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Author Topic: Speed controller questions  (Read 1744 times)

BlueWotsit

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Speed controller questions
« on: March 26, 2008, 09:10:59 AM »

Couple of questions

1) Which of the following figures from a motors specifications should I look at for choosing a speed controllers size

Nominal voltage 9,6 V
Operating voltage range 7,2 ... 14,4 V
No-load speed 14600 min -1
No-load current drain 3,1 A
Current drain at max. efficiency 18 A
Stall current 120 A

2) When cooling a speed controller, what is the best method to use

thanks
Andrew
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roycv

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Re: Speed controller questions
« Reply #1 on: March 26, 2008, 09:45:24 AM »

Hi BW. sounds like you are running a pretty powerful motor!  Perhaps around 200 watts (10volts X 20 amps)  Most speed controllers will handle the voltage so it is the current and the enormous stall current which are the principle concerns.  Almost certainly run with a fuse of some sort.
If you can measure the current taken from the battery when driving the propeller in the water this will help a lot.  Choose a prop that runs as fast as possible without cavitating as the motor will be running more efficiently.  A rule of thumb here is to run the motor at 20% of the stall current which hits the best efficiency of most motors.

Cooling.
I cooled an Electronize ESC by simply making a plate the same size as the base plate and soldering 2 x 1/8th dia. brass tubes to it with a silicon flexible tube connecting 2 ends together and a small scoop at rear of prop, to pick up the water and an exit tube in side of boat.  Screw or attach the base plate to the ESC and use heat transmitting grease as the interface.

Connect together with flexible tubing and this cooled the ESC to pond water temperature when running at 15 amps and 12 volts (180 watts).  The batteries (5.1 Ah cyclons)  were almost too hot to handle.

Perhaps you can bear this in mind when choosing the ESC.

Hope this helps, regards Roy
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BlueWotsit

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Re: Speed controller questions
« Reply #2 on: March 26, 2008, 10:16:46 AM »

Hiya - forgot to mention the motor is a Graupner 700BB turbo 9.6v, and many thanks Roy
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Fil

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Re: Speed controller questions
« Reply #3 on: March 26, 2008, 06:35:34 PM »

Hi Andrew

What are you using the motor for, Scale models or Fast Electrics?

You must always consider the amps.  It is this that will cause the bigest problem to the motor and speed controller.  The higher resistance you create, ie poorly fitted prop shaft causing friction or a big propeller will cause the motor to draw more amps.  More amps more heat eventually things wont work anymore.

If you can tell me what the application is I can give you more specific advice.

The best way to cool a speed controller is to mount a heatsink to it and have this water cooled.

Phil
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Stavros

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Re: Speed controller questions
« Reply #4 on: March 26, 2008, 07:01:56 PM »

Bluewotsit just contact action man FLJ at Action he will put you right


Stavros(Just a very satisfied Customer)
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ministeve

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Re: Speed controller questions
« Reply #5 on: March 26, 2008, 09:07:17 PM »

i recently purchased an action condor 20 and am over the moon with it running a power hungry 540 motor talk to FLJ he knows his stuff
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BlueWotsit

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Re: Speed controller questions
« Reply #6 on: March 26, 2008, 09:58:35 PM »

thanks guys

This ones going in a rarity for me --- a fast electric
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FullLeatherJacket

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Re: Speed controller questions
« Reply #7 on: March 26, 2008, 10:57:07 PM »

I'm sorry guys, but none of our ESCs will handle this motor in a fast electric. Our stuff is really more for scale boats, where the best way to cool a speed controller is to take the load off it!

Good luck with your search - I'm sure there's plenty of folks out there who know the answer.

FLJ
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wombat

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Re: Speed controller questions
« Reply #8 on: March 26, 2008, 11:03:13 PM »

The nominal voltage of the motor is 9.6V (8 cell operation) - if you are running on 12V the currents seen will be a little higher - the stall current will go up to 150A - the other currents will go up similarly.

With modern ESCs, the heat output wont be that much on a motor like this - for example an ACTion Condor 20 on full load will dissipate about 1 watt in each of the output transistors. This will give a temperature rise on full load of about 30C - well within the scope of most boat interiors. Water cooling will not really add anything.

You can gain a bit of extra cooling by mouinting the ESC low in the hull - if the esc has a heatsink case, just mounting it on the hull will give a few degrees of extra cooling just because of the cooling effect of the water over the hull - but fuse very carefully - if the ESC goes into meltdown it could burn through the bottom of the hull. Not possible with the ACTion ESCs but then it is probably unnecessary.

Fusing is important - the fuse is there to protect the ESC from a stalled motor. It shouldn't fuse in normal full power running, but should only just stay running - any increase in current should cause the fuse to go. Use the closest value above the normal operating current you can. Remember the rating on the fuse is not the current it blows at but the maximum current that it will allow to flow without blowing. How long it takes to fuse after that depends on the overcurrent - for example blade types fuses will carry a 10% overcurrent for 100 hours typically and a 35% overcurrent anything up to 10minutes. The fusing time will only fall below 1 second for an overcurrent of 250% (i.e. 70Amps). If oyu use a single fuse put it on the input to the ESC - if you have space, put fuses on the input and the output of the ESC. Have the one on the input of the ESC the next size up at least to the one on the output. The output fuse protects the ESC against the motor stalling out, the input fuse protects against the ESC failing. This is not as important with an ESC that uses relays (e.g. ACTion Condor 20) as failure of the output transistor will drive either full speed or no speed. With a bridged ESC (e.g. MTronics, ACTion P93) if there is a transistor failure there is the danger of shorting the supply causing meltdown or even fire. ALWAYS ALWAYS fuse the input to the ESC

Wom
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BlueWotsit

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Re: Speed controller questions
« Reply #9 on: March 27, 2008, 04:17:33 PM »

Thanks to all for the input and guidance - especially Wombat for his very detailed answer - appreciated
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