what happens when you overvolt?

[parajared]

I am curious about what happens when you overvolt on two levels:
1) to your hub: how much voltage before you get enough voltage to jump through the insulation to the other wires.
2)to your fets:
I have heard two contrasting views on this:
----1. If you exceed 100v on a 4110 fet it will blow
----2. You may dump as many volts as you want into your fets so long as you don't exceed x amount of watts (ie.. 3000 watts on a 12 fet and 5000 on a 18 fet)

Which one is right, how much insulation does one need per x voltage?

 

[Pure]

1, Heat is your main concern. Over volt enough and your motor will cook itself long before you need to worry about voltage jumping insulated wires.

2, Pretty sure fets are voltage limited, but pump enough current and they will still fry.

 

[amberwolf]

Motor: you'd have to know what class insulation was used on the windings.

FETs: Check the spec sheet. Max ratings are just that--the max rating that they *guarantee* they will still work at. They might still work at a thousand times that, though it's very unlikely. Might also fail at 0.00000001V above that, but also highly unlikely. No way to know where they will fail until they do.

 

[Jeremy Harris]

Motor heating is primarily from current, so increasing the voltage but keeping the current the same means the motor gets very little hotter, if at all. Increase the current and the motor will get hotter.

The only effect voltage has on motor heating is from the slight increase in frictional and iron losses when running at higher rpm, and these are usually fairly small for most hub motors.

Increasing the voltage may exceed the maximum ratings of components in the controller - you need to check that the FETs, commutation capacitors and voltage regulators inside the controller are OK for a higher voltage.

Increasing the voltage increases the maximum motor rpm. This may or may not make the bike faster, depending on whether it's already current limiting at maximum speed.

 

[dogman dan]

Yes, but how many of us lower the amps when we increase the volts to keep the watts the same? Not many, as seen by the number of people that have ridden 5 min too long when jumping to 72v 40 amps, which often was increasing both volts and amps, tripling the watts. Fun though. 8) Even melting one down is fun in a perverted way.

I'll generalize now, using the 9 continent 2807 motor as an example. It's designed with the idea that you will run it on a bike with 36v and 20 amps. You can still melt one at that watt level if you stall it hard enough, but in my road tests I never could make it actually melt on paved roads with max grades of 10%. Max speed is about 23 mph. 26" wheel btw.

Same motor but now running on 72v 20 amps. Max speed is now about 30- 35 mph. I've never melted a 9c motor with this wattage either, but I have not tested this setup as extensively. Never took it to Emory pass, to ride 10 miles of 8-10% grade continuous and find out if it would melt. Riding around closer to the house, I've never seen one overheat with 72v 20 amps.

Same motor now running 72v 40 amps. Really perky now, and able to just touch 40 mph before the battery voltage drops a few v. But a long ride, say 30 min can get a motor dangerously hot. I've melted one with a 40 min ride. the solder on the phase wires connecting to the windings melted and the motor stopped. Didn't melt the winding, though it sure is black now. Motor still runs after repair. I have also toasted hall sensors at this power level, and then replaced them on the same motor. Toasting the halls happened after a 30 min ride.

Same motor at 90v 40amps. 47mph possible, but 43mph most of the ride. The motor gets very hot very fast. Didn't finish a race, and on mile 11 burst into flames, having a temp reading of 450F inside. The flames was the string inside that ties the windings in place combusting. That motor now is burnt, windings shorted, the varnish on the copper wire melted and shorting.

So what happened? As I undersand it, at some point the copper in the motor just can't use more current. It's maxed out. From then on, more current just makes heat, and at 90v 40 amps, clearly a LOT of heat. Then the motor melts. I would guess this point is somewhere between 1500w and 3000w, based on how much hotter the motor gets if you give it up to 3000w. In use of course, the motor doesn't draw 3000w continuous. But enough 2500- 3000w spikes can do the trick.

Because you keep seeing more speed as you increase the wattage, clearly the motor gets to use some watts above 1500w. But my guess is that the efficiency gets worse and worse. Once you have 1000w going into heat, that's just like an electric space heater, and it warms up quite fast. Too fast for holes in the hub cover to help you, except to let the smoke out.

 

[Jeremy Harris]

Yes, but how many of us lower the amps when we increase the volts to keep the watts the same? Not many, as seen by the number of people that have ridden 5 min too long when jumping to 72v 40 amps, which often was increasing both volts and amps, tripling the watts. Fun though. 8) Even melting one down is fun in a perverted way.

I'll generalize now, using the 9 continent 2807 motor as an example. It's designed with the idea that you will run it on a bike with 36v and 20 amps. You can still melt one at that watt level if you stall it hard enough, but in my road tests I never could make it actually melt on paved roads with max grades of 10%. Max speed is about 23 mph. 26" wheel btw.

Same motor but now running on 72v 20 amps. Max speed is now about 30- 35 mph. I've never melted a 9c motor with this wattage either, but I have not tested this setup as extensively. Never took it to Emory pass, to ride 10 miles of 8-10% grade continuous and find out if it would melt. Riding around closer to the house, I've never seen one overheat with 72v 20 amps.

Same motor now running 72v 40 amps. Really perky now, and able to just touch 40 mph before the battery voltage drops a few v. But a long ride, say 30 min can get a motor dangerously hot. I've melted one with a 40 min ride. the solder on the phase wires connecting to the windings melted and the motor stopped. Didn't melt the winding, though it sure is black now. Motor still runs after repair. I have also toasted hall sensors at this power level, and then replaced them on the same motor. Toasting the halls happened after a 30 min ride.

Same motor at 90v 40amps. 47mph possible, but 43mph most of the ride. The motor gets very hot very fast. Didn't finish a race, and on mile 11 burst into flames, having a temp reading of 450F inside. The flames was the string inside that ties the windings in place combusting. That motor now is burnt, windings shorted, the varnish on the copper wire melted and shorting.

So what happened? As I undersand it, at some point the copper in the motor just can't use more current. It's maxed out. From then on, more current just makes heat, and at 90v 40 amps, clearly a LOT of heat. Then the motor melts. I would guess this point is somewhere between 1500w and 3000w, based on how much hotter the motor gets if you give it up to 3000w. In use of course, the motor doesn't draw 3000w continuous. But enough 2500- 3000w spikes can do the trick.

Because you keep seeing more speed as you increase the wattage, clearly the motor gets to use some watts above 1500w. But my guess is that the efficiency gets worse and worse. Once you have 1000w going into heat, that's just like an electric space heater, and it warms up quite fast. Too fast for holes in the hub cover to help you, except to let the smoke out.

No need to lower the amps. If you put, say, 50 A through a motor and it gets to, say 80 deg C, then doubling the voltage and still putting 50 A through it means it will still get to about 80 deg C.

It's current that determines motor heating, by and large, not total power. Running a motor faster (higher voltage) can make it run either more, or less, efficiently, depending on the original rpm and the increase in torque demand.

There is clearly a bit of human nature that kicks in here, as few will want to run at double the voltage and keep the current the same, and increasing the current WILL make the motor run hotter.

The major (maybe 90% plus) cause of heat in a motor comes from the I²R losses, in other words the square of the current x the motor winding and wiring resistance. Double the current and you get four times the heat. Double the voltage and keep the current the same and you'll get only a little more heat.

Motors don't care about voltage too much, or power for that matter. Motor heating is so dominated by resistive loss from current, and so dependent on motor torque, that the other losses are usually pretty tiny, especially for a hub motor that won't be spinning very fast.

 

[parajared]

The major (maybe 90% plus) cause of heat in a motor comes from the I²R losses, in other words the square of the current x the motor winding and wiring resistance. Double the current and you get four times the heat. Double the voltage and keep the current the same and you'll get only a little more heat.

Yes, this was my hypothesis when I wrote this thread. I found it strange that people were running 50 amps down their phase wires, and began to study ohms law, and the rules of resistance. I figured the 18ish gauge coils in everyone's motor abided by the same rules as regular wires, and presumed that our forum's attempts to modify controllers, battery cables, phases wires ect.. in an attempt to improve performance was all an exercise in futility because internal coil wire resistance just sheds off the extra amperage in heat.

I understand why manufacurers don't build their controllers high voltage, because increased voltage = increased top speed, and they are building e-bikes, not e-motorcycles, but I was wondering why with so much knowledge of how electricity works on this forum we don't see more 200+ volt builds to accomodate for our tiny coil wires. I presumed people were running into uncomfortable ride, or high voltage problems?

 

[Jeremy Harris]

Yes, this was my hypothesis when I wrote this thread. I found it strange that people were running 50 amps down their phase wires, and began to study ohms law, and the rules of resistance. I figured the 18ish gauge coils in everyone's motor abided by the same rules and presumed that our forum's attempts to modify controllers, battery cables, phases wires ect.. in an attempt to improve performance was all an exercise in futility because internal coil wire resistance just sheds off the extra amperage in heat.

I understand why manufacurers don't build their controllers high voltage, because increased voltage = increased speed, and they are building e-bikes, not e-motorcycles, but I was wondering why with so much knowledge of how electricity works on this forum we don't see more 200+ volt builds to accomodate for our tiny coil wires. I presumed people were running into uncomfortable ride, or high voltage problems?

It's a game of compromises, especially for hub motors, where their large diameter means they tend to have a lot higher wire losses and where rpm is fixed by the wheel diameter (unless they are geared). Spinning a motor faster does mean that you get more power from a given size of motor and a given amount of heating, but spin a motor too fast (in the sense of the number of pole commutations per second) and you start running into problems with core losses. These are a function of switching rate - higher means more loss. Hub motors can run into this problem if pushed, because they have a high pole count, so have a higher commutation frequency with respect to rpm than a smaller diameter motor, like a big RC outrunner, for example.

High voltage also brings safety problems, at least for commercial products. Anything that is going to be CE marked (the EU approval mark) will need to be certified against the Low Voltage Directive if it runs at more than 75 V DC, or 60 V AC. There are similar safety regulations in other countries, so this limits the open sale of commercial ebike stuff (rather than the hobby stuff we tend to buy) to voltages below these levels. Complying with the safety certification for stuff at higher voltages than this gets to be problematic, as few of the parts, connectors, etc we use would pass safety certification at, say, 200 V.

 

[dogman dan]

Thanks for the dope slap.

In my ignorance, I thought increasing the watts was increasing the current. I thought increasing either amps or volts increased the current.

Seems to explain why I don't get motors much hotter running at 72v 20 amps, than I do running 48v 20 amps.

 

[Jeremy Harris]

No offence intended, Dogman, sorry if it came over as if I was taking a poke. You're right, running at the same current will keep the motor at around the same temperature, at least until you get to the point where core losses start to play a big part in getting things hot. I think the problem is that people often up the current when they up the voltage, as the thirst for power can be pretty satiable.................

 

[parajared]

Spinning a motor faster does mean that you get more power from a given size of motor and a given amount of heating, but spin a motor too fast (in the sense of the number of pole commutations per second) and you start running into problems with core losses. These are a function of switching rate - higher means more loss. Hub motors can run into this problem if pushed, because they have a high pole count, so have a higher commutation frequency with respect to rpm than a smaller diameter motor, like a big RC outrunner, for example.

Ok, I think I understand what you are saying.

You are saying the number of pole commutations per second increases and causes heat. Is that a reference to pulse width modulation, which I think means every time the motor recieves a pulse in it's work cycle it acts like a resistor because every time it turns on then off again it has to overcome resistance thus generating heat. Increasing the voltage increases the pulses because you aren't going to cycle along at full throttle now, the controller basically has to turn on, off, on, off, on, off, to roll along at the same speed.

Would this also mean that you could change gear ratios in a geared hub motor and overvolt without core losses?

 

[amberwolf]

Seems to explain why I don't get motors much hotter running at 72v 20 amps, than I do running 48v 20 amps.

And why I came close to cooking my 2807 on Crazybike2 by staying at the same 14s and increasing the battery current from teh controller from 40A to 80A by swapping from a generic 12FET to a monstrously-modified Methods' 18FET. :lol: Only a little different at 16s. (and I have no idea what the phase amps might be for either one)

It was something I failed to consider before trying it, and only thought of after getting the motor so hot I couldn't even really touch the windings (thru the cooling holes), and almost melting the (thin) phase wires.

 

[dogman dan]

Seriously, thanks for the dope slap, your corrections have done worlds for my understanding. I truly appreciate it when you or others take the time. I'm lost in this electronic stuff half the time. I'm no electronic guru. I'm the guy who rode far enough on some basic stuff to know it's capabilities.

I really thought it was just a matter of a motor design having a max watt limit. My crude experiments suggest that 20 amps is fine for a 9c motor, but that 40 amps is pushing it and needs a serious watch on the heating. So I end up guessing that 30 amps would be relatively safe. But I thought it was a function of the wattage.

Beyond a certain point, more volts may be just taking it even further past the point you already shouldn't have crossed. This seems to be the case when I went from 72v to 90v. With the same amps controllers, the 90v definitely heated up much faster than 72v did. It was about 7 mph faster, so the motor was spinning pretty fast at 47 mph for a hubmotor designed for 25 mph.

Sweet spot for these generic 800w hubmotors seems to be 35 mph and under in my opinion. Though they can go faster, it may not be all that practical to.

 

[amberwolf]

It is *also* a function of the wattage, as there is a somewhat proportional amount of power that is lost in the motor as heat for any given power input (vs motor characteristics and load and speed, etc.). So if you put 10KW into the motor but at only 10A, if the motor is only 70% efficient at those particular conditions, it's still going to melt it because you have 3KW of heat in there.

But apparently, because of the core losses in laminations, and resistive losses in windings, higher winding currents are more of an immediate problem than the total power input. But winding (phase) currents aren't constant under a given load, like battery current essentially is. They are pulsed with the PWM (for throttle control) and commutation (usually trapezoid on our ebike controllers) steps.

So this makes another issue: depending on the controller design and/or programming, you may have a 20A controller that could still melt the motor down because it's programmed for very high phase currents, so it is sending say (WAG example) 150A pulses down the line. You lose some as heat in resistance of the phase wires getting to the motor, then more as heat in the resistance of the actual windings of the phases, then still more in the laminations because of the changes in current flow as PWM is switched on and off and commutation steps occur to spin the motor, where current flow actually reverses thru any given set of windings for various combinations--that current flow has to slow and stop before reversing, and the magnetic fields in the stator laminations create heat when forming and falling because of eddy currents inside each lamination. Thinner laminations help, up to some point I don't yet understand.


Those core losses, from the laminations, are part of why it gets so much hotter above some certain speed, because after that point it's switching commutation steps fast enough that the eddy currents in the laminations are so high that it makes a lot of waste heat in the process of cancelling them out and changing the field direction, for each step in spinning the motor. So thinner laminations for faster motors, as I understand it, makes them more efficient at those higher speeds (but I am not sure what that does at the lower speeds, as there is always some trade-off).

I'm still just beginning to actually grasp what's going on inside these things, so my explanations might not make sense yet (or even be partly incorrect in detail).

 

[Jeremy Harris]

It is *also* a function of the wattage, as there is a somewhat proportional amount of power that is lost in the motor as heat for any given power input (vs motor characteristics and load and speed, etc.). So if you put 10KW into the motor but at only 10A, if the motor is only 70% efficient at those particular conditions, it's still going to melt it because you have 3KW of heat in there.

But apparently, because of the core losses in laminations, and resistive losses in windings, higher winding currents are more of an immediate problem than the total power input. But winding (phase) currents aren't constant under a given load, like battery current essentially is. They are pulsed with the PWM (for throttle control) and commutation (usually trapezoid on our ebike controllers) steps.

So this makes another issue: depending on the controller design and/or programming, you may have a 20A controller that could still melt the motor down because it's programmed for very high phase currents, so it is sending say (WAG example) 150A pulses down the line. You lose some as heat in resistance of the phase wires getting to the motor, then more as heat in the resistance of the actual windings of the phases, then still more in the laminations because of the changes in current flow as PWM is switched on and off and commutation steps occur to spin the motor, where current flow actually reverses thru any given set of windings for various combinations--that current flow has to slow and stop before reversing, and the magnetic fields in the stator laminations create heat when forming and falling because of eddy currents inside each lamination. Thinner laminations help, up to some point I don't yet understand.


Those core losses, from the laminations, are part of why it gets so much hotter above some certain speed, because after that point it's switching commutation steps fast enough that the eddy currents in the laminations are so high that it makes a lot of waste heat in the process of cancelling them out and changing the field direction, for each step in spinning the motor. So thinner laminations for faster motors, as I understand it, makes them more efficient at those higher speeds (but I am not sure what that does at the lower speeds, as there is always some trade-off).

I'm still just beginning to actually grasp what's going on inside these things, so my explanations might not make sense yet (or even be partly incorrect in detail).

Generally core losses are small, much smaller than I²R losses in the copper (at least for the low commutation rate motors we tend to work with on ebikes). Core losses are also proportional to rpm, not power, so increase with increasing rpm. There are some other small losses that are proportional to flux density, so dependent on current, rather than power, but these tend to be pretty small.

If you're running a high speed motor and reduction drive then you may get to the point where core losses start to become significant, but few hub motors get close to the commutation rate needed to make core losses a significant issue, at least at modest speeds.

 

[dogman dan]

Would 47 mph on a 26" rim qualify for fast enough to cause some core losses worth worring about? Seemed like the heat really increased when I went from 40mph club, to almost the 50 mph club.

Even when not cornering hard on the track,it got hot really fast. Just the extra power working hard to overcome the wind resistance? Theoretically, I'd added another 1000w. I don't know what I was actually pulling out of the battery, because my CA maxed out at 100v, and I was starting off with 110v.

 

[Miles]

Would 47 mph on a 26" rim qualify for fast enough to cause some core losses worth worring about?

About 600 rpm?

How many poles?

Dividing by 60 and multiplying by the number of pole pairs gives you the fundamental frequency.
For 46 poles (23 pole pairs), that's 230Hz.

I don't think that's so excessive, even for 0.5mm laminations.

Most likely it's the greater torque needed to go the extra 7mph.....

 

[parajared]

update 9/5: tried it thanks to Lyen for building a controller that can take high voltage.

result: motor spins faster, but heats up like crazy at low speeds. Runs cool at high speeds. Phase wires completely cool even after 3000 plus watts run through them.
I still don't understand why people don't overvolt like crazy though on their mid-drives and just gear reduce. There must be a reason other than worrying about electrocuting yourself. I mean that's a pretty good one, but still seems like a good idea to me other than that.

 

[jumpjack]

Very interesting thread, thanks to all contributors.

High voltage also brings safety problems, at least for commercial products. Anything that is going to be CE marked (the EU approval mark) will need to be certified against the Low Voltage Directive if it runs at more than 75 V DC, or 60 V AC.

I see it actually says 75V DC, 50V AC

BUT
talking of a BLDC motor... does it fall in DC or AC category?
I ask because I see most (90%) of electric motorbikes I see around are 48V; only mine (!!??) is 60V. (It's a Chinese XINSILU e-scooter: 1500W/60V).

I found an used 48V e-scooter for 100 bucks : fully functional, but with dead batteries; and it has top speed 28 mph, while mine has 37 or more.
So I'd like to bring the old scooter to new life by replacing batteries and possibly increasing its speed, regardless of torque/power decrease.

Do you think I could just change the controller in such a way the motor receives up to 60V rather than just 48, but keeping current low to prevent motor damage? It's rated 1800W/48V, but I have no datasheets. It's an old Atala Lepton, just for the record.

How can I select the limiting additional resistor to prevent too much current from burning the motor?
And which controller would be more suitable?

 

[parajared]

Yes, you can run at any voltage, you just have to up the amperage. More amperage= the need for larger wires. That's why 24 volt golf carts have battery cables as big around as your thumbs and huge controllers to go with them. It's actually no biggie to run low voltage assuming you have the right wires.

 

[miro13car]

Good topic
Overvolt?
Depends on what ebike system
On intelligent designed to NAmerican/Western standards ebike DD motor/controller nothing will happen even if you apply triple of operating voltage
Simply - electronics it will sense voltage higher than designed V treshold on power wires and not power up system.
It is called overvoltage protection.
Point is
Well design system protects itself but you must pay a bit more for such design
Both Eplus and Tidal Force USA designed and built ebikes are protected like that.
Why overvolt them, they are already 30mph capable on just 36V.

 

[jumpjack]

do Kelly controllers allow increasing voltage and keeping current indipendently as low as it was at standard voltage?
Which one is suitable for a motor currently controlled by a 48V/60A controller?