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RV Doctor ColumnRV Doctor #336 Hello Doctor, I have a 34' 1990 Class A motorhome. My problem is that when using shore power my coach batteries do not stay charged. Just running a few interior lights for a few hours will drain them to where I have to start the engine and keep letting the engine alternator charge the batteries. The three coach batteries are only a few months old, but sitting in the driveway with shore power (and even solar panels) connected, I can't keep the batteries charged for very long. Could this be related to the battery isolator? Ryan Vestal, (Little Rock, AR)
Ryan, the auxiliary battery bank, which powers all the interior 12-volt accoutrements such as lighting, water pump, furnace fan, etc., receives a replenishing charge via many different methods. Since we use motorhomes to live in, it stands to reason that there be more than one method typically employed for the house circuits. The engine cranking battery, on the other hand, exists for one sole purpose; cranking the engine and powering the engine/chassis related 12-volt components. Typically the alternator supplies a steady charging current to both types of battery systems. This segment of your charging system apparently is still doing its job, so that rules out the battery isolator as the culprit. Another method of charging is through solar panels and a sophisticated charge controller. Your solar array simply may not be large enough to handle the capacity of three batteries. The most common method of keeping the house batteries up to par is through the use of a charging inverter or converter. Many newer rigs come equipped with a state of the art battery charger integral to the AC to DC converter as well as the DC to AC inverter when plugged into shore power (or by running the generator). Back in the early 90's, however, it was primarily the AC to DC converter that was relied upon to keep those batteries charged. Most charging converters of that era were of the automatic variety, as they all are today. In other words, when you plugged in the shoreline, the converter "automatically" switched the source of the DC current from the batteries and took on that job as its primary task. Parallel (no pun intended) with that task, a charging module was automatically activated and not only did the converter convert, it also began automatically charging the battery bank. Usually an electro-mechanical relay (internal to the converter) was used to switch from battery power to converter power. Repeated use, higher and/or lower than normal voltages, dust and corrosion of the contacts internal to the relay would oftentimes cause the relay to fail. The result was that even though the motorhome was plugged in to campground power, the on-board batteries still provided the crucial DC current for the accessories. This sounds like your symptom. It could be a faulty relay in the converter or it may be a faulty charging module in the converter. In either case, it will be necessary to have that converter looked at by a professional service technician. Most RV shops, however, are not equipped to delve into internal converter repairs, but there are specialty shops around the country that do just that. In many cases, however, it's a wise decision to forego internal repairs to antiquated charging converters using old technology. Newer, lighter and more efficient charging converters are readily available today. It's always been my advice to upgrade to one of the newer, solid state, microprocessor-controlled charging converters employing three or four-step charging algorhythms when it's time to repair or replace that old unit. But, specialty companies do stand ready to repair your old charging converter if you so desire. The newer technology will come with a larger price tag, but the payoff will yield many years of quality battery charging. In all honesty, the older-style charging converters were not very good battery chargers; they were great converters, but the battery charging capability left something to be desired. If you like this rig and you are a serious RVer, consider an upgrade to the newer style.
Dear Gary, water pressure is a problem in our motorhome. The onboard water pump puts out more water pressure then the city water hookup. When connected to city water we go through an adjustable pressure regulator set at 55-PSI, a dual stage water filter, (paper and carbon block) and then into the coach. Taking a shower is quite slow. I've tried placing the pressure regulator before and after the filter and there is no difference in water pressure. I've also tried the little in line water filters and a preset 40psi regulator with both types of filters with the same results. I changed the back flow valve in the coach city water inlet when the problem first came up (it was bad), but with no improvement. The only time we get any increase in water pressure is when we remove the filter and then it's not that much and the onboard pump still puts out more pressure. I've been told that you can augment the water pressure by running the onboard pump when hooked up to city water but that goes against my old teachings to never run the onboard pump when hooked up to city water as you can damage it. What's your opinion? Garvin Newell, Jr., (Ft. Worth, TX)
Garvin, though in-line water filters sometime reduce the available pressure in the line, it's hard to conceive of one reducing it that much. Check to be sure the filter you are using is approved for RV use. It's quite possible there is simply too much restriction through that type of filtering media. In any case, you may want to ramp up the adjustable pressure regulator a bit to get more inlet pressure up to the RV. The lines inside the RV should have been tested at 100 PSI, though I am in no way advocating using that much water pressure on a continuing basis. But certainly 60 - 65 or even 70 PSI would still be safe and perhaps give you adequate pressure for your shower. Though redundant, it's doubtful that running the water pump while connected to city water will harm the pump; that's what its integral check valve is designed for. If you really like that particular filter and can safely set the regulator to a higher output, I'd probably go that route first. Otherwise, I'd look into a freer-flowing filtering media.
Dear Gary, my rig is an older 1975 Fleetwood motorhome and my problem is in how the wires are routed for the fresh water tank probes. The monitor panel does not read accurately for the water tank. The probe is in an upper corner of the tank and is vertical, top to bottom. There are two disconnected wires on the terminal protruding from the top of the probe. Any suggestions? Jim Linton, (Nuevo, CA)
Jim, considered "state of the art" in 1975, that vertical probe consists of a square plastic center core outfitted with five, metallic rods positioned on the outside of the plastic core. The rods extend vertically into the fresh water container to the individual depths as depicted on the monitor panel. The fifth probe is considered the "common" probe and will be the longest metal rod on the probe assembly and it's usually located on one corner of the square center core. All five of the metal rods were prone to develop mineral deposits after years submerged in the fresh water. The probe assembly can be removed for cleaning by disconnecting the five wires (or three in your case) and unscrewing the complete assembly from the fitting on top of the water tank; it's a simple pipe thread. Clean the rods with a soft bristle brush and perhaps some light steel wool. Be sure to thoroughly rinse it with fresh water before re-inserting it into the tank. The routing of the harness throughout the RV can be confusing. It's quite possible the four individual level wires are run in parallel with the same levels on the two holding tanks and are routed to the respective holding tank locations before they terminate at the monitor panel itself. Each of the three tanks has a dedicated common probe and all three are eventually routed to the monitor panel location. It is nigh impossible to determine exactly how the harness is actually routed inside the RV. It may be possible to run a new five-wire harness from the top of the fresh water tank directly to the monitor panel, or it may be necessary to run the new harness to one of the holding tanks. Each level on each tank will share the same colored wire; in other words, the wire at the 1/4 mark on the water tank will be the same color as the wire at the 1/4 level on the two holding tanks as well. Simply match up the colors and your monitor panel should indicate the correct level in the fresh water tank. Use wire nuts to connect the wires from the new harness to the probe assembly so you can remove it for cleaning in the future. If the water tank still does not register on the monitor panel or the two cut wires are too short to splice onto, I would consider upgrading to one of the newer designs of monitoring level indicators; one that is non-evasive and easily installs onto the outside of the containers.
Dear RV Doctor, I changed my alternator from a 130-amp to a 200-amp. My battery isolator is only a 160-amp. What is going to happen to the isolator? Will I have to change the isolator? Will it go bad if I don't change it? It is a Sure Power Model 1602 rated at 160 amps. Thanks! Jim Arnold, (Brackney, PA)
Yes Jim, it will be necessary to upgrade the isolator to one rated higher than the output of the alternator. It would also be a good idea to check the amperage rating of all the conductors in the charging system as well. While it's a very good idea, especially for those I like to call "serious RVers" to upgrade to a higher output alternator, the entire system must be in balance; all parts must be able to carry the additional current. Think of it as the "weakest link" theory. The system is only as strong as its weakest link. You may have a high output alternator, even a properly sized isolator, but if the conductors or terminals are undersized, they become the weakest link. It's my policy to have the charging source, in this case the alternator, be the lowest rated component in the system. All the other components should be sized accordingly to more than carry the entire output current rating. Running with an undersized isolator will eventually burn out one or both of the diodes in the isolator, thereby ceasing any charge current going to that particular battery bank. I'd recommend a 240-amp, dual battery isolator, using the schottky-type diodes for your application.
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