Connecting multiple +5v to the board via ESC

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spagoziak
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Connecting multiple +5v to the board via ESC

Post by spagoziak »

Alex & experts,

How bad is it to leave all 4 +5v lines from my ESC's connected to the board in full? What's going to happen if they remain that way?

Thanks!
spag

Alexinparis
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Re: Connecting multiple +5v to the board via ESC

Post by Alexinparis »

I've never heard stories about ESC burning or malfunctioning when connecting every 5V together.

I think it depends on the ESC BEC techno (switched or linear regulator) , but I don"t know exactly the risks.

spagoziak
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Re: Connecting multiple +5v to the board via ESC

Post by spagoziak »

Hm, thanks for the reply, Alex. I think I'll not worry about it. Seems like it may be just a myth?

gompf
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Re: Connecting multiple +5v to the board via ESC

Post by gompf »

Hi!

It maybe a risk! It doesn´t depend on the basic technology (switching/linear), e.g. iirc it´s possible with YGE-BLMCs (switching BEC), but on the circuite/layout/interconnection.
The two main risks are:
-Doesn´t work as it shoud which means that the main load is driven by the BEC with the highest output Voltag (few mV) and you will not get additional current out of the parallel circuite. If you draw much more current than rated for one BEC they will die just one after another, depending on their output voltage.
-Oscillations between the ICs because you have 3 instances trying to regulate one voltage with some RC-constants in the 5v line filters. This may also overload/burn the BECs.

Good way for parallel connection of linear regulators is to add a serial resistor of about 0.1 Ohms in the 5V lines (1 per BEC). This will give you a significant voltage drop under load so it balances the output current between the different 5V lines.
For the oscillation problem it´s most safe to test the whole circuite with running motors.

If you can find the type of the regulator IC you may find the information how to connect this type in parallel in the datasheet. Sometimes it´s just possible without problems, sometimes not recommended.

Regards,
gompf

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matbogdan
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Re: Connecting multiple +5v to the board via ESC

Post by matbogdan »

I've burned 3 ESC turnigy plush like this way. When i've connected the main power i've produced allot of white smoke. Never and i am very serious with this connect in parallel the +5V of the 2 or more ESC.
If you really want to do this, put some diodes that will match the current flow so you can stop the ,,electrons'' :P before they reach your SBEC.
Or simply just cut 2 of 3 red wires and you will be fine.

noobee
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Re: Connecting multiple +5v to the board via ESC

Post by noobee »

matbogdan wrote:I've burned 3 ESC turnigy plush like this way. When i've connected the main power i've produced allot of white smoke. Never and i am very serious with this connect in parallel the +5V of the 2 or more ESC.
If you really want to do this, put some diodes that will match the current flow so you can stop the ,,electrons'' :P before they reach your SBEC.
Or simply just cut 2 of 3 red wires and you will be fine.


do your plush escs use switching bec or linear bec?

mon_lolo_fr
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Re: Connecting multiple +5v to the board via ESC

Post by mon_lolo_fr »

Turnigy PLUSH 10 are operating in linear mode (as in the HK documentation !)

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UndCon
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Re: Connecting multiple +5v to the board via ESC

Post by UndCon »

No need to cut any wires - if you do it will be hard to program your ESC's afterwards.
Use a needle or similar to lift up the tab on the servo connector and pull it out backwards. secure the positive with some heatshrink tube and you are good to go.


//UndCon

algerbens
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Joined: Thu May 19, 2011 2:19 pm

Re: Connecting multiple +5v to the board via ESC

Post by algerbens »

The Battery Elimination Circuits (BEC) are constant voltage sources. They supply a constant voltage under varying current demands , in this case the constant voltage level is typically 5 volts. The constant voltage output from several BECs will not be the exact same voltage under varying current loads. With the BEC outputs connected together the circuits will interact. In the case of our ESC/BECs the output voltages will probably close together and one of the BECs (the one with the highest output voltage output) will supply most of the current and everything works fine. But, why have these BECs unpredictably interacting when the interaction issue can be simply eliminated by not connecting several of them together?

ziss_dm
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Re: Connecting multiple +5v to the board via ESC

Post by ziss_dm »

Hi,
The 99% of cheap chinise esc's have 2-3 7805 connected in paralel inside the ESC. Like this one:
http://www.hobbyking.com/hobbyking/stor ... duct=13430
http://wii-esc.googlecode.com/svn/doc/S ... y-nFET.jpg

I cannot see any reason, why they would not work in parallel. Just do not expect that that 4 2 amp BEC's could handle 8 amp load. ;)

regards,
ziss_dm

gompf-2
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Re: Connecting multiple +5v to the board via ESC

Post by gompf-2 »

Hi,

with this design it´s OK because each 7805 in the BEC circuite has a 22Ohms(?so big?) series resistor (R30-32). It´s save but you´ll never have stable 5V at the output as there is a load depending voltage drop trough this resistors, the 5V are regulated in front of them.
When I think further it may be even better to use all BECs with this design in parallel because this woud spread the current over more of this series resistors. This woud decrease the load depending voltage drop, in theory.
I have the 12A blue series, they have only one regulator IC in the BEC line without series resistor so I didn´t check it in RL.

Regards,
gompf

algerbens
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Re: Connecting multiple +5v to the board via ESC

Post by algerbens »

Within a single inexpensive ESC , the BEC three terminal voltage regulators that are paralled, are usually from the same manufacturing batch and are mechanically bonded to maintain the same temperature and minimize regulator to regulator output voltage levels.

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EOSBandi
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Re: Connecting multiple +5v to the board via ESC

Post by EOSBandi »

Guys,
Rule number one: Do not trust in your Esc-s regulator, use a separate BEC. That extra couple of gramms pays itself back. You will have less noise, more stable 5volt.

Never ever under any circumstances tie together the bec outputs of your esc-s. linear regulators are not designed to use paralell. If you see such a bec solution on a esc, do not trust it.
A

flyman777
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Re: Connecting multiple +5v to the board via ESC

Post by flyman777 »

hi,
it is not desirable to connect more 7805 paralell.
No datasheet does evoke that possibilty.
Effectively it's possible in a circuit but not recommanded. You must have ballast resistors (or diodes) about 1 - 0,1 ohm to perform the voltage balance between the regulators. That is only possible on a proper PCB but not between different ESC with long wiring.
So you must connect the BEC of only 1 ESC.
But must you have so much power, 1 RX2,4GHz # 80 mA, 4 ESC # 60 mA, CPU+Sensors # 40 mA, 2 LEDs # 20 mA , that to say we must have badly about 200 mA max for a ESC 1A. This regulator will dissipe then # (12 - 5)*0.2 = 1,4W, this heat must be dissipate so that this ESC must be ventilated.
If you must have more power, use a external switching BEC, but it not linear and can introduce some noise in the supply ( use external inductors and capacitors to filter).

A+
flyman777

2.4g Shaun
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Re: Connecting multiple +5v to the board via ESC

Post by 2.4g Shaun »

matbogdan wrote:I've burned 3 ESC turnigy plush like this way. When i've connected the main power i've produced allot of white smoke. Never and i am very serious with this connect in parallel the +5V of the 2 or more ESC.
If you really want to do this, put some diodes that will match the current flow so you can stop the ,,electrons'' :P before they reach your SBEC.
Or simply just cut 2 of 3 red wires and you will be fine.



Hi, this advice isn't strictly true. Turnigy have, on their latest Plush 10A esc's, 2 linear Becs soldered in parallel , to double the Bec output to 2A. The Hobbywing equivalents have only one.

The important point is if they are switching or linear.. Parallel switching or mixed switching and linear could cause issues. Parallel linear ones have never caused me issues over the last 10 years of many many hours of flying multi engine, multi esc models.

But as mentioned 1 Bec will provide sufficient current for a Multiwii controll board and sensors / IMU, so it does no harm to remove the positive lead from the Bec signal lead on all but one of them. The reason I don't do this is to provide some level of resiliance in case one of the Becs fails, which has happened to me..

At the end of the day its your choice, but I'm certain turnigy wouldn't sell the 10A plush with 2 Becs in parallel if this caused problems

If you smoked your esc's there could be many reasons why this happened, but it is wrong to assume that the paralled becs caused this as your becs were linear.

Cheers,

Shaun

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