That's right, absolutely NAC. Electrical question

[Huw Powell]

The only problem with that is that "starter batteries" are not designed 
for "deep cycle" needs, which this is.

- Huw

On 5/30/2013 7:37 PM, Tony Hoffman wrote:
> 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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