Solar panel question

Lance Jones · April 23, 2009, 12:11:50 PM

Yes Stu, once this is done, I'll add to wiki. BUT FIRST, a question. I obtained a 20 watt solar panel -- don't ask any questions..... My question is, with a 20w output and the appropriate power box, how quickly should this charge a series 27 AGM 2 battery bank?

This kinda comes from: http://c34.org/bbs/index.php/topic,4929.0.html [Ed. - Stu]

Ted Pounds · April 23, 2009, 01:10:09 PM

It depends only on how discharged the battery is. At 20W your panel is putting out about 1.5amps. So if you have used 15 amp-hours it will take about 10 hours to put it back.

Stu Jackson · April 23, 2009, 01:10:35 PM

Lance, the question begs the answer, because "it all depends" on how depleted the battery is when you start.

If you check the WM catalog under solar, there are any number of convenient conversion factors between watts and amps and hours of output that will determine how many AMPS for how many HOURS you can replenish from any given solar panel.

But, and this is a BIG but, because of battery acceptance (see: http://c34.org/bbs/index.php/topic,4787.0.html) it'll take WAY longer than the amps input times the time used to fully charge the battery because it "accepts" less, regardless of the input, as the bank gets fuller.

Lance Jones · April 23, 2009, 02:00:08 PM

Actually the #1 bank was down to 10 volts and #2 was at 11. WOW, I just acquired a second 20 w & controler for use on the other bank. Gotta love this job!

Stu Jackson · April 23, 2009, 02:07:11 PM

OK, I'll try this technique with you again

STOP!

Please read the Ample Power Primer, here: http://www.amplepower.com/technical_documents/index.html

There's a discussion of what to do with seriously discharged batteries. Give it a try. Manage, Test & Troubleshoot. Download the whole package.

Ron Hill · April 23, 2009, 06:55:56 PM

Lance : Over the years I've noted that the solar panels aren't a straight math equation of 1.5amps per hour as they are charging @ 15 volts !!
We'll let the electricians on this Message Board decipher that for us and give them something to chew on.
A thought. Ron

Ken Heyman · April 24, 2009, 09:06:18 AM

Last season I began using a 22.5 watt 15 volt solar panel. In fact I used it under a palstic tarp over the the winter to trickle charge the batteries (2 paralleled banks of 2 six volts in series. Additionally I charged through a regulator. This system kept my batteries nearly fully charged at (between 12.75 and 13) volts all winter. In the summer sun of course the panel is more efficient. I think you will find that your panel is much more effective keeping your batteries "topped off" than charging your deeply discharged batteries. If you can follow Stu's (and others) advice and find a good source on bringing back deeply discharged batteries you will be better off. I have followed the advice in Calder's book dealing with boat systems (I forget the exact title) and have been pleased.

Lance Jones · April 24, 2009, 09:40:42 AM

My issue was that my battery charger died and allowed my batteries to bleed down (I keep my fridge on). One bank is near 12 and the other dropped to 10. So, I have a one time issue of recharging. I have a backup batter charger I'll take out tonight. I was wondering if that one panel would recharge the low bank for the 2days I've been away. After I replace the charger, the solar will be for keeping stuff up while on the hook and not running the engine.

Stu Jackson · April 24, 2009, 10:44:28 AM

Let's perhaps help you organize this process.

1. What kind of "backup" charger do you have? If it's a cheap automotive charger, you could well destroy what may be left of your dead batteries. The Ample Power Primer and Calder's suggest how to attempt to retrieve dead batteries. I wold expend primary efforts to repair or find the fix for your TrueCharge charger before anything else, especially if it may be a simple thing like the fuse. That's why I linked your two messages this morning. You may have a one time job of recharging, but it should be done right, or else you'll end up with two useless piles of lead and plastic.

2. Do an Energy Budget (see: http://c34.org/bbs/index.php/topic,3976.0.html). Given you solar panel output into your house bank, you may/will see that there's NO WAY a small solar panel will ever keep up with the draw of the fridge, which, when ON all the time uses 60AH per day. Please, "do the math."

3. You noted: "the solar will be for keeping stuff up while on the hook and not running the engine..." What is "stuff?" Again, your energy budget will show you that you won't expect to get much out of it.

4. "I was wondering if that one panel would recharge the low bank for the 2 days I've been away." From what, to what? No, it appears that it simply won't, we discussed that earlier.

As Ken clearly said, the only thing a small panel like that will do for you is to keep you house bank topped off DURING A WEEK that you're away from your boat and everything is turned off. It will ONLY take care of the inherent discharge of the 1% to 2% drain of a wet cell battery. Really, that's ALL it will do.

Lance, you also mention "one bank" being one voltage and another a different voltage. Is this your house bank of two individual batteries? If they are tied/wired together, the two batteries are called a "bank."

Stu Jackson · April 24, 2009, 10:49:51 AM

Quote from: Ron Hill on April 23, 2009, 06:55:56 PM
Lance : Over the years I've noted that the solar panels aren't a straight math equation of 1.5amps per hour as they are charging @ 15 volts !!
We'll let the electricians on this Message Board decipher that for us...

The answer is twofold:

1. See my reply that discusses acceptance - it'll take much longer than straight math would infer.

2. A solar panel that's less than 1 1/2% of your house bank in amp hours does not need regulation, and the 15V is only occurring when there's direct sunlight. With the small amount of amps compared to the size of the bank based on this %, the bank can handle the small amount of higher voltage without damage. For any panel larger than that a regulator is recommended. The regulator controls the voltage out. Many have small panels and also have elected to include regulators. All regulators come with diodes to prevent outward migration of amps when it's dark out, but most panels also have the diodes built in anyway.

Ted Pounds · April 24, 2009, 11:10:27 AM

Lance,
Go ahead and use your backup charger. The most important thing to do is get some juice back in the batteries ASAP. The longer they sit the more the plates are subject to sulfation. But make sure you monitor the charging. Like Stu said those auto chargers can kill batteries. The important thing is to make sure it doesn't boil off the electrolyte. Add distilled water as needed. And when they're up to a healthy voltage disconnect the charger.

Stu Jackson · April 24, 2009, 11:15:32 AM

That's one way to do it, but before you do, find out what voltage the backup charger is putting out, because if it's only 13.8 V or if it's a constant higher voltage, you may not be following the guidelines to bring back dead batteries, which I referenced the necessary information for you to read. Ted's right ot do it asap, but doing it fast may not be doing it correctly.

Lance Jones · April 24, 2009, 12:47:26 PM

Thanks for the info.

I have 4 AGMs organised into 2 banks. One is for house the other for starting. Here is what happens, and is on, when we are on the hook. While sailing during the day, we only have our stereo/GPS/VHF on. All other electric is off.

1) Interior lights (All LED now)
2) Anchor Light (LED)
3) Pressure water (As needed)

In the AM, we run the motor to:
1) Heat the water
2) Charge batteries.

My back-up charger IS an automotive; but, it has settings for AGM and variable voltage settings based on the charge remaining in the batteries. I don't intend to do a rapid charge. I'll leave it over night on a long term charge setting.

Lance Jones · April 24, 2009, 12:55:59 PM

I think what people are missing is that this is a short term solution to my problem. The solar is a long term solution to our short term sailing.

When my charger is repaired or replaced, that will be my primary mode of replenishing the batteries. The solar will augment that and help keep the batteries up when out sailing for the weekend or long holiday's.

Here is the info on the Solar Panel (x2):
Pm Watts: 20
I pm Amps : 1.18
V pm (Volts): 17
High Efficiency Mono Crystalline

Stu Jackson · April 24, 2009, 02:46:34 PM

Quote from: pogmusic on April 24, 2009, 12:47:26 PMI have 4 AGMs organised into 2 banks. One is for house the other for starting. Here is what happens, and is on, when we are on the hook. While sailing during the day, we only have our stereo/GPS/VHF on. All other electric is off.

Completely Off Topic

I would urge you to consider making three of your batteries into one big house bank and the other for a reserve. You will get longer life out of the new bigger house bank, and all with the same investment in lead. Indeed, with the addition of a small automotive bank for a new reserve, you could have a tremendous house bank capacity with all four of your AGMs and run your fridge all you want. I find it odd, at best, to hear someone who runs their fridge all week, but won't when actually on the boat, unless I'm missing something in your post which didn't include the fridge when sailing. Your boat, your choice, but...

The only one who I've ever agreed with about having split and equal house banks is one of our Past Commodores Dave Davis, who has four golf cart batteries in his OEM battery box, races a lot, rarely anchors or moors out, and doesn't want to add any more weight to the boat.