Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-14-2012, 07:09 AM   #1
4 Rivet Member
 
timzog's Avatar
 
1980 20' Caravelle
Ogden , Utah
Join Date: Oct 2010
Posts: 422
Blog Entries: 20
24V panel and 12V battery?

Hi,
I'm planning on adding solar to my 1980 20' Caravelle and have decided that 150 to 200 watts will be plenty for my needs. My question is the following. Could a 200+ watt 24V panel be used efficiently with a mppt controller like the Morningstar to charge a 12V battery system? I've seen several 24V panels that would fit perfectly on my roof that are ~240 watts with a peak of about 30V for less than $350. To me it looks like that would be cheaper with a $200 mppt controller than 2 120 watt 12v panels (at least $250 x 2) with a $50-$100 controller and would provide the alleged benefits of mppt for battery maintenance. Also, somewhat smaller gauge wire and connections could be used from the panel to the controller at the higher voltage. If the controller were placed close to the batteries than you would only need a short stretch of heavier gauge wire for that connection. One panel vs two also means less mounting hardware. Ay thoughts from experienced solar folks would be appreciated.
Thanks,
Tim
__________________

timzog is offline   Reply With Quote
Old 03-14-2012, 07:38 AM   #2
Rivet Master
 
RickDavis's Avatar

 
1961 24' Tradewind
1969 29' Ambassador
1970 21' Globetrotter
Jamestown , Tennessee
Join Date: Jul 2008
Posts: 1,781
While this is speculation on my part since i have not used 24 volt panels I would not be inclined to do this myself. Panel wattage seems to be determined based on the max voltage the panel puts out.
For example a panel putting out 30 volts at 4 amps would be 120 watts. By the time you go through your regulator you will be down to aprox 15 volts, still at 4 amps so the practical results are 60 watts of charging power. In other words half is wasted by the regulator switching on and off and a good bit will disapate as heat.

The same logic applies to the 12 volt, really about 18 volt panels normally used.. except not as much is lost due to the lower difference between panel voltage and the voltage the charge is regulated at.

In reality the 250 watts of panels I am using as I write this will deliver a maximum of 14 amps (rarely, 10 is more common unless the air is really clear)

14 amps x 14.7 volts, where my regulator is set is slightly under 180 watts in the real world. As is typical of any product they do what the can to bump the numbers up.

At any rate, I would not go with 24 volt panels if i was buying them. If free that would be another story.

Please note I am not a solar engineer, didn't even stay at a holiday inn last night.

We are serious boondockers and have used solar for years.

Solar powered in southern FL. at the moment
__________________

__________________
Rick Davis 1602 K8DOC
61 tradewind, plus a few others
13 Ram 2500 TD
99 Dodge TD 577K miles

RickDavis is offline   Reply With Quote
Old 03-14-2012, 07:58 AM   #3
Rivet Master
 
arodriguez60's Avatar
 
1959 22' Flying Cloud
1969 25' Tradewind
1983 34' Limited
fairview , New Mexico
Join Date: Mar 2005
Posts: 574
Images: 85
If you use a good quality MPPT controller you should do good. I have a morningstar MPPT controller and a Rogue MPPT controller. I have experimented with 12,27,and 36 volts to the rogue. It has been very efficient in charging my Batteries. What you should be careful about is not geing to high of a voltage to the controller . In the winter when the panels are cold they can produce a lot of power and overload the controller. The rogue is made for 12 - 24 volt systems . A 24 volt system is about 36 volt panels. Mppt controllers are not on off switched like your pwm controllers. They are very efficient.
__________________



Avion C11
1959 Flying Cloud
1969 Tradewind
1973 Safari
1983 34 ft Limited
2004 F250 superduty ext cab
2014 F350 longbed superduty crewcab
arodriguez60 is offline   Reply With Quote
Old 03-14-2012, 08:53 AM   #4
4 Rivet Member
 
timzog's Avatar
 
1980 20' Caravelle
Ogden , Utah
Join Date: Oct 2010
Posts: 422
Blog Entries: 20
Thanks so much for the quick responses. The Morningstar Sunsaver MPPT claims to be able to handle up to 15 amps and up to 75V max PV open circuit voltage. They claim the efficiency to be within 91 to 97% depending on output power. I believe that the mppt controllers convert the higher voltage to 12V so with an mppt controller and a 240 watt panel at 24V (10A), wouldn't it put out 20A at 12V (minus 2-10% efficiency losses)? I thought that Watts was the unit that would stay constant. This may be too much for the Sunsaver to handle actually, but there may be other controllers that could.

http://www.morningstarcorp.com/en/support/library/SSMPPT_ENG10_111.pdf
timzog is offline   Reply With Quote
Old 03-14-2012, 09:07 AM   #5
Maniacal Engineer
 
barts's Avatar
 
1971 25' Tradewind
Menlo Park , California
Join Date: Jan 2010
Posts: 1,224
Images: 1
Blog Entries: 4
What the MPPT controllers do is to place the optimum load on the panels for the amount of light presently striking them; this generates the most power possible from the panels under varying conditions. It is then converted (I'm not an electrical engineer but it looks like a switching power supply) to the right voltage and current for your batteries to accept the most charge possible considering their current charge level.

Whether or not the particular panels you're considering are a good match for the controller is a good question - it sounds like you're inside the specified limits - but make sure to buy sturdy panels that will handle the RV environment. The panels on my Airstream certainly lead a more interesting life than the one's on my neighbors roof with vibration, shock and routine 60 mph winds.

- Bart
__________________
Bart Smaalders
Menlo Park, CA
http://tinpickle.blogspot.com
http://smaalders.net/barts
barts is offline   Reply With Quote
Old 03-14-2012, 09:48 AM   #6
Rivet Master
 
RickDavis's Avatar

 
1961 24' Tradewind
1969 29' Ambassador
1970 21' Globetrotter
Jamestown , Tennessee
Join Date: Jul 2008
Posts: 1,781
Quote:
Originally Posted by timzog View Post
Thanks so much for the quick responses. The Morningstar Sunsaver MPPT claims to be able to handle up to 15 amps and up to 75V max PV open circuit voltage. They claim the efficiency to be within 91 to 97% depending on output power. I believe that the mppt controllers convert the higher voltage to 12V so with an mppt controller and a 240 watt panel at 24V (10A), wouldn't it put out 20A at 12V (minus 2-10% efficiency losses)? I thought that Watts was the unit that would stay constant. This may be too much for the Sunsaver to handle actually, but there may be other controllers that could.

http://www.morningstarcorp.com/en/support/library/SSMPPT_ENG10_111.pdf
The 24 volt panel will put out ten amps. This will not increase as you regulate the voltage downward so it affectively so the 240 watt panel affectively becomes a 120 watt panel as your battery sees it.

You are correct that 20 amps at 12 volts would be 240 watts but this is a series circuit so the current thru the rregulator will be the same as from the panel.

I am not up to date on the newer controllers so something may be different than what I am familiar with
__________________
Rick Davis 1602 K8DOC
61 tradewind, plus a few others
13 Ram 2500 TD
99 Dodge TD 577K miles

RickDavis is offline   Reply With Quote
Old 03-14-2012, 12:19 PM   #7
Rivet Master
 
arodriguez60's Avatar
 
1959 22' Flying Cloud
1969 25' Tradewind
1983 34' Limited
fairview , New Mexico
Join Date: Mar 2005
Posts: 574
Images: 85
Here is an excerpt from the Arizona Wind And Solar site.
Using an MPPT controller with high voltage panels

The only way to get full power out of high voltage grid tie solar panels is to use an MPPT controller. See the link above for detailed into on MPPT charge controls. Since most MPPT controls can take up to 150 volts DC on the solar panel input side, you can often series two to four of the high voltage panels to reduce wire losses, or to use smaller wire. For example, with the 175 watt panel mentioned above, 2 of them in series would give you 66 volts at 7.6 amps into the MPPT controller, but the controller would convert that down to about 29 amps at 12 volts. Charge Controllers for Solar Electric Systems
__________________



Avion C11
1959 Flying Cloud
1969 Tradewind
1973 Safari
1983 34 ft Limited
2004 F250 superduty ext cab
2014 F350 longbed superduty crewcab
arodriguez60 is offline   Reply With Quote
Old 03-14-2012, 12:49 PM   #8
Rivet Master
 
RickDavis's Avatar

 
1961 24' Tradewind
1969 29' Ambassador
1970 21' Globetrotter
Jamestown , Tennessee
Join Date: Jul 2008
Posts: 1,781
Quote:
Originally Posted by arodriguez60 View Post
Here is an excerpt from the Arizona Wind And Solar site.
Using an MPPT controller with high voltage panels

The only way to get full power out of high voltage grid tie solar panels is to use an MPPT controller. See the link above for detailed into on MPPT charge controls. Since most MPPT controls can take up to 150 volts DC on the solar panel input side, you can often series two to four of the high voltage panels to reduce wire losses, or to use smaller wire. For example, with the 175 watt panel mentioned above, 2 of them in series would give you 66 volts at 7.6 amps into the MPPT controller, but the controller would convert that down to about 29 amps at 12 volts. Charge Controllers for Solar Electric Systems
An interesting read.. Apparently the addition of the dc to dc converter changes the ball game and my previous statements would only be correct for the controllers previous to the MPPT. My apologies for not being up to date.

When i put the system on this trailer i purposely looked for a controller with out any of the fancy stuff and settled on a specialty concepts model that basically runs up to a certain voltage and shuts off until the voltage falls.
Nothing against newer technology, however the previously used PWM controller did generate RF noise I could hear in my Ham radio equipment. The same could be true of the MPPT. Wonder if anyone knows.

At any rate the simple controller I use must be ok even without all the fancy stuff as my exide golf cart batteries will be 9 years old in June and are still doing fine. I do monitor the system with a trimetric 20 20 meter.
Anyway, sorry for the partial misinformation
__________________
Rick Davis 1602 K8DOC
61 tradewind, plus a few others
13 Ram 2500 TD
99 Dodge TD 577K miles

RickDavis is offline   Reply With Quote
Old 03-14-2012, 12:55 PM   #9
Rivet Master
 
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
I also think that the MPPT charge controllers have a minimum voltage that they need, and so be sure you check that issue. One larger panel may not have a high enough voltage to make the MPPT controller work properly. Usually they use several panels in series and even the single higher voltage panel you are considering might not be high enough to make the conversion system work right. Strange, huh?

Ah, the wonderful world of electronics in 2012.... everything you thought you knew may be wrong. And I include myself in that category.
idroba is offline   Reply With Quote
Old 03-14-2012, 01:02 PM   #10
Rivet Master
 
arodriguez60's Avatar
 
1959 22' Flying Cloud
1969 25' Tradewind
1983 34' Limited
fairview , New Mexico
Join Date: Mar 2005
Posts: 574
Images: 85
You must be doing something right. 9 years is a long time. The goal with everything we do on our electrical systems is to get a good system.
__________________



Avion C11
1959 Flying Cloud
1969 Tradewind
1973 Safari
1983 34 ft Limited
2004 F250 superduty ext cab
2014 F350 longbed superduty crewcab
arodriguez60 is offline   Reply With Quote
Old 03-14-2012, 01:44 PM   #11
4 Rivet Member
 
timzog's Avatar
 
1980 20' Caravelle
Ogden , Utah
Join Date: Oct 2010
Posts: 422
Blog Entries: 20
Based on what I read it sounds like in principle the higher voltage panel with mppt could work. I think the savings from only one panel, less roof real estate, only 4 mounting feet, and smaller cables could easily offset the additional controller cost. Thanks for all your comments.
I'll try to put together a list of all the components each approach would require.
Tim
__________________

timzog is offline   Reply With Quote
Reply

Tags
12v


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
Best RV Battery? topjimmykw Batteries, Univolts, Converters & Inverters 52 04-07-2017 06:28 PM
Battery not charging Bgreen Batteries, Univolts, Converters & Inverters 8 03-15-2012 05:17 AM
Need a new battery monitor? guntertl Batteries, Univolts, Converters & Inverters 4 03-13-2012 06:43 PM
Battery Recharge Ggroth Batteries, Univolts, Converters & Inverters 6 03-13-2012 02:10 PM
HItch ball height via AS and via Leveling mefly2 Hitches, Couplers & Balls 5 03-13-2012 01:56 PM


Featured Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 10:16 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.

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