Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: SlimRick on June 12, 2009, 09:30:47 am

Title: Current draw from motors
Post by: SlimRick on June 12, 2009, 09:30:47 am
Does anyone have a rough idea of what current is likely to be drawn from a 12v motor taken from a car heater blower?  Just a rough idea would be good som I can get the ESC's ordered.
Title: Re: Current draw from motors
Post by: andrewh on June 12, 2009, 10:00:12 am
It would depend entirely on the load (propellor)

I take it thse are the one in your Perkasa - the props have cleaned up well!
If you telll us the prop diameter somebody will know the anticipated current draw per motor
Stavros is running one brute motor in his Perkasa - that might give you a top end estimate

Title: Re: Current draw from motors
Post by: derekwarner on June 12, 2009, 10:13:35 am
As unbelievable as it may sound....those 12V car ventilitation/heater fan motors are approx 3 amp @ stall & you need a pair of multigrips to stall the motor...try the thumb & forefinger test  just results in burnt or getting very HOT  thumb & forefinger   %% Derek
Title: Re: Current draw from motors
Post by: Seaspray on June 12, 2009, 01:22:34 pm
I've a ford escort rad fan motor fitted to the 72 inch long KG5 class battleship.

It draws 1 maybe 2 amps and will run all day on a 12v 7 amp gell. I have a 2 or 2 1/2,  3 blade propeller.

Can do a good scale speed + Runs on a Electronize HVR 43 ESC.
Title: Re: Current draw from motors
Post by: SlimRick on June 12, 2009, 02:21:44 pm
I'll have a measure of the props when I get home tonight - from memory they are 25-30mm diameter.  Not sure of the pitch.  The Perkasa has 2 of these fitted, and looks like they were wired in parallel - I'm assuming so only one ESC would be needed.  Any disadvantages of doing this?
Title: Re: Current draw from motors
Post by: FullLeatherJacket on June 12, 2009, 02:42:11 pm
I have to interject here, to prevent this chap from going down what I'm pretty sure is the wrong road.

Blower motors and big lead-acid batteries are super for tugs, but this isn't a tug.
25mm or 30mm props on a model this size are a complete waste of time. I had a 32mm prop on my Shamrock, and that's only 28" long and weighs nowt. You need at least 45mm and preferably 50mm to get this thing moving properly, and that's with 3 blades.

If you are going to fit "sensible" motors e.g. MMB900 then use a separate ESC for each and don't even think about lead-acid batteries. Like I always say, the clue is in the word "lead". NiMH is the way to go. There are issues with LiPo batteries in certain circumstances - which I won't go into now.

Having seen Dave Jones' big Perkasa going on one of these motors with 20 cells, quite why anyone should contemplate any other set-up is a bit of a mystery now. He reckons he gets 55 minutes' running time - and Stavros is not known for tootling his toys around the pond at walking speed.

Suit yourself. Works for Stavros.


O - I quite forgot Barry Boy's 46" Swordsman, which has TWO Darke Horse geared 785s in it. You need a safety belt just to watch the video of it going.........