# MPPT charge controller

#### juliantech5

Jul 3, 2018
12
I'm working on a concept pocketqube and am currently developing the power management system, I'm looking for the easiest and most efficient way to regulate 3.3v from a battery and charge it using MPPT. I will be using gallium arsenide triple junction cells, It will have a power consumption of under 20ma at 3.3v and needs regulated voltage for the atmega 328p au chip and other IC's, the cells I will be using have a Voltage (Open Circuit) of 2.62 V and Current (Max Power) of 14.6 mA. I have found chips such as the SPV1040 that claim to integrate MPPT circuits, I will need to charge a 3.7v cell (aprox 500Ma). I have a very basic understanding of charging circuits so my question is, are there any efficient MPPT/Battery charge controller IC's on the market or easy to design/already existing devices? Obviously form factor is important since this will be going in a a very reduced space.

All input is deeply appreciated and and collaborations are welcome since working out all aspects of such a project is somewhat complicated.

Thanks,
Julian

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
MPPT only really makes sense if you're charging from a source which is capturing power directly from some fluctuating external source (e.g. wind, solar, wave).

MPPT used from a battery might optimise the fastest charge, but it would not maximise the total energy transferred from the battery, and it would almost certainly cause the battery to get very hot.

Can you explain in more detail what you need to do (rather than how you think you should do it)?

#### juliantech5

Jul 3, 2018
12
MPPT only really makes sense if you're charging from a source which is capturing power directly from some fluctuating external source (e.g. wind, solar, wave).

MPPT used from a battery might optimise the fastest charge, but it would not maximise the total energy transferred from the battery, and it would almost certainly cause the battery to get very hot.

Can you explain in more detail what you need to do (rather than how you think you should do it)?
Ok I think I didnt it explain very well , I need to charge a 3.7v battery with solar cells and then output 3.3v for the satellite's components, space is minimal and I have no electrical engineering experience.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Ok. MPPT generally requires that you have a switch mode DC-DC converter controlled by a microcontroller.

At its simplest, it continuously tunes the DC-DC converter to achieve the highest charge current. A more complex circuit may alter the behaviour based on battery voltage, temperature, or state of charge.

In your case I'd probably go looking for an integrated solution - is there a device designed to do all this in a single package? My first search would be for MPPT related items on Digi-Key.

In your second part, producing a 3.3V rail, the simplest approach is a linear regulator, but that's going to generate more heat, which is typically wasted energy. However, if you need to keep the electronics warm, it may even be useful.

You may also need to consider the dropout voltage of your regulator and maybe how much your 3.3V rail is permitted to sag (what is the minimum battery voltage?). An inverting type of DC-DC converter can get you around some of these issues, but you also lose a common ground rail.

I assume you're talking about a cube sat, and in that case, for maximum performance you're going to need to balance a whole lot of things.

#### juliantech5

Jul 3, 2018
12
Ok. MPPT generally requires that you have a switch mode DC-DC converter controlled by a microcontroller.

At its simplest, it continuously tunes the DC-DC converter to achieve the highest charge current. A more complex circuit may alter the behavior based on battery voltage, temperature, or state of charge.

In your case I'd probably go looking for an integrated solution - is there a device designed to do all this in a single package? My first search would be for MPPT related items on Digi-Key.

In your second part, producing a 3.3V rail, the simplest approach is a linear regulator, but that's going to generate more heat, which is typically wasted energy. However, if you need to keep the electronics warm, it may even be useful.

You may also need to consider the dropout voltage of your regulator and maybe how much your 3.3V rail is permitted to sag (what is the minimum battery voltage?). An inverting type of DC-DC converter can get you around some of these issues, but you also lose a common ground rail.

I assume you're talking about a cube sat, and in that case, for maximum performance you're going to need to balance a whole lot of things.
In this case it will be a pocketqube that is 5x5x5cm, so just a downscaled cubesat. The pocketqube will then launch other smaller satellite boards, these however will not have a battery and only require a regulated voltage from 2 solar cells. Temperature is generally not an issue since all the chips on the satellite have been tested to low temps and can withstand the temperature fluctuations. The 3.3v regulated voltage on the pocketqube itself is not an issue since the battery is fairly large and the idea is to keep it at more than 60% every cycle to reduce wear since it will be expected to do thousands of cycles a year, solar power is also more than enough considering the pocketqube itself will just be transmitting a simple beacon consuming around 50mw after having launched the other satellites. However on the satellite boards space is even more minimal and the solar cell produced just enough power for all the electronics considering the linear voltage regulator I previously used. Is there any more efficient way such as an integrated buck converter? And regarding MPPT chips, I mentioned one in the original post, the SPV1040, it seems perfect for the job and theoretically I just can wire that up along with a battery protection circuit, right?

Thank you so much, help is really appreciated.
Satellites combine so many aspects of engineering its really impossible to do on your own and electrical engineering is not my specific strong point hahah

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,875
Satellites combine so many aspects of engineering its really impossible to do on your own and electrical engineering is not my specific strong point
Perhaps you can convince someone on your satellite development team, someone who has electrical engineering expertise, to join Electronics Point and start a new thread exploring the power management problems associated with solar-powered electronics in low-earth orbit. I must assume this is a LEO project rather than something attempting to reach synchronous or Lagrange orbital positions.

Also, could you elucidate a bit on why the already-small pocketqube is launching even smaller devices with their own small solar-cell power systems? What is the purpose of adding to the already considerable amount of junk payloads orbiting Earth? Do these "micro-satellites" gather any useful information and send it back to ground stations via telemetry transmitters? And why does the now-empty pocketqube, after launching it's micro-satellite payload, have (or even need) a beacon transmitter à la Sputnik? Any estimate of the orbital life time for the pocketqube and its payloads?

#### juliantech5

Jul 3, 2018
12
Perhaps you can convince someone on your satellite development team, someone who has electrical engineering expertise, to join Electronics Point and start a new thread exploring the power management problems associated with solar-powered electronics in low-earth orbit. I must assume this is a LEO project rather than something attempting to reach synchronous or Lagrange orbital positions.

Also, could you elucidate a bit on why the already-small pocketqube is launching even smaller devices with their own small solar-cell power systems? What is the purpose of adding to the already considerable amount of junk payloads orbiting Earth? Do these "micro-satellites" gather any useful information and send it back to ground stations via telemetry transmitters? And why does the now-empty pocketqube, after launching it's micro-satellite payload, have (or even need) a beacon transmitter à la Sputnik? Any estimate of the orbital life time for the pocketqube and its payloads?
This is indeed a LEO project however it is still in a very early development phase, As LEO implies these are launched into a considerably low orbit that last from a couple months to weeks. The main goal is to try and reduce the current size of picosatellites in space while still maintaining all the functionality of a regular picosatellite, The sprites will have an accelerometer, a magnetometer, a temperature sensor and whatever sort of mission specific sensor is needed. They will have full uplink and downlink capability and will basically function like any other satellite, with such a small formfactor you are able to reduce the cost of a single satellite launch for smaller experiments and expanding the aerospace sector to the masses. Hopefully these sprites will also integrate active attitude stabilization that has never been tested on such a small level (among a huge amount of other things), another big feature will be its use of LoRa radio that will allow anyone with some spare change to pickup these transmissions these transmissions with off the shelf parts (Lora also hugely reduces the power needed to send information over such long distances compared to other conventional radios). The problem with such a small non standardized formfactor is that it cannot be launched unless the launch provider creates special dispensers, therefore the easiest way is to launch them from a larger standardized mothership. This mothership will need to be able to give us downlink data on its current state and launch the board satellites after a set period of time and in the case of failing, report it to us. If we are going to integrate a system to launch the board sats, why not add down link capability and receive more data on the state of of the mothersip and its orbit.

Sorry for boring you on this one, There is a LOT of stuff to take in mind and I really thank you for your help.

PD: (The mothership is not a beacon as launching any sort of satellite requires being able to turn of the transmitter)

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,875
The mothership is not a beacon as launching any sort of satellite requires being able to turn of the transmitter
Seems like a reasonable requirement. My misunderstanding was a result of your earlier statement:
the pocketqube itself will just be transmitting a simple beacon consuming around 50mw after having launched the other satellites
With electronics becoming more and more compact and less massive, there is very little penalty involved with including persistent telemetry with the "mothership."

The amateur radio community (AMSAT) has been involved for many years with the launch of small "repeater" satellites as "piggy back" passengers on commercial satellite launches. I have never taken much interest in this, mainly because of the difficult requirements for tracking a LEO satellite horizon-to-horizon with a narrow-beam antenna (necessary for a decent signal+noise to noise ratio). Lately that has become almost a "piece of cake" with stepper motors, driven by microprocessors getting satellite ephemeris data off the Internet controlling an altitude-azimuth (alt-az) yagi-uda antenna array. I may actually "look into" it now that I am retired and have some "free time" on my hands.

Sorry for boring you on this one
I doubt you are boring anyone here. This is pretty eclectic group of people with lots of different interests, some mainly interested in electronics, some interested in how electronics will aid their real hobby. For example, at least one of the moderators is an active member of the "maker community" and they get involved with all sorts of projects such as home-built CNC mills and routers, 3D printers, electric go-carts and skateboards... there may even be some budding "rocket scientists" here. On the Alibre Forum (3D CAD) that I belong to there is at least one real rocket scientist who sometimes takes his work home. So, don't assume that just because your project isn't mainstream, and doesn't involve how to control LEDs or motors with PWM circuits, that it is boring. You folks should set up a blog online so we can follow your progress, up to and including launch, and maybe you could invite others to help log the telemetry from the picosatellites after a successful launch and orbit insertion.

BTW, in the very near future, acceleration-hardened picosatellites will be launched from rail guns, not rockets, and a mothership to disperse them will not be necessary. This concept began during WWII when miniature "radar" sets were incorporated as proximity fuses into anti-aircraft artillery projectiles. This was waaay before transistors, much less integrated circuits, were available. It was a definitive "proof-of-concept" that a useful electronics package could be made to survive the accelerations imparted upon it from being fired from a cannon. The technology is sooo much more advanced today in every dimension you can possibly imagine. But good luck on your pocketqube launching bus. That's still "bleeding edge" technology for a few more years.

Hop
73 de AC8NS

#### juliantech5

Jul 3, 2018
12
Seems like a reasonable requirement. My misunderstanding was a result of your earlier statement:

With electronics becoming more and more compact and less massive, there is very little penalty involved with including persistent telemetry with the "mothership."

The amateur radio community (AMSAT) has been involved for many years with the launch of small "repeater" satellites as "piggy back" passengers on commercial satellite launches. I have never taken much interest in this, mainly because of the difficult requirements for tracking a LEO satellite horizon-to-horizon with a narrow-beam antenna (necessary for a decent signal+noise to noise ratio). Lately that has become almost a "piece of cake" with stepper motors, driven by microprocessors getting satellite ephemeris data off the Internet controlling an altitude-azimuth (alt-az) yagi-uda antenna array. I may actually "look into" it now that I am retired and have some "free time" on my hands.

I doubt you are boring anyone here. This is pretty eclectic group of people with lots of different interests, some mainly interested in electronics, some interested in how electronics will aid their real hobby. For example, at least one of the moderators is an active member of the "maker community" and they get involved with all sorts of projects such as home-built CNC mills and routers, 3D printers, electric go-carts and skateboards... there may even be some budding "rocket scientists" here. On the Alibre Forum (3D CAD) that I belong to there is at least one real rocket scientist who sometimes takes his work home. So, don't assume that just because your project isn't mainstream, and doesn't involve how to control LEDs or motors with PWM circuits, that it is boring. You folks should set up a blog online so we can follow your progress, up to and including launch, and maybe you could invite others to help log the telemetry from the picosatellites after a successful launch and orbit insertion.

BTW, in the very near future, acceleration-hardened picosatellites will be launched from rail guns, not rockets, and a mothership to disperse them will not be necessary. This concept began during WWII when miniature "radar" sets were incorporated as proximity fuses into anti-aircraft artillery projectiles. This was waaay before transistors, much less integrated circuits, were available. It was a definitive "proof-of-concept" that a useful electronics package could be made to survive the accelerations imparted upon it from being fired from a cannon. The technology is sooo much more advanced today in every dimension you can possibly imagine. But good luck on your pocketqube launching bus. That's still "bleeding edge" technology for a few more years.

Hop
73 de AC8NS
Yes indeed, the current technology allows you to send and receive information with little to no power and LoRa makes it even easier, I am currently about to take my HAM radio operator exam so I am also quite new to this but I have always found it interesting to be able to receive data from a satellite at home, hopefully LoRa will make it even easier to tune in. Its very nice to see such a welcoming community and I really thank you for your post, I will definitely keep you informed on this project and the blog we are currently creating.

Interesting concept regarding the launch of picosatellites with railguns, considering the weight of these is under 5g it is exciting to see what the future has to hold and I definitely hope to prove some points with this project on how far we can really push miniaturization of satellites.

Anyways thanks again for your contribution

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
considering the linear voltage regulator I previously used. Is there any more efficient way such as an integrated buck converter?

Switching regulators are typically more efficient. (The larger the voltage difference the larger the potential efficiency gain).

#### juliantech5

Jul 3, 2018
12
Switching regulators are typically more efficient. (The larger the voltage difference the larger the potential efficiency gain).
So something like this?
https://www.digikey.es/product-detail/es/texas-instruments/TPS62120DCNR/296-27815-1-ND/2407328
or this?
https://www.digikey.es/product-deta...d/AP3015AKTR-G1/AP3015AKTR-G1DIDKR-ND/4505611

The texas instruments seems to have better efficiency but the difference is minimal, I cannot seem to find efficiency graphs on any datasheets from linear regulators though.

So these regulators along with the SPV1040 could be used? The board sats will just have direct regulation from the regulators and the mothership will charge the battery with the SPV1040 and an overdischarge/overcharge etc protection and then output via a regulator. I'll post a schematic asap since I'm not 100% sure on where capacitors go.

Thanks again.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,875
Interesting concept regarding the launch of picosatellites with railguns, considering the weight of these is under 5g
There are problems still to be solved in using railguns to orbit anything. Atmospheric friction is the big elephant in the tent. What goes up into orbit eventually comes back down, and re-entry into the Earth's atmosphere burns up unprotected objects as their kinetic energy is converted back to heat.

Obviously the same problem occurs when accelerating an object to orbital velocities through our dense atmosphere. It is possible to reach the required velocities by accelerating in a vacuum, but after exiting the railgun aerodynamics comes immediately into play. Perhaps an ablative shield could be used to protect a small payload whose mass is on the order of five grams, but the mass of the ablative shield is likely to be hundreds or thousands of times larger. No matter: it would still be worth the effort just to simplify the launch-to-orbit scenario. Plus, this technology doesn't require huge amounts of real estate and support for cryogenic fuels and oxidizers that rocket technology currently requires. Any entity with moderately deep pockets could build a picosatellite launch facility and locate it anywhere in the world. I would imagine China, India, or Japan would be at the forefront just as soon as picosatellites become valuable enough to pay for the effort involved... maybe twenty years (or less) from now.

Back in the 1970s, a physicist I knew was working at Wright-Patterson AFB near Dayton, OH on multi-stage light-gas guns to accelerate projectiles to orbital collision velocities to test the survivability of manned spacecraft and astronaut spacesuits. He became an expert at photographing high speed events and later became involved with rail guns, to the extent that he recruited an Australian physicist and an English military technologist to write proposals on how to build them. Years later our paths crossed again and he bragged about building a rail gun in California that could shoot "one pound to Jupiter," That didn't impress me much since I knew that once an object achieves escape velocity from the Earth (or whatever massive body it happens to be sitting on at the time) it can go pretty much anywhere it pleases with very little expenditure of additional energy. It's getting out of the gravity well that is difficult with current technology.

None of these ideas is new. Robert Anson Heinlein wrote about it in his novel The Moon Is A Harsh Mistress.

#### juliantech5

Jul 3, 2018
12
There are problems still to be solved in using railguns to orbit anything. Atmospheric friction is the big elephant in the tent. What goes up into orbit eventually comes back down, and re-entry into the Earth's atmosphere burns up unprotected objects as their kinetic energy is converted back to heat.

Obviously the same problem occurs when accelerating an object to orbital velocities through our dense atmosphere. It is possible to reach the required velocities by accelerating in a vacuum, but after exiting the railgun aerodynamics comes immediately into play. Perhaps an ablative shield could be used to protect a small payload whose mass is on the order of five grams, but the mass of the ablative shield is likely to be hundreds or thousands of times larger. No matter: it would still be worth the effort just to simplify the launch-to-orbit scenario. Plus, this technology doesn't require huge amounts of real estate and support for cryogenic fuels and oxidizers that rocket technology currently requires. Any entity with moderately deep pockets could build a picosatellite launch facility and locate it anywhere in the world. I would imagine China, India, or Japan would be at the forefront just as soon as picosatellites become valuable enough to pay for the effort involved... maybe twenty years (or less) from now.

Back in the 1970s, a physicist I knew was working at Wright-Patterson AFB near Dayton, OH on multi-stage light-gas guns to accelerate projectiles to orbital collision velocities to test the survivability of manned spacecraft and astronaut spacesuits. He became an expert at photographing high speed events and later became involved with rail guns, to the extent that he recruited an Australian physicist and an English military technologist to write proposals on how to build them. Years later our paths crossed again and he bragged about building a rail gun in California that could shoot "one pound to Jupiter," That didn't impress me much since I knew that once an object achieves escape velocity from the Earth (or whatever massive body it happens to be sitting on at the time) it can go pretty much anywhere it pleases with very little expenditure of additional energy. It's getting out of the gravity well that is difficult with current technology.

None of these ideas is new. Robert Anson Heinlein wrote about it in his novel The Moon Is A Harsh Mistress.
There still are some kinks to work out as you said but taking in consideration the fact that this technology has huge military potential I expect this to develop very fast, the simplicity if a railgun is also minimal compared to millions of parts on liquid fueled rockets. Advancements in nanotechnology and composites will soon make it possible to resist being thrown out of a barrel at mach 6.
Interesting friend haha, as you said its just getting out of earth's gravity that requires the bulk of the energy.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,875
Advancements in nanotechnology and composites will soon make it possible to resist being thrown out of a barrel at mach 6.
True "really soon now" if not already. But low-earth orbital velocity is around 28,000 km/h or nearly mach 23. That's why the railgun "barrel" needs a vacuum inside while the sabot carrying the picosatellite is accelerated. Probably will need considerable length too, compared to current military railguns, to limit the acceleration to a survivable amount. Not familiar with what state-of-the-art integrated circuits can tolerate, but 1000 g would not be an unreasonable goal, maybe 10,000 g for a shorter acceleration time. I do know that the smaller the circuits get, the more tolerant they become to acceleration. Haven't run any numbers yet, not even back-of-the-envelope estimates, but the possibilities are exciting.

#### tomwalki

Jul 5, 2018
3
Hi Julian, Have you got a launch sorted yet for your PocketQube? We are putting together a cluster for next year, with 5 PQs signed up already and a few slots remaining. Your going to run into a lot of issues deploying sprites from a PQ. Since the swarm technologies incident, life for Picosat builders has become much more difficult, so maybe wise not to go below 1p if you want approvals.

#### juliantech5

Jul 3, 2018
12
Hi Julian, Have you got a launch sorted yet for your PocketQube? We are putting together a cluster for next year, with 5 PQs signed up already and a few slots remaining. Your going to run into a lot of issues deploying sprites from a PQ. Since the swarm technologies incident, life for Picosat builders has become much more difficult, so maybe wise not to go below 1p if you want approvals.
I am in contact with Gauss for a possible launch next year too, Indeed I have been looking at the issue and I am aware that Kicksat had the same problem, I am not launching from the USA though. Do you have any information on legislation for picosatellites in europe?
May I ask what project name you are working on?
Thanks.

#### tomwalki

Jul 5, 2018
3
Are you part of the EASAT-2 team? Our Unicorn-2 PM alejandro might know, he is from spain. I founded and run Alba Orbital. We have have been building PocketQubes for 5 and half years (longer than anyone else in the world by some margin) What size of PocketQube are you looking to do? Our cluster 2 is 25k euro for a 1p, 40k euro for a 2p, 60k euro for 3p. We have stuff going gauss, but has been delayed for about 5 years, so we got frustrated and started our own thing. You need to come to our developers workshop in delft in march.

#### juliantech5

Jul 3, 2018
12
Are you part of the EASAT-2 team? Our Unicorn-2 PM alejandro might know, he is from spain. I founded and run Alba Orbital. We have have been building PocketQubes for 5 and half years (longer than anyone else in the world by some margin) What size of PocketQube are you looking to do? Our cluster 2 is 25k euro for a 1p, 40k euro for a 2p, 60k euro for 3p. We have stuff going gauss, but has been delayed for about 5 years, so we got frustrated and started our own thing. You need to come to our developers workshop in delft in march.
Oh wow! Hey tom! I am not part of EASAT-2 though I have had a brief talk with them in the past, I am just working on a 1P satellite on my own, I would love to come to the workshop in delft! Great job you guys are doing over at Alba orbital.
I'm having a bit of trouble finding information regarding the FCC regulations on picosatellites, do we need to get licenses if launching from Russia being a European satellite?

#### tomwalki

Jul 5, 2018
3
You won't need FCC. Mainly national spectrum people, IARU, ITU and any national space entity for the space object registry. Send an email to [email protected] and we can chat more offline

#### juliantech5

Jul 3, 2018
12
You won't need FCC. Mainly national spectrum people, IARU, ITU and any national space entity for the space object registry. Send an email to [email protected] and we can chat more offline
Ok thanks tom i'll send an email over!

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