Emergency solar control

[Drift Woods]

My solar controler went out and FedEx won't have my new one to me till Friday. I want to connect one 100 watt panel direct and cover 4 cells to lower the voltage to 14. Will this work or is it time to start the engine up and let it run?

Thanks in advance, Woody

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[skipmac]

I'm not an expert on solar panels but from my limited knowledge it will depend on how your panel is wired and which cells you cover. Solar panels, like batteries, can be wired in series and parallel but panels are generally wired in a combination of the two.

Also a question, what's the voltage of your panel uncovered? Specs might call it open circuit voltage or Voc.

I think the safest option is to disconnect the panel from your batteries, hook up a volt meter, cover some cells and look at the voltage on the meter.

[fallingeggs]

This same question was asked and answered by Maine Sail and Stu Jackson just a few days ago. See if you can find that thread.

I believe the answer was that you would be running with scissors if you connect the panels directly to the batteries. You in theory can connect them and manually monitor voltage at the terminals till they hit 14.4 (or whatever bulk voltage you batteries call for) then manually disconnect the panels. But if you don't pay attention and disconnect at the right time or will fry your bank.

Converting panel cells may slow things down or give you more headroom to make an error...

Good luck.


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[Drift Woods]

I checked the open voltage and it's at 18.6 now. This is more experimental then necessary, going to West marine after lunch.

I'll look for Stu's thread on the subject.

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[Paul Elliott]

Covering cells will not reduce the output voltage in a controllable manner, and it will reduce the current, also not easily controlled. All I can suggest is to connect the panel directly and monitor the battery voltage, disconnecting when you hit your target.

[pesarsten]

I would think that the size of the battery bank would be important to know before giving an opinion , but.......

If you have a decent size bank of 300 or 400 amp hour capacity, connect it up until your batteries get to 13.6 , then turn on the fridge. I would have to believe that with normal power usage, the single 100 watt panel won't get you above 13.6. If you are leaving the boat and can't moniter then I would not leave it connected.

[Drift Woods]

It worked without any problems. I left both 100 watt panels exposed to full sun and the batteries pulled the voltage down. After checking the voltage every half hour, it never went above 13.8 at the posts.

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[Paul Elliott]

Originally Posted by Drift Woods

It worked without any problems. I left both 100 watt panels exposed to full sun and the batteries pulled the voltage down. After checking the voltage every half hour, it never went above 13.8 at the posts.

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But, unless you have a load that magically draws just the right amount, the batteries will eventually over-charge. You will need to regularly monitor the voltage to avoid an extended over-charge.

[Jim Cate]

Originally Posted by Drift Woods

It worked without any problems. I left both 100 watt panels exposed to full sun and the batteries pulled the voltage down. After checking the voltage every half hour, it never went above 13.8 at the posts.

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Fancy that! Despite all the doom predicted, it worked, just like you thought it would, and like I reported (in that other thread) we have done for years.

Obviously, it does require some monitoring, and is not suitable for long term unattended, low load usage. For a typical cruising boat, the ongoing loads help avoid overcharging. Undercharging is a far more prevalent worry!

Well done!

Jim

[Drift Woods]

Originally Posted by Jim Cate

Fancy that! Despite all the doom predicted, it worked, just like you thought it would, and like I reported (in that other thread) we have done for years.

Obviously, it does require some monitoring, and is not suitable for long term unattended, low load usage. For a typical cruising boat, the ongoing loads help avoid overcharging. Undercharging is a far more prevalent worry!

Well done!

Jim

Yes Jim I read the thread you are referring to, it was suggested above. This morning after resting all night the 320 house bank was almost 80% after changing the previous day. So instead of buying a backup I plugged my panels in and turned on the fridge ( also mentioned above.)

Thanks for the help, Woody

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[roverhi]

Left one panel hooked up to brand new 300 amp hour battery bank with no current load for a couple of days. Now know for certain you can blow up batteries.

Would only do it in conjunction with a volt meter and frequent checking with hydrometer. Definitely wouldn't leave panels unattended while hooked up. A relatively constant load like refrigeration would probably suffice to keep from overcharging the batteries but be careful.

[Jim Cate]

Originally Posted by roverhi

Left one panel hooked up to brand new 300 amp hour battery bank with no current load for a couple of days. Now know for certain you can blow up batteries.

Would only do it in conjunction with a volt meter and frequent checking with hydrometer. Definitely wouldn't leave panels unattended while hooked up. A relatively constant load like refrigeration would probably suffice to keep from overcharging the batteries but be careful.

Hoping to never find out for myself, so would you mind telling us what the actual failure mode was? I assume that the term "blowing up" was not literal (I hope).

Jim

PS How big was the panel?