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Old Aug 15, 2015, 03:33 PM
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Help!
Dual batery full redundant regulated powersupply

Hi you all

I am trying to design a dual battery full redundant regulated power supply.
- no single point of failure
- No current limiting
- fix output voltage ( for now )
- both batteries need to be used

I have now this


- until second red line : is on/off switch ( using emcotec dpsi switch later more )
- until third red line : use of both batteries
- until fourth line : linear regulator no current limiting

the p channel mosfet don't have the correct part name. I am looking still for a correct low Ron P channel mosfet .

the 6 pin header is for the emcotec switch. Pint 2 is commen for both on and off. en 1 and 3 are then On and Off. I am still looking for the male connector for this.


So does this work, a I am not that good at analog electronic design ?
Or are the any improvement ?
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Old Aug 15, 2015, 04:55 PM
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I was checking every thing and realized that the power switching part is not working because off switch is connected to the ground.

Here is a drawing on what I found when I opened up the dpsi switch

On the left is what I have seen in the switch only the diode I am not sure.
It can take full 2s voltage for the power led.

on the right a new design to steer the on/off P channel mosfet

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Old Aug 16, 2015, 12:29 AM
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Quote:
Originally Posted by amigob View Post
Hi you all

I am trying to design a dual battery full redundant regulated power supply.
- no single point of failure
- No current limiting
- fix output voltage ( for now )
- both batteries need to be used
?
What is your application? Model airplanes?

If you're using a two cell LiFe or A123 battery pack for receiver power, they will work just fine by directly parallel connecting them to your receiver.

My club members that are flying $$$$ models are using either a pair of 2S1P A123's for the 30 cc gassers, or a pair of 2S2P A123's for the really big models.

Each battery pack has its own on-off switch, and each has a separate connection to either the receiver, or power junction box.

I've got well over 100 A123's in my various models, mostly for electric power to the brushless motors up front. Never had any A123 battery ever short out. In fact, even if severely damaged by being left to run dead, they can be jump started and recharged. Damage is done though, since a jumpstarted A123 will loose around 30% of its Ampere Hour rating.
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Old Aug 16, 2015, 03:30 AM
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Applications is planes, and I have personal experiences that two times lifepo on Spektrum 9000 series receiver was not enough. One of the servos ( Rudder ) short circuit on a 90" 3D plane, and it got in to a chain reaction because the servo cable became so hot that it started to melt other servo wire and receiver, so that eventually the voltage dropped below 4 volt ( telemetry, that is very close to brownout ).

Above is the first step to a 100% redundant power box, that only can work
with serial ( Futaba SBUS ) data from receiver, where every set of two servos has it own micro controller that receives data from 2 receivers ( that meas that every side of the plane has 2 or 3 micro controllers).
Every servo will get its own poly fuse and level shifter. And every servo will have its own check if it is still working.

found a picture: I know I shouln't have tide the servo leads to gether



recognize what this is/was :
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Old Aug 16, 2015, 09:46 AM
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You complicate things too much... the basics of the most complicate power boxes are simpler than you think.
First, for redundancy you need two power sources and a simple switch, done with two schottky diodes, nothing else. This arrangement will take power from both packs, discharging them equal, same degree.

For the case when one servo overcharge the power, the solution is called poly-fuse or resetable fuse, one for each servo, chosen for the appropriate current of the application.
So no electronics, no schematic, everything can be assembled on an universal test board.
For those not so skilled, this guy sell the board ready to use:
http://rc-miskolc.emiter.hu/rc-misko...-board-english
The pictures are enough to retrieve all the elements I described above, a hint, the yellow bugs are the poly-fuses.

Everything else added to the above is pure fanciness, imo, bells and whistles.
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Old Aug 16, 2015, 09:59 AM
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I don't agree.

But I want to discus the above electronics, not if somebody finds it necessary or not. ( this for is full of that )

I Thought about it very good and for me it is necessary. And I have a lot of other requirements, that are going to be added that can't be bought at this point in time.
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Old Aug 16, 2015, 01:51 PM
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The fact you don't agree don't change that I am right.
These are the basics, you can start build from there. Without poly-fuses on each servo, that receiver melt will happen again. Is all about damage isolation and stop propagation.
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Old Aug 16, 2015, 02:55 PM
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maybe you should read before you post

quote from post #4
Quote:
Every servo will get its own poly fuse and level shifter. And every servo will have its own check if it is still working.
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Old Aug 16, 2015, 06:54 PM
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To Complicated???

Duplicated by accident
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Old Aug 16, 2015, 06:58 PM
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To Complicated???

Duplicated by accident
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Old Aug 16, 2015, 07:00 PM
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To Complicated???

Quote:
Originally Posted by amigob View Post
I don't agree.

But I want to discus the above electronics, not if somebody finds it necessary or not. ( this for is full of that )

I Thought about it very good and for me it is necessary. And I have a lot of other requirements, that are going to be added that can't be bought at this point in time.
It looks like the output of your circuit consists of a 2 Volt DC voltage reference, along with R1 and R2 with a MosFet to regulate the output voltage to 5 VDC. That makes the MosFet a linear regulator.

Linear regulators on 9 Volts DC and 5 Volts output results in a four volt DC voltage drop on the MosFet. Assuming no heat sink on your MosFets, they can handle perhaps 1.5 Watts maximum heat loss. At the 4 Volt DC voltage drop across your MosFets, that's only a continuous rating of 0.37 Amps DC output current due to the heating of the MosFets.

Not to mention the very good chance that your MosFet could be a very good high powered oscillator under some load conditions. Yeah, I've worked with MosFets, and have made more than a few very good, high powered oscillators. And, fried a few in the process.

Your Zener diode is a two Volt DC unit. Checking the specs on that diode, it needs a minimum of 5 milliamperes, preferably 10 Ma to properly run it into the "Knee" of its voltage/current curve.

Your R3 with a value of 2.2 Kohms will only provide around one or two ma. That is going to affect the output voltage of your linear regulator. Not to mention what will happen to the output voltage when it is subjected to a temperature variation between perhaps 32 F to 100 F.
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Old Aug 17, 2015, 03:16 AM
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Thanks vollrathd,

The output is still not fixed yet, I probably go with 3.3 zener, and I already adapted the resistor to 1k.
That would give around 6.6 volt.

The FET's will get 100-150 cm2 of cooling copper on the PCB with good thermal relief
that will increase the output current drastically. But I need to test if it is enough, else I will add a fan. When you see how I will put everything together, you will see how simple that will be.

The oscillation, I am a little bit worried about, some people say it will others say it won't. My on experiences is it doesn't, but still I am worried about it.
- when does that happen, how to test it ?
- is it then with very high frequency, the opamp is a 5Mhz.

What would be the best way to stop it from osculating ?
- having an input filter on the opamp or using an opamp output filter ?
- does adding more capacity on the output suppress this problem ?
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Old Aug 17, 2015, 05:27 AM
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Surely if there is to be redundancy, each arm needs to be of a different design and construction ?

If there is a design flaw, which for example is triggered by a particular set of power supply conditions, and it caused a failure of some type, it would affect both arms of the redundancy equally.
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Old Aug 17, 2015, 05:59 AM
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@ Stuart

Mhhh, That is definitely something to think about. But that would not be easy, because the two channels should behave the same.

The middle part of the schematic is switching between BAT1 and BAT2, if there is different behavior ( timing ) then both channels will try to power the servos at the same time or worse non of the two will power the servos.
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Old Aug 17, 2015, 12:08 PM
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Quote:
Originally Posted by amigob View Post
Thanks vollrathd,

The output is still not fixed yet, I probably go with 3.3 zener, and I already adapted the resistor to 1k.
That would give around 6.6 volt.

The FET's will get 100-150 cm2 of cooling copper on the PCB with good thermal relief
that will increase the output current drastically. But I need to test if it is enough, else I will add a fan. When you see how I will put everything together, you will see how simple that will be.

The oscillation, I am a little bit worried about, some people say it will others say it won't. My on experiences is it doesn't, but still I am worried about it.
- when does that happen, how to test it ?
- is it then with very high frequency, the opamp is a 5Mhz.

What would be the best way to stop it from osculating ?
- having an input filter on the opamp or using an opamp output filter ?
- does adding more capacity on the output suppress this problem ?
I fixed my oscillation problem by putting a 0.1 uF ceramic capacitor between the output and the gate of the MosFet. That didn't always work though. Tried the same with a MosFet driving the field winding of a 12 Volt alternator years ago, and was never able to kill the oscillations.

That got expensive, since every time the MosFet went into oscillations, it blew out. And, it only took a few seconds. The MosFet was rated at 100 Volts, and was protected by an MOV. Also tried using a MosFet in a battery analyzer I built many years ago. The problem with oscillations was so severe, I finally replaced it with a power transistor circuit. Having a high frequency OpAmp isn't going to help matters.
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