24v vs. 12v - any advantages?

Discussion in 'Electrical Systems' started by Lady Sophie, Nov 26, 2012.

  1. SPARK1
    Joined: Nov 2010
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    SPARK1 Junior Member

    Not true.

    You need an even amount of cells, but could use the same amount of cells.
    e.g. If you need 800 amp hour capicity at 12 volt, you only need 400 amp hour capicity at 24 volt. If your battery is 100 amp hour, then you will need the same amount of batteries. You could also use much thinner cables between the bateries.
  2. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    The higher the DC volts the more wear on relays, switches. Maybe even motor brushes.
    There was a push to go to 48vdc and the car companies could not do it and have a decent service component lifespan.
  3. SPARK1
    Joined: Nov 2010
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    SPARK1 Junior Member

    The difference in voltage between 12 and 24 volts will make almost no difference in life span of any of the components that you mention. Rather the higher current will have a much bigger difference in lifespan. Look at when you you weld. It is the current that you increase to get a stronger arc.

    Look at a 230 volt electric drill. There is minimal arcing on the brushes, bur if the load increases (current increases) this leads to a stronger arc and heating of components. This is AC, but at this low voltage, there is not much difference between AC and DC.

    So, if anything, 24 volts will lead to longer service life of components.
  4. Lady Sophie
    Joined: Aug 2007
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    Lady Sophie Junior Member

    Thanks for all the good responses. I have selected to run a mixed system 12 and 24. My stock alternator is 12v and only charges a dedicated 12v starting battery. I have added a 24v alternator to the engine which provides charge to the 24v bank. I have selected Trojan L16P-AC 6v batteries and will wire them in series-parallel to produce 840 Ahr at 24v. I am planing on ocean passages and will depend heavily on solar, wind and water generation with the diesel as emergency backup.

    A comment was made that the same number of cells can produce either 12 or 24 v. The redox potential of the lead acid cell is 2.1v (approx). It requires 12 cells to produce 24 volts and only 6 to produce 12.

    I am not an expert on battery systems but was a process development engineer at Delco Remy Division Central Engineering in Anderson, Indiana, when GM tried to convert the automotive world to 24v. We produced the starters, alternators and batteries for GM. Fisher Guide Division, also in Anderson, produced the switches, lighting and instrumentation. From an engineering view point, both Fisher Guide and Delco, 24v was the more robust system and we were all pushing for it. However it was too great a change for too little benefit in the automotive world at large and the initiative failed.

    The main drawback to 24 volt is that the readily available popular voltage is 12. I have found most components are available in 24 v but usually at a surcharge (lower market demand) and longer delivery times. There may be some items, GPS, etc. that are easily available only in 12v so I have allowed for two inverters which should be fine as the amp draw on these components is low.

  5. Mark Cat
    Joined: Jun 2011
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    Mark Cat Senior Member

    Lady Sophie,

    The starting battery voltage is a fundamental starting point for many marine electrical requirements. Sometimes, due to legacy equipment and devices, starting and house are different voltages.

    For ground up 24V DC designs on larger vessels I like to have both starting and house set at 24V. For commercial there may be a smaller additional emergency power 24V bank and panel.

    If needed cabin 12V LED lighting can be powered by a regulated switching DC to DC converter from 24V feed local to the lights.

    As far as automotive 24V usage, many of the early electronic control modules and radios had linear regulators with logic running at 5V. Using a 24V supply required additional power dissipation (heat sinking) than 12V. Today some large control modules have switching supplies, but most are still linear.

    I find the problem with relays is in the characteristics of the load and if the contacts are protected against arcs. Most of the time for automotive the contacts are not protected against arcing. So the ones that fail first (output contacts damaged) usually power an inductive load, like an electric cooling fan for example. A bad relay will still "click" on, but the load remains off.

    All for now,

    Mark Cat
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