Question about solar panel voltage near the same voltage as the battery

[jflorey2]

The energy density is irrelevant for me.

?? You said that weight was important.

Genasun GV-5 MPPT can only do 5A which isn't enough.

OK. You said "My current plan is to use 30 Sunpower cells in series which will put out ~100 watts (17v 5.8A)." Assuming C60's, that means you'll never get over 5 amps in realistic conditions. You'll also get closer to 15-16 volts under realistic operating temperatures.

I looked into linear regulators, but I don't know enough about them. All of the regulators I could find were for 1.5A or less. How would I go about this?

The MIC29752WWT will go to 7.5 amps and drop out .4 volts. Needs a big heatsink.
However, doing a shunt may be easier. A massive zener may be all you need. (Needs an even bigger heatsink but might be OK for an airborne application; you have a LOT of airflow.)
Or do a zener with a MOSFET for higher power. Google "make a zener diode out of a MOSFET."

Solar cells you mean? Hard to beat Sunpower's C60 for $2.39 per cell.

And are 20-22% efficient. Alta is over 30%. But again, you pay for the efficiency.

[jflorey2]

This is how the guys in my post above did their setup. Notice they have the solar panels dumping right into the esc. I thought having two separate power sources like that would cause problems. Why isn't it?

In the drawing the panels are connected to the battery through a switch. The Arduino drives the switch. This allows the Arduino to implement PWM charge regulation. Adding an inductor and a diode would allow the Arduino to do MPPT charge regulation. (Would require more software of course.)

[scotty562]

?? You said that weight was important.

I should have been more clear. Overall weight is important, but the battery is just going to be a glorified capacitor so it doesn't matter if it's lipo, nicd, lead acid or whatever. it will be small so any difference in chemistry won't make a noticeable difference.

OK. You said "My current plan is to use 30 Sunpower cells in series which will put out ~100 watts (17v 5.8A)." Assuming C60's, that means you'll never get over 5 amps in realistic conditions. You'll also get closer to 15-16 volts under realistic operating temperatures.

I was concerned running it at 5A for a long period of time might damage it, but 5A is the continuous current. On the specs it says GV-5-Li-16.7V-RETAIL 75W. So it's close, but not quite where I want to be. I'll keep this in mind though this is the closest I've seen to what I'm looking for.

The MIC29752WWT will go to 7.5 amps and drop out .4 volts. Needs a big heatsink.

That's cool I'll definitely keep this in mind.

However, doing a shunt may be easier. A massive zener may be all you need. (Needs an even bigger heatsink but might be OK for an airborne application; you have a LOT of airflow.)
Or do a zener with a MOSFET for higher power. Google "make a zener diode out of a MOSFET."
And are 20-22% efficient. Alta is over 30%. But again, you pay for the efficiency.

I'll do some research on this thanks for the info.

And are 20-22% efficient. Alta is over 30%. But again, you pay for the efficiency.

Ah I'll look info them.

[scotty562]

In the drawing the panels are connected to the battery through a switch. The Arduino drives the switch. This allows the Arduino to implement PWM charge regulation. Adding an inductor and a diode would allow the Arduino to do MPPT charge regulation. (Would require more software of course.)

How does having two different voltages not cause any problems?

[jflorey2]

How does having two different voltages not cause any problems?

If the panel voltage is too high, it will collapse down to the battery voltage.

If the battery voltage is too high, it will discharge and droop lower and lower until it matches the panel's MPP voltage.

[Sunking]

The energy density is irrelevant for me. For normal flying yes, I use lithium ion batteries.

Don't be stupid, energy density is the most important thing with any vehicle, especially a plane. That is why there are no commercial electric planes. A 3S 2200 mah Lipo weighs 145 grams. An equivalent lead acid would weigh 5 times that. FWIW a lead acid has no problems being over charged. They just wil not fly.

>Genasun GV-5 MPPT controller - 80 grams and will give you 16.8 volts to charge a 4S lithium ion battery - and do MPPT

It can only do 5A which isn't enough. They have a 10A version, but it's 185g. I could probably take the plastic off and save a bunch of weight, but I'd rather not butcher a $159 piece of tech. I'd love to find something like this that works for me though.

Your next problem is there are not many LiPo's made for a plane that can handle 10 amps of charge current. Example a 3S 2200 mah battery which is small, can only be charged at 4 to 5 amps max. Not going to do you much good if your motor is burning 20 amps.

You are catching all the crap on RCG because you are ignoring physics. Not going to fly here either.

[Sunking]

So how much do these 100 watts of cells weigh? What will the Gross weight of the plane be? That includes everything, motor, esc, battery, solar, airframe. Once you get a weight use this Calculator to determine motor size. Select Outrunner and put your numbers in and use a TRAINER as that is the lowest power you can run. With all those cells I can imagine 6 pounds. With a small TRAINER SIZE motor requires you to run at full power because a TRAINER and GLIDERS are underpowered aircraft.

Using 6 pounds requires 85 watts per pound or a 500 watt motor. Straight and level flight will pull 35 amps from a 4S 2100 mah battery. So ask yourself what is a 100 watt panel going to buy you? 100 watts at 4S on paper works out to only 7 amps. In reality best be 5 amps around noon hour on a bright sunny day. Mornings and afternoons much less. So now you are carrying all this extra weight, you are burning 35 amps and the panels give you 5. You have not gained anything. You just made you rplane a lot heavier requiring more power and shorter run times. 35 amps on a 2100 mah battery is 4 minutes. Panels gave you 30 more seconds. Get rid of al that weight and a smaller power plant and you can get 10 minutes.

FWIW 35 amps on a 2100 mah battery is 17C. You have to use a LiPo. There is no other battery that will work.

[scotty562]

[QUOTE=Sunking;n342698]
Don't be stupid, energy density is the most important thing with any vehicle, especially a plane. That is why there are no commercial electric planes. A 3S 2200 mah Lipo weighs 145 grams. An equivalent lead acid would weigh 5 times that. FWIW a lead acid has no problems being over charged. They just wil not fly.


Maybe in a traditional plane. This plane is going to be SOLAR powered. The solar panels are obviously the most important part.

That is why there are no commercial electric planes.

There are lots of reasons there are no electric commercial planes. It's a good thing I'm not trying to make one.

They just wil not fly

This lead acid battery flies just fine. https://www.youtube.com/watch?v=-eHv3F9bkto

Your next problem is there are not many LiPo's made for a plane that can handle 10 amps of charge current. Example a 3S 2200 mah battery which is small, can only be charged at 4 to 5 amps max. Not going to do you much good if your motor is burning 20 amps.

https://hobbyking.com/en_us/graphene...5c-w-xt60.html At least that's one problem solved. This plane will only ever come close to pulling 20A when taking off which is part of the reason the battery is there to begin with.

You are catching all the crap on RCG because you are ignoring physics. Not going to fly here either.

I'll take your advice on the solar and electrical aspect, but it's pretty clear your rc knowledge is out of date. I'm not saying I'm going to be successful. I'm simply trying to fill in my knowledge gaps and try. It's already been done so even if I am successful it won't be a big deal.

[scotty562]

Don't be stupid, energy density is the most important thing with any vehicle, especially a plane. That is why there are no commercial electric planes. A 3S 2200 mah Lipo weighs 145 grams. An equivalent lead acid would weigh 5 times that. FWIW a lead acid has no problems being over charged. They just wil not fly.

Maybe in a traditional plane. This plane is going to be SOLAR powered. The solar panels are obviously the most important part.

That is why there are no commercial electric planes.

There are lots of reasons there are no electric commercial planes. It's a good thing I'm not trying to make one.

They just wil not fly

This lead acid battery flies just fine. https://www.youtube.com/watch?v=-eHv3F9bkto

Your next problem is there are not many LiPo's made for a plane that can handle 10 amps of charge current. Example a 3S 2200 mah battery which is small, can only be charged at 4 to 5 amps max. Not going to do you much good if your motor is burning 20 amps.

https://hobbyking.com/en_us/graphene...5c-w-xt60.html At least that's one problem solved (10C charge rating). This plane will only ever come close to pulling 20A when taking off which is part of the reason the battery is there to begin with.

You are catching all the crap on RCG because you are ignoring physics. Not going to fly here either.

I'll take your advice on the solar and electrical aspect, but it's pretty clear your rc knowledge is out of date. I'm not saying I'm going to be successful. I'm simply trying to fill in my knowledge gaps and try. It's already been done so even if I am successful it won't be a big deal.


Also why do I have to post a short answer and then edit it to post a full response?

[scotty562]

So how much do these 100 watts of cells weigh?

Each cell weights 7g

What will the Gross weight of the plane be? That includes everything, motor, esc, battery, solar, airframe.

I already have the plane done. I'm going to convert my one my current planes. The total weight minus battery is 1342 grams (everything minus wings 880gr, wings 462gr). 30 cells * 7 grams a piece adds another 210 grams. Add a 300 gram battery brings the grand total to 1852 which is super light for a plane with an 82" wing span.

I will need to make the wings bigger so figure another 150-200gr. So I estimate ~2000 grams until it's all said and done.

Using 6 pounds requires 85 watts per pound or a 500 watt motor. Straight and level flight will pull 35 amps from a 4S 2100 mah battery. So ask yourself what is a 100 watt panel going to buy you? 100 watts at 4S on paper works out to only 7 amps. In reality best be 5 amps around noon hour on a bright sunny day. Mornings and afternoons much less. So now you are carrying all this extra weight, you are burning 35 amps and the panels give you 5. You have not gained anything. You just made you rplane a lot heavier requiring more power and shorter run times. 35 amps on a 2100 mah battery is 4 minutes. Panels gave you 30 more seconds. Get rid of al that weight and a smaller power plant and you can get 10 minutes.

FWIW 35 amps on a 2100 mah battery is 17C. You have to use a LiPo. There is no other battery that will work.

Your starting weight is over 700 grams off for starters which makes the rest of your numbers off. I don't care whether you think it will work or not. I just want to try. This is just a project to do for the fun of it.

These guys have done it. If they did so can I. https://www.youtube.com/watch?v=rMkPjBf6dNQ

[jflorey2]

These guys have done it. If they did so can I. https://www.youtube.com/watch?v=rMkPjBf6dNQ

Yep, several people have done it. AeroVironment has a 6kg drone that will fly for 9 hours in decent sun.

[Sunking]

This lead acid battery flies just fine.

Do not kid yourself. Listen to the audio. The author said it sucked. He had to run full power and had to land after two passes. Two points made ought to hit you like a ton of bricks.

1. The lithium battery weighs 184 grams, the Pb weighs 963 grams or 5.2 time heavier.
2. Voltage sag on PB is not acceptable because Pb batteries cannot supply high C-rates. 1C is beyond their capacity.

One thing he did not tell you is about Mr Peukert and the tax he collects on batteries. Lead acid batteries are specified C/20, lithium at 1C. A 2 AH battery discharged at say 0.1amps, or C/20, yields 2 AH of energy. Take the discharge rate up to 1C or 2 amps you now have a 300 Mah battery . Lastly he failed to mention you cannot discharge a PB fully without damaging it.

So can you make a Pb battery fly. Yeah but why would anyone do that?

Your starting weight is over 700 grams off for starters which makes the rest of your numbers off

how do you figure that? What 700 grams? I just ran numbers because you did not specify what weight, prop diameter, and whether it was a 3S or 4S battery. Run your numbers and see what it comes up with.

I'll take your advice on the solar and electrical aspect, but it's pretty clear your rc knowledge is out of date. I'm not saying I'm going to be successful. I'm simply trying to fill in my knowledge gaps and try. It's already been done so even if I am successful it won't be a big deal.

How do you mean up to date? I know you can add solar to a plane, but there is a good reason you do not see it much.

[karrak]

To the OP you do not need to worry about a charge controller in this application. LiPo Batteries are cheap so if you should happen to over charge one no big deal, and it is almost impossible to do with Solar. You would have to leave the plane outside turned on for a day or more in the sun with the battery in it. No one in their right mind does that as it is a huge Safety No-No.

If I had made this statement I would be banned. If you had a full battery connected to the solar panels with little or no other load out in the sun under the charge rates we are talking about it would be minutes or tens of minutes, not a day or more before the battery would start smoking or worse.

With 32 solar cells (Vmpp~18.6V), running a 4S battery at 16 volts sounds good. Will all your electronics and the motor run at this voltage?
I see on the diagram that you posted that they have a switch mode supply to drop from 16V to 12V. If you can run the motor at 16V and maybe the control electronics at 12V it would be good.

As a safety precaution to protect your battery and your plane I would have an electronic switch that would disconnect the solar panels if the voltage got too high and for the control electronics to shutdown or slow the motor if the battery voltage gets too low.

Now I look at the diagram you posted that is pretty well doing what I am suggesting

With 32 solar cells you are looking at an optimum power output from the panels of ~110W. You are going to have a very tight energy budget if you need an average motor power of ~80W to stay in the air. 80W equates to ~72% of the optimum output from 32 cells. I would think that reducing the energy usage to 50%-60% of the optimum solar output would be a goal to aim for.
Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[scotty562]

You said:

They just wil not fly.

I showed you a video of a guy flying one.

Do not kid yourself. Listen to the audio. The author said it sucked. He had to run full power and had to land after two passes. Two points made ought to hit you like a ton of bricks.

No one was debating whether or not it sucked or was a good idea. Obviously flying a lead acid battery is going to suck. You said it couldn't fly and obviously it can.

1. The lithium battery weighs 184 grams, the Pb weighs 963 grams or 5.2 time heavier.
2. Voltage sag on PB is not acceptable because Pb batteries cannot supply high C-rates. 1C is beyond their capacity.

Literally no one is saying flying pb is a good idea. I said I would consider anything if it was a better idea than what I was planning.

One thing he did not tell you is about Mr Peukert and the tax he collects on batteries. Lead acid batteries are specified C/20, lithium at 1C. A 2 AH battery discharged at say 0.1amps, or C/20, yields 2 AH of energy. Take the discharge rate up to 1C or 2 amps you now have a 300 Mah battery . Lastly he failed to mention you cannot discharge a PB fully without damaging it.

So can you make a Pb battery fly. Yeah but why would anyone do that?

For fun apparently.

how do you figure that? What 700 grams? I just ran numbers because you did not specify what weight, prop diameter, and whether it was a 3S or 4S battery. Run your numbers and see what it comes up with.

You ran your napkin numbers and then used that information to show how solar on a plane was pointless is what I'm pointing out. My numbers say it should take 50 - 70 watts to keep my plane in the air. I should know because I have a volt and amp sensor on the plane. Those numbers are with my 825 gram 4s4p ncr18650b battery with an all up weight of 2142 grams.

How do you mean up to date? I know you can add solar to a plane, but there is a good reason you do not see it much.

Scale a solar plane up far enough and a man can cross the globe using nothing but the power of the sun. If that's not amazing then we really are living in the future. For my purposes adding solar to a plane will allow me to stay in the air for as long as I want. Even if there were no good reasons to do it. Sometimes people do things just for fun that other people do not think are fun.

[SunEagle]

Each cell weights 7g



I already have the plane done. I'm going to convert my one my current planes. The total weight minus battery is 1342 grams (everything minus wings 880gr, wings 462gr). 30 cells * 7 grams a piece adds another 210 grams. Add a 300 gram battery brings the grand total to 1852 which is super light for a plane with an 82" wing span.

I will need to make the wings bigger so figure another 150-200gr. So I estimate ~2000 grams until it's all said and done.



Your starting weight is over 700 grams off for starters which makes the rest of your numbers off. I don't care whether you think it will work or not. I just want to try. This is just a project to do for the fun of it.

These guys have done it. If they did so can I. https://www.youtube.com/watch?v=rMkPjBf6dNQ

Interesting video. I was impressed with the ability that it can run that long and that far using the solar cells to keep the battery charged but I have some questions on what I saw and what was presented in the details at the end.

The prop on the plane was a folding type yet the details showed a fix type. Also I am not convince the motor shown on the working model was the same as shown at the end of the video.

The plane was pretty skinny and clean yet somehow they installed a 3000mAh 4S battery, 20A ESC, video camera transmitter, gps, antenna, etc. I have a few friends that have FPV type planes and they have a lot of "gingerbread" hanging on it.

The solar cells were "blank" (without any grid to collect the electrons) so I am not sure how they worked.

So I am not sure exactly what was used for the FPV video run.