Tinkering With Janky Solar Power

About three years ago I picked up the Harbor Freight 45 Watt Solar Panel Kit with good intentions. The kit was on sale (I think ~$130) and I figured, “why not? This could be a great backup power system.” Unfortunately, it’s not great and it’s no good as backup power for much of anything most folks would use it for. It does, however, provide some electricity and I figure I should use it. After the purchase I fiddled around with it, then put it away until this spring. I decided to give it another go and challenge myself. My goal was to not plug my cell phone into a wall charger for as long as I could.

I’m happy to announce it’s been about a month and a half since my phone has been plugged into the power grid. This is no big feat by any means but I’m sure I’ve saved a dandelion plant somewhere (probably my yard) with my reduced carbon footprint. Really, I’m not a tree hugger and I feel that the whole climate change argument is just another way for someone (other than me) to make money. Whether climate change is man made or not, it still doesn’t make sense to pollute our environment. But ultimately, this experiment isn’t about saving trees or polar bears, it’s about something more important: saving me pennies. I won’t be getting rich any time soon with this, but a penny is a penny.

The three HF panels come with a frame, charge controller and a couple 12V CFL bulbs and socket. The frame is just some grey PVC pipe, bolts and wing nuts (not galvanized and now rusty, jeez) to hold it all together. Each panel has a 2 pin connector which mates with a parallel combining cable that connects to the charge controller. The charge controller ‘looks’ nice. On the back of the controller is a fuse, solar panel connections, and battery connections. The front has a USB Port, 3V 1/8” jack, 6V 1/8” jack, 2 x 12V 1/4” jacks, Inverter and 12V car lighter output. The shell is aluminium which is actually very solid. There is a voltage display which can be turned on/off with a push button switch and a low voltage warning LED. The insides of the controller are a different story. This low end charge controller uses PWM charging and not MPPT which higher end chargers use. The circuitry is probably typical of a cheap Harbor Freight product. It’s a spaghetti mess of wires, although I’m guilty of the same (see my USB power pack below).

The jankyness of this setup is not all because of Harbor Freight. Who wants to throw more money at poor purchase decision that’s probably not worth it? I have 3 sealed lead acid batteries connected in parallel that were pulled from dead uninterrupted power supplies (UPS). These batteries were not in good shape as they sat for a long time without use. I have a battery desulfator that I used to revive the batteries. The batteries and charge controller are stored in my awesome plastic bin that sit on a wire rack on the floor.

Under the rack is a 300 watt inverter with 2 outlets which is used to charge my drill batteries. I’ve had the inverter for a long time and it sat unused for at least 10 years. It’s so old that when I googled “Travel Power” “HM300” the first result was an eBay auction listing it as “vintage.” Fortunately, the inverter still works.

The USB port on the HF Controller no longer works. I connected a USB hub to it which immediately began to smoke. My volt meter shows 12V on the USB port so I taped over the port. I whipped up a 2 port USB charging board with a LM317, perfboard and socket 7 heatsink. I used a voltage divider to get 2.2V on the D+/- lines so that devices can pull higher current. While it’s been nice charging stuff with the solar panels, it’s also a pain to leave my phone or tablet in the back room where I can’t hear the notifications. I solved this problem by building a portable USB power bank that can be charged from the solar panels and moved anywhere in the house.

Last year I ordered a replacement laptop battery for a customer of mine from eBay but I received the wrong battery. The seller promptly sent the correct one and did not want the wrong one back. Last week, I cracked open the laptop battery and did some testing. The circuitry in the laptop battery handles charging and does in fact have over/under voltage/current/charge protection. All I needed to charge it was supply 12-13V. I crammed the 6 lipo cells into the case from a 3.5” Desktop SD Card Reader. Power input to charge the pack goes through a standard 2.1mm DC jack. I put a diode in line with input to only allow power into the pack. There are two USB ports (scrapped from a laptop) that have a voltage divider to provide 2.2V on the D+/- pins. The ports are powered by a TPS63061 buck/boost switchmode regulator. The regulator circuit was the output part of a lipo charger test design I did that I ended up not using. I cut the regulator portion off the PCB to use in the battery pack. I had to put a diode in line with power to the regulator as it has an over voltage cut off of 12V (the pack when fully charged is 12.6V). There’s a switch for two modes on the pack: OFF/Charging or USB On. An LED is tied to the regulator to indicate that the regulator (USB Port) is on. So far I’ve been able to charge a cellphone at least 5 times with the pack but it needs further testing.

Ultimately, my janky setup works but could use some improvement. The panels are mounted to the frame that is currently on the ground in a garden bed. They will need to be moved soon so that some veggies can go there. There is no spot in the yard that gets sun all day. The neighbors on either side of me have huge maple trees. I could put them on the detached garage but that’s too far away to make it useful. I could put them on the house but then I wouldn’t get direct sun til around noon but they will probably end up on the house. The charge controller pretty much sucks and after the USB failure, I don’t trust it. There’s some open source MPPT charge controller designs out there based on the Arduino platform. I will probably build one of those and reuse the HF controller housing. The batteries work, but are crap and need to be recycled. At some point I need to get a single lead acid battery. As janky as my setup is, it functions and it’s been a fun experiment.

Harbor Freight Charge Controller Schematic

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