Battery relocation - floor penetration question

CharlieRN

I am considering moving the batteries on my T@B 320S BD from the exterior cargo box to the storage compartment under the right bench (photo below). There is enough room for both batteries (a pair of BB 100 Ah LFPs) to be located in a fore/aft configuration and I can also mount both my Renogy DC-DC charger and Victron Smart Shunt on the back wall, getting them out of the weather.

I would plan to leave the existing electrical connections in the cargo box, but also will rewire things a bit with a positive and negative bus in a waterproof enclosure. I will need to run the battery cables forward from the interior compartment which will entail making a penetration somewhere through the floor of the camper. Any suggestions on where and how to do this?

It looks like there is already a floor penetration in the adjacent rear compartment that houses the Elwell A/C unit (see photo). It would be great if it was possible to use it for the battery cables, but it looks like the guide tube is not large enough to handle two 8 AWG cables. I haven't yet removed the corrugated plastic shield on the underside of the camper to check things simply because it is held in place with a ton of fasteners. I assume that I will need to remove it in its entirety, but thought I'd ask before going through all of that tedious work.

A final question: Is there an alternative to what I suggested that does not involve going through the floor? Any and all suggestions greatly appreciated.

Right-side bench storage compartment

Rear bench storage compartment (existing penetration visible adjacent to wall, in front of duct hose)

Denny16

Depending on where your WACO power converter is, I would just wire the new battery location directly to the WACO, which is where the batteries in the front tub are connected.  This would shorten the battery cable run, allowing you to use No8 AWG cable.  You can get a Marine grade, two conductor cable from a Marine supply company, which will simply fishing the cable from your proposed new battery location to the WATC, keeping the wires above the floor running inside the bench/bunk units.
 Cheers 

CharlieRN

Denny16 said:

Depending on where your WACO power converter is, I would just wire the new battery location directly to the WACO, which is where the batteries in the front tub are connected.  This would shorten the battery cable run, allowing you to use No8 AWG cable.  You can get a Marine grade, two conductor cable from a Marine supply company, which will simply fishing the cable from your proposed new battery location to the WATC, keeping the wires above the floor running inside the bench/bunk units.
 Cheers 

Thanks and while I'd love to be able to do that, I don't think if will work for what I have in mind.

I should have emphasized in initial post that I am also installing a DC-DC charger. My understanding is that the 20 amp charger needs to connected more or less directly to the alternator/TV battery via heavy gauge cable. The table I looked at seems to indicate that 8 AWG will work. The run in the camper that I think I need is to get from the DC-DC charger to the cabling coming from the TV that is connected to the car's battery. The camper run will be wire-wrapped to the 7-pole harness and terminate in an Anderson connector to mate with that on TV.

Isn't the existing 12v wiring to the WACO fairly light gauge (12 or maybe even 14 AWG) so the charger would not get enough current if wired this way?

mgreen2

The factory puts them on the other side. 

CharlieRN

Apologies for both the long post and for the inadequate previous explanation of things.

The complicating factor in my install is the DC-DC charger and the fact that the existing wiring for the camper is in the cargo box, where the battery presently resides. While I can shoehorn the two BB LiFePO4 batteries in there, it's a tight fit. My cargo box has a large cutout in its rear and admits a fair amount of water. This means I need to also add some shielding to keep water away from both the DC-DC charger and the Smart Shunt .

With respect to the DC-DC charger, this is something BattleBorn recommends for their LiFePO4 batteries for a couple of reasons. As explained to me by the BB tech, lithium batteries can draw a lot of current, that could exceed the ability of the alternator on the TV to provide. If that happens, the alternator can be damaged. In practice, the 7-pole harness is usually not up to the task, and the resistance in the harness prevents the draw from damaging the alternator. While the alternator won't be damaged, it's also unlikely that the house LFP batteries will be fully charged. The DC-DC charger will both prevent the excessive current draw that could damage the alternator, while providing enough current and the proper charging profile to top up the house batteries (assuming you're driving long enough). Another reason I'd like the batteries inside is to insulate them from colder weather. The BMS on BB batteries is supposed to cut things off if the temperature gets to either extreme, but having them inside helps reduce the possibility that the BMS will need to do that

I've attached a crude drawing of what I think things should look like. I will need to pass four 8 AWG wires from the bench storage box out to the front of the camper. The easiest way to do that (I think) is run them through the floor under the storage box. All the existing connection terminations, including to the WFCO, are in the cargo box. My plan is to attach them to a bus that will also be attached to the house batteries.

I'm pretty new to this, and would appreciate any feedback.

SLJ

Did exactly what you're planning. Ran flexible conduit under the floor to up front to where the original battery was and ran 8 gauge wire through it and put all the original connections in a junction box. Put an in-line fuse at the batteries.
More info: https://solocanoes.com/camper.htm

AndreO

Hi @CharlieRN,

I am just in the process of completing such an update to my Tab400. Greater distances but the same process.

Hard to see in your diagram because I can't zoom in but it looks like you bypassed the Victron shunt with your dc-dc charger. If so the victron will not track charge added.

As far as cable size I would suggest to run your numbers based on dc-dc amp capacity. Try out this site for wire/fuse sizing. It provides lots if info and a clearly explained calculator.

 https://faroutride.com/wire-calc/

 If you'd like I could also send you my wiring diagram for comparison.

Good luck.

homerd

Mgreen2's photos very helpful, any wiring diagrams?

pthomas745

"lithium batteries can draw a lot of current, that could exceed the ability of the alternator on the TV to provide. If that happens, the alternator can be damaged"

This "exploding alternator" has approached internet legend quality.

Did Battleborn have any examples of this actually happening?  In what situations?  "Could draw a lot of current" in what situations? In what size of a battery bank?  With what size alternators?  Why can't their BMS control for this? 

Lithiums are 90 percent a straight drop in replacement.  It shouldn't be this hard (and this spendy) to add a lithium to your trailer. 

Rant complete!  I fully respect your mods here.

CharlieRN

I suspect that there have not been many controlled experiments to determine alternator damage @pthomas745, and as far as I can tell, there is not much in the way of actual field data available either. That said, it's not just Battle Born suggesting the use of DC-DC chargers to mitigate possible alternator damage. For example, Victron also has a video (found at about the 10 minute mark) that suggests the use of a charger. You would be correct to note that Victron is not exactly a disinterested party, so there's that negative.

As to the question of why Battle Born's BMS can't control for excess draw, that's a legitimate question but one I did not think to ask of their tech during my calls. The tech I spoke with stated however that alternator damage while possible, was not particularly likely because of wiring restriction in the harness. His suggestion, again as a not disinterested party (e. g., they sell Victron chargers), to use a DC-DC charger had to do more with the BMS's need for occasional charging to 100%. The tech pointed out that this can be achieved with an external charger as well however. I'll also point out that there is also no guarantee that it will occur even with a DC-DC charger, since that is also time dependent.

My impression overall is that a DC-DC charger falls in between the "nice-to-have" and "essential" categories. I'm convinced that as you wrote, the "'exploding alternator' approaches internet legend quality" and that the chance of damaging your alternator is relatively low. While installing a DC-DC charger is not an inexpensive proposition however, it is quite a bit less costly than replacing an alternator. The DC-DC charger also accommodates the house battery's charging profile, while as I understand it, the charging system of your TV follows a fixed, single voltage profile.

Again no expert, just someone repeating what is hopefully reasonably accurate info that others may find useful.

elbolillo

I can only speak to my recent experience on a 5300+ mile trip we took during March. I have two 100A BB LiFePo4 batteries installed in the front tub of my 2021 Tab 320S pulled by a 2021 Honda Pilot. Besides the roof-mounted solar, I also have a Victron MPPT 100/30 Solar Charge Controller to connect my Renogy 100W solar suitcase. During our trip around the SW USA, we always had the 12v fridge running. The lowest the batteries discharged was to 78%. With an abundance of sunshine, I was generally able to completely charge the batteries while camping and during travel, the roof solar was enough to provide sufficient charging. I have considered a DC-DC charger but have gotten conflicting info from BB, and at the end of the day, I haven't seen any evidence that my current setup is adversely affecting the alternator of my TV. Plus, adding the DC-DC charger is extra work I'm not willing to attempt at this time.

AndreO

If you want the dirty details search utube for:

"How to not blow up your Alternator when

charging Lithium."
Victron very clearly explain and demonstrate what can happen.

I should note that even with a dc-dc charger there are many variables to concider as it is likey no two installs have exactly the same setup. Dc-dc manufacture and model, Batteries (size, charge rating, voltage, etc.)  altinator capacities, distances from the TV to dc-dc charger then to batteries. Etc.

I found it took alot of reseach to figure things out. So it's likely going pro is the best choice for those who are not handy or don't want to invest the time.

pthomas745

That Victron Video is the entire source for all of this. Everyone references that video when they discuss the "issue".  I don't suppose YouTubers are in the habit of purposely frying alternators, but you might think someone could test and duplicate and show their work.  The video came out almost two years ago now. 

There are many comments on their methods over in Will Prowse's DIY Solar forums...not all of them complementary, most because of the assumptions made about the efficiency of alternators, battery state of charge...and on and on.

This is the type of thread you get in response when asking questions about this.  (Some of this is useful, but I can't really tell).  Does having a lead acid battery in the vehicle create the "resistance" that the lithiums seem to need?   How many people will try to recharge a large lithium battery bank that has been driven down close to "zero?"

https://diysolarforum.com/threads/charge-lifepo4-400ah-with-alternator-alone.26677/#post-317776

The good news is my vehicle has never successfully charged my battery ( and I stopped caring, but maybe someday).  So, I don't really have an issue.  But it is hard to suggest to a new battery owner who wants to buy a lithium battery (like everyone else) but gets hung up with "do I have to buy a new converter and new wiring and a new battery charging setup for my vehicle, too?"

I appreciate the conversation in this thread.  Always interesting!

PixandMsBee

SLJ said:

Did exactly what you're planning. Ran flexible conduit under the floor to up front to where the original battery was and ran 8 gauge wire through it and put all the original connections in a junction box. Put an in-line fuse at the batteries.
More info: https://solocanoes.com/camper.htm

I am in the process of doing this now. Would you please let me know how and where you went through the floor? Also, it appears that the wires from the tongue box will need to be looped under the frame, or did you have another solution?  Camper is a 2022 320_s Boondock.

Thanks!

CharlieRN

@PixandMsBee I posted a narrative and some photos of my installation on the forum a while back. You can access it via this link: https://tab-rv.vanillacommunity.com/discussion/15437/yet-another-lithium-battery-installation#latest

The penetration is adjacent to an existing factory penetration in the adjacent compartment with the Air 8 unit. I chose this because it was clear that there were no obstructions. As far as running the wiring to the tongue, I dropped the splash guard to do the run; it is over the frame members and exits at the front, near the "V" of the frame.

Hope this helps. Feel free to PM me if you need more info

SLJ

PixandMsBee said:

SLJ said:

Did exactly what you're planning. Ran flexible conduit under the floor to up front to where the original battery was and ran 8 gauge wire through it and put all the original connections in a junction box. Put an in-line fuse at the batteries.
More info: https://solocanoes.com/camper.htm

I am in the process of doing this now. Would you please let me know how and where you went through the floor? Also, it appears that the wires from the tongue box will need to be looped under the frame, or did you have another solution?  Camper is a 2022 320_s Boondock.

Thanks!

Ran the flex under the floor at the front left corner of the bench (you can just see it with a clamp around it in the photo). It came straight forward and out by the tongue underneath. (number 4 in picture below) and then up behind and into the front tub.