An Electric Primer for Fuel Guys

[sjslhill]

Paul,

I understand the high voltage classes, the 7.4V one is strange to me.

thanks,

Steve

Hi Steve,

How would you explain the need for 150 amps for the N2 class? How do more amps affect these motors at such a low voltage? Does more amps create more RMP or Torque or what exactly?

More amps are drawn because people use bigger props and/or higher KV motors. They can do that because Lipos will deliver those amps easily without heating up. You could do the same thing with sub-C cells, you just have to replace them often. For example, the rigger Joerg went 140 with. If he pulled the 32 sub-cs out and swaped with a 10S pack changing nothing else his amp draw would still be the same or slightly lower but he would have gone faster because lipos don't drop voltage like Sub-cs do. Why, internal resistance of the cells, Sub-Cs being much higher.

A 32 cell pack peaks at around 40 volts, a lipo 10S pack at 42 volts. Under the high amp loads the 32 cell pack would drop to roughly 29 volts and the lipos around 39 volts. At least that's how it's been shaking out in my open class 10S2P boats compared to running 32 cells.

Paul.

 

[Don Ferrette]

A 32 cell pack peaks at around 40 volts, a lipo 10S pack at 42 volts. Under the high amp loads the 32 cell pack would drop to roughly 29 volts and the lipos around 39 volts. At least that's how it's been shaking out in my open class 10S2P boats compared to running 32 cells.

Now can someone show a cost comparision between these two & also the amps capacity of both.

 

[Mark Bullard]

A AC brushless motor or what we would call a induction motor will not increase speed. Their speed is base on the number of poles at the Synchronous RPM. The Synchronous RPM in AC motors is a very simple math formula....So with this formula a 4 Pole motor will turn only 1800 RPM's at 60hz. So the end results is the motors that ya'll are using will not increase speed with voltage but only with a change of Hertz.

I am not certain how to respond to this Mark; what I do know is that any FE brushless racing motor will most certainly run twice as fast with twice the voltage - there is no argument here, just fact. As I understand the BL ESC's function, it uses a fixed frequency (9KHz, 19KHz, 38KHz, whatever is programmed), but the controller turns the power on and off at that frequency. The more time the power is turned off, the less goes to the motor so the motor speed is lower - that is how the motor is throttled. With no interruption of the power, the motor runs at maximum speed. That speed is determined by the maximum voltage applied and the resistance/efficiency of the motor windings.

The limit to output power today is the ESC, not the motor (at least not with the better-quality racing motors). No matter how much amperage is available from the battery, the ESC will fail before the motor will, and with most ESCs today that is below 200 amps. That's today....tomorrow who knows....but we need to understand what today's limits are first.

The output power of an FE motor is based upon the input voltage/amperage at the motor after the ESC and the efficiency of the motor. If 14.8 volts and 100 amps are supplied to the motor, the max output will be around 1200 watts, or 1.6 horsepower (ca. 746 watts per horsepower). The rest of the power is wasted generating heat. (One of the main reasons that BL motors produce more power than brushed motors is their efficiency; BL motors are usually above 80% efficiency at maximum power while brushed racing motors were often only 60-70% efficient. The rest of that energy was wasted as heat.)

While many seem fixated on amperage, experienced FE boaters know that if possible it is better to achieve power by increasing the voltage. This gives high power without having to use high amperage - that means lower temperatures in the cells and the ESC. High power means larger boats, and since power is volts x amps there are two different ways to get there. With today's technology, voltage rules.

I've tried to answer Mark and include some additional information - I hope this isn't too confusing for anyone. If so please let me know. :blink:

.

There not a problem with the answer that you gave. It all goes back to the buzz words that are used. And I think that what the ESC company's are trying to do is copy brush motors by giving you more RPM's with more voltage. And these are the buzz words that they are using. I think that the real numbers are what you said in the programed frequency. These numbers are what we call the carrier frequency. It is how fast the IGBT's switch on and off to build the sine wave. This frequency helps smooth out the sine wave and takes the chop out or what we call the saw tooth pattern out. The IGBT is two high speed transistors that operate on the positive side and the negative side of the DC buss to create one phase. There has to be three sets of IGBT's to run a 3 phase motor. I wish I could draw on this page if I could it would be easier to explain. In Variable Frequency Drives "VFD" the voltage does vary with the speed of the motor. When you lower the frequency the motor will build heat. This is the reason why the voltage is lowered. The variable frequency is what the manufactures are not telling you about.

Constant torque can be acheived by allowing the voltage to follow the frequency.

So by using the Synchronous RPM formula, a 4 pole motor that is turning 40,000 RPM is using a frequency of 1333.33 Hertz with a programed carrier frequency to help smooth out the sine wave. This RPM can be achived at any voltage but the ESC that ya'll use may not be able to acheive this.

Mark

 

[Tim_Duggan]

Don,

Another interesting comparison between the 32 cell Sub C pack and the 10S LiPo would be the weight.........

We use IGBT's (Intergrated Gate Bipolar Transistors) to generate high frequency for induction heating coils. Drastically increases warm up time and temperature stability over the old halogen lamp based systems we used to use.

I'd never really thought of that system like a "brushless motor setup" but it makes perfect sense. Mark mentioning IGBT tweaked me to it!

Tim.

 

[sjslhill]

TP5000-10SX

Dimensions = 166 x 45 x 84

Weight = 1198 grams

$579.99

32 IB4200 cells

23mm x 43.5mm per cell

weight 71g per cell

$208.00

Don,Another interesting comparison between the 32 cell Sub C pack and the 10S LiPo would be the weight.........

We use IGBT's (Intergrated Gate Bipolar Transistors) to generate high frequency for induction heating coils. Drastically increases warm up time and temperature stability over the old halogen lamp based systems we used to use.

I'd never really thought of that system like a "brushless motor setup" but it makes perfect sense. Mark mentioning IGBT tweaked me to it!

Tim.

 

[Don Ferrette]

 

[sjslhill]

Don,

Some will run 2 X this 5,000 pack in the future or 10,000mah in T class.

TP5000-10SX Dimensions = 166 x 45 x 84

Weight = 1198 grams

$579.99

32 IB4200 cells

23mm x 43.5mm per cell

weight 71g per cell

$208.00

THIS is exactly what I've been getting at. 3 times the cost, 1/2 the weight & we won't even talk about the HUGE difference in space requirements (read smaller hull even faster), kinda puts the guy who can't afford almost $600 for just one pack at a bit of a disadvantage doesn't it?? :huh:

No offense but this push for these seem to be driven by those with deep enough pockets. What about the "little guy"?? Think he's gonna stick around to get his ass handed to him every weekend? <_<

 

[jayt]

Guys, I'd appreciate it if we stuck to the technical side on this thread. Steve: if you want to argue about what might happen - please take it to another thread. No politics here please! :angry:

.

 

[Jeff]

Mark, your pespective is coming from an unlimited power source(The grid). The overcurrant device whether breaker or solidstate moter starters allow such a high amprege spike to get the rotor starting to move yet then come down to a safe operating currant. In no way can this be achieved in a small dc input varible drive speed control. It would simply burn up. We use a very limited amout of power availble(battery) and the voltage decreases thus raising amps or dropping off performance during a run. The software needed to make this work is not the same as things with an unlimited power source. Your comparing what you know to something you don't completly understand. Much like saying a motor whether nitro or gas is gotta be the same cause it is a motor. Exaust port timing, compersion ratio, blowdown time and efective port timing are all differant depending on fuel. Who wants to talk about pipes? A pipe is apipe right, stinger lenght, internal stinger or chamber size, we'll it's justa pipe right.

Jeff

 

[Mark Bullard]

Mark, your pespective is coming from an unlimited power source(The grid). The overcurrant device whether breaker or solidstate moter starters allow such a high amprege spike to get the rotor starting to move yet then come down to a safe operating currant. In no way can this be achieved in a small dc input varible drive speed control. It would simply burn up. We use a very limited amout of power availble(battery) and the voltage decreases thus raising amps or dropping off performance during a run. The software needed to make this work is not the same as things with an unlimited power source. Your comparing what you know to something you don't completly understand. Much like saying a motor whether nitro or gas is gotta be the same cause it is a motor. Exaust port timing, compersion ratio, blowdown time and efective port timing are all differant depending on fuel. Who wants to talk about pipes? A pipe is apipe right, stinger lenght, internal stinger or chamber size, we'll it's justa pipe right.Jeff

Jeff,

I am not talking about inrush current of a electric motor starting across the line or grid as you said. I am talking about a 3 phase motor or a brushless DC and VFD control that can drive them. The Variable Frequency Drives "VFD" is very much the same thing that ya'll are running on your boats. The VFD is a device that takes the input power and converts it to straight line DC and then the IGBT's copy's a AC type voltage or sine wave but with a variable frequency for speed control. There is no way that your 4 or 2 pole brushless motor will vary speed by changing the voltage alone. If I take one of your motors and run it on the grid it will run the base Synchronous RPM for the pole of the motor. My test panel in my shop is a variable transformer that will go from 0 volts to 5000 volts but at frequency of 60Hz. This is the operating Hertz in this country. So I get the same Hertz out that is put in. By taking your motor and connecting it to my test panel I can run the motor from 0 to 40 VAC with no problem and the motor will not run over 1800RPM's for a 4 pole or 3600RPM's for a 2 pole. If you have a Oscilloscope hook the input 1 lead to U-phase with the reference lead to V-phase then hook the input 2 lead up to the V-phase with the reference lead to the W-phase. Now run you ESC and you will see that the voltage changes but what you really want to look at is the frequency change. The frequency is what makes the RPM change not the voltage. The voltage only changes to help on the heat build up.

Mark

 

[Mark Bullard]

Don,Another interesting comparison between the 32 cell Sub C pack and the 10S LiPo would be the weight.........

We use IGBT's (Intergrated Gate Bipolar Transistors) to generate high frequency for induction heating coils. Drastically increases warm up time and temperature stability over the old halogen lamp based systems we used to use.

I'd never really thought of that system like a "brushless motor setup" but it makes perfect sense. Mark mentioning IGBT tweaked me to it!

Tim.

Tim,

You hit the nail right on the head. The only way a Induction Heater will work and control the heat range is by changing the frequency. And this is what changes the speed of a induction 3 phase motor or a brushless motor.

This site will give you a better understanding of electric motors http://en.wikipedia.org/wiki/Electric_motor

You should read about AC 3 phase motors. But they do have all types of motors listed. You will see a listing on Brushless DC motors but the motors that ya'll are using do not have a feed back device and since they don't have this device it will make it harder to understand listing.

Mark

 

[jayt]

The racing motors we use today are sensorless (no active feedback sensors), unlike the sensored ones we used when BL motors started in boats in the late 1990s. But there is feedback from the current BL motors - the ESC senses the rotor position from back EMF and adjusts the timing advance accordingly. This works quite well unless the motor induction is very very low.

The racing ESCs we use today do not change freqencies, they are programmed for a specific frequency and change the amount of time that power is fed to the motor to control the throttle. The most common frequencies are 9, 19 and 38 MHz, and with many controllers the end user can choose whichever frequency he wants. Some frequencies work better with specific motor designs, depending on the number of poles and the inductance of the motor windings. With some motors it doesn't seem to matter.

I do know that if you take a motor with a Kv of 2000 rpm/volt and feed it 7.4 volts it will spin around 15,000 rpm at a load of 30 amps; plug in another pack for 14.8 volts and you get about 30,000 rpm again at 30 amps. Not theory, just fact.

.

 

[Jeff]

Mark, maybe this will help you understand. Take your 1/4 hp motor and the variable frequency drive and put it in your sport 20 hull. Would it fit? Would it even float? Do you think I could put a 800cc Rotax engine in a sport 20? No. We are dealing with things that are small enough to work in a toy boat. They just don't follow the same designe parameters as full sized.

Jeff

 

[Mark Bullard]

Well I tried to enlighten ya'll on the simple principal electric motors and how they work. But it seem that ya'll know more about it than I do. I have over 40 years in the motor repair and rewind and your motors are no different than the ones that we repair. My primary repair that I do myself is repair servo, stepper, and spindle motors for CNC machines and robots. And yes I do have to work on the more simple motors too sometimes. And yes if I did decide to run electric I would be on top of the game and ahead of ya'll went I start.

Mark

 

[Jeff]

Just like captain Kirk, to boldly go where no man has gone before.....

 

[Kevin Whitehead]

The racing ESCs we use today do not change freqencies, they are programmed for a specific frequency and change the amount of time that power is fed to the motor to control the throttle. The most common frequencies are 9, 19 and 38 MHz, and with many controllers the end user can choose whichever frequency he wants. Some frequencies work better with specific motor designs, depending on the number of poles and the inductance of the motor windings. With some motors it doesn't seem to matter.

The 3 most common frequencies used in R/C brushless controllers are 9.6, 19, and 38 kHz.

As Jay noted, the frequency is not changed to vary the speed of the motor. The pulse wavelength is varied to change the speed. It is not a sinewave like the (industrial?) controllers that Mark is referring to. The waveform is trapezoidal. Full on or full off. The wave would be a squarewave but motor inductance rounds some edges.

 

[Tim_Duggan]

Jay,
Is there a limit to the number of motors now in the larger classes? I use to run 2, 3 or even 4 - 05 motors on a gearbox.

Pardon my ignorance, but what advantage did you see by running multiple engines on a gearbox? Is this or was this a common practice in FE? Single propshaft & prop or multiples? Considerably Larger props able to be used? Less current draw?

I'm genuinely interested to hear your answers. (Being a Nitro guy I'm used to multiple engine boats having separate drivelines as being the normal.)

Tim.

 

[Mark Bullard]

The racing ESCs we use today do not change freqencies, they are programmed for a specific frequency and change the amount of time that power is fed to the motor to control the throttle. The most common frequencies are 9, 19 and 38 MHz, and with many controllers the end user can choose whichever frequency he wants. Some frequencies work better with specific motor designs, depending on the number of poles and the inductance of the motor windings. With some motors it doesn't seem to matter.

The 3 most common frequencies used in R/C brushless controllers are 9.6, 19, and 38 kHz.

As Jay noted, the frequency is not changed to vary the speed of the motor. The pulse wavelength is varied to change the speed. It is not a sinewave like the (industrial?) controllers that Mark is referring to. The waveform is trapezoidal. Full on or full off. The wave would be a squarewave but motor inductance rounds some edges.

Ok if you take what you are saying about the programmed frequency of 9.6, 19 and 38khz. Then a 4 pole motor at speed with you controllers would be 288,000, 570,000 and 1,140,000 RPM's based of the Synchronous RPM formula. I don't think so!

Kevin describe the very thing that I have been saying. The programmed frequency that you say can be changed is what we call the carrier frequency. It is the frequency that is used to build the pulse wavelength. This is what make some motor sound like they have a herd of BEE's inside the motor or what makes the motors sound like they are giving out musical notes. Now you said that the pulse wavelenght is varied to change the speed. What do you think that this is? It is the Frequency that the motor is run at and what gives it speed. There again based on the Synchronous RPM formula. Our standard housewhole voltage is 60Hz. This means the the wavelenght or sine wave is turn on and off 60 times a second. To slow a motor you must slow this time down or lenghten the wavelenght. To increase speed you must speed this time up or shorten the wavelenght. This is why changing the voltage will not change the speed. Yes the wave form is trapezoidal or a square wave. But by turning the voltage on anf off at right time will build a sine wave. It may look like a saw tooth pattern but it is a sine wave and by lenghten ot shorting the wavelenght it will change the speed of the motor. How the other programmed frequency comes into play is by smoothing out those corners or to make a better looking sine wave. The higher this frequency is the better the sine wave looks.

With all this said we have just described a PWM VFD AC drive. Or Pulse Width Modulated Variable Frequency Drive.

Mark

 

[Kevin Whitehead]

The racing ESCs we use today do not change freqencies, they are programmed for a specific frequency and change the amount of time that power is fed to the motor to control the throttle. The most common frequencies are 9, 19 and 38 MHz, and with many controllers the end user can choose whichever frequency he wants. Some frequencies work better with specific motor designs, depending on the number of poles and the inductance of the motor windings. With some motors it doesn't seem to matter.

The 3 most common frequencies used in R/C brushless controllers are 9.6, 19, and 38 kHz.

As Jay noted, the frequency is not changed to vary the speed of the motor. The pulse wavelength is varied to change the speed. It is not a sinewave like the (industrial?) controllers that Mark is referring to. The waveform is trapezoidal. Full on or full off. The wave would be a squarewave but motor inductance rounds some edges.

Pulse wavelength was the wrong term to use.

The duty cycle or time that the pulse wave is in a high state is changed. Pulse width modulation. Speeds up by increasing the time the pulse is high. Slows down by decreasing the amount of time the pulse remains high.

The frequency of the waves remains stable at 9.6 kHz, 19 kHz, 38 kHz, or in some controllers a user setting somewhere between them. Not at the basic commutation frequency.

 

[Dennis Whitt]

As far as gear boxs or trannys are concerned,There was a time that we used twin 05 car motors geared into one drive.Ed hughy was the pioneer in that feild.What it did was to split the amperage acroos both motors and also make use of the torque put out by both motors.

You are also correct in that it allowed us to turn a larger and higher pitched prop with just a single 05 car motor.

I still use gear boxs in my offshore boats even with brushless motors.It is just a matter of prefferance now.I like to be able sellect props based on what the hull likes not what the motor can handle.

I also like the gear drives because I can run a boat in offshore and in oval trim just by switching out the gearing.Same ride but more speed or more runtime.Also at the onset of the newer brushless motors like Hacker,Fiaggo and lehner,Nobody new wich winds were the correct ones for the task. So useing a gear box gave me a margin of error.So if I was off a wind I could still gear it propperly for my application.But again,All of these motors have been out a while and all of the homework has been done.Purchasing the corect wind motor is as easy as jumping on here and asking.Man I love the internet.Hope this helps.Dennis