Dual Voltage (12 & 24) Electric Circuits

LadyInBed

LadyInBed

Well-Known Member
Joined
2 Sep 2001
Messages
15,222
Location
Me - Zumerzet Boat - Wareham
montymariner.co.uk
My boat came with a 12v and a 24v electric circuit which means two alternators and five batteries - a 120Ah 12v house, two 120Ah in series for the 24v house and a 70Ah 12v starter.
I've lived with this for twenty one years! adding supplimentry charging in the form of a Rutland 913 24v wind gen for the 24v house and 2x80 watt 12v solars in parallel through a dual o/p reg for the 12v house and starter.
The twenty year old wind gen is reaching end of life - blades are unballanced and output is low, so I have been thinking about a refurb or replacement which would cost quite a lot.

I then had what I think is a flash of inspiration - Ditch the wind gen and the 24v alternator (which has always been a pita as it is driven off the 12v alternator), put the 2x120Ah 24v house batteries across onto the 12v house battery giving me a 3x120Ah 12v house bank and run the 24v circuit from a 12V to 24V, 20A (480 Watt) DC to DC Step Up Power Converter.

The 24v bank supplies:
Rich (BB code): 
Item                24V        Power    Usage
                    Current    Watts 
Fridge (24v/12v)     2.50    60.00     Always
Fwd Heads            8.00    192.00    Hardly ever
Fresh Water Pump     3.80    91.20     Always
Shower Pump          6.50    156.00    Hardly ever
Deck Light           0.50    12.00     Hardly ever
Total:               21.30   511.20

What do the team think?
Would it work, as it appears to be a simple solution?
 
Sounds a bit confusing. A 24 v system has advantages in high current demands such as engine start anchor winch, bow thruster and inverter. It is not clear if 24v is an advantage for a fridge 12v is OK also.
I think then that an ideal system would be 24v starter 24v alternator. These could feed/ charge a 12v domestic battery system. Or alternatively feed /charge a 24v domestic battery system with VSR and with converter for those services requiring 12v. (this is typical of larger boats)
Ultimately whatever suits you for the amount of changes you are willing to make. However I don't think a 12 to 24v converter is so common but 24 to 12 is. So suggest keep 24v alternator get rid of 12v alternator. ol'will
 
Thanks William.
The majority of the electronics is 12v, also is the engine starter motor and the anchor winch, so to go to a 24v system as you describe would be quite costly. I don't know why the boat was put together with dual circuits (boat is home completed) so what I have is what I've got!
Surprisingly, a 12 to 24v 20amp converter isn't that expensive, less than £30 and to wire it in in place of the 24v battery bank would be quite easy to do with no rewiring to any appliance.
It appears to be a simple solution, so I'm wondering if I've missed anything.
 
Certainly worth a try. Presumably you'd rewire the fridge to run on 12v. And if and when the pumps need replacing you could get new 12v versions. I'm not sure how reliable a £30 converter would be - more expensive ones are available which might work better long-term.

Incidentally, you said you have 5 batteries, but you only listed 4. Is there a fifth somewhere?
 
I have a similar system but the other way around, 24V by design with 24/12 converter and 24V dual alternators. The fridge used to have its own 24/12 converter but the new fridge accepts a range of voltages, so the converter was removed and is available (PM me). My situation is very easy as only a few instruments are 12V. Downside of 24V is that sometimes there is a good price hike in marina stuff at 24V. A good source of very low cost 24V cabin stuff is from the trucking industry, where LED lights and stuff are 24V and very low cost, anyway thats not the point. My next upgrade is to bin the twi alternators and fit a single 24V modern system.

I think you should stick with 12V primary system, ditch the alternators and only have one modern, efficient 12V charging system, fit the 12/24 converter and tidy up, as you suggest. If the alternator is a 24V Lucas old style, they can be sought after by military vehicle restorers and fetch good money, rather than scrap value.
 
pvb said:
Presumably you'd rewire the fridge to run on 12v. And if and when the pumps need replacing you could get new 12v versions.
Click to expand...
I don't think that I would bother, as the switch and fuse panels are split, one to 12, t'other to 24 so that would mean installing another 12v panel and I'm running out of space.
I'm not sure how reliable a £30 converter would be - more expensive ones are available which might work better long-term.
Click to expand...
I'm not sure that expensive is always better, things like tools are but electronic circuit boards are more debatable. the item that I have in mind is a EBILUN 12V To 24V DC Step Up Power Converter, 20A 480W Price: 28.34
Incidentally, you said you have 5 batteries, but you only listed 4. Is there a fifth somewhere?
Click to expand...
Ah! yes, well spotted. I had until recently 2x70Ah batteries in parallel so I could switch to either 12v bank to use as the House bank and not have a dedicated Start battery but one of the 70's went U/S, but luckily it's buddy recovered. Under the new proposed regime with a 360Ah bank, that will become a dedicated House bank.
 
LadyInBed said:
I'm not sure that expensive is always better, things like tools are but electronic circuit boards are more debatable.
Click to expand...
?
can be a little bit pot luck but generally the cheapo ebay electronic kit I have onboard is turned on 24/7 for years on end just fine. A few moments on google/youtube will likely come up with some reviews,. One thing which might bite you if you do any HF radio is RF noise from power supplies, though your fridge is probably by far the noisiest RF thing you'll ever have on a boat. The max constant power datasheet figure might be a little optimistic as well...... ?
 
LadyInBed said:
I then had what I think is a flash of inspiration - Ditch the wind gen and the 24v alternator (which has always been a pita as it is driven off the 12v alternator), put the 2x120Ah 24v house batteries across onto the 12v house battery giving me a 3x120Ah 12v house bank and run the 24v circuit from a 12V to 24V, 20A (480 Watt) DC to DC Step Up Power Converter.


What do the team think?
Would it work, as it appears to be a simple solution?
Click to expand...

With the 24v loads you listed it'll work OK, but i would buy a better DC-DC converter.
 
  • Like
Reactions: pvb
LadyInBed said:
I looked on Battery MegaStore at the Victron Energy Orion 12/24-20 DC-DC Converter IP20 – ORI122420020
but at £155 I'm reckoning that it is too sophisticated for my needs!
The items being driven are not sensitive to voltage stability or ripple, so I'm going to try the £30 version. If it doesn't do the job the lost outlay will only be small.
Click to expand...
Its sophisticated and expensivebecause it is designed to operate as a multistage battery charger.
Sterling ones are the same.

To use it purely as a power supply, without a 24V battery, you don,t need a battery charger..
 
VicS said:
Its sophisticated and expensivebecause it is designed to operate as a multistage battery charger.
Sterling ones are the same.

To use it purely as a power supply, without a 24V battery, you don,t need a battery charger..
Click to expand...
I didn't notice that it was also a multistage battery charger.
Thanks, that puts my mind at rest in going 'cheap' "inexpensive" :love:
Thanks for pointing that out Vic.
 
Last edited:
You must log in or register to reply here.

Share this page

Top