Re: Electric Conversion log for Kahleesea
I was just involved in a spirited (and polite by the most part) debate over 12 vs 24 vs 48 Vdc marine electrical systems that may be applicable to some extent to your project.
12 vs 24 vs 48 Vdc Marine Electrical Systems
So here is my position, based on 40+ years of experience in various industries, designing, developing, installing, troubleshooting, repairing and marketing electrical products and systems, for the average ICE propelled rec cruising boat from 20 to 50 ft:
1. 48 Vdc is more prone to arcing and damaging contacts than 12 Vdc.
2. Damaged, arced contacts may cause a high Z connection.
3. High Z connections can heat up and cause fires.
4. 12 Vdc high Z connections, though less likely to occur, are more likely to manifest themselves easily (by improper load operation), prompting the boater to investigate and repair the problem before a fire ignites.
5. Receiving an electric shock is likely when contacting 48 Vdc, and unlikely at 12 Vdc.
6. While the 48 Vdc shock itself is not likely to be lethal, the involuntary instinctive response to electric shock can very well be more dangerous than the shock itself (e.g. jerk hand back into rotating machinery).
7. Most marine electrical products rated for 48 Vdc are more expensive.
8. Using 48 Vdc to reduce cable and connector size, may save some money, but will increase impedance, making the installation less safe.
9. From a builder standpoint, one has to calculate the cost / weight savings in cable gauge reduction against the cost / weight increase of the 48 Vdc breakers, switches, electrical products, etc.
10. From a modification standpoint, for up to a 3 kW moderate duration load (e.g. inverter) and a 6 kW temporary load (e.g. thruster) changing system voltage (even locally) is rarely worth the cable size reduction advantage. (I have evaluated many.)
11. For higher loads of longer duration, regardless of DC system voltage, the same power will be required, the battery bank will have to be very large, and it will be discharged rapidly, requiring ICE generator re-charging in most cases, that could have simply been used to power the appliance(s) in the first place, reducing the high stress on the batteries and electrical circuits.
12. Developing a high load, high voltage DC system, and using a DC-DC converter to power safety equipment, introduces a potential single point of failure node, that could render all 12 Vdc safety and nav equipment and lighting inoperable.
13. Below 50 ft LOA, a 12 Vdc electrical system in conjunction with a proper corresponding AC system, will provide excellent service, providing the best compromise between cost, weight, safety, reliability, ease of use, maintenance.
14. In the case of an electric propulsion system, being a > 3 kW and long duration load, a higher voltage DC electrical system is justified.
This system should be completely isolated from the vessel 12 vdc system, the latter having it's own charging systems, to ensure multiple charging source redundancy assuring power availability to all safety equipment in the event the propulsion electrical system (or DC-DC converter) fails.
14. All of these same principles hold true for a 12 Vdc vs 24 Vdc decision. (The electrical product costs will be closer but so will the cable and connector cost.)
15. Above about 50 ft, a 24 Vdc primary electrical system may be justified for a new build.
16. Above about 50 ft, a 24 Vdc local electrical system may be justified for a modification such as a windlass or thruster.
17. Some will propose a design solution they feel is more exciting for them to develop, rather than follow more traditional and proven solutions that are better justified by safety, reliability, life expectancy, and cost.
18. Everyone is absolutely free to disagree with these statements, and do as they wish on their boat. But if you make poor decisions that end up in property damage or personal injury, for you or your loved ones, hold YOURSELF personally accountable, and please don't park your vessel near mine. ;-)
We may all disagree on some or all points, but that's OK, as long as we treat one another with respect, and keep the best interest of forum members
[Disrespectful part edited out. Please get the message]
Last edited by MarkofSeaLife; 02-20-2019 at 03:38 PM.