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.