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**howson** · 02-19-2022, 10:32 AM

Originally posted by AlexPeterson View Post

The truck has to "see" the trailer's batteries "through" the Renogy charger.

First--noted that was your first post so welcome to Grand Design's (technical) Owners' Forum. Since you've got your signature line figured out I assume you've already seen and read the Welcome Letter (thank you!).

For your question: I do not have an F-150 and my 40A Renogy is configured differently, but I'd expect that once the D+ signal is applied to the Renogy the truck should "see" the trailer battery and provide the charge power.

My '17 SuperDuty also has conditions that must be met before power is applied through the 7-pin charge wire. For example, if the driver's door is open there's no power. Once the door is closed, power is applied. I'm guessing "seeing" the trailer battery will be similar, thus the need to apply the D+ signal. (I use the trailer's running lights as the source for the D+ so I can control when the Renogy is working.)

Guest is our resident Renogy 20A guru but he has a GM (I'll restrain myself from the obvious comment I could make!) so his truck might be a bit different. Jim will be along in due time with an input.

Howard

**Guest** · 02-19-2022, 12:01 PM

Originally posted by howson View Post

First--noted that was your first post so welcome to Grand Design's (technical) Owners' Forum. Since you've got your signature line figured out I assume you've already seen and read the Welcome Letter (thank you!).

For your question: I do not have an F-150 and my 40A Renogy is configured differently, but I'd expect that once the D+ signal is applied to the Renogy the truck should "see" the trailer battery and provide the charge power.

My '17 SuperDuty also has conditions that must be met before power is applied through the 7-pin charge wire. For example, if the driver's door is open there's no power. Once the door is closed, power is applied. I'm guessing "seeing" the trailer battery will be similar, thus the need to apply the D+ signal. (I use the trailer's running lights as the source for the D+ so I can control when the Renogy is working.)

Guest is our resident Renogy 20A guru but he has a GM (I'll restrain myself from the obvious comment I could make!) so his truck might be a bit different. Jim will be along in due time with an input.

Howard

LOL. Thank you Howard.

Yes the Ford is different where they use a relay where Ram and GM has not used a relay so on the later two applications, the 7 way should be unplugged once stopped for an extended period. However, things can change since newer trucks incorporate trailer security systems. While all these trucks are underway, all connections between the trailer and TV are the same. Neg to Neg and Pos to Pos.

No truck controls the 7 way circuit to varying load which is why most are unhappy with the capability of charging through the 7 way plug. Voltage can vary based on the state of the TV battery and GM will raise overall voltage if the tow haul switch is active. Where the difference comes in like in your 40amp DCDC with dedicated heavy cable is the Renogy is pulling power from the TV battery (as much as 60 amps in your case) and is pushing power to the trailer battery bank. So your alternator will see this demand on the TV battery and will respond.

I've ran the 20 amp Renogy through my 7 way where I was privy to the drawings so caution needs to be conveyed where changes to trucks can be made all the time. So the safe bet for those that want a dedicated LiFeP04 charge profile could do the following without worry in using the 7 way for power. Use the 20amp Renogy model and jumper the LC side to limit the output to 10 amps which will result in no more than a 15 amp draw on the TV circuit. I would be surprised if there is a 7 way circuit out there that cannot handle 15 amps.

I would test the Renogy outside the trailer and connected between the truck and trailer. I did this check to be certain how it would respond and once satisfied, installed it in the rig. With some logic on the F150 that may interfere with the Renogy, the relay may need to be bypassed. Check with your dealer if this is necessary and possible.

Jim

**AlexPeterson** · 02-19-2022, 01:34 PM

Howard, thanks for the welcome! Jim, thanks for the thoughts!

Great idea to test the DC-DC charger externally first. Who knows how the Ford will control that circuit - I suspect the Ford dealer's guys will have no idea. The manual does indicate a 30amp fuse for the circuit, so we'll see how it does. These newer vehicles are getting too smart for their own good... The battery(s) do have Bluetooth, so I can see what sort of current the TV is putting into them.

Alex

**Guest** · 02-19-2022, 03:39 PM

Originally posted by AlexPeterson View Post

Howard, thanks for the welcome! Jim, thanks for the thoughts!

Great idea to test the DC-DC charger externally first. Who knows how the Ford will control that circuit - I suspect the Ford dealer's guys will have no idea. The manual does indicate a 30amp fuse for the circuit, so we'll see how it does. These newer vehicles are getting too smart for their own good... The battery(s) do have Bluetooth, so I can see what sort of current the TV is putting into them.

Alex

Alex,

Your welcome.

The one constraint that Ford puts on this would be the one below that may need a work around where the input of the Renogy will not show the trailer battery voltage since its an isolation device. You could trick the relay with a jumper or jump the relay itself but without seeing how Ford wired this, I would not state to do that without more information.

The trailer battery voltage is within
5 volts of the vehicle battery

**AlexPeterson** · 02-19-2022, 03:49 PM

Jim - this is exactly what I'm expecting - the truck won't "see" the tt battery. I will try a 5k or so resistor between the input and output of the DC-DC charger if it doesn't work at first. A tiny amount of current would go one way or the other through this resister, depending on relative voltages, but it should be irrelevant. Whether this works or not will depend on what the input resistance of the circuit in the Ford is that examines this voltage. Normally those types of circuits have a high input impedance. I will report back in ~April when I have the truck and trailer in one spot!

**Yoda** · 02-19-2022, 09:21 PM

Guest howson

Yoda is now very confused - yep easy to do. I am still wondering why the 7 pin charge line should be "disconnected" when using a 60A DC-DC charge. or any direct connected DC-DC charger, For my flooded battery set up the truck will see the trailer batterys as the charge draw will be directly from the TV battery's (fused and protected of course). I confirmed this with my Ford service manager a while back. At the time I did not ask abut the 7 pin connector charge line, nor did he mention doing anything special.

The max voltage will be 14.4 - 14.6 (both TV and trailer batterys same type) so as far as circuit voltage the TV and 5th wheel will be the same. I cant see how the charge amperage wold make a difference. Now a thought - when the MPPT solar chargers goes into equalization voltage during travel the truck wold see 15.6V, bit that was not an issue for my old truck - or I do not know if it was as I was not mentoring when driving.

When I go to lithium I can possible see a reason why due to the higher operating voltage of the trailer batterys, but can it actually back feed through the 7 pin harness and would not the 30A TV fuse protect the TV. To get to the TV it would be feeding back through the trailer circuit breaker to get to the charge line as the charge line is tied into the trailer positive buss bar and not direct to the batterys.

Also the Renogy install instructions do not say anything about the stock TV charge line that I can see and none of the YouTube videos on install mention disconnecting that line that I remember

So what am I missing? Remember I like to let the magic smoke out of wires.

Thanks in advance for education me.. This will be installed on my 2022 F350 if it ever gets built - Now March 7th

Thanks Keith

On edit - Howard I did see you post here https://gdrvowners.com/forum/operati...e-borns/page10. A current flow takes the path of least resistance as long as the 2awg wiring stays connected there should be no issues and if disconnected the DC -DC charger wont work. I still not wrapping my head around the need for the 12v+ charge line being disconnected as it is fused too?

**howson** · 02-20-2022, 08:18 AM

Originally posted by Yoda View Post

I still not wrapping my head around the need for the 12v+ charge line being disconnected as it is fused too?

I did not disconnect the +12v charge line due to any worries about "backfeed". I disconnected the wire as the charge source (battery and alternator) are configured for a different battery chemistry (lead acid) where the Renogy is configured for what I have in the trailer (LifePO4).

Think of it this way: you have a lithium RV battery on your workbench and it needs to be charged. Conveniently, there's a lithium-capable charger available so it's connected to the battery. Sitting on the workbench nearby is a lead-acid battery charger. Would you connect the lead-acid charger to the battery in addition to the lithium charger? No--of course not. All I did when I disconnected the charge wire is stop using the "wrong" charger.

Originally posted by Yoda View Post

Now a thought - when the MPPT solar chargers goes into equalization voltage during travel the truck wold see 15.6V, bit that was not an issue for my old truck - or I do not know if it was as I was not mentoring when driving.

Lithium batteries do not use and should NOT be subjected to an equalization charge. My posts are based on the setup in my RV, thus the discussion assumes the requirements for a LifePO4 battery chemistry. For the batteries in your RV, Keith, (I think they are AGMs?) you'd be wise to double-check how all of this applies to that configuration.

Originally posted by Yoda View Post

So what am I missing? Remember I like to let the magic smoke out of wires.

Look at the diagrams again, Keith. My interpretation of AMSolar's blog post is there is a potential for current to travel on the negative wire ("ground") through the 7-pin connector that could exceed it's capacity. The negative wire is NOT fused.

Again, (hopefully) a simple example.

A 16ga ground wire is attached from a device to a battery (assume the wire is well within the capacity ratings for the device). A (fused) positive wire is also attached to the device. No problem, right?

Now add a second device but with only a new positive (fused) wire from the battery. A second negative is NOT added. Each positive line is more than capable of carrying the amperage, but now the negative is carrying TWICE the amperage.

Now let's imagine that ten or more devices are added, all with (fused) positive wires to their device from the battery but there's still only the one single negative 16ga wire going back to the battery. What's going to happen? That negative wire is going to melt and fail. None of the fuses will blow as the amperage going through them is appropriate for their rating and the (positive) wires are each carrying just their load. But that 16ga negative wire likely won't be able to handle all ten loads returning to the battery.

That, in essence, is what AMSolar (I think) is trying to convey. They are worried about unplanned amperage (large, DC-DC current) traveling on a relatively small, unprotected wire (-12vDC return in the 7-pin). The conclusion for me and my system is it's not a concern. Why? Because I added another (large) path on the negative side straight from the Renogy to the battery.

And you're absolutely correct--if the negative wire should somehow become disconnected (input side of the Renogy) it will stop working.

**Guest** · 02-20-2022, 09:23 AM

Excellent Howard.

For the positive wire on the 7 way, the fuse can simply be removed at the TV since this wire can connect the TV + to the trailer + depending how its wired with a DCDC. The ground wire on the 7 way should be disconnected when using a high current DCDC. Am I in the Matrix?

Jim

**Yoda** · 02-20-2022, 11:16 AM

Originally posted by howson View Post

Lithium batteries do not use and should NOT be subjected to an equalization charge. My posts are based on the setup in my RV, thus the discussion assumes the requirements for a LifePO4 battery chemistry. For the batteries in your RV, Keith, (I think they are AGMs?) you'd be wise to double-check how all of this applies to that configuration.

And you're absolutely correct--if the negative wire should somehow become disconnected (input side of the Renogy) it will stop working.

Howard - I am running 4-6V Crown CR260's they are flooded - same as the truck batterys for now. The equalization voltage is correct. Crown recommended that charge rate for 3 hours monthly

So if I am reading correctly I can leave things connected as my battery types are not different. When I switch to the lithium I will need to disconnect the 12V+ charge wire.

As for understanding I am getting there. With the 12V- 2 awg negative wire tied to the battery , and to the trailer negative side, I should be good as all of my negative wiring is bonded/tied to the trailer frame through various points. I plan to tie in the DC-DC through my Lynx power in bar. The negative side ties to the trailer frame through the BM 712 shunt (2/0 wire) which should allow me to see if the charger is working.

Thanks
Keith

On edit - in case folks are wondering about the exposed positive buss bar, this is a lynx power in component and has a cover. https://www.victronenergy.com/dc-dis.../lynx-power-in

Victron also has a smart one that holds fuses https://www.victronenergy.com/dc-dis...nx-distributor

The intent of the photo was to show the negative side of my install that all negative paths go through the 712 shunt (2/0 cable running between the battery isolation switches) to the negative buss bar and then to a frame connection on the left. All 2/0 cabling.

**howson** · 02-20-2022, 11:45 AM

Yoda
Only possible exception is using the frame as the negative return path for a large DC current. Since there are many paths from the frame back to the battery, that opens more possibilities for current to find "errant" ways back "home".

I can't defend that opinion with a chapter-and-verse reference as I'm not an engineer, but if there's a worry about the path electricity can travel it seems to be sensible to limit those paths.

Keep the magic smoke in the wires, Keith.

Howard

P.S. Also sending you a PM...

**AlexPeterson** · 05-02-2022, 08:07 PM

Bumped - see edit to first post.

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Will 2022 F-150 "see" the trailer battery through a Renogy dc-dc charger?

Will 2022 F-150 "see" the trailer battery through a Renogy dc-dc charger?

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