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Old 12-10-2018, 07:36   #1
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How to run high power 12V loads from a 48V house bank?

So you've got a 48V house bank (and you can't just rewire it to be 24V or 12V).

For something like lights and chart plotters I'm guessing something like a Victron Orion-Tr 48/12-30 dc-dc converter ($240) would work fine. That's 30 amps (40 amps peak) to run your lights, electronics, VHF, radar, refrigeration, etc. And if you needed to separate a refrigeration load or something, additional 10amp or so converters are pretty affordable.

An electric winch, windlass or autopilot might pull 2kW though. Converters that can handle that much power like the Sensata/Magnum units might cost you around $4,000, which seems totally impractical.

At that price you might as well just have a secondary 12V bank for those loads run by a single 100ah LiFePO4 and... I guess a 10 amp dc-dc converter to keep it charged up from the main bank?

I'm just generally confused about all this. How do people run 48V banks (I know it's very rare) and still run high power 12V (or 24V) loads?

As far as I can tell, 48V inverter/chargers don't include high power converters to 24/12V.

Is this a case of: "It's so easy, if you have a big inverter, just DIY your own high-power rectifier and take the small efficiency hit of going from 48VDC to 120VAC to 24/12VDC"?

Other than wiring or device pricing, would there be any advantage to making sure your autopilot ram, windlass and electric winch is 24V instead of 12V? Is 48V to 24V an easier problem to solve?
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Old 12-10-2018, 07:49   #2
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Re: How to run high power 12V loads from a 48V house bank?

You seem to not understand the point of having a 48 Volt house bank. It is so you can run the high power loads with 48V instead of 12V and avoid the problems and expense with running very high amperage wiring.

Running high power loads on 12V out of a 48V battery bank defeats the whole purpose for installing the high voltage battery bank in the first place.

It is a little harder (and more expensive) to find a 48Volt anchor windlass (for example) but they do exist. And you'll save a bundle with smaller size wire so it might be a wash.

And a 2kW autopilot?? Really? I have a 53 foot boat and mine draws less than a quarter of that at peak power...
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Old 12-10-2018, 07:56   #3
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Re: How to run high power 12V loads from a 48V house bank?

Sorry to be that guy, but why would you choose 48V for anything but propulsion or maybe aircon?

Industrial-sized DC-to-DC conversion is what's needed, but will be pricey.

I'd think a separate smaller 12V bank and distribution, but big enough to carry anticipated loads, then use the DCDC functionality to keep that charged off the main 48V system

may be more cost effective.

24V is the highest DC I'd recommend for even a big boat, but so much conversion down to 12 will be required. The fatter wires required by 12V don't break or wear out.

Maybe consider just going all-mains, 120V or 240V AC? 48V inverters must exist.
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Old 12-10-2018, 08:09   #4
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Re: How to run high power 12V loads from a 48V house bank?

Quote:
Originally Posted by john61ct View Post
24V is the highest DC I'd recommend for even a big boat, but so much conversion down to 12 will be required. The fatter wires required by 12V don't break or wear out.
John,

I am not sure what you mean when you say "so much conversion down to 12V will be required." Virtually every piece of marine electrical hardware these days is either 10-30V input, or easily available in a 24V version.

I run a 24V boat and need converters for only two things: the NMEA2000 power supply, and the SSB. Running the SSB from a converter is a far better way to do it than directly from a battery, because the voltage is stable at 13.6 even when transmitting.

Yes, 20 years ago a 24V system was something exotic and rare. Not at all anymore.
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Old 12-10-2018, 08:10   #5
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Re: How to run high power 12V loads from a 48V house bank?

Well, I think the point of having a 48V (or 24V) battery is that is allows you to install bigger and more efficient 230VAC (or 115VAC) converters. For some of us this converter is by far the biggest power load on the boat. (Electric oven, induction cooktop etc...)
It is a real PITA to connect converters above 3000kW to a 12V battery, especially when they are not closeby.
I am afraid however you then need a 12V battery pack and a DC/DC converter/charger (some Victron orion can be used as chargers) for the remaining 12V loads. And this in turn adds complexity. Not an easy choice.
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Old 12-10-2018, 08:13   #6
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Re: How to run high power 12V loads from a 48V house bank?

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You seem to not understand the point of having a 48 Volt house bank.
The Electric Yacht 20.0SD is 48v for example. And the Torqeedo 48-5000 battery you might use to power it that weighs half as much as a typical Group27 setup for the same 5kWh is 48V only.

I just haven't seen any 48V windlasses or winches so I assumed even if they existed they'd probably be prohibitively expensive.

I thought I'd seen 2000w in the B&G T2 Pilot Ram drive unit manual, but after double-checking it's actually about 270w so I was way off. Thanks.

That doesn't really help answer my question though.
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Old 12-10-2018, 08:22   #7
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Re: How to run high power 12V loads from a 48V house bank?

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Sorry to be that guy, but why would you choose 48V for anything but propulsion or maybe aircon?
For propulsion.

Quote:
Originally Posted by john61ct View Post
I'd think a separate smaller 12V bank and distribution, but big enough to carry anticipated loads, then use the DCDC functionality to keep that charged off the main 48V system may be more cost effective.
Yeah. That's all I could come up with. It's not the end of the world. But you lose some of the volume and weight advantages of choosing something like a Torqeedo 48-5000.

Quote:
Originally Posted by john61ct View Post
Maybe consider just going all-mains, 120V or 240V AC? 48V inverters must exist.
Are 120VAC winches/windlasses readily available and reasonably priced? I hadn't seen any after a few quick searches.
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Old 12-10-2018, 08:28   #8
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Re: How to run high power 12V loads from a 48V house bank?

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Originally Posted by billknny View Post
Virtually every piece of marine electrical hardware these days is either 10-30V input, or easily available in a 24V version.
yes wrt marine-specific

But at a large premium, and very limited selection for the little household / mobile stuff, can be under $20 from Amazon or eBay, $100+ for a 24V version if you can even find it.

But each of us have our preferences and legacy design issues.
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Old 12-10-2018, 08:31   #9
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Re: How to run high power 12V loads from a 48V house bank?

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That doesn't really help answer my question though.
A separate 12V (or 24V) bank will be simpler, or at least cheaper.

Non mainstream "pioneering" setup will always cost lots more than following the well beaten path.
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Old 12-10-2018, 08:36   #10
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Re: How to run high power 12V loads from a 48V house bank?

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A separate 12V (or 24V) bank will be simpler, or at least cheaper.

Non mainstream "pioneering" setup will always cost lots more than following the well beaten path.
Makes sense. Thanks.
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Old 12-10-2018, 09:59   #11
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Re: How to run high power 12V loads from a 48V house bank?

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).


Thanks
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Old 12-10-2018, 10:51   #12
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Re: How to run high power 12V loads from a 48V house bank?

There are serial/parallel switching setups.

As in trucks or race cars cranking a 24V starter from a usually paralleled pair of 12V banks.

Yandina's "trollbridge" auto switches to 24v for trolling motors.

But going to that level for this use case would be a Science Project, KISS is very important for bank longevity, safety and reliability.
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Old 12-10-2018, 10:55   #13
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Re: How to run high power 12V loads from a 48V house bank?

I agree with john... wiring batteries looks good on paper, but trying to get the same battery to provide multiple voltages at the same time sounds like a recipe for disaster.
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Old 12-10-2018, 10:57   #14
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Re: How to run high power 12V loads from a 48V house bank?

Quote:
Originally Posted by ssmoot View Post
I'm just generally confused about all this. How do people run 48V banks (I know it's very rare) and still run high power 12V (or 24V) loads?

The best choice is to obtain a 48v windlass, winch, etc. In some cases these can be purchased. In other cases it may be possible to have a 24v or maybe even 12v accessory modified for 48v operation by an electric motor ship. In most cases, these things use shunt-wound motors and a voltage change only requires modification of the field windings.


There isn't much 48 volt gear because vessels large enough that 24v no longer makes sense usually have hydraulic systems, 3 phase 208v (or 480 or 600v) generators, or both.




Quote:
Other than wiring or device pricing, would there be any advantage to making sure your autopilot ram, windlass and electric winch is 24V instead of 12V? Is 48V to 24V an easier problem to solve?

The component cost of DC-DC voltage conversion runs with current rather than power or voltage. Because 24v accessories draw less current, the converter would be cheaper, smaller, and cooler running for the same amount of power. Whether these benefits are available in a packaged off-the-shelf product, I do not know.
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Old 12-10-2018, 11:30   #15
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Re: How to run high power 12V loads from a 48V house bank?

I have a 48V nominal battery and I serve 12V loads off a 120VAC-12VDC power supply. I use two paralleled 1500W supplies for redundancy, although my observed peak demand is only about 1200W.

These power supplies are much less expensive than converters, and they funnel all the loads through a single control point (the inverter), both of which I really like.

Now, my loads are in an RV on land, so the criticality is much lower. I was tentatively planning to use a small, intermediate battery for navigation equipment on my boat, but so far the uptime on land has been 100%, so now I am going to wait a little while and see. My pack is composed of many parallel 48V strings, so in a failure scenario, conceivably one string could be isolated and tapped for emergency 24/12V.

Still, there is a lot of merit in just having a 24V or 12V lead acid battery in the circuit.

I am interested in what others decide here. I'm glad you started this thread.
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