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Old 05-21-2009, 02:08 PM   #1
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Exclamation Moved Batteries...did I just screw up?

Seeking some thoughts on a battery relocation I just performed. I may have made a mistake and was hoping for some insight.

First, due to a weight imbalance in my rig, I moved the house batteries from under the passenger side (under stairs) to the drivers side bays attached to a slide. I left the chassis battery in it's location under the steps on the passenger side. In addition to moving the two existing group 29 wet cells, I added two more group 29 wet cells to the relocated area so I now have a bank of 4 x Group 29s. (I will replace with a 4 x 6 volt Trojan or Interstate system someday, but not today).

In order to get power from the batteries, I routed approximately 16 ft of 2 gauge AWG through a drilled hole in the back of the bay, and over the chassis heat shield to the old battery location and connected to the distribution blocks in the old battery bay.

Now, here's where I think I may have screwed up:

1) 2 gauge should be fine for carrying power from my batteries to the distribution panel. I don't use a large inverter and my average DC load would be around 20 amps with peaks around 50 amps. I would still have less than a 3% voltage drop at that peak rate...not an issue. HOWEVER....

2) I did not consider the charging side of the equation. I have a Progressive Dynamics PD9260 converter/charger. It is located about 4 feet from the previous batter location and connected with the factory 6 gauge to the distribution panel about 6 - 7 feet away. With the bigger charging load for the larger battery bank and additional line losses, am I at risk for not fully charging the batteries?

Let's assume at 14 volts I have about a 2% loss from the charger to the panel, and another 3% from the panel to the batter bank, I am now looking at 5% total voltage loss at full 60 amp charging load, or roughly .7 volts. That means the batteries will only see 13.3 when the charger is at 14. Further, the charger will see a higher voltage than the batteries are at and may prematurely taper off bulk charging and lower the charging voltage before it should. (Correct me if my calculations/assumptions are off).

Bottom line...did I screw up? Do I need to move the charger to a location closer to the batteries and run a 1/0 gauge wire directly to the battery bank? I could locate the charger under the dinette seat and route new cable straight to the battery bank, but that would require bypassing the distribution panel so the order would be converter > batteries > distribution panel instead of converter > distribution panel > batteries as it is currently set up. Is that a problem?

Thanks,
Mc2guy
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Old 05-21-2009, 02:43 PM   #2
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Mc,

It is all about amps and feet. How many max amps will you be using/charging?

Here is one grid for amps, feet, gauge at 12V.

Amps and Wire Gauge - 12V Circuit

Just remember that the feet are for both ways, i.e. 15 feet away time 2. (total length)

I think for the most part a 5% voltage drop is acceptable, and used for max feet for a given gauge, more than that, wires may get warm.

Harold
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Old 05-21-2009, 03:08 PM   #3
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I would be concerned with that much weight in the slide - you might be looking at slide problems down the road...
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Old 05-21-2009, 06:08 PM   #4
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Chances are you won't see to much of a problem with the distance, although you are pushing it abit.

However, I do agree with Alan... weight could be a problem for you. a 6-volt Trojan Deep Cycle battery weighs about 66 lbs. Multiply that times four and that's 264 lbs just in batteries on your slide. I don't know about Winnebago, but my Fleetwood according to factory recommendations says a max. of 300 lbs in the large street side slide out. This would mean your at the max. even with nothing else loaded in your slide compartments. Plus the 264 lbs is concentrated in a small area (footprint) and the slide floor may not support that for too long a time.

So to answer your question I think maybe you did screw up.
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Old 05-21-2009, 07:38 PM   #5
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One other very important issue is venting off the hydrogen gasses produced during charging. Wet cell batteries have to be vented to prevent a possible explosion! Now if you did not have to worry about weight in the slide you could get around the venting issue by use of AGM batteries and end up with a better battery bank for boon docking anyway.
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Old 05-21-2009, 09:22 PM   #6
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One other very important issue is venting off the hydrogen gasses produced during charging. Wet cell batteries have to be vented to prevent a possible explosion! Now if you did not have to worry about weight in the slide you could get around the venting issue by use of AGM batteries and end up with a better battery bank for boon docking anyway.
I did actually vent the compartment so any hydrogen will get extracted through natural convection as it rises. The weight now has me concerned, not about the floor as there is a steel frame under it, but about the total weight on the system.
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Old 05-21-2009, 10:11 PM   #7
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I would call Winnebago customer service; they should be able to tell you if you are overloading the storage bay.
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Old 05-22-2009, 03:31 AM   #8
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Quote:
Originally Posted by hdossett View Post
Mc,

It is all about amps and feet. How many max amps will you be using/charging?

Here is one grid for amps, feet, gauge at 12V.

Amps and Wire Gauge - 12V Circuit

Just remember that the feet are for both ways, i.e. 15 feet away time 2. (total length)

I think for the most part a 5% voltage drop is acceptable, and used for max feet for a given gauge, more than that, wires may get warm.

Harold
MC2GUY,
did you run both the hot and ground #2 gauge to the old battery location?
if you did, an option might be to choose a closer chassis place to ground the new batteries with a heavier cable (not on the slide). the engine or frame ground would be appropriate.
then, use your 2 #2 cables in parallel for the + side. if you do that, make sure that you have a good ground with a heavier cable to the chassis or frame where the original batteries were.
the loading of your slide compartment would be an important consideration.
i went with 2 lifeline gpl-6ct 6v 300 amp agm batteries in parallel mounted on their sides under the stairs on my moho.
if i were to move my starting battery, there is enough room under the stairs to mount 2 more lifeline batteries on their sides in my moho.
besides the expense involved, i would have a weight issue too.
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Old 05-22-2009, 09:00 AM   #9
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I did actually vent the compartment so any hydrogen will get extracted through natural convection as it rises. The weight now has me concerned, not about the floor as there is a steel frame under it, but about the total weight on the system.
I have the same concerns about hydrogen as RVWizard. In addition to venting, Did you also make sure the bay is well-sealed from the living quarters above? Any wires or furnace ducts running through the bay? If so, are the places where they go through the floor well sealed?
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Old 05-22-2009, 01:56 PM   #10
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I have the same concerns about hydrogen as RVWizard. In addition to venting, Did you also make sure the bay is well-sealed from the living quarters above? Any wires or furnace ducts running through the bay? If so, are the places where they go through the floor well sealed?
The compartment is completely isolated from the living quarters. WAY more isolated that the factory location under the steps as a matter of fact. The bays are sealed from the living quarters and actually separated by about 6-10" of open air space. The entry points into the bay are limited to the vents I installed and the cable routing I cut...that's it.

BTW, I understand everyone's concern regarding venting the batteries, and I have, but you have to be really cooking your batteries to create any discernible amount of hydrogen. In fact, you would have to have them at full boil for a while before you will gasify enough electrolyte to cause a combustible amount of hydrogen. With a smart charger, you should be gassing very, very limited amounts over time.
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