Good luck having positive results with 3S and using 12v regulators. As mentioned, they need a higher voltage going in than the desired output.
Under load, you will not be getting 12v. Do the math. Your 12v regulator will shut off or output lower voltage and your equipment will shut off. There is no point to this setup. Your intent is to filler the ripple. Do that. A filter and a regulator are completely different circuits, even if the regulator has a filter on it.
My last post is for 4S Lipo recommend DC-DC step down to 11V.
I guess I have a lot of good luck as it works just fine for me. The maths also seems fine to me.
My post before that is for 3S using DC-DC set up converter with two voltage dropping diode. Again I am a lucky guy as it works fine for me. The maths also seems fine to me.
Are you suggesting removing the regulator and putting a 4S 16.9V fully charge Lipo via a L-C filter directly connected to a 12V Cam and 12V Vtx.. I havent had any luck with this. Others have found the Vtx get cooked from over voltage supply
Use your brain. If you know a setup would fry something, most likely that isn't what I'm talking about.
Using a setup up/buck converter is fine, but now you are wasting a ton of energy just to filter the ripple.
Seems like I keep saying this, but a simple LC filter would be the right choice here.
OK. But his thread topic is for ideas on how to power a FPV model from a single 4S Lipo. I have offered my ideas that work for me.
How do you suggest to the group to power the FPV gear from a 4S lipo without wasting a lot power.
Greg you have a very condescending attitude and are not being very helpful. Ok, we get it, you fly with just an LC filter on 3S. Great! In fact I was flying earlier today using exactly that setup. Does it work? Of course it does. But I'm looking for a little more peace of mind knowing that if I ever fly my battery too low or if a cell fails, I will still have a solid video link to bring it home as I do not have a RTH yet. If you think you will never get into a situation like that, you are fooling yourself or aren't taking any risks.
Yes, using diodes to go from 12.6 -> 11 -> 12 wastes a little energy, but I wouldn't call it a ton. If he was stepping down to 5v with diodes and then boosting to 12, that would be wasteful... I already have a bunch of diodes, and the boost converter is less than $7 shipped. That's cheap insurance, if you ask me.
Last edited by SecretSpy711; 6th May 2012 at 10:08 PM.
Have you even tested what you are wanting to do?
My whole point here is the added regulator isnt going to save you. RTH sure as hell won't either in that situation.
Rth isn't a magic button either. Not when power is concerned.
You also have an odd theory of voltages when all this "what if" scenario is taking place. Try your setup at lvc under load.
Also, we have already gone over how to solve the 4s to 12v situation. Sander was kind enough to post a layout of components for it. If you want to do it right, from an engineers point of view, follow what he posted.
No I haven't tested it but only because I'm still waiting for the regulator to arrive. I plan to fully test it on a variable power supply first to see just how low the input can be, and still get 12v out. Then I will test it under load.
I don't expect anything to be a magic bullet and save me, as most everyone here knows, that comes with experience. But have you seen Sentry's "IFR" video? Obviously he is using a camera / vTx that can withstand a much lower voltage than my stuff, but think about if the video had cut out at 9v (2:27) like most of the 12v-rated equipment out there. It was too far out to see visually and would have been lost. A regulator could keep it going, so you could glide it in, and not worry about the video dropping out. Servo control would be the last to die.
What is so odd about my theory? I am simply making my power system to be "single fault tolerant" in engineering terms. Read TBS's article about single battery setups. They use 5v equipment for this very reason, but I would argue that you can still use 12v equipment with the same degree of reliability if you use a SEPIC converter or diodes-&-boost: http://team-blacksheep.com/article/page:13
View this video on YouTube
Last edited by SecretSpy711; 7th May 2012 at 12:28 AM.
Hi SecretSpy711.
I originally tested the step-up converter with the 2 x drop diodes on a variable bench power supply. I have been using this design for a number of years before the SEPIC DC-DC, anyvolt, etc were generally available.
The DC-DC has good filtering. Note there are 3 large caps 220uF rated 35V DC working on the PCB. I do not use a separate DIY L-C filter.
I have shown the V drop diodes I have been using IN4004. This general purpose silicon rectifier diode is rated 1A continous. I have not had a failure of a DC-DC PCB or the 2 x drop diode. To-date that is touch wood.
Normal operation of a DC-DC step-up switch mode converter is as the V input drops the I (Amp) input increases to mainain the regulated V output. The data sheet for the switch mode IC LM2577S gives the max I input as 3Amp max.
Therefore for max reliability of the DC-DC the drop diodes could be 3Amp rated. IN5404 is a general purpose easy to get diode rated 3Amp continuous. The diode will fit the space on the DC-DC converter same I have shown with the IN4004 diode. So maybe you could consider this higher rated diode IN5404, or any equivalent 3A rated silicon diode in your build and test.
An example I have of a lost FPV model saved.. I lost my FPV glider by flying behind a hill and losing LOS. I took my groundstation to the location where I thought the model was located. The model was still transmitting video. Hung up in a tree was seen in the Video. Lipo was down to 6V. The FrSky rx was also still alive and transmitting telemetry RSSI using a Turnigy DC-DC 5V. I traced to the strongest signal. Bingo..one happy boy..found before dark and before the lipo had completely discharged.
Lindsay
Last edited by Pisces; 7th May 2012 at 03:42 AM. Reason: typos and my spell check wont work with the lab
Use an LC filter and tap into the balance plug on the lipo and pull 3S voltage out of there. That's what I'm doing on my latest 4S plane.Originally Posted by Pisces
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