Thread Tools Search this Thread Display Modes
Old 09-03-2015, 11:46 AM   #1
Rivet Master
dznf0g's Avatar

2007 30' Classic
Oswego , Illinois
Join Date: Jul 2010
Posts: 8,196
Regard prior questions re. 15 watt solar batt. maintainer

The question of whether a 15 watt solar panel is sufficient for battery maintenance while in storage has come up before and I now have some data to discuss definitively. My answers, in the past were based on remote a storage situation and finding the batt full after weeks at the lot. My trailer is now on my own pad at home, so I can offer some daily observations.


1) two group 29 Interstates

2) parasitic drain of 100mA due to Trimetric monitor (~30mA while off, ~60mA while on and checking), Morningstar controller (~60mA) and converter (LED light is on even though 120V is disconnected ~10mA?)

3)Store switch is off

So roughly 2.4Ah are consumed per day. The panel supplies about 700mA at direct overhead sun angle (net is 600mA per Trimetric)

7 hours of usable charging at an average (observed SWAG) 400mA = 2.8Ah of charging per day

In a perfect world (in the desert or very consistently sunny areas) 15 watts is more than enough.

Here is a real world observation though. I had 5 days of very cloudy days. At the end of the 5 days, the batts were at 96% and showed a deficit of about 8Ah.

If the following days had been 100% clear, it should take a little less than 3 days to "break even" and be at 100% again.

I am in day 3 of the "recovery" from cloudy weather (It has been partly to mostly sunny for 3 days) and it appears it will take most of 4 days to fully recover to 100%.

So, is 15 watts enough? Barely, and I'm not sure that floating between 95 and 100% on an ongoing basis is a reason to worry about battery health or freezing.

BUT, if i had it to do over again, I'd look for a 20 or 25 watt panel.

YMMV, of course, depending on your parasitic drain, Latitude, average weather, and solar setup.

"If the women don't find you handsome, they should at least find you handy." - Red Green
dznf0g is online now   Reply With Quote

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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Lithium Batt Solar Install 2015 Classic ghaynes755 Generators & Solar Power 54 12-14-2015 12:42 PM
Correct procedure with regard to stolen Airstream Antonio Airstream Lifestyle 12 04-21-2015 07:51 PM
plug-in battery charger/maintainer TerraYacht Batteries, Univolts, Converters & Inverters 5 07-19-2014 11:44 PM
Need another 65 Watt UNI-SOLAR kooshka Generators & Solar Power 5 09-13-2010 08:37 AM
Advice on 15 Watt solar battery charger rywnc Generators & Solar Power 2 05-03-2010 08:09 AM

Virginia Campgrounds

Reviews provided by

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 10:03 AM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.

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