That's right, absolutely NAC. Electrical question

[Tony Hoffman]

Or add a second battery, wired in series to the stock one for the purpose
you need and pull from the two of them for 24V, and plenty of amperage so
it won't go dead in short demand. This is exactly how older Cummins were
wired, 24V starter and alt, 12V everything else.

HTH,
Tony

On Thu, May 30, 2013 at 3:45 PM, Richard J Lebens <rick-l at rocketmail.com>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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