RV electrical system upgrade complete

[Davexxxx]

Found this thread, where 2 people who have Battleborn batteries noted no problems.

https://www.f150gen14.com/forum/threads/towing-rv-with-lithium-battery-with-my-pb.10669/#post-216319

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[towpro]

Do I even need to remove the fuse for pin 7 charging? with the thin wire plus distance, even with the alternator charging how much will it really draw?

 

[Davexxxx]

Do I even need to remove the fuse for pin 7 charging? with the thin wire plus distance, even with the alternator charging how much will it really draw?

That is the confusing part for me.

We normally talk about electricity as a "draw" thing. Thats why the concern with LiFePO4. They can draw, a lot, quickly, potentially beyond the limits of the wire and some alternators.

But when we talk about power sources, like a battery bank, alternator, or converter charger, that seems more like a "push" thing.

And then there is the Truck's BMS, which counts how much goes out and controls how much goes into the truck's batt.

I have something I have to do first but later today, I'm gonna take a measurement at the 7 pin, with the truck off, then on.

Then, I have a known good but somewhat discharged 12V LA (the original from the trailer), hook up jumpers and measure the flow.

Then, I have a known bad L&G 12V LA and try the same thing and see if the numbers change and if so, to how much.

 

[Buyer2021]

Does the brake controller's signal, use the power line from the 7 pin?

No:

Note that the brake lights are independent of the brakes themselves. In certain failure modes it is possible for brake lights to work without the brakes themselves working, or vice-versa.

IF your set up is like mine, the house batteries will power the brakes. But I don't know if thats a great idea.

Perhaps you and others reading understand this, but to be sure ....

The house battery plays a role in activating the brakes only when a 'trailer breakaway' occurs; that is, in the worst-case situation when the trailer separates from the tow vehicle and the pull-pin in the breakaway switch on the tongue of the trailer is pulled-out by the lanyard attached to the tow vehicle.

At all other times (e.g. normal towing operation) all of the power required to activate the trailer brakes is via the brake controller circuits indicated in the diagram above and the house battery has no role in that.

This emergency breakaway system can (and should) be tested by pulling the breakaway switch pin completely out when the trailer umbilical cord is not plugged-in to the tow vehicle socket, and listening carefully at the trailer wheels for the 'hummm' of the activated brake magnets. Replace the breakaway switch pull-pin and confirm the brake magnets are silent.

This test is harmless and should be done on occasion to confirm your emergency breakaway system is functional. Just don't forget to re-insert the breakaway switch pull-pin promptly after completing the test.

 

[Buyer2021]

Do I even need to remove the fuse for pin 7 charging?

IF, for whatever reason, you do not want to have battery charging from your truck to a particular trailer, I suggest you do not alter anything on your truck; instead, break that connection on the trailer so your truck remains fully functional for all other purposes / trailers. This avoids any possibility of a fault being detected by the truck or other unintended consequences.

Most trailers have some sort of junction box where the umbilical cord wires terminate and transition to the trailer wiring. Here is mine shown with the 12V charging feed from the truck intact, and then disconnected:

Note that only the 12V feed from the umbilical cord is removed from the applicable stud in the junction box; all other wires on that stud remain. In this case, the house battery is connected to the breakaway switch circuit via that stud (for emergency brake application as described in the previous post) and remains functional, as do all other trailer functions.

In my case (YMMV) I choose to not have charging from my truck to my RV having an LiFePO4 battery; however I do need charging from the truck for my utility trailer with a small LA battery for the breakaway system. This approach keeps my truck 'plug-and-play' compatible with all of my trailers.

Just for your consideration and only if one wants to disable charging from their truck for a particular trailer.

 

[Davexxxx]

Truck off
Truck battery = 12.58V
7 pin = 0
Truck on
Truck battery = 14.94V
7 pin = 14.94V

It did not like being wired directly from the 7 pin to a known good by somewhat discharged LA batt. Gave a healthy spark and I decided not to push it.

Turned solar off, opened Victron app. showing coach batts at 95% charge, at 13.30V and normal parasitic loads of -0.33A and -4W.

Plugged in the truck and turned it on.

Same app shows 13.32V
7.28A
97W

= Net charging capacity at the 7 pin of 7.62A

So, higher than I'd seen some claim but nowhere near approaching a problematic level.

I'll discharge the house batts and try it again.

If it even hints at looking ugly, I'll shut it off.

 

[HammaMan]

Truck off
Truck battery = 12.58V
7 pin = 0
Truck on
Truck battery = 14.94V
7 pin = 14.94V

It did not like being wired directly from the 7 pin to a known good by somewhat discharged LA batt. Gave a healthy spark and I decided not to push it.

Turned solar off, opened Victron app. showing coach batts at 95% charge, at 13.30V and normal parasitic loads of -0.33A and -4W.

Plugged in the truck and turned it on.

Same app shows 13.32V
7.28A
97W

= Net charging capacity at the 7 pin of 7.62A

So, higher than I'd seen some claim but nowhere near approaching a problematic level.

I'll discharge the house batts and try it again.

If it even hints at looking ugly, I'll shut it off.

Great example of why a DC-DC specific charger is needed IF you wanted to rely on the vehicles 12v system -- with the PB you don't need to, but for use in another tow vehicle AND boondocking you may desire such. Personally I'll chase little things like if for nothing else than to make it more complicated. The size of your batteries plus the solar really makes that ~360 watts or so you could get from the 7 pin's plug laughable as again it's only when being towed that you're able to get it.

If you deplete the LFP down to 10v or so (highly unlikely, everything should shut down at 11v), the amperage could jump. Those batts can discharge down to 10v. Not sure of the wiring size and associated droop, but the low resistance of the LFP has them eating as much as you throw at them. The part that makes it not a big deal is the wire length. If you have 15 volts at 20 feet of 14ga, a depleted LFP batt would possibly blow the fuse. However if the LFP has 11 volts measured at it, there's too much voltage drop for the current to exceed the fuse. Now your bank size is such that it can stay down at that low voltage for a while even though the LFP has less than 10% of its capacity below 12v -- a 600ah bank could draw that for an hour and wires heat up. At the same time just plugging in the victron for 30 minutes would have it well outside of that dip.

This is just a generic voltage / state of charge for LFP. As you can see at 12v (3v x 4 cells) the battery is nearly completely drained (resting voltage, not loaded). Ignore everything else, look at the big group of curves.

Furthermore, if you're not using the TT, don't keep the batts at such a high SOC. LFP lasts forever even under full daily charge cycles, but by not abusing them, 20-30 years+ of life is easy to achieve.

 

[Davexxxx]

As of when I did the initial parameter setting the other day, I set the cut off for the inverter at 20% SOC.

That would assure plenty of reserve for DC circuits and a reminder to plug it in once in a while.

Its out there running the air conditioner off the batts right now. App showed 5 something hours left at that load.

It could use a vacuuming from all the work I've done it it lately too. That ought to burn some ah.

I'll take them below 50% and see how it goes.

 

[HammaMan]

As of when I did the initial parameter setting the other day, I set the cut off for the inverter at 20% SOC.

That would assure plenty of reserve for DC circuits and a reminder to plug it in once in a while.

Its out there running the air conditioner off the batts right now. App showed 5 something hours left at that load.

It could use a vacuuming from all the work I've done it it lately too. That ought to burn some ah.

I'll take them below 50% and see how it goes.

If you haven't seen my posts about the 30ah LFP aux batt in my truck, here it is (charting). This is showing the voltage of my PB's 12v bus. You can extrapolate where the LFP's SOC is against the voltage. Most of the time there's not more than 6-9ah missing (when you see it get into the 12.75v range despite being parked most of the time). This basically keeps the under-hood AGM at 100% continuously. Posting charts here for easy reference -- not trying to derail the thread. Even with the fan 5 trick my highest running voltage quickly drops to around 14.2v. If fan 5 isn't used, the truck reverts to eating the 12v batts as the BMS doesn't want 100% SOC on the batts. Roughly 10 weeks. The bumps are ~15 minute runs across town sans the 1/4 mile testing. The little random dips are fordpass polling the truck.

The event around 3/17 was 15 minutes of unloading the truck with exterior+interior lighting on. I always remote start sans recently run. That's where you can see the truck eating the batts since the key isn't in and fan 5 isn't on.

https://www.f150gen14.com/forum/threads/testing-an-aux-batt-solution.17547/page-2#post-434670

 

[Davexxxx]

Solar off, ran the AC all afternoon plus vacuumed, batts still at 57%

Hooked it back to up the truck, yielded an 8A draw from the 7 pin.

Doesn't scare me.

The fridge is running now. I'll check again in the morn but unless things materially change, I don't see any reason to disconnect anything, or add new parts.

Run it like it came.

 

[Davexxxx]

Ran the fridge overnight without pre cooling. That took the batts down to 46%.

Plugged in the trailer harness. Net amp draw from the LiFePO4s is 8.45.

IFs thats a 30 amp circuit on the truck. I'm not seeing anything to be worried about and a potential 8 amps, is too much to throw away IMO.

 

[Davexxxx]

Side benefit of moving the batts inside., is there is now room for a trailer tongue box where the original battery was.

Houses the sewer hoses and fittings, black tank flush hose, gloves and hand cleaner, with plenty of room for the wheel chocks and jack pad for while under way.

I will have to either modify the existing hard tank cover, or go with a soft one but I like the trade off, a lot.

 

[towpro]

nice box, mind showing where I can get one?

 

[Davexxxx]

Highly recommend. Surprised to the upside.

https://www.amazon.com/EASYBERG-Aluminum-Trailer-Flatbed-Organizer/dp/B0CJR84VK5/ref=sr_1_7?

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