Why 12volts on narrowboats?

[The Construct]

This has probably been asked loads of times but why is 12V chosen for narrowboat lighting, fans etc? The batteries are usually at one end so long runs are inevitable creating volt drop problems. So why not 24V or say 48V.

I'd be interested in your views

[Paul C]

Some boats these days are 24V.

[Grebe]

In general terms cars and light vans were 12v and boats used car/van based engines which were fitted with 12v electrics, leading to 12v auxiliaries.

[Arthur Brown]

Simple! The automotive industry picked 12v and that ruled the accessories market, all the lights switches and pumps you could want in the car and caravan industry are 12v.

[Gibbo]

In general terms cars and light vans were 12v and boats used car/van based engines which were fitted with 12v electrics, leading to 12v auxiliaries.

 

Absolutely, plus 12 volt radios, HiFi's, power supplies, bulbs, and all the other stuff, plus replacement alternators, starter motors etc for maintenance are much more widely available, and usually cheaper, which leads to 12 volts winning even if 24 volts is technically preferable.

 

48 volts opens up a whole new can of worms because the charge voltage is above 50 volts which technically brings it into the remit of the European Low Voltage Directive (another humongous pile of legal bullshit paperwork from Brussels) and all its strict legal requirements.

[The Construct]

Absolutely, plus 12 volt radios, HiFi's, power supplies, bulbs, and all the other stuff, plus replacement alternators, starter motors etc for maintenance are much more widely available, and usually cheaper, which leads to 12 volts winning even if 24 volts is technically preferable.

 

48 volts opens up a whole new can of worms because the charge voltage is above 50 volts which technically brings it into the remit of the European Low Voltage Directive (another humongous pile of legal bullshit paperwork from Brussels) and all its strict legal requirements.

 

Leaving the engine electrics alone, I was wondering about the 12V distribution and the inherent volt drop issues. But some are 24V now, I didn't know this. All the consumer stuff could be supplied via DC/DC converter whilst distributing a higher voltage than 12Vdc, but I don't know how practical this is.

 

Why would 48V be a problem, most boats have 240V on them?

[Nickhlx]

Leaving the engine electrics alone, I was wondering about the 12V distribution and the inherent volt drop issues. But some are 24V now, I didn't know this. All the consumer stuff could be supplied via DC/DC converter whilst distributing a higher voltage than 12Vdc, but I don't know how practical this is.

 

Why would 48V be a problem, most boats have 240V on them?

 

If the new vehicle nominal voltage of 36 volts ever catches on, perhaps we will see more 36 volt based accessories...

 

I wouldn't be surprised though if each had a "36V to 12V" dropper built in....

 

Nick

[Gibbo]

Leaving the engine electrics alone, I was wondering about the 12V distribution and the inherent volt drop issues. But some are 24V now, I didn't know this. All the consumer stuff could be supplied via DC/DC converter whilst distributing a higher voltage than 12Vdc, but I don't know how practical this is.

 

If you're going to introduce DC/DC converters to up the voltage, then down again at the other end, you might as well go the full hog and use 230 volts outright and reduce the losses to almost nothing. Upping 12 volts to (say) 50 volts or 100 volts, or any other voltage, introduces the same losses as upping it to 230 volts (despite what some might tell you).

 

Why would 48V be a problem, most boats have 240V on them?

 

Indeed, and all 230 volt equipment has to comply with the Low Voltage Directive (LVD) (as would any 48 volt installations/equipment). However 230 volt equipment is ridiculously common so economies of scale have swallowed all the costs of compliance with the LVD. If you sell a million of something, spending 10 grand to get it through compliance testing gets swallowed to almost nothing per unit. If you only sell 10,000 of them that's added a quid to the cost of each unit. A quid on the manufacturing cost of a light bulb fitting can make it unviable.

 

If the new vehicle nominal voltage of 36 volts ever catches on, perhaps we will see more 36 volt based accessories...

 

I wouldn't be surprised though if each had a "36V to 12V" dropper built in....

 

Nick

 

Indeed, and that was originally going to be 42 volts if you think back. That got killed stone dead because the charge voltage would then be in the region of 50.4 volts which just brought it within the remit of the Low Voltage Directive. Vehicle manufacturers already have horrendous costs with all the vehicle legislation and to also have to type test for another one put an end to the idea.

 

36 volts will also fall on its arse. Although if copper continues to rise in price at the rate it is it might just stand a chance.

[Chalky]

If you're going to introduce DC/DC converters to up the voltage, then down again at the other end, you might as well go the full hog and use 230 volts outright and reduce the losses to almost nothing.

 

The traction batteries on Hybrids and Electric Vehicles range from 180V up to about 400V. These often use a DC-DC converter to generate the 12V nom supply. Nice big devices in the 2 - 3 kW region and water cooled. There is one Japanese manufacturer who uses a 400V battery then uses a DC-DC converter to up the voltage to 650V for the traction drive - 40kW!

 

The batteries are going to be common place on the 2nd hand market one day once they've passed their sell by date as traction batteries. They'll be fine as domestic batteries and pretty bomb proof. Main issues will be cost, "interesting" failure modes, and the fact that 400V DC is lethal compared to AC.

42V was the big thing 10 years ago however since then the demand for power has risen dramatically. It's going to be interesting what voltage is settled on. 48V charged from an alternator will be above the EU thresholds, 48V DC-DC converted from a traction battery won't.

Edited June 22, 2012 by Chalky

[Gibbo]

..."interesting" failure modes...

 

You should be in marketing not engineering

 

I totally agree with the rest of your post.

[The Construct]

If you're going to introduce DC/DC converters to up the voltage, then down again at the other end, you might as well go the full hog and use 230 volts outright and reduce the losses to almost nothing. Upping 12 volts to (say) 50 volts or 100 volts, or any other voltage, introduces the same losses as upping it to 230 volts (despite what some might tell you).

 

{snip}

I didn't make myself clear, I was thinking about connecting the batteries in series (say 24v (or more now 36v has been mentioned)) and supplying lighting etc throughout the boat. Where a socket is needed for an appliance, fridge or TV or whatever, stick a DC/DC converter to get down to 12V. It would mean less copper installed, it may mean lower losses (for a specific cost) and may have an effect on the efficiency of the 'leisure batteries'. My canvas is blank at the moment so I am just wondering if the optimum has already been achieved or whether there is a bit in it for improvement.

 

Its interesting to read your posts, theres a lot going on in the automotive industries which I didn't (don't) know about, so thanks for all the replies, and please keep 'em coming.

[Paul C]

MOtorcaravans and caravans use 12V for their domestic equipment. 24V stuff does exist, for the small market including trucks. With the economies of scale, 24V stuff is much more costly than 12V. So there would need to be a strong reason to change. 12V is a kinda standard for domestic stuff, its difficult to get the necessary momentum to change standards. A good example is the Betamax vs VHS war - Betamax was technically better, but flopped.

[RLWP]

You should be in marketing not engineering

 

I totally agree with the rest of your post.

 

Oh, there is a lot of creativity in automotive engineering. 'Unplanned thermal incidents' is one of my favourites

 

Richard

[Gibbo]

I didn't make myself clear, I was thinking about connecting the batteries in series (say 24v (or more now 36v has been mentioned)) and supplying lighting etc throughout the boat. Where a socket is needed for an appliance, fridge or TV or whatever, stick a DC/DC converter to get down to 12V. It would mean less copper installed, it may mean lower losses (for a specific cost) and may have an effect on the efficiency of the 'leisure batteries'. My canvas is blank at the moment so I am just wondering if the optimum has already been achieved or whether there is a bit in it for improvement.

 

Its interesting to read your posts, theres a lot going on in the automotive industries which I didn't (don't) know about, so thanks for all the replies, and please keep 'em coming.

 

So, say you series the batteries up to 48 volts. All your 48 volt cabling, switches, fuses, distribution panels etc have to comply with the LVD. As do all the DC/DC converters. And, perhaps more importantly, the installation itself (though legally this is a bit grey at the moment). The market isn't big enough to allow the "economy of scale" to get the cost of those components down sufficiently to beat the cost of big fat 12 or 24 volt cables.

 

To put it another way: cable for 12/24 volts (sized for equal losses on any system), at the present time, will be cheaper than all the associated DC/DC converters required on a higher voltage system.

 

If you stick with 24 volt systems, then you are out of the LVD, but even then, and allowing for the fact that you need a quarter of the cable size for equal losses with a similar 12 volt system, the convenience and "cheapness" of 12 volt equipment still wins.

 

Look at it yet another way: Why not simply use 230 volt everything on the boat? One inverter will allow you to do that (and they are now cheap due to economies of scale). The equipment is cheaper, your electrical losses are minimal. Where's the problem? The problem is that the inverter wastes power, as would all those other DC/DC converters. Some people still do it, and for many it works, because it's cheap: 12 to 230 volt inverters are cheap (economies of scale), 230 volt equipment is cheap (economies of scale). But DC/DC converters running from (say) 48 volts to 12 volts are not cheap (because no bugger wants them so the market is tiny), so there's really no point in doing it.

 

Oh, there is a lot of creativity in automotive engineering. 'Unplanned thermal incidents' is one of my favourites

 

Try "non-catched fatal exception" in software (yes I actually experienced that phrase recently).

 

There seems to a be a whole group of semi-literate people who make a handsome living out of coming up with a technical sounding phrase for "an engineer f&*%ed up somewhere".

[Keeping Up]

There seems to a be a whole group of semi-literate people who make a handsome living out of coming up with a technical sounding phrase for "an engineer f&*%ed up somewhere".

 

I think they're all rather busy at the moment, on a short-term contract to Nat-West Bank.

[Speedwheel]

Completely but can I just say, it's great to have Gibbo back!

[Gibbo]

I think they're all rather busy at the moment, on a short-term contract to Nat-West Bank.

 

 

That might anger a few people.

 

They might have had more success if they'd used real software engineers instead of people with a degree in "software marketing".

 

Completely but can I just say, it's great to have Gibbo back!

 

Ahh you won't be saying that in a few weeks when my un-PC jokes start again

[Speedwheel]

Ahh you won't be saying that in a few weeks when my un-PC jokes start again

 

It was those I liked the most!

[Timleech]

Some boats these days are 24V.

 

Nothing new about 24V on narrow boats. It was around in the 1960s.

 

Tim

[Chalky]

I didn't make myself clear, I was thinking about connecting the batteries in series (say 24v (or more now 36v has been mentioned)) and supplying lighting etc throughout the boat. Where a socket is needed for an appliance, fridge or TV or whatever, stick a DC/DC converter to get down to 12V.

 

Have you seen the cost of a reasonable quality DC-DC converter? If it's any reasonable power rating you'll also need a cold plate (cooling device) to manage its thermals.

There's also the efficiency issue. Using fast diodes you'll be in the 90 to 95% efficiency, Mosfets and synchronous rectification will get it higher (possibly up to 97%) but it'll cost. You'll also have all the EMC / RFI issues created by the fast switching transients and if you run more than 1 you'll end up with them hetrodyning unless you run them synchronously (more cable).

 

I'd stick with 12V and bigger cables - I like to get away from work when I'm boating.

[RLWP]

And if they start heterodyning you know what you'll have? Flutter on your bottom*

 

Richard

 

*Apologies to Flanders and Swann

Edited June 22, 2012 by RLWP

[Gibbo]

Have you seen the cost of a reasonable quality DC-DC converter? If it's any reasonable power rating you'll also need a cold plate (cooling device) to manage its thermals.

There's also the efficiency issue. Using fast diodes you'll be in the 90 to 95% efficiency, Mosfets and synchronous rectification will get it higher (possibly up to 97%) but it'll cost. You'll also have all the EMC / RFI issues created by the fast switching transients and if you run more than 1 you'll end up with them hetrodyning unless you run them synchronously (more cable).

 

I'd stick with 12V and bigger cables - I like to get away from work when I'm boating.

 

I'll paraphrase Chalky....

 

Don't. Just don't.

[Chalky]

 

Try "non-catched fatal exception" in software (yes I actually experienced that phrase recently).

 

 

The one I like is "undocumented feature" aka bug

[Gibbo]

The one I like is "undocumented feature" aka bug

 

Shush, I usually hook that one into "unimplemented feature". There are several in my latest beta incarnation.

[Grace and Favour]

Shush, I usually hook that one into "unimplemented feature". There are several in my latest beta incarnation.

 

Ah well . . . . . beta late than never

 

 

(good to see you back, Gibbo!)