"Rescue Charging" my house batteries

[The Game is Afoot]

I searched the forums and didn't find others talking about this particular scenario. I would love some wisdom! I need a way to safely recharge my house batteries using shore power, as a stop gap measure, during this cold snap.

I bought a Victron smart charger (12v, 20A, link), but I am uncertain on how to use it safely with my setup (pic of my setup below):
- My best plan currently is to throw the big red battery switch then hook the charger to the batteries and let it do its thing. Positive clamp to + pole battery A in the bank, negative clamp to - pole of battery D.
I am all ears if there's a better way! I am not adept in electrical work, but eager to learn from the many on here more experienced than me!

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Context: My Victron inverter (Multiplus II) is crapped out and pending a probable replacement under warranty. At this point it only allows passthrough AC current on shore power to the bus (this allows my 2 mini splits to run just fine). It no longer inverts anything (no DC to AC) and does not charge the house batteries (SOK LiPO4 12v 100Ah 4x in parallel). But, practically speaking, the DC and AC don't communicate even though everything is wired for that (fyi, had this all professionally installed by Cis Solar Designs; everything worked great before the inverter went on strike).
My solar still charges the batteries fine, but winter sun + this cold snap has me running a battery deficit every day - watching my batteries slowly tick downwards.

The eventual plan is to get the inverter repaired/replaced. Once my shore power and ginny are tied into the system again all my problems in life should be solved. :biggrin:

 

[Rucker]

A walmart battery charger should work just fine in your scenario. Just be sure to check charge regularly in case the stupid charger doesn't know how to handle LiFePo.

Connect red to positive and black to negative bus bars (so the charging is captured by your shunt, assuming you have one).

 

[cadillackid]

I have a couple of the 30 amp version of this charger.. you can look up the proper charging voltage for your batteries and use the victron connect app to program the charger to match the batteries.. it works great... from the factory i tyink it comes set up for AGM and not Lithium... theres also a custom option where you can get the charging datasheet from your battery manufacturer and set it up..

 

[The Game is Afoot]

Thanks!

Many thanks to you both! I greatly appreciate the input. We eked through the last few days without bottoming out our batteries. Charger arrives tomorrow and we should be off to the races.

 

[Jono14]

That charger should work well. At 20A it will take a while - like 20 hours to fully charge 400Ah of battery if there are no other loads, but it will work.

Turn off the big red switch and both solar charge controller breakers before working on it to stay safe.

Also to keep it safe, the battery connection should be fused. The best way is probably to make DC wires using 6-10AWG wire and connect directly into the Lynx distributor (bus bars like Rucker said) - its just 2 phillips screws to take off the cover and 13mm wrench for the nuts. You will need 5/16 lugs crimped on that match your wire for the lynx end and bare stripped ends that clamp into the charger.
The negative wire goes on the lower bus bar and the positive on the upper bar but on the bottom end of the Mega fuse.

If you have an open slot in the Lynx distributor, and can add a ~50 amp MEGA fuse then that could work well. If you only have larger fuses, then you will need larger wires to keep it safe. For example, 6AWG can use a 100A fuse. If you don't have any extra Mega fuses, you may be able to buddy up on one of the solar charge controller connections depending on their fuse size. (I am happy to help with the details if you send a pic of the inside of the Lynx)

Once it is connected to the Lynx distributor, you can turn the breakers and switch back on and open the Victron Connect app to program the charger. Using the pre-defined settings for LiFePO4 batteries should work fine for SOK. This way you can just leave it plugged in and the charger will be smart enough to stop when the batteries are full and the shunt will track the progress correctly.

Then you can just plug it into an extension cord to shore power and you should be good to go.

 

[Ozbozz57]

I'm using an inexpensive Mean Well switching power supply that converts 120 AC to 14 to 15 volts DC. It's wired through a relay that switches off the solar panel input and switches on the power supply input to the charge controller that manages my battery bank. This happens automatically by simply plugging the bus into shore power. I have flooded lead acid batteries, but the charge controller I use can be set up for any battery chemistry. It is a bogart engineering sc-2030. The point here is that the batteries are always being charged by the same set of rules, no matter whether the power is coming from the sun, or 120 volt cord.