48V as main DC voltage on boat - anyone?

[ramblinrod]

Clearly, there are pros and cons to every design decision made on every boat.

This marine electrical system designer must consider these when making decisions on what system voltage to use:

1. What loads need to be operated.
2. What system components are needed to operate these loads.
3. What layout of system components (typically in a circuit diagram).

The designer specifies the required characteristics of the components needed to meet design intent.

The manufacturer selects, installs, and connects these components, in compliance with the designers specifications and applicable marine electrical standards.

For North America, the most common are ABYC for electrical products, and NMEA for electronics, with much crossover between each, and in concert with at least a half dozen other safety agencies.

12 Vdc has been selected and become the defacto standard for marine electrical systems in rec. boats up to about 50 ft.

This is because it provides the best overall compromise, for all factors considered, as determined by the system designer.

Size of cables is only one factor.

ALL FACTORS should be considered when selecting system voltage.

When obtaining information from the internet, one really needs to consider the source.

The suggestion that circuit breakers should not be used as on/off switches is incorrect.

Some circuit breakers may be designed for set/reset over-current protection only (e.g. Blue Seas - Pushbutton Reset Only Circuit Breakers).

Circuit Breaker - Push Button Reset Only

For on-off circuit switching, one needs to install a "switch" in conjunction with one of these circuit breakers.

It is not that one "shouldn't" use the circuit breakers as an on-off switch.

One simply can't; there is no provision to do so.

Others (e.g. Blue Seas "A" series, probably the most popular circuit breaker in the industry) has the following design description, "Magnetic hydraulic circuit breakers that combine switching and circuit protection into a single device."

Blue Seas "A" Series Circuit Breaker

This has been the defacto standard on-off switch/circuit breaker used in 20 to 50ft rec. vessels for the last 30 years or more.

Additionally, to suggest that a carbon build up cannot occur in a marine DC switch is completely false.

While contacts may be made of metals to improve conductivity, arc extinguishing, and help prevent corrosion, an arc most definitely can develop carbon deposits on these materials (including even plastics), which along with deformation due to material erosion and transfer, can most definitely contribute to the development of a high impedance connection, resulting in heat generation, and possibly fire.

The higher the DC voltage switched, the greater the potential for arcing, resulting high impedance connection, heat generation, and possible fire.

This is one of those factors that the marine electrical system designer must consider when selecting the system voltage, which is commonly specified as 12 Vdc, for this and other reasons, weighing all pros and cons.

As mentioned previously, for most rec. boats under 40+ft, a 12 Vdc electrical system is the best compromise.

EEE (everything else equal), the risk of fire increases with electrical system voltage.

Therefore, it is wise not to increase system voltage, without considering these risks.

They are real; they can hurt people.

For most rec boats above 40 ft, all factors considered, it will rarely be the best compromise of pros and cons to select a 48 Vdc marine electrical system. The one exception is for electrical propulsion systems; I won't bother to get into the reasons for this.

In my opinion, it is much wiser to have a discrete 12 Vdc electrical system, complete isolated and independent of this system for energy storage and charging, so that if the propulsion electrical system fails, all other electrical devices on the boat will still function, until the propulsion electrical system is repaired.

Additionally, as mentioned previously, for all other vessels, having high current loads such as thrusters, windlasses and inverters above 2 kW each, that are in excess of about 30 ft from the main 12 Vdc bank, considering all pros and cons, it may be best to have a 12 Vdc primary electrical system to run all other equipment, and a discrete secondary 12 Vdc system mounted near these devices.

(As mentioned, in my experience after analysing the needs of many different boats, this usually occurs at ~ 42 ft, if the house bank is aft of the companionway, and ~50 ft, if the house bank is amid ship in the salon.)

I don't recommend increasing system voltage to 24 Vdc, except for the case of a discrete, isolated electrical system (typically up in the bow), to power these devices when a close-proximity 12 Vdc system can't feasibly meet demand.

To change the vessel main electrical system to 24 Vdc (or higher) as required to power these high load devices more effectively, combined with one or more DC-DC converter to power all lower voltage circuits creates a significant safety risk.

Should one of the high voltage/high load electrical devices fail rendering the high voltage electrical system completely inoperative, all electrical devices on the boat could be rendered inoperative including safety devices like gas sniffers, communications, and navigation electronics.

Of course anyone can hack their boat to use a higher main electrical system voltage, the option is there, but after weighing all the pros and cons, is this really wise?

After analysing the circumstances and weighing all of the pros and cons in each case, for rec. vessel under 50 ft, in my opinion, it likely is not.

[evm1024]

Originally Posted by evm1024

SNIP

Oh - I should note that circuit breakers are not designed to be used as off-on switches. But we do tend to use them that way.

When using circuit breakers as switches or using switches at a DC voltage higher than their rating (higher AC too of course) the problem shows up primarily as greatly reduced life spans.

SNIP

Originally Posted by RR

The suggestion that circuit breakers should not be used as on/off switches is incorrect.

I think that these 2 comments represents the differences between how some of us view systems.

I posited that Circuit breakers are not designed to be used as switches. This is not the same as saying that they cannot be used as switches. In fact I did point out that we do use them as switches in common practice.

Point A - There are circuit breakers that are specifically designed to be used as switches. They carry a number of certifications (SWD, HID, etc).

Rod references the Blue Seas A series circuit breakers as perhaps the most common breaker used in Recreational Boating. And I agree. He quotes the Blue Seas summary for the A series breakers where it says:

Magnetic hydraulic circuit breakers that combine switching and circuit protection into a single device.

And yet if you were to look at the Blue Seas documentation you would not find any place where they say that the A series breakers are designed and certified to be used as a switch.

As many of us know Blue Seas does not make the A series breakers. They are actually made by Carling Technologies. Carling says:

Well known for their proven reliability, Carling Technologies' A-Series hydraulic magnetic circuit breakers are compact, temperature stable and designed for precision operation in OEM markets requiring general purpose as well as full load amp applications. When front panel operation and aesthetics demand a clean, contemporary design, the visi-rocker or paddle actuators are ideally suitable. A sealed toggle actuator style is also available and ideal for harsh environment applications requiring additional sealing protection. Optional rocker-guard and push-to-reset bezels, which help prevent inadvertent actuation, are also available.

You may note from the Carling datasheet that these breakers are rated for 10,000 cycles but that no where in the datasheet does it specify that they are rated or approved for switch service (be aware that you can get A series with an additional internal switch - don't be confused)

See the datasheet here: A-Series Compact Hydraulic Magnetic Circuit Breaker

That Blus Seas has taken the 10,000 cycle rating and made a marketing decision to sell A series as breakers with switching capabilities. That is a marketing decision and not an engineering specification. Blue Seas figures that the typical A series breaker will get far fewer than 10,000 cycles in actual use.

I called the Carling product support phone and asked if the A series were rated for switching applications. Carling said that they were not. Off the record the application engineer said that with a 10,000 cycle rating they should be OK in the typical boat breaker application where they were used as switches with a low duty cycle. As in turn them on when you go out for the day the off again when you close the boat up.

I should add that the typical Carling switch that Blue Seas sells are rated for 150,000 cycles. The difference between a breaker and a switch is profound. 10,000 to 150,000.

Further here is a write-up for another breaker manufacturer in common use:

... even though some of the breakers are rated to be able to turn loads on and off for maintenance purposes, their use to switch power on and off on a daily basis is not approved, and should be discouraged.

It is really common to use breakers as switches. But as I stated they are not (for the most part) designed to be used as switches. But, we do use them that way. And get away with it with the 10,000 cycle rating. You might say we are bending the rules rather than breaking them.

So Rod I am correct that breakers that are not designed and certified for switch duty should not be used as switches. But as I noted we do it anyway in common practice.

[KTP]

We went with Gigavac switches, which are rated at something like 80V DC and 350 amps.

Not that expensive either compared to Blue Sea. About $30 a switch

[evm1024]

Originally Posted by RR

SNIP

Additionally, to suggest that a carbon build up cannot occur in a marine DC switch is completely false.

This is a gross misrepresentation of my statement. A straw man as it were. I did say:

Originally Posted by evm

Oh, No carbon build up in the contacts in use in switches now days. The contacts in those switches and breakers are made from copper, copper alloys or silver alloys. Pitting and welding are the "pitfalls".

Also,

Originally Posted by RR

While contacts may be made of metals to improve conductivity, arc extinguishing, and help prevent corrosion, an arc most definitely can develop carbon deposits on these materials (including even plastics), which along with deformation due to material erosion and transfer, can most definitely contribute to the development of a high impedance connection, resulting in heat generation, and possibly fire.

The higher the DC voltage switched, the greater the potential for arcing, resulting high impedance connection, heat generation, and possible fire.

You will have to tell us the source of the carbon....

You are of an age (as am I) where the points on a car were made with steel rivets that were prone to carbon fouling. Mostly the carbon originated from the oils that found their way into the distributor and onto the points. As well as from the carbon in the steel used in the points.

But looking at boats:

The Carling breakers typically used in our boats (A series) have a number of options for the contact rives. Most common is gold or Palladium.

During (mostly) break operation the arc formed tends to pit the rivet and form oxides.

I'll grant you that just for genetal use you can call those oxides carbon deposits even though we both know that they are not carbon.

Originally Posted by RR

EEE (everything else equal), the risk of fire increases with electrical system voltage

But it is not EEE. Or at the best to claim EEE is misleading. The voltage goes up and the current goes down for the same wattage.

Take the case of a 1000 watt windless.

Let's say that the solenoid contact has a 0.01 ohm resistance (typical for a car type solenoid) and that at 12 volts we get 83.33 amps current and
at 24 volts we get 41.666 amps.

The voltage drop in the 12 volt system at 83.33 amps across the 0.01 ohms is (83.33 * 0.01) 0.833 volts. And the power dissipated in that resistance is (0.833v * 83.33A) 69 watts.

The voltage drop in the 24 volt system at 41.66 amps across the 0.01 ohms is (41.66 * 0.01) 0.4166 volts. And the power dissipated in that resistance is (0.4166v * 41.66A) 17 watts.

It is extremely well known that resistive electrical losses decrease by the square with increasing voltage. Keep in mind P=I^2*R

It should be obvious that a 48 volts system would only need 20.833 amps for that same 1 KW windless and that the power loss in the solenoid would be (20.833 * 20.833 * 0.01) 4.3 watts.

Now tell us again which voltage is more likely to cause a fire EEE?

Originally Posted by RR

Therefore, it is wise not to increase system voltage, without considering these risks.

Which risks are you speaking of? Are you confusing a dead short at a higher voltage with fire risk in well designed systems?

Sure if you short a 24v or 48v feed you will get a lot more power and thus heat at the short. This is especially true of batteries that have huge current sourcing capabilities (like LiFePO4 etc). Did you leave out circuit protection in your design?

EEE also means that the designer is fully qualified to design the 24v or 48v system as they are to design the 12v system.

[ramblinrod]

Originally Posted by evm1024

So Rod I am correct that breakers that are not designed and certified for switch duty should not be used as switches. But as I noted we do it anyway in common practice.

Here is the product definition from the Blue Seas website, regarding the "A" series breakers...

"Magnetic hydraulic circuit breakers that combine switching and circuit protection into a single device."

These have been installed in 100's of 1000's if not millions of boats as the sole means for the user to switch 12 Vdc circuits on and off.

Your statements above are clearly mistaken.

[evm1024]

Originally Posted by ramblinrod

Here is the product definition from the Blue Seas website, regarding the "A" series breakers...

"Magnetic hydraulic circuit breakers that combine switching and circuit protection into a single device."

This clearly defines these devices as "switches" as well as "circuit protection" devices ;-)

That it is designed with a toggle lever for user operation to open and close a circuit clearly makes it a switch.

That these has been installed in 100's of 1000's of boats as the sole means to switch circuits on and off, is absolute proof that you were not correct at all.

Did you miss the part where I asked the support engineer if these breakers were supported for use as switches? And they said no!

No, you did not miss that part you are ignoring it.

[ramblinrod]

Originally Posted by evm1024

Did you miss the part where I asked the support engineer if these breakers were supported for use as switches? And they said no!

No, you did not miss that part you are ignoring it.

I could care less, who you claim to have asked, and what you claim they said, your are clearly mistaken.

The breakers I referenced, are defined by Blue Seas, as a "switch and circuit protection device", and are sold as such in the millions.

You are clearly mistaken.

[ramblinrod]

Originally Posted by evm1024

Now tell us again which voltage is more likely to cause a fire EEE?

I clearly stated that the risk of fire increases, due to a high impedance connection, with higher DC voltage.

This is 100% true.

Please re-read post # 142 that clearly demonstrates how.

[Checkswrecks]

48V is coming and is not too far off.

The reason is that the automotive industry is the 800 lb. gorilla in transportation. When cars went from 6 to 12 V, boats followed. The auto makers and safety agencies have agreed that 48V is going to be the new standard, because it works better in battery powered vehicles and makes them less expensive to build.

https://www.greencarcongress.com/48v/

https://www.nytimes.com/2018/02/08/b...-48-volts.html

https://jalopnik.com/everything-you-...olt-1790364465

There will still be 12V parts available so don't worry for the foreseeable future, but over the next 10 years expect to see increasing use of 48V.

[evm1024]

Originally Posted by ramblinrod

I could care less, who you claim to have asked, and what you claim they said, your are clearly mistaken.

The breakers I referenced, are defined by Blue Seas, as a "switch and circuit protection device", and are sold as such in the millions.

You are clearly mistaken.

I have no idea why you do not care when the manufacturers support engineer says that the breakers in question does not have a switch rating.

And as I explained Blue Seas is not the manufacturer and Blue Seas has decided that the breaker is OK to use as a switch.

I have no problem with using the A series breakers as a switch and a breaker in my boat. That was never the question.

As a reminder I stated:

Originally Posted by evm

Oh - I should note that circuit breakers are not designed to be used as off-on switches. But we do tend to use them that way.

To which you replied:

Originally Posted by RR

The suggestion that circuit breakers should not be used as on/off switches is incorrect.

Clearly you have not read the manufactures datasheet on the A series breakers. If you did you would know that they have no specific rating for Switch Duty applications.

In fact the Blue Seas datasheet also makes no specific reference to switch duty.

It appears that you are relying on Blue Seas suggested description "Combines switching and circuit protection into a single device".

I'm sure that you will agree (as I do too) that having a 10,000 cycle life on a circuit breaker makes it useful as a switch in boating applications.

BUT that does not make my statement incorrect. In essence all circuit breakers that are not designed and rated for switch applications should not be used as switches.

Thus my statement is correct.

And your assumption that Blue Seas saying that you can use their A series breakers (made by Carling) as switches does not mean that (all, the vast majority, most) circuit breakers can be used as switches. And thus you are incorrect.


Again - I am quite happy to use A series breakers in my panel to turn lots of things off and on. 10,000 cycles is what i call a long life breaker.

Any design engineer can tell the difference between using a breaker with a 10,000 cycle life and a break with a switch duty rating. Why fight it!

[evm1024]

Originally Posted by ramblinrod

I clearly stated that the risk of fire increases, due to a high impedance connection, with higher DC voltage.

This is 100% true.

Please re-read post # 142 that clearly demonstrates how.

I did read that post. It clearly demonstrates that you have picked 10 ohms out of the air to "prove" your point. And have overstated by implication the frequency of faulty contacts.

Gosh, 120 volts here in the USA and 240 volts most other places - There must be thousand and thousands of houses burning up when the light switch contacts have "high" impedance.

I suggest that you re-read post # 154.

[ramblinrod]

Originally Posted by evm1024

Gosh, 120 volts here in the USA and 240 volts most other places - There must be thousand and thousands of houses burning up when the light switch contacts have "high" impedance.

CORRECT!

Many house fires are caused by faults in the 120 Vac/240 Vac electrical distribution system.

In summary...

High impedance connections cause arcing.
Arcing generates heat.
Heat causes fire.
The risk of arcing increases with system voltage.
The risk of fire due to a high impedance connection increases with system voltage.
Case closed.

[Adelie]

Originally Posted by evm1024

. . . .

Gosh, 120 volts here in the USA and 240 volts most other places - There must be thousand and thousands of houses burning up when the light switch contacts have "high" impedance.

. . .

Switches for AC do not have the same issues as DC switches as was previously indicated.

[ramblinrod]

Originally Posted by Adelie

Switches for AC do not have the same issues as DC switches as was previously indicated.

You are absolutely, positively, 100% correct.

The arcing issue is much more of a problem for DC than for AC, but it can still be an issue with 120 and 240 Vac.

The issue for ant contact surface (be it a crimp, terminal block screw, what have you, when the contact is first opened, can cause an arc.

The arc itself generates a great amount of heat.

Any contaminants in the air, such as dust, pollen, or dander, may be burned and deposited as carbon on the contact surface, increasing it's impedance for the next time, and the next time, and so on and so on and so on, until we end up with a high carbon, high impedance connection.

12 Vdc may produce a small arc, 24 Vdc more, 32 vdc more yet, and 48 Vdc even more.

Increasing system voltage, increases the risk of arcing, high impedance connections, heat generation, and fire.

This should be taken into account when considering increasing DC system voltage. If one doesn't have to, my recommendation is, then don't. Why make your electrical system less safe?

For some marine electrical propulsion systems, designing a 48 Vdc electrical system to power the motor, say 10 kWhr (~13 HP), after weighing the pros and cons, may be justified.

But that system must be designed, fabricated, and maintained properly taking extreme caution to avoid high impedance connections to avoid starting a fire.

Running 48 Vdc around the boat for circuits that don't require it, not such a great idea.

Running all the 12 Vdc safety gear from a DC-DC converter off the propulsion 48 Vdc electrical system, also not a great idea.

[evm1024]

Originally Posted by Adelie

Switches for AC do not have the same issues as DC switches as was previously indicated.

Exactly! I rest my case....

For the record the leading cause of house fires in the USA -

1) Cooking
2) Kids Playing with Fire
3) Smoking
4) Heating: Space heaters mostly
5) Electrical: An overloaded circuit or faulty extension cord specifically
6) Candles
7) Fireplace
8) Dryers
9) Flammable Products
10) Christmas Trees