Ninebot One Z : Z6-Z8-Z10

[mrelwood]

19 hours ago, RoberAce said:

 

That is the most fun looking riding I’ve yet to see on the Z10! Too bad I couldn’t hear anything you said. A recap on the tire pressure and other things you might’ve said would’ve been great.

[houseofjob]

@mrelwood might be mistaken, but I don't believe Chooch is on this forum, @RoberAce is just re-posting Chooch's video here

Edited June 29, 2018 by houseofjob

[mrelwood]

1 hour ago, houseofjob said:

@RoberAce is just re-posting Chooch's video here

Ah, sorry. Can’t keep up with names and faces (actually posture/behavior/gear, as faces are often covered)...

[RoberAce]

1 hour ago, mrelwood said:

Oh, lo siento. No se puede mantener el ritmo con nombres y caras (en realidad postura / comportamiento / engranaje, ya que las caras a menudo están cubiertas) ...

exactly, is not me, is Mr Colton E. Gregory

Edited June 29, 2018 by RoberAce

[Scatcat]

@houseofjob did a nice teardown video on YT:

The MOS looks tiny. Seems to be 15810 which I believe are TO-220 or TO-263, but I would love to get @esaj's input on those.
The markings seem to be:
15810
6KOBT VC
CHN 752

[RoberAce]

what do you think?

[winter]

 

Edited August 18, 2018 by nte

[esaj]

5 hours ago, Scatcat said:

The MOS looks tiny. Seems to be 15810 which I believe are TO-220 or TO-263, but I would love to get @esaj's input on those.
The markings seem to be:
15810
6KOBT VC
CHN 752

Based on quick googling, it's STH15810-2 from ST Microelectronics:  https://www.verical.com/datasheet/stmicroelectronics-fet-mosfet-sth15810-2-1812787.pdf

The casing's a surface-mount "H²PAK-2":

(Nevermind the markings on the packages above, it's just for general image of the package)

It sheds heat through the backplate that's connected to the board (that's also the drain, so they can be soldered directly to ground plane on low-side and motor phase-planes on high-side). The junction-to-case -thermal resistance is lowish at 0.6C/W (max), but the junction-to-PCB -thermal resistance is 35C/W (max) on a square inch FR4 with 2oz CU (70µm), which is a bit high, but the ground plane is likely large, no idea how thick. Don't know about the planes for the phases.

There seem to be twelve of those, so at least they share some load. Apparently the gates aren't tied directly together like with (at least earlier) Gotways, but have separate gate resistors (like R10 for Q2 and R9 for Q5) and turn-off speed up diodes (D1 and D4 for aforementioned mosfets), so the design seems a bit better, no ferrites to kill off any ringing, but I haven't seem them in any other design than the SBU/Firewheel.

R_DS(on) is 3.4-3.9 milliohms, which isn't superbly low but not bad either (a little lower than with the IRFB4110's in Gotways, about twice higher than the IRFB4368's used in KS16's, so they heat up more). Q13 & Q14 look like they're for the battery lines. On the other hand, the gate charges and rise/fall times are low, so they likely have smaller switching losses and can be turned on and off pretty fast?

U1 & U2 look like they could be for current measurement from the two phases. Gate drivers and the MCU are likely behind the board.

 

Edited June 29, 2018 by esaj

[novazeus]

1 hour ago, esaj said:

Based on quick googling, it's STH15810-2 from ST Microelectronics:  https://www.verical.com/datasheet/stmicroelectronics-fet-mosfet-sth15810-2-1812787.pdf

The casing's a surface-mount "H²PAK-2":

(Nevermind the markings on the packages above, it's just for general image of the package)

It sheds heat through the backplate that's connected to the board (that's also the drain, so they can be soldered directly to ground plane on low-side and motor phase-planes on high-side). The junction-to-case -thermal resistance is lowish at 0.6C/W (max), but the junction-to-PCB -thermal resistance is 35C/W (max) on a square inch FR4 with 2oz CU (70µm), which is a bit high, but the ground plane is likely large, no idea how thick. Don't know about the planes for the phases.

There seem to be twelve of those, so at least they share some load. Apparently the gates aren't tied directly together like with (at least earlier) Gotways, but have separate gate resistors (like R10 for Q2 and R9 for Q5) and turn-off speed up diodes (D1 and D4 for aforementioned mosfets), so the design seems a bit better, no ferrites to kill off any ringing, but I haven't seem them in any other design than the SBU/Firewheel.

R_DS(on) is 3.4-3.9 milliohms, which isn't superbly low but not bad either (a little lower than with the IRFB4110's in Gotways, about twice higher than the IRFB4368's used in KS16's, so they heat up more). Q13 & Q14 look like they're for the battery lines. On the other hand, the gate charges and rise/fall times are low, so they likely have smaller switching losses and can be turned on and off pretty fast?

U1 & U2 look like they could be for current measurement from the two phases. Gate drivers and the MCU are likely behind the board.

 

i need the cliff notes. is this good or bad?

[esaj]

9 minutes ago, novazeus said:

i need the cliff notes. is this good or bad?

Neither   It's just a description of what I see, and a little bit of comparison with what I know about the components used in Gotways & KS16S and general mosfet motor driver design. In reality, unless it's really bad from the get-go, you can't really say if it's "enough" without knowing the entire circuit, and even after that, testing (there's a lot of variables we don't even know about, like how much thermal resistance is there between the junctions and the ambients, does the load share equally between paired mosfets, how well the heat from the mainboard compartment flows off...). If the boards don't blow their mosfets, then it's... good enough?  

Edited June 29, 2018 by esaj

[novazeus]

2 minutes ago, esaj said:

Neither   It's just a description of what I see, and a little bit of comparison with what I know about the components used in Gotways & KS16S and general mosfet motor driver design. In reality, unless it's really bad from the get-go, you can't really say if it's "enough" without knowing the entire circuit, and even after that, testing. If the boards don't blow their mosfets, then it's... good enough?  

for me, it’s like a monkey looking at a watch, i’m clueless.

[Unventor]

13 minutes ago, novazeus said:

for me, it’s like a monkey looking at a watch, i’m clueless.

To me it seems to be all up in the air..I do not have a clue so...does it smell like bananas...does it taste like bananas...and can it play Crysis 6?

(To those not familiar with Crysis it was a benchmark game reference for a gaming pc back in the old days).

Nope I don't care..as long I do not have to tinker with the wheel every 2nd mile...(read gotway q/a Joke ?) and not having to bring a portable BBQ to make use of when wheel catches fire.

So does it ride? Does it feel solid and safe? And is it fun? But since Ninebot forgot about Europe...I might just as well forget about it. So back at looking at KS18L for my part...

Sorry Marty just had to Bing this to you attention @Marty Backe ??

Edited June 29, 2018 by Unventor
Note I have to..no....MUST tag Marty to this

[esaj]

29 minutes ago, novazeus said:

for me, it’s like a monkey looking at a watch, i’m clueless.

Yeah, it gets a bit deeper into electronics design and physics, but it's not really complicated... Still, I'd say it's not worth to spend time learning all of it, unless you have a personal or professional interest.

The thermal stuff is (relatively) easy to understand. You've got what is called "thermal resistance", usually given in C/W (Celsius per watt) or K/W (Kelvin per watt), which are basically the same thing (0 kelvin = absolute zero temperature, which is about -273.xx celsius, but the "change" of 1 kelvin is the same as 1 celsius). When you know (or can calculate) the power dissipation in the part, and know the thermal resistances, you can calculate how hot the part runs. There are usually multiple thermal resistances involved, like junction-to-case, case-to-sink and sink-to-ambient. You just sum these up to get the total thermal resistance.

So, let's say we'd have a mosfet with 0.3C/W thermal resistance from junction to case, 0.5C/W for case-to-sink and 5C/W from heatsink-to-ambient. That would total 0.3 + 0.5 + 5C/W = 5.8C/W. Now, if we'd dissipate 5W on the mosfet, the junction temperature (which is usually limited to about 175C, above which it gets destroyed) would be:

Ambient temperature (the surrounding air basically) + 5W * 5.8C/W = 29C above ambient. If the ambient temperature was 25C, the junction would be 29C above that, so 25+29C = 54C  (25C is usually used as "room temperature" in the calculations, but actually most people keep their room temperature around 21C). 54C is still well within the safe range, so no problem there. But in a closed mainboard compartment, if the heat is "trapped" inside, the ambient will start to rise, and even that could become a problem (of course, then the ambient would already be about 146C, which is HOT). I'm too lazy to change those to fahrenheit...

 

As a longer example, and since here we don't know the values for the PCB and ambient for the wheel, I'll just be lazy again and copy paste the calculations I've used for my electronic load (a device that purposefully loses most/all of the power in the mosfets) from another thread in the off-topic:

When mosfets are used as switches, like in our wheels, they are just turned "on" (fully conducting) and "off" (not conducting), with as fast change between these states as possible. Generally as small as possible internal resistance is wanted, so that they don't overheat due to the power loss (heat) caused by the that internal resistance when current flows through. In this case however, we want to do the exact opposite: use the mosfet to cause a power loss, loading the DUT with a set current draw. This means that majority of the voltage from the DUT is dropped over the mosfet. As an example, 10A running through an internal resistance of 20 milliohms (btw, the brand-wheels usually use mosfets with internal resistances in single digits in milliohms) causes a power loss of:

R = 20mOhm 

I = 10A

P = U*I  (Power equals voltage times current)

U = R*I  (Voltage equals resistance times current)

We could first calculate the voltage drop and then the power, but as a short-hand, placing   U = R*I   to   P = U*I   yields   P = R*I²    =>

P = 0.02ohm * (10A)² = 2W

Not that much really, 2 watts. Of course this doesn't take into account the momentary higher power loss during turn-off and turn-on in the wheels, but that's irrelevant to the electronic load. 

When the voltage drop over the mosfet becomes bigger, the wattage shoots up fast. Let's say we have a 12V power supply under test, and we draw 10A from it, dissipating the power as heat in mosfet. Some part of that 12V will be dropped over the measurement resistor in the constant current sink, in case of a 50 milliohm measurement resistor, using the U = R*I -equation, 0.5V will be dropped over the resistor. That leaves 11.5V drop over the mosfet. How much power is being dissipated in the mosfet?

P = U*I   =>   P = 11.5V * 10A  = 115W

Ok, that's a different ballgame now. 

Originally, I was looking for 200V TO-247 -encased mosfets for this, but the model I had earlier picked was out of stock. Instead, I went with 100V / 57A (continuous) -rated IRFP3710PbF ( https://www.infineon.com/dgdl/irfp3710pbf.pdf?fileId=5546d462533600a401535628fd1a1ffa ). I was mostly looking at the casing, maximum current and voltage, and price when picking these. They've got an internal resistance of 25 milliohms, which is of no concern, since the op-amp shouldn't fully "open" the mosfet anyway, so the "resistance" of the mosfet is higher in use. The only case where it's fully conducting is if the DUT cannot produce enough current to cause any limiting to occur, in which case the internal resistance is already meaningless.

Now, the datasheet of that mosfet says that the maximum power dissipation is 200W. Like discussed earlier here in the forums (and maybe in this thread, I don't remember ), this is the theoretical maximum which the device could withstand, in practice, other considerations usually limit you to a much lower value.

The datasheet lists the thermal resistances as 0.75 C/W for Junction-to-Case (maximum), 0.5 C/W for Case-to-Sink (typical) and 62 C/W for Junction-to-Ambient (maximum). The operating temperature for the junction is -55 to +175 C. Since I'm using a heatsink, the relevant numbers are the Junction-to-Case and Case-to-Sink. Junction-to-Ambient -value is used for non-heatsinked device in free air. If not using a heatsink, and dissipating 115W on the device, the junction temperature would be

115W * 62 C/W = 7130C above ambient

That's one dead mosfet there, it would melt completely far before reaching that temperature. When using a heatsink, the total thermal resistance would be

Junction-to-Case + Case-to-Sink + (possible thermal paste resistance, but the datasheet in this case states that the Case-to-Sink is for "greased flat surface", ie. with thermal paste applied ) + Sink-to-Ambient

Using the values from the datasheet and the "worst case" 5.5C/W -thermal resistance from the heatsink (if using only a 4-5cm long piece of the block), that would be

0.75 C/W + 0.5 C/W + 5.5C/W  = 6.75 C/W

For 115W, that would mean   115W * 6.75 C/W = 776.25C above ambient

Still far too high, as the device will likely fail if the junction goes above 175C, and with a typical ambient room temperature around 25C, that means the upper limit is about 150C for the thermal resistances.

Using a longer heatsink block with 2.5C/W for the sink-to-ambient, we get

0.75 C/W + 0.5 C/W + 2.5C/W  = 3.75 C/W

How about now? 115W * 3.75 C/W = 431.25C

Still way too high. So, with this cooling, it's impossible to keep the device cool enough while dissipating that much power. In fact, it would require a thermal resistance of about 1.3 C/W to be able to dissipate 115W with 25C ambient temperature. Event then, it'd be running right at the limit, and if the ambient temperature around the heatsink went up (if it were enclosed for example, and the air surrounding the heatsink would linger around going up in temperature), it could still fail.

There are a couple of solutions, either limit the power dissipation to lower values or increase cooling, either by using better or larger heatsinks, or adding fans. I plan on using the cooling block I have now, and to use a somewhat conservative value of 6C/W for the thermal resistance. For ambient temperature, I use 40C (conservative value, likely it will be lower but having some safety buffer in case the ambient temperature starts to raise), leaving me with 175C - 40C = 135C buffer. With these values, the maximum wattage I could dissipate would be

135C / (6C/W) = 22.5W

So a far cry from the theoretical absolute maximum of 200W for the device (to my understanding, the maximum wattage in the datasheets is a theoretical value above which no amount of cooling will be enough to prevent the device from getting destroyed). But it's somewhat of a conservative estimate, as the actual thermal resistance is likely lower (using longer heatsink blocks per device) and I could still add fan or fans blowing on the heatsink.

Edited June 29, 2018 by esaj

[Shad0z]

16 minutes ago, esaj said:

Yeah, it gets a bit deeper into electronics design and physics, but it's not really complicated...

O_o

[Mark Lee]

17 minutes ago, esaj said:

Yeah, it gets a bit deeper into electronics design and physics, but it's not really complicated... Still, I'd say it's not worth to spend time learning all of it, unless you have a personal or professional interest.

The thermal stuff is (relatively) easy to understand. You've got what is called "thermal resistance", usually given in C/W (Celsius per watt) or K/W (Kelvin per watt), which are basically the same thing (0 kelvin = absolute zero temperature, which is about 273.xx celsius, but the "change" of 1 kelvin is the same as 1 celsius). When you know (or can calculate) the power dissipation in the part, and know the thermal resistances, you can calculate how hot the part runs. There are usually multiple thermal resistances involved, like junction-to-case, case-to-sink and sink-to-ambient. You just sum these up to get the total thermal resistance.

So, let's say we'd have a mosfet with 0.3C/W thermal resistance from junction to case, 0.5C/W for case-to-sink and 5C/W from heatsink-to-ambient. That would total 0.3 + 0.5 + 5C/W = 5.8C/W. Now, if we'd dissipate 5W on the mosfet, the junction temperature (which is usually limited to about 175C, above which it gets destroyed) would be:

Ambient temperature (the surrounding air basically) + 5W * 5.8C/W = 29C above ambient. If the ambient temperature was 25C, the junction would be 29C above that, so 25+29C = 54C  (25C is usually used as "room temperature" in the calculations, but actually most people keep their room temperature around 21C). 54C is still well within the safe range, so no problem there. But in a closed mainboard compartment, if the heat is "trapped" inside, the ambient will start to rise, and even that could become a problem (of course, then the ambient would already be about 146C, which is HOT). I'm too lazy to change those to fahrenheit...

 

As a longer example, and since here we don't know the values for the PCB and ambient for the wheel, I'll just be lazy again and copy paste the calculations I've used for my electronic load (a device that purposefully loses most/all of the power in the mosfets) from another thread in the off-topic:

When mosfets are used as switches, like in our wheels, they are just turned "on" (fully conducting) and "off" (not conducting), with as fast change between these states as possible. Generally as small as possible internal resistance is wanted, so that they don't overheat due to the power loss (heat) caused by the that internal resistance when current flows through. In this case however, we want to do the exact opposite: use the mosfet to cause a power loss, loading the DUT with a set current draw. This means that majority of the voltage from the DUT is dropped over the mosfet. As an example, 10A running through an internal resistance of 20 milliohms (btw, the brand-wheels usually use mosfets with internal resistances in single digits in milliohms) causes a power loss of:

R = 20mOhm 

I = 10A

P = U*I  (Power equals voltage times current)

U = R*I  (Voltage equals resistance times current)

We could first calculate the voltage drop and then the power, but as a short-hand, placing   U = R*I   to   P = U*I   yields   P = R*I²    =>

P = 0.02ohm * (10A)² = 2W

Not that much really, 2 watts. Of course this doesn't take into account the momentary higher power loss during turn-off and turn-on in the wheels, but that's irrelevant to the electronic load. 

When the voltage drop over the mosfet becomes bigger, the wattage shoots up fast. Let's say we have a 12V power supply under test, and we draw 10A from it, dissipating the power as heat in mosfet. Some part of that 12V will be dropped over the measurement resistor in the constant current sink, in case of a 50 milliohm measurement resistor, using the U = R*I -equation, 0.5V will be dropped over the resistor. That leaves 11.5V drop over the mosfet. How much power is being dissipated in the mosfet?

P = U*I   =>   P = 11.5V * 10A  = 115W

Ok, that's a different ballgame now. 

Originally, I was looking for 200V TO-247 -encased mosfets for this, but the model I had earlier picked was out of stock. Instead, I went with 100V / 57A (continuous) -rated IRFP3710PbF ( https://www.infineon.com/dgdl/irfp3710pbf.pdf?fileId=5546d462533600a401535628fd1a1ffa ). I was mostly looking at the casing, maximum current and voltage, and price when picking these. They've got an internal resistance of 25 milliohms, which is of no concern, since the op-amp shouldn't fully "open" the mosfet anyway, so the "resistance" of the mosfet is higher in use. The only case where it's fully conducting is if the DUT cannot produce enough current to cause any limiting to occur, in which case the internal resistance is already meaningless.

Now, the datasheet of that mosfet says that the maximum power dissipation is 200W. Like discussed earlier here in the forums (and maybe in this thread, I don't remember ), this is the theoretical maximum which the device could withstand, in practice, other considerations usually limit you to a much lower value.

The datasheet lists the thermal resistances as 0.75 C/W for Junction-to-Case (maximum), 0.5 C/W for Case-to-Sink (typical) and 62 C/W for Junction-to-Ambient (maximum). The operating temperature for the junction is -55 to +175 C. Since I'm using a heatsink, the relevant numbers are the Junction-to-Case and Case-to-Sink. Junction-to-Ambient -value is used for non-heatsinked device in free air. If not using a heatsink, and dissipating 115W on the device, the junction temperature would be

115W * 62 C/W = 7130C above ambient

That's one dead mosfet there, it would melt completely far before reaching that temperature. When using a heatsink, the total thermal resistance would be

Junction-to-Case + Case-to-Sink + (possible thermal paste resistance, but the datasheet in this case states that the Case-to-Sink is for "greased flat surface", ie. with thermal paste applied ) + Sink-to-Ambient

Using the values from the datasheet and the "worst case" 5.5C/W -thermal resistance from the heatsink (if using only a 4-5cm long piece of the block), that would be

0.75 C/W + 0.5 C/W + 5.5C/W  = 6.75 C/W

For 115W, that would mean   115W * 6.75 C/W = 776.25C above ambient

Still far too high, as the device will likely fail if the junction goes above 175C, and with a typical ambient room temperature around 25C, that means the upper limit is about 150C for the thermal resistances.

Using a longer heatsink block with 2.5C/W for the sink-to-ambient, we get

0.75 C/W + 0.5 C/W + 2.5C/W  = 3.75 C/W

How about now? 115W * 3.75 C/W = 431.25C

Still way too high. So, with this cooling, it's impossible to keep the device cool enough while dissipating that much power. In fact, it would require a thermal resistance of about 1.3 C/W to be able to dissipate 115W with 25C ambient temperature. Event then, it'd be running right at the limit, and if the ambient temperature around the heatsink went up (if it were enclosed for example, and the air surrounding the heatsink would linger around going up in temperature), it could still fail.

There are a couple of solutions, either limit the power dissipation to lower values or increase cooling, either by using better or larger heatsinks, or adding fans. I plan on using the cooling block I have now, and to use a somewhat conservative value of 6C/W for the thermal resistance. For ambient temperature, I use 40C (conservative value, likely it will be lower but having some safety buffer in case the ambient temperature starts to raise), leaving me with 175C - 40C = 135C buffer. With these values, the maximum wattage I could dissipate would be

135C / (6C/W) = 22.5W

So a far cry from the theoretical absolute maximum of 200W for the device (to my understanding, the maximum wattage in the datasheets is a theoretical value above which no amount of cooling will be enough to prevent the device from getting destroyed). But it's somewhat of a conservative estimate, as the actual thermal resistance is likely lower (using longer heatsink blocks per device) and I could still add fan or fans blowing on the heatsink.

Thanks @esaj I read the whole essay, now I'm going to take couple of Aspirin for my headache...

[esaj]

5 minutes ago, Mark Lee said:

Thanks @esaj I read the whole essay, now I'm going to take couple of Aspirin for my headache...

Headache you say?   

That small "basics of power dissipation/thermal calculations"-part is extracted from this:

And that's hardly the longest post in the thread. Then there's the 66-page report I did on the robot design for an university of applied sciences -course project (which I attended as a non-student and just for fun)... Well, ok, the other guy wrote maybe 15 pages of that 

 

Edited June 29, 2018 by esaj

[esaj]

Split some off-topic posts here: 

 

Not of interest to anyone who want to know about Ninebot Z

[winter]

 

Edited August 18, 2018 by nte

[Vikas]

Holy smokes!!!!! this esaj is a frikkin genius?

 

[esaj]

25 minutes ago, Vikas said:

Holy smokes!!!!! this esaj is a frikkin genius?

Hardly, there are real electronics engineers in these forums that would run laps around me and could likely point out a gazillion mistakes in my logic and designs     But this is getting really off-topic, so let's stick to the Ninebot Z's.

[winter]

 

Edited August 18, 2018 by nte

[Mark Lee]

More I learn, I can't help but realize how little I truly know.  Namaste...

[fryman]

So, the theory that a higher voltage wheel (84 vs 51.8 Z10) is better; is not true?

[mrelwood]

13 minutes ago, fryman said:

So, the theory that a higher voltage wheel (84 vs 51.8 Z10) is better; is not true?

Nothing is that simple. Voltage is just one part of the equation. It is easier and cheaper to make a high powered wheel operate at a higher voltage, but saying one is better than the other is a bit like saying that blue is better than red.

 

(It’s not. Red is better. )

[Harold Farrenkopf]

2 hours ago, mrelwood said:

Nothing is that simple. Voltage is just one part of the equation. It is easier and cheaper to make a high powered wheel operate at a higher voltage, but saying one is better than the other is a bit like saying that blue is better than red.

 

(It’s not. Red is better. )

Wrong, blue has more energy than red