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

[rruff]

If you want small and to go w/ a ready made DCDC charger, the National Luna is small, but excellent.

For $700....

 

[dstefan]

For $700....

Well there is that! But it’s less expensive than burning a rig down, which is surely what I would do, if I made my own DCDCI charger!

 

[jonyjoe101]

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?

Years ago I tried charging from the alternator cigarette plug to my lifepo4 which was at 20 percent, thinking I would at least get 15 amps charge rate. But I was only getting 2 amps charge rate max. I don't drive much which is why I never tried using the alternator as a source to charge my lifepo4. I was using 14 gauge wire that time and the distance was about 6 feet from plug to lifepo4 battery.

I use the boost buck converter to charge from my 465ah li-ion house battery (12,6 volts) to charge either lead acid or smaller 10ah lifepo4 I keep around.

You can connect solenoids or the smaller 12 volt 30 amp automotive relays to switch on the charger. You would need an "overvoltage control relay" (about 10 dollars) to run everything. This smaller relay will activate the larger relay. These overvoltage control relays are fully programmable. You can program it to activate the relay when the start battery reaches 14 volts (engine running) and disconnect the relay when engine is turned off and voltage drops.

 

[DaveInDenver]

people making diy power stations, so you might try that.

Not an influencer but I run a DIY battery box. I had some of the components already so if starting from scratch I might have made a few different choices. It has come together over time as I change things, experiment, etc.

Having commercial off-the-shelf devices can be handy with apps and such. I do tweak settings from time-to-time and I like having voltage, current and temperature at several different spots at my fingertip on my phone.

In any case, you can often run a solar controller and DC-DC charger in parallel as long as only one is active. You'll want to verify that with the manufacturers of any specific one. Mine are fine being in standby connected to the battery but not active (no input) when the other path is handling charging. Their outputs are high impedance when not active as you'd expect. Some designs will remain partially powered and may measure battery voltage when there's no input, others may turn completely off with no input. There's no universal way it's done.

I have two dedicated inputs, one for solar and a second one for 12V DC in. I normally run the DC-DC charger, whether from a source like the truck or a AC-DC power supply if I have 120VAC available. During the summer I usually just leave the box in my truck connected to the 12V system. It's got an ignition sense and low voltage disconnect, so it doesn't charge unless the engine is running. I don't leave it in the truck in the winter but the DC-DC and BMS both would prevent low temp charging, but I figure there's no reason to abuse the cells in very sub-zero if I park at a trailhead for a ski trip.

When I want to run solar I physically unplug the DC input and connect a solar panel to a different input connector. One day I'll come up with a fool proof way to share an input that I switch or has sensing but this way's worked so I don't feel the urgency. I run a series string of 12V panels, so open circuit could be as high as ~44V and the DC-DC absolute max input is 17V, so I need to be sure there's no inadvertent mistake possible, voltage or connector type sensing, a crowbar on the DC-DC input perhaps. Two different connectors is simple and fine for now.

In the photo the blue box is a Victron Orion-TR Smart Isolated DC-DC (18A), the black is a Morningstar Sunsaver MPPT solar (15A), the board on the left is my Overkill BMS, cells under the shelf beneath it. There's a fuse block on side of the divider in the middle for all the various circuits. The box has come together over time, originally it was a lead-acid on the left and it was sized for that exactly, and just the solar controller and a fuse block. But I added the DC-DC later, then went to LFP, so the organization is ad hoc. Mk2 of this will grow slightly externally so I can use larger cells and an actually planned layout, but it works fine. I went from a 65 A-hr lead acid to 74 A-hr LFP, so I've gained about half to almost a full day of real world usable capacity and dropped about 15 lbs in weight, so even though it's not a major step up it's more than a marginal improvement.

 

[rruff]

In any case, you can often run a solar controller and DC-DC charger in parallel as long as only one is active.

That surprises me. Why wouldn't they both work at the same time? They both key off battery voltage and will supply as much current as they can until it's full.

 

[DaveInDenver]

That surprises me. Why wouldn't they both work at the same time? They both key off battery voltage and will supply as much current as they can until it's full.

It's not a simple yes/no. You're right that multiple chargers can and often do run in parallel. The problem is coordination. You have multiple control loops running and there's no guarantee they'll operate well together. This is more of a problem you'd have with smart or multi-stage charging.

One getting confused with a state, maybe missing a trigger to change state or might drop into an error state if what it thinks should happen didn't. You could end up over- or undercharging. It's also potentially a problem with some simple power supplies that might not stay in regulation if there's something else active on the common bus. There are ways to do control right (keeping in mind we're talking about switching supplies, not totally dumb linear circuits but some linear circuits may not like multiple sources or/and loads in parallel either) and there's corners you can cut or assumptions you might make during design.

Some products are intended to work smartly in parallel, some you might have to configure to expect parallelism or to be a master or follower, some do everything fine without intervention. This is very common with grid-tied inverters, which have to coordinate well with the world. It could be a class of controllers, such as one brand's MPPT not liking dissimilar devices in parallel while their PWM are fine. There's just too many variables to suggest doing this without qualification.

Being high impedance in an off state for any device makes it essentially invisible to the bus, so it's the fail safe condition and should be safe in most cases to assume. It's not always true but should be very rare that a device can't hang on a bus in an inactive state. Some may prefer to be powered but signaled to be off, some may need to actually be completely unpowered on their input.

To answer your question, that's why I suggest referencing datasheets/manuals or calling your tech support and asking. They may say it's OK without any conditions, they may say only if you use products from them (this could simply be due to them testing the configurations) or only ones that share a common communication protocol, they may say you cannot do it under any conditions.