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Author Topic: Two batteries - again?  (Read 1021 times)

tonyH

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Two batteries - again?
« on: June 16, 2017, 08:52:31 PM »

Sorry but this is just a sort-of repeat of a thread which ran (according to a warning from Martin) 730 days ago.

Assuming the battery (LiPo) capacity is great enough, can I run 2 brushless motors and 2 esc's off 1 battery safely and are there any major pitfalls?

The earlier thread started mentioning brushed motors/SLA batteries etc. so a brushless/Lipo specific answer would be appreciated.

Cheers

Tony
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JimG

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Re: Two batteries - again?
« Reply #1 on: June 16, 2017, 09:14:02 PM »

The simple answer is yes. make sure that the C rating of the LiPo is suitable for the total current to both motors. (Maximum current is C times capacity. eg  a 30C 4000mAh pack can give up to 120A although best to keep down to around 60A max.)

Jim
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microgyros

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Re: Two batteries - again?
« Reply #2 on: June 16, 2017, 09:54:27 PM »


Frequent mention of  "any metal-to-metal joints?" seems to be allowed so the very real potential pitfalls of sharing one battery deserve repetition. These are common to brushed however.
  • common mode noise superimposed on the pwm input signal to each esc.
  • in the event where one main -ve esc to battery connection comes apart while the corresponding +ve stays intact all of the motor current is sent to the battery through the back door route through the narrow gauge black cables.
I've taken steps to mitigate effects of both in esc design because modellers will do as they please, regardless of warnings.


A noise problem can be solved with a ferrite toroid on one of the 3-way esc input leads. Opto isolation prevents both potential problems as does two separate batteries.
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JimG

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Re: Two batteries - again?
« Reply #3 on: June 17, 2017, 07:41:05 AM »

Two motors and 2 escs to one battery is commonly used in electric flight without problems. If both escs use a bec for power then it is usual to remove the red wire from the plug of one so only one provides power to the receiver. Some systems do come with a ferrite ring on the wires to the receiver.

Jim
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malcolmfrary

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Re: Two batteries - again?
« Reply #4 on: June 17, 2017, 09:54:53 AM »


  • in the event where one main -ve esc to battery connection comes apart while the corresponding +ve stays intact all of the motor current is sent to the battery through the back door route through the narrow gauge black cables.
The ability of the return to carry the current required wire is often overlooked until either unexpected controls happen, or the light gauge wire does what light gauge wire does with too much current, and becomes a fuse.  It is also a potential way of introducing full voltage to bits of the circuit where full voltage should not go.  A lot of attention gets paid to distributing power, the at least equally important return tends to be forgotten.
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steamboat66

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Re: Two batteries - again?
« Reply #5 on: June 17, 2017, 01:05:38 PM »

i have built multirotors, one of which has 6 ESCs all connected to one master supply. no problems.
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microgyros

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Re: Two batteries - again?
« Reply #6 on: June 17, 2017, 01:58:58 PM »


I want to clarify that nobody yet has sought to dissuade TonyH from using 1 battery safely in his boat. I pointed out two major pitfalls asked for and described two preventative measures.


Opto isolated escs and ferrites wound onto escs are now very common and due to the growth in multicopters and standalone switching becs. The boat punters  for whom I have repaired their damaged gear were always surprised and initially ignorant of the potential hazards and the preventative measures needed.

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tonyH

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Re: Two batteries - again?
« Reply #7 on: June 17, 2017, 08:26:30 PM »

So, can it be summarised that 2 brushless motors/2 esc's can be used with 1 battery BUT it is preferable that opto esc's are used along with ferrite ring to reduce interference.
Opto means that a second power source is required for the Rx which adds to the weight so you might as well use 2 batteries.
If weight is critical then you're lumbered?

Or have I misread the situation totally?

Tony
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microgyros

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Re: Two batteries - again?
« Reply #8 on: June 17, 2017, 09:53:29 PM »



So, can it be summarised that 2 brushless motors/2 esc's can be used with 1 battery BUT it is preferable that opto esc's are used along with ferrite ring to reduce interference.
Opto means that a second power source is required for the Rx which adds to the weight so you might as well use 2 batteries.
If weight is critical then you're lumbered?

Or have I misread the situation totally?

Tony
You can use two escs with one battery. Just don't hook up the second esc with alligator clips or only the positive wire when you find it works perfectly on the bench. That is the two most memorable instances where I was asked to do repairs.


If you get mysterious signal problems where one throttle affects the other then the obvious first step is to wrap one lead round said ferrite OR look up the internet on how to opto-isolate one of the escs. The purpose of opto isolation is to break the ground loop, the wound ferrite is to impede differential current that could circulate via a ground loop. Both measures would be redundant. Two opto escs would also be redundant and would require you to install an additional bec. I wouldn't waste time looking for a marine opto esc.
 So if you have a high permeability ferrite then wrap one of the 3-way cables through it.
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tonyH

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Re: Two batteries - again?
« Reply #9 on: June 17, 2017, 10:36:38 PM »

Thanks all for the input.

If it all blows up I'll just have to stick with steam!

Tony
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