2025 PowerBoost Drawing Power from Trailer Battery

[Davexxxx]

If I didn't have a PB and all else was equal, I'd certainly use a DC to DC charger.

But with 600ahs and 1200W on the roof, coupled with the ease of PPOB, should I need it, don't see the need.

That said, I'd use a separate, much heavier ga. umbilical, rather than run through the 7 pin. Fer Sher.

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[Buyer2021]

But with 600ahs and 1200W on the roof, coupled with the ease of PPOB, should I need it, don't see the need.

I'm in the same boat, even without the PPOB.

Even with a bit more modest 400Ah / 800W on the roof, given my camping electrical use-habits, I've not had need to supplement my charging with help from the truck or shore / generator power, and my boondocking has not been constrained at all.

So, no DC/DC charger for me, though I recognize 'YMMV' for some folks.

It's amazing how many options we have today that didn't exist just a few years ago.
.....
The sheer lack of boondocking anxiety is liberating.

Ain't that the truth!

 

[Davexxxx]

It's amazing how many options we have today that didn't exist just a few years ago. I've been RVing for a while and so much has changed regarding keeping the lights on.

The Powerboost is like the safety net for almost any battery based strategy. No matter what strategy I take with batteries, solar, chargers........if I get in a 12V jam, I can just crank up PPOB and fill in the energy gap!

The sheer lack of boondocking anxiety is liberating.

Yep. Its a whole different ball game.

LFPs are better and much cheaper, in a wider selection of sizes and the same for solar.

Our last trip was 47 nights. Dry camping all but 2, much of it in Ntl. Forest, or BLM land.

Or even if you want to stay in campgrounds, you have a much wider, easier choice of vacancies and cheaper too.

Power is no longer an issue. Water and waste, are our only limiters now.

 

[Snakebitten]

Yep.
Water and tank use now require more scrutiny than keeping the ice cream from melting.

Fortunately, even a no-hookup campground will have bathrooms and showers. So long comfortable "boondocking" sessions are plentiful enough.

 

[tsigwing]

Why?

Because it feeds directly to the battery on my camper and it was easy to get to.

 

[P.S.N.]

...
Understood, but this is about charging when driving, not when parked / camping under trees. If you disconnect the charge wire within the seven-pin wiring block at the trailer, your solar will likely fully-replace the charge you would otherwise get from the truck when towing.

Buyer2021, thank you for your reply.

Note that I started this thread to talk about the PowerBoost drawing power from my trailer's LFP vs charging it via the seven-pin. I have learned that this should be expected because, if left to their own devices, connected batteries like to balance one another. The F150's batteries are probably at 12.6V-12.8V when charged while my LFP is at 13.6V-14.6V when charged. Since the LFP has a higher voltage, the truck's 12V system will pull power from the LFP in an attempt to equalize, unless the F150 has a device that can recognize what is happening and stop it, like a really smart battery isolator. I have learned that my 2025 PB does not have such a device, if one even exists, hence the flow of power from my travel trailer to my F150 vs the other way around.

I understand some on this forum do not believe this, but the physics makes sense to me and I have posted proof that it happens. I would love to see similar proof from others, using the same test procedures, to show that the opposite is happening to others so I/we can learn from it.

Question to all: Will allowing this small reverse flow of DC energy harm the PB's 12V system? Some popular RV techs say it will, but I don't understand how.
- Reference: https://www.facebook.com/share/r/1FxW1irgRk/

I know I can charge my trailer's LFP with my 7.2Kw PPOB, that is why I got it. I am trying to understand what is happening with the seven-pin and if it will cause any long-term problems with my PB as I tow down the road if I do nothing to stop this reverse flow.

 

[Snakebitten]

If an LFP battery equalizing with an AGM battery will harm a Powerboost 12V system, several of us are in big trouble!

Some of us have replaced our auxiliary AGM battery with an LFP Auxiliary battery for the soul purpose of them equalizing while the truck is parked or undriven.

It was pioneered by a mad scientist here on the forum, and the results were just too tempting for those of us who are anal about Ford's anemic battery charging strategy. (it leaving our trucks vulnerable to the Jeckyl/Hyde behavior of the truck if/when the voltage drops below some threshold)

So I believe you when you say that it's possible for your truck's AGM to suck electrons from your LFP if allowed.

 

[JEB]

Buyer2021, thank you for your reply.

Note that I started this thread to talk about the PowerBoost drawing power from my trailer's LFP vs charging it via the seven-pin. I have learned that this should be expected because, if left to their own devices, connected batteries like to balance one another. The F150's batteries are probably at 12.6V-12.8V when charged while my LFP is at 13.6V-14.6V when charged. Since the LFP has a higher voltage, the truck's 12V system will pull power from the LFP in an attempt to equalize, unless the F150 has a device that can recognize what is happening and stop it, like a really smart battery isolator. I have learned that my 2025 PB does not have such a device, if one even exists, hence the flow of power from my travel trailer to my F150 vs the other way around. I understand that some on this forum do not believe this, but the physics makes sense and I have posted proof that it happens.

Question to all: Will allowing this small reverse flow of DC energy harm the PB's 12V system? Some popular TV techs say it will, but I don't understand how.
- Reference: https://www.facebook.com/share/r/1FxW1irgRk/

I know I can charge my trailer's LFP with my 7.2Kw PPOB, that is why I got it. I am trying to understand what is happening with the seven-pin and if it will cause any long-term problems with my PB as I tow down the road if I do nothing to stop this reverse flow.

I doubt that you will have significant problems while driving down the road. While underway, you truck’s charging system will keep your AGMs at an above-resting voltage and any systems running on your trailer (like the refrigerator) will help keep your house batteries at a below-resting voltage reducing or eliminating the imbalance between your truck and trailer. If really concerned, turn your solar charge controller off when hooked up to your truck to further reduce the imbalance.

 

[Davexxxx]

Buyer2021, thank you for your reply.

Note that I started this thread to talk about the PowerBoost drawing power from my trailer's LFP vs charging it via the seven-pin. I have learned that this should be expected because, if left to their own devices, connected batteries like to balance one another. The F150's batteries are probably at 12.6V-12.8V when charged while my LFP is at 13.6V-14.6V when charged. Since the LFP has a higher voltage, the truck's 12V system will pull power from the LFP in an attempt to equalize, unless the F150 has a device that can recognize what is happening and stop it, like a really smart battery isolator. I have learned that my 2025 PB does not have such a device, if one even exists, hence the flow of power from my travel trailer to my F150 vs the other way around. I understand that some on this forum do not believe this, but the physics makes sense and I have posted proof that it happens.

Question to all: Will allowing this small reverse flow of DC energy harm the PB's 12V system? Some popular TV techs say it will, but I don't understand how.
- Reference: https://www.facebook.com/share/r/1FxW1irgRk/

I know I can charge my trailer's LFP with my 7.2Kw PPOB, that is why I got it. I am trying to understand what is happening with the seven-pin and if it will cause any long-term problems with my PB as I tow down the road if I do nothing to stop this reverse flow.

I certainly would have thought there'd be, or should be, a backflow diode.

I'll suggest an easy experiment.

Check the charge voltage recommended by your LFP's manufacturer and their stated resting voltage. Gonna guess you're in the lower to mid 14s for the former and high 13+ for the latter. Remember, the LFP BMS, if functioning properly, won't allow a charge beyond 100%

Then take a voltage reading at the truck batt, with the engine on. I did some testing on my truck on the fan speed 5 thing and found voltages at the truck battery ranging between 14.41 and 14.46.

Then run the same test hooked to the trailer.

 

[Davexxxx]

I certainly would have thought there'd be, or should be, a backflow diode.

I'll suggest an easy experiment.

Check the charge voltage recommended by your LFP's manufacturer and their stated resting voltage. Gonna guess you're in the lower to mid 14s for the former and high 13+ for the latter. Remember, the LFP BMS, if functioning properly, won't allow a charge beyond 100%

Then take a voltage reading at the truck batt, with the engine on. I did some testing on my truck on the fan speed 5 thing and found voltages at the truck battery ranging between 14.41 and 14.46.

Then run the same test hooked to the trailer.

Another test, would be to drain the LFPs. Pick a number, 60% SOC.

Then check batt V at the truck and the Victron monitor.

 

[P.S.N.]

I certainly would have thought there'd be, or should be, a backflow diode.

I'll suggest an easy experiment.

Check the charge voltage recommended by your LFP's manufacturer and their stated resting voltage. Gonna guess you're in the lower to mid 14s for the former and high 13+ for the latter. Remember, the LFP BMS, if functioning properly, won't allow a charge beyond 100%

Then take a voltage reading at the truck batt, with the engine on. I did some testing on my truck on the fan speed 5 thing and found voltages at the truck battery ranging between 14.41 and 14.46.

Then run the same test hooked to the trailer.

That is good to know about the F150's voltage under load.

My LFP can go as high as 14.6V for a full charge, but the manufacturer recommends no more than 14.4V for longevity. The manufacturer also recommends a float charge at 13.6V. Here is an example from my solar MPPT of the manufacturer's recommended charge settings.

 

[Davexxxx]

That is good to know about the F150's voltage under load.

My LFP can go as high as 14.6V for a full charge, but the manufacturer recommends no more than 14.4V for longevity. The manufacturer also recommends a float charge at 13.6V. Here is an example from my solar MPPT of the manufacturer's recommended charge settings.

Which Victron app does that come from?

It matters, because while their solar charge controllers and or Inverter chargers, can limit incoming power and timing that goes through them to the batts, I don't think the monitors can. The smart shunt maybe but I don't recall that feature when I set up the BMV 712. Its basically just a counter, not a gate.

But the LFP BMS is a gate. Unless yours are pretty old and from the bottom most tier anyway. Even the cheapest LFPs now have over charge protection, as well as other features.

Moving on ... If your truck puts out engine battery voltage similar to mine, since it is higher than absorption and float voltage, unless full and shut down by the LFP BMS, the direction should be to the camper. It should be to the camper anyway, if nothing else, than to power the running lights.

In truth, when I tested mine, I didn't bother to verify direction of flow. I was just measuring amps through the 7 pin, at various LFP states of charge. Started at around 5 at full as I recall, topping out at 8, with the LFPs down to 60%. The results made sense and confirmed no risk to the truck, so I didn't take it further. Something around 9K towing miles confirms that.

 

[P.S.N.]

Which Victron app does that come from?

It matters, because while their solar charge controllers and or Inverter chargers, can limit incoming power and timing that goes through them to the batts, I don't think the monitors can. The smart shunt maybe but I don't recall that feature when I set up the BMV 712. Its basically just a counter, not a gate.

But the LFP BMS is a gate. Unless yours are pretty old and from the bottom most tier anyway. Even the cheapest LFPs now have over charge protection, as well as other features.

Moving on ... If your truck puts out engine battery voltage similar to mine, since it is higher than absorption and float voltage, unless full and shut down by the LFP BMS, the direction should be to the camper. It should be to the camper anyway, if nothing else, than to power the running lights.

In truth, when I tested mine, I didn't bother to verify direction of flow. I was just measuring amps through the 7 pin, at various LFP states of charge. Started at around 5 at full as I recall, topping out at 8, with the LFPs down to 60%. The results made sense and confirmed no risk to the truck, so I didn't take it further. Something around 9K towing miles confirms that.

It is from a Victron SmartSolar 100/30 MPPT (https://www.victronenergy.com/solar-charge-controllers/smartsolar-100-30-100-50).

Your 2023 PB is slightly different than mine, given you have the belt divine starter/generator and my 2025 PB does not. I am concerned there is a difference in how the updated PB analyzes (if at all) and provides power to the charge wire in the seven-pin trailer connection for I absolutely saw a continuous draw from the trailer to the truck, even at 2,100 RPMs, as shown in my original post. What I have not measured is if this stays steady when the engine is under load for long periods for I did not take a measurement then (I was busy towing).

I am not concurned with my trailer's LFP for it has a very sophisticated BMS--it better be good for I paid a lot of money for it--I am mostly worried about my 2025 PB, yes I also do not want to drain my travel trailer battery for every amp counts when we are dry camping/boondocking. Yes, I can run my PPOB but that uses gas and I would prefer only using it when I need to, not because something is built wrong (if the latter, I want to fix it).

 

[Davexxxx]

I hear you but absent conflicting info from a trusted source, I'd lean toward trusting Snake's observation re that part. i.e. not involved in charging.

I agree that you need to find a definitive answer and correction, if OEM failure, or a workaround, if not. I'm no kind of Wizard but I know there are such things as directional diodes that either should have been in place, or can be put in place. And they aren't expensive.

It was one of the first wide spread improvements to solar panels. In ancient times, they could back feed to the sky at night.

 

[P.S.N.]

I hear you but absent conflicting info from a trusted source, I'd lean toward trusting Snake's observation re that part. i.e. not involved in charging.

I agree that you need to find a definitive answer and correction, if OEM failure, or a workaround, if not. I'm no kind of Wizard but I know there are such things as directional diodes that either should have been in place, or can be put in place. And they aren't expensive.

It was one of the first wide spread improvements to solar panels. In ancient times, they could back feed to the sky at night.

I had forgotten about Snakebitten's response on the starter/generator. Thank you for the reminder.

I am still stuck with a known and unwanted draw between my trailer's LiFePO4 and truck, which other forum members seam to deny that it happens with or without saying I'm wrong. So would you conclude that this is a trailer wiring problem more than a truck problem?

I like your "directional diode" idea. If I cannot find a proper fix for this, I may go down that road.

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