Tapping 12V from the truck to charge Battle Borns

[howson]

Bbytes -- Neil's configuration (truck power feed) was the original D+ source I used, too. What I found is my '17 Ford SuperDuty cuts the power to the 7-pin every time the driver door is opened. I usually double-check the output using the VictronConnect app so need to be close enough for the bluetooth to connect--typically this means I need to get out of the truck. I didn't want the Renogy turning on and off unnecessarily or powering up (or down) without my explicit command.

None of the choices are "right" or "wrong"--just get 12v to the D+ and it will work.

Howard

[ncitro]

Bbytes -- Neil's configuration (truck power feed) was the original D+ source I used, too. What I found is my '17 Ford SuperDuty cuts the power to the 7-pin every time the driver door is opened. I usually double-check the output using the VictronConnect app so need to be close enough for the bluetooth to connect--typically this means I need to get out of the truck. I didn't want the Renogy turning on and off unnecessarily or powering up (or down) without my explicit command.

None of the choices are "right" or "wrong"--just get 12v to the D+ and it will work.

Howard

Yeah I tried the seven pin at first as well and had a similar result. When I did this one I tied it to the 4 AWG wires coming to the input of the Renogy. Those are hot regardless of the seven pin plug (assuming the upfitter is on) and works great. But since I've got 18 AWG connected to the 4 AWG that's on the 60 amp breaker I fused it as well.

[howson]

ncitro and other readers of this thread,

While researching an answer to a recent question on charging a LifePO4 battery from a tow vehicle I stumbled across a blog post from AMSolar at https://amsolar.com/blog/high-curren...pin-connection that initially caused me some concern. The blog is also posted below for convenience.

The purpose for this post is for the other electrical-types here on the forum to critically review my conclusion and to challenge it if I missed something.

Let me start by stating in my opinion it is not an issue on my setup. I'll explain over the course of this post.



First -- a look at a typical setup without a Renogy. Hopefully the diagram is easy enough for most everyone to follow. It only shows applicable items--other components and wires that did not add to the intent were left out on purpose.

Wire gauge and fuse sizes on the '17 Ford SuperDuty are to the best of my knowledge. Wire gauge on the camper is what is in my '19 315RLTS (installed by GD). Also note the diagram uses Conventional Flow (versus Electron Flow).




Next is the Renogy system in my camper, greatly simplified for ease of viewing. Note the charge wire on the camper side is disconnected (I did this on purpose). The 60A "fuses" are actually circuit breakers...I used the fuse symbol for easy reference.




Below is what I believe is AMSolar's concern. Note the larger size of the arrows through the 7-pin return path indicating a larger current flow. AMSolar states the only way to avoid this is to disconnect the -12vDC return in the 7-pin connector, thus the only return path for the camper's lights and brakes is through the Anderson connector. I did not (and won't) disconnect the -12vDC wire in the 7-pin. More explanation embedded in the diagram.

Update: Version 2 of the diagram below incorporates feedback from forum member AlexPeterson . See post 141 below.




Thanks for reading and (please) if I overlooked something fire away.

Howard

[ncitro]

howson That's an interesting read, I think I feel the same way as you, I sometimes do not even hook up my Anderson cable, so I like to keep the factory wiring there. Definitely will keep an eye on it though.

[Guest]

Howard,

I have brought this up in the past where its good that we have additional confirmation. I believe this was on the topic of using the auto alternator as a generator topic. The small ground wire on the 7 way can also be overloaded as well when using welding cable for a high current charging method. So two dedicated cables should be ran all the way back to the TV battery and the ground and power lines on the 7 way should be disconnected to prevent backfeeding.

Jim

[AlexPeterson]

Howard - great write-up! Some of the Renogy current will indeed go back through the 7-pin's ground, the question is how much. I assume the TV uses a larger wire for the 7-pin gnd since it has to take the lights, charge line return and brakes (I admit I haven't studied the details of how the brake circuits work). Electricity does not just take the path of least resistance - it will be divided into the three paths in this case: the physical hitch, the 7-pin's ground and your Anderson ground. Calculating the ratios of these currents is just a matter of knowing each path's overall resistance. Obviously, your setup is working fine, and I suspect the 7-pin's ground line is not taking very much current.

[wygieman]

Thanks for reading and (please) if I overlooked something fire away.

Can you further explain why you disconnected the 7-pin charge wire? I missed that in your other descriptions (eg final wiring diagram post 66). Are you worried about backfeeding the truck or something more subtle.

[howson]

Can you further explain why you disconnected the 7-pin charge wire? I missed that in your other descriptions (eg final wiring diagram post 66). Are you worried about backfeeding the truck or something more subtle.

Unfortunately there's two conversations going on in parallel. Keith asked a similar question in the other thread. Here's my response:

---

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.

---

See post 8 in the Will 2022 F-150 "see" the trailer battery through a Renogy dc-dc charger? thread at https://gdrvowners.com/forum/operati...7279#post77279 for the full conversation.

[Jlawles2]

howson Howard, it almost looks like the AM solar statement is a giant CYA. This is to keep people from not installing the proper negative wire to the charger. Also states that by pulling the negative wire from the 7-pin may cause the trailer lights and other systems to not work correctly.

Wonder if someone could 3d print an anderson housing with a set of contacts that open when the plug is inserted to break the negative in the 7 way.

[howson]

Electricity does not just take the path of least resistance - it will be divided into the three paths in this case: the physical hitch, the 7-pin's ground and your Anderson ground. Calculating the ratios of these currents is just a matter of knowing each path's overall resistance.

A much better way of stating it, Alex. I hope you don't mind but I've included what you wrote above in "v2" of the last slide (and credited to you) in post #138.

Thanks for the response.

Howard

[AlexPeterson]

A much better way of stating it, Alex. I hope you don't mind but I've included what you wrote above in "v2" of the last slide (and credited to you) in post #138.

Thanks for the response.

Howard

Howard - no need to credit me, but thanks.
Alex

[howson]

25 June 2022 Update

An exact duplicate of the setup installed in my 2017 Ford F-350 (which continues to work without any issues) was mirrored on my friend's Dodge Ram 3500. Within 20 minutes of running the setup the 60A breaker popped on his setup. Further investigation revealed the setup in his truck will pull slightly over 60A (popping the breaker) while my Ford never exceeded ~58A. There are a number of reasons for this result, but the bottom line is the original spec'd 60A breakers and relay are too small for the continuous load from the battery to the Renogy. The 60A breaker and relay were replaced in my friend's truck with 80A versions and the install works as expected. (Both of our setups were used extensively over thousands of miles on a recent trip.)

Updated schematic below for reference. (My install still has the 60A versions as there are no faults, but a new install should have the 80A versions. Also note that any relay used must be rated for continuous use. If unsure contact your retailer to ensure the relay being considered is appropriate for the use intended.)

Howard

[ncitro]

25 June 2022 Update

An exact duplicate of the setup installed in my 2017 Ford F-350 (which continues to work without any issues) was mirrored on my friend's Dodge Ram 3500. Within 20 minutes of running the setup the 60A breaker popped on his setup. Further investigation revealed the setup in his truck will pull slightly over 60A (popping the breaker) while my Ford never exceeded ~58A. There are a number of reasons for this result, but the bottom line is the original spec'd 60A breakers and relay are too small for the continuous load from the battery to the Renogy. The 60A breaker and relay were replaced in my friend's truck with 80A versions and the install works as expected. (Both of our setups were used extensively over thousands of miles on a recent trip.)

Updated schematic below for reference. (My install still has the 60A versions as there are no faults, but a new install should have the 80A versions. Also note that any relay used must be rated for continuous use. If unsure contact your retailer to ensure the relay being considered is appropriate for the use intended.)

Howard

I also found my 60A would trip on my Ford. I couldn't get an 80 in time so I installed a 100 and have had no issues. The 4AWG should be good for 100A so I never changed it.

[Yoda]

ncitro and other readers of this thread,

While researching an answer to a recent question on charging a LifePO4 battery from a tow vehicle I stumbled across a blog post from AMSolar at https://amsolar.com/blog/high-curren...pin-connection that initially caused me some concern. The blog is also posted below for convenience.

The purpose for this post is for the other electrical-types here on the forum to critically review my conclusion and to challenge it if I missed something.

Let me start by stating in my opinion it is not an issue on my setup. I'll explain over the course of this post.



First -- a look at a typical setup without a Renogy. Hopefully the diagram is easy enough for most everyone to follow. It only shows applicable items--other components and wires that did not add to the intent were left out on purpose.

Wire gauge and fuse sizes on the '17 Ford SuperDuty are to the best of my knowledge. Wire gauge on the camper is what is in my '19 315RLTS (installed by GD). Also note the diagram uses Conventional Flow (versus Electron Flow).




Next is the Renogy system in my camper, greatly simplified for ease of viewing. Note the charge wire on the camper side is disconnected (I did this on purpose). The 60A "fuses" are actually circuit breakers...I used the fuse symbol for easy reference.




Below is what I believe is AMSolar's concern. Note the larger size of the arrows through the 7-pin return path indicating a larger current flow. AMSolar states the only way to avoid this is to disconnect the -12vDC return in the 7-pin connector, thus the only return path for the camper's lights and brakes is through the Anderson connector. I did not (and won't) disconnect the -12vDC wire in the 7-pin. More explanation embedded in the diagram.

Update: Version 2 of the diagram below incorporates feedback from forum member AlexPeterson . See post 141 below.




Thanks for reading and (please) if I overlooked something fire away.

Howard

WOW has this evolved - excellent discussion. After doing my own research I am convinced the its a CYA to disconnect the 7 pin charge line form the truck. When I do my 60A install I will not be disconnecting that line - it will be left alone Other than adding a power stud to one battery terminal I am not messing with the stock system. Besides it already fused at 30A at the truck regardless of the current direction......so how could there be an issue?

Now I am not an electrical engineer - just a civil (registered PE), but from my 3 years of high school electronics. classes, late 60's (transistors blew my mind) and my several electrical college classes, I had ingrained into me that current always takes the path of least resistance.

I learned that the hard way in high school after building a short wave set ( from a kit) Class requirement) We were then required to test it and record any contacts. Now remember back on the late 60's most plugs were two pronged (no ground) I went to change antennas and got caught between full 110 and ground as the chassis of my radio was hot. Fortunately my instructor saw it happen and tackled me off my stool breaking the connection. I was OK - a few hand burns where I had a hold of the antenna connections. He immediately put new safety measures in place where we check for a hot chassis (had team mate verify) and he installed ground lugs throughout the classroom that were required ti use (made up ground clips in class. I helped in that project (lots of soldering) - That's where I learned exactly what happened - I was the easy path to ground .

So to sum this up withe a #2 from the battery positive to the charger and a #2 back to the battery I feel confident Howard is correct - very slim chance of high amperage ever getting to the 7 pin charge wire, And if it does it is already fused so nothing can happen....well unless DR Who shows up

Excellent work Howard and to those AlexPeterson that added tho this.

Just my thoughts

Keith

BTW if there is ever a contest to the person blowing the most fuses on thier RV let me know

[Jlawles2]

Yoda Keith, do we really want to know how many fuses you melted?

Now Relays with a bad slide motor, I will say at least 4. Then after the dealer magically fixed it (they only replaced the relay which promptly went out the next time I ran the slide), I took the slide motor out, polished the burnt armature and it never missed a lick again.

Dealers who run slides in and out on just the 7 way should be tied to a ground rod, soaked in salt water and forced to hold the hot line on an electric fence. The 7 way may run the cable type slides, but it's more likely to cause issues with the less than stellar brushed motors.