Replies to This Discussion

Permalink Reply by Bradley J Carr on June 7, 2012 at 6:10am

Simon,

I know there is a way to make a voltage monitor and have it switch to another when it gets down so far.

What my question is:  Why would you need this if you just parrallel two batteries and then you would have the same amount of flight time even if you could switch between the two?

Because one problem I see with switching is hopefully you could make it fast enough that it wouldn't have a chance for the esc to shut down.  Also if it didn't switch fast enough then you would lose the APM and GPS location. 

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Permalink Reply by Simon Howroyd on June 7, 2012 at 6:24am

Hi Bradley,

One of the sources would be a fuel cell not a LiPo and doesn't have the performance of a LiPo.  Depending on flight modes, the power supply would need to be one or the other chosen by me (or the onboard controller).  Eg on take-off or landing you would want to be on the LiPo not the fuel cell.  Matching the fuel cell voltage to the LiPo max 12.6v or something is very tricky and IMHO not a good idea without a charging circuit which is a pain.

Switching isn't ideal, the APM etc would all be on a separate circuit so not affected by the switching, which led me to think 2 ESC's and 2 motors is the solution.  Not gracious, light, cheap nor pretty mind you!

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Permalink Reply by Bradley J Carr on June 7, 2012 at 6:35am

Would you beable to tie both power supplies together with a voltage regulator and capacitor that would keep the voltage at what you want it to be.  Then if your power supplies don't match perfectly your not hurting anything?  This is interesting and I don't know enough about the power supplies your trying to use besides the LiPo

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Permalink Reply by Simon Howroyd on June 7, 2012 at 6:39am

Yes this is certainly a possible solution in theory.  Do you know of any voltage regulators (DC DC converters?) that will be light and small enough for flight?  Gotta be able to sustain 1kW power don't forget if it had an 80A ESC.  Cheers!

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Permalink Reply by Bradley J Carr on June 7, 2012 at 6:46am

Yea I was just thinking about that.  How close can you match the voltage?

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Permalink Reply by Bradley J Carr on June 7, 2012 at 6:38am

I have seen something before when I was working on something here in the hospital.  A company used two separate power supplies just for redundancy.  What was interesting was they used a zener diode to control the voltage they wanted.  I am going to see if I can find the book it was in.

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Permalink Reply by Simon Howroyd on June 7, 2012 at 6:43am

Cheers mate, that's a great help if you can!

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Permalink Reply by Bradley J Carr on June 7, 2012 at 6:58am

Now that is the were I see the problem.  80 Amp that is going to be tough.  How close can you get the voltages to each other?

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Permalink Reply by Simon Howroyd on June 7, 2012 at 7:05am

Probably get the fuel cell to peak no more than 2-3v above 12v that is required.  I assume it won't be 80A going through the zener though?...or is it when it breaks down?

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Permalink Reply by Bradley J Carr on June 7, 2012 at 7:48am

Well that is what I am looking into.  I am not sure there is going to be a cheap and easy way to do with something that is small and light.  I think the only option would be is to build a circuit that would use two triacs that can handle the current.  Triacs with heat sinks, triacs can switch very very fast and I am not sure the ESC would ever see it switch.  Making a switching circuit with triacs.  Using a 555 timer or j/k flip flops. it would be light and cheaper.  and might get you what you want.

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Permalink Reply by Bradley J Carr on June 7, 2012 at 7:50am

Also the 80 amps is what the ESC is rated at.  I wonder what the operating amperage would be.  I would think the only time you would ever see 80 amps is when you jam the throttle full and it has a huge load on it. Cruising speed would be a lot less.

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Permalink Reply by Simon Howroyd on June 7, 2012 at 8:00am

Thanks for the help, all interesting stuff.  I'm trying to keep stuff as off the shelf as possible though so soldering up a circuit is not what I want to do.

An H-Brick DCDC converter would possible provide enough power for cruise, 30A from Onecall Farnell, often used for power over ethernet systems so it is regulated to 12v.  I guess I could then directly connect the output f this in parallel with the LiPo.

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