Pro's and con's of 12 or 24 volt habitation voltage.

[SquirrellCook]

As I was inspired to think about this after reading another comment on it.
Personally "Murky" is 24 volt base vehicle with 12 volt habitation wiring.
The New build "Betty" again is a 24 volt base vehicle, but nothing has been done that would steer me one way or another.
What are your opinions and why?

Mark

 

[wildebus]

As I was inspired to think about this after reading another comment on it.
Personally "Murky" is 24 volt base vehicle with 12 volt habitation wiring.
The New build "Betty" again is a 24 volt base vehicle, but nothing has been done that would steer me one way or another.
What are your opinions and why?

Mark

There are pros and cons to both options.
The way I see it, if you have a 24V vehicle, having a 24V Leisure Battery setup will let you:

Easier Bi-Directional Charging from Vehicle to Leisure and Vice Versa - you just need one voltage standard for charging and don't have to convert up or down. You can if you prefer use a basic relay or mechanical switch to connect the two systems rather than voltage converters.
This allows you to have a simple split-charge system for Alternator charging of Lesiure Batteries, or EHU and Solar charging can feed the Starter Battery as well as the Leisure Battery in as simple a way as on a 12V Vehicle/12V Habitation setup.
You can get a bigger solar harvesting on a given Solar Controller at 24V compared to 12V as almost all are current limited more than they are power limited. This means either more panels on the same controller, or you can use a 'smaller' (cheaper) controller. On larger PV arrays, the Controller saving when going into a 24V system compared to a 12V system can actually be pretty significant.
Higher Voltage and Lower Current (to achieve the same power) means you can use thinner cable if you want; and for a given cable gauge, you get less losses at the higher voltage.
If you want to use an inverter, you pull less current from the battery - that means you really can get away with a lesser gauge DC cable (which can be pretty significant when it comes to inverter levels of power).

Downsides - you will need some 12V circuits almost certainly, so will need a DC-DC converter in the picture.
You need a 24V battery array of course - so you will need an even number of batteries (so multiples of 2 12V ones, or multiples of 4 6V ones) - This could be awkward in some cases (for example, I changed my 4 x 12V batteries earlier this year to a bank of 3 x 12V batteries. If I has been setup at 24V, I could not have used 3 batteries).
Having said that, when you have a pair of 12V batteries, either setup in Parallel (for a 12V system) or Series (24V system), it is much easier to keep an eye on the batteries when in 24V/Series and make sure they stay balanced compared to doing that on a 12V/Parallel setup.

 

[SquirrellCook]

I can see the benefit of 24 volts on large current drain items.
Though some items are really stuck on 12 volts, for example.
Toilets, roof fans, cooker extraction hoods, smaller range of water pumps, radio's and tv's

Batteries I would normally only ever charge as 12 volts, so in parallel not series. So the same 12 volt battery chargers.
That said, if I was running a multiplus I wouldn't have much choice.

Air and water Eberspachers I would run as 24 volts

Multiplus and the Smart solar are about the same money.

A 10amp DC DC converter should be enough, but throw in a safety margin and say 20 amps

Batteries you'd use the same number as capacity is capacity.

As a pessimist I run independent mains charging for both engine and habitation.
Both of which can be used for charging each other as I run an inverter as a spare from the engine start batteries.

Just not seeing it as a clear choice at the moment, sometimes those seeds that get planted in your head grow to well out of control!

 

[wildebus]

It as not as simple as saying you would have the same number of batteries.
say you wanted 2,500Wh of Storage - that is the equivalent of 200Ah at 12V - or 100Ah at 24V.
at 12V, you could get 1 x 200Ah Battery, or 2 x 100Ah Batteries. But if you want to run at 24V, you MUST get a pair of 12V batteries, or a single 24V.
Like I said, I have 3 batteries - ok for 12V, no use for 24V.

you are talking Victron when you say Smart Solar. Again, they are not about the same money.
Say you have 500W of solar on the roof - on a 12V system, you would need to plump for the 100/50 - £315 from On Board Energy
If you have a 24V system, you could get the 100/20 - that is £153 from On Board Energy. That is not "about the same", that is half the price!


PS.

As a pessimist I run independent mains charging for both engine and habitation.
Both of which can be used for charging each other as I run an inverter as a spare from the engine start batteries.

If you really were a pessimist, then you would need 4 mains batteries chargers! what if the 12V mains charger breaks? I can't charge Habitation. What if the 24V charger breaks? I can't charger Starter. You have the same voltage both ends and if one charger breaks you can use the other, can't you

Sure, you can do as you say, but you did ask the question ....

 

[SquirrellCook]

At the moment we are 24 volt base vehicle with 12 volt habitation.
24 volts is provided by two 90ah 12 volt batteries each having it's own 7ah 12 volt charger.
12 volts is via two 220ah 6 volt batteries, charged in series with the same 7ah 12 volt charger.
As the distances and locations are very close, any charger can be swapped around between batteries.

I would keep the same setup for the new build engine batteries, but having been sold on the idea of a multiplus things change.
At the moment we are looking at locating the habitation batteries towards the back of the vehicle along with much of the associated toys.
Yes you are correct in saying the cost of solar charging reduces with a 24 volt system.
The solar will consist of 4 panels, two running the length of each side of the roof.
Each side will be connected in series with the pairs in parallel, providing about 10 amps stall and 75 volts OCV
The multiplus is all about fridge starting, and I'd like to think 800watts would do it. I expect the 24 volt version would do it better.
As a safety margin I might go for the 1200watt version.
Another plus for 24 volt multiplus is using the second charge output for holding up the engine batteries, though using something like a Meanwell DC DC converter you could take the 12 volts up to 24 although halving the charge current.

As for the batteries I'd like to up the capacity too, so either two more 220ah 6 volt ones, or if the budget improves a pair of lithium's at 100ah 12 volt each. Those little 6 volt batteries are heavy.

All this said, there is still the pull of 12 volts by all the other habitation toys.

 

[GEOFF]

One advantage with 12v vehicle battery is that almost any other MH would be able to help (jump start) in the event of a flat battery. Geoff.

 

[wildebus]

Interesting way to charge the batteries. Clever idea And redundancy there as well (or at least no single point of failure).

Yes, the Multipluses do have the "trickle charge" connection for the starter. I don't use it as I have a VSR style Split-Charge so that gets enabled anyway and so get battery charging that way.
Something that can be awkward with the trickle charge of a starter battery doing that which can cause an issue is if you have a split-charge system with a B2B that auto-switches on when detecting a higher voltage (most do nowadays). The voltage of the starter battery will rise and get to the threshold, turn on, and the B2B will start to pull current out the starter battery at a higher rate then the trickle charge is putting in - so the effect is your trickle charge is actually causing the starter battery to drain!
This chart is quite amusing .... in this case it shows the effect of putting a 20A battery charger on the starter battery - and how that "charger" results in a drain instead, due to the 40A B2B kicking on.

REDARC SB-Voltage by David, on Flickr

Interesting observation on the Fridge. You have the 240V Fridge, as do I and that is fed by the inverter of course. If you had the 12V version of a compressor Fridge, you would still get that in-rush current surge. This is a downside as just as you have to oversize the inverter to cope with the 240V inrush, you would need to oversize the DC-DC converter to cope with the 12V Current inrush (but the extra cost of the bigger DC-DC is offset by things like the cheaper solar controller for example.

 

[wildebus]

One advantage with 12v vehicle battery is that almost any other MH would be able to help (jump start) in the event of a flat battery. Geoff.

True - but that is one aspect of the 12V vs 24V debate you don't tend to get a choice over!

 

[SquirrellCook]

So at the moment still leaning to the 24volt side and a little of topic I've been reading up on the Multiplus 24/1200/25.
Connectivity, it seems that this is not a Bluetooth device. So I'd have to convert to using the VE port? I read that once you use the VE ports you loose the ability to use Bluetooth. So yet another device is required. Colour control? Very expensive. Would you have the same functionality if you connected to your devices via a Raspberry pie? Is there any cabling limitations? Every step seems to add complications. Though this issue is shared with 12 and 24 volt setups.

 

[wildebus]

So at the moment still leaning to the 24volt side and a little of topic I've been reading up on the Multiplus 24/1200/25.
Connectivity, it seems that this is not a Bluetooth device. So I'd have to convert to using the VE port? I read that once you use the VE ports you loose the ability to use Bluetooth. So yet another device is required. Colour control? Very expensive. Would you have the same functionality if you connected to your devices via a Raspberry pie? Is there any cabling limitations? Every step seems to add complications. Though this issue is shared with 12 and 24 volt setups.

You are correct that it does not have native bluetooth. However there is a solution - https://www.victronenergy.com/accessories/ve-bus-smart-dongle.
This should work with all Multipluses with a VE port and to connect it you just use a standard RJ-45 Network Cable.
One word to note - this needs a minimum version of firmware on the Multiplus to work and if you need to update it you need to have a VE.Bus Mk3-USB Dongle - https://www.victronenergy.com/accessories/interface-mk3-usb - to connect the Multiplus to a computer in order to run the Updating software (you cannot use the RJ45 port on the Multiplus to an Rj45 Port on the computer or a Router).
I suppose you could if you needed to update it go to an approved supplier to buy the Dongle and see if they will update the firmware whileyou are there?

This Smart Dongle actually works very nicely with the same Victron Connect app as you use on the Solar Controller a(nd interestingly enough provides more control then the Front Panel OR using the VE.Configure software ).
I like the information it provides and the display on the screen - informative and logical. I can post some screenshot examples of one I setup if you like? (just looked and there are some examples here - https://www.victronenergy.com/live/vebus_smart_dongle_manual )

PS. If you DID use a Victron unit like a CCGX or a Venus GX, you would just use an RJ45 Network Cable to connect. If you used a Raspberry Pi you would need the Mk3-USB Dongle.