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EXTENDING THE FRAME FOR 12 VOLT BATTERY - FR-202

At 04:14 PM 10/1/03 -0400, Dick Masse wrote:
>"What to do about battery(ies) - the frame is new for the 6V batteries but I was hoping I could get a 12V and put it in the existing frame..."

Okay, there is a prerequisite for this course. Please start by reviewing Changing to a single 12 volt battery. This gives information about battery sizes, increased cranking current, increased battery life, reduced cost, but also reduced reserve capacity.

The key to this problem is that the smallest (commonly) available 12 volt battery is about 1-1/2 inches longer than the original 6 volt batteries (nearly square) used in the MGA, so you need to extend one battery carrier (usually the right side) about 1-1/2" at the back edge (a little cut and weld operation). When doing this you DO want to have enough space for the original rubber pads (about 1/4" thick) which fit in at the front and back ends of the carrier frame.

Find battery sizes and numbers here: www.rtpnet.org/~teaa/bcigroup.html. If you're reading this you probably don't care to review again just how small the original 6 volt batteries were. The smallest commonly available 12 volt battery is the group 26, which is 6-13/16 wide x 8-3/16" long (7-3/4 tall including the posts). This will be very close to 8" long on the bottom, so the original carrier in the MGA needs to be lengthened about 1-1/2" to accept the battery and the rubber pads. The group 26R is reverse polarity, which is just the same as having the posts on the opposite side of the battery. When buying the battery, pay attention to which post you want on which corner. Or you can buy a battery with the posts on the center line, or which may also have side terminal connectors (which you probably will not use). The center post battery may be easier to install, given that you can turn it around to put the hot or ground post at either end. The group 21 battery is about 1" taller, which could be a problem during installation (and I wouldn't recommend even trying it).

When I did my MGA restoration many years ago the bottom frames of the battery carriers were badly rusted (nearly gone), but the side supports were still in decent condition. Considering that this is possibly the most corrosion prone part of the chassis, I fabricated new base frames from 1/8 inch thick steel angle stock, welded them to the original side supports, and I have never regretted it. Now 18 years and 190,000 miles later they are still in good serviceable condition. I do however clean and repaint them about as often as I need a new battery(ies), so they may indeed last indefinitely.

My first work was for standard size frames for the original 6 volt batteries. Eight years and two (expensive) sets of old tech 6-volt batteries later I decided to convert it to a single 12 volt modern battery. As the base frame was already 1/8 inch thick steel stock, the frame extension was pretty easy. I just cut off the back inch of the frame, formed a new steel angle to make new shallow "U" shape 2-1/2 inches long, and welded that to the existing stubs. Your battery frame extension might be a little more work, depending on your starting point and how neat you like to make it.

Once your new single 12 volt battery is in place it will need a new ground cable connection and most likely a new hold-down clamp. If you use an angle clamp bar across the top corner you may need to buy longer J-bolts (available at any auto parts store). Also be sure not to allow the clamp bar to come into contact with the hot post battery cable terminal. There are also various clamp bars available that bridge across the center of the battery, even a rubber bungee type clamp bar that can be secured with the original J-bolts.

There are all sorts of advantages to using a single 12 volt battery, and only two disadvantages that I know. For a concours car show you may lose points for not having the original twin battery set up. And if you leave the lights on when the car is parked, the single battery will run down a little quicker, having less reserve capacity than the original twin batteries.

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