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Author Topic: Max Safe Amps/Volts ?  (Read 4826 times)

John Mk2

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Max Safe Amps/Volts ?
« on: October 05, 2010, 12:25:20 PM »

Hi All trying to find out if the B/L motor in my  H.O.R App/Cat will be safe on lipo 6s 35c ? Its a FSD F-540-36764 Xl  Useing a 125amp (150 burst) Suppo E.S.C ,38mm Prop
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #1 on: October 06, 2010, 06:54:33 AM »

According to a quick bit of research its a 2075 Kv motor which means at 6S it will want to spin at over 45000 RPM, you want to aim for 30-35000 rpm, any more and the props just cavitate so 4S would be my recommendation.

If  the Kv of the motor is different just divide 35000 by the Kv and that will give you the voltage to run at.

Nick
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John Mk2

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Re: Max Safe Amps/Volts ?
« Reply #2 on: October 06, 2010, 08:49:00 AM »

Thanks Nick  :-)) Its got a 2770 kv sticker on it  {:-{ Thats the bit i cant work out {:-{
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #3 on: October 06, 2010, 09:05:08 AM »

Well 2770 is a 3S motor, don't think it will like 60,000+ Rpm %% you would want use around a 1500Kv for 6S ;)

Nick
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Circlip

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Re: Max Safe Amps/Volts ?
« Reply #4 on: October 06, 2010, 09:44:03 AM »

Life was so much easier before "Inrunners" and "Outrunners" although the 380s and 400s etc. started to muddy the water. 2770kv seems to translate as 2770 revs per volt.

  Regards  Ian.
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #5 on: October 06, 2010, 10:00:42 AM »

Bang on Ian,

Having Kv (RPM per Volt) makes it easier to pick a motor for an application, how fast does a 540 rev at 12 volts? maybe its a 27 turn or a 12 turn or a 55 turn. all the same motor in dimensions, vastly different in application.

Nick
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Circlip

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Re: Max Safe Amps/Volts ?
« Reply #6 on: October 06, 2010, 10:13:56 AM »

Listen Pal, we had ED Bees, Hornets , Racers and Hunters. No Problems  :-))  {-) {-) {-)

  Regards  Ian.

 Sorry, could be classed as flipant hijacking. Where does the designation determine a 3S or 6S ??
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John Mk2

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Re: Max Safe Amps/Volts ?
« Reply #7 on: October 06, 2010, 10:32:19 AM »

Sorted now  :-)) Have been mislead i think  >:-o When i got the boat they said it was fitted with a Suppo 125 amp E.S.C so i programmed as one all sorts of snags (cutting out not starting ect) Just tryed the 70amp program & its fine  ;) NOT happy with all that messing about  >:-o >:-o
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #8 on: October 06, 2010, 10:33:37 AM »

Hi Ian,
 
What are those, Ancient technology I guess ;D

The 3S 4S etc is number of cells in the pack, In reference to Li-pos generally.
3S, 3 Li-po cells in Series, they can also have a second set of numbers Ie 3S2P,  3 series 2 parallel, to make a double capacity 3 cell battery.
Each cell has a nominal voltage of 3.7 volts and a fully charged voltage of 4.2V

Nick
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Circlip

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Re: Max Safe Amps/Volts ?
« Reply #9 on: October 06, 2010, 11:24:57 AM »

Thanks Nick, I realise what the 3S etc. refers to, but how do you link this to a 2770Kv as a 3S motor??

  Regards  Ian.
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mattycoops43

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Re: Max Safe Amps/Volts ?
« Reply #10 on: October 06, 2010, 12:04:58 PM »

Motors are not designated with 3s or 4s, as you can use the battery you want to get different performance. However, they will have a voltage upper range, (normally 5s on cheaper motors) where it will run on higher voltage but nto for very long!

Matt
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #11 on: October 06, 2010, 12:22:54 PM »

Hi Ian,
Matty is right , you can run the 2770 Kv on 5S but it will will have a no load RPM of 51000 RPM, which is too high for FE use, A gearbox could be used but most FE are direct drive.

11.1 volts X 2770 Kv = 30747 RPM if you went to 4S you would be looking at 41000 RPM, too High for direct drive, the props have an upper limit of around 35000 RPM before they cavitate.

Nick
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LOCURA

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Re: Max Safe Amps/Volts ?
« Reply #12 on: October 10, 2010, 08:38:58 PM »

I presume that getting more power means looking at a different factor to volts, I thought that a higher kv meant more power, but it means using less volts.?????  <:(

Cheers
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John Mk2

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Re: Max Safe Amps/Volts ?
« Reply #13 on: October 10, 2010, 09:01:00 PM »

K.V does not mean power {:-{  Its the wattage the motor can kick out.
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John Mk2

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Re: Max Safe Amps/Volts ?
« Reply #14 on: October 10, 2010, 09:08:34 PM »

Mines sort now due to misunderstanding useing the wrong E.S.C program settings. Like a rocket now on lipo 4s :o :o   
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #15 on: October 11, 2010, 05:00:51 AM »

Just to clear up, Kv means nothing more than RPM per VOLT, it has NOTHING to do with watts and amps.

In general lower Kv motors are larger and can handle more power. Exceptions do occur.


Power (watts) is = volts X amps

Most motors will have a maximum watt rating,
Amps are controlled by the size of the prop(load)
Voltage of course is fixed by the battery pack.

 For example a 300 watt motor may draw 15 amps at 12 volts on a certain prop, consuming 180 watts of power, put the same motor and prop on 24 volts, amps will double, but power goes up 4X 24 X 30 = 720 watts far exceeding the motors capability. you would need to prop down so the motor is drawing only 12.5 amps to keep it within its power rating.

Nick
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LOCURA

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Re: Max Safe Amps/Volts ?
« Reply #16 on: October 18, 2010, 07:36:01 PM »

Hi Nick

As you will remember I do not understand electrics..... HELP.

Sigma 51" and 50 mph !!!

Just been discussing using a Leopard 5690 / 1090. This gives max volts 33. Max amps 160.
Max Power 5.5 Kw. BUT what "watercooled" ESC will cope..  Hydra 240 only covers 25 volts  (240 amps)  (6 lipos). but will it take 5.5 Kw?

The Hydra HV 120 may cope?? at a price!   Anything cheaper as good?

How long on a Lipo 6s 5000?

Cheers

Richard
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nick_75au

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Re: Max Safe Amps/Volts ?
« Reply #17 on: October 19, 2010, 06:56:07 AM »

Hi Richard,

Not quite, 5300 watts for the Castle 240 LV, Hobby king have a Aquastar HV 240 amp, Off Shore Electrics have the better quality Swordfish with the same specs, not sure on prices but from quick research there is not much difference.

There is a guy on RC groups running a big boat using a Little Screamers boat motor and he runs for 2 minutes on 5000 mAH packs, can run slightly longer but is protecting them.

Nick
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LOCURA

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Re: Max Safe Amps/Volts ?
« Reply #18 on: October 19, 2010, 05:03:52 PM »


      Thanks again for your time Nick

                 Richard
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