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24volt inverter question

Discussion in 'General Electronics Discussion' started by cygnusv, Aug 25, 2017.

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  1. cygnusv

    cygnusv

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    Oct 7, 2014
    My boat has 4x Trojan 6 volt batteries which gives me a small 225ah 24 volt emergency mains power backup at 230 volts. My original quasi sine wave inverter was obviously limited to what it could safely be used to power. For this reason, I want to upgrade to a pure sine wave unit.
    My problem is this. Trojan deep cycle batteries prefer a bulk charge rate of 29.6 volts, and so far I've not found a pure sine wave unit that will allow this voltage without complaining. My old inverter has an upper voltage cutout at 30.5 volts.
    I have set my Victron mppt controller to 28.4 volts but this seems a waste of solar energy.
    Is there an efficient way to step down from 29.6 volts to 28.4 so that I can satisfy my Trojans without upsetting the inverter?
    Many thanks, Stu
    PS. I'm running fridge, freezer and flat screen so thought maybe a 1500 watt inverter (same as my old one) should cope.
     
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The Victron MPPT (nice to see someone using 'class' equipment....) is very efficient and you won't actually 'lose power' by setting its output to 28.4V - the correct voltage BTW - due to its switched-mode technology and 90% (ish) efficiency.

    Your bulk charging rate (29.6V) seems dodgy to me and it's not a voltage I'd use on a battery bank at any time.

    And your load(s) seem well under the 1500W level of need! I know inverters are efficient even at low conversion rates but you'd still lose less power by fitting a smaller, true sine wave, inverter dedicated to fridge/freezer/TV and keep the 1500W one for the beefier stuff (whatever it is you need 1500W for that is...).
     
  3. debe

    debe

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    Oct 15, 2011
    Why would you run a fridge & freezer of 240V?. My daughters Yacht uses fridge & freezers using Danfoss DC 12/24V compressors.
     
    cygnusv likes this.
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    It's what the battery's datasheet states...
     
  5. kellys_eye

    kellys_eye

    4,281
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    Jun 25, 2010
    In which case......

    I was basing my experience on 12V batteries at 14.2V each... the last time I used cells (or batteries under 12V) was when I had to do a daily service on 2V cells used to make up the emergency battery banks on merchant vessels!
     
  6. cygnusv

    cygnusv

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    Oct 7, 2014
    Apparently most deep cycle batteries prefer the higher voltage, and as stated, is what Trojan recommends.
    To answer another point made. 24 volt fridges and freezers are extremely expensive when compared to mains, hence our use of mains equipment.
    Maybe we'll have to stick to the lower voltage......
     
  7. cygnusv

    cygnusv

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    Oct 7, 2014
    I've just had a thought. Most vehicles and boats etc with 24 volt systems have alternators that charge at 28.8 volts peak. What is the point of an inverter set to a high voltage limit of 28.5 volts. Seems to exclude the inverter from anything but something like our Victron that can be adjusted through an app,
    I'll be more than interested in your thoughts about this. I'm defo a bit confused....
     
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