DC/DC Renogy Trailer Install

[Short_Shot]

Yeah man. You'll be fine with 10a output if it's actually 10 awg. If you try to run it at 20a you might have some issues.

If it's 12 gauge or less don't do it at all.

For me, my truck has garbage wire in it and I'm just gonna get a 20 foot 8 gauge cable with Anderson connectors and idle my truck for an hour or so if absolutely necessary.

 

[Zwy]

I'm going to run a 2 hour timed test at 6.7a.

When the wire gets hot it is bouncing off the 10 amp maximum output of the power supply. If it exceeds this by a small amount the power supply will shut down the output, the charger will go to zero, and the tester will register <1v and shut dish the test. This will record the time stopped and total mah drawn before a significant fault (hot wire running away) occurred.

And with that started I'm going to get lunch.

It would only take 42 hours of driving to recharge 400Ah of batteries that are discharged to 20% at 92 watts.

As amps increase supplied to the DC to DC thru a small gauge wire in order to keep voltage up, the voltage drop will increase (your data shows it) and more amps will need to flow increasing heating and voltage drop more. If you had a supply of enough amps, the wire would have let the smoke out. At some point, the wire self destructs. Over time, excessive heating of the wire will increase it's resistance.

What's interesting to note is there is a 25% loss of wattage from the input to the load (30 watts). That loss is heating of the wire. It is wasted energy.

 

[Short_Shot]

It would only take 42 hours of driving to recharge 400Ah of batteries that are discharged to 20% at 92 watts.

As amps increase supplied to the DC to DC thru a small gauge wire in order to keep voltage up, the voltage drop will increase (your data shows it) and more amps will need to flow increasing heating and voltage drop more. If you had a supply of enough amps, the wire would have let the smoke out. At some point, the wire self destructs. Over time, excessive heating of the wire will increase it's resistance.

What's interesting to note is there is a 25% loss of wattage from the input to the load (30 watts). That loss is heating of the wire. It is wasted energy.

Now you're just reiterating the obvious.

However it will take a lot more than 30c wire temps in a chassis wiring scenario to cause appreciable degradation over time.

Also, OP stated ages ago he just wanted enough current to cover the appliances while driving. He stated that 10a is enough.

Op however is planning to use only 33% more power than my test with 400% more wire cross section.


And I'm still trying to figure out how to get my solar panels to output 80% of rated power on a rainy day. Care to explain that one??

What magic panels do you have so I can go buy some?

 

[Zwy]

Now you're just reiterating the obvious.

Pointing it out as some might not understand what is occurring in the "testing" you performed.

However it will take a lot more than 30c wire temps in a chassis wiring scenario to cause appreciable degradation over time.

Also, OP stated ages ago he just wanted enough current to cover the appliances while driving. He stated that 10a is enough.

I think instead of installing 8 ga you should simply go with the OE 12 ga to prove your point.

Interesting after your "testing" you will now upsize on the wire like I stated should be done.

Op however is planning to use only 33% more power than my test with 400% more wire cross section.

It will take more than 33% more watts going into the DC to DC, as amps increase, the wasted energy from heat increases exponential.

And I'm still trying to figure out how to get my solar panels to output 80% of rated power on a rainy day. Care to explain that one??

I never said that any panel would output 80%, show me where I stated it. What post number is it?

 

[Short_Shot]

Let us know when you have something useful to contribute to this thread besides cherry picking individual statements, mixing them up out of context, and then patting yourself on the back for being grossly incorrect and frankly out of line.

Nobody cares what your opinion on what's useful or worth doing is. Especially when you blatantly ignore the application requirements multiple times.

I had actually ordered a 50a power supply and a big enough load tester to give you your 10a over 10awg and prove that it's less voltage drop and less wire heating than my test, but in light of your incessant childish comments I've canceled the order. You're not worth the effort.

You should be able to figure out that 10awg @ 10a is way less voltage drop than 10a over the same length 16awg since you're the expert here anyways.

I was always going to upsize my installation. I never said I wasn't going to. I will be running 20a. OP will be running 10a and his 10awg is fine. No part of this opinion has changed at any point in this discussion. You're just taking multiple things out of context and mixing it up repeatedly once again. Stop confusing what I'm doing with my install and what OP is doing with his.

Oh and you made the 80% claim when you utterly ignored the context of my statement about a charger being useful on rainy days then continuing to go on a rant about how more panels is better.

 

[Zwy]

You sound angry Short, I think you should chill out man.

I'm bowing out this thread, you seem to have taken things personal and just want to argue for arguments sake at this point.

Have a nice day.

 

[AndyRonLI]

Seque, Side Bar, Grey Beard Story.
The internet is an odd place and it was from the very beginning
I worked at a place called Playnet, back in the early 80s
First real online gaming space. I had the backgammon game.
We were online less than 1 week, and the company owner called us together and reminded us.
1- All the families in the test group (all 50 of em) were the families of investors who paid our wages
2-When online a person can represent themselves as a 20 year old nursing student when in fact they were in Jr high
3 - So .. dont flirt online with the investors daughters
A week later
4 - Dont argue on line with the investors

Eventually every thread becomes an argument or a flirtation.

Weird isn't it.
Andy

 

[alfaeric]

After wading through all of the arguments, since all I want to do is make sure my fridge is powered when we drive, the 10A info was very helpful. Although, I'll probably wire for 20A. And (horror of horrors) use the 7 pin connector, since it's rated for 40A. Since we will start out with a charged battery, most likely, we will never actually run 20A. And the fridge does not take much power to run.

 

[Short_Shot]

After wading through all of the arguments, since all I want to do is make sure my fridge is powered when we drive, the 10A info was very helpful. Although, I'll probably wire for 20A. And (horror of horrors) use the 7 pin connector, since it's rated for 40A. Since we will start out with a charged battery, most likely, we will never actually run 20A. And the fridge does not take much power to run.

Yeah I've never found real information on the connector ratings.

However, like yours, my truck is fused for 40a on that wire. Sadly it's either 14 or 12awg (pretty sure it's 14) and regardless that's too small even for 10 amps when considering heat from the engine bay and high outdoor temps.

I'd be comfortable with 10 awg for a 10a charger if it was already installed but since I'm doing 18a and installing it myself.... 8 for me.


Even further I haven't made my mind up to actually install it. I don't intend to use it other than cloudy weekends where solar isn't enough for my roughly 25ah daily use. I can just idle my truck for an hour and a half for a negligible amount of fuel.

Not ideal of course but whatever. I could bring my inverter generator too if I wanted and run my AC.

My point is even low current dc to dc chargers have their uses.

Even someone with 400ah of battery might very well be able to "struggle" through a night with only a couple vent fans and a smaller fridge running with a "useless" small charger.

 

[AndyRonLI]

So a tiny tidbit of data. For my 2016 F350 Superduty I find the following fuses callouts

For the passenger compartment

13​	15​	Right turn signals and brake lamps, Right trailer tow stop turn relay
14​	15​	Left turn signals and brake lamps, Left trailer tow stop turn relay
15​	15​	High-mounted stop lamps, Backup lamps, Trailer tow backup relay, Reverse signal interior mirror

And for the engine compartment

No.​	A​	Protected components​
10​	40​	'15-'16: Trailer tow
22​	30​	Trailer tow electric brake
26​	30​	Trailer tow park lamps
70​	10​	Trailer tow backup lamp
90​	25​	Trailer tow battery charge
100​	25​	'11-'14: Trailer tow turn signals

Now... what exactly is that 40 amp fuse for?

This was from a generic chart
I will check my owners manual.
But this at least leads me to believe that Ford finds 25 amps of trailer battery load acceptable.

I am going to see what that 40 amp circuit does.
Should have looked for this earlier! DOH
Andy

 

[Short_Shot]

So a tiny tidbit of data. For my 2016 F350 Superduty I find the following fuses callouts

For the passenger compartment

13​	15​	Right turn signals and brake lamps, Right trailer tow stop turn relay
14​	15​	Left turn signals and brake lamps, Left trailer tow stop turn relay
15​	15​	High-mounted stop lamps, Backup lamps, Trailer tow backup relay, Reverse signal interior mirror

And for the engine compartment

No.​	A​	Protected components​
10​	40​	'15-'16: Trailer tow
22​	30​	Trailer tow electric brake
26​	30​	Trailer tow park lamps
70​	10​	Trailer tow backup lamp
90​	25​	Trailer tow battery charge
100​	25​	'11-'14: Trailer tow turn signals

Now... what exactly is that 40 amp fuse for?

This was from a generic chart
I will check my owners manual.
But this at least leads me to believe that Ford finds 25 amps of trailer battery load acceptable.

I am going to see what that 40 amp circuit does.
Should have looked for this earlier! DOH
Andy

Nah. My silverado has a 40a fuse for that and tiny wire.

They don't intend for it to ever hit 40a due to the designed in voltage drop limiting charging.

A dc to dc charger "corrects" for that and will pull enough current to be a problem.

 

[alfaeric]

So a tiny tidbit of data. For my 2016 F350 Superduty I find the following fuses callouts

For the passenger compartment

13​	15​	Right turn signals and brake lamps, Right trailer tow stop turn relay
14​	15​	Left turn signals and brake lamps, Left trailer tow stop turn relay
15​	15​	High-mounted stop lamps, Backup lamps, Trailer tow backup relay, Reverse signal interior mirror

And for the engine compartment

No.​	A​	Protected components​
10​	40​	'15-'16: Trailer tow
22​	30​	Trailer tow electric brake
26​	30​	Trailer tow park lamps
70​	10​	Trailer tow backup lamp
90​	25​	Trailer tow battery charge
100​	25​	'11-'14: Trailer tow turn signals

Now... what exactly is that 40 amp fuse for?

This was from a generic chart
I will check my owners manual.
But this at least leads me to believe that Ford finds 25 amps of trailer battery load acceptable.

I am going to see what that 40 amp circuit does.
Should have looked for this earlier! DOH
Andy

Can you "trace" any of those to the 7 pin connector?

Seems that both 10 and 90 could be the 12V supply to the trailer. That being said- with some margin built in, using the stock wiring would limit charging to the 20A charger if one used the base 7 pin connector. More than that would need a dedicated system.

 

[AndyRonLI]

So Fuse 90 is indeed a 25 amp fuse, removing it does interrupt power to the power terminal of the 7 pin connector. My first time getting the Fuse Box cover off on my F350 Diesel... Pain, and my first experience with trying to remove a Ford Cartridge fuse... Pain. But did confirm that fuse is what it says it is. And at least the alternator and wiring are protected with a 25 am fuse. In theory I wont pull more than 10 so maybe drop that to a 15 amp for extra protection??
Getting dark and the mosquitoes are coming out, so I stopped. I will check that 40 amp one. That might be an upstream fuse that all the trailer functions draw through, except likely the brake. That would protect the connector. That will be the next check.

I will also get under the truck and see what its wiring looks like hopefully it is 10ga or better. Though I know some folks have found the 7 pin harnesses can use an upgrade. I bought a newish truck to avoid going under it. Oh well.
Thanks
ANdy

 

[alfaeric]

If it were me, I would not limit it.... I have one of the Renogy DC/DC units, and for the 20 A set up, they suggest 25a fuse for the supply, and 20 for the delivery. So you are meeting the supply spec out of the box.

One other note- when I posted the 7 pin is rated for 40A- I just mean the connector, based on multiple answers to a google search. The supply has to be set up to meet that capability. But, IMHO, that makes the 20A DC/DC system a pretty perfect match if you don't want to add a dedicated charging system.

 

[Short_Shot]

If it were me, I would not limit it.... I have one of the Renogy DC/DC units, and for the 20 A set up, they suggest 25a fuse for the supply, and 20 for the delivery. So you are meeting the supply spec out of the box.

One other note- when I posted the 7 pin is rated for 40A- I just mean the connector, based on multiple answers to a google search. The supply has to be set up to meet that capability. But, IMHO, that makes the 20A DC/DC system a pretty perfect match if you don't want to add a dedicated charging system.

He's not meeting that if the wire is too small though.

Remember the voltage drop causes a current increase when using a dc to dc charger. If he runs 20a output with that charger and it's a 12 gauge or smaller then it'll probably pop the fuse.

That's the opposite of what happens with a direct connection which is a current decrease due to low voltage, because the battery can't "force" (I use that term lightly) current like the charger does.


I only reiterate that because he's now unsure if the wire is 10 gauge or larger.

 

[alfaeric]

He's not meeting that if the wire is too small though.

Remember the voltage drop causes a current increase when using a dc to dc charger. If he runs 20a output with that charger and it's a 12 gauge or smaller then it'll probably pop the fuse.

That's the opposite of what happens with a direct connection which is a current decrease due to low voltage, because the battery can't "force" (I use that term lightly) current like the charger does.


I only reiterate that because he's now unsure if the wire is 10 gauge or larger.

So you are wondering if Ford installed a wire that is too small for the fuse that it assigned to that circuit? Seems to me that it would be kind of odd for an OEM to undersize a wire for a fuse. Especially since they would be very aware that you are delivering power from the fuse location to the 7 pin connector- which would run the entire vehicle.

And the voltage drop would have to be quite a bit all the way to the charger- even if it dropped to just 12V going in, it's still under 25A. The system would certainly see a power draw- similar to the fans, or something, and the system would react to up the alternator output- to 14.5V. To pop a 25A fuse, the voltage drop from the supply to the charger would have to be 2.5V. To get 2.5V drop in 12g wire, starting at 14.5V- the calculator I see says that you would need 200ft of 12G wire.

I just don't see an OEM that would under spec a wire to a fuse. Seems like it would be far more likely that it would be oversized than undersized.

 

[Short_Shot]

I'm not wondering.

I KNOW they do this.

This is standard practice because they intend it to be connected to nothing more than a lead acid battery for trailer brakes. With a lead acid battery and just the right voltage drop it will limit charge current as the battery becomes more and more charged.

This whole thread was discussing this issue.

It's simply a fact. Under load (when my battery is low) my trailer output drops from 14.4v at the fuse to less than 12.5v at the trailer.

This is intentionally designed this way with lead acid batteries in mind because they can't force higher current from less voltage.


It's an intentional design choice. When you're using anything on a trailer that pulls a load the voltage on the trailer wire drops so low its effectively shut off because the trailer battery is higher voltage.

 

[Short_Shot]

Oh and the voltage drop is in fact high enough to cause a problem.

You don't need a 2.5v drop to have an issue. At 20 feet @ 20 amps and 14v the drop is 1.6 volts which is over 10%. That means a 10% increase in current which causes additional vdrop which necessitates a different equation to determine where it settles (that I can't recall right now to save my life).

My truck has a 40a fuse from the factory and what looks like 12 or 14 awg wire. It's definitely not larger than 12 but I don't know how thick the insulation is.

20 feet of 12awg at 40a would be a calculated 23% voltage drop.

At the 18 amp output of the charger I own that voltage drop is 10%, which then actually increases the current in the wire enough to further drop the voltage, and the actual drop comes closer to 12% or more.

Which then exceeds the rating of the wire, but not the fuse.

So yes. They absolutely do undersize this wire.


And where did you come up with 200 feet?

 

[alfaeric]

200ft for a 2.5V voltage drop at 25A for 12g wire covered in PVC. Similar calculator.

Or you can calculate it yourself- for 2.5V drop at 25A- V = IR, so R would be .1 Ohms. A different chart (which I should have looked at), 12G wire is 1.6ohms/1000 feet, so .1 Ohm is ~75 feet. Still much longer than the truck. So perhaps you have other voltage drops in the system.

But you can do want you think you need to do.... I know what I will do.

 

[Short_Shot]

Then explain the voltage drop I had for 10a over 25 feet of 16awg as shown in my previous post?

I experienced, documented, and posted just over 18.3% voltage drop, which was expected and fairly close to what this calc spits out. It makes sense, as it's likely the wire I used had slightly higher resistance than "optimal" copper.

Every calculator I've used shows more or less the same value, with slight variations on the resistance value of the copper.

I could go measure the actual wire and get the calculation closer but I'm busy with this here pizza.