Charging - Auxiliary Alternator vs. DC-DC/B2B. Which is Better?

[Vance Vanz]

Hi All,

I will be starting my complete build this coming winter 2022, similar specs to an EarthRoamer LTi. We will eventually be traveling from Alaska to South America if COVID permits-full time living in the rig for 18-24 months.

I have already read many of the threads in the “Power Systems” section of this forum and did a bit of digging online. Maybe I already know the answer to my question (Auxiliary Alternator is the best choice given my power system), but I would like some additional clarity on the pros/cons, or which is better, related to charging a 900Ah lithium battery bank using an additional auxiliary alternator or a DC-DC/B2B charger.

I’ve already owned a camper van with a similar off grid power system, slightly smaller, and it had an auxiliary alternator. I know most of the custom build shops in the campervan industry pretty much only run auxiliary alternators for lithium offgrid power systems. It appears that most DIY’s in the Expedition Portal prefer/are running the DC-DC charges. Given my power requirements, and need to primarily charge when driving, I’m assuming the auxiliary alternator is best. Please educate me if I’m missing something.

Truck:
2022 F550 Lariat, 7.3L Gas, 397A dual alternator, 78A dual battery.

Significant Electrical Specs-Camper:
900Ah lithium battery bank, 12-1,300W solar, A/C unit, Induction cooktop, fridge/freezer, combo microwave/convection oven, puck/under cabinet lighting. Heating/hot water will be off of gasoline (Rixon unit) from the truck, or shore power if present. No generator or LP. This will be an offgrid system, all electric, except for the few items noted coming off of gasoline. We are not planning on using much if any shore power.

Auxiliary Alternator:
I’m currently looking at the Nations kit, 280A [$1,999] or 370A [$2,199] alternator, which comes with a MC-614-H Balmar regulator/temp sensor and all the additional/needed mounting brackets, belts, etc. I’m open to other alternators/kits that anyone may be aware of and recommendations on the 280A or 370A noted above.

DC-DC/B2B:
It appears Sterling (Waterproof 12-12V 120A IP68) has the highest rated DC-DC/B2B charger, 120A, and you can wire two of them together to get a total of 240A [$625 x 2 = $1,250]. I’m also open to other/higher rated DC-DC/B2B charges that anyone may be aware of.

Thanks in advance for your time and wisdom !

 

[Rando]

In theory anyway an auxiliary alternator is a way better solution. A DC-DC charger is a kludge to adapt an unsuitable power source to power/charge a battery bank, they add inefficiency, complexity and cost to a system. An alternator with the correct controller to produce the charge profile you want is a far more elegant solution.

Now on the practical side, I don't know who actually makes a good programmable alternator or alternator regulator, but I am sure someone in the ExPo brain trust does.

The funny thing is, almost all current automotive alternators are digitally controlled (via LIN or the like) so it would take about $20 in parts and a week or two of coding to build a 'smart alternator charge controller' that would allow you to dial in the correct charge profile for your house battery to any old automotive alternator.

 

[DiploStrat]

Define "better."

Couple of thotz:

-- Your specs are way beyond what would ever be needed to cross South America, or Africa, for that matter. 400-600Ah of lead acid would do it all. Lithium has lots of advantages, but it is not required. And, full disclosure, I built an 800Ah lithium battery for my truck.

-- Most 12v air conditioners pull between 50 and 75A when the compressor is running and the compressor typically runs between 50 and 75% of the time. Naturally, there are lots of variables, but running an air condititioner can easily draw 300-600 Ah, depending on conditions.
That is a LOT of recharge, no matter how you do it. Especially as more and more lithium manufacturers are calling for lower charging rates.

-- 1500w of solar hits a kind of sweet spot. 75A of charge against a 50A load would keep you ahead of the game for a few hours in good sun. Probably the only way to get this on a 550/5500 format vehicle is with a double layer of solar panels. (A great idea, BTW.)

-- Assuming a proper mounting, proper belts, af 100% duty cycle rated alternator, and a proper regulator that controls alternator heat (at least) - then I would go with a dedicated alternator. Several respected builders are doing this. Sadly, it appears to be next to impossible to separate the two alternators of a factory dual alternator setup, so you are looking at a bracket for a third alternator.

-- Failing any of the criteria above, then a B2B is probably the safest and most effective way to charge lithium with a stock alternator set up.

Take air conditioning out of the equation and all of this is really easy.

As with all of this, YMMV, I am merely recounting from my five years of doing what you are planning.

 

[shirk]

Have a look at what these guys are doing to control alternator and handle bi-directional DC-DC.

DC DC Digital Switching Lithium Battery - Safiery | Efficient Power Conversion

Discover the power of DC DC digital switching with Safiery's Lithium battery solution. Enhance your power conversion with Victron technology. Continue reading for more details.

www.safiery.com

Wakespeed seem to have the same unit called the WS3000R listed on their 2021 pricelist pdf.

Wakespeed Charge Smarter - Wakespeed

Intelligent Engine-BasedCharge Control Wakespeed is leading the charge in RV, marine, and commercial transportation applications. Offering smart DC charge control systems, Wakespeed’s advanced alternator regulator, the WS500, is the first of its kind and delivers unsurpassed quality and...

wakespeed.com

The Safiery site has good info outlining a hybrid 48v-12v system and how it better handles these modern requirements for induction/AC/fridge-freezer/icemaker/coffee.

 

[Vance Vanz]

In theory anyway an auxiliary alternator is a way better solution. A DC-DC charger is a kludge to adapt an unsuitable power source to power/charge a battery bank, they add inefficiency, complexity and cost to a system. An alternator with the correct controller to produce the charge profile you want is a far more elegant solution.

Now on the practical side, I don't know who actually makes a good programmable alternator or alternator regulator, but I am sure someone in the ExPo brain trust does.

The funny thing is, almost all current automotive alternators are digitally controlled (via LIN or the like) so it would take about $20 in parts and a week or two of coding to build a 'smart alternator charge controller' that would allow you to dial in the correct charge profile for your house battery to any old automotive alternator.

Hi Rando,

Thanks for your input related to the recommendation of going with the alternator. Yes, hopefully the Expo brain trust will provide various options of alternator setups they are using. I'm going to do some more digging myself.

 

[Vance Vanz]

900Ah of lithium can draw a huge current. I suggest dedicated alternator.
Leave the truck system more or less alone and reliable.
Fwiw,
My big camper, I use two alternators. Its oldschool 24V Army truck. For economy I went 12V for the house systems.
In off chance one system or the other craps out, Its still workable to operate both systems from one alternator until proper repairs can happen.

Thanks Verkstad. I will definitely leave the factory setup alone if using an auxiliary alternator.

 

[Vance Vanz]

Define "better."

Couple of thotz:

-- Your specs are way beyond what would ever be needed to cross South America, or Africa, for that matter. 400-600Ah of lead acid would do it all. Lithium has lots of advantages, but it is not required. And, full disclosure, I built an 800Ah lithium battery for my truck.

-- Most 12v air conditioners pull between 50 and 75A when the compressor is running and the compressor typically runs between 50 and 75% of the time. Naturally, there are lots of variables, but running an air condititioner can easily draw 300-600 Ah, depending on conditions.
That is a LOT of recharge, no matter how you do it. Especially as more and more lithium manufacturers are calling for lower charging rates.

-- 1500w of solar hits a kind of sweet spot. 75A of charge against a 50A load would keep you ahead of the game for a few hours in good sun. Probably the only way to get this on a 550/5500 format vehicle is with a double layer of solar panels. (A great idea, BTW.)

-- Assuming a proper mounting, proper belts, af 100% duty cycle rated alternator, and a proper regulator that controls alternator heat (at least) - then I would go with a dedicated alternator. Several respected builders are doing this. Sadly, it appears to be next to impossible to separate the two alternators of a factory dual alternator setup, so you are looking at a bracket for a third alternator.

-- Failing any of the criteria above, then a B2B is probably the safest and most effective way to charge lithium with a stock alternator set up.

Take air conditioning out of the equation and all of this is really easy.

As will all of this, YMMV, I am merely recounting from my five years of doing what you are planning.

Thanks for the reply and information DiploStrat.

I know "better" is subjective and relative to the specific system and personal preference.

900Ah is pushing the excessive side. We have always ran with a 600Ah system in the past. Since we will be in this things full time, have the weight capacity, funds, want to run the A/C when we need it, are going with a slightly bigger fridge/freezer than our old build and may be plopped down at a surf break for 5-7 days at a time without moving, we wanted a little extra cushion.

Thanks for the input on the solar. We are planning on running a slide out/stacked solar panel arrangement to conserve on space and make sure we don't cut ourselves short. Seems like you can never have too much solar .

Seems like the auxiliary alternator is the way to go, just need to get more input from others related to those they are specifically running and/or recommend.

5 years, good on you; I'm jealous!

 

[Vance Vanz]

Have a look at what these guys are doing to control alternator and handle bi-directional DC-DC.

DC DC Digital Switching Lithium Battery - Safiery | Efficient Power Conversion

Discover the power of DC DC digital switching with Safiery's Lithium battery solution. Enhance your power conversion with Victron technology. Continue reading for more details.

www.safiery.com

Wakespeed seem to have the same unit called the WS3000R listed on their 2021 pricelist pdf.

Wakespeed Charge Smarter - Wakespeed

Intelligent Engine-BasedCharge Control Wakespeed is leading the charge in RV, marine, and commercial transportation applications. Offering smart DC charge control systems, Wakespeed’s advanced alternator regulator, the WS500, is the first of its kind and delivers unsurpassed quality and...

wakespeed.com

The Safiery site has good info outlining a hybrid 48v-12v system and how it better handles these modern requirements for induction/AC/fridge-freezer/icemaker/coffee.

Hi Shirk,

Thanks so much for passing this along. Looks like I've got some reading to do . I'll check em out.

 

[john61ct]

Only read the title.

Not either or.

DC-DC is needed for LFP.

Extra alt is likely not needed, unless it delivers a higher rate, the DC-DC is not a limiting factor

and that higher rate is actually needed.

 

[Vance Vanz]

Hi All,

I thought I would add some additional information to the post after doing a bit more digging.

I contacted Safiery and Wakespeed (Thanks Shirk) related to their DC-DC/B2B equivalent alternator chargers, Scotty and WS300R respectively. Given my power system, they and several other vendors I spoke with recommended going with an auxiliary alternator as opposed to a DC-DC/B2B charger.

After speaking with Wakespeed related to an auxiliary alternator, they recommended their WS500 alternator regulator as an alternative to the Balmar MC-614 charge regulator. In addition to a temp sensor for the alternator and batteries, the WS500 can also monitor voltage, amps and receive input from the batteries/BMS via CANbus. An alternator charge regulator, in conjunction with a smart BMS, addresses the major concerns of running an auxiliary alternator: 1. Alternator overheating 2. Alternator rectifier diodes failing because of over voltage after disconnect by a BMS. 3. Rush/overcharging the batteries and shortening their lifespan. If anyone knows of any other reputable alternator charge regulators to consider, please chime in.

Now for auxiliary alternators with associated mounting kits for a F550:

1. Nations Alternators, has been previously noted. It is my understanding that they offer 12, 24 and 48V options and can incorporate the Wakespeed or Balmar charge regulators. (Still waiting on confirmation from Nations related to 24 and 48V options, but several other vendors have told me they offer them-will update once known)
2. American Power Systems, also has 12, 24 and 48V options, can incorporate the Wakespeed or Balmar charge regulators and has a mounting kit.
3. Mechman, currently does not offer an alternator for anything bigger than a F350
4. Balmar, can't find a vendor with a larger alternator and associated mounting kit for a F550

If anyone knows of any other reputable alternators and/or mounting kits for a F550, please join the party!

 

[RAM5500 CAMPERTHING]

I am mostly done building a similar rig (2020 Ram5500) for similar purposes...

I've been doing this 20 years + and have learned many things along the way, often the hard and expensive way, or though friends failures.

My opinion usually isnt the popular one, and i am perfectly fine with that. I've done all of Mexico, Arctic on a bike. Arctic in a truck, bla bla bla.

Key to all of this is K.I.S.S.

My original plan was for 900ah lithium.

I have the Houghton Bel Aire Air Conditioner, Isotemp electric Water heater, tru-induction dual cook top, huge 105L fridge (that hasnt been shut off since i installed it, true story), and a 1500 watt convection microwave oven. Everything in my rig is setup to be electric except for the furnace (diesel).

I started with one 300ah lithium, and built everything to house the other 2 batteried at a later date. More on that later...

You can look at paper specs, crunch numbers and such until you are blue in the face, but the real world #s often dont match them, if ever...

I ordered my truck with dual alts (440amps) also, with plan of using one for the house and one for the truck. As @DiploStrat (hes very smart) said, its basically impossible to separate the 2 in a modern vehicle.

I debated how i wanted to approach charging the house batteries for quite awhile, end of the day, i wanted it to be easy as possible for back country repairs.

I eventually decided on a Sterling 60amp (they also make them in 120amp version) B2B charger, over a 3rd alternator, for a variety of reasons:

1. Reliabilty: Sterling has been around a LONG time, and is well known all throughout the world for their products. I've seen MANY MANY high output fancy big $ alternators fail in the field over the years. No one will ever change my mind on this spouting paper specs and claims of lifetime warranties and such. Good luck with a lifetime warranty claim in South America.
2. Cost: The 60amp unit was around $500. Almost half of what a fancy pants alternator addition kit would cost. Cost wasnt a huge deal for this build, as its my midlife crisis so i am going all in to do it right, but i can buy a spare Sterling and carry with me on long trips and be ahead of the game in case of failure.
3. Simplicity: The install is super easy and can be mounted wherever you'd like. Mine is mounted inside the habitat, and if by some chance it failed, it could be swapped out in 5 minutes, literally.
4. Programmability: The Sterling can be easily programmed for any charging profile you need and fine tuned as needed.

I built my system with (2) 375watt LG residential panels wired in series to a victron 3000 multiplus inverter/charger and Victron componentry throughout.

I now have 22 days/nights in the camper, using the AC, hot water heater, induction stove, microwave, etc excessively to test my system/needs and move along accordingly with the build.

I havent got my single 300ah battery below 30% even with all the heavy appliance usage. The solar gets it up to charge fast.

I timed leaving camp with 50% battery power to how long the B2B gets it all back to 100% while driving, and it was a little more than 2.5 hours. And thats just the 60amp version. They also make the 120amp version.

Here are my .02 so far:

- Yes the AC uses a lot of power, but i only need to run it on high for an hour or 2 and the box is nice and chilly comfortable for 5-6 hours in 90 degree heat. Insulation is key!
- Yes, the induction stove uses a lot of power, but there aren't many meals on earth that take more than 15 mins or so of run time, so its a minimal draw in the grand scheme of things.
- Hot water heater takes about 45 minutes to get 4.5 gallons of water to damn near scalding temps. Its a power suck, but short draws have minimal impact.

So yeah, a lot of these things draw a lot of power, but the times they are drawing that power are fairly short, and dont have as much of an impact as you'd think. Both the AC and Water Heater draw a little bit more that HALF of what their specs state, just an FYI.

As of now, for ME, my 300ah lithium has been sufficient. I am going to add a second 300ah for a total of 600ah, but 900ah definitely isnt needed. In fact, i am only adding the second 300ah for redundancy in case the other one fails.

My link below to my videos cover all the appliances i used, etc....

I look forward to following along your build. Any questions, feel free

My bottom line unsolicited opinion is, for a truck you plan on taking South America, etc, some fancy specialty alternator that would be hard to source down there sounds like a bad idea

If you're dead set on adding a third alternator, i would HIGHLY HIGHLY suggest sticking with OEM instead of aftermarket. I cant stress this enough. OEM alternators, even the high amp ones generally last 10+ years without issue. I would take this all day any day over some aftermarket one with claims of higher output.

 

[RAM5500 CAMPERTHING]

1. Mechman, currently does not offer an alternator for anything bigger than a F350
2. Balmar, can't find a vendor with a larger alternator and associated mounting kit for a F550

If anyone knows of any other reputable alternators and/or mounting kits for a F550, please join the party!

Many companies just stop their parts listings at the 350/3500 range due to popularity.

I can say for a fact, the Ram 3500 and Ram 5500 use the same alternators, mounting, etc... Its the same motor, and electronics...

I am willing to bet a cold beverage Ford is the same

 

[vtsoundman]

Look for the ambulance/tow truck/commercial duty upfitters for alternator solution. American Power Solutions is one such company.

A separate DC/DC is not reqd if you have a programmable alternator controller/dedicated alternator (like a balmer).

Are you trying to run the DC a
A/C while driving?

If so two sol'ns:
1) Run the AC off the batt bank, then connect the aux alternator to the main battery bank - the balmer unit will reduce the alternator field current to keep it from cooking.

2) 75-100A is not a large load for a dual F550 alternator setup. running the DC AirCon off the factory system is easy.

However, why are you looking at a 3rd alternator??

If you really do have dual 200A factory Alternators, go with 2-3 DC/DC converters in parallel....unless you plan on driving your large battery bank to very low SoC and absolutely must charge it backup within a few hours. I'm partial to Kisae DMT1250 - it is a 50A unit and also has a built in MPPT solar input. The alternator driving side can be parallel, but the solar cannot (the output can be tied together, but the the inputs of the MPPT converters must be kept separate. This is great b/c you can run multiple mini arrays).

The factory already figured out these things are going to be loaded for hours on end...f550 dual alt kits are geared towards severe duty (which lithium batts are)...a 900Ah 12V bank is kind of odd - why? You should be looking at higher voltages for that large of a system - better efficiencies, less cabling and fusing, etc



Sent from my Pixel 4a using Tapatalk

 

[Vance Vanz]

Hi RAM5500 CAMPERTHING,

Thanks for the information and data related to what you are experiencing in the field. I've followed your build and have learned lots from it. There is a bit of a debate on 600Ah or 800-900Ah, which is the sweet spot or overkill, for this type of build. 600Ah would be the minimum and 800-900Ah the maximum. We had a similar build in a campervan, to what we are doing in the F550. 600Ah was not enough, but that was in a campervan which basically has no insulation, no matter how you try and insulate it .

 

[Vance Vanz]

Hi vtsoundman,

Thanks for the input.

I'm not trying to run A/C while driving, just want to be able to charge the battery bank quickly when driving, 3-4 hour range.

A third alternator is an option to keep the factory system and house system separate. The 397A total dual alternators are designed to handle all the loads of the truck and some additional accessories, but Ford does not recommend pulling more than 60-80A off the factory alternators. This is not enough reserve in the alternators to charge my battery bank using a DC-DC charger(s) at the rates I would like.

Running a higher voltage output for the auxiliary alternator is an option and can be a good idea for efficiency purposes, costs savings etc., but Ive decided to stick with a 12V system for many reasons.