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Nice setup @Davexxxx (y)

I note that the Victron Multiplus installation instructions make reference to the amp rating of the fuse between the battery and the Multiplus, but are silent as to type.

For whatever reason the installation instructions for my Xantrex Freedom XC 2000 Inverter/Charger specifies the use of a Class T fuse in that location, so that's what I'm using in a BlueSea holder.
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In my small 5th wheel I'm running a BestGo 400Ah / 5.12kW LifePO4 battery with a PV array of 800W nominal rating (four Rich Solar 200W @ 37.6Vmp) wired in parallel through a Victron Smart Solar MPPT 150/60 -TR Charge Controller. I've disconnected the 12V battery charging line from my truck (3.5EB) in the trailer so have no DC-DC charger; I find the solar keeps the battery charged just fine with my use habits (YMMV).

This setup meets all of my electrical demands when boondocking for an unlimited duration, and like you, I can run my Fujitsu 12kBTU Mini-Split air conditioner for several hours+ daily to cool things off when desired. That's a variable-speed inverter compressor unit which has a low starting load and pulls very few amps once the trailer is quickly cooled-down.
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HammaMan

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PB has 12v power to spare. I'd tap that batt charging power line from the 7 pin at 30 amps to make sure it's full on the way out if boondocking (requires DC/DC upconverter)(120v line to it can also be used during tow for a higher charge rate during travel if needed). Otherwise only start the truck as needed (no need to run overnight with stored power). Take into account the long charge time otherwise. You're limited to 120a aka 5 hours if depleted.
 
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I've disconnected the 12V battery charging line from my truck (3.5EB) in the trailer so have no DC-DC charger; I find the solar keeps the battery charged just fine with my use habits (YMMV).
I haven't gotten that far yet but need to do some testing soon.

There is not consensus about this. Some say that Lithum batteries, being able to take such a high charge, will waste an alternator and choose to disconnect the power line in the trailer harness.

Others say, that tiny little wire can't overload anything and is fused in any event.

But as we discussed last eve. electricity will go where it can, sometimes a lot at a time and it won't care how inconvenient we find it. :D

I was gonna set up the original flooded LA coach batt with jumpers to the 7 pin on the trailer and throw an amp clamp on it. See what happens.

Other than trial by fire, I don't really know of a different way to test it.
 

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I haven't gotten that far yet but need to do some testing soon.
.......

Other than trial by fire, I don't really know of a different way to test it.
Understood, but of course your PB is a different animal from my 3.5EB.

Given your PB's on board 7.2kW of AC power, it strikes me that configuring a way to connect that to your trailer shore power input while underway is the way to go (?). Disconnect the battery charge DC feed completely as I have done, let your Multiplus running on 'shore power' while underway handle all of your charging needs (assisted by your solar array). That way you avoid any and all possible concerns and/or limitations related to DC charging from the vehicle, no?

Aside - I certianly like the idea of the PB with 7.2kW, and would maximize all it can provide. The main reason I didn't go with a PB is that it isn't offered with a SuperCab+6.5ft box, and that cab/box configuration is an overriding priority for me.
 
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Understood, but of course your PB is a different animal from my 3.5EB.

Given your PB's on board 7.2kW of AC power, it strikes me that configuring a way to connect that to your trailer shore power input while underway is the way to go (?). Disconnect the battery charge DC feed completely as I have done, let your Multiplus running on 'shore power' while underway handle all of your charging needs (assisted by your solar array). That way you avoid any and all possible concerns and/or limitations related to DC charging from the vehicle, no?

Aside - I certianly like the idea of the PB with 7.2kW, and would maximize all it can provide. The main reason I didn't go with a PB is that it isn't offered with a SuperCab+6.5ft box, and that cab/box configuration is an overriding priority for me.
I know a few here have done that (use the 7.2, while underway).

1) I don't think I'll come near to needing it.

2) Would rather spend that time, money and weight, on more panels. (200w existing, going to 1,200w)

At the same time, I don't "need" the charge available via the 7 pin but throwing away a capability, shouldn't be done for no reason.

I'm a parts changer, not an electrical theorist. I've studied this stuff for a couple yrs. but built on the work of others. Enough that I can read the wire and fuse charts and calculators but not enough to build them from scratch on my own.

So, I appreciate Hammerman's (or anyone's) constructive criticism but need to at least try to understand it, rather than blindly follow it.

I nosed around enough last night, to be convinced that I should have used a class T at that location. I don't think I'm in disaster mode but it is a change I should probably make. It appears that Dakota Energy is attacking the problem, by using terminal fuses at each battery but I'm not sure they are enough for the worst case of a simultaneous batt bank short.

I hate having this brand new ANL fuse and holder just be wasted but the easiest solution would be to just replace it with Class T.

Back to the 7 pin charging. I've seen the vids where alternators are wasted by lithium batts and need special regulators to prevent it. I'm obviously comfortable in altering a new TT but however robust the charging system on a PB is, it is finicky and there is no chance, I'm altering the systems on the truck. Certainly not while under full warranty.

So, I'm back to, "No problem, don't sweat it" or, "Beyond this point, be Dragons."
 

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Powering down the road is as simple as connecting up a 12ga extension cord. Just reduce the incoming max amperage setting on the victron. Connecting to the 7 pin's power pin would require a DC/DC voltage booster. Without the fan 5 trick in the PB, the voltage won't be there, and if it was, the wire size combined with its length results in a useless amount of current being present. Without the fan 5 trick, your trailer would likely be sending power into the truck as it's got a higher voltage than what the PB likes to run at. (I have a LFP in place of my aux batt, trust me, the truck is happy to consume them instead of generating its own 12v power)
 
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On a motorized RV (or boat), it seems to be a real problem, related to wire size.

Specifically for towables though, through the 7 pin, probably not.

Battle born says don't sweat it.



Rv guy, shows why its not an issue and as Hammerman figures, the lithiums will likely send power to the truck, rather than the other way around (trucks BMS safeguards this?).



Boat guy, shows why with on board alternators, its a huge problem and why but notes that having lead in the string, as we would in our trucks, eases the problem.



So, thinking this through, Ford has the system gimped anyway and this gimping, is controlled by the trucks BMS. Its only gonna send as much as the trucks BMS allows, based on the truck's battery condition.

The 7 pin is powered by the truck's battery, so any draw goes through the lead first and is again, controlled by the truck's gimped BMS.

LI charge parameters are 14.2-14.6V, at a max rate of 200A (x 2 ?), so they can take it if needed but the Trucks BMS is never going to see that directly, taking it's readings from the AGM in the truck.

So, no issues. Have I got that right?
 

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Connecting to the 12v system is pretty much useless w/ the PB and LFPs w/out a boost converter. Just not enough voltage to do anything otherwise. The likely outcome would be the trailer sending power back to the truck. The PB isn't like a traditional alternator vehicle, even then today those still will reduce voltage when desired SOC is achieved.

Not sure if it's really worth it given you have 120v on-hand continuously. If you don't want to run a cord to the victron and reduce its intake amperage, you could use a standalone LFP batt charger powered by extension cord. I just don't see any real benefit here though given you're going to have sufficient solar and seem to plug-in at campgrounds.
 
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Connecting to the 12v system is pretty much useless w/ the PB and LFPs w/out a boost converter. Just not enough voltage to do anything otherwise. The likely outcome would be the trailer sending power back to the truck. The PB isn't like a traditional alternator vehicle, even then today those still will reduce voltage when desired SOC is achieved.

Not sure if it's really worth it given you have 120v on-hand continuously. If you don't want to run a cord to the victron and reduce its intake amperage, you could use a standalone LFP batt charger powered by extension cord. I just don't see any real benefit here though given you're going to have sufficient solar and seem to plug-in at campgrounds.
This part of the discussion isn't about getting more power to the coach batts. I'm gonna have plenty. This part is about determining whether or not I need to safeguard the truck from the coach batts. while plugged into the 7 pin.
 

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This part of the discussion isn't about getting more power to the coach batts. I'm gonna have plenty. This part is about determining whether or not I need to safeguard the truck from the coach batts. while plugged into the 7 pin.
If it's setup currently to tap the 7 pin's power, I'd isolate it under the bed at your batt bank if possible. Does your trailer have a dedicated break-away battery for the brakes? If so let the 7 pin power it.
 
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Without the fan 5 trick, your trailer would likely be sending power into the truck as it's got a higher voltage than what the PB likes to run at. (I have a LFP in place of my aux batt, trust me, the truck is happy to consume them instead of generating its own 12v power)
Rv guy, shows why its not an issue and as Hammerman figures, the lithiums will likely send power to the truck, rather than the other way around (trucks BMS safeguards this?).
If intent on DC charging from a vehicle, this is where the Victron Orion-Tr Smart DC-DC chargers (distinct from Victron Orion-Tr DC-DC converters**) comes into beneficial play.

The referenced line of Victron chargers absolutely prevents current-flow from the trailer to the vehicle no matter the relative state of each; it's an absolute 1-way gate (acts a mega-diode, if you will, but on a much more robust electronic principal).

The referenced line of Victron chargers also act as a voltage boost device. That is, the volts available from the vehicle are boosted to volts useful to charging an LiFePO4 storage bank (and this is user configurable). For example, if you want to charge your LiFePO4 bank up to 14.x volts, the Smart DC-DC Charger can do that even when the volts out of the vehicle are lower for whatever reason.

One nice thing about all of this given you're already invested in many Victron components - all is managed via the Victron Connect App those devices already use.

** I mention the similarly named Victron Orion-Tr DC-DC converters because they are slightly lower-price, so might come to one's eye in shopping. Note the converters do not offer similar advantages for your interest - they serve as buck/boost converters but lack the sophisticated multi-stage charging algorithm capability you would want for your purpose. They're great for constant-voltage power supply and power-regulation applications (the latter being how I use the Victron converters in my RV).

EDIT - sorry, I see @HammaMan has covered most of this.
 

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i am also up to the point of needing to decide which way to go on this DC DC charge line in my 7 pin connector. I have 140Ah lithium in the RV (for starters) , which is charged by 400w solar (which will grow). We used to dry camp with 200ah AGM and 300w solar with no problems, but new rig has 12V refrigerator.

I realize the Lithium systems run higher voltage, and my RV could end up charging my truck. I am thinking of just pulling the fuse for the 7 pin power wire and deal with the cost of a CD to CD charger later if I need it. All my towing is in daytime so Solar will charge. and if I have to I could tap into my power boost output to charge using internal Lithium charger if needed.

Also is there a reason my Lithium can't power my break away switch?
 
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If it's setup currently to tap the 7 pin's power, I'd isolate it under the bed at your batt bank if possible. Does your trailer have a dedicated break-away battery for the brakes? If so let the 7 pin power it.
No dedicated battery for the brakes. The coach batteries (now LiFePO4) via the Lynx, connect to the existing copper buss bar, which is connected to several self re-setting circuit breakers, under the front of the trailer, inside the underbelly area. The 7 pin, connects to those.

Regarding wiring,, at that location, its still essentially the stock configuration. The stock bat was on the tongue, wired to the same location. The ground to the frame nearby and the + feeding the buss bar. Removed it and it's house connection cables and ran new cables from the Lynx to the buss and ground and rerouted the existing solar wires that went to the stock batt, to the new solar disconnect in the equipment area.

I think I could just disconnect the 7 pin power wire at that buss / breaker set but the PB computer might error out on that. ???

In any case, I don't want to disconnect anything without need and I really don't want to add any electrical parts to the truck.
 

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The truck shouldn't care about the B+ missing. The brakes are not related to it. It's literally a B+ charging wire to provide power to the trailer's batts if it contains one. Isolate / label the wire and you're good to go.
 
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i am also up to the point of needing to decide which way to go on this DC DC charge line in my 7 pin connector. I have 140Ah lithium in the RV (for starters) , which is charged by 400w solar (which will grow). We used to dry camp with 200ah AGM and 300w solar with no problems, but new rig has 12V refrigerator.

I realize the Lithium systems run higher voltage, and my RV could end up charging my truck. I am thinking of just pulling the fuse for the 7 pin power wire and deal with the cost of a CD to CD charger later if I need it. All my towing is in daytime so Solar will charge. and if I have to I could tap into my power boost output to charge using internal Lithium charger if needed.

Also is there a reason my Lithium can't power my break away switch?
IF your set up is like mine, the house batteries will power the brakes. But I don't know if thats a great idea.

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

At the moment, I'm much more nervous about installing a DC-DC charger (on a PB) than leaving things as they are, plugging in as normal and checking for problems.

Both Victron and Epoch batteries, have apps, where I can get near enough to real time data of what is happening. This can be double checked, with an amp clamp under the truck, on the 7 pin hot line.

With the solar disconnect in the off position, I can measure how much is coming into, or out of the batts through the 7 pin.

The batteries are currently around 96%, so if anything looks scary, if probably won't get better with a lower SOC.

If everything is copacetic, I'll more deeply discharge the batts and try again.

I need a baseline though. I've read the 7 pin normally only delivers a couple amps. I'd like to nail that down, to be sure.
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