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7 watt solar charger

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dmpilc
Master Marine Consultant

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USA
4593 Posts

Initially Posted - 10/02/2014 : 09:59:56

Ordered from Sportsman's Guide, a 7 watt solar charger for 12 volt batteries for $19.79 (member's price, regular price about $23.) It came with a 6 ft wire with battery clips attached, 2 removable tilt poles, and mounting brackets. Got it hooked up to my lawn tractor to test it out. Aluminum frame, glass front, 15.2" x 15.7" x 1", currently producing about 22 volts DC.
Comes with blocking diode to prevent power loss overnight.

Edited by - dmpilc on 10/02/2014 10:03:02

redeye
Master Marine Consultant

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3476 Posts

Response Posted - 10/02/2014 : 12:15:39

Wow.. prices have changed considerably....

Do you have a charge from your dock, or engine?

I have a 12 watt solar charger and a charge controller ( no dock or engine charge) and I think of it as a trickle charger, good to top off a battery and keep it topped off as long as I don't let the battery get down much at all...

Nav lights, fish finder, led house lights... and anchor light.

I normally run a bundle of around 10 leds in an anchor light all night which may be .08 amps each led = .8 amps all night... seems to work fine my panel
always shows my battery at 13.5 to 14 volts.

I worry about running the battery down and the 12 watts not being enough to give a full charge, rather than a float charge.. Part of the reason I've never added a "regular" stereo system ( 40 watts max blasting )

Edited by - on

Voyager
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USA
5397 Posts

Response Posted - 10/02/2014 : 21:16:11

Not to be a bummer but I have done my power budget for nav lights, radio, stereo, GPS, depth gauge and cabin lights and I bought a 20W panel with a 30W backup panel. My Honda engine also generates 12A while I'm motoring in and out of the harbor (no more than 1/2 hour for a day sail).
If my 20A panel generates 1AH for 8 hours each day and the engine produces 6AH, I can get 8AH x 6D + 6AH or 56 AH in a typical week. That means I can 1/2 discharge my 80AH battery and have enough juice to fully recharge the battery in a week.
If I use the boat twice in the week, I can add the 2nd panel or run the engine for a few hours motorsailing.

Edited by - on

Chief RA
Chief Technical Advisor

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USA
191 Posts

Response Posted - 10/07/2014 : 15:49:48

12 amps seems exceptionally high for a small outboard plus you must run at near top RPM to attain that.
A 20w panel will produce about 4 amps for a 10 hr solar day assuming a 25% efficiency which is how to figure it. Your motor probably produces about 4 amps in 30 minutes. Running her once a week for 30 minutes plus solar will produce approximately 32 amps each week. With regard to controllers: they are not needed with a solar panel that can only produce what amounts to a trickle charge. West Marine advises that a controller is needed only if your panel produces more than 1.5% of your battery bank ampere hour total. Running your battery under load with a meter reading of less than 12v is not a good idea.
Resp., Chief, Electronic Engineer, FCC lic#1890

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islander
Master Marine Consultant

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USA
4024 Posts

Response Posted - 10/08/2014 : 06:16:27

Bruce has a Honda 8HP. I have a 9.9. Both will give you 12amps at 3000rpm.

quote:
The BF8 and 9.9 provide 2 Amps at 1000 RPM. and offer an amazing 12 amps at only 3000 RPM. This helps to maintain the battery charge or keep electronics going - even at trolling speeds.

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Chief RA
Chief Technical Advisor

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USA
191 Posts

Response Posted - 10/08/2014 : 09:58:09

Great amps for that size motor! Note that I stated "approximately 32 amps", so raise it to 34 amps. Chief

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TakeFive
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2272 Posts

Response Posted - 10/08/2014 : 10:03:51

quote:
Originally posted by Chief RA

Great amps for that size motor! Note that I stated "approximately 32 amps", so raise it to 34 amps. Chief

Don't you mean amp-hours?

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Chief RA
Chief Technical Advisor

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191 Posts

Response Posted - 10/08/2014 : 10:36:48

No, not necessarily, original post states "per week" which indicates A/H's. Chief

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islander
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USA
4024 Posts

Response Posted - 10/08/2014 : 12:06:35

quote:
With regard to controllers: they are not needed with a solar panel that can only produce what amounts to a trickle charge.

So for the electrical engineers here I have a few questions myself. I have a 15 watt solar panel that puts out just under 1/2 amp optimal. An unregulated panel can put out 20-27 volts optimal from what I had read. Can this be good for a 12volt battery? How about everything that runs on 12volts that is hooked up to the battery. (Just about everything when the master switch is on) I don't want 20-27 volts running into my chartplotter,Radio etc. My second question is without regulation, Once the battery is fully charged whats going to stop the panel from overcharging the battery? At the time I installed my panel I put in a 7amp controller just to be safe and because I didn't know the answers to my questions.

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Chief RA
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191 Posts

Response Posted - 10/08/2014 : 16:13:03

Islander: The high DC readings from a solar panel are read without load. They usually run from 18 to 22 volts but as soon as you put a large capacity power source to it the voltage is loaded down to barely more than the battery has. A trickle charge size panel will do no more harm than an AC source trickle charger as long as the panel NEVER can exceed 1.5% of your A/H total of your battery bank. As long as it is that small a charger the voltage can never rise but a small thickle charge value above full charge voltage.
Due to the extreme size of your battery bank the bank its self acts as a regulator for the trickle charge since it is such a miniscule source compared to the bank. The bank when fully charged and hot will read 13.2 volts. Let it cool down and it will read 12.8. With the small panel attached the bank might read maybe 13.4v as it must be always higher than the bank voltage in order to do its job of maintaining full bank charge. Another way to tell if you have a good system is to feel if your batteries are hot and do you need to add water every month or so. If this condition exists then put a controller on especially if you are away from your boat for weeks at a time.
Hope this helps explain the issues for you Islander and others. I taught Electronics for many years. Chief

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TakeFive
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2272 Posts

Response Posted - 10/08/2014 : 19:04:09

quote:
Originally posted by Chief RA

No, not necessarily, original post states "per week" which indicates A/H's. Chief

I re-read your post and did the arithmetic. With the numbers that you stated, I am still pretty certain that you mean 32 or 34 amp-hours per week, not amps per week or amps per hour.

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Chief RA
Chief Technical Advisor

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USA
191 Posts

Response Posted - 10/08/2014 : 19:14:11

OK, A/H can be used as well. Chief

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redeye
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3476 Posts

Response Posted - 10/09/2014 : 04:20:42

Thank you very much Chief and Bruce.. Helps me alot. After running the numbers several times I think of my power budget as pulling down the battery 6AHs for every day I use it, and 4AHs added for every day not in use, sun permitting...

Understanding the voltage reading is without load, and the difference, was extremely helpful also.. ( that usta bug me and I would try not to think about it )

David.. Forgive me if that was a hijack....

Edited by - redeye on 10/09/2014 04:23:02

islander
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USA
4024 Posts

Response Posted - 10/09/2014 : 05:06:00

Thank you Jim, That explains what I thought might be the answer to my questions but wasn't really sure. I learn something new everyday.

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Chief RA
Chief Technical Advisor

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USA
191 Posts

Response Posted - 10/09/2014 : 08:07:39

You guys have been very helpful as I have set up my boat so it was particularly nice to get to help.
I am going back to Bodega Bay for my last trip in about a week and will bring Compass Rose home to her boathouse for the winter. The last trip we got 24 cod on 2 fishing trips in the outer bay.
Amazon sells a cigarette lighter plug in unit called an "INNOVA 3721 battery & charging system monitor" for only 15 bucks that constantly displays your battery bank voltage down to hundredths of a volt. I have one and it is great to monitor my voltage level, especilly since I have a DC reefer. My solar has worked great and seldom see even under reefer load below 12.00 volts. (Not good to get under 12) This is with many foggy, cloudy days in a row! Later, Chief

Edited by - Chief RA on 10/09/2014 08:18:06

islander
Master Marine Consultant

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USA
4024 Posts

Response Posted - 10/09/2014 : 09:25:18

Funny that you mentioned the INNOVA 3721 battery & charging system monitor. I have one and highly recommend it for monitoring the battery voltage without getting an expensive meter.

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Chief RA
Chief Technical Advisor

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USA
191 Posts

Response Posted - 10/09/2014 : 09:41:23

Yes Scott they are definately an excellent tool for us! I hope everyone analyzed the basic solar calculation concepts I used to take into account the area where they are and thus the % of sunshine they get. Chief

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dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 10/09/2014 : 14:24:18

Not a hijack, Redeye. I just wanted to post that the 7 watt charger was out there for a very reasonable price. I'm trying it out on my C-22 battery in the driveway. Since I sold the C-25, I gave up the wet slip as well, as the C-22 has a racing bottom, no anti-fouling paint.

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