How to run high power 12V loads from a 48V house bank?

[nebster]

Originally Posted by iabmatos

How feasible would be serving 12V or 24V loads from part of the 48V bank?

Say, you have 4 X 12V-batteries in series: A + B + C + D.

You can serve some 12V loads from individual batteries, distributed to minimize unbalancing the whole system. Same for 24V loads, taken from pairs of batteries (A+B, B+C or C+D).

It's, unfortunately, infeasible. There's no way to guarantee that we can load each substring exactly evenly, and when you run a big lithium battery bank, you spend a lot of time and money making sure that the individual series elements all stay very close to each other ("balanced").

Good idea, though!

[ssmoot]

I think dual banks would probably make the most sense assuming a retrofit. That way there's no need to rewire anything.

So say I have a Seawind 1260.

Throw the ElectricYacht 20kW saildrives on there along with a pair of the Torqeedo 48-5000 packs. That saves 115kg.

By swapping the 400ah AGM house bank out for a couple 100ah LiFePO4 batteries you save about 100kg in the salon.

Run an inverter for big AC loads off the 48V bank. Add a 48-12 converter to keep the 12V bank topped up (Victron says you can use theirs as battery chargers).

There are a lot of advantages. It's lighter. You get get back a ton of storage in the salon and engine compartments. It's silent. It's both cheaper and more powerful than an Oceanvolt SD15 setup. You get a huge house bank and large inverter.

But it's way too expensive for me. I figure it'd cost about $48K minus whatever you might get for your diesels, AGM and saildrives. Which is maybe $8K if you're lucky? That's still $40K plus a haul out, engine pulls, replacement saildrives and glassing over the old through-hulls.

And that doesn't include the solar upgrades you'd want, an energy recovery watermaker (refilling your 160gal water tank">fresh water tank would almost completely drain your 48V bank based on 50wh/gal for a 120VAC watermaker), a bigger generator or anything else you might want to really take advantage of the platform.

Fun exercise anyway.

[john61ct]

Yes if the rationale for going to 48V is propulsion or DC powered aircon, then low cost and normally-practical considerations are pretty moot already.

The idea of putting both a DC-to-AC inverter and an AC-to-DC PS/charger in line fed by a 48VDC bank just to charge a 12VDC bank, is just. . .

No have words.

But then I've been a big fan of Rube Goldberg since I was six. . .

[ssmoot]

Originally Posted by john61ct

The idea of putting both a DC-to-AC inverter and an AC-to-DC PS/charger in line fed by a 48VDC bank just to charge a 12VDC bank, is just. . .

I wasn't clear.

The 48V bank would handle three loads: Propulsion, AC Inverter/Charger and a 48V to 12V DC-DC Converter. The converter would charge the 12V bank which powers windlass, autopilot, electric winch, lights, nav, refrigeration, etc.

You might even have two converters. They're cheap enough ($100 to $240 for the Victron Orion units). And that way if one failed, or your batteries failed, you'd still be able to charge your 12V, or run most of those loads off your 48V bank instead and just go have to use the windlass and winch manually until you got a replacement.

So you wouldn't go 48VDC to 120VAC to 12VDC in that system. You'd go 48VDC to 120VAC *or* 48VDC to 12VDC.

[john61ct]

Aha, praise be.

I do come across the DCACDC setups surprisingly often, thankfully never yet for a big target bank, mostly for gadgets.

[Cpt Pat]

>At that price you might as well just have a secondary 12V bank for those loads run by a single100ah LiFePO4 and... I guess a 10 amp dc-dc converter to keep it charged up from the main bank?

That sounds like the best solution. Use the 48 Volt bank for propulsion only. Run everything else off the separate 12 volt bank. You may want to consider separate shore power chargers.

That way, if you run down your propulsion bank, you still want everything else to continue to function. Provided you haven't offended the wind gods, you still have alternate propulsion available (sails).

No dc-to-dc converter runs at 100% efficiency. You're better off cost and complexity wise just having two separate banks.

Some of the respondents here don't seem to understand that you can't just go out and buy a chartplotter, radar, lights, etc. that runs on 48 volts.


Caveat: If you use any dc-to-dc converters, make sure they don't destroy your ability to receive on your VHF radio. Some are all-band transmitters.

[GrowleyMonster]

Can you replace the 12v motor with a BLDC motor and 48V controller? There are also brushed 48VDC motors that can run straight off the 48V pile, or if you want controllable speed, through a PWM controller. If changing the motor is absolutely out of the question, as others have suggested you could have a 12V or 24V or whatever bank near the load, and charge it with a DC/DC converter from the big bank, though this would not be very efficient. Another option is to use a PWM controller to run your windlass from the 48V bank, though this is risky. You have to be sure that you don't overvolt the motor.



There are indeed 48V inverters. I have two of them. My bank is 48V and it is used for both propulsion and house loads. My underway lighting is all 12VDC and the 12V loads are small enough to go through one of the two 20A DC/DC converters.

[smac999]

Nobody has a 48v house bank. That is silly.

If you have have a 48v propulsion bank. You need to make a 12 or 24v house bank. Charge the house bank from the 48 if you wish. With a dc to dc converter. The bank will take the spikes of the windlass etc. No need for huge converter.

[Lepke]

Originally Posted by smac999

Nobody has a 48v house bank. That is silly.

I have a 48v house bank. Actually several. Because 48v gives better options in inverters, and I can use smaller cables. Both from the batteries and to whatever load. I can have additional 48v banks much further away from the inverter without huge cables. I use a Magnum MS-PAE inverter the produces 120v/240v from a single inverter. I've converted the windless motor and other appliances to AC that opens up a world of choices. Choices in equipment that are cheaper and last longer. Especially longer than DC motors. When running the mains, I never run a generator anymore. Just a 48v alternator and the inverter.

Running a few 12v items like bilge pumps comes from a separate 12v system. My lights, except for emergency lights, are AC. I can sit on the hook for a week with the reefer and freezers running. I only start a generator when I have to choose make water or pickle the membranes and then I charge the batteries. I would never go back to a 12v inverter. My old one serves as an emergency backup.
Oh! And my 48v inverter will even run the water heater if I choose.

[john61ct]

Big boat then, and a big budget.

Lots of inefficiencies there, but I guess plenty of energy available on demand, dino juice being consumed pretty regularly to drive that 48v alternator.

Please give details on that bit, is that your **main** charge source when off grid?

[john61ct]

Also the mains charger, presumably the same on from AC genny also from shore power?

[GrowleyMonster]

It must be admitted that 12VDC systems are inherently inefficient compared to higher voltage. Strange that the world is so stuck on 12V. Well, at least we don't see many 6V car batteries anymore. I think that is what is driving the whole thing. My next boat will probably have a 96V bank. For house and for backup propulsion. I may be closing on a 44' Bruce Roberts in need of much internal carpentry within the next few days. Lots of room for batteries!

[Q Xopa]

Originally Posted by Lepke

I have a 48v house bank. Actually several. Because 48v gives better options in inverters, and I can use smaller cables. Both from the batteries and to whatever load. I can have additional 48v banks much further away from the inverter without huge cables. I use a Magnum MS-PAE inverter the produces 120v/240v from a single inverter. I've converted the windless motor and other appliances to AC that opens up a world of choices. Choices in equipment that are cheaper and last longer. Especially longer than DC motors. When running the mains, I never run a generator anymore. Just a 48v alternator and the inverter.

Running a few 12v items like bilge pumps comes from a separate 12v system. My lights, except for emergency lights, are AC. I can sit on the hook for a week with the reefer and freezers running. I only start a generator when I have to choose make water or pickle the membranes and then I charge the batteries. I would never go back to a 12v inverter. My old one serves as an emergency backup.
Oh! And my 48v inverter will even run the water heater if I choose.

Yes, as others have requested please give some details of particularly your 48v alternator and your ac windless conversion.

Thanks.

[ssmoot]

Originally Posted by Cpt Pat

No dc-to-dc converter runs at 100% efficiency. You're better off cost and complexity wise just having two separate banks.

An Orion-Tr 48/12-30 is 87% efficient, provides 360w continuous and 430w peak (for 10s). Which seems like enough to power everything but the winch, windlass and autopilot ram (a secondary one could pilot the ram by itself though) directly off the 48V bank. So that seems like the simplest solution to me.

The sticking point is the electric winch and the windlass. So you're kinda stuck with the 12V bank, but I think maybe two (for redundancy) really small batteries in parallel would be best as long as they can provide enough current. A Relion RB50 (12V 50Ah) weighs 14.8lbs and can provide 50A continuous and 100A peak. So that seems right-sized and would let you run your winches and windlass for about 25 minutes continuously. Use a pair of those then and you're good. Saves you about $800 and even more space over the pair of 100Ah batteries.

[ssmoot]

Originally Posted by GrowleyMonster

Can you replace the 12v motor with a BLDC motor and 48V controller?

That seems ideal? But I'd really have no idea if the size of motors used in a particular winch or windlass is particularly common and you could find a BLDC to fit in the same housing with the same rotor size to press a gear onto?