Switching from 12V to 24V

[coopec43]

Yes OK. Using A DCDC charger (or similar approach converter, regulator etc) to solve the problem is the way to go in the short term.

In the longer term I'm switching to 24V and I like Guyrj33's approach.

NOTE: Clive has stated his starter will function with 24V input.

It's only the bulbs and the fans that are a concern.

The bulbs could be replaced with 24v bulbs or possibly with LED units that are multi-voltage.

The fans, well i'd try them on 24v and see if the're ok. Most likely the'll just spin faster.
If that's not acceptable and you want to keep the fans, then you could add a small DC DC converter to each fan.

Maybe I should have read this article before posing my problem!

12 Volts DC or 24 Volts DC?

Boat Electrics - 12 Volts DC or 24 Volts DC?


Clive

[atoll]

did you read the next article as well,regarding using an equaliser?
not ideal using an equaliser,tapping into a 24v bank IMHO,better to have a dedicated 12v battery for engine start and a dedicated 24v house bank.

Boat Electrics - DC Converters and Equalisers

[coopec43]

Originally Posted by atoll

did you read the next article as well,regarding using an equaliser?
not ideal using an equaliser,tapping into a 24v bank IMHO,better to have a dedicated 12v battery for engine start and a dedicated 24v house bank.

Boat Electrics - DC Converters and Equalisers

Not yet Atoll but I will! Actually I'm looking forward to reading it. (I thought I should be out working on the yacht)

Thanks for your help.

Clive

[Thalas]

I believe Delos is on a 24V bank. Brian seems pretty dialed in. Is it likely that Delos was wired that way when he bought it or did he convert? And if so, what would be the advantages? They recently reduced propane by moving to things like induction plates for cooking. I'm assuming that has to be 110V through the inverter, right?

[smac999]

Originally Posted by coopec43

So if I used one 12V battery to power some lights and the other 12V battery to power the rest of the lights it wouldn't be very clever?


Clive

no you will never be able to charge them properly. one will always be lower then the other. as a 24v charger will put the same charge through both, even if one is lower. you can buy battery balancers. but it should just be done correctly instead.

[coopec43]

Originally Posted by smac999

no you will never be able to charge them properly. one will always be lower then the other. as a 24v charger will put the same charge through both, even if one is lower. you can buy battery balancers. but it should just be done correctly instead.

Thanks for that. I had assumed (incorrectly) the charge would go into the flatter battery first before charging them both.

Clive

[noelex 77]

I have owned yachts with both 12v and 24v house systems and I am sold on the advantages of 24v for larger cruising yachts.

Traditionally a 24v house system involved the careful selection of equipment, but this has changed. These days most marine equipment is fine with either 12 or 24v right out of the box, even consumer equipment such as a phone charger that was traditionally powered by mains or a 12v cigarette lighter plug is likely to be USB powered and most of the USB plugs are fine with a 24v input.

For those very few devices where 24v is not possible, cheap 24/12v converters are available. There are only two devices on my boat that need 12v, all the rest run on 24v.

The main advantage of 24v is in the more efficient running and greater availability of larger appliances. On my yacht the anchor windlass, bow thruser and main alternator are all of a size that is simply not available in a 12v model. I could compromise and fit smaller units, but why.

The other advantage is reduced voltage drop and much easier wiring, both for the boatbuilder and for any subsequent installations. For example, the main power feed from my batteries to the switchboard is 120mm sq or 4/0 gauge cable. To achieve the same percentage voltage drop for a 12v system, it would require three 120mm sq wires (or six with the negative side) or a single cable of around 400mm sq! The latter is going to be very hard to find. Both are going to be very hard to fit. Termination would be complicated. Even large battery switches and fuse holders will only accept a single 120mm cable.

So if you are building a new yacht, or replacing the wiring and electrical system on an existing boat, consider the advantages of a 24v system.

[rgleason]

I have considered having a 24vdc House Bank with a Victron Orion 24DC/12DC Converter to provide house panel (lights, Nav, etc). I don't expect we would convert entirely to 24vdc as it would require too much replacement.

Our main loads are

1. Starter. - Is it hard to find a Yanmar 24vdc starter? That change would help cable sizes a lot.
2. Danfoss Refrigerator. - I should check the electrical specs, perhaps it will run 24vdc, but it is connected to the house panel. It is just 4.2-6.5 amps so it is probably not worth changing and relocating the source.
3. Navigation with Radar on - I don't think this is worth changing either.
4. It might help if we were to install a windlass.

A 24 volt system requires a 24volt alternator. There are not that many of these marine types available. In looking at the output curves for 24vdc, it seems to me like they require higher rpm to get started and the amp output is reduced from 12vdc (of course it makes sense). If you interested in producing power at low rpm with a 12vdc alternator, say

• 800 engine rpm (alt rpm 1760, with 2.2 ratio) of at least 40amps.
• 1000 engine rpm (alt rpm 2200, with 2.2 ratio) of at least 85amps.

That is perfectly reasonable and achievable.
With a 24vdc alternator is it achievable to produce the following:

• alt rpm 1760 = 20 amps?
• alt rpm 2200 = 42 amps?

I believe the solar MPPT controllers can handle 24vdc systems, both Victron and Genasun.


What other issues are there with such a 24vdc system?

[coopec43]

rgleason

ALTERNATORS

I bet my marinised Perkins 4-108 diesel still has the same alternator as a tractor or industrial diesel cousin.

auto alternators vrs marine alternators - Cruising Anarchy - Sailing Anarchy Forums

http://www.cruisersforum.com/forums/...tor-52508.html

STARTER MOTORS

All mechanics and diesel fitters I have spoken to say there is no drama using 24V on a 12V starter motor. (Several have pointed out I could do damage to the starter motor if I attempt to start a motor with flat batteries) My B-I-L was a diesel fitter with Caterpillar and he said they started a diesel engine with a 12V starter motor using 24V and they had no problems in 20 years.

DANFOSS COMPRESSOR

My Danfoss compressor in a Waeco/Adler Barber/Dometic (!!!) system can be run on 12V or 24V but they prefer 24V.

[coopec43]

Now this is interesting.......

12v Motors on 24v
Motor current rating
Motors are specified to run at a stated rpm at a particular applied voltage with a specified loading – that at which the motor takes its maximum continuous current.

If you run the motor under a lighter load than this ‘name plate rating’ its current consumption will reduce and its speed will increase slightly.

If you increase the load, then the motor’s current consumption will increase and its speed will reduce. Obviously you are now exceeding the motor’s continuous rating so it will start to get hotter than it should. The greater the overload, the quicker the motor will heat so there is a time limit on such an overload. However it is usually safe to run a motor at a 300%-400% over current for, perhaps, a minute – although this will vary from motor to motor.

Motor voltage
If you run a 12v motor from 24v its current drain and speed will still depend on the mechanical loading. However under no load it will now run at twice the speed at which it originally ran with 12v. Heating in the motor is still related to the current – so you can still run it at its full rated mechanical load/current. However if the motor is badly balanced you may expect noise and vibration as the general construction may be inadequate for the faster speed. There may also be a problem with brush wear since the brushes are being asked to switch the current twice as fast. These effects are, however not very likely and usually the speed increase is quite OK.

There is one caveat on this. The motor is an inductive device and the commutator and brushes are a mechanical, switch. Such a mechanical switching system will have a limit on the maximum rate at which is can work and if this is approached, the commutation breaks down. Exactly what the limits are, I would not like to say but one effect is noise – and extreme noise can, on occasion, cause a controller to fail. The effect is quite rare – but beware of excessive over-revving.

Motor speed limits
Limits on motor speed are not simply the bearing quality. If you rev a motor hard enough – centrifugal force will take over and the rotor will fly to pieces. Also brush and commutator design is important. Depending on the design these will have a maximum switching rate and operating above this speed will cause tremendous brush arcing. In extreme circumstances this will generate severe noise transients which can destroy the controller. This is unlikely: we have only ever seen one customer do this: he was running 12v motors on 36v and blew two controllers! These motor limits are not things a controller manufacturer can really comment on: you need to consult the motor manufacturer.

If you overload the motor, its current rises in the same way whether the motor is running from 12v or 24v. However on stall the current from 24v could be twice that from 12v, so the motor could get four times as hot (heating is proportional to the square of the current). This however won’t happen when you are using a good controller as the controller will limit the current to its designed value. Also the controller varies the voltage on the motor so you are probably not going to use the motor at full voltage in any case.

Another consideration is that, if you put too much current through a permanent magnet motor, it is possible to slightly demagnetise the magnets. This is cumulative: the motor’s performance will drop slightly each time you do it. However, for battery motors, is is probably fairly safe to assume that, at the rated voltage, the current drawn when the motor is stalled will not reach this demagnetisation level. If you were to run a 12v motor off a 24v battery the stall current could then be excessive if it weren’t limited by the controller.

Therefore, provided you chose a controller suitable for the motor you use, you can usually run a motor 12v motor from a 24v battery with no effect except that full speed is doubled.

https://www.4qd.co.uk/docs/12-24-36-or-48v-operation/

[coopec43]

rgleason

"What other issues are there with such a 24vdc system?"

Solar Panels If you want a small simple power system, 12 volts will probably be easiest. You can use 12 volt DC directly in very small systems, adding 120 volt AC with an inverter. 24 volts battery systems have some technical advantage. If you think you will have more than 500 watts of solar modules, consider 24 volts.(Pangeabuilders)

Bilge pumps

Inverters You can get much bigger inverters on 24V or 48V than 12V.

Clive

[john61ct]

Victron MPPT is happy to output 12V or 24V as detected on boot up.

You get double the Watts capacity per controller going to a 24V bank,

e.g. 75/15 at ~$130, go from 220-260W @12V up to ~500W @24V

Efficiency gains from MPPT are greater with higher voltage panels, 40-65Voc rated would be ideal.

[Pelagic]

Originally Posted by noelex 77

I would keep the engine, start battery etc 12v.

The 12v start battery can be charged by a second 12v alternator, or a DC-DC 24/12 charger from the 24v alternator.

I think the OP has it figured out

IF all that is needed is a 24v Start battery, a big advantage of that is an Emergency Parallel switch from the 24v House Bank and stronger cranking power.

Then a simple DC/DC 24v/12v convertor for any 12v circuits would keep all the fans and any other 12v demands available

[coopec43]

Originally Posted by Pelagic

I think the OP has it figured out

IF all that is needed is a 24v Start battery, a big advantage of that is an Emergency Parallel switch from the 24v House Bank and stronger cranking power.

Then a simple DC/DC 24v/12v convertor for any 12v circuits would keep all the fans and any other 12v demands available

Did you read Noelex's comment #37? (I don't have room for a second alternator and it would be an engineering nightmare)

[rgleason]

I have a BD80 Danfoss Compressor, the Danfoss manual I found on line shows

BD35/50/80F/250GH/100CN: 12V DC systems: 10.4V (9.6V min.) - 17V max. ;
24V DC systems: 22.8V (21.3V min) - 31.5V max.
BD35F/BD35K: Solar systems: 10V - 45V, no battery protection.

I wonder if the controls are also 12vdc or 24vdc?
I'll contact Ozifridge. I wonder if 24v would perform differently.

From your chart the 26si chart, the 24v version appears to produce approximately 1/2 the amps as expected. The charts shows that startup is later in the rpm curve, as expected.

Observation: Balmar's alternators seem to produce more power at lower RPM generally. Don't know of that is true with the 28si.

Motor Starters at 24v it appears they run faster, when the solenoid kicks in and the start gear is engaged the motor will be running faster. There will be greater loads on the gear at start. It does not appear to matter if one starter ran 20 years.

The other question I have is with 24v starters will there be a likelyhood of greater transients which can affect electronic gear?

These alternatives for equipment might be very useful.


Nolex's comment that Nav equip works with 24v now and many other pieces of equipment would have to be checked for the particular boat equipment. The House panel breakers would have to be checked too. Lights, masthead light and LED's would have to be changed. Also all the 12vdc plugs that have USB chargers would have to be checked too.


Leaving the house panel 12vdc with a Victron Orion DC/DC might be easier, provided the engine starter could be 24vdc, or alternatively have a start battery that is 12v and also put the House panel on that with the DC/DC converter between? I am having a problem with how that works. I haven't thought it out.


OP and Pelagic might have a good approach for some boats.