Running in waves and motor heat

[LJH]

I have a question for you guys, I just went to 18cells (IB4200's) in my OM29 with a 11XL,K42 prop and a Baracuda 125. I have run the set up 4-5 times now in everything from flat water too pretty big waves. In flat water the set up seems to be great, motor and ESC are completely comfortable to touch and the batterys are not much above ambient temp. As the waves build so do the temps, now I know running partial throttle will heat up the ESC, the reason I went with a B125 thinking that I would be pulling somewhere around 50ish+ amps (in flat water I seem to be pulling somewhere around 45-50A average calculating out run time VS. Mah put back into the pack) . Last night I was running in some pretty big waves so most of the time was spent at 50-75% throttle with bursts of WOT. The boats seemed to spend as much time out of the water as it did in the water and after 4 or so minutes I think I was starting to thermal the ESC, it would shut down for a few seconds and then go again. I ran her for a another minute (total run time was just over 5 minutes) and when I opened her up the motor and ESC were pretty warm, I was able to hold the motor for 10 seconds or so before it became uncomfortable (very scientific I know) and the ESC was a bit cooler but still warmer then I have experienced so far. So my question is does the loading and unloading as well as partial throttle heat a motor more then running pretty much flat out? I guess it could also come down to the fact that when there are waves I spend more time accelerating then when the water is flat and I can pretty much punch it and hang on.

Cheers,
Jim

[Doozie870]

I think the partial throttle caused it, not sure why but most people I have seen race, run their brushless boats like a on off switch for some reason.

[LJH]

Doozie,
It seems that way....I have been flying E-powered planes for 10+ years now and and went BL 5 years ago and use partial throttle all the time....you just have too when you are flying 3D. I guess you could call running FE boats in waves as 3D boating :D .

If I went to a smaller prop with that help with heating when running partial throttle? Or maybe I should just run fewers cells when the waves are up.


Cheers,
Jim

[Doozie870]

Wouldnt hurt thats for sure, you would think that brushless would be better at varying speeds as it regulates the firing rather than adding resistance like a brushed esc.

[ReddyWatts]

If a motor is spending a lot of time out of the water, then it is like running in an unloaded condition. A brushless controllers automatic timing advance is designed for the motor to have load. If the motor is run without load it is runing out of time and will run hotter. Have you ever noticed how quickly a motor will heat up on the bench with no load?

I had understood that NOT running full throttle just made the controller run hotter, not the motor, but maybe a lot of hard accelerations could make it hotter from higher amps (watts/heat)? You also have power surges when the boats prop lands in the water again.

[SJFE]

I seem to remember reading that most marine bl controlers are suited best for WOT. Running them below causes excessive heat and shortens over all life. I am guilty of this due to my driving style. I am still unconfortable with wot turns. I still wana set the weight and use the power for controle. It stems from my touring & pan car days. I'm workin on it..lol

[Rex R]

most speed controlers(brushed, bl, esc or mc) are not happy with part throttle running. think I recall reading that esc's are most stressed below half throttle, from 80 - 100% throttle they work best.

[LJH]

RW,
That is a really good point....had not thought about that, I am going to guess that you hit the nail on the head.


In regards to running below WOT, yes it causes a controller to heat more but as long as you have enough over head this should not be an issue, though I fly a number of my planes with a CC 25amp ESC where WOT pulls 27-28amps and I fly them a lot well below 50% throttle. I have hundreds, if not thousands, of hours flying BL powered planes at less then WOT and have never had an issue. I fly everything from a 30 watt Tiger Moth which usually gets flown at less then 1/4 throttle to 1000 watt aerobatic ships where if you flew WOT all the time the wings would come off it. I am not buying the idea that a BL controller cannot be used at less then WOT, though I know it will cause more heating in it.


Thanks fr your ideas guys.


Cheers,
Jim

[SJFE]

So Jim whats a good plane to get ur your feet wet in? I have allways wanted a centerline thrust electric ducted fan jet :) Shoot me a pm if ya would please sir.

[ReddyWatts]

A difference in boats and planes is that the airplane motor is always loaded. I guess in a dive it can become less. The air cooling also gives them an advantage. Boats hulls are sealed and this causes a problem for cooling the controller. Water cooling is really a joke unless we use hollow cooling plates directly on the controller FETs. I had thought about a sealed air ducted ram to force outside air through a sealed tube and box container for the controller. The problem would be if you flew the hull or ate a rooster the controller would probably get wet. hmmmm..........

I wonder if you could use a gas fuel filters that would stop the water but let air through? hmmm.........

If that would work you could use air scoops like on a nitro hull to cool everything? hmmmm......

[ReddyWatts]

or if the controller had cooling fins that could be mounted through the top of the hull and the electronics remaining sealed inside the waterproof hull. Continue to use water cooling for the motor plus use the water exhaustand air to cool the external controller fins. "Wa La" a super cooled controller.

No kids this evening, can you tell that I am bored???

[SJFE]

Hey now thats somthing I wana try. Some cooling fins mounted up in a scoop...yeah thats doable.

[kck741]

ReddyWatts,that would be an awsome setup to try