Solar Panel, MP3 Player, Powered Speakers - Please Help :)

rody084 wrote: »

Here are the components which have been installed:
Solar Panel (12-18v / 30W / 1.67amp max rated):
Battery (12v Sealed 7.5Ah):
Charge Controller (4.5A / 12v): http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/PWM-Type-Solar-Charge-Controllers/Morningstar-Charge-Controllers-PWM/Morningstar-SunGuard-45A-12V-PWM-Charge-Controller/p793/
DC Timer:
MP3 Player (Sansa):
Speakers (Insignia):

Rough Diagram:
SOLAR --> MORNING STAR CONTROLLER --> DC TIMER --> BATTERY
Then from the battery, there are two parallel paths:
1. BATTERY --> INVERTER -->SPEAKERS
2. BATTERY --> CAR SOCKET --> USB ADAPTER --> MP3 Player

The system runs great when the battery has a full charge. It is currently nice and sunny these days so we get a decent amount of sun (for what we get here in the San Francisco Bay Area).

The timer is set for 10 hours of operation during daytime hours.

The system stops working after about 24-48 hours.

Last time I was out there, the following were the readings I was getting with my multimeter:
Battery Voltage: 11.8v (this was after I charged the battery using my car for a couple of minutes)
Solar Panel Voltage: 13-17v (dropped as the day went on)
Solar Panel Current: 0.16amps
System Draw: 0.3 – 0.5amps (with everything on and the MP3 player charging itself as well). This fluctuated depending on the bass notes of the music.

• 0.5 amps * 10 hours = 5 Amp*Hours used...

• 5 AH used * 1.15 recharge * 1/4 hours of sun = 1.44 amp panel

Again, I am new to the science behind electronics, so I am not sure how exactly I am to calculate amp-hours from what I read on my meter. After extensive Google-searching, I remain confused as to whether I need to multiply my reading by 3,600 seconds (which would mean my little system is drawing 1,800amps…hmmm…) or if the reading I see IS the amp-hours, or if I am just really in way over my head!

• 1 Watt * 60 seconds per minutes * 60 minutes per hour = 3,600 Watt*Seconds

Some conclusions I have been able to make on my own thus far:
1. The solar panel is not getting enough light (given that it is rated for 1.67amps and is only giving me 0.16 with sunny skies). I plan to angle it more horizontally and see if I can find a better exposure

2. The inverter is not a great way to go since it must cause a certain degree of inefficiency in the system

3. The MorningStar controller does NOT charge the battery if battery voltage has dropped below 8v (according to the manufacturer). Thus, when the battery discharges below 8v, the system never charges again until I come over with my car.

4. The battery is undersized given the fact that there is more draw than input into the system.

5. I am considering upgrading the battery, but know this will only postpone the inevitable. I also am not sure what the best type of battery would be (given that it is not somewhere that it can be maintained with much frequency). I was looking at Optima Yellow-Top batteries so far.

Sorry for the long post, but I would love to be able to get this art installation functional for more than 24-48 hours at a time since I can only go over there every 2 weeks or so to give it a boost.

Thank you for reading through this. I would greatly appreciate any advice on what components I may need to upgrade/change/add in order to get this to be functional for at least a period of 2 weeks. I conceivably COULD come over every 2 weeks to give a quick recharge with my car if necessary, but would much rather have it all operate on its own (my using gas to charge it also defeats the whole environmentally-friendly solar aspect of the art piece).

rody084 wrote: »

Next time I am able to visit the system, I am going to un-mount the panel and try to re-position it. However, I do need to have a plan in place for the winter where there may be days that there is insufficient sunlight to provide enough (or any) charge.

I cannot recall seeing a reading higher than 12.1v on the battery, even when it was new. Also, now when I charge it with my car, I might get up to about 12.8v or so and then it pretty quickly drops down to 11.9-12v (even just being unplugged). Should the battery be reading 12.7v when fully charged? (so far, I’ve only had a chance to skim the FAQ page you sent)

Now that I think about it, when I tested the current coming from the solar panel, I tested between the panel controller and the timer by taking the meter from a connection point just before the Sunguard controller and putting the other lead at the timer (along the same pole). However, I did not disconnect the wires since whenever I do (and the controller does not detect the presence of a battery) the controller does not send a charge through.

1. Connect battery to your loads. Get working
2. Connect battery to your timer, then reconnect + from your load to + on your timer--get working (I am guessing here--but this is the basics).
3. Connect your charge controller to the battery bank.
4. Connect your solar panels to your charge controller.

I feel like I must be missing something obvious here, but could you help me understand how the reading on my meter translates into AH? My meter read around 0.5amps of current being drawn by the system… does that mean it is 0.5AH? Or am I seeing an amp/second?

• In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 1018 electrons, or one coulomb per second constituting one ampere

Once I get the panel unmounted, I will try taking more readings to see if I get closer to this. I am beginning to suspect that I am using my multimeter incorrectly (or at least placing it incorrectly)

In this case, it seems like I should set up the system to have enough reserve battery to operate for some dark days without bringing it below safe battery levels. I won’t be able to set up a battery monitor nor go over there too frequently to check levels so perhaps I need to figure this into the sizing of the battery(s) What are your thoughts?

Would Vmp in this case be 18v (which is the top end of what the panel is rated to deliver)? How does this differ from Voc which you mention further below?

Fortunately, my meter is brand-new and I DID set it to 10amps.
Did the way I previously describe sound correct in order to obtain an accurate reading (measuring from the cable connection between the panel and the controller to the timer (after the controller)? I did not disconnect the wires… should the meter be bridging (ie: be in-line) between two points rather than along-side connected wires?

Should the panel be reading 20-22v even though the specs rate it for a maximum of 18v output?