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Old 07-11-2006, 09:36   #1
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practical 24V system?

I know that a lot of boats use 24V systems for bow thrusters and windlasses, and that the cost of those items in 24v is not much over the 12v model, which made me wonder if anyone has converted their cruising sailboat over to 24V?
Is the cost of converting the small items like lights, radios, etc. still too high to make this practical? It seems that there is some advantage in using 24V for large loads like high output alternator, windgenerator, fridge. If you were looking at a bare hull and starting from scratch would you consider going the 24V route for all or part of the system?
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Old 07-11-2006, 11:27   #2
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24/12 V systems

Many vessels have converted to a mixed 24/12 V system for the reasons that you have given. The "key" to making this work is to use a 24 V shore charger AND a product such as made by Vanner and Newmar which is a "switch-mode" dc/dc converter that is a specialty item. What the device does is divide exactly in half the voltage appearing across the 24V battery bank so that 12V house loads can "tap" off of the first 12V half of the bank. Obviously you need to choose the most efficient product for your application and make sure that the power rating is sufficient for the battery bank as well as the 12V loads else the 12V loads will "drag" down the 12V section unevenly from the "upper" 12V section.

Another solution is to use a switch-mode DC/DC converter that converts the 24V bus to a regulated nominal 12.6V (or so) strictly for 12V loads.

One unhearalded advantage of using the first method to deliver 12V current is that one automatically gets a battery bank that equalizes the voltages across each 12V battery thereby helping to keep each battery "tracking" the other.
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Old 07-11-2006, 11:49   #3
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We have a mixed system. A 24 volt bank made up of (6) 8 volt golf cart batteries and a 12 volt system made up of (4) 6 volt golf cart batteries.

It is a fairly simple system to understand and it gives us lots of flexibility. We charge from shore through two chargers a 12 volt and a 24 volt. They charge each bank independently and you can charge either seperately. We can also charge both banks through the generator the same way. We can charge either bank with its respective alternator 12 or 24 volt. We have a Dc to Dc converter so we can supplement the 12 volt bank with the larger 24 volt bank.

I like the system and have found it gives us of lots of flexibility. We run the big stuff with the 24 volt and house loads with the 12 volt. If an alternator dies we can charge with the generator and the charger. If the generator dies we can charge with the alternators. We have no solar or wind charging.
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Old 09-11-2006, 04:20   #4
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Whatever happened to the 42V PowerNet?
” At the time of the first AABC (Advanced Automotive Battery Conference) in Las Vegas in 2001, it was widely expected that the 12-volt automotive battery (14-volt PowerNet) would progressively be replaced by a 36-volt battery (42-volt PowerNet), in order to cope with increased electrical loads. ... A general switch from 14-volt (12-volt battery) to 42-volt (36-volt battery) for conventional automobiles is now regarded as extremely unlikely ...”
See the “Report From AABC* 2006" ~ By Mike Weighall
http://www.evworld.com/view.cfm?sect...e&storyid=1042

*Advanced Automotive Battery Conference
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Old 09-11-2006, 08:41   #5
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Gord, I'm told that 42V automotive standards have been dumped because the car makers finally figured out that when you put 42V across a switch or relay, instead of 12V, you need more robust contacts and 42VDC-rated contacts and parts just aren't price competitive. Same for electronic controls, they're just not as available in "50VDC" ratings.

Dunno if that's bunk or not, just the explanation I heard for why the new standard in auto electrics has fallen by the road.
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Old 11-11-2006, 14:48   #6
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The automotive market is so huge in terms of electronic/electrical volumes that ANY relay contact requirements WILL be met by manufacturers almost overnight. There are a multitude of problems with getting such a far-reaching standard to be accommodated, one of which is the manufacturing cost of the requisite dc/dc bi-directional converters which are necessary to convert 12V nominal from/to the nominal 42V levels. We haven't even begun to discuss the "political" problems always hindering widespread acceptance of any standard.

Probably the European auto manufacturers will merely introduce the technology into their vehicles with or without a standard being adopted. Look for Mercades or BMW to come out with such implementation. To be sure, whoever first delivers an engine without camshafts utilizing electronic (could be solenoid but probably something akin to piezoelectric or electro-hydraulic) driven valves. That is a huge reason alone to use a higher voltage standard.
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Old 11-11-2006, 14:58   #7
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Rick, the scuttlebutt I've heard says that the relay (and more important, switch contacts) simply *cannot* be met in a reasonably cost effective and reliable manner.

That may be totally wrong, but in theory 42VDC systems and electric direct drives (i.e. for power steering) were going to be deployed by now--and something has prevented that from happening, with no official comment from the many sources that said we'd be on 42VDC systems by now.

Could just be they've decided not to make any changes until they are most economically phased in, i.e. by major platform changes like GM's "skate" with a complete new engine and power system. (Why waste money upgrading systems you're looking to scrap?<G>)

Since the only reason we have a 12VDC spec in cars and trucks today is the US Navy...I don't see any incentive for carmakers to make a similar change.
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