Solar Charger Teardown

2017-12-08 | By All About Circuits

License: See Original Project

Courtesy of All About Circuits

The Charger

The device in this teardown is a solar charger that contains an internal battery for charging external devices, such as phones, while on the go. The unit itself can charge the internal battery by either using a USB power adaptor or by using the solar cell present on the top of the unit. Charging the battery by using an external USB power adaptor will give a much quicker charge while the solar panel will allow for the unit to charge while out and about (but take longer as a result). The unit is very rugged and has rubber edges to prevent damage when dropped. This rubber casing also provides a level of splash proofing making it ideal for outdoor use. Interestingly, solar cells can still operate in low light conditions such as overcast days and such cells are most efficient during partial cloud where direct sunlight hits the panel and distant clouds reflect even more sunlight onto the panel.

The solar power pack

The back of the unit shows information regarding the power input/output of the unit and also reveals the construction method for the device. The unit is held together with 8 screws, has a power input rating of 5V / 2A, a power output of 5V / 2.1A, a charging current of 120mA, and a battery capacity of 12000mAh. This impressive battery capacity is able to source 12A for one hour but this also means that the unit would take approximately 100 hours (or 4.16 days) to charge fully with solar power alone.

The back of the solar battery pack

Product information found on the back of the unit

One of the 8 screws keeping the unit together

The solar charger has multiple IO ports for connecting devices to and these ports include two USB A ports, and one USB micro B port. Assuming these ports follow the USB standard, a typical device drawing 2A can expect to operate for up to 6 hours continuously on a full charge!

USB A Port

Micro USB Port B

USB A Port on the front of the unit

Opening the Charger and Seeing the Battery

Removing the 8 screws allows the back to come off with ease and immediately the main feature, the battery, stands out. The size and length of the cables coming from the battery clearly indicate that large currents are to be expected. Taking the battery out was difficult (and nerve racking), as it was stuck down using strong double sided tape to the back case. What made this task potentially dangerous was the chance of either damaging the battery by piercing it or bending it. This battery pack consists of two batteries stuck together and has a combined amp-hour rating of 12Ah which is an incredible amount of energy for a lithium-ion battery. Should anything go wrong this battery pack would quickly catch fire and cause serious damage! Some may think that this is an over-exaggeration but companies who put lithium-ion batteries in their products will often keep them in a secure metal case so that old batteries don't cause fires.

Removing the front cover

This battery is massive!

The Main PCB

With the world’s largest li-ion battery removed, it’s time to look at the main PCB. The majority of the space is occupied by the solar panel itself and the main PCB is held down with just two screws.

The main PCB and solar panel

All of the components on the PCB are surface mount parts, which help to automate the production process as much as possible (also making it cheaper to produce). Some of the spotted components include an inductor (4R7), semiconductors, capacitors, resistors, and ICs. One very common feature on this PCB is the many stitching via which suggests that this circuit uses switch-mode rather than linear regulators to regulate voltages. This is beneficial in such a circuit due to the fact that linear regulators are incredibly wasteful while switch-mode designs can be as efficient as 95%. Since the solar panel may not produce a voltage large enough to charge the li-ion battery, a buck boost can also be expected (and may involve the large inductor) which can bump up the voltage output.

The main PCB

The back of the PCB only consists of several LEDs and a single push button which is used to show the charge on the battery and enable the power back respectively. Again, more evidence of switching devices comes from the fact that the PCB is almost entirely a power/ground shield on the underside which acts like a Faraday cage to absorb stray EM radiation.

The underside of the PCB

The engineers who developed this product are clearly concerned about other manufacturers copying their design. As a result, the main controller has had its ident removed, making the IC nearly impossible to identify. One way to get around this is to look at the pinout and try to match it to a known IC. However, many microcontrollers are now using common footprints, making it harder to identify. Another way to identify the part is to etch away the plastic casing using hydrofluoric acid and observe the silicon die. However, I lack such chemicals and thus cannot see the die.

The main controller IC

The only other identification that the PCB has is "XHD-234OM" and the date that the product was most likely manufactured on (2017.02.17).

The ident on the PCB

Summary

This solar charger shows how portable power packs are becoming more powerful with larger battery capacities and more efficient solar cells. Once again, the importance of EMC control is also shown with the use of stitching via and large ground planes which if omitted would make the product fail basic FCC and EC rules.

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