Solar Charging of Wet Cell Batteries.

[Koinonia]

Also voltage output has to do with angle of the panel to the sun, the suns strength and any shadows.  Panels are usually rated upon a 5 hour day of direct sunlight.  Its not uncommon for a panel to put out more than spec voltage at peak times, this is when the better charge controllers come into play.  Cheaper controllers may simply bleed off this extra power as heat, where as a more advanced controller will take this extra power at peak time and use it as amps to be more efficiant.  Are the two panel voltage readings comeing from identical panels?  If not that would be good reason for differant readings as well.  Also if there is a shadow from something as this as a stainless shroud it can cut down power output drasically, just because a shadow may cover 2% of panel output may be cut by way more.  Reason is many 1.5 volt cells are in series to make up say a max of 15volt output.  Remember old Christmas tree light strings that had bulbs in series, one goes out and the whole string of lights goes out, its the same thing with that string of solar cells. so if you cast a shadow and cancel out two out of ten strings of cells that little shadow just coste you 20% of the output.  This is why alot of boats have their cells on top of a bimini behind the aft shroud or spanning their davits to be in the least likely getting a shadow.  Youll notice some people put their panels on the coachroof under the boom, not a good location. 

[Shawn]

"Youll notice some people put their panels on the coachroof under the boom, not a good location."

Not optimal for sure, but it can also be the only position for a decent sized panel on a smaller boat. On a 23 you can't do behind the aft stanchions as it would block access to the outboard and interfere with the kick up rudder. No enough clearance under the boom to go above the bimini. Not enough room in front of the mast to go bigger than about a 10 or 15w panel. Putting a 40w panel in a position that will be shaded sometimes is much better than not having the panel IMO.

Shawn

[Koinonia]

Good point, Im actually not very crazy about on top of the bimini but I dont have davits yet to mount it on yet. 

[Salty19]

Salty and Skip -

Skip reported the 15.7 volt measurement at the output of the solar cell, with no battery connected. This is an open circuit measurement and I would not consider it reliable. All voltage sources will tend to float high when they are unloaded. With the battery load connected, he measured less than 13 volts which seems normal to me.

Wes

I'll buy the fact that the solar voltage will run high unloaded, but would it drop from 15's to mid 12's with the battery load?  No way unless the battery has very high resistance.

A measured 12.46 volts is actually low for a lead acid battery that is supposedly fully charged, indicating roughly 75-77% charged.  This is almost certainly caused by internal resistance in the battery..typically sulfation is the culprit (or a bad cell, but voltage would drop considerably less than 12.46).  A frequent cause of sulfation is exposure of the internal plates to air (ie lack of water/acid).  Add the fact that just after charging, the battery state is "excited" so the voltage runs higher than steady state operation for a short period.  A fully charged lead acid battery voltage reading taken just after removing from a charger should be 12.8--12.9 or so..perhaps up to 13.1 depending on the charger output and the battery specs--but the reading should drop after a few minutes continuing over the course of a day or so down to 12.7 or darn close. If it reads anything less than this, it's not fully charged and probably will never be able to gain full charge again (assuming that even with a real charger the reading is the same).

With the solar charger on the battery, one would expect to see more than steady state battery voltage but less than unloaded charger voltage.
Seeing 12.4 volts on a battery with the charger attached tells me it will be lower without the charger (assuming all is working OK).  Normal is 12.7 or darn close..anything less and it's not fully charged.

Skip try measuring your voltage after an hour of no solar charging. This will remove the surface charge which is the reading you've collected (artifically high due to surface charge).  Betcha voltage drops from 12.46 to, well, somewhere quite a bit lower. If it hits 12.2, you're at 50% charge.  12.0 volts...25% charge. 11.9...it's darn near toast. That means your battery cannot charge beyond that percentage of total capacity-or that simply the battery wasn't fully charged from solar when you disconnected it. I'll guess the former since it's boiled away water due to excess charging voltage in the past.  I'm really curious to know what you find out.

The amp reading on the charger is weird.  Then again you are in northern WI..the sun angle would be lower. Could have a bad cell too.

Note the voltage figures here are for a lead acid battery.  AGM's run higher charging and steady state voltage as a general rule. I'm sure there are exceptions here from one brand/model to the next.

[Koinonia]

That is odd, do you have another battery that the panel can be hooked up to, so those readings can be compared.  Could be a bad cell.   Even though there are mathmatics for electricity and DC is pretty easy and straitforward it still does some cooky things.

[brackish]

Interesting discussion, lots of good info.  I had to replace both the house and start batteries this year.  They both lasted seven years, and I'm told that is pretty good.  I've never used solar, have a Guest 5/5 charger and leave the boat plugged in with the charger on when at dock.   Batteries have always managed through a 4 day cruise, the longest I've done, by just using the motor when necessary.  Replaced maintenance free flooded lead acid with the same.  Long discussion on the TSBB some time ago concluded that my use/charge profile indicated that was the best bang for my buck and that AGM would not pay back for the extra cost.  I don't know if that is true but it sounded reasonable at the time.

[ciswindell]

"Youll notice some people put their panels on the coachroof under the boom, not a good location."

Not optimal for sure, but it can also be the only position for a decent sized panel on a smaller boat. On a 23 you can't do behind the aft stanchions as it would block access to the outboard and interfere with the kick up rudder. No enough clearance under the boom to go above the bimini. Not enough room in front of the mast to go bigger than about a 10 or 15w panel. Putting a 40w panel in a position that will be shaded sometimes is much better than not having the panel IMO.

Shawn

I have a 135 watt Kyocera panel mounted on my stern pulpit on my 23 above the outboard and have never had a problem with access to the outboard or the kickup rudder.  I am running two 6 volt Trojan batteries with a charge controller and never run out of power.  However this is a little overboard for my setup....all led running and cabin lights, fan, VHF, and a really loud stereo.  Bought the big batteries and panel because I plan to put refrigeration on in the future.

Chris

[Shawn]

Chris,

"and have never had a problem with access to the outboard or the kickup rudder. "

Do you have the factory rudder or the Ida Sailor Rudder which comes up vertically? Any pictures of your install? When I was planning it out it looked like anything back there would totally block the outboard as I work over the rail to get to the outboard.

Sounds like your setup is much bigger than needed but refrigeration will change that. My 40w panel drives all LED cabin and nav lights, chartplotter, windmeter, VHF and an autopilot fine with just one group 27 battery. I just added a fan but haven't use it much yet.

Shawn

[Koinonia]

Chris,

Do you have room in the boat for a big cooler?  My refrigeration is a Dometic 33qt refrigerated cooler/freezer and it works great.  Im my 27 its on the floor lengthwise with the boat against the forward bulkhead where I have a 12v outlet.  To keep it from moving I just have a non slip mat under it and it never moved even while in some rather choppy waves i the gulf, lots of other stuff went flying though!  I like this and use the ice box as dry storage mostly for canned goods.  The cooler is expensive for a cooler but cheaper and much easier than a coldplate in the box.  Ive had both and Id call it an even draw between the two setups.  On my old boat with a coldplate I had to replace a little circuitboard once and that sucker was almost 500 dollars, ouch!

For batteries I have two optima blue tops only because they came with the boat and are pretty new.  A great battery bank for the buck are 6volt golf cart batteries.  Sams club has the best price Ive seen so far and they can take a beating.  Look at how many people run golf carts untill they havnt anything left.  On a previous boat I had a bank of 4 of these.  I was living aboard and with the TV, stereo, lights, refrigeration, ect I had power for 8 days untill the volt meter read 12 volts.  4 of these is overkill in most boats but a friend has 2 wired to make 12 volts and does fine.  It is good to check their water levels about once every 6 months.

[skip1930]

Wow! You skippers have more electricity and ancillary stuff on board than you have 'boat'.

lol skip.