Reply
 
Thread Tools Search this Thread Display Modes
 
Old 06-04-2013, 12:39 PM   #1
Rivet Master
 
SteveH's Avatar
 
2005 39' Land Yacht 390 XL 396
Common Sense , Texas
Join Date: Sep 2007
Posts: 5,311
Question for you solar "Gurus"

Actually several questions....assuming one group 27 battery being used at night down to maybe 60%, could a 45 watt solar panel be used during the day with no controller, and is my math right that it would charge at a max rate of 3.5 Amps?

Same battery, what size solar panel could be used continuously without a controller?

Thanks for your input.
__________________

__________________
Regards,
Steve
SteveH is offline   Reply With Quote
Old 06-04-2013, 01:59 PM   #2
4 Rivet Member
 
steverino's Avatar
 
2010 27' FB Flying Cloud
Ivins , Utah
Join Date: Aug 2009
Posts: 276
Images: 3
You should only expect peak output from panels 2-3 hours per day, and that will decrease due to season, cloud cover, whether any shade is falling on the panels, and temperature. As well, with no controller, the rate would decrease as the battery's voltage rises due to state of charge.

Replacing 40 A-Hr's even at at a max rate of 3.5 A would require over 11 hours of full-on sun.
__________________

steverino is offline   Reply With Quote
Old 06-04-2013, 02:15 PM   #3
65th Anniversary CLIPPER
 
masseyfarm's Avatar

 
1996 36' Clipper Bus
Tub City , British Columbia
Join Date: May 2009
Posts: 3,271
Images: 55
If you are in direct sun, a quality 40w panel will be capable of boiling your battery if there is no draw on it and it gets repeated days of sun. You can check the battery regularly for the level of the acid solution to determine how much effect it has. You must keep the battery plates wet.

A controller for that size panel is cheap insurance if you want unattended service.

I have no controller on two systems, but those two systems will overload onto my main system if they exceed 13.2v at the battery. I use SurePower 1315-200 Separators for this.

Dave
__________________
"LOVE and LOSS, are two of the greatest emotions one can experience. -- I went to school to learn about "WHAT GOES UP MUST COME DOWN" but I had to live my life to learn the lesson of: 'WITH LOVE THERE WILL BE SORROW'."
David Stewart. (after loosing my NAVIGATOR)
masseyfarm is offline   Reply With Quote
Old 06-04-2013, 02:45 PM   #4
4 Rivet Member
 
2008 16' Safari
Destrehan , Louisiana
Join Date: May 2009
Posts: 395
You really do need a controller.
Unless you are will to manually monitor your battery all day long and turn off the solar supply when the battery is topped off.
For a 45 watt unit and 12 volt system, they are cheap.
__________________
dlb435 is offline   Reply With Quote
Old 06-04-2013, 02:48 PM   #5
Rivet Master
 
SteveH's Avatar
 
2005 39' Land Yacht 390 XL 396
Common Sense , Texas
Join Date: Sep 2007
Posts: 5,311
I seems that no one has understood my questions, so again: assuming one group 27 battery being used at night down to maybe 60%, could a 45 watt solar panel be used during the day with no controller?

Same battery, what size solar panel could be used continuously without a controller?

Your input is appreciated.
__________________
Regards,
Steve
SteveH is offline   Reply With Quote
Old 06-04-2013, 03:40 PM   #6
65th Anniversary CLIPPER
 
masseyfarm's Avatar

 
1996 36' Clipper Bus
Tub City , British Columbia
Join Date: May 2009
Posts: 3,271
Images: 55
Your question is a catch22. If you have an adequate size panel to recharge your battery every day, then it will require a controller to avoid damage over a fairly short period.You are in Texas and I assume the sun shines there quit a bit.

An 11W panel would be about the limit to avoid unattended damage but would not recharge that battery in one day.

The other thing that happens is, that the battery will boil without a controller or you to monitor it, and the acid spill will cause further parasitic drain and lower your overall capacity of the system. (makes a mess also)

Dave


Quote:
Originally Posted by SteveH View Post
I seems that no one has understood my questions, so again: assuming one group 27 battery being used at night down to maybe 60%, could a 45 watt solar panel be used during the day with no controller?

Same battery, what size solar panel could be used continuously without a controller?

Your input is appreciated.
__________________
"LOVE and LOSS, are two of the greatest emotions one can experience. -- I went to school to learn about "WHAT GOES UP MUST COME DOWN" but I had to live my life to learn the lesson of: 'WITH LOVE THERE WILL BE SORROW'."
David Stewart. (after loosing my NAVIGATOR)
masseyfarm is offline   Reply With Quote
Old 06-04-2013, 04:08 PM   #7
Rivet Master
 
SteveH's Avatar
 
2005 39' Land Yacht 390 XL 396
Common Sense , Texas
Join Date: Sep 2007
Posts: 5,311
Quote:
Originally Posted by masseyfarm View Post
Your question is a catch22. If you have an adequate size panel to recharge your battery every day, then it will require a controller to avoid damage over a fairly short period.You are in Texas and I assume the sun shines there quit a bit.

An 11W panel would be about the limit to avoid unattended damage but would not recharge that battery in one day.

The other thing that happens is, that the battery will boil without a controller or you to monitor it, and the acid spill will cause further parasitic drain and lower your overall capacity of the system. (makes a mess also)

Dave
All of these things I understand, and do not argue. At this point, I am not concerned with recharging the battery in a day, but NOT OVERcharging it. What I want to do is keep the battery charged with a solar panel during times of storage/not being used.

The other thing I want to do is use the 45 watt panels without a controller. This is because the trailer I wish to use it with (17' Casita) does not have space for the controller to be installed internally, and I do not want to leave it setting on the ground outside.

Perhaps I should have asked how much current from solar panels my battery will take without overheating, daily from say 11 AM to 6PM (7 hours)?

It's a simple matter to figure out how much current the panels will put out during peak sunlight, but I don't know how long during the day that will happen, and what the battery will tolerate.
__________________
Regards,
Steve
SteveH is offline   Reply With Quote
Old 06-04-2013, 04:13 PM   #8
Rivet Master
 
1977 Argosy 24
Currently Looking...
Milltown , Wisconsin
Join Date: Mar 2006
Posts: 1,069
He is asking a "yes or no" question, and no one has answered it yet! Lots of good info, but no answer.
__________________
ventport is offline   Reply With Quote
Old 06-04-2013, 06:11 PM   #9
Rivet Master
 
richinny's Avatar
 
2011 34' Classic
Westchester Cty.NY , / Miami FL
Join Date: Jul 2007
Posts: 3,122
i would think that once the battery is charged, more that a trickle charge (think battey maintainer) can boil the battery.
__________________
Ricky
2012 F150 Super Crew 5-1/2' bed Ecoboost 4x4 3.73 elec. lock diff. Propride hitch
give life. kidney & pancreas transplant 9/9/06
Ingrid-my unofficial '"World's Oldest Streamer" 1909-2008 R.I.P.
richinny is offline   Reply With Quote
Old 06-04-2013, 06:23 PM   #10
Rivet Master
 
kscherzi's Avatar
 
2013 27' FB International
El Dorado Hills , California
Join Date: Jan 2013
Posts: 1,136
Images: 24
Sunforce sells a 5 watt panel for trickle charging. So I think 45 watts is probably too strong for 24/7 uncontrolled charging.
__________________
kscherzi is offline   Reply With Quote
Old 06-04-2013, 06:52 PM   #11
Rivet Master
Commercial Member
 
lewster's Avatar
 
Vintage Kin Owner
Naples, FL , Hood River, OR
Join Date: Dec 2005
Posts: 7,279
BatteryMINDer has a nice 15 watt panel combined with a 3 stage controller:
BatteryMINDer 12 Volt 15 Watt Solar Battery Charger: BatteryMart.com

This is a maintainer for a fully charged battery, not a charger. You certainly need more than 15 watts to charge a battery
__________________
Lew Farber...ABYC Certified Master Marine Electrician...RVIA Certified Master Tech ...AM Solar Authorized Installation Center...AIRSTREAM Solar & Electrical Specialist...Micro Air 'Easy Start' Sales and Installations
lewster is offline   Reply With Quote
Old 06-04-2013, 07:18 PM   #12
Rivet Master
 
Gene's Avatar
 
2008 25' Safari FB SE
Grand Junction , Colorado
Join Date: Sep 2007
Posts: 10,840
Steve,

I think I understand you, but calculating how much charge you get depends on the clearness of the day (clouds, haze) and the direction of the sun. To get maximum charge, you have to move the panel(s) to face the sun all day. Your results may vary. Our panels work very differently depending on those factors.

It sounds like you have no way to plug the Casita into shore power or you wouldn't be asking this.

If the converter is a multistage, I guess there is a way to control the input to the batteries, but I don't know how. It seems to me the part that controls the charge may be in the 120 v. circuit. But if it were wired into the input from the truck battery, maybe it would work. I think you would have to look at the circuit diagram for the Casita converter to see how to wire it. Or, just attach it to the battery and monitor the battery voltage until it is charged. That would require you to sit by it all day drinking beer and eating chips and salsa. That may make it worth it. I'd be glad to sit with you and watch the meter every once in a while, but the danger is we will both fall asleep and forget about the charge.

Our solar panel controller is not all that big, but neither is a Casita. Yet, it could be mounted in a box about 8" x 6" and a couple of inches deep and placed somewhere near the converter. Then you need wires to the panel(s) and the converter. But…

I think you want to connect directly to the battery. That is simple, but has drawbacks because you can't control the charge except by watching it or determining how long you can leave it alone. Even then, you'll have to check it periodically. And are you going to mount the panel(s) on the Casita, or trust that no one will take them?

If this is simply to keep the battery charged while stored, you'll only need to do this once a month or so. Then a voltmeter will tell you when the battery is charged and you do this on a day when you can check it every couple of hours. But I do like the beer and chips method.

I don't think I've answered your question at all, but it was fun to speculate on possible solutions and make it more complicated than it need be. Maybe a windmill is another approach….

Gene
__________________
Gene is offline   Reply With Quote
Old 06-04-2013, 07:30 PM   #13
Rivet Master
 
DanielB's Avatar
 
1974 31' Excella 500
Charleston , South Carolina
Join Date: Nov 2010
Posts: 1,073
Blog Entries: 8
A tidbit from Handy Bob: The RV Battery Charging Puzzle « HandyBob's Blog

"Converters are set to maintain the batteries at the “float” voltage, about 13.5 volts, and supply a trickle charge (2-3 amps, or 25-35 watts) to keep the batteries full, while not over charging them and boiling them dry"
__________________
As I grow older, I pay less attention to what men say. I just watch what they do.
- Andrew Carnegie
DanielB is offline   Reply With Quote
Old 06-04-2013, 07:32 PM   #14
3 Rivet Member
 
Jim J's Avatar
 
2014 30' Flying Cloud
Austin , Texas
Join Date: Jul 2006
Posts: 152
Images: 117
Blog Entries: 7
Yes you can use a 45 W panel without a controller to do that but it would not be the preferred way to charge your batteries.

Your math is probably OK but solar cells do not output a constant voltage. It varies due to amount of light and what the load on them is. A 45 watt panel will produce 2.5 to 2. 7 amps during peak exposure. So you might get 15 -20 Amp Hr per day into your battery.

Charging Information For Lead Acid Batteries

If you follow the link you will see that lead acid batteries do not like to be charged quickly. So take advantage of the Solar charge controllers that have been developed to manage your battery charging for you.

Low current charge controllers are very small and can easily be mounted inside your trailer frame near the battery box.

I am currently building a solar battery maintainer using a 15 watt panel and a charge controller I got from Northern Supply. I have had good luck with this system on my sailboat. It kept the batteries well charged and prolonged their life. I typically used the boat once a week and left the solar panel in place the rest of the week. Cost is less than $150.

What I have read suggests the maximum wattage without a charge controller is in the 10 to 12 watt range. This works out to less than one amp into your battery,

A group 27 deep cycle battery may have a capacity of 100 amp hr. If you need to replace 60% of that with a 12 Watt solar panel at 0.6 Amps x 10 hr per day, it will take 10 days to recharge in the summer. Your results will take longer due to temperature, amount of sunlight, efficiency of the panel, age of the battery etc.
__________________

__________________
Jim J is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 08:28 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.