Converting 12V Leisure Electrics to 24V

wildebus

Forum Member
I mentioned I would be adapting a vehicles lesiure electrics from 12V to 24V .... Well today was the Day :)

The van in question was a 7.5t Horsebox on a 4,5l Mann Chassis and owned by Asterix from the Motorhomer.com Forum. The following is what was done, the pros and cons of 12V vs 24V and the cost implications of the change.
Changing the battery bank itself from a pair of 12V in Parallel to a pair of 12V in series was straightfoward and needed minimal parts.

Summary by system area:

1) Split Charge system
The existing system was a Redarc B2B/MPPT Controller, but this had failed.
12V Option. Fit another B2B Charger.
24V Option. Fit a VSR.
VoltageProsCons
12V SystemBetter Charging ProfileHigher Cost
24V SystemLower Cost
Allows Starter Battery to charge from Leisure Battery charging systems (Solar, EHU)
Will not charge Battery to full extent due to Alternator voltage limitations.
Needs Heavier Cable.

2) Solar System
The existing 660W (800W potential) Bifacial PV Array had connected to a Redarc B2B/MPPT Controller, but this had failed so an replacement was required.
12V Option. Fit an MPPT Controller capable of at least 50A and potentially 70A.
24V Option. Fit an MPPT Controller capable of at least 25A and potentially 35A.
VoltageProsCons
12V SystemHigher Cost due to Higher Output Controller
24V SystemLower Cost due to Lesser Output Controller

3) Inverter
There was an existing 24V 1600W Modified Sine Wave Inverter that came with the Horsebox. This was servicable and a good brand (Waeco).
VoltageProsCons
12V SystemNeed to buy another Inverter to have 240V off-grid electrics
Less efficiency from 12V supply
Heavier Cable to supply cable
24V SystemNo cost to use existing Inverter
Lighter Cable to deliver same power

4) 12V Leisure Electrics
There was the various array of 12V Electrics to be serviced - Fridge, Lights, etc.
VoltageProsCons
12V SystemNo changes required12V Supply Voltage varies on battery level
24V System12V Voltage level can be more consistantNeed to install a DC-DC Converter to provide a 12V supply from a 24V

Costs of going 24V:
Using a VSR instead of a B2B provides a saving of approximately £200.
The 24V system means a Victron 100/30 is suitable. a 12V System would require at least a 100/50 or even a 150/60 in the Victron range. Using the 100/30 on a 24V system provides a saving of approximately £100 over the 100/50 on a 12V system whilst also providing more capability.
Using the existing 24V Inverter instead of purchasing an equivalent spec 12V Inverter provides a saving of around £200.
Needing to fit a DC-DC Converter suitable to support a Compressor Fit is a cost of around £130
Not needing to buy a device to allow the Starter Battery to charge from EHU and Solar would be a cost saving of around £60

Summary:
Updates and Purchasing Products were required whichever route was taken, but taking the 24V route meant a saving of over £400.
Clearly some of the saving was down to already having a 24V inverter.
The downside to the charging compromise of using a VSR instead of a B2B is mitigated by having a quality Smart MPPT Controller and a decent PV array to 'take up the baton' plus the benefit of getting the same Smart Charging available to the Starter Battery.

System following installation (but before cable tidying & clipping)

Horsebox Systems
by David, on Flickr
(Sorry for poor pic. Didn't notice until too late to take another)
 

wildebus

Forum Member
The more I look at 24 volt habitation, the more your selling it to me Dave.
I have a 12V system myself. All my high power devices are 240V so rely on the Inverter for those (which I am perfectly ok with).
I was very tempted at the time I got the Victron Multiplus to switch from 12V to 24V as I knew there would be a benefit but I didn't.
TBH, I really should have!
As it happens, I could NOT easily go 24V any more as I am now running 3 x 12V batteries, but that would not be an insurmountable task even then. I suspect that when/if I do another van it will be 24V :sneaky:


Couple of extra comments on the 12V-24V changeover that didn't mention in the first post ...
Asterix had a switchable 240V AC-12V/24V DC Mains Charger - that meant no cost either way here, but for others, it could be an incurred cost if they have a charger that is not switchable.
There is also the extra little gizmo that ideally would be fitted when you have a pair of 12V in series - a Battery Balancer. They can be had from around £15 posted (the HA02 looks reasonable) and I would recommend one.
 

RAW

Forum Member
Thinking about it on Sylvia there is a long run between the two leisure batteries
Would need the 240V charging system replacing as that is 240V to 12V
Current Solar System would work with 24V fine

QUESTION then is would it be alright to have a long run of cable between two batteries connected in Series, probably not the best way I would imagine would be the answer and could be done.
 

SquirrellCook

Forum Member
QUESTION then is would it be alright to have a long run of cable between two batteries connected in Series, probably not the best way I would imagine would be the answer and could be done.
I'd be thinking about how I would charge them? One or two battery chargers? Use a battery balancer? One or two BMV's?
 

RAW

Forum Member
I'd be thinking about how I would charge them? One or two battery chargers? Use a battery balancer? One or two BMV's?
Think two battery chargers would make it all extremely complicated, just one BMV is OK as you configure it for whatever the system is so it would be like 2 x 120AH 12V = 1 x 240AH 24V I think
 

wildebus

Forum Member
I don't think a 24V system would work well with the batteries so far apart. The batteries really need to be identical I would say to operate correctly.
You can "get away" with more on a 12V system with multiple batteries as if one battery was not very good, it wouldn't be that evident, as the other/s can fill in, but in a series setup, you need both sides of the series (0-12V and 12V to 24V) to do their bit.
The interlink tends to be fairly chunky between the two batteries as well to avoid voltage drop between the two. Yesterday I used 16mm cable for most of the charging connections (and could have used smaller) but the cable between the two batteries I used 35mm cable over a distance of around 4 inches to avoid any possible voltage drop over the cable. If you had a long run, you would used 50mm, 70mm or even pair up 50mm. Expensive!
 

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