# The Converter Fails Quietly And Takes The Bank A failing converter changes nothing an owner can see. Lights work, the pump runs, the coach behaves. Underneath, the bank is either never reaching a full charge or being held at a voltage that boils it. The bill arrives months later as a set of batteries. ## Two failure directions, neither of which announces itself A converter turns shore power into twelve volts and keeps the house bank charged. When it fails outright the coach eventually goes dark and the owner knows immediately. The expensive failures are the partial ones, and they run in two directions. Output too low means the bank never reaches full charge and slowly sulphates. Output too high means the bank is held above its charging voltage indefinitely and loses electrolyte. Both are silent, both take months, and both end with a bank that has to be replaced. What makes it worse is that everything else keeps working, so nothing prompts an investigation. A coach on shore power at a storage lot runs its lights, its detector and its fridge board off a converter that is technically producing power, and the batteries sit there being quietly ruined by it. Owners find out when they leave the pedestal for the first time in months and the bank cannot carry an evening. At that point the conversation is about a bank, and the converter that killed it is still bolted to the wall. ## A float voltage that never becomes a real charge Lead acid batteries need to be taken up to a bulk charging voltage to fully convert the sulphate on their plates back into active material. A converter stuck at a float level, or one whose output has drifted down with age, keeps the bank at perhaps eighty percent forever. The unconverted sulphate hardens over weeks into crystals that no longer respond to charging, capacity falls, and the process accelerates because a partly sulphated plate has less area to work with. Nothing about that is visible from inside the coach. The symptom that eventually surfaces is capacity rather than voltage. The bank still reads a respectable number at rest and then collapses under any real load, which is the same signature as the slide fault described elsewhere in this category and for the same underlying reason. Owners frequently replace batteries at this point, get another season, and then replace them again, because the converter is still doing exactly what it did to the first set. Two banks in three years is a converter finding far more often than it is a battery quality problem. ## Electrolyte boiled off in a coach nobody visited The other direction is louder in its results and just as quiet while it happens. A converter holding a flooded bank above roughly fourteen volts continuously drives the electrolyte to gas off, the level drops below the plates, and the exposed plate area is permanently lost. On a coach in storage with nobody checking cells, that can happen across a single season. The evidence is unmistakable when the caps finally come off: low levels in every cell, a crust on the terminals, and often a corrosion bloom on the tray and on anything metal in the bay. Sealed batteries make it worse rather than better. An AGM has no caps to top up, so the water lost through the pressure valves does not come back, and the failure is invisible until capacity testing reveals it. Owners who chose AGM specifically to avoid maintenance are the ones most exposed to this failure mode, which is an uncomfortable thing to explain and true. A converter that runs hot to the touch, or a battery bay that smells faintly of sulphur, is worth investigating the same week rather than at the next service. - Flooded cells low across the whole bank, not just one - White or blue corrosion bloom on terminals, tray and nearby brackets - A converter that is noticeably hot with the coach lightly loaded - A sulphurous smell in the battery bay - A sealed bank that tests short of capacity with no history of deep discharge ## Older converters that only know one voltage Plenty of coaches from the nineties and early two thousands were built with a single stage converter, a device that produces one fixed voltage and has no charging profile at all. Those units were never good for battery life and they were cheap and reliable, so they are still out there in large numbers, often still working in the sense that they produce power. On a coach that lives plugged in, a single stage unit is a slow bank killer, and no amount of battery quality compensates for it. Replacing one with a modern multi stage converter or a combined inverter charger is one of the better value upgrades available on an older coach, because it protects a component that costs considerably more than the converter does. Inverter and charger replacement runs $750 to $4,500 across three to fourteen hours, and a plain converter swap on a coach with accessible mounting sits at the bottom of that. Where the existing unit is integrated into the distribution panel, the work is larger, because the panel has to be addressed rather than the box. ## Three readings at the battery post that settle it Anyone can check this without special equipment. Reading one: with the coach unplugged and everything off for a few hours, measure across the battery posts. That is the rested state of charge and it is the baseline. Reading two: plug in to shore power and measure again after ten minutes. A functioning converter on a partly discharged bank should be pushing the voltage up noticeably above the rested figure. Reading three: leave it plugged in for several hours and measure once more, which shows whether the unit steps down to a float level or simply holds high indefinitely. The pattern is the finding. No rise at all means the converter is not charging, whatever else it is doing. A rise that never steps down means a single stage unit or a failed control, and it is the overcharge case. A rise that is small and immediately settles low means undercharging. Write the three numbers with the times, and note the battery chemistry, because the correct target voltages for flooded, AGM and LiFePO4 are all different and a reading is meaningless without knowing which bank it was taken on. - Rested reading, coach unplugged, nothing switched on - Ten minutes on shore power, same leads, same posts - Several hours on shore power, to see whether the unit steps down - Battery chemistry noted, since target voltages differ for each - Ambient temperature noted, because charging voltage is temperature dependent ## A charge profile that was never written for LiFePO4 Lithium conversions make this a bigger problem rather than a smaller one. A LiFePO4 bank wants a different charging voltage and no float stage at all, and a converter built for flooded batteries applies neither correctly. Some conversions work anyway because the battery's internal management protects itself by disconnecting, which the owner experiences as a bank that mysteriously stops accepting a charge. Others quietly undercharge forever, so an expensive bank delivers a fraction of the capacity it was bought for. The uncomfortable part is that a lithium upgrade sold as a drop-in replacement rarely is one. The bank is the visible half of the job. The charging side, the converter or inverter charger, the alternator path if the coach charges while driving, and the low temperature cutoff behaviour all have to match the chemistry, and on most coaches at least one of them does not. Owners who bought batteries first and asked about charging afterwards are the majority of the lithium work that comes through here, and the second half of that project is usually the larger one. ## What replacement costs against what neglect costs The decision is straightforward once the numbers are on the table. House battery replacement runs $500 to $5,500 across two to ten hours depending on chemistry and bank size. A converter or inverter charger sits inside its own band and is frequently the smaller of the two. Replacing a bank without correcting the charging source means buying the larger item twice, and the second purchase arrives on roughly the same schedule as the first, which is the pattern owners describe when they say their coach eats batteries. There is a case where the honest answer is to do nothing yet. An owner with a serviceable flooded bank, a single stage converter, and a coach that only sees shore power a few weekends a year is losing very little, and the upgrade can wait for the next battery replacement when the labour overlaps. What does not wait is a converter measuring high, because that one is actively destroying something. Telling the difference takes three readings and about ten minutes of attention, which is the cheapest maintenance available anywhere on a coach. ## Related - [/services/mechanical-systems/battery-charging-system/](https://ocrv.guru/services/mechanical-systems/battery-charging-system/) - [/services/mechanical-systems/electrical-repair/](https://ocrv.guru/services/mechanical-systems/electrical-repair/) - [/the-center/calculators/](https://ocrv.guru/the-center/calculators/) - [/prices/](https://ocrv.guru/prices/) --- Source: https://ocrv.guru/blog/systems-and-power/the-converter-fails-quietly-and-takes-the-bank/ OCRV Center, 23281 La Palma Ave, Yorba Linda, CA 92887. (949) 799-3387. Serving Laguna Niguel, California. All work performed in shop. No mobile or roadside service. Licences: California Bureau of Automotive Repair ARD00288521; EPA CAL000367879. Published ranges are ranges, not quotes. Every figure traces to https://ocrv.guru/prices/.