Help with powering my raspberry pi server

Hi, I'm new here and need guidance.

I have 3 computers which I need ro keep running 24/7 because I'm using them as a server cluster. I have purchased a 100amp pwm solar charge controller and I have two batteries which I can use for this project. Details of my load and batteries are below.

1. Raspberry pi 5 drawing 5 volts 4 amps

2. Raspberry pi zero 2w drawing 5 volts 2 amps

3. Mini ethernet switch drawing 5 volts 1 amp

4. One single 12 volts 90 ah lead acid battery

5. One single 3.2 volts 72 ah CalB LifePo4 battery.

Those are the items i have on hand right now along with the 100 amp pwm charge controller. Please I need to know the right size of solar panels that I can purchase and wire up which would be able to provide enough power to directly supply current to the three devices I have as loads above during the daytime and then be able to recharge any one of/both of the batteries I have to be able to power the loads during the night when the sun goes down.

I am a complete novice in electrical matters but I am willing to learn. I do not have any cash right now to purchase an additional battery so I need to make do with the setup I have on hand right now and plan for an upgrade soon. I just have to purchase the right solar panel size and type to give me the juice I need to at least power my devices during the day and then I can depend on whatever my battery backup can give me at night for the time being.

I am in Africa, we have good sunshine most of the day. All my devices arr rated at 5 volts max. I fear I bought an oversized pwm charge controller for my setup (100 amps) hence my worry that I might have to splurge on solar panels to feed such a hungry controller.

My humble questions are thus, can I use a lower rated solar panel with the 100 amp controller? Is there a minimum wattage of panels that can be used on the 100 amp controller? Will it hurt the system if I under-feed the controller power from the panels? I don't think I have the cash to buy anything more than a 150 watt panel at the moment but I desperately need this system up and running one way or the other.

Tha is all. I appreciate your advice.

Yes you can.
And use a 12 volt usb charger direct on the battery and you can easy run that systeem on it.

My self use a 12volt usb Dp systeem so i can charge my laptop with it

That pwm is not a problem .
It can do lower amps to .
And how bigger how les it will overhead .

U use on the total systeem
5v x 7a = 35 watts
35 watts ÷ 12 volt = 3a x 10hours run = 30Ah for a night .
Means 24 hours with out charging
You run 70/75Ah .
So you can run 1 day on that 90Ah battery with out charging and have a small spare on it .
But you use a lead battery so you need a 180Ah for a 24 hours run .
A lifepo4 you can use a 100% so that is a 90Ah battery

So your solar input have to be more than you use on a full 24 hours .
So you can charge and the systeem running will charging

That one cell battery of lifepo4 you can do nothing with a pwm .
So you need 4 of them to make a 12 volt systeem

Thanks for your words Suijkerbuijk

From what you wrote i understand that I would have to rule out using the LifePo4 battery with the charge controller thus leaving me with the 12v 90AH lead acid battery only, this is not an issue because I plan to add another cell to it in future.

Then from your calculations you stated that my load will eat up a total of 12v 30AH out of the lead acid battery for the full 10 hrs of all night use after which the sun comes up and starts recharging the battery. This is nice to know. DOES THIS MEAN MY PRIOR IDEA OF BUYING A SINGLE 150WATT SOLAR PANEL TO USE IN MY SETUP IS A GOOD IDEA?

Now i see you saying that using a 12v usb car charger can work for me but i am afraid the amp rating might not be sufficient to power the 3 loads i have at 7amps total. Most of the PD car phone chargers i see in my area have a maximum current output of 3amps.

I have looked at some items to buy along with the solar panel to help my project and I'd like you to take a look at it to see if I'm on the right path. I do not want to discharge the lead acid battery below 50% at any time to prolong its service life plus i need a way to draw power efficiently for the 3 computers i have as loads. I have attached pictures of the items I am looking to buy for you to see if I am not veering away from the safe path. Let me know what you think and if it is wise to purchase the items below to use in my setup along with the solar panel.

Pic 1. A device to meter and cut off load from the 12v lead acid battery once it discharges to its 50% threshold.

Pic 2. A 5v 10a buck converter that all 3 machines can be wired to to get power from the 12v battery.

OR

Pic 3. 5v 5a & 5v 3a Ubec power supply transformers that I can use to wire the machines to (If am using this then i plan to wire the bigger raspberry pi to the 5v 5a piece and the remaining 2 machines to the 5v 3a one)

What do to think? And is the 150 watt solar panel good enough for my power needs?

Thanks again for your help.

Most usb charger do 2x 5volt 2.1a. so its in your rang to power one Raspberry on one usb port.

But a bucket Converter will do the job just fine.

For the Solar panel 1x150watts on 22 volt on a pwm.
Oke it will never use the most out of the solar panel.
Its how a pwm works and mppt do more power out of the same panel.

So a 150watts do about max 10a on a mppt.
On a pwm its about 6a .

10x10a hours charge is about 100Ah
But you only have a about max on 5 hours a day .
So that is 50Ah charge in that 5 hours on a mppt.

6x10= 60Ah on 10 hours .
So that 30Ah in 5 hours.

The rest it do charge but not on max performense.

Understand its raw estimation.

And Afrika have more sun and have more uv .
A solar panel works on uv .
So it can run longer on its max performance.
Not in a cloud and rain country that i'm in.

Personal i will set in the future a extra 150 watt panel on it.
So you have in Cloud days if that is in Afrika .
Have a good charge ..

For the rest is just try and error.

I understand about that 2 second lifepo4 cell.
Both together will have that 7 volt what is normal what you need to power that Raspberry Pi with a buck converter .

And thare are 6 volt mppt on the market .
I do not know if you can use those on a lifepo4 battery .


Here you see one.
You can contact them and ask.
What is the solar panel volt input .
And can it be use on a lifepo4.

Some pwm can do lifepo4 by adjust the volts parameters.
But most are stupid pwm and you can not adjust it
One of the reason we go for a mppt that you can adjust .

Suijkerbuijk thanks again. I've seen the maths you showed me and it's all making sense now. I myself want the system to be as minimal as possible.​

Since i will need to make use of just one single solar panel for this setup due to space constraints I think it will be better for me to use the mppt charge controller and the solar panel along with the 12 volts 90 AH lead acid battery to power my project for now. If I can squeeze out 40AH for the night time it will be exactly what I need.

Can i buy a 250 watts solar panel to use with the pwm charge controller for more power? Will it give me more amp current to run my computers and charge the battery optimally when the sun is up? If i can get 5v 10a during a good sunny day I believe it will be fine for me.

I will look into the mppt controller you recommended, But I see its a 6v minimum, this means that I will need to buy another 3.2v lifepo4 battery along with the new solar panel which will make everything more expensive for now.

What I get a 250 watt solar panel? Please just tell me the right power of a single solar panel that I can use to give me the 5v 10a with a pwm controller during a sunny day. I will instead buy that panel type and forget about the 150 watt which seems obviously underpowered. I want to connect just one single panel to the charge controller and get the juice I need. Thanks once again.

I'd use a POE (power over Ethernet) switch instead of a generic Ethernet switch and add PoE Hats on the raspberry pis. Then the pis are powered directly from the network switch, no need for USB adapters but you'd need a case that can house both the pi and the hat. Check the network speed on whatever hat you might get, if you need a gig make sure the hat can do it (Some are only 100).

These are just some examples, there are many others:

PoE Hat for pi zero:


PoE Hat for pi 5:


PoE network switch powered by battery directly:

The solar charge controller will have a maximum output of 100A, so in a 12V battery it should support up to 1,200 watts of solar panels.

That is a maximum, it is fine going lower. As long as the solar panel you buy has a voltage output that is within the range of the charge controller's input, then you can choose any panel.

The 12v 90AH battery is only good for about 45AH for reasons you already know. This means it'll store about 540WH of useful energy.

Your two computers and ethernet switch consume 35W (note that this is their maximum draw - if you measured them I expect they'd be much lower). That means that if the battery is fully charged it will run the computers for at least 15 hours. Again, probably longer unless you're really running those pi's at their maximum computing power. Another way to estimate this is to ignore the battery and just calculate how much power you need for a full day of pi power: 24 hours x 35w = 840WH. Since there are losses in the wires, charge controller, battery, and 12v-->5v converter, add an additional 30%, meaning you need to collect 1,200WH each day.

The solar panel needs to take in enough power to fully charge the battery and power the computers. The problem I have with estimating this is I don't know enough about your location to provide any sort of prediction, so my estimate will be very pessimistic.

Assuming a stormy season with only 2 hours of full sun a day, or 20% of the usual sunlight filtering through clouds and rain on average through the day, and assuming a relatively optimal tilt and aim for the solar panel, you may need a 600W solar panel (or two 300W, or three 200W, etc).

Further, you may be charging the battery at 50A during the sunniest part of the day, so that 100A PWM controller might be the right size for what you need.

I've made very pessimistic calculations, assuming when you say 100% run time then you really mean only a few minutes of downtime a year. If you are in a very sunny location, and the computers take 20-50% of their maximum power, then this system is oversized for your needs. If you're ok with a few days of downtime a year, then it's also oversized for your needs. But if you really need 100% uptime (actually about 99.99%) then 600W to 1,200W of solar power, and your current battery and solar charger will get you that.

The low voltage cutoff you show will work fine - it supports up to 10A from your 12v system, so it'll easily handle the 35W load without problems. Your load is small enough and battery large enough that I don't think you'll experience a lot of problems with that protection circuit switching on and off repeatedly right at the voltage setpoint, but there are voltage cutoff switches with hysteresis that are better - they switch off at a set voltage, say 10.5V, but don't siwtch back on until a higher voltage is reached - say 11V. This reduces chances of damaging things by switching them on and off repeatedly because the battery voltage recovers when the load is removed. Another solution is to use this switch, but power it from its own output. Then use a pushbutton to switch it on by connecting the output to the input with the pushbutton. That way when it turns off it won't turn back on until you press the button.

The 12v to 5V converter you show should work fine. Depending on its efficiency it may take more of the energy than expected, and if so you'll want to measure it and make sure you account for it. If it's particularly cheap it may be noisy and may cause problems for the pi computers, but I wouldn't expect that.

I don't know about the BEC converters you show. They might work fine, they might not.