Mixed 24V & 12V systems

[wooslehunter]

I have a 24V engine system & everything else is run from 12V. So, I have a 24V battery bank, a 12V bank & two alternators. The 12V alternator is rather a bodge though & I'd like to get rid of it. It all came about because a previous owner installed an engine that needs 24V. I can't convert that to 12V which would be the best solution. I can convert all of the lighting to 24V but the VHF, GPS & other instrumentation still has to run from 12V. So the obvious solution is a converter. I used to design switched mode power supplies so understand the technology.

This has to be a common problem for anyone with a 24V engine system. You can obviously get some very cheap & ropey ones & I'll stay away form those. Clearly peak loading has to be way above the normal loading since if I'm transmitting on VHF & the autopilot is operating, the load can be 20A or more wile everything else will only draw 1 or 2A. The converter has to be capable of that. One possible problem is VHF interference. Switched mode converters are by their very nature a source of rf interference.

So does anyone have a recommendation for converters or experience of ones that are noisy/unreliable?

 

[nigelmercier]

I would be inclined to use separate, appropriately rated, converters for each bit of equipment.

 

[superheat6k]

Not recognised as good practice, but if this were my boat, and the loads were restricted to low current items not easily changed to 24v then a mid tap from the batteries presumably in series would likely suffice, but convert as much kit as possible to 24volts, and do not leave such 12v services on unless in direct use.

 

[prv]

It sounds like the only thing that forces your boat to be 24v is the starter motor on the engine. Is there really no 12v alternative?

Pete

 

[NormanS]

I have a 24V engine system & everything else is run from 12V. So, I have a 24V battery bank, a 12V bank & two alternators. The 12V alternator is rather a bodge though & I'd like to get rid of it. It all came about because a previous owner installed an engine that needs 24V. I can't convert that to 12V which would be the best solution. I can convert all of the lighting to 24V but the VHF, GPS & other instrumentation still has to run from 12V. So the obvious solution is a converter. I used to design switched mode power supplies so understand the technology.

This has to be a common problem for anyone with a 24V engine system. You can obviously get some very cheap & ropey ones & I'll stay away form those. Clearly peak loading has to be way above the normal loading since if I'm transmitting on VHF & the autopilot is operating, the load can be 20A or more wile everything else will only draw 1 or 2A. The converter has to be capable of that. One possible problem is VHF interference. Switched mode converters are by their very nature a source of rf interference.

So does anyone have a recommendation for converters or experience of ones that are noisy/unreliable?

For very many years, my previous boat had a mix of 12v and 24v, again because the large Gardner engine required 24v. At first I took a 12v tapping from the 24v bank, but over time, this ruined batteries. I installed a 12v alternator, with a dedicated 12v battery for the few things that had to be 12v, like VHFs, and everything worked well with no problem. If your 12v alternator is a "bodge", why not improve it?

 

[William_H]

If I had a 24 volt boat I would fit a set of 24v batteries for starting as you have. I would have converter to 12v (14v) as a battery charger to a dedicated 12v service battery for lights etc. I would drive the converter with a VSR so it only charged the servicee battery when engine alternator is charging.
I would run bow thruster and anchor winch off the 24v system again enabled by a VSR only when engine is running.
I would run a fridge off 24v again via VSR or run it on 12v service system with obviously a much larger 12v battery.
In the event of dscharged or failed engine start battery I would have a jumper lead 12v battery to half way of the 24v bank so giving some boost.
Or if you are really keen have 2 batteries in parallel in the 12v system which can be reconfigured to 2X 12v in series to boost engine start battery. Either tricky switching or remove terminal clamps to reconfigure.
Sorry I don't have any info on interference from 24 to 12v converters but if all else fails you could have a kill switch for when interference is a bother.
good luck olewill

 

[geem]

If I had a 24 volt boat I would fit a set of 24v batteries for starting as you have. I would have converter to 12v (14v) as a battery charger to a dedicated 12v service battery for lights etc. I would drive the converter with a VSR so it only charged the servicee battery when engine alternator is charging.
I would run bow thruster and anchor winch off the 24v system again enabled by a VSR only when engine is running.
I would run a fridge off 24v again via VSR or run it on 12v service system with obviously a much larger 12v battery.
In the event of dscharged or failed engine start battery I would have a jumper lead 12v battery to half way of the 24v bank so giving some boost.
Or if you are really keen have 2 batteries in parallel in the 12v system which can be reconfigured to 2X 12v in series to boost engine start battery. Either tricky switching or remove terminal clamps to reconfigure.
Sorry I don't have any info on interference from 24 to 12v converters but if all else fails you could have a kill switch for when interference is a bother.
good luck olewill

I have a 24v set of batteries and 24v engine. Lots of electronics can run on either such as my some Raymarine instruments. Lights are easily run of 24v leds. i have converters for vhf and some electronics, fm radio, etc. when i bought the boat i considered converting everything to 12v but realised you just dont need to. I use 4 24v/12v converters in total and carry a couple of spares. no big issue. i would ditch the extra alternator and stay with the single domestic battery bank.

 

[john]

I'd advise against tapping 12v from a 24v battery bank. My old boat had this and although it worked well, the batteries rapidly decline. I think Nigel Calder discusses it and describes it as a method used by old fishing vessels. In the course of buying batteries over the years, I found you could get much better ah capacity by building your 24v system from 6v (golf cart type) batteries.

 

[testmonkey]

VHF, GPS & other instrumentation still has to run from 12V.

As a side note, might not be true in this particular scenario, but actually many GPSs and instruments accept 9 - 30V input range.

 

[Deleted member 36384]

I have 24V twin alternators (single engine) and battery banks. Most of the stuff is 24V but the 12V stuff runs from 12V switch panel powered from a BEP DC DC Converter 24/12 like this, mine is an older model, but similar: -

http://www.bepmarine.com/home-mainmenu-8/product-402/dcvr-20a-dc-dc-converter-20a

There is a limit of course to the converter current load so you may require more than one to power a couple of separate distribution panels to avoid tripping the converter. It has a built in circuit breaker. On the light front you may find that it is just a bulb change over required. I have bought new domestic lights and they are dual voltage, where the wiring is sized for 12V.

 

[JSYmartini]

My boat is 24v with the few 12v bits running off 2 small dc/dc converters as others have mentioned. My batteries are 12v wired in pairs in series to make 24v. I don't know for sure but I'm guessing 24v batteries are going to be more uncommon, more expensive, and less choice available.
Ideally your autopilot pump motor would be 24v, it's a lot of draw and would need a fair size converter

 

[prv]

I don't know for sure but I'm guessing 24v batteries are going to be more uncommon, more expensive, and less choice available.

I don't think anybody uses 24v batteries on boats, they're always made up of 12v or 6v batteries in series.

Pete

 

[fisherman]

I have two converters, one runs a 12v fusebox, one is dedicated to one of the VHFs. No problems over the 20 or so years they've been there. £30 to £40 each. Many instruments seem to be 10v-30v tolerant.

 

[ccscott49]

My boat ios 24 volt, as are m,y engines, I also have 12 volt VHF and some other stuff, instruments etc, I use a 30 amp 24-12 converter, cant remember the type, but does the job admirably and I get no interference from it.

 

[NormanS]

As a matter of interest, how energy efficient are these converters? How much is lost as heat?

 

[JSYmartini]

I found you could get much better ah capacity by building your 24v system from 6v (golf cart type) batteries.

I quite like this idea for the house bank assuming of course it holds true without being overly expensive

 

[JSYmartini]

As a matter of interest, how energy efficient are these converters? How much is lost as heat?

One of mine gets very warm, don't know how that translates into power loss but there must be some loss.

 

[William_H]

Relating back to my previous thread. A 24 volt system does use less current so more starting power or able to start bigger engines with 24v system. However you would still have the need for a isolated domestic power supply which even when depleted would not hamper engine start and recharge. hence IMHO you need 2 battery ssytems easiest done with a 12v battery for services. good luck to all olewill

 

[ccscott49]

As a matter of interest, how energy efficient are these converters? How much is lost as heat?

Mine doesn't get very warm atall, but I doubt I ever draw more than 15 amps out of it, just got a high capacity one for belt and braces, seems very efficient to me. Do not be tempted to "tap" off 12 volts froma 24 volt bank, it will knacker that battery, ask me how I know!!!

 

[rogerthebodger]

If the 24 VDC is only used for engine starting Vetus have a system for their 24 VDC bow thruster when the boat normally has 12 VDC that for a short tine (when the bow thruster is running) connects 2 batteries normally in parallel (12 VDC) to series (24 VDC).

Here

http://www.vetus-shop.com/vetus-ser...olt-thruster-with-12-volt-charging-p-941.html