Comparative Safety: 12v v 24v v 48

[evm1024]

I see that you are still avoiding the question.

ABYC has changed the requirements. One does not need 1000 hours to sit for the exam. As I noted.

It is easy enough to look up someone:

https://abycinc.org/mpage/findatech

I am not ABYC certified. I have not listed my certifications, degrees etc on this list other than I think I noted a captian's license in some posting. I don't think that I will.

Falling back on higher voltages are more dangerous is disingenuous. You do know that DC and AC are different and post different risks. You know that risk based on voltages is broken down into bands. That is why ABYC states voltages less than 50 volts. You know that 10 ohms in a lose connection poses a fire hazard regardless of whether it is 12 volts, 240 volts, 48 volts or 120 volts.

Oh well....

[ramblinrod]

Originally Posted by evm1024

One does not need 1000 hours to sit for the exam.

They do to become a certified tech.

See ABYC Certification

Falling back on higher voltages are more dangerous is disingenuous.

Maybe where ever "disingenuous" is defined as "true", "accurate", "correct".

You do know...

Yes.

I know how to ensure that my work meets ABYC standards, is safe, cost effective, meets performance expectations, and is reliable under all conditions likely to be encountered.

You do know that ABYC standards are for the "minimum" level of safety recommended, correct?

This is the bar that some try to just scrape to minimize cost and maximize profit.

Not my way.

I treat every customer boat like it is my own.

My bar is much higher; it is how safe I want it to be to ensure the vessel and precious cargo returns to port safely, every time.

48 Vdc where not required?

Nope, doesn't clear the bar.

[evm1024]

Originally Posted by ramblinrod

They do to become a certified tech.

See ABYC Certification




Maybe where ever "disingenuous" is defined as "true", "accurate", "correct".



Yes.

I know how to ensure that my work meets ABYC standards, is safe, cost effective, meets performance expectations, and is reliable under all conditions likely to be encountered.

You do know that ABYC standards are for the "minimum" level of safety recommended, correct?

This is the bar that some try to just scrape to minimize cost and maximize profit.

Not my way.

I treat every customer boat like it is my own.

My bar is much higher; it is how safe I want it to be to ensure the vessel and precious cargo returns to port safely, every time.

48 Vdc where not required?

Nope, doesn't clear the bar.

Oh good, progress. 48 Vdc is safe where required. Thanks for admitting that 48 Vdc is safe.

It is clear from your posting that the ABYC recommendations are safe. That they are the minimum for safety and that voltages less that than or equal than 50 volts are safe when installed to ABYC spec or better.

Thank you for admitting that.

SNIP - deleted a snarky sentence.

[DeepFrz]

This topic brings me back out of hibernation:-)

Welcome back S/V Jedi.

[CatNewBee]

The higher voltage increases the safety in high demand applications, simply by reducing currents. To handle currents above 400A requires very serious installations in 12V, because a weak contact can produce a lot of heat. For the same load in 48V you need 1/4 of the current, easier manageable and therefore safer in operation.

A proper installation is in any case a necessity too.

The problem with 48V battery systems is balancing. If one battery in series has a problem there may be serious side effects like boiling or exploding cells. With lithium set ups, it is in fact safer, because this expensive batteries get usually cell monitoring by a BMS and there are protection mechanisms in place monitoring health, soc and temperature, some even load, what is usually not the case in lead acid configurations.

[Jim Cate]

Rod, I wonder if you have any documented cases of folks being seriously injured, either by shock or by consequent injury, on boats with systems of greater than 24 volts and less than 50 volts dc?

If I follow your arguments correctly, your main objection to such voltages is in personal hazard to the operator, not in electrical failures which have been shown to not be greatly more hazardous if at all. If this worry is valid, there should be a rich history of injury to fall back on for proof.

Jim

[CatNewBee]

I have 5 x 62V Voc solar panels in parallel, 52V Vmp, 1600W.

I tried myself with two fingers on one hand how it feels like accidentally touching the two poles. Well it hurts, it is very unpleasant, but nothing serious, not comparable to a 240V shock at all, and even this is rarely lethal I can tell. It really depends on the circumstances, conductivity and paths of the current through your body.

While I would not recommend it to try it yourself, I can tell, I am still alive. It is OK to have respect of voltages and currents and to take per-cautions when working on electric circuits, but it is not magic or more dangerous than any other work.

On boats you deal not only with 12V, but also with inverter, generator and gear on shore power levels of 110 / 240 / 380V. 48V is nothing special in this regard.

[Dockhead]

Originally Posted by CatNewBee

The higher voltage increases the safety in high demand applications, simply by reducing currents. To handle currents above 400A requires very serious installations in 12V, because a weak contact can produce a lot of heat. For the same load in 48V you need 1/4 of the current, easier manageable and therefore safer in operation.

A proper installation is in any case a necessity too.

The problem with 48V battery systems is balancing. If one battery in series has a problem there may be serious side effects like boiling or exploding cells. With lithium set ups, it is in fact safer, because this expensive batteries get usually cell monitoring by a BMS and there are protection mechanisms in place monitoring health, soc and temperature, some even load, what is usually not the case in lead acid configurations.

This drifts us back into the lithium power architecture discussion we had a few months ago, but it's a closely related subject.


Once you free your mind from lead-acid paradigms, all this is not a big deal, I think. I've actually had a boiled cell which could have turned into a fire, on a lead-acid bank. I think a lithium bank with proper controls is much better in this regard, compared to a dumb lead bank.



And the question keeps coming up about how to deal with 12v equipment, on a 48v boat. One good answer is in our old discussion, I think -- if the battery bank is lithium, then rather than using a dropped, you can use a small lead bank, or even a single 12v lead battery, fed from the lithium bank, for all of the low power low voltage systems. And then leave the high power stuff on 48v or 32v or whatever you choose.



Thinking about what I have on board my own boat, DC powered gear is very sharply divided between low power and high power stuff, very different, and deserving of separate systems, I think:


High power:


Inverter
Winches (4x)
Windlass
10 horsepower bow thruster
Pilot hydraulic pump

(Electric davits, since removed)



Any one of these items uses order of magnitude or more of power of even the most power intensive of the low power stuff:


Low power:


24v:

LED lighting
Nav lights
Radar
Refrigeration

Water pump
Macerator pump
2x electric toilets
2x Gray water pumps

Central heating: furnace, pumps, 3x fan coils

TV antenna amplifier
Charging points


12v:
Instruments, sensors, nav gear, nav network, boat computer & monitor
Radios
Stereo system





I think for a boat with a similar amount of equipment, it might make perfect sense, and might not be any kind of overcomplication, to make the backbone of the system 48v, with all the high power gear run directly from that.


Then, a small 24v lead bank (maybe 2x 12v batteries) fed from the main system with a DC-DC charger


Then, a small 12v lead bank (maybe just 1x 12v battery) fed from the main system with a DC-DC dropper, for the GMDSS emergency systems -- nav gear, radios. Having a separate battery bank for these systems is required on ships, so this is redundancy which is really worth it.





It seems to me that running very high current equipment like inverters, and especially inverters, since the loads can be sustained, higher voltage must surely be much safer. The huge currents at lower voltages are surely difficult to make safe.

[CatNewBee]

I agree, if you design a system from scratch.

If you need to convert an existing system, it would become an expensive project replacing all the power gear, winches, windlass, pumps, trusters etc., that would exceed the costs of the battery by far.

On some yachts there are separate 12V buffer batteries near the bowtruster or windlass to reduce the wire size, current and voltage drop along the installation, may be a viable workaround.

Another design may be a 48V or even higher enclosed system for electric propulsion and inverters with a step down / step up charger to a second 12V or 24V LFP bank for all low voltage on board electronics and lights, that also allows charging back from the alternators to the house bank. Even a high voltage bus installation with local small and efficient step-down power supplies may work quite well without a separate 12/24V installation. It is what we use in our houses on land for ages with 110V/240V and PSU's for our computers, smartphones, tv sets and anything else.

[Dockhead]

Originally Posted by CatNewBee

I agree, if you design a system from scratch.

If you need to convert an existing system, it would become an expensive project replacing all the power gear, winches, windlass, pumps, trusters etc., that would exceed the costs of the battery by far.

On some yachts there are separate 12V buffer batteries near the bowtruster or windlass to reduce the wire size, current and voltage drop along the installation, may be a viable workaround.

Another design may be a 48V or even higher enclosed system for electric propulsion and inverters with a step down / step up charger to a second 12V or 24V LFP bank for all low voltage on board electronics and lights, that also allows charging back from the alternators to the house bank. Even a high voltage bus installation with local small and efficient step-down power supplies may work quite well without a separate 12/24V installation. It is what we use in our houses on land for ages with 110V/240V and PSU's for our computers, smartphones, tv sets and anything else.

I was thinking of a system designed from scratch (my hopefully new build boat), but I think that this would be suitable also for a conversion IF you are not stuck with existing high power gear.


Because the low power systems can be left more or less just as they are.


But there might be different reasons why it's not hard to upgrade the high power gear. Maybe you want to upgrade it anyway.


And in some cases you might be able to just swap the motors.


In any case, for the new build, I would want a crack electrical engineer designing it, and I would not interfere too much after giving the performance specs and other main parameters. I learned from hard experience with buildings to let the pros do their work without too much interference, however knowledge an amateur, we may be.

[transmitterdan]

DH, if you want to discuss this send me a PM. I am an experienced high power engineer that happens to own a boat. I don't charge anything for sharing my experience.

[ramblinrod]

Originally Posted by evm1024

Oh good, progress. 48 Vdc is safe where required. Thanks for admitting that 48 Vdc is safe.

Strawman Alert: I made no such claim.

Electricity in general is not safe.

In general, danger increases with voltage (unless additional mitigating safety factors are employed).

Therefore, my recommendation is to always use the lowest voltage possible practical.

So typically a vessel has a relatively safe 12 Vdc system.

I recommend using this where possible and practical to power appliances, rather than installing a more dangerous higher voltage system, just to save a few bucks on smaller cable (which actually increases danger more), just to spend that much or more, on higher voltage components and DC-DC converters (which actually reduce safety even more yet).

[transmitterdan]

Originally Posted by ramblinrod

Strawman Alert: I made no such claim.

Electricity in general is not safe.

In general, danger increases with voltage (unless additional mitigating safety factors are employed).

Therefore, my recommendation is to always use the lowest voltage possible practical.

So typically a vessel has a relatively safe 12 Vdc system.

I recommend using this where possible and practical to power appliances, rather than installing a more dangerous higher voltage system, just to save a few bucks on smaller cable (which actually increases danger more), just to spend that much or more, on higher voltage components and DC-DC converters (which actually reduce safety even more yet).

Sigh....

[CatNewBee]

You are right for a typical low-power marine set-up, the 12V are sufficient, like 6V installations on older cars with weak headlights . When the headlights go to 55W/65W bulbs, 2x21W blinkers, 2x21W or 4x21W brake lights, stereo radios, electrical heating of seats and rear windows, electrical mirrors etc, 6V installation hit a barrier and 12V was introduced to make the installation more stable and more safe.

Trucks have 24V board systems, also busses and other commercial vehicles, commercial boats and larger yachts have also often 24V board systems for this reason.

If you go to a super yacht or a larger vessel, you will find 10kVA inverters, even 3-phase systems with 380V to power all the A/C units , refrigeration and galleys. Some run generators 24/7 some use lithium batteries for a quiet sleep. When it comes to inverter in this power range you are safer and better off with high voltage batteries, no question at all. If you look at hybrid / electrical propulsion the engines are also not at 12V, they use higher voltages to keep the currents in the installation under control.

So it depends on what you want to have on board. A dinghy even do not need an electric system, you can run your navigation lights on AAA batteries and do visual shore navigation.


In my opinion, it is a mistake to only look at the voltage, you have to consider both, voltage and current when deciding about a set up and safety. Higher currents make things complicated, so sometimes it is better to increase the voltage in an installation to make it more reliable.

I agree of course, for a bare boat with only navigation lights, some illumination inside and a chart plotter and a camping fridge where your power draw is around 10..20A, it makes no sense to go for 48V or even 24V.

If you regularly go over 400/500A, things are different. It starts with the wire gauge, the fuse holders and fuses, the solenoids, the switches and so on. This is a completely different playground.

[CatNewBee]

... BTW, there are the same appliances for 110V and 240V in our households, I would not claim the installations in the USA with 110V are safer then the 240V in the rest of the world, simply because 110V are less then 240V.

This is simply not the case, 110V plugs and outlets seem to be much more dangerous than the 240V gear. I would even see an advantage on the 240V side when it comes to high power gear, for workshops even 380V / 3 phase is safer and better than single phase 240V installations.