Mixed 24V & 12V systems

[wooslehunter]

I have an older Watermota Sea Panther engine that needs 24V for the starter. I also have normal 12V system for everything else. So, I have two alternators: one for 24V & one for 12V. I'd rather like to get rid of the 12V one & there are several options.

1. Use a 24V domestic battery bank as well as the engine bank. I can convert the nav & internal lights to 24V easily enough. But I will need to use a 24v - 12v converter to run all the 12v stuff. Anyone have any recommendations for this. It will require a large peak load since it will have to provide enough for the VHF in transmit & the autopilot, plus of course anything else drawing current at the time. Any suggestions for a converter. teh advantage of this is that I can charge both banks fro the engine mounted 24V alternator & also if I haev to, start the engine from the domestic bank just like a conventional dual battery 12V system.

2. Keep the 12V domestic bank & charge via a 24V to 12V charger. I won't be able to start from the domestic bank but I can't do that now. But, if the charger went down, I'd lose the ability to charge the domestic bank. Any recommendations for the charger.

Any other suggestions, how do people with 24V systems cope with the requirement for 12V to run domestics? Having a 24V domestic bank & only using 1 battery for 12V is a non starter as it will lead to imballanced discharge.

 

[stuhaynes]

I have an older Watermota Sea Panther engine that needs 24V for the starter. I also have normal 12V system for everything else. So, I have two alternators: one for 24V & one for 12V. I'd rather like to get rid of the 12V one & there are several options.

1. Use a 24V domestic battery bank as well as the engine bank. I can convert the nav & internal lights to 24V easily enough. But I will need to use a 24v - 12v converter to run all the 12v stuff. Anyone have any recommendations for this. It will require a large peak load since it will have to provide enough for the VHF in transmit & the autopilot, plus of course anything else drawing current at the time. Any suggestions for a converter. teh advantage of this is that I can charge both banks fro the engine mounted 24V alternator & also if I haev to, start the engine from the domestic bank just like a conventional dual battery 12V system.

2. Keep the 12V domestic bank & charge via a 24V to 12V charger. I won't be able to start from the domestic bank but I can't do that now. But, if the charger went down, I'd lose the ability to charge the domestic bank. Any recommendations for the charger.

Any other suggestions, how do people with 24V systems cope with the requirement for 12V to run domestics? Having a 24V domestic bank & only using 1 battery for 12V is a non starter as it will lead to imballanced discharge.

I did this about 10 years ago on this boat, changed the whole thing to 24 volts. As you say, the lights are easy to do but it did mean (for me) a new alternator, starter motor and bilge pump etc. The only thing I didn't change was the water pump. At the time the pump was newish so I bought a 24 to 12 volt dropper unit. Unfortunately this thing produced a massive amount of heat which I didn't like. Ended up biting the bullet and changing the water pump too. Never regretted it.

There are experts on here (doesn't include me unfortunately!) that will give you more meaningful advice.

 

[MudShipper]

Input voltage

Before looking at 24/12 converters and spending your hard earned, take a look at what you actually need for your electronics. A surprising amount of the more modern kit will work on a range of input from 10 v up to about 40v to accommodate exactly this variety in supply.

 

[David2452]

Before looking at 24/12 converters and spending your hard earned, take a look at what you actually need for your electronics. A surprising amount of the more modern kit will work on a range of input from 10 v up to about 40v to accommodate exactly this variety in supply.

Indeed, I recently did an almost full Garmin suite install on a 24v boat and the only thing I needed 12v for was the N2K network, supplied that with a small 5a Victron 12 - 24v dropper.

 

[Pete7]

Indeed, on a previous boat the Garmin worked much better on 24v rather than dropping out if the voltage goes too low with 12v. The only thing I needed 12v for was the VHF via a converter. Even the fridge preferred 24v.

Pete

 

[wooslehunter]

I didn't think the electronics would take 24V & checked. They don't as I thought so I still need 12V. I would not consider a "dropper" type converter as they will dissipate too much heat. Hence a 24 - 12 switched mode converter is what I would use.

 

[rjcoles]

I have the same problem, new Perkins engine that is 24v and the rest of the boat 12v.
My solution (and I hope that it will work) is to replace the existing 24v alternator with a new 100Amp 12v alternator and also add a second 100A 12v alternator. These alternators will be controlled by an Adverc dual alternator controller and wired totally separately from the engine.
The engine will have a 24v battery setup that will be charged by an Adverc 12 to 24v 10A charger from the 12v domestic bank. I have had to add a couple of 24v relays to turn on 12v equipment that is controlled by the engine (blower, Adverc power feed etc). The proof of this pudding will hopefully be tested latter this year.

 

[SHUG]

A good option is a 10A, 24 to 12V converter from Maplin
See: http://www.maplin.co.uk/10a-dc-24v-to-12v-voltage-convertor-390224

 

[LadyInBed]

2. Keep the 12V domestic bank & charge via a 24V to 12V charger. I won't be able to start from the domestic bank but I can't do that now. But, if the charger went down, I'd lose the ability to charge the domestic bank. Any recommendations for the charger.

I use a mixed 24 & 12v system. The engine has a 24 & a 12v alternator and I have a 24v wind gen. I use (for 10 years now) an earlier version of this Waeco to charge the 12v banks from the 24v bank via the wind gen when sailing / anchored / on mooring.
As for charger going down, if your domestic bank were 2 x 12v in parallel you could always arrange them in series and charge them on the 24v system.

 

[Beyondhelp]

Analogue/linear DC-DC converts will get hot. Proper switching DC-DC converts will hardly get warm dropping 24-12v dc, even at high currents. Just have to make sure you get a reasonable one not a cheap one that is likely to fail interference tests.

 

[William_H]

I have the same problem, new Perkins engine that is 24v and the rest of the boat 12v.
My solution (and I hope that it will work) is to replace the existing 24v alternator with a new 100Amp 12v alternator and also add a second 100A 12v alternator. These alternators will be controlled by an Adverc dual alternator controller and wired totally separately from the engine.
The engine will have a 24v battery setup that will be charged by an Adverc 12 to 24v 10A charger from the 12v domestic bank. I have had to add a couple of 24v relays to turn on 12v equipment that is controlled by the engine (blower, Adverc power feed etc). The proof of this pudding will hopefully be tested latter this year.

Yikes I guess it is too late but I would have spoken against that arrangement.
24V system is far better for all your large load systems so if the engine is set up for 24v be grateful.
I would get a 24 to 12v converter which would charge a 12v battery for domestic loads. This will give you the domestic power (lights) isolated from vital engine start battery.
However if you want to run a fridge then do so on 24v which will mean you should have a domestic 24v battery isolated like any 12v system. Use a switch mode converter 24 to 12 for gear that demands a 12v supply either with or without a battery.
Either way you will need a 24v (28v) Voltage sensing relay to turn off the converter when 24v not being charged and also to isolate the domestic 24v battery if you go that way. good luck olewill

 

[Frankie-H]

KISS. My anient Moody has a 24 volt system. Batteries are all wired in series and parallel to give me 500 Ah on 24 volts. I live on the boat and do not believe in a starter battery bank. Ist change 12 years ago I increased the domestic bank and cut down on the starter bank. 2nd change 5 years ago. I did away with the starter bank completely. We are very good at monitoring the state of our batteries and all our batteries get regular use.

I run a full 24v system but there are several things which need a 12v supply. I simply took a little used circuit and ran it through a dropper. I have a 12v fused switch panel on the chart table and 12v sockets if needed.

My ancient but still happily working B&G system is 12v from new and has its own dropper.

This system has now been working full time for 16 years and I do not see any reason for changing. I agree that some modern equipment is multi voltage and if and when I have to replace, I might simplyfy things even further.