Episode 28:

Adding a kill switch to the

starter batteries

It was a challenge last winter to start the bus, and it’s only gotten worse this year. Even in the milder weather the batteries seem to drain if the bus is idle for a few days. I’ve had the bus in to the dealership to diagnose related issues, and learned how difficult (and therefore expensive) it can be to find the cause of such a phantom drain. My brute force way of dealing with the issue has been to open the battery bay on the outside of the bus, and use a socket wrench to disconnect the negative battery terminal while the bus is parked. This has been a nuisance, and not entirely effective (I think because the batteries were getting old.) I’d heard of truckers using a kill switch to disconnect the battery when parked. I decided on that solution. Given the large current that passes through the battery cables especially when engaging the starter, the kill switch needs to be designed to handle the current. So do the cables. It’s counter-intuitive, but electrical cable gauges use smaller numbers as cables get thicker. House wiring is typically 14 or 12 gauge. To handle the heavier current that a dryer needs, you’d use 8 gauge wire. For the kill switch I used wire smaller than 0. 4/0 to be exact. At about $24CAD per linear foot for each of red and black cables, I paid the dealer more than it would have cost from other sources. The sticker shock led to me place the kill switch as close as possible to the starter batteries, while still inside the passenger compartment. Last winter I found that, on several occasions I had to recharge the starter batteries using a typical battery charger plugged into the generator. In addition to the kill switch, I also added positive and negative bus bars in the bus interior. That means I can now charge the starter batteries from inside the bus. Finally, when I start wiring the bus interior, I’ll be able to easily hook up this Renogy DC-to-DC charger that will allow the alternator to charge the house batteries when the bus is running.
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