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Battery Equalizer —you have at least one
Hi All
On our last trip out we had a part fail, which transformed Prevost Life into something less than we normally enjoy.
Our coach is a 1994 Marathon conversion. We have a 24 volt house bank that is charged at 24 volts ( 28 really) by the bus alternator or the inverters. The inverters take 24 volts out of the batteries to make 110 volt AC power for many appliances in the coach. Other converters may do this differently, but the Marathon approch is great because it allows the fastest charging of the house bank. In 12 years we have never had any problems until this last trip.
All Prevost coaches have a 24 volt engine start battery bank which supplies power to the starter, as well as many other circuits like the DDEC computer, headlights, dash instrumentation, etc. Some of these loads ar 12 volt systems. This electrical power is taken out of the middle of the engine start battery bank. By doing this, one half of the bank would be electrically depleted over time. So Prevost installs a Vanner Battery Equalizer on the front wall of the engine bay, right in front of the engine start battery bank. This device takes 14 volt power from the batteries, converts it to 12 volts, and recharges the part of the bank that is low. This all happens at the same time as the 12 volt portion is being depleted so the entire bank drops voltage together. Every prevost has one of these I think. Terrific when it all works…..
In our case, the house bank also provides power for some 12 volt loads , like interior lights, the toilet, the back up camera and stereo, etc; and this bank has an identical Battery Equalizer. It failed. Then half your battery bank loses voltage and can not be easily recharged. For example, half the bank remains at 12 volts, the other half is depleted to say 9 volts. Now apply a charging current to the entire bank and the higher part gets overcharged, and the lower part never comes up to full. Even connected to shore power, it does not get to 12.6 volts. Life grows dim inside, lights are dim, the back up camera has ultra low contrast, the stereo might not turn on. The inverter can only provide power for minutes instead of hours. Oh the humanity!
These battery equalizers are not readily available at an auto parts store or RV supply place. It would require getting one on line mail order or from Prevost or Marathon. The manufacturers instructions say there is no maintenance required for many years of service. My coach is 19 years old, I guess they were right. But I now carry a spare since I have 2 of them.
By the way, proper operation is very easy to check, . There are 3 large terminals on the bottom of each one, ground, 12 volt and 24 volt. Measure the voltage between ground and 12, and between ground and 24 on a partially discharged battery bank. The 12 reading should be EXACTLY half of the 24 reading. Use a digital voltmenter. Vanner does not repair them, but they said there were two 70 amp fuses inside my older design, those could be changed if that was the only problem. In my case, it was something else, the fuses were good.
Posting this in the hope I save someone else the trauma of dealing with such a disaster on the road.
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7 Replies
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Peter’s post is very good. What is unsaid is that if you have a 24 volt house you have to be aware of both the 12 and 24 volt circuits in your coach and how they relate to one another. The 12 volt side should be 1/2 of the 24 volt voltage within 1/2 volt. If there is a greater variance than that you need to suspect a failed or failing equalizer.
The chassis is equipped with the Vanner monitor so you are likely going to get a warning on the dash at the first sign of a problem. Most if not all conversions may not have such a convenient way to verify everything is OK on the house side of the DC circuits.
Some coaches have a 12 volt house, and the only equalizer on those coaches will be the one provided by Prevost for the chassis.
When I speak of 12 and 24 volts those are strictly nominal values. At rest a fully charged battery should have a voltage of 12.7 or 12.8 volts, and if the batteries are used in series to create 24 volt circuits the voltage will be 25.4 to 25.6 volts. With the engine running to charge the batteries the voltages are likely to be 13.8 and 27.6 respectively, more or less. When the house is being charged by the inverters the voltages will vary depending on the type of batteries, and the stage of charging the inverter(s) is in.
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Looks like I’ve developed the same problem. My coach has the Vanner equalizer for the chassis batteries and a second Sure Power 52210 model for the house batteries which is where my problem seems to be. Does anyone know a source for a 100 amp equalizer? Sure Power has a new model number for theirs and the best price I can find is $549. I will try Marathon and Prevost tomorrow as well as the local heavy truck repair places. There are a few used ones of the original vintage on Ebay but they’re stilll $400 and I don’t feel like chancing it.
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Verify the equalizer is bad first before ordering one.
Some equalizers have a fuse or rest button so that is one thing to check. The Vanner web site has PDF files you can download or their owner’s manuals which are excellent at explaining how to verify the equalizer operation.
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It definitely appears to be the problem. On shore power at bulk charge I’ve got 28.1 on one leg and only 11.6 on the other. Readings on my Techlink are virtually identical. I will see if there is a reset or internal fuse. Thanks.
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Yep, our very own Advertiser, Inverter Service Center can fix you up with a great price on an equalizer.
Go here: Inverter Service Center
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If the 12 volt side is showing 11.6 volts you need to get that voltage up to the proper fully charged voltage. You might have to separate the batteries and charge them individually.
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Problem fixed. A new Vanner battery equalizer from Inverter Service Center took about 30 minutes to install and basically restored order to the coach systems within minutes. I drove down and picked up the unit and met the folks at ISC. They are very knowledgable and I learned a lot about inverters just chewing the fat with them.
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