I Need Help Solar Powered USB Hub Charging Station Design and Modules

[Sibrah]

Good day forum members,
I am trying to put together a USB Charging Hub Station that takes solar panel output voltage of DC 12v, 18v or 24v and regulates its into 5v DC for charging purpose of a combination of about 50 phone and phone batteries.
That's an estimated 400w of load if one device takes 8w.

I have the option of going on Ebay or Aliexpress to order a regulators and USB Buck converter but I am trying to avoid the inefficiency associated with chaining many pre-made circuit modules.
Most of these modules come with around 88% efficiency and any attempt at chaining three of such modules in series will drop the final system efficiency to around 70%. I don't want that but want a single module or implementable circuit design that preferably takes 18v and bucks it down to 5v (USB hub value) reliably.

Solar Panel : 18v ==> 18v to 5v USB regulator ==> TP4056 Lipo chargers​

Above is an improvised block diagram for the project breakdown module by module.​

NB: Also of interest is a backup battery to help support fluctuating solar power input but i consider that after the above challenge is solved considerably.
I am also eyeing the addition of a wind mill source to make it more reliable.

 

[rjenkinsgb]

Look at the "Simple Switcher regulator ICs.
eg. an LM2576 can convert an input of anything up to 40V to 5V with up to 3A output current.

https://www.ti.com/lit/ds/symlink/lm2576.pdf

Personally, I'd design in the option of battery backup from the start, even if the batteries are not initially included.
As in, base the solar panel output on 30V to be able to charge a 24V battery system.

The 24 - 30V range of a nominal 24V lead acid backup battery setup is well within the input range of regulators such as above and keeping the battery voltage higher (24V rather than eg. 12V) halves the current draw from the batteries, which would be considerable at your maximum 400W output.


Smallish solar panel setups for battery charging often just use a shunt regulator to dump any excess if the batteries are already fully charged and/or there is not as much demand as available power, so there are no conversion losses as such as that stage, just a series (schottky) diode to prevent any power flow back to the solar panels when they are dark.

That gives you a pretty efficient (80%) 5V source in one stage. Each regulator could run two 5V outputs at up to 1.5A each, or more lower current rated ones.

 

[Diver300]

I don't see why you would be chaining many modules. You would have a 12/18/24 to 5 V converter, followed by several 5 V to Li-Ion chargers. The power is only going through 2 modules. The 5 V to Li-Ion chargers will be in the phones, if I have understood what you are wanting to do.

There are lots of wide input voltage range converters that give 5 V. A very quick look on eBay found this:- **broken link removed** You would need around 6 of those with 8 or so phone connected to each regulator.

400 W is a lot. It is a big solar panel. If you want 50 outputs, it might be cost-effective and easier to handle if you had 5 panels, each with 10 outputs. 400 W at 5 V is 80 A, which is getting into currents that are more difficult to handle. 80 phones will need a few metres of wiring join them up, so you will have 80 A for a few metres, and you want to keep voltage drops low, so you will be buying big wires.

The problem with charging phone on solar power is that the phones will usually expect 5 V at anything from no current up to the rating of the supply. Solar panels create a voltage dependent on the temperature, and their maximum current is dependent on the brightness of the light. If you take too much current, when you have one too many phones connected, or a cloud goes past, then the current will be limited. The output voltage will drop, the buck regulator will try to take more current from the solar panel, the voltage will drop further, and that will go on until the buck regulator cuts out. Then the phones turn off, the regulator recovers, and the phones will start charging, and then it all goes wrong again.

You can get this effect when a charger is connected with a poor USB lead. The device sees 5 V, turns on charging, the current increases, the voltage drop due to the poor lead increases, and the device sees a lower voltage and turns off. Then the voltage rises and the charging turns back on.

The speed of this oscillation depends on how fast the devices turn back on. It may be several seconds for some phones. Having a lot of phones on charge will cause this unless you don't run anywhere near the maximum output of the solar panel, so you won't get the most from your expensive panels.

You mentioned efficiency, but (power out)/(power in) is largely irrelevant for solar panels where the power in is free. What is far more important is (power out)/(cost of equipment). If you need to run fewer phones to get stability, the power efficiency of your converters is irrelevant, and you will have to pay for more setups to charge the number of phones you want.

Where a battery is being charged from a solar panel without any intermediate voltage, the problem doesn't exist. There are two approaches. One is to chose the solar panel voltage to be about right for the battery, have no voltage conversion, and then dump power when the battery is full. The other approach is to have a voltage converter, usually a buck regulator, and to continually adjust the voltage ratio of the converter to get the most power from the solar panel. This is called maximum power point tracking, or MPPT. Obviously MPPT systems will normally also shut off when the battery is full.

For a system where you want to charge many phones, having an intermediate battery will increase the availability a lot. The battery will smooth out any surges in power consumed or dips in power supply, while solar panel output can be used to its maximum at any state of charge of the battery (unless full), at any amount of sunlight, and whether or not the phones happen to be connected. You will need something to monitor state of charge of the battery, and to cut off the phones when flat.

Obviously the battery increases cost, so the (power out)/(cost of equipment) value may not be any better than would be obtained by having more panels.

 

[Sibrah]

Look at the "Simple Switcher regulator ICs.
eg. an LM2576 can convert an input of anything up to 40V to 5V with up to 3A output current.

https://www.ti.com/lit/ds/symlink/lm2576.pdf

Personally, I'd design in the option of battery backup from the start, even if the batteries are not initially included.
As in, base the solar panel output on 30V to be able to charge a 24V battery system.

The 24 - 30V range of a nominal 24V lead acid backup battery setup is well within the input range of regulators such as above and keeping the battery voltage higher (24V rather than eg. 12V) halves the current draw from the batteries, which would be considerable at your maximum 400W output.


Smallish solar panel setups for battery charging often just use a shunt regulator to dump any excess if the batteries are already fully charged and/or there is not as much demand as available power, so there are no conversion losses as such as that stage, just a series (schottky) diode to prevent any power flow back to the solar panels when they are dark.

That gives you a pretty efficient (80%) 5V source in one stage. Each regulator could run two 5V outputs at up to 1.5A each, or more lower current rated ones.

So what lead acid or lithium battery charger module would you recommend for a system like this?
At 400w of load, I am estimating I will need a 50AH, 12v ( 600wh ) lead acid or lithium battery or similar capacity but don't know which BMS or charger module will help me easily integrate the battery, the BMS or charger circuit and the 18v solar output.
Thanks.

 

[Sibrah]

Diver300, please what would be a good BMS or battery charging circuit for a 50ah, 12v lead acid battery? I am targeting one that takes 18v from solar and integrates the backup battery with the load system or off about 400w.
I have gone through your informative post and I am impressed.

 

[Diver300]

I'm sorry but I don't know of any particular circuit that would be good for batteries that big.

I've done some low current, low voltage charging (charging a phone battery directly from a solar cell of about 6 V. I looked into MPPT charging, but decided that it wasn't worth it as the possible gain from a really efficient charger circuit was small, and the next size up solar panel would be fine.

Also I've seen problems with charging turning on and off when there is resistance in the way, and switch-mode power supplies taking too much current and doing damage when the supply voltage is too low.

Unfortunately, I don't have any direct experience of 12 V solar charging equipment. I suggest you look at caravan / motorhome solar chargers.