher input current is required.

Output power cannot exceed input power, (if the wheel is driving a load and not being driven).  The ratio of output power divided by input power is efficiency.  Since the windings of the motor have resistance, they dissipate power and cause parastic voltage drops.  Pick any efficiency as an example and still, lower voltage means higher input current.

 

 

[lizardmech]

5 minutes ago, Chriull said:

... i am looking forward to @lizardmech's answer ...

They effectively work as a bidirectional buck/boost converter. When the motor runs it acts as a buck converter converting higher voltage into low voltage with more current. When braking it becomes a boost converter, converting the low voltage BEMF into a high enough voltage to charge the battery.

As to more voltage reducing current it depends on motor variables, if you do not change the motor windings increasing voltage will not reduce the amount of current needed to produce enough torque, the top speed of the motor will increase proportionately. If you rewind the motor with more turns you can achieve more torque with less current. There's also one other thing to be aware of, the stator iron laminations can only cope with a fixed amount of flux, adjusting motor turns and voltage will only change how much current is needed to reach that limit. This is where it can cause very low efficiency, if the controller allows currents beyond the saturation limits the amount of torque gained in comparison to the increased current. If the motor is near saturation 50% more current may only result in an extra 10% torque. 

[Marty Backe]

6 minutes ago, Duf said:

Yep I saw Andy's tilt back.  I assume you didn't have the Gotway app running so you don't know what the temp readings were when it died? I have a feeling they were way in the red.

The app was running but I was looking at the temps. I'm sure you're right that the ACM was running hot, just not hot enough to kick in the tilt-back. It would be nice if you could adjust the temperature where tilt-back kicks in. Then a person could choose to only run their wheels at cooler temperatures. That would have saved me.