TV Alternator configuration question

[BigSky]

I am buying a new 3/4 T TV to pull a new 25 ft Trade Wind. The GMC 2500 options are to have a single 170 amp alternator, upgrade to a 220 amp unit, or install both, with the 220 amp being primary and the 170 amp being secondary.

My goal is to extend the boondocking capability as long as possible by being able to fully charge the trailer battery pack from the TV either while driving or while parked.

With that said, which of those alternator configuration options would be best for this use?

I want to get the initial TV purchase configuration correct, so appreciate any and all input on this, or other advice on the best electrical system (including solar and battery) configuration.

Thanks!

[BGClassic]

That sounds familiar. I ordered our F350 with a 390A alternator option. The truck has two alternators. I have not yet added a DC-DC converter/charger, but have the capability.

It won't put a whole lot of charge into the batteries while driving, but will help. I don't know if I'd want to idle the TV engine to charge batteries, though.

I like my 3000VA generator and 400Ah battery bank. Your Trade Wind should have a large bank, correct? Solar? I think the portable generator makes more sense, personally.

[ROBERT CROSS]

Simplest answer...buy a dual-fuel generator.
We've used ours for 15 yrs...still happy.

Bob
🇺🇸

[Wazbro]

If you're planning on idling your TV to charge the trailer realize prolonged idling is one of the worst things you can do to an engine and it is worse for diesels then it is for gas engines.

[KeithT]

If you want the most I’d get the twin alternators just to be safe. Put two Victron Orion 50 amp dc-dc chargers and the appropriate wire and you should get 100 amps (1200+ watts?) of charging while driving. Sounds like you’d have plenty of headroom with your alternators and not have to worry about overloading the system. Could maybe do 150?

If you are hiring someone to do the work I would talk to them before ordering the truck. The installer will likely know more than what you will find here.

I assume idling would be a last resort sort of thing, not something you’d plan on doing.

[foobar]

My 2024 F350 has:

1) 150A, 24v alternator dedicated to the 2kw propower 120v inverter system (150A * 24v = 3600w peak power, less at reduced rpm)

2) 250A, 12v alternator (3000w peak power, less at reduced rpm)

My Airstream has an additional smartplug on the battery box, a 1320ah lithium battery bank, a victron 3kw multiplus (with a built-in 120A battery charger), and an automatic transfer switch to switch between the standard shore power smartplug and the new smartplug on the battery box. The smartplug on the battery box is connected to the truck via a short 10gauge pigtail. The pigtail connects to a weatherproof nema receptacle on the truck that is fed from the propower outlet in truck bed.

I also added a set of three, 50A victron orion xs dc-dc units in the trailer for a high current dc charging capability. These are connected to the 1320ah battery bank via 1/0 welding cable. They connect to the truck via a 1/0 pigtail using Anderson SB250 connectors. I routed 1/0 welding cable to the f350 battery terminals through a high current solid state relay (the relay is enabled or disabled via an upfitter switch). There are a bunch of resettable marine grade breakers throughout this installation to protect all of the wiring segments, but I didn't describe those to keep the system description simpler.

So using the above equipment, I take advantage of both of the F350's alternator capacities.

Using the 2kw propower, I feed 120v to the Airstream's 3kw multiplus. The multiplus can either pass the 120v through to the 120v inverter output to directly drive hvac units or microwave, etc., or it can generate up to 120A of charge current for the battery bank (or some combination of both capabilities).

Using the high current dc-dc capability, I can supply another 150A of charge current to the battery bank.

My orion xs on the 7 pin interface can contribute another 20A of charge current and the 800w Solar array on the Airstream roof can contribute up to 65A of additional charging current.

In total, I can generate 120A (multiplus) + 150A (dc-dc's) + 20A (7-pin plug) + 66A (solar) = 356 Amps

The 1320ah battery bank can accept up to 0.5C in terms of continuous charge current without degrading the batteries for a max charging limit of 660A. So my 356Amps of charging capability is perfectly safe.

Not counting on solar input, I can restore approx 300ah of battery capacity per hour of driving.

Given the total capacity of our battery bank, we can last around 6-7 days without any solar recharging while we usually run out of water or fill up the grey tank in 5-6 days. The net result is we almost never need to charge while camping (so the truck is almost never tasked with charging while idling). I.e. we nearly always charge up when towing instead.

We typically drive 3-4hrs between camping locations, so we can restore 900 - 1200ah between each campsite.

In addition, we now have enough charging capacity to run 1 a/c (1600watts) in parallel with supplying 200A of charge current to the battery bank. This is a game changer for us. We can run an a/c while on the road during hot weather so we arrive with a cool trailer instead of having to wait for hours for both a/c's to try and cool down the thermal mass of the entire trailer). We are using this capability right now as we move between campsites in 95-97F weather. The trailer stays at 75-77F for the duration of the tow. Makes lunch stops quite pleasant.

FYI, Our diesel f350 alternators can generate the peak alternator output at the cruising rpm of around 1200rpm (redline on the F350 is 4000rpm). If we need to charge the trailer batteries while camping, the trucks electronics automatically sense the load on the smart alternators and adjust the rpm at idle to match the alternator load. At the full alternator load our charging apparatus places on our truck, the truck ramps up the rpm to 1100.

I hope this information is helpful.

[foobar]

To directly answer the original question, get the highest total alternator capacity option you can purchase. This will provide higher output capacity at lower rpm without overstressing the alternator.

With 410A capacity, you can comfortably extract up to 200A at reasonable rpm using dc-dc's.

[richard5933]

Automotive alternators don't like to be used at/near their capacity for too long - this causes heat and heat destroys them.

Best is to have plenty of excess capacity, which seems to be done here by installing both alternators. With the dual system you can run a pair of dedicated 4ga or 6 ga wires to the rear bumper of the TV and use that to power a DC-to-DC charger in the trailer. You'd be able to dump lots of charge into the trailer's batteries quickly this way without any noticeable effect on the TV.

Also, if you had to idle to charge the trailer having the dedicated second alternator dumping high amperage into the trailer batteries would drastically minimize the needed idle time.

[27ftToaster]

You will need to run a separate pair of heavy duty cables with a circuit breaker, from your one of your truck batteries to an Anderson Connector at your hitch, then continue from your hitch to your Shunt (if you have one), then your DC-DC charger, and then to your battery bank. Due to the length of the required cable runs, you will need no smaller than 2 gauge wiring for the 50A DC-DC charger. If you want to charge faster, you'll need something like 1/0 gauge and two 50A DC-DC charges. I would highly recommend the Victron 50a chargers as they run cool. I have two 30A DC-DC chargers in parallel, and they run very hot. They are mounted to wood and will burn your fingers when touched.

Depending on your battery bank and how low your batteries are depleted, I have found my chargers, which produce typically about 50 amps (you won't generally get the max output) only takes two hours per 100ah. You didn't mention your battery capacity, so you can do the math. For me, if I am down to 25% of my 400ah, it takes about 6 hours of driving to fully charge. Less on a sunny day.

[dsatwork]

OP, I agree with all that say more power is better... choose all the above.

@Foobar You totally sidelined me and now I want to see your build, do you have a link to a post or blog for more info?

[foobar]

Originally Posted by dsatwork

OP, I agree with all that say more power is better... choose all the above.

@Foobar You totally sidelined me and now I want to see your build, do you have a link to a post or blog for more info?

Unfortunately, I haven't had the time to put together any info on the build.

I took a couple of photos of the truck to trailer power umbilicals this morning. See attached photos. I will try and remember to take a few more when we reach our campsite this afternoon in Nebraska.

The yellow connector in the photo is for the 120v power umbilical.

[dsatwork]

nice thanks for the info

[BigSky]

@foobar. Thank you for that reply and the follow-up photos. That sounds and looks exactly like the build I was dreaming of doing. Any idea of the cost? Sounds like you did the work yourself - how many hours have you put into this?

Anything you would change if you did this again?

Again, thank you for sharing!

[foobar]

Hi dsatwork and BigSky, I designed the system and specified the components but I worked with Graham Carr at gcrvupgrades to implement the bulk of the system. He did an excellent job with the implementation

I have some additional photos of portions of the system.

Graham fabricated a T fuse holder and welded it to the top of one of the two battery holders in the engine bay. This fuse protects the 1/0 welding cable in the truck and the umbilical to the trailer. The first couple of photos cover that.

Next, the solid state relay is mounted under the passenger side of the F350 to the truck frame. It's looking pretty grimy, but the relay and its terminals are sealed tightly.

The three 50amp Orion xs dc-dc chargers on my high current 12v dc system are mounted under the curbside twin bed in the front corner along with the 4th orion xs charger on the 7 pin interface. This is where Airstream put the 12v dc wiring mess in my trailer (everything has been cleaned up and organized st this point). Note: All 4 orions have heat sinks and are mounted vertically on the inner aluminum shell for heat dissipation purposes. Unfortunately, I don't have a photo of this dc wiring compartment hsndy.

The 150Amp 12v dc umbilical feeds the three Orion xs units via a busbar in the old dc wiring compartment. 4 gauge wire is used from the busbar to each orion xs unit. 50 Amp resettable breakers protect each 4 gauge wire. These breakers are located in the front storage compartment above the battery box (see photo).

The output of each orion feeds another busbar from which another 1/0 welding cable carries the combined output (150Amps) to the battery bank via a 250A resettable marine grade breaker to protect the final 1/0 cable run to the battery. You can spot this breaker above the batteries in next to the last photo. The batteries and the multiplus are located under rear lounge seating above the rear axle next to the bulkhead by the fridge.

The last photo is a screenshot of my phones vrm screen showing over 3kw of charge power being supplied to my battery bank (solar + multiplus charger + 7-pin orion xs charger + 3x orion xs dc-dc's). The 1320ah battery bank started at 60% capacity. 2.5hours of towing later, the battery bank was fully charged (528ah was restored to the bank).

We are on the way to BC in Canada to join up with the 2025 Airstream Club Alaska Caravan. The charging system is performing flawlessly (this is our first opportunity to really try it out and stress test it).

[RedSHED]

Engineering that involves enough energy to give you "the new look" is kind of a buzz. A couple hundred amps at 15-16v is that kind of energy.

If something gets chafed, a bolt vibrates loose, or a big part of the load gets dumped in a hurry for some other reason, you have just a handful of milliseconds to break down the field. I don't recommend this as a promising area for home-brew. Not saying it cannot be done, but ... dang.

Anyway, 220 ought to be plenty for most RV use.

Here are some thoughts

1. The tow vehicle will draw something like 20 amps at idle without a big light or HVAC load.
2. The big dual alternators are mostly for a) emergency vehicles like ambulances, b) something with a lot of lights and a big load. Typically a snowplow. For RVs a dual system is most often a "want" rather than a need. I believe a KW day cab has 1x170A.
3. The alternator ratings are at specific hub speeds and temperatures. A nominal 220A alternator may only deliver 150A at idle on a really hot day. There will be a 30-40A difference based on temperature.
4. After a start at -40, you might find 2x220A producing as much as 450-460A at 15-ish volts and 1000 engine RPM (assuming a 3:1 pulley ratio if memory serves). Dump a bunch of load at that point and it'll probably get weird, and maybe expensive or worse.

[richard5933]

Originally Posted by RedSHED

Engineering that involves enough energy to give you "the new look" is kind of a buzz. A couple hundred amps at 15-16v is that kind of energy.

If something gets chafed, a bolt vibrates loose, or a big part of the load gets dumped in a hurry for some other reason, you have just a handful of milliseconds to break down the field. I don't recommend this as a promising area for home-brew. Not saying it cannot be done, but ... dang.

Anyway, 220 ought to be plenty for most RV use.

Here are some thoughts

1. The tow vehicle will draw something like 20 amps at idle without a big light or HVAC load.
2. The big dual alternators are mostly for a) emergency vehicles like ambulances, b) something with a lot of lights and a big load. Typically a snowplow. For RVs a dual system is most often a "want" rather than a need. I believe a KW day cab has 1x170A.
3. The alternator ratings are at specific hub speeds and temperatures. A nominal 220A alternator may only deliver 150A at idle on a really hot day. There will be a 30-40A difference based on temperature.
4. After a start at -40, you might find 2x220A producing as much as 450-460A at 15-ish volts and 1000 engine RPM (assuming a 3:1 pulley ratio if memory serves). Dump a bunch of load at that point and it'll probably get weird, and maybe expensive or worse.

I think that it's important to remember that the load at idle is not really the concern here, as most vehicles will have a minimal load at idle.

Modern vehicles have some heavy-draw circuits that didn't exist a few years ago. The ABS braking system can pull a heavy load when activating, the new electric-assist power steering systems, lighting, HVAC systems, etc. all add up to quite a load on the truck's alternator. When larger systems are operating the stock alternator may be running with only 20-30 amps to spare.

If a vehicle has a factory option for a second alternator, then to me it's a no-brainer to get it and set up the system to maximize capacity and to make sure that it runs with as much head room as possible. Electronic equipment will last much longer when not run at/near its upper limits.

Being able to add a second battery and/or alternator is nothing new. My 1999 Suburban K2500 has the ability, and all that was necessary to properly upsize the system was to get the factory-option heavy-duty wiring harness for the alternator setup. This allowed the larger alternator install with higher charging capacity. Nothing homemade was necessary.

There are people wanting to run DC-to-DC charging systems nowadays that can quickly dump a high-current charge to a large lithium battery bank, and having the second dedicated alternator is a great way to do this without overtaxing the TV's alternator.

[RedSHED]

Originally Posted by richard5933

I think that it's important to remember that the load at idle is not really the concern here, as most vehicles will have a minimal load at idle.

Right. So a small alternator is fine for nearly all circumstances. The normal architecture has all the electrical load coming from the battery - any alternators exist to keep the vehicle's battery or batteries at a stable voltage. The alternator may be controlled the engine controller or some other box. This is because of sound engineering Reasons. Lots of them.

Electronic equipment will last much longer when not run at/near its upper limits.

Being able to add a second battery and/or alternator is nothing new. My 1999 Suburban K2500 has the ability, and all that was necessary to properly upsize the system was to get the factory-option heavy-duty wiring harness for the alternator setup. This allowed the larger alternator install with higher charging capacity. Nothing homemade was necessary.

There are people wanting to run DC-to-DC charging systems nowadays that can quickly dump a high-current charge to a large lithium battery bank, and having the second dedicated alternator is a great way to do this without overtaxing the TV's alternator.

If you have a dedicated second alternator that's part of the vehicle's system, it's going to send power to the battery or batteries. If it does not, you'll hope there's a fault code. Example: suppose the #2 spins a pulley in the summer. You'd want to know before you mount the snowplow and it's 10 below.

On the other hand, if it's something home-brewed, then it isn't a part of the OEM's system.

IMO it is most healthy to think of these things as a plasma cutter that you spool up and set loose.

They will bite hard if you let them.

[highheat7]

not to put you on the spot, but approximately how much did that build out cost?

[pboomerx]

Originally Posted by BigSky

I am buying a new 3/4 T TV to pull a new 25 ft Trade Wind. The GMC 2500 options are to have a single 170 amp alternator, upgrade to a 220 amp unit, or install both, with the 220 amp being primary and the 170 amp being secondary.

My goal is to extend the boondocking capability as long as possible by being able to fully charge the trailer battery pack from the TV either while driving or while parked.

With that said, which of those alternator configuration options would be best for this use?

I want to get the initial TV purchase configuration correct, so appreciate any and all input on this, or other advice on the best electrical system (including solar and battery) configuration.

Thanks!

I bought mine with max alternator capacity
Charging via 40A dc to dc converter no problem

Cost on option sheet is negligible considering overall vehicle cost

[TLowe43q]

I’ll bet others have commented on this, but very little current passes to the battery through the 7-pin while underway. I have nothing specific, but 5 amps is probably about it. Don’t count on TV charging unless you go with a DC-DC charger and special wiring/connectors …