Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-11-2020, 04:16 PM   #1
INA
1 Rivet Member
 
2020 27' Flying Cloud
Seattle , Wa
Join Date: Jan 2020
Posts: 12
Solar power charging

Newbie question here. We have 180 watts of solar installed. We started the day at about a 75% state Of charge. We spent about 6 hours traveling in the Florida sun and ended the day at 85% charge. There was nothing much on in the trailer except the fridge. Inverter was off. I’m looking for suggestions/recommendations.
__________________

INA is offline   Reply With Quote
Old 05-11-2020, 05:04 PM   #2
Rivet Master
 
2018 25' International
Slidell , Louisiana
Join Date: Sep 2017
Posts: 861
So 6hr in the sun times 160 Watts divided by 14.4 volts = 67 Ah but let's subtract for average sun angle 25% loss and battery and wire resistance losses 15% so about 43 Ah. Now I'll assume you traveled with 12V power on so subtract another 2 amps times 6 hours or 12 Ah and we are down to 31 Ah. You have 200-240 Ah capacity so the 10% is say 22 Ah that leaves 9 Ah unaccounted....

Its not too far off but not great either. Maybe I forgot to subtract for something.
__________________

__________________
Brian
BayouBiker is offline   Reply With Quote
Old 05-11-2020, 06:16 PM   #3
Rivet Master
 
AirMiles's Avatar
 
2018 27' Globetrotter
Apollo Beach , Florida
Join Date: Feb 2017
Posts: 1,337
I always use three times solar panel wattage as an estimate of daily watt hours on a good solar day. In this case its 3 x 180W = 540Wh. Then I divide this 540Wh figure by 13.5V, which I assume is the average voltage while charging. This 540W / 13.5V = 40Ah of battery charging. Then we need to reduce this by the 2A draw of an Airstream times six hours, or 12Ah. So the 40Ah of battery charging gets reduced by 12Ah which was used and therefore 28Ah would be actually added to the batteries. I would say 28Ah should add more than 10% to your battery charge state, but then you may have had some cloud conditions that would affect charging. In addition to this, the tow vehicle should have added some Amps to the battery, but my experience is that I'm lucky to get mid-single digit Amps from the tow vehicle. Even if that was 7A, that would have been an additional 42Ah of battery charging.

I don't know what device you are using for your percentage state of charge, but it appears to me that it is not very accurate. What device is telling you your state of charge? What was the voltage reading before and after the trip? What kind of batteries are you using?

You are probably using factory solar. The factory solar controller may be less efficient that my aftermarket solar installation on which I base my estimates. I know the factory solar controller is much less efficient than the Victron solar controllers I have used. I know the wiring between the factory solar controller and the busbars is of much smaller gauge than I used in my installations and therefore would suffer more voltage loss. Many have upgraded the factory solar controller with a high grade solar controller and have gotten much better results.

So even though we used different formulas, BayouBiker and I are pretty much in agreement with our estimates of charging. I think the lost Amps we are looking for are a result of the factory solar controller and the thin wire between the solar controller and the busbars. I would upgrade the solar controller to a Victron 100/30 and increase the cable size between the new Victron solar controller and busbars to 6 gauge to improve performance.
__________________
2018 GT27Q, 45 nights 9,860 miles, 600W Solar - Produced 75kWh, PD4655L, 6V Batteries, Champion DualFuel, ProPride&BOSP, 16" tires, 2019 F250 PSD
Sold: 2017 FC25FB, 316 nights 40,150 miles, 400W Solar - Produced 200kWh in 216 days
2013 Casita SD17 89 nights 16,200 miles
(To RF)
AirMiles is offline   Reply With Quote
Old 05-11-2020, 07:33 PM   #4
Rivet Master
 
jeffmc306's Avatar
 
2019 27' Globetrotter
McHenry , Illinois
Join Date: Apr 2018
Posts: 802
Blog Entries: 4
Apologies to the OP but I have a follow up question for AirMiles.

AirMiles, any idea where the factory solar controller is located on a 27’ Globetrotter? Based on your observations I’d like to replace the factory Atkinson PWM controller with a Victron MPPT but so far haven’t stumbled across the physical Atkinson unit. Any hints on where they installed it?

Thanks!
Jeff
__________________
2019 27’ Globetrotter FBT Walnut/Dublin Slate
2018 FC23FB
2019 Ram 2500 6.4 Hemi Laramie Blue Ox 1500#
WBCCI# 10258
April 3, 2020 Retirement Plan RETIRED!
jeffmc306 is offline   Reply With Quote
Old 05-11-2020, 10:14 PM   #5
INA
1 Rivet Member
 
2020 27' Flying Cloud
Seattle , Wa
Join Date: Jan 2020
Posts: 12
Factory installed AGM batteries. The controller is also factory-installed. State of charge was derived from the factory installed display.
INA is offline   Reply With Quote
Old 05-12-2020, 05:46 AM   #6
Rivet Master
 
2018 25' International
Slidell , Louisiana
Join Date: Sep 2017
Posts: 861
So we can assign the missing ~10Ah to phantom voltage, or more inefficiencies than the 15-20%, or we could say the readout is inaccurate and the battery charged 15% and not the 10%. Perhaps the before and after readings were not taken precisely at the beginning and end of the drive.

INA do you have any thoughts on where the 10Ah may have gone?
__________________
Brian
BayouBiker is offline   Reply With Quote
Old 05-12-2020, 07:25 AM   #7
3 Rivet Member
 
2014 27' FB Eddie Bauer
Coldwater , Ontario
Join Date: Jun 2017
Posts: 152
If by “derives from the factory installed display” you mean that you’ve converted from a voltage reading to a battery percentage then this is a nearly meaningless method of determining battery percent state of charge with accuracy.
Assuming the battery was actually at 75% SOC it would have very soon entered, if not already be, into the absorption phase. At this point in the charge cycle you will not receive a linear charge. Ie, the solar panels may be capable of providing X Amps, but the batteries are only able to accept X-y Amps as the charge amps tails off.
Add in the fact the factory solar panels are a long way from ideally aligned to the sun and quite possibly, even likely, impacted by obstacle shadows from objects on the roof and the inefficiencies inherent in most factory installations and you have plenty of opportunities for loss of charging inefficiencies.
Many more, and better controlled, charging scenarios are needed to assess your concern further.
bbandeddie is offline   Reply With Quote
Old 05-12-2020, 08:10 AM   #8
Rivet Master
 
2018 25' International
Slidell , Louisiana
Join Date: Sep 2017
Posts: 861
bb makes some good points. realize though that the controller has displayed the percent of charge based on its voltage and current sensors and its firmware. Still the numbers are likely not that accurate...

Consider, most modern chargers will transition to absorption charge between 80% and 85% where current profiles decline rapidly from max of 40+ amps. But the 160 watts is quite low to begin with so it will enter absorption mode a bit later. Then consider late in the afternoon its probably about 7-8 amps max. Figuring two batteries gets us to 3 amps max per battery after subtracting trailer load. Most charge profiles won't approach 3 amps till about 95% charged.

More food for thought.
__________________

__________________
Brian
BayouBiker 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Shore power Battery charging with Solar Dkoelfgen Electrical - Systems, Generators, Batteries & Solar 9 12-15-2019 10:41 AM
Solar Power- Pauper Power Charging Ray Eklund Boondocking 63 06-16-2019 08:50 AM
Battery charging on solar NOT shore power rmroy Electrical - Systems, Generators, Batteries & Solar 36 11-02-2018 07:34 AM
Zamp solar 200 watt portable solar charging kit Cascadian Airstream Classifieds 0 05-11-2018 08:13 PM
Batteries charging from solar but not shore power johndorst Batteries, Univolts, Converters & Inverters 3 11-16-2016 03:18 PM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 10:42 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.