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>> Home > Forum > Electrical Related > ESC problem
ESC problem
(733 views)
Author Message
sheaffy
(Seaman)





Forum Posts: 3
20th Oct 2016 12:42  
>> Permalink
mdlbt.com/24005

Hi there, bit of a newbie to ESC's

Need some advice on what AMP rating to get for the current setup any and all help is appreciated.

Prop -> Graupner Jet Propulsion Unit 5 (2347) (G2347)
Flange Diameter: 78mm
Shaft Diameter 7mm


Motor -> Graupner HPD 2948-3760 7.4V Brushless Motor
Operating voltage range : 7,4... 24 V
All-up weight, approx. : 180 g
Free shaft length: 10 mm
Output : 2000 W
Number of poles: 4
Permissible motor direction : R und L
Case length: 58,2 mm
Shaft diameter: 4 mm
Max. charging rate: 105 A
Case diameter: 29 mm
Revolutions/Volt: 3760
Part No: G7757


Battery -------
7.4v 2s 40c 5600mah

Boat ->
Weight: will be 8 Kilos once equipment fitted.
currently around 5 kilos.

length:1.3m

I hope that this information is suitable and can help with my question.

many thanks 😀
Ashley

Haverlock
(Fleet Admiral!)





Forum Posts: 425
20th Oct 2016 20:18  
>> Permalink
mdlbt.com/24016

Your ESC should be 150-200A. The "Max. charging rate: 105 A " is a mistranslation the motor has a max current rating of 105A as a rule of thumb add 50% minimum for an ESC.

The battery you have specified can deliver over 200 A so your wire needs to be heavy duty. Since its a LiPo battery you need to handle with some care. Get a LiPo charger and make sure you do not discharge it below app. 3.4V per cell ( most ESC have a built in cut off ).


Graupner Brushless Control Navy V150 should fit the bill




"that's not a bug its just an undocumented creature."

Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)
Dave M
(Fleet Admiral!)





Forum Posts: 1428
21st Oct 2016 11:28  
>> Permalink
mdlbt.com/24020

Hi Ashley
Welcome to the site.
With such high currents it would be advisable to fit a fuse in the wiring to the battery.
I would reiterate Haverlock's advice, LiPos need correct handling in both the charge and discharge. The lowest recommended charge (should be with the paperwork received with the battery) for your battery should be observed and should be set in your ESC. Don't store them charged, the safe voltage is 3.7volts per cell and most decent chargers have a facility to discharge to this voltage.
A Wattmeter would be useful the check the actual current under load. Exceeding the motor or battery rating will cause damage and for about £20 a Wattmeter will save you time and money.

The Graupner Jet Drive is interesting to me as I am awaiting two jet propulsion units from KMB for my Shannon lifeboat. There is a max rev limit of 20000 revs on these units so it is important to match the brushless revs or risk damaging the bearings. I can't find specs for the Graupner but I suggest you check your documentation.
Good luck and please keep us posted.
Dave


Live long and prosper

Dave
sheaffy
(Seaman)





Forum Posts: 3
21st Oct 2016 14:01  
>> Permalink
mdlbt.com/24022

Thanks for the reply, the boat was working and producing considerable thrust. for around 8-9 minutes, then fuzzed out.....

We had a 160A ESC -> link to the ESC that blew. https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?id...

we had the esc set to 50% output anyway. so there shouldn't be too much of a problem. its a big boat, all fibreglass custom built.
and houses electrical equipment so weighs a fair bit too.

After the research i did, i concluded that the 160A ESC should be enough, however after looking at some equations, this may help?

the motor is 2000W and running at 7.4v..
so acording to the equation, it should be 270£ or have i got this wrong? this is on the assumtion that it uses the full 2000W of power.

DC watts to amps calculation
The current I in amps (A) is equal to the power P in watts (W), divided by the voltage V in volts (V):

Perhaps the AMP rating on the site is incorrect?

Dave M
(Fleet Admiral!)





Forum Posts: 1428
21st Oct 2016 19:07  
>> Permalink
mdlbt.com/24024

Hi Ashley
Your calculation is correct at full loading.
I can understand your logic regarding using the ESC at 50%. This I believe will limit the voltage output of the ESC which at full loading will result in increase amp draw.
In selecting a power set up it is easier to limit the current draw to about half the motor rated max, in your case 105/2 = 52 (approx) amps. Using a 7.4v battery will result in a wattage of 385 at 52 amps.
You can ensure your model is running at this rating by fitting a Wattmeter between the ESC and motor and measuring the Watts and /or current whilst holding the model in the water.
The 160 amp (max current) ESC should be good for 80 amps continuous so well within the spec for your motor.
If you are drawing more current than 50amps its possible the motor is overloaded for the thrust propeller in the unit. A 3760Kv brushless is more suited to a model plane or helicopter. A brushless with a Kv of 300 to 800 would be much better, drawing less current and giving you longer sailing time.
As regards the amp rating, my experience is that almost all manufacturers quote the max current value rather than the sustainable running current value. Probably why most use an ESC rated at twice the expected running current.
With the wattage values you are running I would expect some form of water cooling would be required for both motor and ESC.
Hope this clarifies and good luck with getting the correct setup
Dave 😀


Live long and prosper

Dave
sheaffy
(Seaman)





Forum Posts: 3
21st Oct 2016 19:38  
>> Permalink
mdlbt.com/24025

Hi Dave, both the motor and the ESC have water cooling,

The boat does need a fair bit of speed as in the use case, speed is of the essence, it is a GPS controlled boat, i set the GPS cords and it goes there, all the technical side is working, from my testing at low throttles, however when i cranked it up thats when the ESC blew..

Luckily all the electronics are on a completely separate power supply 😉 so they are all safe 😊

Do you have any links to products that you would recommend?

Regards
Ashley




Dave M
(Fleet Admiral!)





Forum Posts: 1428
22nd Oct 2016 08:18  
>> Permalink
mdlbt.com/24027

Hi Ashley
All Wattmeters are much the same. Can be sourced on E-bay but also from OK suppliers eg Component Shop http://www.componentshop.co.uk/catalogsearch/result/?q=meter... - their 150Watt meter is £17.95. Just about to leave for the Blackpool Show so no yime to post further
Dave


Live long and prosper

Dave