[RE-wrenches] Tiny load problem

Wed May 12 03:28:30 PDT 2010

48 volts is a consideration and I have done many, but the problem is still
the 26 AC watt load and the inverters efficiency at that light a load. Just
hate to burn that much DC to generate that little AC. I am unsure if it is
better at 48 volts or not.

Maybe I should not sweat it but it just bugs me. It probably comes from
years of looking at "E meters" and playing with loads. 

Bob

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan
Sindelar
Sent: Wednesday, May 12, 2010 2:09 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Tiny load problem

Bob,
If I step back and look at your question, another bigger question comes up:
if you are designing a system with two inverters in order to double charging
current, you must have a pretty good sized battery bank. In general, I would
suggest that you look at a 48V system, rather than 24V, once it gets to that
size. Equivalent charging rate, but smaller wire, lower component amperage
requirements and fewer battery strings to get the capacity you're apparently
looking for.

Allan Sindelar
 <mailto:Allan at positiveenergysolar.com> Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
 <http://www.positiveenergysolar.com/> www.positiveenergysolar.com

Phil Undercuffler wrote: 

If the normal connected loads are within the capacity of a single inverter
(which may actually be possible -- I run my whole house off one Outback
FX2024, microwave, dishwasher, washing machine and all) then you can just
leave one of the inverters in sleep mode or disable output but leave
input/charging enabled.  

Which inverters are you planning on using for the generator charging?
Depending upon which brand or how sophisticated you want to be, there are a
couple ways to skin this cat.  Easiest and cheapest is to simply not connect
up any AC output wiring or stacking cables to the second inverter, and
program it to stay asleep and charge only when it sees AC input power. 

I used to be religious about making sure my inverter was asleep, and even
had a second baby inverter to power a handful of full time or sensitive
loads.  However, it got difficult trying to explain why you couldn't just
plug the vacuum cleaner into just-any-old-outlet, and as my electronic
widget count expanded it became less and less advantageous to have that baby
inverter.

Phil Undercuffler
Conergy

On Tue, May 11, 2010 at 9:58 AM, bob < <mailto:reellison at gmail.com>
reellison at gmail.com> wrote:

I am sizing a system that will have dual inverters to shorten generator
charging in the winter and enough solar to charge the rest of the time. 

Here's the problem, the inverter will not be able to get into sleep mode at
night.

There are 2 cell chargers and a "cpap" machine having to run all night.

It only totals 26 watts, has anyone found a better way to do this without
having to keep an inverter awake to produce 26 watts?

I would like to dedicate a Morningstar 300 watt inverter for the job but the
system is 24 volts and Morningstar has no plans to make one in 24 volts.

Anyone got any other ideas, or am I best to just deal with it?

Thanks,

Bob

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