First Impressions: Paxcess Rockman 200

I had been using a Monoprice PowerCache 220 to store and use power generated by my small Harbor Freight solar array. Due to its degrading battery and erroneous thermal protection circuit, I bought a Paxcess Rockman 200(*) to replace it. Thanks to its lithium chemistry battery, the Paxcess is far smaller and lighter than the Monoprice unit it replaced. Which made a good first impression as something I noticed before I even opened the box.

Two means of charging were included with the Rockman 200, giving users two choices of power source. Either use an automotive “cigarette lighter” power socket adapter, or use a household AC voltage power adapter. But I intended to charge from solar power, so I had to fashion my own charging adapter. Fortunately the Rockman 200 used commodity barrel jacks (5.5mm outer diameter, 2.1mm inner diameter) so it was easy to build one from my most recent purchase(*) of such connectors. This was much easier than the hack I had to do for my Monoprice.

Once up and running I was indeed able to charge from my Harbor Freight solar array. The maximum no-load open circuit voltage of these panels were around 21V, lower than the 24V maximum input voltage limit of the Rockman 200. The Rockman 200 had a far more informative display than the very limited one on board Monoprice PowerCache 220. I like to see how many watts the solar array is delivering, and seeing the number of watts being drawn by anything I had plugged in. Unfortunately, there were two disadvantages relative to the PowerCache 220.

  1. It is not possible to use the AC power output while charging. Like the Monoprice, 12V DC and USB DC power output can be used while charging. But while the Monoprice was willing to deliver AC power while charging, the Paxcess is not.
  2. When drawing DC power while charging, the cooling fan always comes on. I suppose this is some sort of DC voltage conversion process. In contrast the Monoprice stays silent if it can stay cool enough. Or at least it used to, before the thermal sensing system broke down.

Neither the Monoprice or the Paxcess attempts to perform maximum power point tracking (MPPT). I realize this means the panel is not operating at maximum efficiency, but a MPPT controller (*) cost significantly more money than their non-MTTP counterpart (*). Given that a standalone controller costs almost as much as the array, or the Paxcess itself, I don’t fault the Paxcess for not doing MPPT.

However, the Paxcess is even more non-MPPT than the Monoprice. The Monoprice pulls the voltage level down to whatever level its internal lead-acid battery is at, which is usually in the range of 11-13 volts. In contrast, the Paxcess drags the voltage all the way down to 9.5 volts, which is even further away from the maximum power point, as seen by varying power input wattage on the information display.

The display also shows a charge percentage for its internal battery. This allows me the option to stay within the 30% – 80% range if I want to minimize stress on the battery. Lithium chemistry batteries have a different care and feeding procedure than lead acid batteries. Speaking of which, with the new battery storage unit in hand, I opened up the old one to try to fix it.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Out with the Lead-Acid, In with the Lithium-Ion.

A little over two and a half years ago, I bought a Monoprice PowerCache 220 (Item #15278) to help store power generated by my cheap Harbor Freight solar array and also to utilize that power by the way of AC inverter and USB power converters. When new, the PowerCache was quite capable of gathering up the day’s solar generation and using that energy to charge various battery-powered devices around the house. Up to and including charging an Apple MacBook Air (2014).

I expected this battery to wear down, I just didn’t know how quickly. Battery University has a capacity loss chart, but that is for lead acid batteries held on standby for long periods of time (like in an UPS) showing the capacity would fade to about 85% after two and a half years. However, this battery was cycled on a daily basis for most of the past 2+ years. And while the charge controller does perform an occasional top-off charge, it’s probably not as much as the battery desires.

As a result of this stressful usage pattern, the battery inside my PowerCache 200 has degraded to a point where it could barely hold enough energy to charge a cell phone. That by itself was not a disaster, as I had anticipated battery degradation and was prepared to revive the machine with a new lead-acid battery. Unfortunately the machine has developed another problem: the thermal protection system has gone amok. Within five minutes of the PowerCache starting up (when everything is still room temperature) the “overheating” warning triangle starts blinking and soon the thermal protection routine kicks in and shuts everything down.

So instead of shopping for a replacement lead-acid battery for the PowerCache 220, I started looking at replacing it entirely. I was pleasantly surprised to see that the cost of lithium based batteries have dropped significantly within the past two and a half years. As of right now, lead-acid based systems are still cheaper, but the price premium for going lithium-ion is now small enough to convince me to make the switch. I’ll pay a little extra, but I’ll get something that’s far smaller and lighter. Thus I bought a Paxcess Rockman 200 Portable Power Station (*) to see how it handles my usage scenarios.

[UPDATE: I opened up the PowerCache 220 with the intent to fix it, but things took an ugly turn and ended up as a full teardown.]


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Samsung 500T Now Runs On Solar Power

I wanted to have a screen in my house displaying current location of the international space station. I love ISS-Above but didn’t want to dedicate a Raspberry Pi and screen, I wanted to use something in my pile of retired electronics instead. I found ESA’s HTML-based ISS tracker, tested it on various devices from my pile, and decided the Samsung 500T would be the best one to use for this project.

One of the first device I tried was a HP Mini (110-1134CL) and I measured its power consumption while running ESA’s tracker. I calculated my electric bill impact to keep such a display going 24×7 would be between one and two dollars a month. This was acceptable and a tablet would cost even less, but what if I could drop the electric bill impact all the way to zero?

Reading the label on Samsung 500T’s AC power adapter I saw its output is listed at 12V DC. The hardware is unlikely to run on 12V directly, since it also has to run on batteries when not plugged in. It is very likely to have internal voltage regulators which should tolerate some variation of voltage levels around 12V. The proper way to test this hypothesis would be to find a plug that matches the AC adapter and try powering the tablet from my bench power supply. But I chose the more expedient path of beheading the AC adapter instead and rewiring the severed plug.

A quick test confirmed the tablet does not immediately go up in flames when given input voltage up to 14.4V, the maximum for lead-acid batteries. Whether this is bad for the device long term I will find out via experience, as the tablet is now wired up to my solar powered battery array.

This simple arrangement is constantly keeping tablet batteries full by pulling from solar battery. This is not quite optimal, so a future project to come will be to modify the system so it charges from solar during the day and runs on its own internal battery at night. But for now I have an around-the-clock display of current ISS location, and doing so without consuming any electricity from the power grid