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.

[Hisham Amaral]

Chuck
You could have used the override switch n your Marathon to get the coach started. There is a switch under the small window by the driver on the wall that you have to power up to jump start the coach. Check, your Marathon manual should have that information, I had that function on my 04 XL2, I think you have the same thing. good luck.

[davidbrady]

Hi Chuck,

I'm trying to recall the converters out there that use 12VDC inverters. The big guys all use 24VDC inverters an 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 than 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.

[cmillsap]

Hi Hish & David,

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. I think the amp/hrs are around 110. The Tech at Marinco suggested a 30 amp charger for this 4 battery bank such as> http://www.boatersland.com/mvt44020300.h...oCc6Tw_wcB

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.

[davidbrady]

Chuck,

I'm going to backpedal on the two lead single bank 24V charger idea. I think you're better off with a charger that provides two banks of charging like the Guest 16202. Gil Johnson just informed me that when the ignition key is in the off position the chassis battery Vanner Equalizer is turned off. This means that charging 12V batteries in series with a single 24V charger may result in unbalanced charge and possibly gassing of one of the batteries. To avoid this problem we had better stick with the tried and true two 12V bank charges wired as Vantare has done in my schematic. I posted links to my schematics on WaGu. Marathon has chosen this approach in their later coaches for probably the same reason.

[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. One less thing to have to deal with.

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

[cmillsap]

Here is a schematic that shows the way David and I are connecting a 12/24V-2 bank-120/230VAC smart battery charger to our Chassis battery bank.

[cmillsap]

If you’re considering adding an on-board battery charger to your chassis battery bank, just be aware that there’s a bit more to the job than just hooking-up a charger to the positive and negative battery cables. The chassis battery bank wiring on a Prevost is fairly complicated and requires a 2 bank 12/24V battery charger to correctly keep each of the 4 batteries equally charged. Therefore, it is imperative that the charger gets connected properly.

First, to determine the proper size charger, the rule of thumb is 10% of the amp hour rating of the batteries. For example, batteries sized at 100 amp/hrs would require a charger that is sized at 20A or 10A on each of the 2 legs. A parasitic draw of more than 3 amps may require an increase in the charger size to compensate.

The charger needs to be located in a ventilated area and upright to allow it to cool properly. There weren’t many placement options on my Marathon. I ended up building a frame for it and attaching it to the floor in my engine bay and plugging it into my engine bay 120V outlet. That outlet is powered through its own circuit breaker in the 120V electrical panel. I just have to remember to flip the breaker off before I run the engine/24v alternator to prevent any damage the charger.

I installed this charger: http://www.amazon.com/Marinco-Charger-Ba...r+%2328220

David Brady was kind enough to help me determine how the chassis battery bank was wired and how to connect the proper battery charger leads to the correct connection points. Without David’s direction, odds are that I probably would have installed it incorrectly. Although Marathon routinely retrofits a chassis battery bank charger in older Prevosts, they were unwilling to give me any direction on the matter. They probably had a liability issue.

This is how I installed my battery charger with a lot of direction from David who is an electrical engineer. I am not suggesting anyone follow my lead. If you aren’t sure, have a professional install it for you.


  Chassis Batteries Schematic Final 2.pdf (Size: 113.9 KB / Downloads: 39)

[Hisham Amaral]

Great job,
I din't understand way Leon did not give you the procedure to add relay so that you don't have to turn off the breaker ever time you start the engine.
Add that to your pre trip to do list. If find a way to connect a relay to the charger I will pass the information on, but I am not a sparky.