Integrating 48V Lithium in 12V System

[Damir36]

Hello, I have a 48V 50Ah LifPo Battery I use for the electric motor of my dinghy. Right now I charge this over the inverter with a 48V charger. Not ideal.
As I use this Battery seldom because I can also sail my dinghy I would like to Integrate this Battery so that it is charged (and discharged) with my housebank and just plugged off when I will use it with my dinghy.

Housebank (on my 30 years old Catamaran) consists of 2200 Watts peak of solar on a few different Victron MPPTs, 4x 280 Ah LifPo Batteries, 1000 smartshunt on Cerbo, two 12v30Amps Orion DC/DC chargers on the motors.

Can I just use an 48/12 V DC/DC charger and plug the Battery in? Will it be charged and discharged ? Are there other things to consider?

Thanks Ralph

[SOLAR SUPPORT]

Originally Posted by Damir36

Hello, I have a 48V 50Ah LifPo Battery I use for the electric motor of my dinghy. Right now I charge this over the inverter with a 48V charger. Not ideal.
As I use this Battery seldom because I can also sail my dinghy I would like to İnternet egrate this Battery so that it is charged (and discharged) with my housebank and just plugged off when I will use it with my dinghy.

Housebank (on my 30 years old Catamaran) consists of 2200 Watts peak of solar on a few different Victron MPPTs, 4x 280 Ah LifPo Batteries, 1000 smartshunt on Cerbo, two 12v30Amps Orion DC/DC chargers on the motors.

Can I just use an 48/12 V DC/DC charger and plug the Battery in? Will it be charged and discharged ? Are there other things to consider?

Thanks Ralph

It is possible to charge the 48V Dinghy battery without using an inverter. Are your house bank 12V or 48V? All you have to do is use a 12-60 or 48-60 Volt DcDc step up converter. In this way, you save up to 10% of the energy required for charging. Once your Dinghy battery is charged, it remains fully charged. If your total electrical energy budget balance is in excess, you can continue to charge your dinghy battery using your inverter.

[Damir36]

Thanks, my house battery is 12V, but is it possible to use this 48V Battery to extend my house 12V batteries and just unplug it wenn it is needed in the dinghy?
What I want is that the 48 V battery is charged by my 12V system when there is excess energy from solar and that it extends my housebank to use when there is not enough solar coming in.....

[Fuss]

Originally Posted by Damir36

Thanks, my house battery is 12V, but is it possible to use this 48V Battery to extend my house 12V batteries and just unplug it wenn it is needed in the dinghy?
What I want is that the 48 V battery is charged by my 12V system when there is excess energy from solar and that it extends my housebank to use when there is not enough solar coming in.....

That’s not going to work. I do something similar but my house bank and electric outboard are both 24 v, so this has much more chance of working. Even so, the outboard battery needs a dc dc charger to get it full when the house bank is at 50% for example.

[mcarthur]

I had great trouble finding a 48-12v DCDC charger. Rumour said Sterling but nothing concrete. I use an MPPT instead and it's working well. You want the opposite of course, a 12-48V DCDC charger - haven't heard of one.

There are a variety of step-up converters, but they don't "charge" (ie. they don't have the smarts to understand charging points, bulk vs absorption, etc. They are just designed to convert from one DC voltage to another. The Victron Orion 48-12 is like that, while the Orion 12-12 are true chargers.

[SOLAR SUPPORT]

A simple and inexpensive DCdc step up converter can step up a 12 Volt supply to 60 Volts and above. I bought one of the bare devices made in China that does this job. I can charge the 12V LFP dinghy battery with 12V LFP service batteries. The device is fixed on the boat, has a switch fuse, and the dinghy battery can be connected and charged with the Anderson plug located at the device outlet. LFP charge profile is simpler than LA. 14.4V output voltage is adjusted. Additionally, it memorizes 10 charging programs with varying current levels. Such a device, whose label says 900 Watts, can only produce 190 Watts at 13.2V input and 14.4V output voltage. As the input voltage increases, the DCDC output power should be increasing towards the label value.

PO dinghy battery is 48V. He can use a similar device to charge the battery. A step down DcDc device is required to use the Dinghy battery to supplement the service battery. However, I believe that enlarging the service battery may be a more economical solution instead.

[mcarthur]

Ah ok, so they do exist.

It's my risk profile: although LiFePO4 are pretty stable I wouldn't be using a unknown noname brand "charger" on a battery. 48v, even if smallish Ah, can still be a danger.

[Mal Reynolds]

Originally Posted by Damir36

Thanks, my house battery is 12V, but is it possible to use this 48V Battery to extend my house 12V batteries and just unplug it wenn it is needed in the dinghy?
What I want is that the 48 V battery is charged by my 12V system when there is excess energy from solar and that it extends my housebank to use when there is not enough solar coming in.....

I believe this converter is bi-directional: 12 to 48 and back. https://www.mastervolt.com/products/...plus-12-48-15/

[PNWSalmon]

Funny story here (at least to me). I charge our Torqueedo battery either through the DC system (cigarette style plug) or the AC system (inverter) or solar (its own panel), depending on conditions.

One day this season, while we were at anchor, we had the Torqueedo charging through one of the cigarette outlets up in the cockpitm and we were doing some boat projects.

I decided that I needed to shut everything down to do something to the electrical system.
We also needed to defrost the fridge, so I got ready to disconnect the DC circuits and the batteries, do my maintenance while the fridge was defrosting.

Well, I disconnected the house bank, disconnected the solar, shutdown the house bank circuit main switch, to start my work. To my surprise, the fridge was still on, the lights were still on. The electrical panel was still on. I was scratching my head and and we spent a few minutes trying to figure out what the heck was going on.

And then I finally realized, once we turned off and disconnected the house bank, the torqueedo was back feeding, through the cigarette plug, and powering all the circuits that were on in the boat. We were running the fridge, a few lights, whatever else was on during the day. I quickly disconnected it, shuddering at the thought of the possible amperage running through those small wire circuits, but also more interestingly, I was really intrigued that we could power the boat off the torqueedo.

So, long story, but I think what you're trying to do is totally possible, it just has to be done right, with appropriate wiring, and the whole thing is certainly tricky. I know the torqueedo is setup to charge small devices, and even comes with an adaptor for this, but I had no idea it would backfeed through its DC charger and power the boat.