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January 22, 2018

Battery System

With the wrap up of the wiring, the only piece of the electrical system left to do was the battery and its associated parts.  I didn't think there was much to change in the battery system untill I got down to some of the details.

First, I dug out the battery cables.  The positive cable looks to be about 6 gauge wire with a crimped tap along its length with four spade connectors. This is where the alternator connects to the battery, and where all of the electrical loads except the starter source their power.  The battery terminal connector was roughly cast or forged brass or bronze.

The ground cable was heavy tinned copper braid that ran from the battery negative terminal to a bolt on the rear plate of the engine.  Crimped and soldered along the way was a tap that was bolted to the firewall to provide the return path the the body.  The tap on my cable was missing.

I thought I could replace and maybe improve the battery cables by making my own.  I started by looking for battery terminal connectors.  I bought a set of these, based mainly on the glowing marketing copy, plus the fact that liked the idea of all connections being made directly to the connector, thus eliminating those taps on the cables.  The description of these items implied, or maybe I just assumed, that they were made of tinned copper or brass.  I was disappointed to find that they are actually made of a coated pot metal.

I also wanted a main battery shutoff.  I ordered one of these, and was disappointed to find that under the nice but misleading brass color was more pot metal.

Now when I started this little project, I had no earthly intention of making my own battery terminal connectors, but as I continued my search, I really couldn't find exactly what I was looking for.  Then, while I was pawing through my scrap metal bin looking for something else, I hit on this sizable chunk of copper and, well, the deal was sealed.

For the negative terminal, I sort of copied the design of the shutoff I bought, but with improvements.  On the store-bought piece, it is just the shutoff knob that holds the parts together.  In my design, the two conducting parts are held together with insulated screws, so the knob can be completely removed and the unit stays solid.  Also. the battery cable connects directly to the piece with a terminal lug, instead of using another barttery clamp as in the store-bought unit.  I robbed the green knob from the commercial unit to use in mine.

Foir the positive terminal, I moved the connection points for the alternator and system loads to the terminal body, instead of a tap on the cable.  The terminals look silver colored because they are coated with tin to prevent copper oxidation.

OK, now for the battery itself.  

The battery for the TR6 was nowhere to be found, but I believe the stock TR6 battery is a group size 24.  To do some mock-ups, I stole a battery out of one of the other cars, but it was smaller, so I jhad to make up the difference with spacers.  During these trials, I decided that I'd really like the battery terminals to be at the rear of the battery, sort of under the cowl.  To me, it looked a little more tidy that way, but it would require that the positive and negative terminals be reversed.  Group 24 batteries can be had with reverse polarity, in which case they are designated  Group 24F.  The problem then became that the 24F battery is pretty tall, and the clearance to the cowl was uncomfortably close.  My solution was to move to a Group 34 battery, which shares the footprint of the 24 battery, but is an inch shorter.  Luckily, the 34 battery is also available in a reversed polarity version called, inexplicably, Group 34R.  After finally convincing the guy at Sears that I really did want a 34R battery and not to worry about what car it was going into, I got the battery.

This is an AGM (Absorbent Glass Mat) battery.  AGM batteries are more expensive than flooded cell lead acid batteries, but are lower maintenance, and much less leak-prone.  The rubber strips hold the battery off the paintwork.

I knew there must be some sort of battery hold down arrangement in one of my boxes of assorted parts, and I finally found it.  It looked pretty acid-eaten, and even after I cleaned it up, it wasn't pretty.  The cross bar was severely pitted and the tension rod threads looked to be just about stripped.

I made a new crossbar out of aluminum, but it looked sort of--I don't know--plain, I guess.

That's it!  Some go-fast racing holes!

Some new tension rods and some nice plastic knobs.

Finally putting everything together.  On the positive terminal, the smaller red wire is 8 gauge to the Power Module.  The brown one is 120 strand (approximately 8 gauge) to the alternator.  The large red is 4 gauge to the starter.  On the negative, black 8 gauge to the Power Module, and black 4 gauge to rear engine plate.  No need for a connection to the body since it is no longer used for any ground returns.

The Power Module get its input power connections.

The last touch.  I love this 3D printer!

All done.

Before I closed the shutoff switch, I thought it prudent to put an ammeter across the switch to see if there would be any current flow.  It read a couple of hundred milliamps.  I didn't understand.  Everything on the dash was switched off.  I studied the wiring diagram.  Where could this current be going?  Long story short, my doors are not installed, and the door switches were closed.  The interior lights weren't bright enough to se in the daylight.  That was good for over an hour.  Glad I didn't start taking things apart.

This was a fun one.  Even the obsessive part with the battery terminal connectors was enjoyable.  In principal, with a little more plumbing, I could try to start her up.  I'll probably wait until Spring, though.

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