How to charge a 48V Battery Bank (for Solar efficiency) with an alternator???

[tmckenna]

Hey guys, currently have a pretty simple setup with on 300ah LifePO4 and an Amazon inverter, but am in the planning phases of my "final" configuration. I was originally planning on doing a 48V battery bank for the solar benefits (more wattage potential) and using a Daygreen DC to DC converter to power the DC circuits in the camper. But I will be purchasing an older 7.3 Ford which you can get pretty beefy alternators for, I've seen up to 390A.

Now my question is that, because obviously the alternator is putting out 12V and my battery bank will be 48V how do you recommend getting the alternator to charge the camper battery. I've looked for 12V to 48V DC to DC converters and they don't support much current. If there is no answer and I have to choose between the 48V for the solar or 12V for the alternator thats fine, was just curious if there was a solution?

 

[HRTKD]

On my newer Ford diesel, the alternator "system" is rated for 390 amps. However, they don't both operate at the same time. One takes a break to cool off while the other runs. Maybe if the load is really heavy, they'll both run, but that's not how it works by default.

If you're talking aftermarket alternators, then that's a different matter.

I chose to stay with 12v for my camper. There's just too much 12v going on make the switch. If you're trying to run two or three air conditioners then the higher voltage battery and inverter is more appropriate.

 

[tmckenna]

On my newer Ford diesel, the alternator "system" is rated for 390 amps. However, they don't both operate at the same time. One takes a break to cool off while the other runs. Maybe if the load is really heavy, they'll both run, but that's not how it works by default.

If you're talking aftermarket alternators, then that's a different matter.

I chose to stay with 12v for my camper. There's just too much 12v going on make the switch. If you're trying to run two or three air conditioners then the higher voltage battery and inverter is more appropriate.

I'm planning on getting an older Ford diesel, specifically an F550 with the International 7.3 motor. There are a ton of aftermarket alternator options, anywhere from 200A to 390A. The reason I was considering doing a 48V battery bank in the first place was for the solar implications. Obviously most controllers are rated for the same current output at different voltages so you can get more watts out of the same charge controller if you do 24V or 48V over 12V. I hadn't even been thinking about alternator charging prior to a couple days ago so thats what raised this concern.

 

[HRTKD]

For what it's worth, I don't use the alternator charge at all for my 560 Ah LiFePO4 battery bank. My 640 watts of solar on the roof does the job nicely. If I need more charging while boondocking, I break out the 640 watts of ground deployable panels.

 

[rickst29]

I do something like this: ~13.5V (under the hood, it's NOT 12v) into a 36V voltage converter. 36V through the bargman "Trailer Battery Charge" wire, with return ground on the ground wire. In the Trailer, a detector Relay switches "high Voltage" on the Trail Battery Charge" ("TBC") to run through an MPPT controller, programmed for charging "12V" LFP batteries.

Right now, that detector Relay disconnects the Solar Panels while conneting the TBC as the "PV +" input to the MMPT. The MPPT handles the Voltage switch just fine, and tunes in the new power source very rapidly. With only one MPPT, I can't run genuine Solar and 36-volt "fake Solar" at simultaneously, but I could do that if I added a dedicated MPPT for the Tow Vehicle TBC connection.
- - -
My 36 regulating boost converter is rated for only 540 watts, and I don't run it even that hard. (I have the MPPT limited to 30A on output, with "Boost CV Voltage" limited to only 14.4V -- about 3.60 charging Voltage "per cell", before dropping to "float stage" 13.8V upon reaching at 13.5V on the pack as a whole (an avg. of 3.375 per cell). 432 maximum watts into the batteries is less than 490 from the Boost Converter (with MPPT conversion and wiring losses consuming up to 60 watts), it's not being strained.

In your configuration, you would need a regulating Boost Converter with 60 Volts on output (in order to provide sufficient over-voltage for an MPPT to feed a "48V" battery pack. MPPT requires MORE input voltage than the battery pack being charged. In any case, we're probably talking about only a few hundred watts (NOT amps) in a configuration like mine. The regular Bargeman cable can be used if you boost within the Tow Vehicle, and load the cable with less than 15 Amps of higher-voltage current. In my configuration, the "Boost" is controlled by an on-the-fly dashboard switch, which I only turn on when pulling my own Trailer. (For other Trailers, I leave the switch disabled, and TBC Voltage == TV "12V" Voltage of about 13.5V).

How many Watts are you hoping to provide to the Trailer, in this scheme? I recommend against a configuration without an MPPT controller on the path, with a "CV" power supply pushing the BMS with lots of amps possibly though and past a "full" SOC.

 

[Short_Shot]

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Only 18a @ 48v nominal output though. But that's nearly 1kw though at 55 ish volts or thereabouts (in not that familiar with 48v charging voltage to be fair).

I'd contact them about running more than one in parallel.

Otherwise you have the option of industrial units but they're vastly more expensive.

 

[tmckenna]

Any reason I shouldn't do the Battery Bank as 12V and just run a 48V to 12V converter off the solar charge controller?

 

[HRTKD]

Any reason I shouldn't do the Battery Bank as 12V and just run a 48V to 12V converter off the solar charge controller?

Yeah, that would be kind of silly. The solar charge controller needs to know the voltage of the battery. It will sense if it is dealing with 12v, 24 or 48v. On some solar charge controllers you can force the voltage setting.

The solar charge controller also needs to know when to stop charging because the battery is full. Hard to do that with a converter in the middle.

If you have a lot of solar panels, you can always use more than one solar charge controller, each with a dedicated string of panels. That's how mine is setup.

 

[tmckenna]

Yeah, that would be kind of silly. The solar charge controller needs to know the voltage of the battery. It will sense if it is dealing with 12v, 24 or 48v. On some solar charge controllers you can force the voltage setting.

The solar charge controller also needs to know when to stop charging because the battery is full. Hard to do that with a converter in the middle.

If you have a lot of solar panels, you can always use more than one solar charge controller, each with a dedicated string of panels. That's how mine is setup.

Yeh I just thought of that now, after making that reply. I realized the converters would probably negatively affect the way the charge controller could regulate the output to the battery.

Hm.

Seems as though there might not be solution, considering the Smart BMS I would use for the alternator circuit would have to go through a converter in the 48V battery bank configuration, or the charge controller would have to go through a converter in the 12V battery bank configuration. (Assuming I was using the victron Easy Solar II in both configurations).

 

[HRTKD]

Deviating from 12v can get a bit messy. Do you really NEED a 48v battery bank?

 

[DJSmiley]

Another option might be a cheap inverter. It's not the most efficient option, and requires some space, but it is an easy and reliable option:

Just hook up a decent 12V inverter to the alternator, and connect a decent 48V charger on its output.

If you size the charger properly, it can also be used when connected to grid on a RV site, just make the source of the charger selectable between inlet on the RV and the output of the inverter from the engine.

 

[tmckenna]

Deviating from 12v can get a bit messy. Do you really NEED a 48v battery bank?

I'm not sure. Originally I was thinking I would do 48V to utilize the Victron Easy Solar II, Which has a built in charge controller but requires a 48V battery bank. That was mostly just to simplify wiring. At this point I think I'm I'm leaning more toward the 12V battery bank now, with separate charge controllers, possibly 2 if need be.

 

[HRTKD]

In my trailer, space was at a premium. Fitting in two solar charge controllers is easy. A big inverter will have to go in a separate compartment (sort of).

 

[tmckenna]

In my trailer, space was at a premium. Fitting in two solar charge controllers is easy. A big inverter will have to go in a separate compartment (sort of).

I'll be in a medium fifth wheel, with a large pass through storage so I think I'll be okay for space.

 

[400bird]

What about installing a second, 48 volt alternator? I'm sure there are dual alternator kits for the 7.3

 

[Poverty Pony]

Victron and probably others make dc-dc converters that will charge a 24V system from the 12V alternator. The Victrons don't have a multistage charge, but you can set them at a reasonable float value and let your solar system keep things topped off. This would make your inverter and battery wiring more reasonable. The conductors from the alternator(s) will still be beefy @ 12V and high current.