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Author Topic: 3x MFA 850's  (Read 4619 times)

TomP

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3x MFA 850's
« on: June 27, 2011, 12:27:26 PM »

Hi can anyone help me please??

I have 3x 850 MFA motors each with their own Mtroniks 40A speed controller. Each motor and speed controller has a 12V 5000mah Nimh battery pack but with the throttle fully opened up the speed controllers cut out and then re sets themselves. Iíve been told itís due to the current draw of the motors causing the voltage to drop to low and the speed controller turns off. If this is the case what is a way around it? Would a capacitor work if so where to connect it or higher mah batteries?

Thank you for any help

Tom
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Pirate

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Re: 3x MFA 850's
« Reply #1 on: June 27, 2011, 04:56:42 PM »

Don't know what vessel you have or what prop size. My advice is to put smaller props on or ones with less pitch. Size and pitch determine amperage draw especially initial draw which can be colossal.
Regards
Pirate
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john s 2

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Re: 3x MFA 850's
« Reply #2 on: June 27, 2011, 05:50:14 PM »

Try connecting two battery packs together (In parallel) use the centre motor and see if all ok. 850s are power
hungry. I have three in my percasa.They would not be my first choice of motor but were fitted when i brought
the boat. I use pbs. John.
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ACTion

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Re: 3x MFA 850's
« Reply #3 on: June 27, 2011, 05:53:03 PM »

MFA appear to use 'Chinese' amps to rate those motors. The peak current is allegedly 11A but they regularly blow 25A fuses and melt P94 ABS cases. Yours are tripping so-called 40A ESCs - draw your own conclusions. Like the man says, try smaller props to start with. Neither of your own proposals would work.
DM
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Stavros

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Re: 3x MFA 850's
« Reply #4 on: June 27, 2011, 11:24:10 PM »

Im with Mr Action on this one I have seem Mtronics speed controller MELT with dire consequencies with those motors,bets thing for them is to use as Ballast.Have seen a 40 amp blow with those motors



Stav
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andyn

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Re: 3x MFA 850's
« Reply #5 on: June 28, 2011, 09:17:31 AM »

Not to repeat everything said already, but 850's are old hat. Avoid them like the plague.....
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Nige52

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Re: 3x MFA 850's
« Reply #6 on: June 28, 2011, 09:34:57 AM »

Interesting Andy, are you saying there is a better equivalent for the 850, or that brushed motors this size would be better with brushless?  :-)
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ACTion

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Re: 3x MFA 850's
« Reply #7 on: June 28, 2011, 10:37:26 AM »

Graupner Speed 900/ACTion 900 motors are the same physical size as MFA 850 but one helluva lot better motor. Less current drawn, smoother, not as electrically noisy and more torque. Shaft diameter is 5mm c/w 6mm for the 850, otherwise they are interchangeable.
Changing to brushless motors would entail buying three new ESCs as well as three new motors. Ouch!
DM
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nick_75au

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Re: 3x MFA 850's
« Reply #8 on: June 28, 2011, 10:58:04 AM »

There is something screwy with the quoted figures, I cant quite put my finger on it, it appears to me that the QUOTED no load RPM is too low, What size prop are you trying to spin because its the prop causing the current draw not the motor.

It would be interesting to do a Kv test on the motor, Spin it at a known RPM, such as in a drill press and measure the terminal voltage. RPM divided by measured volts = Kv ( RPM per volt)

Nick
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andyn

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Re: 3x MFA 850's
« Reply #9 on: June 28, 2011, 10:58:27 AM »

MMB/ ACTion motors are a million times better than an 850, as Dave has said.
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TomP

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Re: 3x MFA 850's
« Reply #10 on: June 28, 2011, 01:48:41 PM »

Hi thank you for your replies.

I have an inline blade fuse which is 20A on each live and neutral supply and to the ESCís, I can hold the boat at full throttle and the fuse is fine never blows. The motors are in a 49" Perkasa, I run both the outside props together and the center comes in at full throttle. The props are 32mm in diameter but I'm not sure what the pitch is, they were made by (I think) prop shop years ago (roughly 16 years) they should be scale for the boat.
When I put a DC clamp meter on the motors they are roughly pulling 17 Amps at full throttle. Here is the details off the component shop web site for the batteries 12.0V 5000mAh SC NiMH Compact Battery Pack. High capacity, fitted with standard ďTamiyaĒ style connector on very flexible, high current leads - 35A discharge capacity!
When the speed controllers do work for 30 seconds the boat goes very well but then just stops in the water until the speed controllers re-set.
I was warned that these motors are not very good but when they work they work very well itís just getting them to work.
I have tried paralleling up 2 battery packs it did the same thing.
Tom
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John W E

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Re: 3x MFA 850's
« Reply #11 on: June 28, 2011, 02:11:39 PM »

   Hi tomp
How do you get the center motor to switch in at full throttle ?

aye
john
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Martin [Admin]

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Re: 3x MFA 850's
« Reply #12 on: June 28, 2011, 02:51:44 PM »


A few questions me Lud!

1. When the whole thing cuts out, is anything red hot?

2. Do all the controllers cut at exactly the same time?

3. How many channels on the radio are you using to control the 3 ESC? (Electronic Speed Controller)

4. Are the ESC's link together on the radio side of things?

5. Does the rudder still work after the ESC cut out?

6. What radio make are you using?

7. where was on the night in question? Do you have alibi? 
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nick_75au

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Re: 3x MFA 850's
« Reply #13 on: June 28, 2011, 07:38:52 PM »

Every thinkg looks OK, 17 amps is probably a little high on the motors.. It sounds like though the battery voltage is collapsing as you said in your first post, Do a test on the motors again with a meter measuring voltage  across the pack. This will cofirm wether the problem lies there. When you paralleled the batteries was it to one motor only?

 I still wonder about the Kv of the motors, a 32 mm prop shoud not pull 17 amps at 10,000 RPM {:-{

Nick
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TomP

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Re: 3x MFA 850's
« Reply #14 on: June 29, 2011, 09:36:08 AM »


A few questions me Lud!

1. When the whole thing cuts out, is anything red hot?

2. Do all the controllers cut at exactly the same time?

3. How many channels on the radio are you using to control the 3 ESC? (Electronic Speed Controller)

4. Are the ESC's link together on the radio side of things?

5. Does the rudder still work after the ESC cut out?

6. What radio make are you using?

7. where was on the night in question? Do you have alibi? 

Hi, is answer to your questions
1. No nothing gets hot or slightly warm

2. I run both the outside motors together so when it happens they both go off at the same time, also the center does the same.

3. Just the 1 channel the center prop comes in via a Fleet relay, the 2 outside props are linked with a Y connector to the reciver.

4. As above

5. Yes the reciver has its own power supply, I have removed all the red wires from the ESC

6. I use a Futaba 10EXP

7. I wasn't there you can't prove it you have nothing on me!!

Cheers Tom
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Martin [Admin]

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Re: 3x MFA 850's
« Reply #15 on: June 29, 2011, 09:50:46 AM »


 Hi Tom!
 May I suggest, you disconnect the Fleet relay ( and everything to the centre shaft motor ) and test it with only the 2 outer motors and see what happens.....
 A bench test should suffice, then a domestic personal hydromatic hygiene expunger assembly test...... in the bath!


 7, We are checking the CCTV recordings!
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TomP

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Re: 3x MFA 850's
« Reply #16 on: June 30, 2011, 09:02:28 PM »

well charged the batteries and have being doing some testing. At full throttle on the motors the voltage drops by .2 volts thats out of the water. I tried all sorts but i could not get the speed controlers to play up. So head scrached for a while then wife called me to do summit walked out of the garage with the controller with the throttle open and there they go cutting out and then re setting and off they go again. So feeling a bit stupid at the moment what i can't understand i'm only 5m away from the boat with aireal out. Surely should be able to go further than that, ive got summit wrong the aireal is no where near power cables and has not been cut what can i do? Do feel stupid should of checked this it was how people want on about the motors being crap made me focus on them doh!!!
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Martin [Admin]

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Re: 3x MFA 850's
« Reply #17 on: June 30, 2011, 10:29:25 PM »

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HS93 (RIP)

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Re: 3x MFA 850's
« Reply #18 on: July 01, 2011, 01:59:41 AM »

Good job you didn't waste your money on new motors and speed controllers then ?

Peter
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TomP

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Re: 3x MFA 850's
« Reply #19 on: July 01, 2011, 10:37:02 AM »

I wasn't going to change them I knew it would be summit silly as the motors were not pulling too much current, the speed controllers were large enough and Component shop recommended me these batteries. So looked at the suppressors on the motors all looked fine until I looked at the centre motor and one of the legs off the capacitor was broken off the bottom DOH!! Sorted now runs a dream!! Thank you for all your help Tom
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Martin [Admin]

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Re: 3x MFA 850's
« Reply #20 on: July 01, 2011, 12:17:25 PM »

Excellent news and just in time for the weekend.


                                                                        .... now, about question 7 !!!!
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TomP

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Re: 3x MFA 850's
« Reply #21 on: July 01, 2011, 12:31:30 PM »

Yeah 7, well it might of been me, but the wife drove me to it!!!
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RaaArtyGunner

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Re: 3x MFA 850's
« Reply #22 on: July 01, 2011, 01:25:53 PM »

Yeah 7, well it might of been me, but the wife drove me to it!!!
As the driver of the getaway car she is now equally guilty as your accomplice O0 O0 :police: :police:
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