Auxiliary Batteries

[RV Utah]

I just purchased a 2003 Coachmen Mirada, 30 foot, with 14,000 miles. I was so excited to find a low mile, well priced unit that I overlooked one thing -- it has no auxiliary batteries! I have to be plugged in or running the motor or generator to run anything! I contacted Coachmen and they claim they have never shipped a unit without auxiliary batteries. There is no sign of there ever being batteries in the compartment under the step. The previous owner did not buy it new and just figured that was the way it was.

Coachmen sent me a schematic of how the batteries should be wired in. It shows that all I have to add is the batteries, cables, a 250 amp fuse and I would be in business. Is it that simple? Has anybody added auxiliar batteries before?

Thanks for your help!

Karl

 

[Just Lou]

Several of us have added additional batteries. to our rigs.  If you can read and understand that schematic, you should have no problem.  Just don't skimp on cable sizes and keep them as short as possible.  Did you look in the other obvious places.. i.e. engine compartment, near the engine battery. etc...?  A previous owner may have relocated them to be closer to an inverter installation.

 

[RV Utah]

Oh yeah. I looked everywhere. I confirmed with the previous owner that it did not have them as well.

Karl

 

[John From Detroit]

About the only argument might be the size of the fuse.

That easy:  Well, electrically yes, mechnically, you have to properly support the batteries (Which may or may not be easy) and make sure they do not go bouncing around or that escaping gas, vapors (which by the way can be explosive) or acid does not go places where harm will occure.

Actually, that part is fairly easy to do (the damage prevention) just make sure the compartment is ventelated

 

[RV Utah]

Most of that was taken care of by Coachmen. The only thing I seem to be lacking is the batteries, the cables, and the fuse. I was just hoping somebody has some experience with this -- it all seems too easy. I can just imagine burning my new RV to the ground. My, wouldn't the neighbors talk!

Based on the schematics, I have a lead from the generator, a lead from the Pos terminal of the chassis battery, and a lead from the aux batts all going to the same solenoid. After I install the two 12V batts in parallel I run a cable to a 250 amp (according to Coachmen) fuse, then to the solenoid. Seems easy, but is it going to charge? Will the emergency start switch on the dash work? Will the charge meter show the state of charge as well? It seems too good to be true. Has to be something missing.

Karl

 

[Just Lou]

That solenoid you described is located in a box near the chassis battery that contains the battery isolator, both battery disconnect solenoids and the solenoid to connect the chassis and aux together for emergency start along with the charging and monitor wiring, etc..  Your batteries should charge and register on your monitors.    BUT!!!  This all assumes that the batteries were indeed the only things missing.  Who knows?  We can't solve the mystery of the missing batteries either.  I'll bet it works.

 

[Gary RV_Wizard]

Yes, it SHOULD be that pretty much that easy, except that there has to be a ground lead on the batteries somewhere.  That solenoid should be part of a power management system that controls charging and power distribution, including things like the emergency start switch and gauges.

I'm a bit surprised the chassis battery has a lead to the same terminal that the aux batteries do, since that effectively puts it in parallel with the aux batteries by tying the positive terminals together. Usually they are isolated by the power management circuitry except when the emergency start switch is pressed.  Make sure you are reading the schematic right.

 

[RV Utah]

I will check that again. I have tried to double check with Coachmen, but I am still waiting for a reply. Appreciate the input.

Karl

 

[Karl]

Karl,

It would be helpful to see the schematic they supplied. Can you scan it in and post it as an attachment? As Gary said, there seems to be some question about how things are connected together.

 

[RV Utah]

Guys, I'm an idiot. While reviewing the schematic I realized that I have an extra lead. Followed it to the front hood (my wife checked under the hood for batteries while I was at work) and found an extra battery. The pos lead on the battery was melted off, no charge in the battery.

Here is my new delimma (besided being an idiot): The dead battery was a 24 volt deep cycle. The Coachman schematic shows two 12v in parallel (pos to pos, neg to neg) which would give 12 volts, right? Why is there a 24 volt in there, and was that the cause of the meltdown? I find it strange. When the coach runs off of the chassis battery it is 12 volt. Why would there be a 24v battery?

Thanks,

Karl

 

[Ned]

There shouldn't be a 24V battery at all.  Of course, that could explain how the post melted.  I would hope that any fuses would blow before any damage was done to the 12V systems.  The correct installation would be the 2 12V batteries in parallel, per the schematic.

 

[Karl]

Like Ned said, there shouldn't be a 24V battery in there at all. Sounds like someone had an extra(?) diesel truck battery and figured "12 volts plus 12 volts equals 24 volts, so I should be alright". DUH! If the 12 volt fuses didn't blow, almost certainly the 12 volt lights would have. The only thing I can think of that would draw so much current as to melt the post and/or cable would be the engine starter motor. If it would normally draw, let's say, 200 amps at 12 volts, it would draw double that (400 amps) when hooked up to 24 volts. Perhaps he tried using the emergency start switch, which would put the 24 volt battery in parallel with the 12 volt chassis battery - not good for a lot of reasons.

 

[John From Detroit]

I'm reminded of a very old joke about a man who sent his wife to the electronics parts store for five 100ohm resistors

She came back with one five hundred ohm resistor cause it was cheaper than five 100 ohm ones.

Oh well.

That said,,, I just got done installing the AGM batteries for the inverter in my coach. (Well, I have a bit of "Clean up" type stuff to do) but I ended up putting them in the compartment with the inverter, after adding a sheet of 3/4 inch plywood to the compartment to support them that is,,, Silll screwing things down a bit.  Looks good though and took charging current (peaked at 15 amps when the display came on, quickly tapering off to, now it's zero) The batteries have not seen a charger since Feburary

 

[Tom]

Do you have a photo or two to share John?

 

[Just Lou]

John, Do you need a ventilated compartment when you use the AGM batteries? 

 

[Ned]

AGM batteries don't need ventilation, they are sealed.  They can even be mounted upside down.

 

[Alaskansnowbirds]

The dead battery was a 24 volt deep cycle. The Coachman schematic shows two 12v in parallel (pos to pos, neg to neg) which would give 12 volts, right? Why is there a 24 volt in there, and was that the cause of the meltdown? I find it strange. When the coach runs off of the chassis battery it is 12 volt. Why would there be a 24v battery?

Thanks,

Karl

Karl,

Could that battery possibly be a 12 volt GROUP 24 battery?

 

[John From Detroit]

John, Do you need a ventilated compartment when you use the AGM batteries? 

Others say no, however I felt the need to add ventelation to the compartment for OTHER reasons, Reasons that actually have nothing to do with the batteries,,, I did that today, fan comes on at about 90 degrees f

I've 8 more fans  (Bought a box of 10 in QZ, I used one in the video compartment cause it was getting real hot there, now it too fans at 90)

Ordered a couple of low power solar charge controllers today... I got a small (5 amp) solar panel and it can kind of over charge if I let it (when I put no load on it other than a voltmeter it said "Low volatage" ... it also said "24 volt system, voltage was 23.something)

 

[Just Lou]

John,
If I'm reading between the lines correctly then your battery compartment is not a "dedicated" battery compartment as mine will not be.  My hesitation to add ventilation stems from not wanting to open the compaqrtment to dust infiltration and thus limiting it's use for additional purposes.  I'm headed to Alaska and have been told to expect a lot of dust at times.  It would help to keep the old tub as air tight as possible.  Thanks, lou 

 

[Ned]

Lou,

If you install AGM batteries, you don't need to ventilate the battery compartment.  If the battery compartment is ventilated, with AGM batteries you can use a hose to clean out the dust.