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Case Study 2

Dead Chassis Batteries

The second case involved a RV that had experienced "dead” Chassis/Starting batteries even though all batteries had been replaced within the previous year. Occasionally these dead batteries would occur after driving many hours, while at other times they were low even after being connected to shore power that provides power to charge the batteries through the integrated Inverter/charger. Numerous attempts had been made to determine where the issue was that would defeat the charging of the chassis batteries. The alternator was checked, the charger portion of the Inverter/Charger was suspected and tested OK, wiring issues from the battery replacement where it was thought that some batteries had been incorrectly connected when installed on the changeover. None of these suspects revealed the problem. It seemed to the owner that all signs were pointing to the Battery Control Center and its associated relay or a defective chassis battery in the bank. It is worth noting that every time the Auxiliary Start or Boost Switch had been activated to add power from the Coach Battery Bank to boost the chassis battery, the boost was provided and the coach always started. Calls to the RV Maker’s Tech Support involved a number or potential checks and tests, all of which did not correct the situation.

The Analysis

With this background I had the opportunity to review the situation. Voltage tests confirmed that the charging system was charging at a rate that brought the coach batteries up to the point where they were sufficiently charged and the Battery Control Center should then connect the charger to the chassis batteries which would then be charged if the control system was operating as designed. Since all the other tests proved there was no other issue, and the fact that the Boost Relay was operating as expected, I concluded that the Battery Control Center was the likely culprit. The big question was "Is the fault in the circuit board (for which there was no longer a replacement) or some other fault?” There did not seem to be any visible electrical damage on the board. There was a fuse that was not blown and a large white multi-pin connector that was plugged into a mating connector mounted to the board. Having experienced numerous issues with corrosion on other applications I removed the connector and examined each pin then reinstalled it. Within a few seconds after doing so, the owner and I heard the relay engage.

The "Solution” – Again!

This relay serves a number of functions. It is the Boost relay that connects the battery banks to provide a "boost” of the chassis batteries when the Boost Switch is engaged. It also isolates or separates the battery banks to prevent discharge under certain situations and it connects the charging system to the "other” battery bank when the first bank is charged to a level where the second one can begin to be charged. Hearing this relay engage, we checked the chassis battery voltage and found it in the high 13V range. It seemed that some of the multi-pin connections were corroded (the coach as 13 years old) and while some functions were operating, others (such as the interconnection of the batteries) was not being carried out because of the corroded connections. The "Solution?” We applied a drop of Corrosion Block® to each terminal and checked the battery charging over the next couple of days. Each time, all indications were that the chassis battery was being charged. The coach started from the chassis batteries and the alternator was providing charging current as designed to the chassis batteries and ultimately to the coach batteries. All systems were operating as designed. Subsequently it was discovered that the engine driven alternator was failing and that one of the connections that "excites" it had also corroded. Replacement of the alternator after 90,000 miles was deemed to be the best solution since these alternators frequently fail around this mileage.

The Conclusion

RVs are unique because they are relatively underused, often used for short periods of times then left sitting dormant. RV’s must withstand wide variations in temperature and humidity and are hand assembled. Very few other high value products can sustain this variety of conditions. These factors lead to corrosion among the connections that carry information between components and create erratic or intermittent electrical issues. These troublesome symptoms are hard to track down and correct. Checking all of the big items in a system can lead to identifying a problem, my experience is that the major systems are much less likely to fail especially when compared to the potential for corrosion over time. Batteries will fail because of the RV usage and are expected to require routine replacement. The remainder of the systems are fairly robust. Thus the weak links in the chain are the interconnections between the components that are susceptible to corrosion. While it would be difficult to maintain a regime of routine corrosion prevention, it may be wise when system demonstrates erratic behaviour to check for corrosion before tackling the bigger items. Those bigger items can only function effectively if they receive the correct information through the wiring connected to them. Having a tin of Corrosion Block® in one’s tool kit is a wise measure and using the chemical wisely could save hundreds of dollars in diagnostic effort and replacement of components that are in fact operating correctly.