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Author Topic: Brushless Motor Problems - Stalling  (Read 987 times)

Davo

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Brushless Motor Problems - Stalling
« on: July 29, 2018, 01:05:24 PM »

(See also Sea Queen going Brushless in the Powerboat section)
My Sea Queen was fitted with a Tornado Thumper 3542/05 1250 kv and a NiMh 12v battery. All was running well but the Taymia connectors were not coping. On advice XT60 connectors were fitted all through (I am ok on soldering) and all seemed well on the 60amp ESC. On the water the boat went off ok but soon stalled. I could here the ESC reset and set off again. Motor slowed and stalled.
Thinking the ESC was now the weak point I fitted a water cooled Hobbyking 120amp ESC. On the water the same thing again, motor just fades away. ESC resets and the same happens again.
On the bench, applying power, the motor revs up but then dies, even with throttle at max. Same in reverse. At neutral the ESC resets and the same thing happens. Both ESCs are set up with their programming cards.
So I bought a new 3548/05 900kv Tornado Thumper motor and fitted that. Same thing happens. Battery is 100% and neither escape makes any difference. Even plugging the battery direct to the ESC (no fuse in circuit) the same thing happens. The RX is on its own power. The TX has new batteries.
I am pretty sure all soldered joints are sound and so I am seeking any advice that might solve the problem. The XT60 connector replacements are the only real change in the system. Could it be a bad joint in the system failing under load?
Any thoughts folks?
David.
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David

gra2

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Re: Brushless Motor Problems - Stalling
« Reply #1 on: July 29, 2018, 01:41:11 PM »

Hi David it could be that the Nimh battery cannot cope with the power drain of the brushless motor.
May need a Lipo battery that will cope.

I have had this experience when trying a gell cell battery with a brushless motor when you need the power the battery cannot cope and stalls.

Graham
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Fastfaz

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Re: Brushless Motor Problems - Stalling
« Reply #2 on: July 29, 2018, 02:46:14 PM »

  I am no brushless expert but this might change your thinking after the last post re gel cell batteries. I have a twin screw Maltby tug running twin 70mm Graupner schottle drives and a bow thruster, the esc's are matched to the brushless motors 30 amp Mtronics, bow thruster 14k motor with a P98 (same power both directions) this all runs from a 14ah sealed lead acid gel cell. This tug will pull you in a rowing boat and the battery lasts all day in towing comps. I can only speak from experience with gel cells and Nimh's but it seems weird that a battery would cause this especially if its fairly new and fully charged. I have had experience of batteries appearing fully charged (13/14 volts showing) then as soon as they go under load out comes the white flag!
      I hope you get it sorted soon,good luck.
                Cheers, Pete.
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john44

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Re: Brushless Motor Problems - Stalling
« Reply #3 on: July 29, 2018, 06:26:38 PM »

Hi David,
You say the Rx has its own power supply, did you remove the red wire from the esc?
Rx plug.
If not that could be your problem because the Rx will be receiving 2 supplies from
Both batteries.


John
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Andyn

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Re: Brushless Motor Problems - Stalling
« Reply #4 on: July 29, 2018, 07:23:49 PM »

Hi David it could be that the Nimh battery cannot cope with the power drain of the brushless motor.
May need a Lipo battery that will cope.
My money is on this. Is your esc currently set up to be expecting a LiPo? I've seen it too many times that an esc is expecting the higher voltage and when the voltage drops under load from a NiMh it goes below the LiPo voltage cutoff range.
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imsinking

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Re: Brushless Motor Problems - Stalling
« Reply #5 on: July 29, 2018, 09:00:48 PM »

You need to set your ESC cell mode to NO PROTECTION if your using niHms, a new ESC is set to LIPO by default, a program card is the way to go ,get the correct one for your ESC , their all different , been there done that, haventh got the t shirt .
Bill
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Davo

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Re: Brushless Motor Problems - Stalling
« Reply #6 on: July 29, 2018, 10:45:55 PM »

Thanks for the above tips. I will double check the ESCs which each have their own programme card from the manufacturer.
I have a 100mm servo lead in line between the ESC and RX, with the red wire disconnected. This allows the system to be put back if required. There is a matched Futaba battery pack for the receiver.
I hope to get there in the end!
Thanks
David
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David

chas

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Re: Brushless Motor Problems - Stalling
« Reply #7 on: July 30, 2018, 07:31:15 AM »

The fact that this happens when the boat is on the bench is odd, there is little load on the battery then. Nevertheless after checking the ESC, I would connect a volt meter to the battery whilst it is connected to the model and observe the voltage when you power up. A dead cell in a NiMH battery is not uncommon.
Chas

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malcolmfrary

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Re: Brushless Motor Problems - Stalling
« Reply #8 on: July 30, 2018, 10:14:47 AM »

  I am no brushless expert but this might change your thinking after the last post re gel cell batteries. I have a twin screw Maltby tug running twin 70mm Graupner schottle drives and a bow thruster, the esc's are matched to the brushless motors 30 amp Mtronics, bow thruster 14k motor with a P98 (same power both directions) this all runs from a 14ah sealed lead acid gel cell. This tug will pull you in a rowing boat and the battery lasts all day in towing comps. I can only speak from experience with gel cells and Nimh's but it seems weird that a battery would cause this especially if its fairly new and fully charged. I have had experience of batteries appearing fully charged (13/14 volts showing) then as soon as they go under load out comes the white flag!
      I hope you get it sorted soon,good luck.
                Cheers, Pete.
A Sea Queen and a tug are very different.  A 14AH SLA would probably cause the Sea Queen to sit down in the water and perform like a tug.  While an SLA can provide an instant burst of enormous current (they start car motors quite well), they can't supply high currents for long without damaging themselves.  NiMH an LiPo both pack a lot more energy into a lot less weight.  For any given capacity, LiPo will be that bit lighter and has the possibility of a much higher C rating, but at the cost of being a bit more finicky about its operating conditions.


The healthy high voltage from an SLA that drops (usually by 2 cell's worth) is a sign of a dud cell.  It has volts but zero capacity, as soon as it gets a demand it loses its charge and becomes a reverse cell, so the pack not only loses that cells contribution, but gets its voltage further reduced by the losses caused by the dud cell trying the reverse charge.  Much the same with NiMH, but the dud cell usually becomes a low quality, low value resistor resulting in large voltage fluctuations.
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Davo

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Re: Brushless Motor Problems - Stalling
« Reply #9 on: July 30, 2018, 11:53:06 PM »

Thanks for all the tips. I checked the battery output at the first connector (to eliminate possible bad joints) and found 12v available. As I powered the motor up the voltage fell to 5v and the ESC auto cut-out. So a low battery was the culprit despite my thinking I had charged it and the evidence of the battery meter (see pic).
A few hours on the charger brought it up to power and all is well again.  It would be interesting to wire in a permanent meter in the boat.
Well, I now have a bigger 3548  motor though 900kv not 1250kv. Perhaps a bigger prop is next.
Many thanks
David
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David

imsinking

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Re: Brushless Motor Problems - Stalling
« Reply #10 on: July 31, 2018, 12:33:45 AM »

 :-))  that's a relief , dont forget , a fully charged battery will  indicate a HIGHER voltage,  in your case a 12v nihm pack should be showing 13.5v - 14.0v , and be fully discharged at 11v or so . . .
Bill 
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malcolmfrary

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Re: Brushless Motor Problems - Stalling
« Reply #11 on: July 31, 2018, 09:01:32 AM »

All of the smart chargers that I have seen just look at the voltage that has been reached.  Some look for a drop in the charge current as their intended voltage is approached.  This is fine with a uniformly healthy pack, but not with a pack where one or more cells has got low capacity.  The dud cell can come up to voltage very quickly leaving the rest to catch up when charging stops, usually in less time than seems reasonable.  This is why I prefer "dumb" overnight trickle chargers.  The dud cell gets re-formed, the relatively low charging current doesn't do the rest of the pack any harm.
A weak point on NiHM packs is the welded strips connecting the cells.  When they start to corrode, they become a high resistance, reducing the current that can be delivered, and dropping voltage under load.  Fortunately, a dead one can be cured with a big enough soldering iron and reasonably heavy wire.
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Davo

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Re: Brushless Motor Problems - Stalling
« Reply #12 on: July 31, 2018, 10:12:11 AM »

Bill,  thanks for that advice. As you can see in the photos that must be what happened. I was fooled by the 89% reading and thought it still OK to use. We live and learn.
The battery is new and has only been used a few times; so hopefully the connectors are ok.
Just need to have some sea trials.
David
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David

john44

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Re: Brushless Motor Problems - Stalling
« Reply #13 on: July 31, 2018, 12:40:43 PM »

Hi David, the fault you have with your batteries I had with 5 off 8.4v 5000mah stick batteries.
They were not 12 months old had little use,kept charged but failed under load just the same
As yours have with duff cells.

I now use lipo,s time will tell


John
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Andyn

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Re: Brushless Motor Problems - Stalling
« Reply #14 on: July 31, 2018, 12:43:16 PM »

The obvious answer is ditch 90's technology and go Li-Po ;)
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Subculture

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Re: Brushless Motor Problems - Stalling
« Reply #15 on: July 31, 2018, 01:31:43 PM »

If you’re concerned about the incendiary characteristics of lipo chemistry, but would like the benefits of high capacity and high current delivery, then I would recommend LiFe Po4 batteries. These have a slightly lower power density, are more expensive in the short term, but cheaper long term as they have a very long shelf and cycle life and are far safer.
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