That's right, absolutely NAC. Electrical question

[Huw Powell]

A switching power supply going straight to 24v from 12v might be better 
taking a trip through 120 AC.  Mouser has a 108w one for just over $200.

- Huw

On 5/30/2013 4:45 PM, Richard J Lebens wrote:
> Start out in a perfect world - 100% efficiency.  The rated output of the supply is 24 @ 3.75 Amps which works out to 90 Watts.  (It probably does not run at it's rated output)  90 Watts at 12 volts will require 7.5 Amps.  8 hours would use 60 Amp-hours which seems to be within a 12 volt deep cycle battery capability.
>
> Now the real world   Guess (I have no clue) that the 24 volt supply is 85% efficient, the inverter 60% which will require 177 Watts at 12 volts or 14.7 amps, beyond the capability of a battery.  Now if the device only needs half that 3.75 Amps you have a much better situation.
>
> Of course a boost regulator that gets rid of all that inefficiency would work a lot better but that would cost money.
>
> Somebody check my math.
>
>     1. NAC.  That's right, absolutely NAC.  Electrical question
>
>        (John Larson)
> So I have this former customer, a charity case, pretty much, with a
> sleeping/breathing problem.  He lives in a 1970 VW bus with only
> occasional access to 110v power.  He uses a respiration helper device
> when he sleeps.  I have the label for the power supply (which has a 24v
> output at 3.75A), and I need to figure out what kind of load that'll put
> on a 12 battery through a 400w 90A inverter.  He already has the
> inverter so we want to try to use it.  I'm planning to install some kind
> of battery isolator, possibly a Ford starter relay (of which I have a
> number) activated by the KOEO position on the ignition switch.  If it
> would be better, I can purchase a dedicated component.  I'm planning on
> using a deep cycle battery and keeping it charged with the alternator
> (and possibly a solar panel, if necessary).  I know there are some of
> you that can do the math while walking and chewing gum, so this one
> should be a breeze!  I'm not one of those people ...................
> Would it be better to just use a 12vDC>24vDC device and forgo the
> 12vDC>110ACv>24vDC?
>
> Cost effective way?  Best way?
>
> Thanks!  John
>
>
>
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