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Old 02-05-2014, 12:39 AM   #1
dahawk
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Default Bus Tie Circuit

Redundant BEC's ?

Might want to try looking into a bus tie circuit:

http://www.rcgroups.com/forums/showthread.php?t=1854050

Watch the video.

A guy in another thread on RCG (nageotte) makes these up for $10.00 ea.

Allows the use of a linear bec with a separate ubec. Fail safe up the kazoo!

If one fails, the other one takes over. I bought 2 of them . One for the Mossy and one for the new P-51

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Old 02-05-2014, 07:23 AM   #2
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Originally Posted by dahawk View Post
Redundant BEC's ?

Might want to try looking into a bus tie circuit:

http://www.rcgroups.com/forums/showthread.php?t=1854050

Watch the video.

A guy in another thread on RCG (nageotte) makes these up for $10.00 ea.

Allows the use of a linear bec with a separate ubec. Fail safe up the kazoo!

If one fails, the other one takes over. I bought 2 of them . One for the Mossy and one for the new P-51

-Hawk
Yup
Got that on all of my giant scale models. Take a look:

Giant Scale Power System:
Battery Backup System
http://www.wattflyer.com/forums/showthread.php?t=63794
http://www.wattflyer.com/forums/showthread.php?t=67094

And the attached JPG's show how its done with an in line type of Shottky Diode rated at 10 Amps each. The articles were posted in wattflyer a year or two ago.

But, after buying all the diodes, servo connectors and shipping charges for these backup units, you're out - - - about $10.00 each.

(That white jumper is required if you're setting up dual ESC's for a twin motor model airplane)


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Old 02-10-2014, 03:51 AM   #3
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You two motivated me to try this for my new Supra build.

Just finished one and it works great! I am using a castle ICE lite 50 and an old Medusa 3.5 amp BEC. I adjusted the voltage output on the ICE so it ended up about .05 volts lower than the Medusa. Thats as close as I could get them to being equal.

Then I grabbed every Y extension I could find and hooked up 12 servos to my rx and proceeded to wriggle the sticks for all I was worth while testing current flow in each side.

The Medusa was supplying under 1 amp while the ICE was supplying over 3 amps! hmmmmm. Dropped the ICE BEC voltage down by .1 volts and now the ICE is providing aprox 1.5 amps and the Medusa about 2.5 amps on average.

The Medusa has really long leads and two splices in the output side so it must have a greater voltage drop than the ICE.

Close enough

Thanks!!!!

Oh - final weight with wires and potting epoxy 4.4 gms.


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Old 02-10-2014, 03:54 AM   #4
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By the way - unless the output voltages are pretty close there is no"sharing" of the load. The higher voltage source does all the work while the lower voltage source sits idle. It will switch over instantly thought if one side fails. Fast enough that my AR8000 cant detect a voltage drop.

I think I need a signature.
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Old 02-10-2014, 04:58 AM   #5
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Originally Posted by Larry3215 View Post
You two motivated me to try this for my new Supra build.

Just finished one and it works great! I am using a castle ICE lite 50 and an old Medusa 3.5 amp BEC. I adjusted the voltage output on the ICE so it ended up about .05 volts lower than the Medusa. Thats as close as I could get them to being equal.

Then I grabbed every Y extension I could find and hooked up 12 servos to my rx and proceeded to wriggle the sticks for all I was worth while testing current flow in each side.

The Medusa was supplying under 1 amp while the ICE was supplying over 3 amps! hmmmmm. Dropped the ICE BEC voltage down by .1 volts and now the ICE is providing aprox 1.5 amps and the Medusa about 2.5 amps on average.

The Medusa has really long leads and two splices in the output side so it must have a greater voltage drop than the ICE.

Close enough

Thanks!!!!

Oh - final weight with wires and potting epoxy 4.4 gms.
Hi Larry
Should you want to try different connectors for the next time you do this, check out these connectors from www.digikey.com used in the thread listed below.

They are available in configurations from two to 25 pins, also available in gold plating if desired. And, they have locking tabs on them.

I've got these connectors on all of my battery balance cables, along with several servo connectors on giant scale models. They work well.

http://www.wattflyer.com/forums/showthread.php?t=64209

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Old 02-10-2014, 05:24 AM   #6
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Thanks Denny!

I think I need a signature.
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Old 02-10-2014, 07:12 AM   #7
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Originally Posted by Larry3215 View Post
By the way - unless the output voltages are pretty close there is no"sharing" of the load. The higher voltage source does all the work while the lower voltage source sits idle. It will switch over instantly thought if one side fails. Fast enough that my AR8000 cant detect a voltage drop.

Yup
With two diodes isolating the two different uBEC's (Or batteries, or uBEC plus battery for that matter) you can disconnect one of them, and watch the output voltage with an oscilloscope. That scope will not see any voltage sag. Period.

The second backup DC supply and its associated isolating diode will take over in time periods of a small fraction of a microsecond. (That's a millionth of a second)

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Old 02-10-2014, 07:26 AM   #8
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Default

Yeah,

My understanding was that the idea was not necessarily to share the load but have a means whereby if say the linear bec failed , the ubec would take over.

The normal set up as I understand it when using a ubec in lieu of the esc is to disconnect the red wire from the linear bec. In this case, the separate ubec handles everything.

With the buss-tie setup, you can have both working even if the voltages differ. Maybe I misunderstood. EE's were guys that made dwg's during earthquakes. LOL
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Old 02-11-2014, 12:08 AM   #9
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Originally Posted by dahawk View Post
Yeah,

My understanding was that the idea was not necessarily to share the load but have a means whereby if say the linear bec failed , the ubec would take over.

The normal set up as I understand it when using a ubec in lieu of the esc is to disconnect the red wire from the linear bec. In this case, the separate ubec handles everything.

With the buss-tie setup, you can have both working even if the voltages differ. Maybe I misunderstood. EE's were guys that made dwg's during earthquakes. LOL

It's all a matter of "Voltage Drops". If you have two different power supplies, directly tied together, if one shorts out, it takes the other one with it. Not a good idea to ever directly parallel connect two electronic power supplies.

If they are isolated with diodes, preferably the Shottky type of diode, that prevents the two power supplies from interacting with each other. Plus, if one shorts out, those diodes isolate the dead power supply from the "Good One".

As for using two supplies, one switching BEC, and the other Linear BEC, it would be best to adjust the switching BEC to about 1/2 Volt or so higher than the linear BEC. That way, the Switching BEC would be handling 99% of the servo load during normal flight. And, if the Switching BEC sagged, or quit, the Linear BEC would take over.

Also, that Linear BEC won't get hot during normal flight since their would be no load on it. Makes it much better for that Linear regulator BEC to be used as a backup.

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Old 02-11-2014, 12:33 AM   #10
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Thanks Denny,

Great explanation Makes perfect sense. Here's what I got going.

http://www.rcgroups.com/forums/showthread.php?t=1854050




Bought 2 of them w/ extensions for $20.00 shipped. Seems like a cheap insurance policy.

-Hawk
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Old 02-11-2014, 03:54 AM   #11
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Originally Posted by dahawk View Post
Thanks Denny,

Great explanation Makes perfect sense. Here's what I got going.

http://www.rcgroups.com/forums/showthread.php?t=1854050




Bought 2 of them w/ extensions for $20.00 shipped. Seems like a cheap insurance policy.

-Hawk
Sounds good!

FYI for other readers of this thread, be a little careful with the leads coming out of those TO-220 case style diode assemblies. They are designed to be placed into a circuit board. Once. Then bolted down and soldered in place. Bending those leads close to the case twice or three times, and they WILL break off. We had unsecured TO-220 type case power FET's break off during normal shipping of our 200 pound circuit breaker controls.

That means those leads must be properly secured against vibration on gasser or glow powered models.

Voice of experience.

FYI, the lead wires of those 9 Ampere rated Shottky diodes is heavy gauge. Putting a sharp bend in them requires a needle nose pliers.

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Old 02-12-2014, 02:46 AM   #12
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Great Idea I like it

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 03-26-2014, 03:21 AM   #13
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Hey Denny

I was doing research for and new plane, and was thinking of a dual receiver power supply system.
In several of your schematic diagrams you show the use of a Shottky diode, digikey #90SQ035-ND

Digikey now shows this when you try to find the diodes; Obsolete item; call Digi-Key for more information. although they do still have a few of these diodes.

Do you have a choice of a new Shottky diode type?

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Old 03-26-2014, 04:14 AM   #14
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Originally Posted by Wildflyer View Post
Hey Denny

I was doing research for and new plane, and was thinking of a dual receiver power supply system.
In several of your schematic diagrams you show the use of a Shottky diode, digikey #90SQ035-ND

Digikey now shows this when you try to find the diodes; Obsolete item; call Digi-Key for more information. although they do still have a few of these diodes.

Do you have a choice of a new Shottky diode type?
Hey, thanks for noticing that the Digikey diode is obsolete.

I found another Shottky diode, also from Digikey. This one is rated for 12 Amps, with a 150 Amp surge rating! (Of course that 150 Amps is for a millisecond or two) It also has heavy duty in-line wire leads.

http://www.digikey.com/product-detai...5CT-ND/2179164 They are down to their last 9000 in stock, so order soon.

Digikey also has a wide variety of "TO-220" transistor type cases available. But, with a whole lot of experience with these, I'd not use them in a model airplane. These TO-220 case type units are designed to be bolted to, and soldered to a circuit board, since just flexing their leads once or three times will break off their leads.

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