Fact or just old tale?

[SweetZ28]

With the new brushless boat comparing them to old brushed boats now the ? is is it bad to drive at slow speed with a brushless boat will it heat things up and burn stuff up ?or is it best to just keep going fast? and why?

Thanks

[rol243]

well compare a cordless drill that has a brushless motor , has multi speeds and an esc. the drill can run at very low speeds without any issues so why cant a brushless r/c motor do the same.

[boatsrnew2me]

the theory is at low speeds the motor and esc are not getting enough cool water flow to keep things cool . going faster improves water flow .going faster also creates more heat so it`s a double edge sword kinda thing

[ray schrauwen]

FETs in escs like to be on or off. When partially on as in partial throttle, excess heat builds in the FETs. When at full throttle, the FETs are on completely and are much happier.

The amount of heat that builds up depends on the load, ie: a hot prop, heavy boat for its size and motor...

Brushed motors build heat more and faster since they are less efficient.

[SweetZ28]

Thank keep the info coming, I thought the same as ray But some guy's say because it's brushless it don't matter now if you run slow all the time? I had this discussion about RC brushless cars also and I said they heat up all the electrics more if you constantly go slow and one guy says no it don't matter with brushless only with old brushed systems back in the day?
Who knows?

[srislash]

The wife's Mahogany boat is in a constant state of half throttle. It runs fine now that I put a water pump on the cooling system. Half throttle meant no water flow and therefore heat. Never was enough to shut anything down but I thought there was room for improvement.

I run a few of my FE boats at part throttle and have never had any issues.
Shawn

[TheShaughnessy]

ok so Ray is the closest here. MosFETS don't like to be on or off they can only be on or off. Partial throttle is achieved by rapidly switching on and off which creates more heat than just being in one state. That being said unless the set up is on the edge of its specifications you should not have an issue. I run a brushless motor in my crawler and I rarely use full throttle and I haven't had an issue to date.

[NativePaul]

Ray and Shaughnessy are correct in regard to brushed ESCs at full throttle the fets just close and let the battery voltage through and the motor does its own commutation, but brushless ESCs need to switch whenever the motor is moving in order to commutate the motor, even at full throttle each FET bank will be switching at the RPM times the pole count (2khz for a 4 pole motor at 30k rpm) which although lower than the standard partial throttle switching frequency of 8khz is still very significant.

What is very bad for ESCs is limiting current with the throttle trim or end point adjustments. Say you have a prop that pulls 120A, but you want more than 2 minutes of runtime from your 5Ah battery, you should prop down, if you just lower the end points so it inly ever sees half throttle it is still switching 120A, just only the on duration is changing and a 120A ESC is still marginal despite measured or calculated current only being 60A.

I am not sure why this is, or whether it is a motor effect or one caused by the ESC, but while brushless motors are much more efficient at full load, they are much less efficient unloaded, if you hold a BL motor and run it unloaded (at partial throttle unless you want to sacrifice your motor) it will heat up remarkably quickly demonstrating it's inefficiency.

[SweetZ28]

Ray and Shaughnessy are correct in regard to brushed ESCs at full throttle the fets just close and let the battery voltage through and the motor does its own commutation, but brushless ESCs need to switch whenever the motor is moving in order to commutate the motor, even at full throttle each FET bank will be switching at the RPM times the pole count (2khz for a 4 pole motor at 30k rpm) which although lower than the standard partial throttle switching frequency of 8khz is still very significant.

What is very bad for ESCs is limiting current with the throttle trim or end point adjustments. Say you have a prop that pulls 120A, but you want more than 2 minutes of runtime from your 5Ah battery, you should prop down, if you just lower the end points so it inly ever sees half throttle it is still switching 120A, just only the on duration is changing and a 120A ESC is still marginal despite measured or calculated current only being 60A.

I am not sure why this is, or whether it is a motor effect or one caused by the ESC, but while brushless motors are much more efficient at full load, they are much less efficient unloaded, if you hold a BL motor and run it unloaded (at partial throttle unless you want to sacrifice your motor) it will heat up remarkably quickly demonstrating it's inefficiency.

So then limiting the throttle by epa is the same as if you just drive around for a couple min at lets say 1/4 throttle with your brushless boat so then your saying it's not good to do then?

[Fluid]

Some good, some bad information. There is no "theory"- just electronic fact. Here are some comments from one of the largest hobby ESC designers in the world:

"A speed controller controls power to the motor by turning full throttle current on and off really fast, 11 to 13 thousand times per second (Pulse Width Modulation or PWM). The percentage of each on/off pulse that is off compared to the part that is on determines how much power the motor sees. I.E. With a pulse that is 50% off and 50% on the motor will see 50% power*. Because each on pulse is 100% of full throttle current, a system set to pull 20 amps at full throttle through a Phoenix 10 will not last if you are throttled back to the point where you only see 10 amps on a wattmeter. The ESC in this case is still switching 20 amps, which it can’t do for long. Actually it is worse than the simple example above. Because an electric motor will always to try to pull as much power as is available to get to its rpm (volts times Kv), when you are running the motor below its Kv speed by switching power on an off, each on pulse will actually be way over the full throttle amp draw. That is why ESCs work harder at partial throttle than full throttle and why we underrate our ESCs. We underrate not so they can handle more current than their rating at full throttle, but so they can handle extended partial throttle operation with no problems." Castle Creations

Now from the motor designers:

"If you throttle to 50% RPM expect to see a 30-40% reduction in over all efficiency over 100%. 90% RPM efficiency will be off by 10% or so. The heat loss is shared between the motor and controller." Steve Neu


.

[srislash]

Thanks for that Jay, I have read it before but it is always a good refresh before my boating starts.

[NativePaul]

Although Castle say they underrate their stuff there, it is not by enough to run at partial throttle for extended times. My Hydro2s run at an average of 45A for 6 minutes with sustained full throttle at about 90A and an Ice100 is not enough and nearly all running Castles in that class are using 200s.

[boatsrnew2me]

heres something that popped in my head that i am wondering about now .

during my quadcopter days everyone wanted their esc`s programmed with "simon k" firmware . it made the esc more responsive to input . it was such the rage that everyone wanted "simon k" esc`s or ones programmed as such .even distributors were marketing their esc`s with simon k firmware .

it made the esc feel more connected to your input .hard throttle punchouts were better ,when descending thru prop wash with your quadcopter it eliminated bad behaviors .

i wonder if this kind of tech has ever passed over to boat esc`s ?probably just a air esc thing . this thread just got me to thinking about it .

[NativePaul]

Probably not, we can gain a bit of runtime without noticeably affecting laptimes by lowering the punch control setting, which basically does the opposite and adds a small amount of soft start to the motors rev increases.

It may be better for us in Naviga though as we tend to run more KV and much smaller props than those in NAMBA / IMPBA so we may be losing that first fraction of a second to cavitation anyway.

[SweetZ28]

Thanks for all the input on this guy's!

[CraigP]

Some folks have heat issues on part throttle because of other issues. When the fetus start to switch fast (carrier freq) the motor coil fly back on each switch cycle. Only the capacitors and batteries can control the amount of voltage that will be made. If you have poor or long wiring, or not enough capacitance to match motor, the ESC will over volt very briefly, like a spike. This happens 8 thousand times a second,per coil! This puts the fetus in avalange mode, essentially breaking down like a zener diode. It causes a lot of heat! It it's hot, get more caps and make sure your connections are rated high enough...

[ray schrauwen]

Darn fetuses.

[Fluid]

Perhaps he meant Festus from Gunsmoke?

Actually he meant FETs, or Field-Effect Transistors.


.

[ray schrauwen]

I know, lol. Spell check sucks.

[CraigP]

I hate spell check!!! I say, leave my stuff alone! I look stupid enough without that.....

[CraigP]

Yeah, I really think hot ESC's are more than just the carrier freq kicking in these fets (not fetus) should take that easily. I have applications switching fets at current at 250Khz, so they can take it. It's usually a symptom of hitting avalanche mode. Google "Avalanche mode with FETs" and I think you'll see the common ground to our heat problem.

[CraigP]

BTW, building a new 34 Vortex Hydro and will be running 8S on 4074 1050kV motor. I'm going to build my own cap board that will include different capacitor technologies running in parallel. Each type handles a certain aspect of the switching spike. Also putting in TVS devices... that stands for "Transient Voltage Surge". They flip off (conduct hard) at a given voltage, keeping the ESC at its rated voltage. I'll let you all know how that works out, maybe post with pics and part numbers. If you can solder, you could build one of these...