you really can’t let the magic smoke out. i mean its fucking impossible to get it back in there, i’ve tried everything, including multi-phasic polarized electron traps, magnetically contained plasma inductors, and even tried bypassing the primary power conduits on the heisenberg compensators to create a phase warp bubble that would slow down time and thus prevent the smoke from moving out while i found a solution, but nothing. The only thing you can do is fully reverse the time stream and travel to the point before it was released and kill your other self before you can burn up the motor and ruin your day.
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Hahaah… @longhairedboy
I think I’ll stick with 8s, maybe in the future I’ll try this. Acceleration on my board now is insane and top speed is around 20 mph(30km/h) and that speed is enough.
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From researching again I still don’t know who to believe about overall results but it does seem an amp is an amp and it alone is the source of inductance and the electromagnetic side of the motor. With more voltsge u can simply push more through quicker and you’ll have a higher top speed. For motor efficiency I’ve read anything from running at half to 80 percent of max no-load rpm as defined by volts times kv is most efficient. On a board the rpm is all over the place and I keep it simple and turn up the voltsge as high as possible and watch the max motor temp.
I bet ur motor would be fine on 12s if u reterminated it to a wye wind to further lower the kv but otherwise I think the bearings might go too fast (think they’d get hot). Other than the bearings the enamel is very likely is the same as on their 12s motor and …there’s nothing else in there. There is the risk with the high voltsge blasting the motor into magnetic saturation quicker, like on a super steep hill, and the motor more quickly will throw amps at the windings and then…the smoke. But as long as u keep aware and check temps on the steepest things I think you’re safe. Me for example, I’m running two 54mm motors (rare size) and 90kv and am always looking for the most voltsge I can get as it just means more speed to me
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Hi, sorry to weigh in late but I think I can help if you are still intersted in solving the question. I’m an EE and a student of motor drive, disclaimer I don’t do motor drive for living and could be wrong, i’m not offering advice, just providing you help to make your own decision.
Please correct me if I’m wrong. Caution: rambling answer with little proofing.
So voltage is good but possibly not for the reasons you’ve stated. Yes, lower current is needed for same power and this is mostly a relief to the battery system and power input, less heating of wires, connectors which really does matter at higher power levels. High current wires and connectors are HUGE to be low ESR (resistance), resistance being death to current. High voltage gives smaller and cheaper soln there. At the motor not it’s not so easy.
What makes a motor turn is current through the winding. This makes a magnetic field, simple enough. Each of the three phases is a just big inductor, a coil of wire where magnetic fields are built and super-impose. Pump in more current, get more field. The more voltage you have, the FASTER the field builds up and the BIGGER the current gets, MORE POWER more fun more torque. Also the max current can be higher, voltage being the driver of current.
A net effect is that for the same power output, higher voltage gives you a lower duty cycle. But the same peak currents in the motor are still required; they are built up faster though, and there’s less ‘sag’ when the load is driven because more voltage, more potential, more grunt. Paracitic resistance in the system is overcome because average current is lower and there’s more voltage to work with anyhow, so the drop on parasitics is lower % of total. Remember that the drive is cut up into portions of on and off, very binary as you’d expect. So for the period that motor is on, the faster current growth is a bit more stressful on the gear. This is compensated by the off time when there is no stress, kind of makes it ok. One issue is that you may throw a magnet, literally pulled off the wall, and it could happen when the motor ages.
Everything is fine until you hit Saturation. Things are great as long as the current is able to keep growing. Saturation is the worst thing in the world. An inductor can only hold so much field/flux/energy before real world effects fuck you day and it stops building up. It’ls like the inductor stops ‘pushing back’, effectively slowing the build up of current, when it stops pushing back the current will FALL OF A CLIFF. At that point the inductor winding becomes a fat short circuit and current rages through the wire making a shit ton of heat and suffering. Short circuits like this are death to your batteries, motor drives, and motors. The MOSFETs will pop, the wires will burn (I’ve burnt through a lot of good wire this way), the batteries will be fatally wounded (ditto) and the ice caps will melt we all drown.
An 8S motor SHOULD be designed to stand up to an 8S source being short circuited through the windings for long enough that your ESC detects the fault and stops the fire from starting. Just need fat wires to make it 8S safe, then no fire, no law suit. Naturally 12S voltage on an 8S safe motor will be incinerated. This stuff is hard to protect against because a short circuit can appear like a normal use at high power, you need to tune to it. Underwriters laboratory care about this sort of stuff and engineers can technically end up in jail, but you won’t sue yourself and will be careful right?.
So I’m saying the 8S rating is probably just a safety thing to stop fires.
The things that will cause saturation are a) asking too much power (which you can handle). b) if you are stalling, and the motor doesn’t commutate at the right speed you’ll stay driving the same winding for ages and it’ll saturate. total stalling = massive current.
What really limits the max voltage to the motor is the amount of flux the winding can support before saturation happens, i.e. how big is the winding = weight in your hand. You can make an algorithm to hit them harder as they go faster, because the motor commutates faster, you have a shorter window to hit it so do so with more gusto. Just DON"T drive it extra hard when it starts to slow down and stall, limit duty cycle at lower rpm, etc. A higher frequency drive helps I think, but this moves problems elsewhere too.
How much do you trust your ESC? I say use the 12s on the 8s motor if you can power limit the system and you trust the ESC will do it fast enough, and design the system not to stall easily or at all, and respect the motor max RPM so your bearing dont’ melt. i.e. use the 8S motor in the 8S motor envelope, but enjoy the better acceleration and torque of the 12S drive.
By the way:
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high high rpm speed doesn’t require high power/current, that’s a function of balance, inertia/weight and bearing quality. LOAD & torque drives up current.
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2200W from an 8S battery system? I’m calling bullshit on that. I have a 10S setup on a big heavy 65mm 12S motor and an esc of my own design (for 2KW) and I’m struggling to get past 750W of real power ~ about 1HP. In my experience batteries just don’t provide that sort of juice. As soon as you ask for more they sag out, voltage goes down, motor starts to slip. Yes, I know I need more expensive batteries and more of them… that aside, even with ‘the batteries of the gods’ 2.2KW = 3HP = NOT likely to happen from an 8S in my experience and you should ask them to tell you how they rate and test the motors to that rating.
Do you do it? Was there a fire?
an inductor won’t saturate but the core within it will.
Now we’re splitting hairs, but you are correct.
I don’t even know what the material is inside my motor. Probably just a laminated iron that’s good for magnetisation. Know is probabably a good thing since that tells you how long you can pump the thing until you saturation. I wonder if they make motors with Ferrite or similar material. The trade offs would be interesting.
Ferrite is more efficient but need be larger http://m.powerelectronics.com/passive-components/ferrite-out-better-core-materials-your-pol-design
I just want to put my two cents in. I’m not an EE but I have many years of experience with small brushless motors from being in RC models hobby.
From my experience over voltage does not kill motors, heat from over loading the motor will kill it every time irrespective of voltage or RPM. More voltage will increase RPM, but you will reach the ERPM limit of the vesc way before the physical RPM limit of the motor.
If you increase the voltage over spec you have to compensate by reducing the load on the motor, in our case this means reducing the gear ratio. Then check your not getting over heating during initial testing.
I am currently running a 270kv 6s rated motor on 12s, it just means I need a 4:1 gear ratio to keep the motor happy and not over load it. If I ran a 2:1 ratio it would definitely over heat.
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