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[DickyD]

One of you chaps will no doubt tell me the answer.

I have a Mtroniks Vision 600 motor voltage, 12V.

ESC. 12v  Overlander 50amp
 50 Amp waterproof boat speed controller.
 50amp Forwards & Reverse. (20Amp reverse).

Battery. Tornado TRC4300 9.6v Sub C Nimh.

Problem. Blows 15 amp fuses under load.

Query. Can I use a bigger fuse ?? ???

[Peterm]

Dicky, in all of my boats, I use  fuses rated about 5 amps below the ESC rating.   The only exception is my lifeboat which has a water-cooled 60 Amp ESC for which I use a 20 Amp fuse.    Try a 10 Amp and see how it goes.    Pete M

[DickyD]

Thanks Peter, bit of a dunce with electrics, tend to be too cautious.
Will try the 10amp fuse.
It runs on a 5amp out of the water but wont under load.
Mind you goes like stink, actually jumped out of kiddies paddling pool and the water was nearly 6" down from the top.

[Stavros]

would not hessitate to use a 40amp fuse in it DickyD Stavros

[DickyD]

Thankyou Stavros.

[Stavros]

Cancel previous post
DickyD you have a problem your ESC is too small for that motor check out the following site
http://www.mtroniks.net/mtroniks_products.asp?CategoryID=5&SubCategoryID=32
They clearly state in the specification that the max current is and I quote 69 amps so your ESC in theory burn out at max power becausethe max amperage of that esc is only 50amps,I would suggest you buy the sonic4super esc from mtronics which has a 75amp limit.Yes I know the price of it but the go on ebay for around 30squid which is what I paid for one recently Stavros

[Shipmate60]

DickyD,
Is the 69 amps the stalled current?

Bob

[DickyD]

I would think so Bob or I'm going to need a bigger battery

Spec from Pandan

 Voltage, 12V

* Off load current, 1.57A

* Max current, 69A

* RPM, 19800RPM

[DickyD]

As this is a 12V motor and I 'm using a 9.6v battery which says on it 35amp disharge is this likely to overload the motor then ?

Please excuse all the questions its just that I am hopeless when it comes to electrics.

[DickyD]

Thanks for the help fellas.
I have been informed by A Model World that the 69amps is the stalled current and that the actual current is a lot less than my 50amp esc. I shall therefore be going for the larger fuse, either 20 or 25 amp.

[glennb2006]

Hi Dicky,

as a function of you using 9.6 instead of 12 volts the curent will be proportionally higher as a result.

A 12volt batter will reduce the current. So will a smaller or finer pitch prop. It will also reduce the amount of water displaced by the prop.

Glenn

[wombat]

Glenn,

I think that this comment is incorrect - reducing the voltage across a motor will not increase the current, it will reduce it. It will also reduce the rotational speed and the torque produced, which could result in stalling - it will also mean the motor is runnig at a lower efficiency.

Dicky, looking at the stats for the system as you outline it.....

The motor is rated at

Off load current: 1.57A - this is the absolute mimimum current the motor will draw if run at the rated voltage. Essenitally it is the current required for the motor to overcome its own internal losses

Maximum current: 69A - this is the stalled current - i.e. at rated voltage with the rotor locked. This is the absolute maximum current the motor will draw at rated voltage. If this is a 12V motor, the motor resistance is 0.17R - on 9.6V this will equate to a stall current of 55.2A - slightly over the ESC rating. Therefore to protect the ESC and the Motor, I would follow earlier advice and use a 45A fuse.

However, you throw another item into the mix....
The battery states its maximum discharge current is 35A - this is not necessarily the maximum current that the battery will supply, but its maximum safe operating current - sustained operation above that limit has the potential to damage the battery because of localised heating effects within the cells.

So....in your place, assuming the motor will give you the speed you want,I would stick with the battery, motor and ESC and fuse the system at 35A possibly using a slow-blow fuse if a suitable one is available, otherwise a striaght 35A fuse.

Wom

[Welsh_Druid]

Hi Dicky,

as a function of you using 9.6 instead of 12 volts the curent will be proportionally higher as a result.

A 12volt batter will reduce the current. So will a smaller or finer pitch prop. It will also reduce the amount of water displaced by the prop.

Glenn

 ???

I just did a test. Boat static in the workshop ( i.e. motor not under load).

24 volts  1.09 amps
12volts     .88 amps
 6 volts     .75 amps.

Just confirms what Wombat said - current reduces  as voltage reduces.

Don B.

[malcolmfrary]

Its the old chestnut about getting the same power from a lower voltage - you need a different motor which will result in a higher current.  If you connect the low voltage motor to a higher voltage battery, you will get much more power, if only for a short time.
If you have a battery with low current delivery (because of high internal resistance) then offering it a load will cause the measured voltage to reduce, and the higher the current demanded (say by having more motors), the greater the voltage drop effect.

[kiteman1]

I blew two speed controllers once at one meeting in a 35lb scale tug because I didn't realise that when you get under way you have to overcome the inertia and the water density according to the ambient temperature.  I tried a higher rated fuse (20amp) on my next try even though the motor only drew 3amps in normal running.  All was ok afterwards.

Any observations would be appreciated with regard to protecting the ESC and motor on models in general for the future ???

[DickyD]

Cured my problem. Larger fuse and a smaller prop.

[glennb2006]

Glenn,

I think that this comment is incorrect - reducing the voltage across a motor will not increase the current, it will reduce it. It will also reduce the rotational speed and the torque produced, which could result in stalling - it will also mean the motor is runnig at a lower efficiency.

Dicky, looking at the stats for the system as you outline it.....

The motor is rated at

Off load current: 1.57A - this is the absolute mimimum current the motor will draw if run at the rated voltage. Essenitally it is the current required for the motor to overcome its own internal losses

Maximum current: 69A - this is the stalled current - i.e. at rated voltage with the rotor locked. This is the absolute maximum current the motor will draw at rated voltage. If this is a 12V motor, the motor resistance is 0.17R - on 9.6V this will equate to a stall current of 55.2A - slightly over the ESC rating. Therefore to protect the ESC and the Motor, I would follow earlier advice and use a 45A fuse.

However, you throw another item into the mix....
The battery states its maximum discharge current is 35A - this is not necessarily the maximum current that the battery will supply, but its maximum safe operating current - sustained operation above that limit has the potential to damage the battery because of localised heating effects within the cells.

So....in your place, assuming the motor will give you the speed you want,I would stick with the battery, motor and ESC and fuse the system at 35A possibly using a slow-blow fuse if a suitable one is available, otherwise a striaght 35A fuse.

Wom

You are (in hindsight) absolutely correct - and I unreservedly apologise for any inconvenience caused by my observations - which are actually correct for loads that are resistive - not inductive - which a motor is.

You have received information which is accurate and proven in other posts, which is a good thing.

So once again sorry.

Ask me one on Petrol or something that burns Methanol and you might get the right answer.

Glenn

[malcolmfrary]

Hi Glenn,
It works for resistors as well, or it did when Mr Ohm wrote his law, which has yet to be repealed.  Reduce voltage offered to a constant load, reduce the current.
 I=V/R.
With a high resistance power supply, the output voltage will be reduced under load, but this is the effect, not the cause.  The only time for practical purposes that the current might rise with reduced voltage is where the motor can no longer turn and is effectively stalled, and this condition will further reduce the voltage.  It is normal to avoid this condition by ensuring that the full voltage is always available for the motor, by having a good supply, and by using PWM ESCs.