On Saturday, 27 February 2016 12:27:16 UTC, David wrote:
On Fri, 26 Feb 2016 23:46:27 -0800, harry wrote:
On Friday, 26 February 2016 18:16:39 UTC, David wrote:
On Fri, 26 Feb 2016 17:03:13 +0000, Fredxxx wrote:
On 26/02/2016 10:59, David wrote:
This first post is a place holder in part, so that I don't forget to
ask the question, as I usually do once I get involved in stuff
during the day.
The Motor Home has mains powered habitation air conditioning - that
is an ELectrolux slug on the roof.
As soon as we know the spec, it might be possible to assist.
So for it to work you need to be on a site with mains electricity.
There is also the issue of the power surge on start-up compared to
the power demand on normal running.
What I would like to be able to do:
(1) Run the A/C whilst driving - that would I assume involve an
inverter which could take power through the 12V electrics buffered
by the habitation batteries (unless the demand needs a direct
connection to the alternator charging circuit instead of via the
charge controller which charges the habitation batteries). This also
allows starting the engine, firing up A/C and then stopping the
engine and letting the A/C run on using the habitation batteries.
For a narrow boat I installed a 3kW inverter (with surge capability),
150A alternator and 4 100Ah batteries. It can be done though
challenging. I doubt you'll have the space to fit a second
alternator.
(2) Run the A/C when away from mains power - using a small Honda
generator which might be able to meet most of the demand apart from
start-up. I am envisaging perhaps the generator pushing power into
the system whilst the A/C takes power out so that the use of
habitation battery charge is slowed. This probably equates to
running a UPS (that is, power in to UPS for charging, power always
out of UPS for running the device) and using a small generator to
keep feeding some power into the UPS during a power cut. The
generator may not fully meet the power demand but it slows the rate
of discharge.
Again without knowing the rating of the air con, and the size of your
portable gen, we're in the dark.
This does seem to demand a lot of inefficiency, though, potentially
with the generator input being converted from 240V to 12V then back
again. It would be nicer if the battery 12V power could be used to
boost the 240V input from the generator so that most of the power
comes directly in at 240V.
Bottom line is that one way may require blending two 240V inputs
into a single output, with obvious (I think) requirements to lock
the wave forms of the 240V together.
You cannot "blend" 2 AC voltages.
Can nobody see my post of 12:29 today?
This contains the details, but I keep getting "as soon as we know the
specs" responses much later in the day.
With regards to blending two AC voltages, how does solar from the roof
blend into the UK grid, then? Thought it was pushed out of an inverter
and synced with mains - depending on how much you are drawing at the
time you should get all inverter (plus some pushed back up the wires)
or part mains and part solar. Or all mains if it is night time!
Or am I missing something about how solar power is delivered from the
rooftop?
Solar power is DC.
It is linked to the mains by means of a grid tie inverter.
The mains AC is used to "create" synchronised AC from the DC.
https://en.wikipedia.org/wiki/Grid-tie_inverter
Synchronisng two separate AC supplies is quite another (more difficult)
matter.
However, in the scenario I am exploring I was looking at blending a source
of 240V AC with the output of an inverter driven by 12V batteries.
So in this case a "grid tie inverter" might do the trick. That is,
blending the output from an inverter and the output from 240V mains.
However I think that this is likely to be far too expensive (from memory
of solar installation quotes) for the application I was considering.
I know that the power demand from the A/C is likely to rule it out in my
specific case but I am now exploring general principles. For instance if
you want to run a microwave or hair dryer which is just over the power
output of your genny.
It does raise the possibility of a very limited solar system (couple of
panels on the roof of a motor home) being able to boost the output of some
of the more flaky (especially continental) on site power supplies on sunny
days.
Cheers
Dave R
--
Windows 8.1 on PCSpecialist box
It's just not technically feasible.
The grid tie inverter runs at 400 odd volts
You need to have conventional AC fitted to the engine of your vehicle.
The only practical solution.