48V as main DC voltage on boat - anyone?

[BigBeakie]

Check the demand loads of your devices vs the capacity of the DC-DC convertor. There are some high capacity ones, one from US & one from Germany, (both used in military applications), but cost was eye watering.

Usually, like the Victron Orions, they are just a few hundred watts so not enough to run the windlass or electric winches.


Sent from my iPad using Cruisers Sailing Forum

[ramblinrod]

Originally Posted by aybabtme

Respectfully, isn't assuming that there's no breaker in between. Bad wiring, as far as I understand it, is mostly a problem when high current loads are involved, leading to heat and fire due to improper connection between two components that heats up, starts melting and goes into a form of thermal runaway (the more it heats up, the more it burns material away, the less material is left to carry current, the more it heats up). Keeping a higher voltage and smaller breakers/fuses means the wires don't carry as much current, so less perfect connections are less at risk of burning up? And if there's short, the breaker/fuse will trigger. All this is based on the fact that higher voltage allows being a lot more stringent on the size of breakers and fuses.

Otherwise, why are people passing 120V AC alongside 12V DC? 120V in your body is going to kill you before 48V does. Why are people not blinking an eye at it, but saying that 48V is dangerous? And as far as I understand, AC has more ways to get into your body than DC, so in that sense for equivalent voltage, is more dangerous.

I'm trying to heed the warning about high voltage and dangers to humans, but I have a hard time buying this argument when put alongside people's counter-statement to use 120V AC. I'm probably missing a piece of the puzzle? Or maybe the conventional belief is wrong? Not sure, trying to figure it out.

You seem to be missing part of the equation.

Transmission line voltage in Canada is 725 kV.

Why don't we bring that into homes?

The amperage drawn by a 1500W heater would only be 2 mA, the wire could be like 32 AWG.

Answer - If that 725 kV was ever unleashed in a house, the POWER could be devastating.

This is why residential voltage in a North America is relatively low at 120 Vac.

So on-board, we commonly have two electrical supplies; 120 Vac for residential appliances and high power consuming items. We have all kinds of special safety requirements around this, because if unleashed, really bad things can happen.

We also have safety requirements around the 12 Vdc system but they are arguably less stringent. The primary reasons are that:

1. It won't electrocute anyone.

2. It takes more current for a lower voltage circuit to start a fire.

So what about devices that run off a 1.5 Vdc battery? Hardly any safety requirements at all. The voltage is low and current is limited.

What if a whole bunch of these small batteries were put into large series and parallel packs increasing the voltage and current available?

Imagine this, we have a cable, with a bad connection, that results in 10 ohms of resistance.

P = E^2/R

If that circuit is powered by 12 Vdc, the power dissipated in heat at that connection is 14.4 watts. Warm, undesireable, but maybe no big deal.

If that same circuit is powered by 48 Vdc, the power dissipated in heat at that connection is now 230 W.

Ouch that is hot, enough to melt cable insulation, start a fire, and burn the boat to the waterline.

So the part of the equation you have missed, is that "current" is not the most important parameter that start fires, POWER (watts) is.

And the higher the voltage, the greater the risk of unleashing more power.

My prediction, the more people that install high voltage DC systems on boats, EEE, the greater the percentage of boat fires.

[KTP]

Originally Posted by ramblinrod

My prediction, the more people that install high voltage DC systems on boats, EEE, the greater the percentage of boat fires.

Except that likely the people installing higher voltage DC systems on boats understand more than the average boater about all of this and thus have proper fuses and proper crimps, use tinned marine wire, etc. Thus it might be that they are a smaller percentage of boat fires.

[ramblinrod]

Originally Posted by KTP

Except that likely the people installing higher voltage DC systems on boats understand more than the average boater about all of this and thus have proper fuses and proper crimps, use tinned marine wire, etc. Thus it might be that they are a smaller percentage of boat fires.

EEE stands for, "Everything, Else, Equal".

If one changes multiple parameters of a scenario, the predictable outcome becomes less certain.

Additionally, there is no guarantee that someone contemplating higher system voltage really understands anything.

In fact, the poster I was responding to declared limited understanding of power distribution.

Kudos for honesty.

Which is why I was taking the time to answer his question, and hopefully to help him avoid a possible mistake.

[ranchero76]

Wow! Almost year later, this thread came back to life
To back up my old opinion - nowadays it's making more and more sense using 48V for many things. There are relatively affordable 1-2-3-5kW 48V latest BRUSHLESS motors on the market with or without gear reducers, with IP67 splash protection (of course, better level of protection can be achieved if needed), they can be used for anything, even as starters for diesel engines. Controllers, LED lights, solar, wind generators, DC-DC and DC-AC inverters - anything is available for 48V systems.

Benefits - 4 times less current comparing to 12V, smaller wires. When done at complete refit/new build stage - many systems can be fitted with SAME motors (brushless, smaller and much more powerful than 12V motors), so with couple spares owner will be fine in any part of the world.

One must be absolutely dumb or extremely unlucky to get killed by 48V - I haven't heard about ANY such case (even though it might exist - anything is possible in our world, people get killed by smartphones that have fallen into the water).
So let's put remark - both installer of such system and end user must have brains and be able to use them as well. I'm pretty sure that chances to be killed by knife are much higher, I don't know why knifes haven't been prohibited yet!

[ramblinrod]

Originally Posted by aybabtme

Otherwise, why are people passing 120V AC alongside 12V DC? 120V in your body is going to kill you before 48V does. Why are people not blinking an eye at it, but saying that 48V is dangerous? And as far as I understand, AC has more ways to get into your body than DC, so in that sense for equivalent voltage, is more dangerous.

I'm trying to heed the warning about high voltage and dangers to humans, but I have a hard time buying this argument when put alongside people's counter-statement to use 120V AC. I'm probably missing a piece of the puzzle? Or maybe the conventional belief is wrong? Not sure, trying to figure it out.

This is an important point that deserves a bit of focus and direct response.

1. Electricity and water don't mix.

2. The marine environment is extremely harsh for electrical systems.

3. 55% of the fires on boats are caused by an electrical fault. (USCG report).

4. Of these, 54% are related to 120 Vac circuits. (Ref: HowtoMarine.com).

5. Only 10-25% of circuits aboard boats are 120 Vac (my WAG).

6. Conclusion: Higher voltage is more dangerous than lower voltage. (So the actual data proves the theoretical greater risk.)

The reason we don't perceive the enormity of the danger present?

De-sensitization.

We are exposed to it every day.

It's like people who live in war torn countries, with machine gun fire and mortar shelling going on all around them.

Same $%$% different day, get over it (actually don't even notice it anymore) and carry on like it isn't there.

In North America, many homes have 240 AC split-phase electrical supplies alongside natural gas.

So what's the big deal? Just click.

Images

Videos

Of all the marine electrical inspections I have performed, every one (100%) has had serious safety issues (yes plural).

The worst, (about 5%), after a few minutes aboard, I step off, call the owner, and advise all power sources must be disconnected and all combustibles removed, before I can safely complete the inspection.

These owners are astounded that their vessel, they may have owned many years, is deemed unsafe, because after all, they have used it for many years and are still around to talk about it. All I can tell them, "Count your lucky stars your boat hasn't burned to the waterline YET, but remember, tomorrow is another day."

So, assuming that your vessel will be similar to all others with respect to wiring deficiencies DESPITE YOUR BEST EFFORTS, and that you most definitely will have electrical wiring deficiencies, would you prefer higher potential or lower potential sources pushing current through those faults?

IMPORTANT POINT: Over-current protection, helps (not absolutely, as fuses and breakers can fail) prevent current from passing through circuits, that are higher than the rating. Many fires, are cause by high impedance connections, where the current passing through the connection is lower than the circuit over-current protection rating.

This risk increases with (you guessed it), system voltage.

There is absolutely no such thing as absolute safety, only degrees of safety.

EEE, the degree of safety when high voltage sources are used, is lower.

Some may say, "OMG, we are all going to die" in complete sarcasm because they are oblivious to the actual risks due to, you got it, "desensitization". Their words may well come back to haunt their survivors.

I also agree that there are inherent risks with just setting foot aboard a boat (hence my policy for electrical source disconnection and combustible removal in severe cases), let alone sailing it, but why, why, why, would one purposefully, or unintentionally through their ignorance, make their pastime less safe? Maybe Darwin at work?

So before "experimenting" with marine electrical wiring, and introducing more potentially dangerous conditions, click the following links:

Images

Videos

If this was your boat (it was someone's, who may also be desensitized or completely oblivious), where would your loved ones be?

Would they be grieving, victims, or dancing on the ashes? ;-)

Sorry, trying to lighten up just a little, but I actually deal with more than my fair share of this stuff.

Is this "fear mongering"?

In my opinion, "No, it is reality checking."

Desensitization lulls people into a false sense of relative safety.

Don't underestimate the danger of electricity, especially on boats, near water.

Stay safe.

[aybabtme]

Thanks everyone for your responses, this has been very informative. I have many months to go before getting to any of these jobs, and will definitely do some proper analysis of the whole shenanigan before moving on anything, especially anything non-standard. It's a lot of money and moving parts either ways, so I'll probably try to make some software simulation down the line with various alternatives to see what makes the most sense overall. If I come to it (big if :P), I'll try to share the results.

[waterman46]

Guess you want this tread closed, but I don't think anyone mentioned that it's optimum to have a 12V battery in the bow, dedicated for the high current windlass (and bow thruster if present). Adding converters everywhere from 48V to 12V seems insanely complicated, hence less reliable. BTW if you care about re-sale value, I don't think many buyers will want a boat with a highly unusual electrical system, no matter how theoretically more efficient it may be. But hey, the world needs experimenters like you, so go for it!

[Adelie]

Originally Posted by KTP

Except that likely the people installing higher voltage DC systems on boats understand more than the average boater about all of this and thus have proper fuses and proper crimps, use tinned marine wire, etc. Thus it might be that they are a smaller percentage of boat fires.

The folks doing it now are mostly DIY folks who research this and understand better than average.

In a short while if it becomes more common the pros will be installing and the folks who are used to 12v will start messing around with the pro installed systems and they will be mucking it up.

[ramblinrod]

Originally Posted by Adelie

The folks doing it now are mostly DIY folks who research this and understand better than average.

In a short while if it becomes more common the pros will be installing and the folks who are used to 12v will start messing around with the pro installed systems and they will be mucking it up.

That is the scary thing. A boater, experiments with the electrical system, decides to move on and sells the boat to someone who knows even less.

Flash, bang, whiff of ozone.

[foggysail]

I believe concerns about safety in a 48V system are needless. Telephone companies used 48VDC in their distribution service for decades. I have never heard/read any safety concerns especially in their battery rooms where the risks would be the greatest. But be careful to not get a ring or a wrist watch across the lines even in a 6V system.

[ramblinrod]

Originally Posted by foggysail

I believe concerns about safety in a 48V system are needless.

Everyone has every right to ignore the math, physics. and statistics. and believe whatever they wish.

[Adelie]

Originally Posted by foggysail

I believe concerns about safety in a 48V system are needless. Telephone companies used 48VDC in their distribution service for decades. I have never heard/read any safety concerns especially in their battery rooms where the risks would be the greatest. But be careful to not get a ring or a wrist watch across the lines even in a 6V system.

I didn’t realize that the telco’s had been siting their distribution centers on barges in a marine environment. Good to know, I’m convinced now.

[Adelie]

A dcouple decades ago the auto industry looked at going to a higher voltage. The voltage they settled on was 42v. Safety issues with DC start about 60v.

So why not 48v or even 54v?
Because while the system would operate at 48v, it would charge at close to 60v and in very cold weather situations would push it past. Hence, 42v.

There are a number of reasons 42v didn't take hold,
- Technology that enabled a single large hot wire to branch off to smaller loads, close to the loads.
-Problems with switch longevity at that voltage DC.
-Sunk costs of existing infrastructure.

I don't see 48v working for general house loads for the same reason's 48v & 42v didn't take hold in the auto industry.

The only places you really need the higher voltages are:
1. Propulsion
2. Windlass
3. Bowthruster

36v would suffice for these uses, though there might still be issues with switch longevity.
The only use where there would be a big benefit to 48v is propulsion.

No matter what the advantages of 48v are though, in the long run 48v will not last once the insurance companies realize their exposure and start to decline to insure boats with 48v systems. So my advice to go with 36v if you really want to switch.

[ramblinrod]

Originally Posted by Adelie

A dcouple decades ago the auto industry looked at going to a higher voltage. The voltage they settled on was 42v. Safety issues with DC start about 60v.

So why not 48v or even 54v?
Because while the system would operate at 48v, it would charge at close to 60v and in very cold weather situations would push it past. Hence, 42v.

There are a number of reasons 42v didn't take hold,
- Technology that enabled a single large hot wire to branch off to smaller loads, close to the loads.
-Problems with switch longevity at that voltage DC.
-Sunk costs of existing infrastructure.

I don't see 48v working for general house loads for the same reason's 48v & 42v didn't take hold in the auto industry.

The only places you really need the higher voltages are:
1. Propulsion
2. Windlass
3. Bowthruster

36v would suffice for these uses, though there might still be issues with switch longevity.
The only use where there would be a big benefit to 48v is propulsion.

No matter what the advantages of 48v are though, in the long run 48v will not last once the insurance companies realize their exposure and start to decline to insure boats with 48v systems. So my advice to go with 36v if you really want to switch.

I normally recommend the breaking point where a 24 Vdc "high load" system starts making sense, is around 45 ft LOA.

This is the size of boat where things like 5 HP (3.8 kW) + bow and/or stern thrusters start coming into play, and 2000W windlasses are over 30 ft from the house bank.

Of course anyone can put a 3 kW inverter on a small boat, but really, this can be mounted within a few feet of the 12 Vdc house bank; the cables will be nothing in relation to the cost of a system voltage increase.

PS, a 12 Vdc 3kW inverter on a 2S2P x6 Vdc (2.7 kWhr) FLA house bank can deliver rated power for about 20 minutes before hitting 50% SOC.

By re-arranging those same batteries to 4P (24 Vdc), while the cable size would be reduced, saving maybe $50, (and costing significantly more in DC to DC converters or changing the entire boat to 24 Vdc, this is still a 2.7 kWhr bank, and will deliver the same amount of inverted 120 Vac power for the same duration.

So one really has to ask the question, WHY BOTHER?