What component do I need to charge power station from a 12v source?

[Martinjmpr]

So the Bluetti, Jackery, etc portable power packs all incorporate a number of features with their LiFePo batteries.

Since I like to make my own, I'm curious to know what exact component charges the battery?

I presume it's some kind of DC-DC charger that is then connected to a step-down transformer so that the device can either charge when connected to a 120vAC source or a 12vDC power point/cigarette lighter plug.

My current setup relies on an external Renogy 20A DC-DC charger mounted in the truck but if I can get a smaller component that is similar I'd love to try and put together my own little home-made "power station," even if it means I'm limited to the probably 10A that a cigarette lighter type connector can provide.

Whatever they use I presume it's very small because those little power stations aren't that big. My 20A Renogy DC-DC charger is pretty big so I'm looking for something smaller that I can incorporate into a smaller overall box.

Thanks in advance!

 

[pcstockton]

MPPT controller

 

[Umbrarian]

Charging a 12V battery from a 12V source requires a DCDC device. RedArc, etc.

 

[plh]

Charge from what? I use a MPPT to charge from solar panels and a 120VAC power supply to charge from the grid. I do not charge from 12VDC, but if I did I would use a 10A (min) constant current / voltage, boost/buck.

 

[Martinjmpr]

Charging a 12V battery from a 12V source requires a DCDC device. RedArc, etc.

So the Jackery/bluetti/goal zero etc must have something like that in it, right? Because they can be charged from a 12v socket. But it must be a small thing because those things aren't very big. That's the specific component I'm looking for.

Yes, of course I can use a DC-DC charger. I actually have one (a Renogy 20A.) But it's very large and would require a much larger enclosure.

I do not charge from 12VDC, but if I did I would use a 10A (min) constant current / voltage, boost/buck.

Right, that's what I'm asking about. What is the actual device that does that? Not a DC-DC charger, those are much too large.

 

[Martinjmpr]

MPPT controller

OK, that makes sense. Can the output of an MPPT controller be adjusted or modified? I assume if it is stepping down voltage from a 19v solar panel to the ~14 ish volts it would take to charge a LiFePo battery.

But if I'm plugging it into a cigarette lighter-type adapter, which probably puts out a maximum of maybe 12.9v, would it step UP the voltage to 14.5 to charge the battery? I understand there would be a loss of amps because you can't create something from nothing but it should still provide at least a slow charge, right?

What I'm trying to do is figure out how to build my own Bluetti/Jackery/Goal Zero type of power supply. Getting the 12v power from a battery is the easy part. The hard part is KEEPING the battery charged. Right now I have a 20A DC-DC charger, but that is external to the box. What I'm looking for is something I can put internally on the box that would allow me to plug it into a 12v power outlet, making it totally portable.

And yes I understand I would obviously not be getting the same 20A of power I'm getting from the DC-DC charger. IIRC the 12v power outlets are typically fused at either 10A or 15A max. I would be perfectly OK with 10A (or perhaps even 8A) of power because the benefit would be that I could plug it into a vehicle and have it constantly charging as I drove.

8A may not sound like much but if my fridge is drawing, at most, probably 4 - 6 AH, the 8A coming from a charging port would not only offset the power used but allow me to keep the power pack fully charged.

This is just a thought exercise at this point but eventually I'd like to be able to build my own, fully self-contained Jackery/Bluetti type of power station.

 

[rruff]

Can the output of an MPPT controller be adjusted or modified?

You don't want to use that. It's for optimizing solar input, and it doesn't limit current. Input voltage needs to be a little higher than the battery voltage for them to work.

There are Renogy devices (and surely others) that have a dual input... basically a DC-DC, and MPPT. But it sounds like you want AC-DC charger as well, and I don't know if you can buy something that does all 3.

I've seen several youtube videos of people making diy power stations, so you might try that.

 

[Peter_n_Margaret]

I charge my 320Ah 12.8V LiFePO4 using 2 sources.....
From 1100W of solar using a 20 year old PWM controller.
My new build vehicle will use multiple MPPT solar controllers simultaneously from 2,100W of solar to charge 700Ah 12.8V LiFePO4.
From the 85A alternator directly, simultaneously with the solar if/when required.

I prefer multiple devices for better options due to failures.
Cheers,
Peter
OKA196 motorhome

 

[Verkstad]

Fwiw,
Sorry, I know loads of guys will crap themself over the lesser efficiency...

I come to like using 120VAC inverter powered from the car.
Flexibility to plug in just about any kind of charger or appliance and at considerable distance over 12AWG outweighs the detriment of lower efficiency.
The inverter manufacturer claims 7-10% loss.
One example,
When I use my big camper with trailer, its about 40' from the alternator to the trailer batteries.
That 120V saves me a fata$$ copper circuit I dont have to assemble or pay for.

 

[jonyjoe101]

to make your own 12 dc to dc charger you need 2 components boost converter (about 10 dollars) and a buck converter (another 10 dollars) and a dc LED volt amp meter.
I build my own and they work great to charge all chemistries Lead, li-ion and lifepo4.
For 12 volt to 12 volt, the boost converter raises the voltage to 20 volts, then the buck converter lowers the voltage to what you need 12.6 (li-ion), 14.4 volt for lead, 14.6 for lifepo4. The reason you need both a boost and buck is to maintain a decent amp rate, if you only try to use a boost or buck by itself you won't get max amps. I charge all my batteries at about 6 amps.

You can also use a laptop power supply (about 19 volts) and just a buck converter (to lower the voltage) to charge from AC. This will also give you about 6 amps.

The boost and buck converters are already CV/CC which is what most batteries need. As the battery gets charge the amps drops. I like building my own because I can dial in the voltage I want, if I want to charge to 12.4 volts instead 12.6 volts, just turn the screw on the buck converter. The LED volt/amp meter makes it easy to see how the battery is charging and adjust the voltage as required.

On these you need a 12 volt fan to keep them cool especially at 6 amps. These smaller converters are rated at max 9 amps but I would never run them at that amperage. They sell larger converters that can handle higher amps.


100 volt / 10 amp DC LED volt amp meter (about 6 dollars)

 

[rruff]

For 12 volt to 12 volt, the boost converter raises the voltage to 20 volts, then the buck converter lowers the voltage to what you need 12.6 (li-ion), 14.4 volt for lead, 14.6 for lifepo4. The reason you need both a boost and buck is to maintain a decent amp rate, if you only try to use a boost or buck by itself you won't get max amps. I charge all my batteries at about 6 amps.

I like your thinking... but a 12ga copper wire will handle 6A just fine, with a small voltage drop over a long distance, and is not expensive or heavy. I think just a small boost from the alternator voltage would do the trick, and ditch the buck.

Is there a solenoid to switch this on only when the alternator is running?

I come to like using 120VAC inverter powered from the car.
Flexibility to plug in just about any kind of charger or appliance and at considerable distance over 12AWG outweighs the detriment of lower efficiency.

Curious about the DC-AC and AC-DC units you are using for this, and if it's turned off automatically or you have to remember to do it manually.

 

[plh]

So the Jackery/bluetti/goal zero etc must have something like that in it, right? Because they can be charged from a 12v socket. But it must be a small thing because those things aren't very big. That's the specific component I'm looking for.

Yes, of course I can use a DC-DC charger. I actually have one (a Renogy 20A.) But it's very large and would require a much larger enclosure.


Right, that's what I'm asking about. What is the actual device that does that? Not a DC-DC charger, those are much too large.

jj101 has a nice answer. The components are available on Amazon

 

[dstefan]

If you want small and to go w/ a ready made DCDC charger, the National Luna is small, but excellent. Been using mine for 4.5 years without a hitch. This is what ATOverland uses in their builds.

NLDC-25 DC-DC 25 Amp Charger

The NLDC-25 from National Luna is a DC to DC battery charger and isolator for a dual-battery system. It will charge an auxiliary or service battery from a vehicle alternator or Solar panel up to 25A output current. Traditional 12V and 24V vehicle alternators as well as variable voltage...

www.equipt1.com

 

[Verkstad]

Curious about the DC-AC and AC-DC units you are using for this, and if it's turned off automatically or you have to remember to do it manually.

Sorry I dont have the thing nearby. I cant share precise details...
The inverter is a real sinewave model made by Vanner.
It can be setup to use its manual on-off switch or can switch itself on-off automatically either thru the vehicle keyswitch or by sensing its input voltage.
Usually I leave it on its voltage sensing function.
As soon as the engine starts, it detects the higher voltage, the inverter switches on. After engine off, It can still run upwards of an hour or so if its AC load is minimal.

The chargers or appliances I plug in are about anything from a Makita Drill, Oster Blender to the recycled charger out of a UPS that charges the AGM trailer batteries.

 

[Martinjmpr]

Fwiw,
Sorry, I know loads of guys will crap themself over the lesser efficiency...

I come to like using 120VAC inverter powered from the car.
Flexibility to plug in just about any kind of charger or appliance and at considerable distance over 12AWG outweighs the detriment of lower efficiency.
The inverter manufacturer claims 7-10% loss.
One example,
When I use my big camper with trailer, its about 40' from the alternator to the trailer batteries.
Thats saves me a fata$$ copper circuit I dont have to assemble or pay for.

Interesting, this is the system I use to charge the camper battery from the truck, using the truck as my "generator:" 1100W inverter attached to the truck battery and 120v AC charger plugged into the inverter. I tested it out in the field for the first time last weekend and it worked great (see my other post in that topic.)