Sneaky Bastard

While exploring battery options, I decided to open up a few of my UPS cases to see who manufactured the batters in the APC Smart-UPS rack-mount units. The answer is CSB Battery Technologies. However, the surprising part was the discovery that the batteries were all bloated and corroded.

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.

For some bizarre reason, the ThickBox CSS file (/wp-includes/js/thickbox/thickbox.css) was hanging display of the administrative interface. An HTTP request for the file would not get a response — I even tried connecting via telnet and typing the request by hand. I moved the file elsewhere and made the same request; the WordPress PHP handler correctly responded with the theme’s 404 page. I put a placeholder file in place, and it worked fine.

The solution was to remove the CSS comments in the stylesheet. I don’t know why this would cause trouble at the web server level. Makes no sense.

/* -------------------------------------------------------------*/
/* ---->>> thickbox specific link and font settings <<<---------*/
/* -------------------------------------------------------------*/
...
/* -------------------------------------------------------------*/
/* ---->> thickbox settings <<<---------------------------------*/
/* -------------------------------------------------------------*/
...

This is an update on the automotive refrigeration project I wrote about last week and the week before. On Tuesday, I took some measurements of the vehicle and the coolers. Using Google SketchUp, I created a model for the cabinet. Here’s a screenshot:

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.