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What type of inverter do I need?

Discussion in 'General Electronics Discussion' started by Django Fawkes, Jun 11, 2012.

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  1. Django Fawkes

    Django Fawkes

    May 16, 2012
    Hi, not sure if this is in the correct forum, so if mods move or delete, i'll understand, but here goes:

    I plan to buy

    and use without plugging directly into mains, but plugged into an inverter which linked to a car battery. As it is pricey for me, I need to be sure what type of inverter I require for either a 12 or 24v battery (preferably 12v) and whether the speaker is suitable to use with this setup. The speaker itself has a power supply which converts mains supply to 48 volts.

    here is the specs:
    Wattage 100 watts maximum
    Input 100V - 240V ~ 50/60 Hz
    Output 48V DC @ 2.08 Amps

    My thoughts is if I connect the AC 240v to 48v DC power supply to the inverter and the inverter to the battery, it should be ok.

    On a further note, it is likely to be an american plug, so I will need an international adapter, making it:

    car battery-->inverter-->international adapter-->AC 240v to 48v DC power supply-->speaker

    Two questions then, first, what type of inverter do I need, say out of this list:

    And is it guaranteed safe and won't destroy the speaker?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I am not sure I understand why you'd want to connect a power supply up to a speaker.

    It would probably kill it instantaneously.
  3. Mongrel Shark

    Mongrel Shark

    Jun 6, 2012

    I think what Django is saying is that the speaker comes with it's own custom power supply, and that it has a built in amp (According to the ebay add) that needs 48v dc @ 2.08w (99.84w).

    Going from 12 or 24v DC to 240v ac only so you can go back down to 48v dc seems like a lot of unnecessary part's, complication and losses to me.

    Most inverters are around 70% efficient, rarely better and sometimes a lot worse. So you lose 30% or your power going up to 240 ac. Then your going to loose another 5-10 (or maybe more) going back down to 48vdc.

    So to get 100w to your speaker. your going to need at least 200w out of your battery.

    Also you need to know how sensitive this power supply is. Will it run on the square wave or modified square wave that many cheaper inverters put out? You may need pure sine wave. If you do go down that path. I would recommend getting an inverter capable of 2 or 3 times the watts you want to run. Just because it is advertised to do say 100w doesn't mean it will do it happily all day. Also many appliances need up to 3x the watts to "start", which is why some inverters have a peak rating. Like 200w with 400w peak. such an inverter will sit on 200w for extended periods, and go to 400w for a short time (min's or even sec's).

    So quick answer to your question. without knowing more about power supply and speaker. I would say get a pure sine wave (sine wave is probably overkill, but safe) inverter, at least 200w 400w peak. Or for one that has no peak rating I would go to 300-400w. because I don't like the idea of running it at max for extended times. Going to 600w would not be a lot of overkill...

    I have a 150w inverter that will not run my 50w laptop charger for eg.

    If it was me though. I would do some more homework on the speakers, and find out how sensitive the built in amp is.(if you can upload a schematic, people here can tell you that). Then find either a DC-DC step up. or get more 12v battery, depending on cost and application in mind for the speaker.

    I just had a (very quick) look for 12-48v step up's and 24-48v and Could only find this one:
    VHB100W-Q24-S48 9 ~ 36 48 2.08 100 480 85 Here For nearly $130 (depending what country you live in, postage could be a lot more)

    the datasheet Leaves a lot of questions though....

    If it was me I'd just get the battery's. it might even be cheaper... How many amp hours do you need? and how are you charging what you have (I assume you have at least 2 already as you said you can do 24v)?
  4. CocaCola


    Apr 7, 2012
    I would just use a DC to DC step up converter, 12 volts in 48 volts out and skip the included transformer if it's not some type of transformer/speaker amplifier all built in one... The ad seems to imply the power supply is stand alone thus eliminate it and replace it with one better suited to your application...

    car battery - boost converter - amplifier - speaker

    I'm not recommending this one, it's just an example of one that appears like it will fit the bill...

    When selecting one pay attention to the output ratings (especially important on adjustable ones like this) this one is rated at 120 Watts max output, you need about 100 Watts for your application thus it appears to be compatible... The short of it mind the output wattage and make sure it's in excess of your needs...

    Also double and triple check the output voltage so you don't fry something... Personally I would hook the output up to a standard household light bulb to provide a decent load and dial it in to 48 volts, then I would fine tune it again when hooked to the actual device... I have not idea how well they cheap modules regulate under different loads, so I would play it safe...
    Last edited: Jun 11, 2012
  5. Django Fawkes

    Django Fawkes

    May 16, 2012
    Ok, thanks for both of your answers @CocaCola & Mongrel Shark, from the info you've given me, I managed to figure out most of what I needed and a shop assistant in Maplin pretty much did the rest. Thanks!
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