Please Review and Comment on this Newbie's Design!

EricR

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Joined
Aug 8, 2021
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36
Hi All!

Please review and comment on this second revision of my first ever design. Greatly appreciated!

Thanks to @Short_Shot, @eXodus , @Zwy , and @HRTKD for valuable feedback on the first revision

Background:

We have a Lance 2185 travel trailer that I want to upgrade from FLA to LFP.

Initially I was going to do a full solar plus hybrid inverter/charger build for our trailer. Then we bought a 2021 F150 Powerboost hybrid with the 7.2kw Pro Power on Board feature that can provide 120V 30A service for the trailer wherever we go! In a completely separate project I am running the 120V 30A from truck to the trailer such that it can be used while we are towing. 😲 Thus, the refrigerator can run on AC (vs propane) and our batteries can be charging - all while going down the road.

Note: When parked, the truck uses the hybrid battery to drive the Pro Power inverter most of the time. The engine runs for about 2 minutes to recharge the hybrid battery as needed. We no longer need the noisy portable generator.

Goals:
  • Keep things safe
  • Keep things simple and easy to install
  • Move the battery position to a closet at the back of the trailer (the soon to be gone FLAs are outside on the trailer tongue)
  • Allow use of 1 or 2 portable solar panels
Already Purchased:
The Idea:

For the times we are at an RV part we will just plug into park power. However most of the time we dry camp/boondock and on on 12V. In this case our batteries should be charged (using 120V from the truck) upon arrival. If after few days the batteries need a charge, or we want to run the air conditioner, microwave or blow dryer, we will simply connect to the truck. So you will notice there is no inverter in the design.

Also, if we are boondocking at a site for several days and going of hiking/exploring during the daytime we can set up the portable panel to recover some power while are out and about. At some point I may mount panels on the trailer roof, but for now I'll just keep it simple.

I've not yet diagramed for PV input. I am hoping for more feedback before I go any deeper into this.

Other:

Using the Energy Audit spreadsheet I have determined a rainy-stuck-in-the-trailer-all-day scenario would come in at 104 Amp Hours (DC). If I'm thinking correctly, that means we should be able to go two days (without solar or running the truck). Right? Also, seeing 104 Ah would be the maximum demand (remember, no inverter) how should I size the primary fuse that belongs within 7" of the battery bank?

Note the distance from the existing AC & DC panel at mid-trailer back to the rear closet where the LFP batteries will be is going to be 10-12 FT (depending on how the exact wire routing works out). About 3 FT of that will be running through a channel right next to existing 120V 10/2 Romex. I'm thinking 4 AWG for the run from the panel back to the batteries. Does that seem OK? Also, can I use this same 4 AWG wire for the battery & charger connections within the rear closet?

Leaning strongly towards the KISAE AC1260 charger - it seems good, and I can exchange the KISAE DMT1250 DC-DC I shouldn't have bought. I looked a several Victrons, yet it seems their under $750 AC powered 12V DC chargers max out at 30 Amps.

Also strongly leaning towards the Victron BMV-712.

Feedback, thoughts and help regarding the diagram, equipment, and safety would really be appreciated (especially wire sizing, fuses, breakers, etc.) Please spare me from bonehead mistakes! Any thoughts or feedback you have on the overall project would also be appreciated. Please let me know if you think it's just a bad approach, or I'm making things harder than needed!

Initial Diagram (NOT drawn to scale):

Trailer_Diagram_3.jpg
Thanks for the help!

-Eric
 

Short_Shot

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Fuses should be sized to protect the cable its attached to.

Cables should be sized by the maximum possible current, not your average usage.

Your 60a charger should have a fuse on it that's larger than 60a by at least 50% in my book, since that charger alone will pop it if the fuse is equal to its rating.

I'm still kind of confused on how you plan to disconnect the converters charger but also still use it. I assume you still want to use the 12v and 120v circuits it's wired into.

Did you figure out how to actually disconnect the charger inside the unit from its AC connection?
 

EricR

New Member
Joined
Aug 8, 2021
Messages
36
Charger Fuse Thinking
The user manual for the 60A charger calls for an 80A fuse. This seems in line with my calculation (if I'm applying the formula correctly): 60A x 1.25 = 75A. The closest ANL fuse I found was 80A, so that is what I have used in the diagram above.

DC Panel Fuse Thinking
The from my work using the Energy Audit Spreadsheet my maximum of all DC loads is 575W / 48A. 48A x 1.25 = 60A. Thus, the 60A fuse to the DC fuse panel.

Battery Bank Fuse Confusion/Thinking
Unlike many designs on this forum, mine does not include an inverter. Without a really large DC load from an inverter and attending wires to protect I'm not sure how to size the main fuse at the battery bank. The max load will be 48A. The charger will be pushing up to 60A. So in my design the charge current is greater than the discharge. The UT1300 batteries specs are 105Ah 1344Wh 150A, and so 2 of them would be 300A.

So, should the main fuse at the battery bank be:
  • 80A based on the max charge current (60 x 1.25 = 80)
  • 350A (or 400A) based on the capacity of the battery bank (300 x 1.25 = 375)
  • Or, neither of the above. :(
I'm thinking 80A (hopefully I'm understanding this correctly).

Thanks!

-Eric
 

EricR

New Member
Joined
Aug 8, 2021
Messages
36
Your 60a charger should have a fuse on it that's larger than 60a by at least 50% in my book, since that charger alone will pop it if the fuse is equal to its rating.
Most everything I have been reading is to add a 25% factor. Is there a specific reason you are recommending 50%?
 

EricR

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Joined
Aug 8, 2021
Messages
36
I'm still kind of confused on how you plan to disconnect the converters charger but also still use it. I assume you still want to use the 12v and 120v circuits it's wired into.

Did you figure out how to actually disconnect the charger inside the unit from its AC connection?
Yes!

The WFCO 8900 series is made up of 3 distinct parts: AC breaker panel, DC fuse panel, and a 120V to 12V converter. The converter portion is actually a user replicable part - installing a new one is quite straightforward.

I will just disconnect the converter portion.

Here is a picture I found on the net where they have removed the converter portion of their WFCO 8900 unit and put an invert in it's place (the silver unit at the bottom). They are still using both the WFCO 8900's AC breaker panel (on the left) & DC fuse panel (on the right).

WFCO_8900_with_Inverter.jpg

Regards,

-Eric
 

EricR

New Member
Joined
Aug 8, 2021
Messages
36
Also, for the 10-12 foot run (from the DC panel at mid-trailer to the rear closet where the 2 batteries will be) I thinking 4 AWG wire. I've checked a few different wire gauge charts/calculators (Blue Sea, Wire Barn, West Marine, etc.) and with a 3% voltage drop the 4 AWG should be good up to 25 feet. That should cover the 12 feet round-trip with a 1 foot margin.

Does this seem correct as well?

Thanks!

-Eric
 
Last edited:

Short_Shot

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Messages
1,812
Most everything I have been reading is to add a 25% factor. Is there a specific reason you are recommending 50%?
Simply because I don't trust hardware to output exactly its rating 100% of the time. Little spikes and whatnot will still be there.

But mostly because your wire can handle a lot more and the cost of a 90 or 100amp fuse is virtually identical to that of an 80 amp one so why not just give yourself that extra margin?

No sense in cutting it that close when you don't need to.

It'll also allow a but of extra capacity for future modifications if you already have the stuff there to handle it.
 
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