Chassis Battery Charging

[cmillsap]

I was getting the bus ready today to take it to the upholstery shop early in the morning so they could start work on upgrading the fabric on our sofa, valances and dinette stools. It had been about ten days since I had started it to charge up the chassis batteries. I went to start it and all it would do was weakly try to turn over the big DD60.

The damn chassis batteries were dead! Obviously, I wasn’t going anywhere in the morning unless I figured out how to solve the issue. Now I don’t have a 24V battery charger and since the batteries were a little over two years old, I decided it was a good time to replace them. I didn’t bother to check each battery as several people had told me that chassis batteries in a Prevost average about a two - year lifespan. So I went to NAPA and bought four 31 series sealed lead acid batteries to replace them. I paid $122 each for four NAPA Commercial Series batteries and installed them in about an hour.

Now if this had happened with either of my three prior Wanderlodges, I would have not been stranded due to a good electrical system design. One thing I really liked about the Wanderlodge was that both the chassis and house battery system was 12V. This provided the ability to tie the chassis and house battery banks together.

If the chassis battery bank had discharged, it was possible to use the house battery bank to start the engine. This was possible because Bluebird installed a control circuit that allowed you to connect the two systems together momentarily simply buy holding down a momentary switch while you started the engine.

Then there was also the ability to have the inverter/chargers charge both battery banks simply by flipping a switch. That made it very convenient to keep the chassis/start batteries charged through shore power or the generator. Another positive was that the generator was capable of charging both banks. So if you had dead chassis batteries, you could charge them simply by running the generator.

Conversely, the Prevost chassis is a 24V system and the converters use a 12V system to supply power to the 24VDC to 120VAC inverter/chargers to power the installed household items such as the fridge and TVs.

Because the voltages are different, you lose the ability to connect the two systems together. Therefore, the chassis battery bank is totally dependent on the 24V alternator to keep the chassis batteries charged. So the bus engine needs to run periodically to keep the chassis batteries charged. The frequency is dependent on the age of the batteries. Some converters have installed solar panels or a 24V battery charger which can be manually turned on to charge the chassis battery bank. My Marathon doesn’t have one or if it does, I haven’t found it.

[davidbrady]

Hi Chuck,

I'm trying to recall the converters out there that use 12VDC inverters. The big guys (Marathon, Parliament, Liberty, Millennium, Vantare) all use 24VDC inverters and most likely the Trace SW pure sinewave series. My Vantare uses the SW4024 and I think your Marathon does too. This means we have a 24V house battery bank that can be used to jump the S60 in the event of dead chassis batteries. My Vantare has a button on the dash to momentarily connect the house to chassis batteries. I also have a 24V Guest charger which is available to charge the chassis batteries. The Guest charger is plugged into a 120VAC house receptacle that's relay controlled by the ignition key. When the key is off the Guest 120VAC receptacle gets power, but only if I don't have that particular load pruned. I'd look again, but I'm pretty sure you should have a 24VDC house system that should be able to jump the chassis batteries. You should definitely wire in a 24V chassis battery charger. Guest makes on as does Xantrex and there are others.

I have to say, I think BB dropped the ball with it's perpetual use of a 12VDC chassis system. It wasn't until the M450 that they went with the long industry standard of 24V and long overdue. How many folks have chased 12V cannon connector gremlins because of the excessive current draw on the pins, in many cases the amperage draw exceeds the rating of the connector. No such issues with our 24V chassis systems.

Also the BB approach in the LXi of requiring the aux batt switch to be enabled to allow chassis battery charging could be better. How many have left the switch enabled, detached from shore power, and found that both chassis and house batteries banks were depleted. BB tried an improvement with the M450 Big Bird relay but even that didn't go far enough. What's really need is a BlueSea Charging Relay which smartly combines battery banks when one or the other is charging and separates them during discharge.

The Prevost converter approach has always been a well defined separation between house and chassis systems to eliminate finger pointing; hence, the converters reluctance to install smart systems like the BlueSea charging relay. My Vantare gives me a complete separation of systems with a house wall outlet to plug a 24V chassis charger in to. There's no chance of the house depleting the chassis bank nor of the chassis bank depleting the house, but there is a receptacle for a chassis charger and there is a momentary switch on the dash to jump start the engine.

[cmillsap]

I don't know, David, but I have to say that in all the years of Wanderlodge ownership, I was never stuck with dead or discharged batteries. I'm excepting the generator start battery of course.

I spoke Dave at Marathon this morning about the chassis battery charger. He told me that my bus does not have a chassis battery charger installed by them. The chassis batteries are only charged when the engine/alternator is running.

He said that Marathon had only recently started installing Guess chargers on the newer coaches. He said there are two installation methods. They install their chargers with the control circuit ran through the Techlink system. They also install a simple system that just plugs into the engine outlet which dictates that it be plugged in when the bus is sitting but needs to be manually unplugged before the engine is started. The simple method is probably the easy way to add a charger.

I did find a button labeled "Jump Start" on my left instrument panel. I just thought it was for jumping the bus from another Vehicle, LOL
Thanks for clearing that up for me. I guess I should have read the manual more closely.

So now I am making progress. I can't charge my chassis batteries unless I run the engine but I can jump start them when they go dead. LOL.

So I need to install a Guess battery charger but I forgot to ask Dave what the correct size is. Anyone know the correct size or Guess charger model for a battery bank containing 4 series 31 sealed lead acid batteries, CCA 950? I can not find the amp/hrs rating on them.

BTY, David, my inverters are 4000W 24V.

[davidbrady]

Hi Chuck,

Schematics for SpongeBob's Guest 24VDC battery charger wiring can be found over here: http://www.prevostgurus.com/database/Con...Manual.pdf. Pages 103 and 111.

I like this 24V 15A Iota:
https://www.batterystuff.com/battery-cha...S2715.html,
http://www.iotaengineering.com/24vdc.htm,
http://www.amazon.com/DLS-27-15-AUTOMATI...B0074JVPEA

SpongeBob runs a now obsolete 24V 15A Guest 2616A.. As you can see from the wiring schematic it's actually a two bank 12V charger with each bank delivering 7.5A. The leads can be paired on a single 12V bank to deliver 15A. It's wired in series on SpongeBob to deliver 7.5A across the 24V bank.

[cmillsap]

A good feature about a Marathon is that the generator battery is kept charged by the same system that keeps the house batteries charged.

The Wanderlodges that I owned required and add-on trickle charger to keep the generator battery charged.

[davidbrady]

That is a good feature Chuck. My Vantare doesn't have a separate generator battery. Instead I have a switch which allows me to jumper the generator to either the house or the chassis battery bank.

Folks,
Chuck and I ran into something interesting with the Prevost 24V chassis bank, or for that matter, any 24V bank made up of 12V batteries in series. Turns out the better way to charge these 24V systems is to use a two output 12V charger as shown in the attached pic. If instead we use a single output 24V charger then we run the risk of over charging one battery in the series while attempting to fully charge the bank. This is true of any bank made up of series connected batteries and is why Li-Ion work best with battery management circuitry. The battery management shunts around fully charged cells in the series so that lesser charged cells can be brought up to charge. The is called "balancing" the cells in the bank. In a 24V chassis bank there are 24V loads and 12V loads which can cause the 12V lead acid batteries to become discharged relative to one another. Attaching a two output 12V charger does a better job of keeping the individual 12V batteries in balance then does a single output 24V charger.

Our banks, both the house and the chassis, are typically 24V which means the house batteries with their dual 24V Trace SW4024 chargers suffer from the same imbalance problem. The Vanner equalizers function as battery balancers eliminating the problem. They do this by monitoring the center tapped 12V battery and the 24V battery and funneling current from one to the other. The trouble with the chassis bank is that when the key is turned off the chassis Vanner is also turned off so we lose the battery balancing effect.