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Mar 23, 2014, 09:55 PM
E sailplane thermal hack
Quote:
Originally Posted by RPinCA
I've used similar inverters in LED circuits made for a display case. They have been around for a while and are quite robust at this point. I like the smart LiPo shown in the link - it's a nice solution at very low weight. Please let us know how it works for you!
I thought so too! I'll keep you guys posted :-)
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Mar 27, 2014, 06:04 PM
Registered User
RPinCA's Avatar
The diode circuit works well. The Voltage plot shows a freshly charged LiFe that came off the Hitec at 3.60/3.59v. It is running the receiver and Altis on its own without the BEC in parallel. For the first 55 seconds or so the voltage was bouncing from 6.1 to 6.0. Before the end of the first minute, while still on the ground, it stabilized to 6.0v (thus, 6.7 at the battery). After a couple minutes flying the EasyStar, the voltage at the receiver reached its nominal level of 5.9v.

Session1 and Session2 show the complete hour and a half period the electronics was on. It started to rain, so Carl and I just chatted as the shower passed. I left the plane on to drain some power while we were waiting. It started to rain harder, so I turned things off... but then the rain passed and we flew again. I enjoy seeing how the barometric pressure rose after the second flights in the clearing skies! Ah, well, simple things amuse simple minds.

You'll note voltage variances while the plane is on the ground. It was on the windy side today, so the EasyStar was bouncing its wings and weather-vaning in the gusts.

The plane uses a small AR6010 Rx with four HS-55 servos. This doesn't draw a lot of current. Even so, I am pleased to see the battery voltage remaining at 5.9v after settling there. While there was a minute of 6.1v at power-on, this is within range of 6v equipment... NiMH's start at 6.1v for a while in the same way, and I've been flying them for years with no issues. Dudley uses NiMH cells in his Explorer, and I imagine many others use them as well. We're all still flying.

Please feel free to use this trivial circuit. As it is new, I make no representations about its longevity, failure testing, or fitness for purpose - use it at your own discretion (my wife's an attorney). But, in my judgment, it is safe and reliable enough to be my battery of choice going forward.

(Pardon me; Session1 and Session2 were misnamed. The rightmost image, starting at 6.1v, is the actual Session1. The center image is Session2.
Last edited by RPinCA; Mar 27, 2014 at 06:06 PM. Reason: Mistake naming session images
Mar 27, 2014, 06:59 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
Good stuff Randy, thanks for sharing. For anyone in a "diode voltage reducing" kind of mood I still have PC boards and surface mount 10A diodes that I'm happy to give away to club members. The user guide for the board is here.

One nice thing about the board is that you can solder in a power switch (I also have some of the switches in stock). On the other hand the nice thing about just using a single diode is that it's nice and simple as Randy says.

Anyway, until I run out club members can have this stuff for free. PM or email me if you are interested!

Chris
Mar 27, 2014, 07:54 PM
It should fly at least once
clive45's Avatar
Quote:
Originally Posted by SoaringDude
Good stuff Randy, thanks for sharing. For anyone in a "diode voltage reducing" kind of mood I still have PC boards and surface mount 10A diodes that I'm happy to give away to club members. The user guide for the board is here.


One nice thing about the board is that you can solder in a power switch (I also have some of the switches in stock). On the other hand the nice thing about just using a single diode is that it's nice and simple as Randy says.

Anyway, until I run out club members can have this stuff for free. PM or email me if you are interested!

Chris
Which club is that Chris?
I love these boards.
Mar 27, 2014, 09:20 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
Quote:
Originally Posted by clive45
Which club is that Chris?
I love these boards.
Hi Clive,
Welcome to the Sacramento Valley Soaring Society forum. Are you interested in using a diode voltage reducer?
Cheers,
Chris
Mar 27, 2014, 10:19 PM
It should fly at least once
clive45's Avatar
Hi Chris, I certainly am. I have 2 units fitted to aircraft and they work perfectly.

I would love a couple more.

Clive
Mar 27, 2014, 10:40 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
Quote:
Originally Posted by clive45
Hi Chris, I certainly am. I have 2 units fitted to aircraft and they work perfectly.

I would love a couple more.

Clive
<blush> Gee I finally figured it out . You're the Clive that bought some of the boards in 2012. Last time you got just the boards and parts, no switches. If you want to get 2 more and not make me solder anything all you have to do is cover US Parcel Post which will probably be the same $6. It always seemed so cheap for all the way to Australia but that's all it cost.

Deal?

Chris
Mar 27, 2014, 10:47 PM
It should fly at least once
clive45's Avatar
Deal, please PM details.
Mar 28, 2014, 10:20 AM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
For anyone else who wants these voltage reducer PC boards for free, I have plenty of boards left but have already exhausted my free supply of surface mount diodes (both types). So if you want the boards you will have to order the diodes from Digikey. They are very cheap ($.63 ea for standard silicon, $1 ea for Schottky power diodes if you need them too). Part numbers are in the user guide on pgs 9,10.

On the subject of parts orders if you want to make a single diode reducer as Randy has described I would be willing to put in a group order for the diodes. My company places parts orders every 2 weeks so I can have them included in the next order at no shipping charge or taxes to club members. Let me know if you want any by mid next week.

Chris
Nov 26, 2014, 10:33 AM
Windy City Flyer
Brian Kloft's Avatar
Greetings Sacramento Valley Soaring Society forum! I am interested in stepping down a small Lipo pack (300mah) to 5V. Has the diode solution been used for Lipos? Are those boards still available?

Any help/information is greatly appreciated!

Brian
Nov 26, 2014, 11:15 AM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
Hi Brian,

Yes I still have boards available but let's make sure they will work for your application. How many cells in the Lipo pack you want to use and roughly how much current will your plane draw? (or how many servos?) I just want to make sure you aren't trying to drop voltage into an electric motor.

Chris
Nov 26, 2014, 04:00 PM
Windy City Flyer
Brian Kloft's Avatar
Hello SoaringDude!

This is for a small glider, so no motor. Only rudder and elevator, and it is a 2S 300MAH lipo pack. The battery is about the size of a pack of wrigley's gum.

Oh and since this is a small glider.. Looking for the lightest, simplest solution!

Let me know if you need anything else.

Brian
Nov 26, 2014, 08:17 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
If your heart is set on using a LiPo pack which has a higher per-cell voltage than LiFe, and if your servos are spec'ed at "5v" then you would need to drop around 3v across something, either diodes in series or a regulator. i.e. each LiPo cell will be ~4.2v at 100% charge.

If it were me with such a basic plane I would probably just use a 4-cell NiMH pack and be done with it, no diodes or regulator needed. If you absolutely wanted to go with a diode voltage reducer it would take 4 or 5 lower-current diodes but keep in mind diode voltage drops are somewhat proportional to current; with 4 diodes in series the regulation factor would be quite poor esp. given your plane's low current consumption with just 2 servos. The plane may work fine anyway but it's not a very good solution IMHO.

If you wanted to use a regulator I would probably go with a Castle BEC which is cheap, proven, and handles higher input voltages well since it's a switcher. I still think a NiMH pack is your best shot for this plane.

Chris
Nov 26, 2014, 08:22 PM
NorCal Electric Soaring (NES)
SoaringDude's Avatar
Thread OP
And I realize when you say it's a small glider maybe you don't have room for a bigger battery pack or even a small regulator. If that's the case I can look up specs for a smaller power diode and you can string 4 in series and try it out. Let me know how small is "small."

I just looked up 1/3AAA NiMH cell packs that are small and 150-200mAh. Maybe your plane could fit a pack like this?
Last edited by SoaringDude; Nov 26, 2014 at 08:34 PM. Reason: Added 1/3AAA pack idea
Nov 27, 2014, 03:03 PM
Registered User
RPinCA's Avatar
Quote:
If it were me with such a basic plane I would probably just use a 4-cell NiMH pack and be done with it
Plus one.

I use a 900mAh Eneloop pack in my Avionik B12. It's very fast, with five servos that sometimes get heavy loads. The pack is good for 4-5 typical 15-minute flights with room to spare. Eneloop (aka TwiCell) packs maintain their charge on-the-shelf far longer than traditional NiMH.

I am one of the folks who posted here. After many experiments with the LiFe pack, I went back to NiMH for its simplicity, low weight and proven track record. It is a 4-cell pack due to Hyperion servos rated for 5V. I am not using the BEC in a Castle Lite 200A ESC, as the motor draws 140A on 3S and 310A on 4S, which could fry the ESC if I'm not careful.

Another interesting solution for you is available. I've read good things about the Shred RC Smart LiPo - assuming you stay within its current specs. A big plus is its direct charging; just hook it up to something 5-15V DC and it charges itself. You could use a 2S or 3S LiPo (8.4/12.6V at full charge), your car battery, or even a USB charger.

... ... ... ...

(Fair warning: this post is highly biased by personal experience and preference!)


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