Hello,
I would like to connect two usb (portable, already regulated) battery packs to one 5v 2A load.
I'd like to do so that when one battery is empty it gets disconnected from the load and gets connected to the solar panel, the other with full charge will be connected to the load, it has to happen as seamlessly as possible. How would you do it ? with some kind of switch or relay? have you got an idea of pcb schematics to realize that ?
Then when that one is empy, then what?
Hello and thanks for the reply.
While the one full is feeding the load the other is charging. so when the full one is empty the circuit must switch to the other full battery. in the event that both are empty, the circuit must disconnect from the load and charge at least one battery.
Do the battery packs give any indication of their state of charge that can be monitored?
Are you using ready-made power banks?
More details about those batteries and how they work internally (based on your description I assume some kind of charge controller for charging, a single 3.7V LiPo cell and a boost circuit for the 5V output).
Can you not charge them while they are delivering power?
I think that's the most practical solution since there is likely no way to communicate with the battery pack.
I am using ready made power banks and I can avoid charging them while in use the output of each is 5v 2a
I was thinking to monitor voltage/amperes from the output of each battery since those are ready made packs
Ready made packs that I'm aware of don't provide any communication of their state of charge to the device they are powering. Granted, you could monitor the power consumed from the power bank but there would be no way of determining the power available. The power pack voltage is likely to vary from 5V to suddenly dropping to 0V when the pack is discharged.
I think @wvmarle's suggestion to charge the packs during use is the best solution.
Then what's the point of having two batteries. You might as well just have one and use it untill it's empty, then charge it
not if the switch is seamless like this I could go on using the device unless both batteries are empty
I was just thinking that if I avoid charging the full battery it will last longer before bloating.....
Many power banks accept charging while in use.
If the charge current is less than the power drawn, the battery charge goes down, and vice versa. When the battery voltage gets above a certain level, the charge controller will cut the charging. Of course there should also be a protection that cuts the output when the battery voltage drops below a certain point.
I don't think the batteries will last shorter this way. Of course I am assuming you use proper quality batteries, as otherwise all bets are off.
I have two 5V power banks that can be charged while in use and one that can not. It disconnects the output when connected to the charger. I now know not to buy another one of those.
The only advantage I see in what you are trying to do is if you have enough solar to charge both batteries during daylight hours. This may benefit you during a cloudy day or two. However, the easier solution to this scenario is buy a larger capacity power bank.
To answer your question, I would have a timed setup where I charge one in the morning, switch over at say 1PM, charge the second one for the remainder of the day. Switch batteries again at maybe 1AM. I'll always be asking myself is that necessary though.
let's say I will charge while in use.... is there a way to switch battery between the two when one is empty ?
I like your idea... which components should I use ?
those will be two of those babies https://www.amazon.it/dp/B0BBM4C3R2?psc=1&ref=ppx_yo2ov_dt_b_product_details, I could let my contraption discharge the battery and note down the time .......
Holy Moly! 50aH for > $200USD.
Why are you going through all this difficulty? You can get a 50aH 12.8V LiFePO4 pack, MPPT charge controller and a few boost/buck converters for ~$150. Why do you feel the need to use that charger? And to get two to swap autonomously without interruption.
Why not start with THIS
If you are going to spend $200 on a battery, buy This one
There's the good old UPS system. Charging and delivering power at the same time, when external power disappears it seamlessly switches to the battery.
It's also how a typical solar installation works - the charge controller allows all excess power from the solar panels to go to the battery, and when the solar panels don't supply enough it comes out of the battery. Again seamlessly.
If a single battery is not big enough, then you will see multiple in parallel. No draining one and then switching to another. Probably because that's not a very sensible or practical solution.
My contraption is portable, and I cannot put the two battery packs in parallel (I have already tried that with commercial ready made regulated battery packs and the result was a disaster), that said...... I could put one as my "external" power and the other as backup battery... I could use this instructable ..... https://www.instructables.com/DIY-Mini-UPS-for-WiFi-Router-V50/ I can modify it knowing that the batteries https://www.amazon.it/dp/B0BBM4C3R2?psc=1&ref=ppx_yo2ov_dt_b_product_details are already regulated. How can I modify it so that I am sure it outputs 2 amperes ? also ... how would you modify it to have two inputs and one output ?
First things first..... Thank you very much.
Sorry, my fault, I might have been too dumb or not have been clear enough 
In fact I forgot to say that my panels already output 5v through the attached usb port.
panel 1 is https://www.amazon.it/dp/B0C7RNFTVP?psc=1&ref=ppx_yo2ov_dt_b_product_details
panel 2 is https://www.amazon.it/dp/B0B3Q5289S?ref=ppx_yo2ov_dt_b_product_details&th=1
I will test the two to find out which one is the best for my contraption, and/or do so that I can swap the panel depending on the situation. I will consider to test a 12v system tho, since one of the panels supports it.... about the timed setup (which I like) knowing that I have an arduino and a raspberry pi .... which components should I need for 5v and which for 12v ? Which for a system that can be configured from a 5v battery to a 12v one at a flip of a switch ?