Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 28-06-2010, 11:42   #1
Registered User

Join Date: Apr 2009
Posts: 60
Solar to Trickle Charge a Battery

I'm an engineer, but the specifics of this one have me looking in circles as I know nothing about solar panels.

Situation:

-1x Solar panel putting out approx 1W @ approx 8-9 volts.
-Nav kit able to survive for 200-300 hours after being fully charged.
-Nav kit fully functional and being trickle charged within 12 hours leaving excess capacity from the solar panel for the remaining week.
-Boat will be used for 6-12 hours per week, so the rest of the time the solar panel can be trickle charging the Nav kit and anything else.

Objective:

I want to continue with the already working system of the solar panel trickle charging the Nav Kit. Now I want to put a 12V battery (like a motorcycle size) to be trickle charged as well. This battery will supply extra power for a chart plotter.

Issue:

Some form of regulation and conversion from 8-9V (varying depending on sunlight) on the solar panel to the 12V battery, including some form of monitoring and knowing when to shut off the trickle charge. Also I'm guessing there should be some form of protection for the solar panel itself.

Solution:

Cheap, simple, tough, strong, bullet proof, utopia etc..

Appreciate any advice.

Cheers.

Ben.
__________________

__________________
bbhflts is offline   Reply With Quote
Old 28-06-2010, 13:01   #2
Senior Cruiser
 
Sailmonkey's Avatar

Cruisers Forum Supporter

Join Date: Sep 2009
Location: Houston
Boat: '76 Allied Seawind II, 32'
Posts: 5,764
I think you're overthinking this. The simplest/cheapest/most robust instalation would be a 5-15 watt 12 volt solar panel connected directly to the 12 volt battery.

NPower 5 Watt Amorphous Solar Panel | Amorphous Solar Panels | Northern Tool + Equipment
__________________

__________________
Sailmonkey is offline   Reply With Quote
Old 28-06-2010, 23:39   #3
Registered User

Join Date: Apr 2009
Posts: 60
Hi Sailmonkey.

Agreed, but don't have the luxury. It's an SB3 with a factory installed Tacktick solar panel, triducer, compass etc.. I can't swap out the existing solar panel and don't want to screw with the existing installation.

Cheers.

Ben.
__________________
bbhflts is offline   Reply With Quote
Old 29-06-2010, 10:03   #4
Registered User
 
denverd0n's Avatar

Join Date: Jun 2008
Location: Tampa, FL
Posts: 3,948
Images: 6
What you need is something to boost the 8-9 volts up 13.5-14.0 to charge the 12 volt battery. I wasn't able to find such a device on their site, but these people could probably build one for you... PowerStream Power Supplies and Chargers for OEMs in a Hurry

You might also find a simple such device on one of the electronics sites.

Or it might be easier and cheaper to just buy an inexpensive little 12-volt panel made for this. Like this one...
1.5 Watt Solar Battery Charger

Good luck!
__________________
denverd0n is offline   Reply With Quote
Old 29-06-2010, 10:18   #5
Registered User

Join Date: Apr 2009
Posts: 60
Hey denverd0n.

I've been researching and you are right, the issue is finding the right regulator to manage the current and boost the voltage. I've found the following and emailed the manufacturers. Hopefully they will get back to me.

Morningstar Corporation SunGuard

All they say is it's a "series" design, not if it is switching regulator with an inductor as described in wikipedia:

Voltage regulator - Wikipedia, the free encyclopedia

Will feedback the outcome.

Cheers.

Ben.
__________________
bbhflts is offline   Reply With Quote
Old 29-06-2010, 10:22   #6
Registered User

Join Date: Apr 2009
Posts: 60
Just got the reply back. the Morningstar doesn't help me.

"Hi Ben,

The SG-4 is not able to boost the solar input voltage to charge a higher voltage battery. When the input voltage drops below the battery voltage, the controller is going to stop charging and isolate the array from the batteries.

I do not know of many controllers that will boost input voltage, most require that the input be at least as high as the present battery voltage.


Regards,

Adam Kehlenbeck
MS Technical Support
www.morningstarcorp.com
support@morningstarcorp.com"
__________________
bbhflts is offline   Reply With Quote
Old 29-06-2010, 10:50   #7
Senior Cruiser

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,401
Images: 7
Quote:
Originally Posted by bbhflts View Post
Hey denverd0n.

I've been researching and you are right, the issue is finding the right regulator to manage the current and boost the voltage. I've found the following and emailed the manufacturers. Hopefully they will get back to me.

Morningstar Corporation SunGuard

All they say is it's a "series" design, not if it is switching regulator with an inductor as described in wikipedia:

Voltage regulator - Wikipedia, the free encyclopedia

Will feedback the outcome.

Cheers.

Ben.
This is a PWM controller. Pulse Width Modulation means rapidly switching the output of the panels on and off which allows the average time on to be longer. Shunt controller means that is shorts out the solar panel. Series controller means that it opens the connection to the panel. So this is not an MPPT controller.

There's a diagram on this page:
http://www.morningstarcorp.com/en/su...eet.01.ENG.pdf

Also I don't think an MPPT controller will work either. I've read on two different brands now that they want the input voltage to be at or above the output voltage (nominal). I don't think the MPPTs are designed to upconvert voltage

From:
http://www.morningstarcorp.com/en/su....IOM.EN.02.pdf

the sunsaver Mppt can accept 12 V , 24 V, or 36
V nominal off-grid solar module arrays. grid-tie solar
module(s) may be used if the open circuit voltage (V
oc) does
not exceed the ss-Mppt 75 Volt maximum solar input
rating. the solar module(s) nominal voltage must be equal
to or greater than the nominal battery voltage. For 24 V

systems, a 24 V or 36 V nominal solar array must be used.
John
__________________
cal40john is offline   Reply With Quote
Old 30-06-2010, 04:16   #8
Registered User

Join Date: Apr 2009
Posts: 60
Hi John.

The more I think of this problem the more I keep coming back to the question of the determents of the Solar Panel Voltage. This from what I gather is essentially determined by the resistance or impedance of the load.

Power Measurement of Solar Panels

So when the manufacturer states it's 8-9V, this doesn't really tell me anything. I guess 9V & 1 W enables me to determine the resistance, but this then leads to the question of what the impedance of the regulator input is.

So I've gone back to the manufacturer of the solar panel and asked for the spec sheet.

Cheers.

Ben.
__________________
bbhflts is offline   Reply With Quote
Old 30-06-2010, 07:10   #9
Registered User

Join Date: Apr 2009
Posts: 60
I think I have it worked out. Seems that it's simply down to market demand and requirements for simplicity and efficiency. It's simpler to construct a solar panel to produce 12V or more and then regulate down. Also adding a DC/DC converter adds to cost and complexity. Seems that I can first use a separate DC/DC converter such as:

STECA Steca Solsum VC

Then the Sunguard.

Morningstar Corporation SunGuard

Efficiency wise, I'll lose about 8mA with 2mA for the converter and 6mA for the regulator.

Anyone see any issue with this?

Cheers.

Ben.
__________________
bbhflts is offline   Reply With Quote
Old 30-06-2010, 07:29   #10
Registered User
 
Strygaldwir's Avatar

Join Date: Dec 2004
Location: Deale, Maryland
Boat: SeaView - Privilege 37
Posts: 1,020
Images: 5
If I understand you would like to take advantage of the amperage left over from the built in solar panel to charge another battery? You'll be getting something like .6 amp/hours at 12 volts, less at the 13 or so volts necessary for the battery. So let say, .5 amp hours. So over the day you'd get something like 2.5 amp/hours per day. Then subtract out of that the nav kit utilization.

So it would not be better to get another solar panel and battery?
__________________
Strygaldwir is offline   Reply With Quote
Old 30-06-2010, 07:38   #11
Senior Cruiser
 
sandy daugherty's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: near Annapolis
Boat: PDQ 36 & Atlantic 42
Posts: 1,178
This may be a silly suggestion, but why not charge two six volt batteries then switch parallel to series for 12 volts when you need it?

Even sillier, use an old computer serial A/B switch to do the switching. Rube Goldberg LIVES!
__________________
sandy daugherty is offline   Reply With Quote
Old 30-06-2010, 08:09   #12
Senior Cruiser

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,401
Images: 7
Quote:
Originally Posted by bbhflts View Post
I think I have it worked out. Seems that it's simply down to market demand and requirements for simplicity and efficiency. It's simpler to construct a solar panel to produce 12V or more and then regulate down. Also adding a DC/DC converter adds to cost and complexity. Seems that I can first use a separate DC/DC converter such as:

STECA Steca Solsum VC

Then the Sunguard.

Morningstar Corporation SunGuard

Efficiency wise, I'll lose about 8mA with 2mA for the converter and 6mA for the regulator.

Anyone see any issue with this?

Cheers.

Ben.
It's easy to step down a voltage, much more interesting to go up. The voltage converter you selected says this in its data sheet:
1. The input voltage has to be at least 2 V higher than the output voltage.

What you're looking for is a DC to Dc boost converter.
Boost converter - Wikipedia, the free encyclopedia

Next problem, most devices are expecting a stable input. Look at the I-V graph of the solar cell in the link you posted. As you draw different amounts of current the output voltage varies. Another problem is that you want to operate the solar cell at its max power point. Multiply the I and V at each point on the graph to see the output power of the solar cell.

Look at the power curve in this link.
The Solar Sprint PV Panel

John
__________________
cal40john is offline   Reply With Quote
Old 30-06-2010, 12:33   #13
Registered User

Join Date: Apr 2009
Posts: 60
Strygaldwir. I'm only planning on using the battery for 4 hours a week. All other days it will be sitting there trickle charging. With an AGM battery there is a very low selfd discharge rate. I might be wrong, but 2.5aH per day would be fine to maintain the battery....I think.

Sandy. I want to minimise the intervention required, but not a bad idea. Hadn't thought of that.

John. Thanks for pointing out the +2V requirement, I missed that. The graph I posted of the cell output was just a sample of measurement. I hope mine is not like that. Anyway, my manufacturer states that it's nominal output voltage is 8.5V. I had a bit more of a dig and this looks like it may do the trick:

In:4V~9V Out: DC 12V Step up Buck Inverter Power Module - eBay (item 350367087671 end time Jul-13-10 22:30:58 PDT)

Of course there is the slight issue of marinising it:-)

Cheers.

Ben.
__________________
bbhflts is offline   Reply With Quote
Old 30-06-2010, 12:58   #14
Senior Cruiser

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,401
Images: 7
Quote:
Originally Posted by bbhflts View Post
Strygaldwir. I'm only planning on using the battery for 4 hours a week. All other days it will be sitting there trickle charging. With an AGM battery there is a very low selfd discharge rate. I might be wrong, but 2.5aH per day would be fine to maintain the battery....I think.

Sandy. I want to minimise the intervention required, but not a bad idea. Hadn't thought of that.

John. Thanks for pointing out the +2V requirement, I missed that. The graph I posted of the cell output was just a sample of measurement. I hope mine is not like that. Anyway, my manufacturer states that it's nominal output voltage is 8.5V. I had a bit more of a dig and this looks like it may do the trick:

In:4V~9V Out: DC 12V Step up Buck Inverter Power Module - eBay (item 350367087671 end time Jul-13-10 22:30:58 PDT)

Of course there is the slight issue of marinising it:-)

Cheers.

Ben.
That's neat. Someone actually built a boost converter with a solar panel in mind.

You're still probably going to have poor power transfer. Solar cells do have that I-V curve and if you don't operate them near the voltage at the knee of the curve you get less power out of it.

Not sure 1 watt is going to charge the battery in the time alloted.

John
__________________
cal40john is offline   Reply With Quote
Old 30-06-2010, 13:21   #15
Senior Cruiser
 
sandy daugherty's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: near Annapolis
Boat: PDQ 36 & Atlantic 42
Posts: 1,178
would this work?

http://www.allspectrum.com/semicondu...71/MAX1771.pdf
__________________

__________________
sandy daugherty is offline   Reply With Quote
Reply

Tags
battery

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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 Batteries for Solar Charge Bash Electrical: Batteries, Generators & Solar 5 08-09-2009 09:53
Solar Trickle Charging During Boat Storage Liberty28 Electrical: Batteries, Generators & Solar 5 18-03-2009 10:56
trickle charge with drain gonesail Electrical: Batteries, Generators & Solar 6 19-09-2007 14:27
One Solar Charge Controller or Two? exposure Electrical: Batteries, Generators & Solar 8 05-03-2007 04:10



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:05.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.