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Old 04-01-2022, 08:12 PM   #21
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My F150 has a 25 amp fuse for the 12 volt to the 7 pin connecter so I think the Truck is protected ... I am not 100% sure of this BUT I think there is a relay that shuts off the 12 volts to the connector when the truck is turned off so no truck battery drain .. How do I know about the 12 volt fuse OOPS I blew it ... it is a "Ford had a better idea" fuse and all the local parts stores did not have it in stock (2020 F150) ..
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Old 04-02-2022, 09:30 AM   #22
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My F150 has a 25 amp fuse for the 12 volt to the 7 pin connecter so I think the Truck is protected ... I am not 100% sure of this BUT I think there is a relay that shuts off the 12 volts to the connector when the truck is turned off so no truck battery drain .. How do I know about the 12 volt fuse OOPS I blew it ... it is a "Ford had a better idea" fuse and all the local parts stores did not have it in stock (2020 F150) ..
We do some remote camping. My main reason for trying to learn all of this instead of just taking it to the dealer is because I want to be able to fix it myself when something goes wrong. I’ve seen Deliverance. I don’t particularly want to have to deep dive into the electrical system of a modern SUV (still scarred from my older BMW X5) -side note- the 6000lb tow capacity, auto-levelling rear air suspension, and trailer sway control baked into the traction control system might seem attractive, but the X5 has been the most unreliable, expensive, electronically glitchy vehicle I have had in 35 years of vehicle ownership-
I don’t want to discover a unique fuse or relay when I’m miles away from nothing. While I hate the idea of increasing my hitch weight by 35%! I am still considering adding a couple of Trojan 6v’s to the tongue.
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Old 04-02-2022, 05:39 PM   #23
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If the charge wire to the truck is fused at a reasonable draw rate I'd say go with the LiFePo batteries. If you have at least an AGM charge setting with your on board you will be better off that just two big heavy GC2 batteries and have the bones to do more. Unplug when stopped for any long duration. Check regularly on state of charge to track the success of the endeavor
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Old 04-02-2022, 05:55 PM   #24
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I’m trying hard to avoid dropping 120 lbs of GC2 on the tongue of my single axle, 375 lb tongue weight trailer. I’m just concerned about the warranty on my (wife’s) brand new car.

I am planning on adding some portable solar panels. I noticed that they sell dc-dc chargers with a mppt cc built in. Perhaps I get one of these and use it for my portable panels as well. I don’t know much about them other than they aren’t cheap.
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Old 04-03-2022, 09:30 AM   #25
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I’ve been digging around for info on the alternator;

Alternator Management System
Alternator management system controls the charging voltage set point in order to improve fuel economy, manage alternator load under various operating conditions, keep the battery charged, and protect the battery from over-charging. ECM controls generating voltage by duty cycle (charging control, discharging control, normal control) based on the battery conditions and vehicle operating conditions.

…does this sound like it would protect the tv battery and alternator from the lifepo’s?
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Old 04-05-2022, 07:31 AM   #26
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I’ve been digging around for info on the alternator;

Alternator Management System
Alternator management system controls the charging voltage set point in order to improve fuel economy, manage alternator load under various operating conditions, keep the battery charged, and protect the battery from over-charging. ECM controls generating voltage by duty cycle (charging control, discharging control, normal control) based on the battery conditions and vehicle operating conditions.

…does this sound like it would protect the tv battery and alternator from the lifepo’s?
Your relatively thin wire will protect the alternator, and a fuse will also. BUT, what comanchecreek and others have described is am ideal setup for a trailer. I too have a similar setup, 280ah lithium, victron dc to dc, mppt cc wired though side port to two cheap 100 watt panels ground deploy. Works fantastic. For your Hyundai, I would not go bigger than an 18amp dc to dc charger because the constant load on the alternator may be higher than what it is designed to do. Renogy makes a unit that combines a dc to dc charger and mppt all in one, but iirc, it is 40 amp, which means at least 50 amp continuous load on your tow vehicle until the battery is charged. Likely too much. The other drawback is it is all in one and when it fails, you have no backup. Separate components limit system failure.
Since you have a 12 volt fridge, your system absolutely needs upgrades *if* you boondock. We prefer primitive camping, no hookups, and a system such as yours as delivered, would not do. It will require further investment unfortunately.
Since a 12 volt fridge will consume about 85 ah a day, I would accept nothing less than 300+ ah lithium to get you through at least two crappy days.

Ground deploy solar is needed where we camp because it is often in trees, and you need the panels to be in pure sun. On the roof would never cut it.
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Old 04-05-2022, 10:13 AM   #27
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Your relatively thin wire will protect the alternator, and a fuse will also. BUT, what comanchecreek and others have described is am ideal setup for a trailer. I too have a similar setup, 280ah lithium, victron dc to dc, mppt cc wired though side port to two cheap 100 watt panels ground deploy. Works fantastic. For your Hyundai, I would not go bigger than an 18amp dc to dc charger because the constant load on the alternator may be higher than what it is designed to do. Renogy makes a unit that combines a dc to dc charger and mppt all in one, but iirc, it is 40 amp, which means at least 50 amp continuous load on your tow vehicle until the battery is charged. Likely too much. The other drawback is it is all in one and when it fails, you have no backup. Separate components limit system failure.
Since you have a 12 volt fridge, your system absolutely needs upgrades *if* you boondock. We prefer primitive camping, no hookups, and a system such as yours as delivered, would not do. It will require further investment unfortunately.
Since a 12 volt fridge will consume about 85 ah a day, I would accept nothing less than 300+ ah lithium to get you through at least two crappy days.

Ground deploy solar is needed where we camp because it is often in trees, and you need the panels to be in pure sun. On the roof would never cut it.
You are describing my needs very well; primitive camping, shaded sites, 12V fridge. I am confident about my choice of ground deploy solar (likely 200W to add to my rooftop 190W) and lithium (leaning towards 200 ah, but could go more). I figure on needing around 100ah/day for our camping style. Renogy does make a 30A dc-dc with mppt that I was considering. I was hoping that this would protect my wife's new SUV (and prevent me from having to use the "2 singles" option for my trailer king bed). I could get a separate (20A or 30A) mppt and 20A dc-dc charger, but as a newb to all of this I am starting to get a little overwhelmed with the complexity of the wiring. The combo controller setup has a nice how-to from Will Prowse to follow.
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Old 04-05-2022, 10:54 AM   #28
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You are describing my needs very well; primitive camping, shaded sites, 12V fridge. I am confident about my choice of ground deploy solar (likely 200W to add to my rooftop 190W) and lithium (leaning towards 200 ah, but could go more). I figure on needing around 100ah/day for our camping style. Renogy does make a 30A dc-dc with mppt that I was considering. I was hoping that this would protect my wife's new SUV (and prevent me from having to use the "2 singles" option for my trailer king bed). I could get a separate (20A or 30A) mppt and 20A dc-dc charger, but as a newb to all of this I am starting to get a little overwhelmed with the complexity of the wiring. The combo controller setup has a nice how-to from Will Prowse to follow.

I would spend the extra coin for victron components, buy once/ cry once. They make an 18 amp which is actually closer to 24 or so amps (they underrate them and they perform better when cooler, full rated at full temp) which means it will be pulling closer to 30 amps from the tow vehicle.



On the ground deploy, I use a cheap but effective epever charge controller with a remote display mounted on the pass through door which is often open when I am at the campsite. This allows me to glance at the current going in to the battery, and tells me when I need to move the panels - something to do in between barley pops.



I don't have the 12 volt fridge, but if I did, I would absolutely have a 300ah lithium battery. The chins at amazon is a strong contender, but there are many choices available for less than $1200. Three battle born will run you close to 3K. But that would give you about three days to consider getting your generator out if it was foul weather. Count on that fridge eating 85ah a day. You can either have battery capacity or production, or hopefully both.
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Old 04-05-2022, 11:44 AM   #29
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I’ve been digging around for info on the alternator;

Alternator Management System
Alternator management system controls the charging voltage set point in order to improve fuel economy, manage alternator load under various operating conditions, keep the battery charged, and protect the battery from over-charging. ECM controls generating voltage by duty cycle (charging control, discharging control, normal control) based on the battery conditions and vehicle operating conditions.

…does this sound like it would protect the tv battery and alternator from the lifepo’s?
If you read the literature from Renogy on their DC-DC Chargers they recommend connecting the Charger input directly to the battery and at least the early instructions recommended the connection be both Pos and Neg wires rather than just positive and using frame for negative.

As I understand the Alternator Management schemes often employ a current sensor between battery negative and frame so the system may not take into consideration any draw from the charger and lower charging voltage.

I installed my DC-DC Charger after just "dropping in" my two LiFePo4 batteries and trying to charge them like a regular trailer battery from my truck. Results were disappointing as charge current was severely limited by truck wiring.

Like Commancheecreek, I installed a run of #8awg duplex marine wire direct from battery to DC-DC Charger. Charging current is now 20 amp and my batteries usually arrive at my next site fully charged, depending on depth of discharge and length of drive.

The 20 amp DC-DC charger won't overload my 130 amp alternator and whenever my ignition is turned off the DC-DC charger turns into a Battery Isolator thus preventing any drain on batteries from my truck.

Note for MH owners----- A DC-DC charger will do a great job of replacing a non-Lithium conventional Battery Isolator for a lot less money and is more efficient.
LiBim's only connect the alternator for short intervals, one model on for 15 minutes, off for 30.

The DC-DC charger will charge continuously albeit at a lower rate but a steady rate.

Renogy offers DC-DC chargers in 20, 40, and 60 amp sizes to match your alternator size.
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Old 04-05-2022, 12:56 PM   #30
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I copied my DC to DC setup from yours Mike. Works great.
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Old 04-05-2022, 01:29 PM   #31
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DC to DC converter

As to the tow vehicle, if it was factory tow equipped, I wouldn't be the least concerned about the lithium battery in the trailer. Just let the electronics and vehicle computer system do its job.

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Old 04-05-2022, 06:49 PM   #32
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As to the tow vehicle, if it was factory tow equipped, I wouldn't be the least concerned about the lithium battery in the trailer. Just let the electronics and vehicle computer system do its job.



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That may not work exactly as you'd expect unless manufactilurer of the tow vehicle anticipated Lithium batteries in the trailer.

The big issue is the amount of current a Lithium battery can draw while charging due to it's extremely low internal resistance.

If there is enough resistance in the truck's charge wire to trailer connector it MIGHT prevent excessive current which would prevent alternator damage or constantly bliwing fuses. Operative word - might.

On the other side of the resistance equation, charging voltage could be reduced to the point little or no charging woukd occur.
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Old 04-05-2022, 07:01 PM   #33
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I recently converted to a 100ah Lifepo4 battery and decided to go with the 40amp Renogy DC to DC convertor.
I tested my trucks 7 pin and it put out 13.3v and 4.6 amps.
I then turned on the DC to DC charger (wired with 2g wire) and the same shunt based meter, registers 13.7v and 40.8amps. Now it will be charged back up within a 2 hour drive to the next site. ( assuming a 80% discharge on the batteries)
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Old 04-06-2022, 09:59 AM   #34
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As to the tow vehicle, if it was factory tow equipped, I wouldn't be the least concerned about the lithium battery in the trailer. Just let the electronics and vehicle computer system do its job.

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The problem isn't with damaging anything, it's, will the battery ever get recharged. Everybody needs to investigate their tow vehicle to find out exactly how the manufacturer addressed the issue. Many don't isolate the RV battery, and many don't allow for much amperage output either by limiting alternator output, or small wire size. You can't just assume you're set up from the factory. My older Duramax pickup ,of course, had the "tow package", but you had to initially install a fuse to activate the wire to the seven pin connector, and there was no attempt at isolation, it was "hot always". I had a terrible time getting my four golf cart batts. to charge much while driving. I have since installed a DC to DC charger with the truck modified to provide a decent amperage off of the alternator as discussed previously. I originally figured with a "tow package" I would be fine. It's not that simple.
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Old 04-06-2022, 10:42 AM   #35
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DC to DC Converters

From experience with 4 different tow vehicles which we've owned, and from my professional discipline having an MSEE, one needs to understand the issues of battery charging. It is rather complex.

A factory configured tow vehicle will have a LARGER alternator than a non-configured tow vehicle. Yes, typically one will have to install a fuse in the fuse block provided for the 12 V line to the 7 pin connector for the trailer.

Depending on the amperage load required by the trailer, there will be some amount of voltage drop, increasing with current demands, through the wiring and connector. This is known as IR loss. The voltage drop is equal to the current multiplied by the resistance. Every connector in the path has some amount of loss. Even there is some voltage drop across the fuse in the fuse block for this line. Again, nothing is free.

A second point is a fact there is nothing free. Thus the input power to the DC to DC converter is actually GREATER than the output power of the converter. Power is defined as voltes times amps which equal watts. Yes, it does boost the voltage on the output which is to overcome the IR loss in the wiring and connectors from the DC source being the tow vehicle battery or alternator, to the trailer batteries.

With our present tow vehicle with its factory tow package, when the TOW MODE is engaged, the alternator output is maintained at a higher output level. The typical buss voltage is 14.6 volts. Otherwise, in the normal mode, the alternator output is reduced to improve fuel efficiency. In some vehicles when the accelerator is rapidly or fully depressed, as in a passing condition, the alternator is effectively shut off to allow more engine power to be available for the passing situation.

If one is a driver that is constantly patting the accelerator, you are most likely disconnecting the alternator during the acceleration pats. DON'T DO THIS! You are correct, your trailer batteries won't likely get charged while driving. This is not the vehicle, not the alternator, not the wiring, it is the driver's habits causing this issue.

If the DC to DC converter supplies 14.4 volts at 30 amps to the battery, via the 7 pin connector, this is 432 watts. The demand from the alternator to the input of the DC to DC converter will be about 20% more, as they are not 100% efficient, such as an input of 13.6 volts at 38 amps for 517 watts. All the DC to DC converter is doing is making up for the IR loss in the wiring. The loss still exists and manifests as heat.

Due to different battery chemistry, AGM, Li-ion, wet cell, etc. will require different charging voltages to attain 100% charge. IR loss is a voltage drop between point A and point B. Yes, manufacturers could use or install a larger gauge wire for this purpose, but at additional cost to us consumers. Oh, that DC to DC converter one just added, that is an additional cost.
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Old 04-06-2022, 01:25 PM   #36
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A factory configured tow vehicle will have a LARGER alternator than a non-configured tow vehicle. Yes, typically one will have to install a fuse in the fuse block provided for the 12 V line to the 7 pin connector for the trailer.
I wonder if your run of the mill family SUV would add a larger alternator to their tow package? It seems from the description that I read that it is a "smart" alternator and getting on and off the accelerator does indeed impact charging. I don't even think that it comes with a "tow" mode. I think most drive it in "smart" mode while towing, so who knows what that means.
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Old 04-06-2022, 02:08 PM   #37
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Vehicle Specs

Look in the owner's manual for your specific vehicle. Most show different models and things about towing that one should know. Specifically in the specifications section.

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Old 04-06-2022, 05:34 PM   #38
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I do love a manual. Really. I’m that guy. which is also why I’m on forums trying to learn more before I am out on the road. There is nothing in the very short Specs section and the chapter on towing says get your dealer to install a hitch and follow your local laws. That’s about it. I appreciate the education that I am getting here. Thanks to everyone that has contributed. I still don’t feel 100% confident making a decision yet. I don’t like trial and error with a brand new vehicle. I guess my concerns are primarily around damage to the vehicle. If I drop in a 200ah-300ah battery will it damage my tv? Will it charge while driving? The vehicle damage is the bigger issue. I understand (I think) that the tv wiring will likely limit the charging of the lifepo batteries and protect the alternator. My electrical knowledge is meagre, but doesn’t that heat up the wire? That doesn’t seem like a good outcome to me. And if I add a dc-dc does that necessitate a heavier gauge wire directly to the battery which can now potentially damage my alternator? Do I need a dc-dc setup that can balance charging my lifepo’s with protecting the alternator and acting as an isolator when the vehicle is off? Will the electronics of the vehicle already be able to do this? I can sacrifice some charging for safeguarding the vehicle.
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Old 04-06-2022, 09:00 PM   #39
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Load measurement?

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Originally Posted by mmartin_tdc View Post
I recently converted to a 100ah Lifepo4 battery and decided to go with the 40amp Renogy DC to DC convertor.
I tested my trucks 7 pin and it put out 13.3v and 4.6 amps.
I then turned on the DC to DC charger (wired with 2g wire) and the same shunt based meter, registers 13.7v and 40.8amps. Now it will be charged back up within a 2 hour drive to the next site. ( assuming a 80% discharge on the batteries)
You indicated using a shunt-based meter. Did you connect the meter between the 12V line and ground with the meter set to read amps? If so, this is not a valid current measurement. You should connect the amp meter between the 12V terminal on the 7 pin connector and the same terminal on the trailer. This will then measure the current flowing from the source to the load. Voltage is measured from source to ground while amps are measured between source and load.

If you have an 80% discharge on the batteries, what exactly is this in reference? A full charge battery will show >12.6 volts. A battery at 80% discharge will show ~11.6 volts. This is below the recommended discharge value and is in the area where battery damage can occur. Repeated discharge to this level will shorten battery life. A battery should not be discharged below 12.0 volts which is 45%.
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Old 04-06-2022, 09:14 PM   #40
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You indicated using a shunt-based meter. Did you connect the meter between the 12V line and ground with the meter set to read amps? If so, this is not a valid current measurement. You should connect the amp meter between the 12V terminal on the 7 pin connector and the same terminal on the trailer. This will then measure the current flowing from the source to the load. Voltage is measured from source to ground while amps are measured between source and load.

If you have an 80% discharge on the batteries, what exactly is this in reference? A full charge battery will show >12.6 volts. A battery at 80% discharge will show ~11.6 volts. This is below the recommended discharge value and is in the area where battery damage can occur. Repeated discharge to this level will shorten battery life. A battery should not be discharged below 12.0 volts which is 45%.
My guess is he is using a shunt based columb counter like a bmv712. Since he converted to lithium, voltage is fairly useless to compute charge levels. You have to count everything going in and out.
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