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Author Topic: Low battery cut out / ESC  (Read 557 times)

hullmanhunter

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Low battery cut out / ESC
« on: April 03, 2018, 07:41:11 PM »


Can you give me some advice please. I'm still struggling with the baitboat which I am building for fishing.

 
I have two 20A HEXFET ESCs connected to an RC mixer module (throttle and rudder)

 
The motors are Mtroniks M600 marine motors and the power supply is 12V sealed lead acid battery.

 

 
The motors are equipped with a pair of left hand and right hand propellors and wired to rotate inboard.

 
On powerup I wait for the ESC to arm themselves following switch on and I find that if I open the throttle very gradually I can just about get the motors running but if I open it up too quickly one or other motor will cut out and the ESC resets. The only way I can get the drive anywhere near useable has been by turning the endpoints on the RC channels down below 50%. I've currently got them at 30%. This means that there is insufficient power to drive the boat adequately because it is quite heavy.


I thought the problem was a bad battery because it seems the ESCs are cutting out because of a voltage drop.


What do I need to do to fix this? In the long run a lighter hull but for now, what if I took off the torque rings ?
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RST

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Re: Low battery cut out / ESC
« Reply #1 on: April 03, 2018, 08:29:31 PM »

Hello,

I tend to steer clear of electrical things as I find it much harder to explain than do myself.  But a couple of things stand-out to me...

1) have you a multimeter? On Volts this would let me check a) with the battery connected whether it's goosed or not (I'd expect more than 12v on full charge with nothing connected, if it's more like 11v then the SLA is potentially goosed). b) is it too big to stick in the bath and measure battery voltage with the motors running at a reasonable rate, again if the volts fall too low then the SLA may be goosed
2) What size are the props and have they been changed from stock (too much current draw)?  Usual recommendation diamater no bigger than motor can size bla bla.
3) Have you tried loosing or removing couplings and a) checking the propshafts move freely between fingertips and b) motor shaft itself turns freely (on motor shaft you shulf feel some incriments of turn like 6 or 10, but no roughness). Take the props off and try running the thing dry -if the same syptoms persist then it's probably not over-propped.

.....higher speed on throttle outeardly sounds like too much current draw to me anyway.

Do you have separate receiver batteries -sounds not?  In that case the BEC (Battery Eliminator Circuit) may be dropping too far below required voltage -something is goosed.  Either that or something is goosed and the ESC's are hitting current limit.  Many might say to upgrade components but there's not necessarily anything wrong with the set-up -you just need to test some things in turn I think.  Removing the mixer and plugging an ESC directly into an RX channel in turn might help identify a problem also.  Think how to check each item in turn separate from other influences.

...PS there's probably no point in taking off the torque rings / bands.  But do as many individual checks as you can and check notes as comparisons.

Hope this helps,

Rich
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unbuiltnautilus

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Re: Low battery cut out / ESC
« Reply #2 on: April 03, 2018, 09:08:54 PM »

Your M600 motors are drawing far too much current at 12v. They may say 6v to 12v but using direct drive, I would be reluctant to exceed about 8.4v. Two options, both of which will be a challenge, either re-motor, suggest either Torpedo 800 or CEM-900T from Jotika ( both bigger motors ), or find a roughly 5:1 reduction gearbox for the M600s. I have run these motors on a 5:1 unit that Robbe used to make and it dropped the amps to about 6.5A per motor at 14.4v. Reduction drives are becoming rare things, although following one of the threads in Tugs, I found an all metal unit from the US of A, at 3.3:1, might do the job.

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hullmanhunter

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Re: Low battery cut out / ESC
« Reply #3 on: April 03, 2018, 09:40:53 PM »

Hello,

I tend to steer clear of electrical things as I find it much harder to explain than do myself.  But a couple of things stand-out to me...

1) have you a multimeter? On Volts this would let me check a) with the battery connected whether it's goosed or not (I'd expect more than 12v on full charge with nothing connected, if it's more like 11v then the SLA is potentially goosed). b) is it too big to stick in the bath and measure battery voltage with the motors running at a reasonable rate, again if the volts fall too low then the SLA may be goosed
2) What size are the props and have they been changed from stock (too much current draw)?  Usual recommendation diamater no bigger than motor can size bla bla.
3) Have you tried loosing or removing couplings and a) checking the propshafts move freely between fingertips and b) motor shaft itself turns freely (on motor shaft you shulf feel some incriments of turn like 6 or 10, but no roughness). Take the props off and try running the thing dry -if the same syptoms persist then it's probably not over-propped.

.....higher speed on throttle outeardly sounds like too much current draw to me anyway.

Do you have separate receiver batteries -sounds not?  In that case the BEC (Battery Eliminator Circuit) may be dropping too far below required voltage -something is goosed.  Either that or something is goosed and the ESC's are hitting current limit.  Many might say to upgrade components but there's not necessarily anything wrong with the set-up -you just need to test some things in turn I think.  Removing the mixer and plugging an ESC directly into an RX channel in turn might help identify a problem also.  Think how to check each item in turn separate from other influences.

...PS there's probably no point in taking off the torque rings / bands.  But do as many individual checks as you can and check notes as comparisons.

Hope this helps,

Rich

Thanks this is sound advice and ill check everything methodically.


It is a brand new battery but I'll check it.
I've tried smaller props but that did n't help. The problem occurs when dry running anyway.


 The prop shafts  seem fairly free running but I've noticed that when the power to the motors cut out the light on the receiver goes out momentarily which can' be good . I'll try a separate power supply for the RC and see if that helps. But I suspect that in the long run I will have to get different motors.


Cheers
Paul
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hullmanhunter

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Re: Low battery cut out / ESC
« Reply #4 on: April 03, 2018, 09:44:21 PM »

Your M600 motors are drawing far too much current at 12v. They may say 6v to 12v but using direct drive, I would be reluctant to exceed about 8.4v. Two options, both of which will be a challenge, either re-motor, suggest either Torpedo 800 or CEM-900T from Jotika ( both bigger motors ), or find a roughly 5:1 reduction gearbox for the M600s. I have run these motors on a 5:1 unit that Robbe used to make and it dropped the amps to about 6.5A per motor at 14.4v. Reduction drives are becoming rare things, although following one of the threads in Tugs, I found an all metal unit from the US of A, at 3.3:1, might do the job.


I was beginning to think that the motors must be the problem. Well I guess sometimes you have to pay to learn. What would happen if I switched to 6V batteries?


Cheers
Paul
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unbuiltnautilus

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Re: Low battery cut out / ESC
« Reply #5 on: April 03, 2018, 09:49:51 PM »

If you can drop to 6v that will reduce the current draw significantly. Speed should still be good, although the chances are the model is a streamlined as a bathtub!
The only issue with a 6v source comes about if you are using solenoids to either drop the doors, or drop lines. These, if fitted, will probably be 12v units. If all your doors are servo activated then no problem.
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hullmanhunter

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Re: Low battery cut out / ESC
« Reply #6 on: April 04, 2018, 08:27:17 AM »

If you can drop to 6v that will reduce the current draw significantly. Speed should still be good, although the chances are the model is a streamlined as a bathtub!
The only issue with a 6v source comes about if you are using solenoids to either drop the doors, or drop lines. These, if fitted, will probably be 12v units. If all your doors are servo activated then no problem.


Thanks. That gives me another option.
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hullmanhunter

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Re: Low battery cut out / ESC
« Reply #7 on: April 04, 2018, 09:40:13 PM »

Yeah it' Defo  the motors! The battery was ok on the multimeter 12.6 V (not fully charged) when I revved up the motors it droppd to a scary 8.5V(briefly). I did nt need to check anything else.


I will have to order some new kit.


Thanks guys.
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Stavros

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Re: Low battery cut out / ESC
« Reply #8 on: April 04, 2018, 10:02:18 PM »

Could well STILL be the batts......charge them up properly and retest also beg steal or borrow another batt tho check properly...what amps are the motors actually drawing




Dave
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malcolmfrary

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Re: Low battery cut out / ESC
« Reply #9 on: April 05, 2018, 10:09:38 AM »

The battery needs to be fully charged to stand up to the starting current of the two motors. 
Although the label on the battery says "12 volts", a reading of 12 and a bit when not loaded is not a good sign.  If the battery does not come up to at least 14 volts, there is something wrong with it.  A dud cell that can still pass some current could still give 12+ volts off the 5 remaining good cells until current is drawn, when the dud instantly reverse charges, dropping 4 volts (the two volts it wasn't giving, plus the two in opposition).
If the motors are driving props that are too big, both the starting current and the running current will be increased.  There are two answers to driving a big prop - either a gearbox or a larger motor.
SLA have never been the ideal choice for continuous heavy current delivery, but in the past their failings were passed over because there was no alternative unlike today.
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john44

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Re: Low battery cut out / ESC
« Reply #10 on: April 05, 2018, 11:39:48 AM »

What battery connectors are you using because we get the same problem if tamiya connectors are used
Where the female connectors work loose due to connecting and disconnecting. Works on low power
Dies on full in or out of the water. Tighten the connectors problem solved.


Just a thought.


John
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