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RV PV Question

  • Thread starter Robbie McFerren
  • Start date
R

Robbie McFerren

Jan 1, 1970
0
Ok, First off I want to let everybody know that this is only a curiosity and
most likely not be implemented.

OK, my RV's 12 volt system is crap, no converter and 14 gauge wire
throughout. I'm not even sure if all the lights are connected, but I will
find out before I set up a PV system. I am permently parked in a campground
and the RV will probably fall apart before it is ever moved again, so I'm
only concerned about wind. I don't know how well PV will work, I have no
way of checking or guessing. Here are the parameters of the system that I
would set up.

Most of the time the PV system will provide a trickle charge with a few
burts of 25 watts to demonstate the system.
I want to be able to provide a 15 AMP charge current from PV.
During power failures and sometimes hot days I will be using up to 75 watts
for lights and whatever my cell phone uses. Power failures may also include
more for lighting and also run an adapter for a handheld TV. I may also Use
an inverter for an electric fan the inverter will be 75 watts and it will
power up to two small fans to keep me cool.
The AC refrigerator will be shut down during long power failures.
A generator is avalible and I may use a battery charger to recharge the
batteries off the generator, every day or two to help the PV system (I am
intentionally underpowering the PV system to save money as the system will
only be used for standby most of the time for short power failures from
thunderstorms.
A 12 Volt deep cycle battery will be used (no starting required).
I will be using line powered devices most of the time and maybe shifting to
DC on hot days to reduce load on the crappy campground wiring.
 
G

George Ghio

Jan 1, 1970
0
Robbie McFerren said:
Ok, First off I want to let everybody know that this is only a curiosity and
most likely not be implemented.

OK, my RV's 12 volt system is crap, no converter and 14 gauge wire
throughout. I'm not even sure if all the lights are connected, but I will
find out before I set up a PV system. I am permently parked in a campground
and the RV will probably fall apart before it is ever moved again, so I'm
only concerned about wind. I don't know how well PV will work, I have no
way of checking or guessing. Here are the parameters of the system that I
would set up.

Well you do have ways to find or guess at how weel PV will work
Most of the time the PV system will provide a trickle charge with a few
burts of 25 watts to demonstate the system.

Twenty-five watts is 2.08 amps at 12V
I want to be able to provide a 15 AMP charge current from PV.

3-75W panels will provide (in therory 18.75 amps) close to what you want.
During power failures and sometimes hot days I will be using up to 75 watts
for lights and whatever my cell phone uses. Power failures may also include
more for lighting and also run an adapter for a handheld TV. I may also Use
an inverter for an electric fan the inverter will be 75 watts and it will
power up to two small fans to keep me cool.

75 Watts is incorrect fo what you want to say.

You are looking at Watts X Time which is Watt hours. So you need to know
how long things will run.

This means that a light which draws 10 Watts and runs for 6 Hours will
use 60 Watt hours. This is 5 Amp hours from your battery at 12 V.

So how long does the;

Cell phone take to recharge.

Fans run

Lights run

TV run

Times their wattage

Gives your daily load in Watt hours.

Watt hours(Wh) divided by the voltage gives Amp hours(Ah)

3-75 Watt panels should support 300 Amp hours of battery.

If your daily load (in Amp hours) is less than this you won't need to
use a charger unless you have no sun for several days.
 
B

Bill Kaszeta / Photovoltaic Resources

Jan 1, 1970
0
Ok, First off I want to let everybody know that this is only a curiosity and
most likely not be implemented.

OK, my RV's 12 volt system is crap, no converter and 14 gauge wire
throughout. I'm not even sure if all the lights are connected, but I will
find out before I set up a PV system. I am permently parked in a campground
and the RV will probably fall apart before it is ever moved again, so I'm
only concerned about wind. I don't know how well PV will work, I have no
way of checking or guessing. Here are the parameters of the system that I
would set up.

Most of the time the PV system will provide a trickle charge with a few
burts of 25 watts to demonstate the system.
I want to be able to provide a 15 AMP charge current from PV.
During power failures and sometimes hot days I will be using up to 75 watts
for lights and whatever my cell phone uses. Power failures may also include
more for lighting and also run an adapter for a handheld TV. I may also Use
an inverter for an electric fan the inverter will be 75 watts and it will
power up to two small fans to keep me cool.
The AC refrigerator will be shut down during long power failures.
A generator is avalible and I may use a battery charger to recharge the
batteries off the generator, every day or two to help the PV system (I am
intentionally underpowering the PV system to save money as the system will
only be used for standby most of the time for short power failures from
thunderstorms.
A 12 Volt deep cycle battery will be used (no starting required).
I will be using line powered devices most of the time and maybe shifting to
DC on hot days to reduce load on the crappy campground wiring.
Your statement 'I am intentionally underpowering the PV system to save
money....' is false economy if it results in a battery that is at low state of
charge for any extended period.

The best way to kill any lead-acid battery is to keep it undercharged.
The second best way to kill batteries to to over charge them without
maintaining the electrolyte (acid) level.

PV systems should be designed for the full situation, otherwise a
lot of money is wasted.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]
 
Your statement 'I am intentionally underpowering the PV system to save
money....' is false economy if it results in a battery that is at low state of
charge for any extended period.

Altho he didn't mention that result...
The best way to kill any lead-acid battery is to keep it undercharged.

Then again, the coulomb (round-trip) efficiency is higher if it's seldom
fully charged, and spends most of its time, say, 90% charged, except for
equalizations. Would that shorten battery lifetime?

Nick
 
L

Landline

Jan 1, 1970
0
George your theory is a tad out.
I would love to have 3 x 75w panels that would produce 18.75 amps charging a
battery system.
In THEORY try 13.0 amps and you will be more on the money.
 
G

Gymmie Bob

Jan 1, 1970
0
We have to consider the DC/DC inverter in between that can act as a step up
for current since the batteries cannot use the high voltage from the panels
in full sun.

The batteries are never 12V though. Base nothing on that figure.
 
S

Steve Spence

Jan 1, 1970
0
LOL, do you ever read what you write, or do you turn off your brain and
let your fingers go to work?

Do you know what a battery does to PV output?

That "dc/dc inverter" as you call it is called a charge controller, and
regulates the pv output as the battery comes to full charge. Only a few
have MPPT capability (MPPT is the technical term for your "step up").

You really ought to stick with topics you know something about. Maybe
xbox or playstation?



Steve Spence
Dir., Green Trust
http://www.green-trust.org

Contributing Editor
http://www.off-grid.net
http://www.rebelwolf.com/essn.html
 
G

George Ghio

Jan 1, 1970
0
Landline said:
George your theory is a tad out.
I would love to have 3 x 75w panels that would produce 18.75 amps charging a
battery system.
In THEORY try 13.0 amps and you will be more on the money.

This would seem to not be the case.

75 X 3 = 225 Watts / 12 = 18.75

This is theory and can happen on a clear frosty morning.

What you have stated (13.0 A) is closer to reality.
 
G

George Ghio

Jan 1, 1970
0
Most people would use a charge regulator.

Gymmie Bob said:
We have to consider the DC/DC inverter in between that can act as a step up
for current since the batteries cannot use the high voltage from the panels
in full sun.

The batteries are never 12V though. Base nothing on that figure.
 
A

Anthony Matonak

Jan 1, 1970
0
In a previous posting from GB he mentioned that he only jokes.
I wouldn't take anything he writes more seriously than he does.
:)

Anthony
 
R

Robbie McFerren

Jan 1, 1970
0
Remember If I build this system, it may only spend maybe 4 to 8 hours a year
at full load. Most of the time it will be charging from PV. During the
winter months there will be no load other than the battery and the
controller. I don't intend on running full 15 amps as I will be trying to
save the battery power and the 4 to 8 hours a year is an inflated figure
unless I do more and more with the system and I would upgrade the system
accordingly.
 
G

Gymmie Bob

Jan 1, 1970
0
MPPT was what I was talking about. I didn't think the childish ones like you
might understand the term though.

Troll harder.
Effort 3 out of 10
Effectiveness 5 out of 10.
Short lived and very obviously a troll for attention.
<PLONK>
 
W

Windsun

Jan 1, 1970
0
Then you should say MPPT. "Step up" is not the correct term.
 
G

Gymmie Bob

Jan 1, 1970
0
I thought a MPPT was a steup current device. What would you call it then?

How many dc step up devices do you know of for PV applications?

Is the terminology really important to you or did I just get caught by
another anal troll here?
 
G

Gymmie Bob

Jan 1, 1970
0
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