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Old Jan 31, 2016, 07:48 AM
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Arrangement for multi-engines.

How is the electrical power organised on multis?

For example; let's say that I want to use 3 motors on a fixed-wing model. The great advantage of electric power is that I can probably avoid having an "engine out", with the associated control problems.

If each motor has a separate power supply, then I could still find myself having to deal with asymmetric flight, if one battery became exhausted prior to landing.

Do you run several motors from a common power supply? Or what?
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Old Jan 31, 2016, 08:59 AM
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Several motors and one battery (or more than one but connected in parallel) is common.

Of course you still have the possibility of one ESC dying or the LVC on one being lower so cutting that motor first if you try to run too long. Nothing is perfect.

Steve
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Old Jan 31, 2016, 09:08 AM
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Quote:
Originally Posted by bogbeagle View Post
... Do you run several motors from a common power supply?...
too long battery wires will kill ESC over time: precautions, solutions & workarounds

Vriendelijke groeten Ron
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Old Jan 31, 2016, 09:27 AM
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I have seen lots of people talk about common power supply. I ran H9 Twin Otter on separate and it was a bit tricky getting back from strong downwind when one cell in a battery failed.

But to be fair the battery had poor reliability record, I found out after from others who experienced failures with particular brand.

Now if I had the two batteries on that plane connected in parallel and then powering both motors maybe I would only have experienced a fair power drop to both motors instead of totally losing one motor due to the bad battery going to LVC.

With good quality batteries I fly with confidence either way.
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Old Jan 31, 2016, 09:33 AM
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And if you want to add some extra wire length it can be nice to have Data Logging ESC. When I did an extra foot or so of heavy guage wire on the 7 Foot 182 the logs showed like 1% ripple, so only 10% of the level that Castle says you should add Caps at to protect the ESC. So there was absolutely no need to add any caps.

http://www.castlecreations.com/produ...-cap-pack.html
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Old Jan 31, 2016, 10:34 AM
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So, a common battery ... with each motor having its own ESC.

Would that be considered to be good practice?

I am thinking of modelling a tri-motor ... Dewoitine 332. Don't want to find myself with no power and unable to reach the runway.

You can prolly tell that I don't have much experience with electric models. I do fly a couple of powered gliders, but nothing fancy.
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Old Jan 31, 2016, 11:44 AM
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My Concorde twiin EDF has separate battery to each motor but my Tu144 has paired batterys....

Which is best ? To be honest logic says PAIRED. In practice ? Yes I have had my Concorde suffer reduction of power on one side ... and its obvious by SOUND when it happens ... the synch of motor sound goes awry. Did it cause loss of model ... no but it sure made my heart race.

The criteria is not whether you have separate batterys - but the capacity you need to fly for a reasonable time. A single battery could be the answer but it would need to be a substantial C rating to cater for the demand on it. With multiple packs paralleled - the C rating can in fact be less - because the packs add up .. I know - some Guru is going to argue this - but I base that statement on actual use and not bench theory.

There is an additional advantage of paralleling packs .. in failure - you only have to replace probably one pack instead of an expensive large single. Second - you can split the packs location so that weight is distributed better.

Nigel
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Old Jan 31, 2016, 01:46 PM
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WRT the 3-engine Dewoitine ... I thought that the centre motor might have its own pack, with the outboard motors sharing a pack.

If either of the packs quits, the model should remain controllable and have at least some power.
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Old Jan 31, 2016, 01:59 PM
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Quote:
Originally Posted by bogbeagle View Post
WRT the 3-engine Dewoitine ... I thought that the centre motor might have its own pack, with the outboard motors sharing a pack.

If either of the packs quits, the model should remain controllable and have at least some power.
Good idea.

Nigel
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Old Jan 31, 2016, 02:17 PM
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Quote:
Originally Posted by bogbeagle View Post
So, a common battery ... with each motor having its own ESC.

Would that be considered to be good practice?

I am thinking of modelling a tri-motor ... Dewoitine 332. Don't want to find myself with no power and unable to reach the runway.

You can prolly tell that I don't have much experience with electric models. I do fly a couple of powered gliders, but nothing fancy.
If the distances are too great, I would put a battery pack local to each motor that could handle the motor's amp draw on it's own, but then link all of them up on their positive terminal to form a sort of distributed battery pack where the local battery pack acts as a transient buffer (sort of like the big capacitors on ESCs) to reduce the voltage spiking on the lines.

I didn't talk about linking up their negative terminals (ground terminals) because that is mandatory if they are all to interact with some other electrical system (i.e. your receiver).
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Old Jan 31, 2016, 02:58 PM
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Crikey ... that sounds a bit complicated.
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Old Jan 31, 2016, 03:02 PM
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Crikey ... that sounds a bit complicated.
Not really...just set up battery for each motor, and then connect them all without moving where they physically are. That's all it really is.
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Old Jan 31, 2016, 05:13 PM
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Crikey ... that sounds a bit complicated.
It's actually just what I said originally...several batteries connected in parallel. Just a confusing way of describing it .

Steve
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Old Jan 31, 2016, 07:11 PM
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. . . I didn't talk about linking up their negative terminals (ground terminals) because that is mandatory if they are all to interact with some other electrical system (i.e. your receiver).
If you do not have a common negative wire that is capable of carrying the expected unbalanced current ( such as if one battery sags earlier than the others) then the puny servo sized wires that link the radio signal to all the ESC's will be forced to carry current that they are not intended to, and carry it through the receiver bus. Better to use a common negative conductor that can carry the full motor current. Of course best of all is to never get near the point where the batteries might be fully discharged with a multi-motor plane. Or any plane for that matter.
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Old Jan 31, 2016, 07:13 PM
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If you do not have a common negative wire that is capable of carrying the expected unbalanced current ( such as if one battery sags earlier than the others) then the puny servo sized wires that link the radio signal to all the ESC's will be forced to carry current that they are not intended to, and carry it through the receiver bus. Better to use a common negative conductor that can carry the full motor current. Of course best of all is to never get near the point where the batteries might be fully discharged with a multi-motor plane. Or any plane for that matter.
Yes, wire up the negative as if they were motor wires and not just token electrical connections.
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