I opened the APC Smart-UPS 2200 first, and I was surprised to find such deformation of the plastic tops. It turns out, these are the best looking of the lot, and they actually slid out of the unit without a fight.

In another rack, I have an old APC Smart-UPS 1000. I didn’t expect it to look like brand new, but I did expect the acid to stay contained within the battery. I destroyed the steel chassis getting these out.

Finally, I decided to check on my APC Smart-UPS 1000 that has only been in service a couple years. Its batteries are also swollen within the chassis. I’d rather not ruin this UPS, and I don’t feel comfortable letting it operate the way it is.

What a fun Friday this has been.

After speaking with a tech at PowerStream about the isolator, I learned that it is intended to be installed in the engine compartment near the vehicle battery, and switch all of the load between the two. I’m sure it’s a fine product, but it’s not right for this system.

Upon further consideration, the Trojan 27TMX battery is a poor choice for this application. It has the right capacity and a great performance to price ratio, however because it’s a flooded lead-acid battery, it’s just not suitable for this application. I had planned on installing it within a plastic battery box, which would be secured to the cabinet. This seemed safe enough, but now I’m specifying a sealed battery, such as a VRLA absorbent glass mat or gel battery. This will be safer, and can be mounted in an orientation that provides a better use of space.

I’m now working on a prototype that uses two 12 volt, 7 amp-hour batteries. To charge the batteries on the bench, I ordered a BatteryMINDer from BatteryStuff.com. The literature I’ve read on this product gives me high hopes.

So, after all these changes, I thought it would be a good idea to be explicit about the system design.

System Definition

Purpose

The purpose of the system is to provide proper storage of temperature-sensitive medical products within a passenger vehicle.

Problem

When the coolers are connected to the vehicle electrical system and the engine is not running, they will drain the starting battery within a few hours. Repeated full discharge of the conventional wet lead-acid battery causes failure.

Solution

A deep-cycle auxiliary battery will be installed to power the coolers when the vehicle is not running. The auxiliary battery will recharge when the vehicle engine is running.

Environment

The system will be anchored within the cargo area of a SUV. As this location is within the passenger compartment of the vehicle, the system must not pose a hazard in the event of a collision or rollover.

Operating Temperature

The system will be used within a vehicle servicing Southern California. The expected operating temperatures are between 0 °C (32 °F) and 55 °C (131 °F).

Load

There will be two coolers (Coleman PowerChill Thermoelectric Cooler) connected to the system. The reported power use is 4 amps at maximum, however this has not been confirmed by testing.

Capacity

The system will typically operate overnight, requiring a battery capacity of at least 80 amp-hours. For longer periods of vehicle inactivity, a charger will be connected to household electrical service.

Unresolved Issues

• Is the power outlet in the vehicle voltage regulated, such that the system cannot determine when it should be active?
• Will the power consumption of the coolers, in addition to the current used to maintain system battery charge, exceed the power outlet rating of 120 watts?
• If multiple batteries are connected in parallel to increase capacity, will the charging system function correctly using its VRLA AGM profile?
• Will the cargo area require (active) venting to prevent heat buildup?

Cabinet Design Considerations

The system will be housed within a cabinet, secured in the cargo area of a SUV. Two cabinets will be placed side-by-side, facing the door opening. The cabinet top will be flat and dimensioned to support the cooler (one cooler per cabinet). The coolers will be secured to the cabinets with hook-and-loop (Velcro™) straps.

The front of the cabinet is recessed to prevent damage to the LCD display and power connectors. The cutouts in the sides and back of the cabinet provide convenient hand placement for lifting, in addition to allowing airflow through the cabinet. The cabinet top will be easily removed for servicing the system.

There are, in fact, two Coleman powered coolers in the back of the vehicle. Currently, one of them is plugged into a 12 VDC outlet in the cargo area; the other is plugged into a power socket on the console (snaking the cord under the back seats). The new circuit provides local power connections for the refrigerators, and includes a voltage display so the charge of the deep cycle battery can be checked.

At a cost of $274.16, it’s a bit pricey. It beats having a dead battery every morning though.

Solution: Put a deep cycle battery into the vehicle. This type of battery can handle the long drain, and it’s separated from the battery under the hood by an automatic isolation switch. When the engine is started up in the morning, it will recharge the deep cycle battery.

PowerStream has a 12 VDC 80 amp solid state isolation switch for this application: PST-SSB2180. A Trojan 27TMX deep cycle battery would provide 105 AH at a reasonable load. The isolation switch is $85; the battery is about $175 and weighs about 55 pounds. Battery Systems in Oxnard carries Trojan, so hopefully it won’t need to be shipped directly.

The mailbox was ordered through Amazon. They call it a Super-Tough Vandal-Proof Mailbox : 20 Pounds of Steel : Made in USA. Quite a product title, but accurate.

In these pictures, the cable company’s junction box looks wildly crooked. That’s only an effect of lens distortion caused by the iPhone. If I had taken the time to pull out a real camera, it would look more accurate.

I have yet to apply the street numbers, secure the mailbox to the support, and install the light that will shine on the driveway. I’ll save that for another day.

I decided it was time to replace the eyesore. This would also be a good opportunity to wire up the yard light that I had planned when putting in the new driveway (four years ago). After gingerly digging to avoid chopping through the cable lines, I discovered that their conduits run exactly where I planned to place the mailbox. I located the new post as close to the driveway as possible. The post hole is 36 inches deep, 8 inches in diameter. I poured some gravel into the bottom and set a form tube. I used a bit less than two 60 pound bags of concrete.

The next step is to order a mailbox online (I was disappointed with Home Depot’s selection) and trim out the post with some redwood to match the fence.