Outdoor solar setup for low power electronics on boat/buoy

[curiousgeorge123]

Hi - First time posting, hopefully this is the right place.

I'm working on a project involving a small autonomous boat/buoy that will be floating out in the water/sun/elements for a long period of time. There will be some electronics on board for data collection, communication, and power management. All the electronics are 5V DC and are being engineered for low power, sleep, etc. Since it will be in and around salt water and sitting in the sun, I am thinking LiFePo4 batteries configured for solar charging and lots of weatherproofing.

This is the part where I have less experience and get confused... what is a battery cell configuration that makes sense? something like 6.4V cells in parallel? I need an MPPT, right? Do I also need a BMS? What is an example of an MPPT or BMS that would suit my use case? Are there modules I can buy that I can integrate with my own electronics package/PCB?

Thanks, Happy to answer questions. I'm new on the forum, so I'm still in the process of reading through and seeing what types of setups others have done.

 

[wpns]

I have contemplated making a beacon or something from a single LFP cell, a small solar panel, a Zener diode, an LED, and a very low power computer like a Raspberry Pi Pico. If the computer will run down to 2 1/2 V, then you don’t need multiple cells in series and a BMS. If your LED emitter won’t run below 3 V, then there’s your under voltage control.

Getting it all running is the hard part, then just find an appropriate container and pot the whole thing in epoxy. or concrete. Or expanding foam.

 

[mikefitz]

example of an MPPT or BMS that would suit my use case? Are there modules I can buy that I can integrate with my own electronics package/PCB?

The simple course of action is to purchace a ready built 12v battery with built in BMS and an off the shelf solar controller, providing there are not size restraints. If size is critical and power very low, then there are modules available. What size bouy/boat and what are the power requirements? Is the project something like,

 

[HarryN]

Probably the easiest way is to build it as a 12 volt battery setup and then a DC converter or USB for the 5 volt.

 

[curiousgeorge123]

The final boat design is around 4 feet long and 1foot wide, so there is some space but I'm hoping to keep things as constrained as possible. Initial testing will probably be in a smaller tupperware that I can buy from a store like Target. My thinking was since everything is going to be 5V, I could use a 6.4V battery. This would keep things smaller and more contained... something like this https://www.amazon.com/WILLQR-Rechargeable-Portable-Replacement-Batteries/dp/B0CLLGB89Z?gQT=0&th=1

An alternative I was thinking about was making my own battery pack, so that way I'm not limited on how to shape/wrap the package... but if I were to make my own pack I'm having a hard time finding a low cost LiFePO4 BMS with decent documentation. I see a few on Amazon, but coming from sellers without datasheets or model numbers (https://www.amazon.com/Midzoo-Protection-Charging-Recovery-LightPower/dp/B0982CLQCS?gQT=1).

Just for my own clarity though, I have read some places on the web saying if I have an MPPT I don't need a BMS, and some places saying I need a BMS. The former makes no sense to me, the BMS is for balancing batteries and the MPPT is for managing PV charging so both are needed. Am I misunderstanding something?

Thanks again

 

[wpns]

Just for my own clarity though, I have read some places on the web saying if I have an MPPT I don't need a BMS, and some places saying I need a BMS. The former makes no sense to me, the BMS is for balancing batteries and the MPPT is for managing PV charging so both are needed. Am I misunderstanding something?

If you have more than one cell in series you need a BMS.

Tthat has nothing to do with an MPPT controller, they are independent.

You been listening to one of those AIs?

 

[HarryN]

Another path would be to use a 6 volt AGM marine battery.

No BMS required, proven arrangement.

Standard settings available for charging.

It might be that your 5 volt electronics can deal with the 6 - 7 volt range of a nominal 6 volt AGM battery.

If not, then it might be possible to find a simple DC - DC circuit to output 5 volt.

In theory, you can pot the whole package to seal it from the environment.

 

[BarracudaBob]

We would need to know the payload and its power requirements. I assume this has a transmitter with a 'heart beat' wake up, read sensors, transmit, receive, sleep, and repeat.

Does it have any warning led at night?

Sounds like a APRS or WSPR Marine Buoy

Or one done by this guy with a modified NexSens Model CB-150 buoy.

 

[curiousgeorge123]

We would need to know the payload and its power requirements. I assume this has a transmitter with a 'heart beat' wake up, read sensors, transmit, receive, sleep, and repeat.

Does it have any warning led at night?

Sounds like a APRS or WSPR Marine Buoy

Or one done by this guy with a modified NexSens Model CB-150 buoy.

It doesn't currently have a red light, but that might be a good idea! Indeed there will be some heart beat to keep everything sleeping and wake up periodically.

Thanks for pointing out these projects, really interesting. My project is similar to the Bouy except I will include an iridium modem to have some minimal two way communication.

I was considering a 6V AGM battery but the discharge curve on the LFP seems much nicer. That being said, if I'm constantly in the sun and charging it might be a moot point... I have little experience with solar so this is partly a learning exercise for me. I'll be running mostly custom electronics, so dropping to 5V DC is no problem.

 

[BarracudaBob]

It doesn't currently have a red light, but that might be a good idea! Indeed there will be some heart beat to keep everything sleeping and wake up periodically.

Thanks for pointing out these projects, really interesting. My project is similar to the Bouy except I will include an iridium modem to have some minimal two way communication.

I was considering a 6V AGM battery but the discharge curve on the LFP seems much nicer. That being said, if I'm constantly in the sun and charging it might be a moot point... I have little experience with solar so this is partly a learning exercise for me. I'll be running mostly custom electronics, so dropping to 5V DC is no problem.

Sounds like a cool project. Would love to learn more. You may even want the AGM battery in the bottom to add stability due to its weight. Hard to believe but Nasa still uses a lot of NiMH for their devices due to the temp range.

 

[AnarchyJet]

How many watts per hour are the electronics? 1'x4' doesn't make much room for solar. You should look at a kinetic charging source and/or small wind generator. That would provide power 24hrs and your battery could be much smaller. Keep 20-30w of solar for redundancy.
You might need to work with someone that can make you some custom electronics. Building a low power 2S BMS and multiple pwm chargers into one board isn't that difficult.
What happens to your buoy if it looses power? Then a boat hits it in the dark and you are liable?
I would build around 2 independent batteries that can both be charged by multiple energy sources and failsafe electronics so one failure allows the system to be powered by the remaining unit.