Sunday, May 13, 2012

Digital Battery Regulators

With the ElectroJeep going to Lithium, I had the opportunity to replace the Volt914's analog battery regulators with the Jeep's digital regulators.  At first, this seemed like a trivial task - just swap out the old analog regs, pop in the new digital regs, and off we go!  Unfortunately, the newer digital regulators have a slightly different component layout - specifically, their power tabs and Regbus connectors are in different places than the analog, so the old boxes I had built for the analog regulators would not work.

However, there was a silver lining to this cloud.  The older boxes were not very waterproof (I had lost 2 regulators to water damage).  Also, I never had put a good battery warmer solution in place.  So, I took this opportunity to do a minor overhaul to the Volt914's battery system while I was at it.

First, I had these nifty devices - they are called "Farnham Battery Heating Pads".  They are designed to take 120V AC and produce 35W of heat each (consuming, of course, 35W of electricity in the process).  In this picture, I have crimped insulated FastOn 1/4" tabs onto the terminals:

To better protect the regulators from water damage, I decided to restore the battery boxes to their original heights, and have the regulators sitting on top of the batteries inside the box.  Fortunately, I never throw anything away (well, my wife may disagree...) so I was able to retrieve the old tops to the boxes and attach them with mending plates (this part of the box is only under compression, so it does not need much shear strength):

For the rear box, I sealed the seam and most of the holes with really thick, sturdy outdoor tape:

For each box, I created a wiring harness for the heating pads.  This is the harness for the rear box.  The harness ends in FastOn connectors - one pair for each heating pad - and one pad per battery.  The other end of the harness is a WeatherPak connector - my favorite:

Here are two of the pads in place int he front box, with the harness connecting them:

And here are the three batteries in the middle box, with the pads underneath and the harness attached:

The last step was hooking up the original MetricPak connectors and battery interconnects.  Here is the rear box with all that wiring in place:

With all the prep work out of the way, it was time to actually do the part of the project which I meant to do in the first place.  I mounted the digital regulators onto 1/8" polypropylene plastic boards. This prevents them from moving around, and it also adds a margin of safety since the poly board will separate the regulators from the battery terminals:

Here is the rear box, all complete.  You might note some sheet-metal screws attaching the poly to the batteries - I was very careful to drill only into the "handle" portion of the AGM-1280T.  This adds further mechanical support to the regulators:

With all the regulators in place, it was time for a test.  The front box is the farthest from the charger, so, if its yellow lights come on when the "test" DIP switch is set on the charger, all is good. All is good:

Finally, I need some way to prevent the batteries from bouncing up and down in the boxes.  I have some very dense foam that I cut circles from - one for each battery - and double-stick taped in place (again, shear strength is not important, these are all under compression from the box top):

And the Volt914 is ready to drive again.  I have not yet attached the battery heaters to any kind of thermostat, so they are not yet plugged in.  Stay tuned - I have a plan which I hope to bring to fruition shortly...