Why 12volts on narrowboats?

[Gibbo]

Ah well . . . . . beta late than never

 

 

(good to see you back, Gibbo!)

 

I see what you did there.

[Albion]

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

 

Richard

 

When I worked for Rover helping to develop the Rover 75 and the BMW Mini we weren't allowed to mention in writing any potentially customer-litigious incident that happened with the cars. This is because certain markets, America for instance, have the right to dig back into all the events and correspondence during development if, later, there is a series of problems once the cars are in the hands of American customers and you can get the arras sued off you. So when one of my V6 Rover 75s was the second car where the engine inlet manifold exploded on start up in the morning I had to tell Siemens (whose car it was for software development purposes) that there had been a 'thermal incident' by e-mail or make sure that I only told them the real reason by word of mouth on the phone. The problem was fixed by the way for those who might still run a Rover 75

Roger

[jelunga]

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.

But will you need a Galvanic isolator?

(is this in the right thread?)

[NB Alnwick]

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.

 

Our boat is 24V - despite what many have said in this topic and elsewhere, we haven't experienced difficulties in finding 24V equipment such as water pumps, waste pumps, TV, lighting, etc. Generally, 24V equipment is comparable to 12V stuff in price because many commercial vehicles, buses, trains and a fair proportion of larger boats have 24V systems. Having said that, there are exceptions that are easily dealt with - as an example our Roberts radio requires 9.6 an input of volts so we built a custom DC to DC converter which is small enough to fit inside the radio case.

[Timleech]

Our boat is 24V - despite what many have said in this topic and elsewhere, we haven't experienced difficulties in finding 24V equipment such as water pumps, waste pumps, TV, lighting, etc. Generally, 24V equipment is comparable to 12V stuff in price because many commercial vehicles, buses, trains and a fair proportion of larger boats have 24V systems. Having said that, there are exceptions that are easily dealt with - as an example our Roberts radio requires 9.6 an input of volts so we built a custom DC to DC converter which is small enough to fit inside the radio case.

 

Yes most boaty electrical stuff is available in 24V as well as 12V, usually for a similar price. It used to be the case that some of the bigger inverters were only available for 24V input, & I seem to remember seeing some big inverters at a higher price for 12V than for 24V. Sometimes there are bargains to be found in 24V, especially end of line or used items, because there is less demand

I think where you will miss out most with 24V is with special deals from chandlers (XYZ water pump 20 quid this month only), and knowing that if something breaks most chandlers will have a replacement on the shelf.

 

Tim

Edited June 23, 2012 by Timleech

[The Construct]

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.

No I haven't done the investment analysis but I take your point about losses. As far as EMC issues are concerned, I thought manufacturers had a requirement to ensure their kit was within spec - compatibility, the clue is in the acronym.

 

I'm getting the idea that it will be best to stick with a standard arrangement i.e. 12V and sling loads of copper at the situation i.e. I suppose its a case of "if it aint broke then don't fix it"

 

Our boat is 24V - despite what many have said in this topic and elsewhere, we haven't experienced difficulties in finding 24V equipment such as water pumps, waste pumps, TV, lighting, etc. Generally, 24V equipment is comparable to 12V stuff in price because many commercial vehicles, buses, trains and a fair proportion of larger boats have 24V systems. Having said that, there are exceptions that are easily dealt with - as an example our Roberts radio requires 9.6 an input of volts so we built a custom DC to DC converter which is small enough to fit inside the radio case.

thats what I was thinking!

 

 

Yes most boaty electrical stuff is available in 24V as well as 12V, usually for a similar price. It used to be the case that some of the bigger inverters were only available for 24V input, & I seem to remember seeing some big inverters at a higher price for 12V than for 24V. Sometimes there are bargains to be found in 24V, especially end of line or used items, because there is less demand

I think where you will miss out most with 24V is with special deals from chandlers (XYZ water pump 20 quid this month only), and knowing that if something breaks most chandlers will have a replacement on the shelf.

 

Tim

 

I guess you are right, its what Gibbo said earlier, it will come down to whats available in the marketplace and of course at what price, and has little to do with the best technically optimum solution.

[OldGoat]

My boat is 24V. A 24V inverter made more sense than a 12V equivalent. I also don't like the idea of paralleing too many battery banks - so doubling the supply voltage made better sense to me.

 

24V alternators give more power for a given frame size than 12V - I have 2 x 24V Delco bus alternators (good old eBay) rated at 70amps each, the equivalent 12v unit would be 100 amps.

Modern electronic devices "don't like high currents" but can cope with higher voltages, so a 24V inverter is likely to be more reliable than its 12V brother.

 

 

 

On the down side I( find it's difficult or more expensive to) source 24V water pumps (bilge / fresh water / shower) so I have dual voltage supplies running throughout the boat and a 12V tap in the battery system.

 

 

Problems solved. Best of both worlds.

[Nickhlx]

My boat is 24V. A 24V inverter made more sense than a 12V equivalent. I also don't like the idea of paralleing too many battery banks - so doubling the supply voltage made better sense to me.

 

24V alternators give more power for a given frame size than 12V - I have 2 x 24V Delco bus alternators (good old eBay) rated at 70amps each, the equivalent 12v unit would be 100 amps.

Modern electronic devices "don't like high currents" but can cope with higher voltages, so a 24V inverter is likely to be more reliable than its 12V brother.

 

 

 

On the down side I( find it's difficult or more expensive to) source 24V water pumps (bilge / fresh water / shower) so I have dual voltage supplies running throughout the boat and a 12V tap in the battery system.

 

 

Problems solved. Best of both worlds.

 

With a 12 volt tap in the battery system, how do you balance the depth of discharge in the part supplying 12 volts with the other half ? Sounds like a potentially expensive consumption of batteries to me if some are being discharged more than others in the string ( and over / undercharged after discharge ) I would like to know more ...

 

Nick

 

 

 

[Guest]

I went with 12V because the thicker cables are heavier and saved on ballast.

[Nickhlx]

I went with 12V because the thicker cables are heavier and saved on ballast.

 

 

 

 

[CV32]

:

 

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

 

I always found them amusing and its great to see people push the boundaries of acceptable comment

[OldGoat]

With a 12 volt tap in the battery system, how do you balance the depth of discharge in the part supplying 12 volts with the other half ? Sounds like a potentially expensive consumption of batteries to me if some are being discharged more than others in the string ( and over / undercharged after discharge ) I would like to know more ...

 

Nick

 

I wondered when anyone would spot that......

IMHO I don't think it really matters provided that you design it in:-

 

Anything that uses power regularly is 24Volt. Fridge,

Inverters Big one

for hoover,

little sinewave one for HiFi TV

etc

lighting.

Radios (24 to 12 converter - not really

needed)

So what's left?

Fresh water pump

Bilge pump

shower pump

Nav lights

Horn

Tunnel lights

Marine band radio

 

Now, these are only used intermittently so I guess any real inbalance is small.

 

'suppose if I was really worried, I'd have spread the 12V devices either side of the tap

 

As it happens - so I'm sorry it doesn't help you - I don't have lead acid batteries. Mine are something else that don't mind being overcharged, run flat, left at any state of charge, so if there was any inbalance one set is overcharged slightly while the other set catches up. The whole system is 1,000 amp hours at 12V so a little inbalance wouldn't make any difference anyway.

 

I still think a centre tap with conventional batteries works without any issues if you either balance the loads or the inbalance is small in consumption terms.

 

 

 

 

 

 

 

 

 

 

 

[RLWP]

When I worked for Rover helping to develop the Rover 75 and the BMW Mini we weren't allowed to mention in writing any potentially customer-litigious incident that happened with the cars. This is because certain markets, America for instance, have the right to dig back into all the events and correspondence during development if, later, there is a series of problems once the cars are in the hands of American customers and you can get the arras sued off you. So when one of my V6 Rover 75s was the second car where the engine inlet manifold exploded on start up in the morning I had to tell Siemens (whose car it was for software development purposes) that there had been a 'thermal incident' by e-mail or make sure that I only told them the real reason by word of mouth on the phone. The problem was fixed by the way for those who might still run a Rover 75

Roger

 

Yep, that's where I learned the phrase.

 

I have avoided another source of thermal incidents on ours - I've taken the undertray off

 

Richard

[The Construct]

My boat is 24V. A 24V inverter made more sense than a 12V equivalent. I also don't like the idea of paralleing too many battery banks - so doubling the supply voltage made better sense to me.

 

24V alternators give more power for a given frame size than 12V - I have 2 x 24V Delco bus alternators (good old eBay) rated at 70amps each, the equivalent 12v unit would be 100 amps.

Modern electronic devices "don't like high currents" but can cope with higher voltages, so a 24V inverter is likely to be more reliable than its 12V brother.

 

 

 

On the down side I( find it's difficult or more expensive to) source 24V water pumps (bilge / fresh water / shower) so I have dual voltage supplies running throughout the boat and a 12V tap in the battery system.

 

 

Problems solved. Best of both worlds.

 

It looks like a good solution, thanks for that.

Ive done a quick Google on pumps & the 24V version appears to be 10-15% more cost than the 12V version - no great shakes!

[Gibbo]

Taking a 12 volt tap from a 24 volt lead acid battery bank, for anything other than absolutely miniscule loads (say less than 0.005% of the battery bank size) is complete madness and will massively reduce the life of the bank.

 

This is a fact.

 

Modern electronic devices "don't like high currents" but can cope with higher voltages, so a 24V inverter is likely to be more reliable than its 12V brother.

 

I don't know where you got that from but it's completely wrong.

[Chalky]

No I haven't done the investment analysis but I take your point about losses. As far as EMC issues are concerned, I thought manufacturers had a requirement to ensure their kit was within spec - compatibility, the clue is in the acronym.

 

 

No it's not! The device will have been tested in a rig to ensure that its emissions and susceptibility meet requirements. It hasn't been tested in your installation which will be totally different to the test rig. They will have uses a LISN ( a network designed to represent cables) - you'll use a cable harness. They'll have a decent earth bonding - you'll have the RF equivalent of a piece of wet string unless you bond it to a big earth plane e.g. the hull which will help solve this but could cause you corrosion problems. You'll also find that your wiring will be long enough to act as a reasonable quality antenna for any RF floating round. You may be lucky, or not.

 

RF interference and susceptibility are a real black art. Although not my speciality I work with some of the best in the industry for dealing with the type of systems fitted to boats. Trust me - it's not as simple as you think.

[Keeping Up]

One way of dropping 24v to 12v is to connect a "backing off battery" that gets charged as the load takes current. Connect its positive terminal to the 24 volt rail and you get 12v at its negative terminal. After a while you swap the batteries around so that the fully charged one changes places with one that needs charging. It used to be quite common in telephone exchanges when I first started working with the GPO.

 

I did this once as an emergency way of getting the VHF radio to work again after its DC/DC converter blew up half-way across the channel; 3 years later the boat owner was still using it that way!

[RLWP]

One way of dropping 24v to 12v is to connect a "backing off battery" that gets charged as the load takes current. Connect its positive terminal to the 24 volt rail and you get 12v at its negative terminal. After a while you swap the batteries around so that the fully charged one changes places with one that needs charging. It used to be quite common in telephone exchanges when I first started working with the GPO.

 

I did this once as an emergency way of getting the VHF radio to work again after its DC/DC converter blew up half-way across the channel; 3 years later the boat owner was still using it that way!

 

Allan, could you draw a diagram for that please? I'm having trouble geting my head around it

 

Richard

[ditchcrawler]

Our boat is 12/24 volt. The engine, tunnel light, horn,nave lights are all 12 volt and fed from the starter battery and are only live when the ignition is on. The car type radio and bilge pump are also 12 volts and constantly live. All the pumps, cabin lights and inverter are 24 volts.

I am surprised about the inefficiency comments regarding DC to DC converters as everyone sings their phrases for running lap ts and mains TVs with the power supply chopped off. Maybe it's just as efficent to run them on 240 volts from the inverter.

[Keeping Up]

Like this Richard

 

 

Backoff by Keeping Up, on Flickr

 

I am surprised about the inefficiency comments regarding DC to DC converters as everyone sings their phrases for running lap ts and mains TVs with the power supply chopped off. Maybe it's just as efficent to run them on 240 volts from the inverter.

 

That's just because the people doing so don't understand them. They contain an inverter so they aren't [particularly efficient; they can even be less efficient than the wiring losses of a 12v feed . Where they do score is that most 240v-12v wall-wart power supplies aren't particularly efficient either.

Edited June 23, 2012 by Keeping Up

[ditchcrawler]

Like this Richard

 

 

Backoff by Keeping Up, on Flickr

 

 

 

That's just because the people doing so don't understand them. They contain an inverter so they aren't [particularly efficient; they can even be less efficient than the wiring losses of a 12v feed . Where they do score is that most 240v-12v wall-wart power supplies aren't particularly efficient either.

My 12 and 24 volt system are only connected by the common earth/ neutral line. 12 and 24 volt alternators, dis boards etc.

[The Construct]

Taking a 12 volt tap from a 24 volt lead acid battery bank, for anything other than absolutely miniscule loads (say less than 0.005% of the battery bank size) is complete madness and will massively reduce the life of the bank.

 

This is a fact.

 

 

 

I don't know where you got that from but it's completely wrong.

 

 

I am trying to understand the context of this fact:

 

If I have a battery bank of say 4 x 110AH 12V batteries and I connect them two in series to give me 24V and then parallel them up then the whole battery bank is 4 x 110AH = 440 AH

 

Now you say a 'miniscule load' of say 0.005% of the battery bank size. 0.005% of 440 AH is 0.22AH. and if I run something for 15 mins, that is equal to 0.055A (15mins/60mins x 0.22) from the battery bank. For a 12V load that is around 0.66VA so that rules out most things such as pumps, even LED lamps are 2W minimum!

 

Now you say connecting such a load will <b>massively</b> reduce the bank life: if a battery bank is good for say 550 discharge/charge cycles, are you suggesting massively means 10% to 50% or what?

 

In conclusion and in live aboard context, you are saying the battery may need replacing say every 2 years (rather than 4 years) due to a 12V tap supplying a 1W load thats on every 15 minutes.

 

I'm trying to get my head around this, because if what you are saying is correct, then 12V taps look a costly option rather than an elegant solution!

[bottle]

If I have a battery bank of say 4 x 110AH 12V batteries and I connect them two in series to give me 24V and then parallel them up then the whole battery bank is 4 x 110AH = 440 AH

 

er... No you will have a bank of 220 Amp.Hr at 24v.

[The Construct]

If I have a battery bank of say 4 x 110AH 12V batteries and I connect them two in series to give me 24V and then parallel them up then the whole battery bank is 4 x 110AH = 440 AH

 

er... No you will have a bank of 220 Amp.Hr at 24v.

Yes I know, I didn't mention the voltage because this is about a 24V (edit) battery bank (end of edit) and a 12V tap.

 

I am happy to concede your point but it doesn't make too much different to the math and the concluding question "Does such a minuscule load (from a 12V battery in a 24V bank) have such a "massive" effect on the life of the bank?"

I'm interested in the answer because it could be significant

Edited June 24, 2012 by The Construct

[bottle]

I thought you knew. ;)but you still have a bank of 220Amp.Hr at 24v, how does a12v tap give you 440Amp.Hr

 

I honestly do not know but am always willing to learn.

 

As to the other bit is beyond my knowledge so will hope that Gibbo comes back.

 

If he does comeback and explains it will probably still be beyond my knowledge.