Re: 12 volt or 24 volt ? (Long)

On 23 Jun 2006 14:18:23 -0700, "Gibbo" <gibbo@xxxxxxxxxxxxxxxx> wrote:

Me and tricky dicky have never agreed on this one.

Lots of people "know" that 24 volt systems are better than 12 volt
systems. But no one ever seems able to come up with a reason *why*.

Will someone give me a *valid* reason for this. Because I can't think
of one. And I've been doing this a *long* time.

Don't say "it's more efficient". That's just arm waving.

Tell me *why* you think it is more efficient. In terms of electrical
efficiency, monetary investment, time spent finding the equipment etc.

Coz I don't think it is. In fact, I *know* it isn't.

On a *very* simple installation, consisting of say a battery and a
starter motor it could be more efficient. Anything more complex and the
disadvantages disappear.

Gibbo

Ok I will rise to the bait ;-)
First costing of components.
You regulaly suggest that 24v equipment is pricier than 12v equipment,
consider the following. (Aquafax list prices as quick and easy to get)

Chargers Victron Centaur
12V GBP 24V GBP
60A 341.47 30A 373.47
80A 629.57 40A 512.19
100A 853.64 60A 586.89

Combi Inverter Victron Multiplas
2500VA 120A 1457.85 3000VA 70A 1457.85

Inverter
1600VA 757.61 1600VA 756.21

Water pumps Same price 12v or 24V
Bilge pumps Same price 12v or 24v

Fridges 12 or 24v Auto switching Same price ;-)

I will certainly grant you that 24v halogen lamps are pricier at 24v
but I do not particularly like halogen lamps for boats.

I also grant that there may be more "deals" around for 12v equipment
due to the greater volumes sold. However I was talking to a guy
recently that picked up a 24v 3000w 70A Victron combi for GBP1200 at
Crick. So deals are not just related to 12v.

Cable sizing and efficiency
The general attitude is 24v needs half the csa of cable compared to
12v. As you well realise this is not quite true.
If we consider a load of 1000w a total length of run of 10m and a
voltage drop at the load terminals of 4% of system voltage the cable
sizes are as follows
12v supply 28.5mm2 ok 35mm2 in real cable
24v supply 7.1mm2 ok 10mm2 in real cable

Granted this 24v system is no more efficient than the 12v system but
this shows the nonsense of "Half the cable size"
If one does wire in "half the cable size" then the 24v system is more
efficient than the 12v system.

Ease of Installation
If we accept that 24v requires smaller wiring than 12v then the wiring
has got to be easier. We have all at some time have been presented
with a 6mm feed to a switch that is designed to accept a 2.5mm wire
max.

I fully expect to be shot down in flames ;-)

I need to walk the dog!

Richard

Nb "Pound Eater" Parkend G+S
.

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