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48V powering 24V appliances

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FloaterBoater

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Aug 28, 2022
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I've been thinking for a while about building an electric system based around 48v batteries. My boat has all electric main appliances, so realistically a 48v system would be best for powering the inverter loads.

The existing DC equipment onboard is all 24v. One of the design problems I've got is not being able to find a 48v -> 24v converter with enough output to manage the total possible DC loads. The biggest one Victron make is only rated to about 15A which would be overloaded with a combination of my toiler flushing and anything else running. I know you can run multiple in parallel, though this does get a a touch expensive.

In the video posted in this thread they solve this problem by having a small 48->24 DC DC charger and then a 24v lead acid battery for the DC loads. https://diysolarforum.com/threads/wow-ultimate-boat-config-on-sailing-yacht.60437/

I hadn't thought of this as a way to manage this down conversion problem. Just curious on thoughts about this approach. What might the positive and negative aspects be. Welcoming any thoughts.
 
I'm in a similar situation, I'm planning on using a MPPT charge controller

48v battery wired into the solar input on charge controller, charging a 24v battery bank

diysolarforum.com

Question: DC/DC converter, SCC

I'm trying to charge a 24vdc AGM battery bank from a 48v agm battery bank, I've had my eye on a 110w victron dc/dc converter, £70~ But was wondering if it's possible to use a solar charger controller as a DC/DC step down converter ? I've got a spare STECA MPPT or two , 15amp, 100v max solar...
diysolarforum.com diysolarforum.com
 
SamG340 said:
I'm in a similar situation, I'm planning on using a MPPT charge controller

48v battery wired into the solar input on charge controller, charging a 24v battery bank

diysolarforum.com

Question: DC/DC converter, SCC

I'm trying to charge a 24vdc AGM battery bank from a 48v agm battery bank, I've had my eye on a 110w victron dc/dc converter, £70~ But was wondering if it's possible to use a solar charger controller as a DC/DC step down converter ? I've got a spare STECA MPPT or two , 15amp, 100v max solar...
diysolarforum.com diysolarforum.com
Click to expand...

I'm curious why an MPPT solar controller as opposed to a DC/DC converter?
 
FloaterBoater said:
I'm curious why an MPPT solar controller as opposed to a DC/DC converter?
Click to expand...

I couldn't find a suitable DC/DC battery charger for less than £80

I got that STECA MPPT for £15 on eBay. Also the mppt is a lot bigger. around 350w Vs the victron Orion DC/DC at 110w
 
SamG340 said:
I got that STECA MPPT for £15 on eBay. Also the mppt is a lot bigger. around 350w Vs the victron Orion DC/DC at 110w
Click to expand...
Uuuhhhh... are you sure it's a real MPPT controller and not just a sticker on a PWM that says the word MPPT? Is there a USB port on the front?

A 30a MPPT controller for 15 is one of those "extraordinary proof required" statements.

As for using an MPPT controller as a step down converter, you may very well need some sort of 24v battery to tell the MPPT controller what voltage it needs to run at. Easy enough with a couple small 12v batteries in series just to provide control voltage and surge buffer.
 
Whats the point of using 48 volts at all ?

Oh No please don't say avoiding "big wires" as the reason to complicate the heck out of everything instead of just making everything 12 or 24 volts.

"Big wires" carrying 12 volts are much more reliable then all the complications of upping and downing voltages all over the place with additional components.

"Wire repair will become critical," he said. I've been told that as we go from 12 to 48 volts corrosion will worsen by a factor of 10.

"Other challenges for a 48-volt system include increased corrosion problems, particularly at ground"

48V is considered a 'safe' voltage, but you can definitely feel it, add salt water dampness and you will feel it zap you.
 
32 volt boater said:
Whats the point of using 48 volts at all ?

Oh No please don't say avoiding "big wires" as the reason to complicate the heck out of everything instead of just making everything 12 or 24 volts.

"Big wires" carrying 12 volts are much more reliable then all the complications of upping and downing voltages all over the place with additional components.

"Wire repair will become critical," he said. I've been told that as we go from 12 to 48 volts corrosion will worsen by a factor of 10.

"Other challenges for a 48-volt system include increased corrosion problems, particularly at ground"

48V is considered a 'safe' voltage, but you can definitely feel it, add salt water dampness and you will feel it zap you.
Click to expand...
The reason for going to 48v is that I'm effectively looking to build a 32A 240v supply. The boat is all electric and routinely pulls close to that when cooking.

There's only one Victron 8000 VA inverter that runs at 24v. 48V brings more choice for inverters at lower cost, easier to build/buy batteries, and yes, smaller wires (though this isn't the primary concern).

My boat is my home 365 days/year. It's not a leisure activity and I don't want to live like I'm camping.
 
pollenface said:
Do you already own these 48v batteries? If not, wouldn't it be most practical to build a 24v system?
Click to expand...
I don't, but also the 24v component of the boats systems make up a nominal portion of the overall electric demand. The primary demand is 240v AC
 
FloaterBoater said:
I don't, but also the 24v component of the boats systems make up a nominal portion of the overall electric demand. The primary demand is 240v AC
Click to expand...
"Primary Demand" doesn't tell us much. What are the 240V AC loads? If you come in under 3000W, then don't bother with 48V.
What are the 24V loads? My boat is 12V, and I seldom go over 15A. I have never hit 30A. So with a 24V boat I would expect you might never hit 15A. You can parallel 2 DCDC converters. Or add a buffer battery as you suggested with a small DCDC charger. I would select an LFP battery not a LA though. But either would work.
 
wholybee said:
"Primary Demand" doesn't tell us much. What are the 240V AC loads? If you come in under 3000W, then don't bother with 48V.
What are the 24V loads? My boat is 12V, and I seldom go over 15A. I have never hit 30A. So with a 24V boat I would expect you might never hit 15A. You can parallel 2 DCDC converters. Or add a buffer battery as you suggested with a small DCDC charger. I would select an LFP battery not a LA though. But either would work.
Click to expand...
The AC loads are (non exhaustive list/all 240v)
  • Induction cook top - 20A max current - can be programmed to run as low as 10A
  • Oven - 13A max
  • Fridge
  • Freezer
  • Washer/dryer combo
  • DAB water pump
  • Main lighting
  • TV
  • Networking equipment
  • Small appliances
  • Diesel boiler
The DC 24v loads are (also non exhaustive)
  • Toilet
  • Gulper pump
  • Emergency LED lighting indoor
  • backup water pump
  • bilge pump
  • Navigation lighting
  • Windshield wiper
The bulk of the load is AC, so i'm trying to design a system which can support the AC loads away from shore line, and assisted by solar in the summer. The vessel is a liveaboard dutch barge and is mine, and my wife's home and office year round. Typical electrical usage averages 6-9 kWh/day. It is also equipped with a 7000 watt 240v generator. With the potential demand reaching 8000 watts /32 amps, a 48v system makes sense in terms of being able to meet demand. The DC loads are really nominal in comparison.
 
Since the bulk of your loads are AC, the easiest solution might be to just use an AC to DC converter or converter / charger for the 24 volt loads.

Since a number of those DC items are pretty critical items, it would be fairly easy to have a modest size, 24 volt AGM or Li battery charged from the charger.

It might even make sense to have a few separate 24 volt systems - depending on location / distance.

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Power converters and battery chargers convert AC voltage to DC voltage for both DC load operation and 12V or 24V battery charging. Explore these IOTA products today.
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Your DC loads seem very minimal. I would use a small buffer battery (for security if the main battery fails) and a small DCDC charger.
 
Use an inductive balancer and split your 24V DC loads as evenly as you can over the two halves of the battery.
 
yabert said:
What about your MPPT solution? Is it working properly?
Maybe those Meanwell RSD-500-24 or RSD-60-24.
Or take a look at those DWE unit, some have adjustable output voltage: https://www.dwe-oss.eu/overzicht/40v-to-24v-dc-converter/
Click to expand...

I decided against it , I was reading about it someone said the trouble when the mppt stops taking input (eg. Battery full) , it will short the pos & neg together, which is ok for a solar panel , but not ok with a big battery bank


End up burning them out I guess

Post in thread 'Charging one battery from another using a Solar charge controller?' https://diysolarforum.com/threads/c...g-a-solar-charge-controller.44851/post-569980



I do have a few spare MPPTs knocking about I might try it and report back
 
Oh! good to know. Thanks to share.
It seem the RSD units are available from 30W to 500W. Sound like a good solution to me.
It's so sad that those small RC hobby charger can't take more than 30-35V at input, if know they will be the best solution IMHO. They are perfect for 24-12V DC/DC charger solution, but it's more complex to find 48-24V DC/DC solution.
 
yabert said:
Oh! good to know. Thanks to share.
It seem the RSD units are available from 30W to 500W. Sound like a good solution to me.
It's so sad that those small RC hobby charger can't take more than 30-35V at input, if know they will be the best solution IMHO. They are perfect for 24-12V DC/DC charger solution, but it's more complex to find 48-24V DC/DC solution.
Click to expand...

I'm also concerned about using a constant voltage PSU for charging AGM batteries, they need looking after . I think it works a lot better with LiFePo4 & a BMS . But again I'm no expert
 
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