DC to the load - what voltage do you use?

 For those of you who run at least some DC directly to loads (bypassing any
inverters you might have for AC), especially those who are entirely off-grid,
what is the typical or most common voltage used?

12V? 12/24V 24V? 24/48V? 48V? 120V? 120/240V? 240V? Variable?

I've found switchmode power supplies for computers for 12VDC and 48VDC.
But not a lot of other things exist for DC, except the basics like
incandescent lighting (most of that appears to be for 12VDC).  I have
not seen anything for 120VDC in particular, including inverters (even
though this might seem to be the just right voltage for incandescent
lights in North America).  The highest DC side voltage I've seen for
inverters (other than the big ones designed to let solar/wind farms
power the grid in three phases) is 48V.

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Modern inverters are so efficient that use of DC is mostly obsolete. I have
a few DC outlets that I use for cell phone chargers and other appliances
that would normally be used in a car. Nowadays 5vdc is becoming popular as
supplied by computer USB ports and is used to charge music players and the
like.

Using AC as the standard for power distribution, lighting, etc. allows
seamless switching to backup generator if inverter system fails or you have
too many cloudy days.

NM

 On 11 Jul 2008 21:49:43 GMT, phil-news-nospam@ipal.net wrote:


    If a homepower-type-person wished to maintain/replace
the cells for a 125 or 250 volt battery bank - the equipment
is quite common. <industrial>   But why ?
... I think I maybe misunderstand your question.
  .. jt

 | On 11 Jul 2008 21:49:43 GMT, phil-news-nospam@ipal.net wrote:
|
|>For those of you who run at least some DC directly to loads (bypassing any
|>inverters you might have for AC), especially those who are entirely off-grid,
|>what is the typical or most common voltage used?
|>
|>12V? 12/24V 24V? 24/48V? 48V? 120V? 120/240V? 240V? Variable?
|>
|>I've found switchmode power supplies for computers for 12VDC and 48VDC.
|>But not a lot of other things exist for DC, except the basics like
|>incandescent lighting (most of that appears to be for 12VDC).  I have
|>not seen anything for 120VDC in particular, including inverters (even
|>though this might seem to be the just right voltage for incandescent
|>lights in North America).  The highest DC side voltage I've seen for
|>inverters (other than the big ones designed to let solar/wind farms
|>power the grid in three phases) is 48V.
|
|
|    If a homepower-type-person wished to maintain/replace
| the cells for a 125 or 250 volt battery bank - the equipment
| is quite common. <industrial>   But why ?
| ... I think I maybe misunderstand your question.
|  .. jt

The question is, _IF_ you take DC all the way to the loads, what voltage is
the common voltage for that.  If you don't do DC at all, and do only AC
instead, then I presume the voltage is the same as what the utility would
normally have provided, because virtually all devices and appliances expect
that voltage (120 volts in North America, 230 volts in Europe).

Maybe another useful question is if you use inverters, what is their DC input
voltage.  If you mix AC and DC loads, are the DC loads on the same voltage as
is fed to the inverters?

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off-grid,

This gets kinda complicated.  Like NoMad said most people gave up on the
idea of running DC appliances because the inverters are very reliable and
efficient (OutBack and Xantrex SW anyway).  I don't know which input voltage
is the most common but some prefer 48 VDC because it is supposedly more
efficient and you can get more powerful inverters in this voltage.  Others
prefer 24 volts because it is easier to find a battery charger in this
range.  Still some prefer 12 volts mainly because (I would think) that
battery chargers and appliances are easy to come by.

Occasionally I will run a DC appliance directly from two of the batteries in
my 48 volt bank but I do not want to run down those batteries so I don't do
it very often.  It's just a whole lot easier to just use 120 VAC from the
inverters or, sometimes, directly from a generator if it happens to be
running to charge the battery bank.

To overcome the 48 volt charger problem I bypassed the voltage regulator on
a Delco alternator and it will output about 85 volts with a 4 HP engine
driving it.  I adjust the engine speed to control the voltage.  This is a
cheap, fairly easy, and efficient way to get a 48 volt charger.  It is also
3-phase which is supposedly much better for battery charging than single
phase.  You can buy single phase power supplies that can be used to charge
batteries but they are fairly expensive, difficult to find (in my opinion)
and are not super-efficient (from what I've read).  OutBack and Xantrex have
inverters with built-in chargers that do a good job but with OutBack you end
up actually running everything from your generator while the batteries are
charging so unless you have a really great precision generator your
microwave won't work very well and your digital clocks will gain/lose time.

From my experience I would say that a single OutBack VFX3648
inverter/charger connected to an X240 OutBack autotransformer is adequate
for a modest off-grid home.  I have two inveters and the only time I use the
second one is for battery charging if my alternator gizmo is not working.
For charging I would suggest (I have a 660 Ah battery bank) a 6.5-7 HP
engine running a permanent magnet alternator.  PMAs have advantages over
regular car alternators and are more efficient.  Of course some solar panels
and a wind generator or other RE source would be nice too.  I have an
OutBack MX60 charge controller.  I could run my alternator through it and it
would control the charging cycles for me automatically but, according to the
meters and all, I lose about 200 watts of charging power doing this.
Personally it's no big deal for me to check it once or twice and adjust the
engine speed as necessary.

Also, I have all of my circuits on one leg of my house panel so I only need
one inverter to run everything without having to turn on the X240.  I only
use the X240 for my well pump.  Of course we cannot run the microwave, air
compressors, washing machine, and vacuum cleaner all at the same time.  But
we don't want to do that anyway.



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