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Old Jun 10, 2012, 04:33 AM
home of the best antennas
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Solar Power Systems for FPV MPPT Chargers and more

Hello guys, I want to tell you that we at www.fpvlr.com are starting work on a very light and compact MPPT charging system

We see solar flight as the wave of the future, so we had some serious objectives in mind.

1. compactness
2. powerful computing(ARM processor based)
3. Powerful charging ... that's charging a 3s lipo at up to 7-8Amp/hours

For those who don't know a MPPT is a Maximum Power Point Tracker, normally it's separate from a charger, but we want MPPT and charger in a single compact unit.

Solar arrays have a "sweet spot" in current demands that yealds maximum watts (Maximum Power) and that is called (Maximum Power Point).

This means that if we try to draw too much from the array, the voltage drops drastically and we lose a lot of power, sometimes as much as half the available power.

The MPPT CONSTANTLY adjusts Amp demand to maximize total produced watts.

The other thing that it does, is convert excess Voltage (at the current being produced) in more current for the charger.

To explain better, if we have 30 cells of moncrystalline 2,9W 5x5 cells they will produce a max of .59 x 5 Amps under full sun, that would mean 17.7v under full sun, but it could just as well drop to 14v and 1A if there is a cloud cover... so we need the extra cells to be able to have always more than 12.6v that we need to charge our 3s pack, but a lot of power gets wasted.

for example with full sun our regular charger would waste 17.7-12.6 = 5.1v

5.1v * 5 A =25.5W that would be wasted... that's between 1/4 and 1/3 of total produced power that the MPPT will transform to more Amps with a 85-90% efficiency.

So in our case that 25.5W would transform in an extra 1.8 A , so we'd be charging our battery at 6.8A instead of 5...

Now this gets automatically adjusted for illumination, angle of the array to the sun etc... in real time.

In the future we can make this interface with an OSD so the Milliamps will roll back while gliding, and it will show you the net milliamps used out of your battery.

Just trying to see how many interested people there would be.

This is a first really, as commercially available mppts are too big for a rc glider and they don't have all the features that we can put in, like telemetry interface etc.

But those features will be for the future versions, right now we are trying to get these main points sorted out.

Unlimited solar flight will be possible.

And this 3.3 meter glider will be the first such model to employ it for testing purposes.
We might also offer short kits for it.

It's called Solar Wonder....
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Old Jun 10, 2012, 04:37 AM
home of the best antennas
United States, FL, Boca Raton
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Any ideas that could be incoporated in the MPPT designs of the future are welcome.
This is a 3-4 month project so it's nothing that can be done right away, as extensive testing of the prototypes is required. We don't want to rush things and than end up with a broken MPPT charger when you are 50km away from base and only have 10A of battery left.
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Old Jun 10, 2012, 04:55 AM
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Hope you opensource that mppt design..you'll have a lot more followers then
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Old Jun 10, 2012, 05:00 AM
home of the best antennas
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Quote:
Originally Posted by msev View Post
Hope you opensource that mppt design..you'll have a lot more followers then
It's not opensource, unfortunately, it's a product...Open source is for something like a osd or multicopter controller, this is a niche product..
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Old Jun 10, 2012, 05:02 AM
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It's a great idea, I would buy one when you get it sorted.
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Old Jun 10, 2012, 05:09 AM
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we are making it suited for a wide input range 8-20volts...
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Old Jun 10, 2012, 05:38 AM
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Are you willing to sell kits then? Non assembled unit or just bare pcbs & a parts list.
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Old Jun 10, 2012, 05:45 AM
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Kondor, how about an adjustable output voltage range.
Either just jumpered for 2S 3S 4S Lipo and perhaps NiMh/LiFe and the correct CV/CC charging regime for each.
Or if you are going down the Atmel route, then programmable ouput options.
R.
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Old Jun 10, 2012, 05:56 AM
home of the best antennas
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Originally Posted by msev View Post
Are you willing to sell kits then? Non assembled unit or just bare pcbs & a parts list.

It's all surface mount... it's not just electronics but a programmed processor that's ipossible to solder on your own unless you have smd soldering experience...
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Old Jun 10, 2012, 05:57 AM
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Why is it needed an ARM for this? an $2 8 legs attiny will do the same job...

Also, still unsure about the MPPT advantage, and I know very well all the theory behind MPPT, if you have a DC-DC convertor able to track the input voltage in a broad range, like 5-12V for a 12V output.
I am using such device, it cost $9 and weigh 20 grams and my measurements doesn't show any major power loss, as in the scenarios from OP...
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Old Jun 10, 2012, 05:59 AM
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RenatoA, aren't the DC/DC buck boost type devices very RF 'noisey'.?
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Old Jun 10, 2012, 06:13 AM
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I don't use UHF, see my post today on this topic
And the charger subject of this thread be sure it's using a DC-DC switching part if they are able to charge 3s from 8V
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Old Jun 10, 2012, 06:15 AM
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Originally Posted by RolandS888 View Post
RenatoA, aren't the DC/DC buck boost type devices very RF 'noisey'.?

If I recall well I was the one to introduce RenatoA to the use of a step-up converter for solar charging...

It's a dirty way of doing things and you are not extracting the full potential of the solar panels, just because you are pulling as much current as there is available it's already a 20-25% loss of total available power.

In order to fly solely on solar power (and it's been done by several people as early as the 80's) you really need a mppt to work always in the sweet spot of the solar panels. Normally to get max watts out you need to keep the voltage up, and just drawing as much current as it's available is not the way to go about it. It needs to be done either with raw analog electronics (big and heavy) or with a digital processor controlled routine.

The arm processor will allow to interface with a OSD or even include a osd in itself with milliamp rollback and other power-monitoring features, as well as allow telemetry functions.

Being able to upgrade the firmware for diffent tipologies of configurations is a plus.

Just think about it... if you fly with 2s or 3s it can adjust by itself , the user has a plug and play solution.

I bet with your buck-boost converter you are putting in your batteries little more than half the watts available.

I have built 3 solar planes, and 2 of them on pure solar, no battery.

What we are trying to achieve is a full 8-10 hour of flying in a day, even cloudy days by flying above cloud cover via fpv.

We are not just limiting our project to putting some current back into the battery while gliding to extend autonomy by 20% or something

Yes we are going to use a dc-dc converter on the front end, but we are controlling the amount of current we want to get from that converter to maximize Watts. The program tries to get current from the dc-dc converter but won't take more once the watt output gets lower, and will digitally adjust this to the condition of the moment.

The MPPT and the boosting will be digitally processed, it will be "smart" non stupid like a simple dc-dc converter.

what happens if you have more voltage? a dc-dc converter will make you lose lots of power.
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Last edited by KondorFPV; Jun 10, 2012 at 06:34 AM.
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Old Jun 10, 2012, 07:01 AM
home of the best antennas
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I saw the step-up down transformer you use, and it's similar to what I used on my mini glider... the main problem with these 20gram things is that they are rated at a maximum of 15W but really it's best to keep it under 10W.

The MPPT charger we are talking about here is for serious solar planes, or drones, able to charge up to 120-150w....from the solar array...

As you would imagine you can't fit 10 of those in parallel in a glider's fuselage..

so we are talking about apples and oranges...
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Old Jun 10, 2012, 07:12 AM
home of the best antennas
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this is the guidelines taken from the ebay regulator you use

Battery Use:

Make sure of the voltage and current of the battery you need to charge
Adjust the constant voltage potentiometer to make the output voltage same tothe charge voltage
Potentiometer Adjustment Direction: Clockwise (increase), counterclockwise(decrease)
Use the multimeter in 10A current scale to measure output short-circuitcurrent, and adjust the current potentiometer to make sure the output current tothe expected charging current value
The charge current of transfer lamp is default 0.1 times of the chargingcurrent (constant current value)
Connected to the battery and try to charging (for previous 5 steps, moduleinput terminal is connected to power source, output load is NOT connected tobatteries)


........................
this is what we need exactly to compare the devices.
it says to adjust current to the expected charging current.

Being a 3s battery 12.6v for chargin, you can only go up to 1A or little more..
not enough to sustain flight in any way imaginable, plus if you set 1A that means you have an output of 12.6w and an input around 15W...

what happens when your panels can't supply 15W?

The regulator attempts to pull 1A from the panels and kills the voltage and kills the watt output.

So the difference in the MPPT device is

1. ability to charge at 10 times the power vs this converter
2. the ability of adjusting power demand to extract the max possible watt from the array at any given moment, inclination, cloud overhead, you name it. All of the available power will always be delivered.
3. ability to interface with a osd for telemetry transmission and power status
4. dependability... will this last a continuous 5-6 hours in operation day after day pulling 1-1.2A from it? I seriously doubt so.




say when you bank the plane
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