Battery Charging On Solar Panels

[nolandinsight]

I couldn't pump the bilge the other day, and discovered the batteries were registering only about 6.5 volts. Two solar panels usually keep the batteries at 12.5 volts. I found where I had knocked a connection loose from a DC ammeter, replaced the wire, and saw the charge quickly increase to the point where the bilge pump worked again. Here is my question.

Do you think the complete circuit including ammeter is required for the DC system to operate, or is it likely that the batteries are so far gone that they require constant power from the solar panels to maintain enough voltage to run the systems?

The navigation lights have not been functioning, so I have only been day sailing with this boat. I've never tried to run anything at night when the solar panels weren't providing a charge.

It seems to me that a fully functioning charged battery without a load would have maintained its charge for the day or two between when the connection came loose and when I went to use the bilge pump. Perhaps there is a load on the system somewhere I'm not seeing, or perhaps the batteries need to be replaced.

I just don't remember enough electrical theory to troubleshoot this problem.

Any ideas?

[romulusm]

The first step I would do would be to fully recharge the batteries, disconnect that connection again and see how the batteries drain. This way you isolate the problem. You need to be sure that they drain in 2 days.

[neilpride]

12,5 v in a sunny day from your solar panels? batterys toasted .... disconect the solar and recharge your batterys with a charger and see if the batterys hold the loads for a while , if not , replace the batterys... my guess...

[noelex 77]

I think your batteries are probably dead, but do a capacity test on them.

Fully charge them.
Put a set measured, constant load on them (strictly speaking this should be related to battery capacity C25 or C100 depending on the battery specs) but any convenient load is fine for a rough test.

Measure how long the battery takes to go flat (usually taken as 10.5v).
Multiply the load by the time that the battery ran it. Compare this to the rated capacity. For most dead batteries will be unequivocal, with a capacity much less than rated. At least you will be sure before throwing them out.

Testing each battery separately is a good idea.

Fully charge them ASAP if you are going to keep them.

If the results are marginal a strong equalisation cycle, or two (if permitted by your battery chemistry) will sometimes restore some capacity.

Before fitting new batteries fix the charging problem so it cannot re-occur.

[sailorboy1]

Originally Posted by nolandinsight

discovered the batteries were registering only about 6.5 volts.

Any ideas?

those batteries are long gone and I would never have any faith in them to allow me to take my boat out, but that's my idea

[foggysail]

If you have a good battery charger at least try to equalize them. You may be able to get them to accept a charge. And if they are lead acid, check their specific gravity after full charging before deciding what to do.

[Paul Elliott]

The poorly-connected DC Ammeter may have very well broken the battery circuit, and the low voltage you measured may have been a result of that. Is the Ammeter measuring charging current, or total battery current (or something else)?

An unloaded or very lightly loaded battery should hold a charge for days or months. If your batteries were truly down to 6.5V, it's unlikely that you will be able to restore them to health. As has been suggested, you should try to fully charge them and see how they hold up.

[SkiprJohn]

Had a similar thing happen to one of our club boats and we thought the AGM battery was toast. It was down around 5.6 volts at test.

We discovered that the bilge pump switch was faulty and even with the small solar panel could not keep the battery up to snuff.

Here's how the experts made the battery come back to life when we couldn't do it with a good charger after taking it home and trying to get it to charge and hold a charge. They hooked it up with a fully charged good battery. Then, charged them both and we were surprised to see that the toasted battery was good again.

Now we need a good bilge pump switch.

kind regards,

[Zil]

If your ampmeter normally indicates the charge currant from the solars, and your ampmeter has a internal shunt (not a separate shunt connected to the meter) then yes the loose wire would stop the charging currant. Loose wire can also short circuit.
Do your running lights operate with repaired wire?
i agree your batteries need better love than that.

[nolandinsight]

Thank you for the replies. We bought the boat a few months ago and have never had an occasion to use it at night. The nav lights DO work now that I've re-wired them.

I believe it's probably time to replace the batteries.

[vientoman]

hate to add a tangent post but I didn't know where to ask my question.....

given the choice, is it best to run solar in parallel or series and is their advantage when it comes to slight partial shading?

I know that there may be an advantage in being able to run smaller guage wires if run in series due to the higher potential voltage.

some particulars of my 12 V system : two 195 W 24V panels going to a tristar 45 MPPT controller.( in other words, should I create a 48V nominal input by wiring them in series or run them paralell 24V nominal ) the trystar can accept up to 150V input so 48V input is not a concern.

[btrayfors]

To the OP:

Your charging voltage, 12.5VDC, is WAY TOO LOW. That's the (resting) voltage you'd expect from a battery which was about 25% discharged. If that's the voltage being used to charge the battery, it will sulfate quickly and lose capacity.

I'd bet, from what you said, that the battery is toast. Replace it, but be sure your charging voltages are high enough: at least 14.4VDC for the absorption phase and at least 13.2VDC for the float phase. If you don't have a smart controller for the solar panels, get one. They're relatively inexpensive these days and will prolong the life of your batteries.

Also, be sure your solar panel/controller is large enough to maintain the batteries.

Bill

[nolandinsight]

Originally Posted by btrayfors

To the OP:

Your charging voltage, 12.5VDC, is WAY TOO LOW. That's the (resting) voltage you'd expect from a battery which was about 25% discharged. If that's the voltage being used to charge the battery, it will sulfate quickly and lose capacity.

I'd bet, from what you said, that the battery is toast. Replace it, but be sure your charging voltages are high enough: at least 14.4VDC for the absorption phase and at least 13.2VDC for the float phase. If you don't have a smart controller for the solar panels, get one. They're relatively inexpensive these days and will prolong the life of your batteries.

Also, be sure your solar panel/controller is large enough to maintain the batteries.

Bill

Bill,

So, I can infer that the charging voltage should be above 14.4v regardless of the condition of the battery, correct?

Does that mean my charging voltage of 12.5 indicates a problem in the solar charging system, or might there be another explanation for the lower than expected charging voltage? Perhaps poor condition of the batteries, or solar charging system that is more of a trickle charger?

Is that even possible, or do trickle chargers still deliver voltage above 14v, with amperage being the variable?

[btrayfors]

Without knowing the specifics of your DC setup, it's very hard to diagnose problems.

What batteries do you have? Flooded? AGM? Gel? Size and type?

How old are they? Have you done any sort of load test on them?

How are they connected? AWG size of cables?

What battery switches do you have and how are they wired?

From what little you said:

1. The charging voltage is way too low (my post above);

2. It's generally not a good idea to go thru an ammeter, if you're talking about the old automotive-type meters. Lots of resistance likely, especially in the wiring and connections.

If you found a loose wire at the ammeter....loose enough to affect the functioning of the bilge pump....you can bet your bottom dollar that there are other problems in the wiring system on the boat.

With a simple multimeter you can trace wiring problems and resistance problems pretty handily. Look for voltage drops in the charging system between the output of the solar panels, onboard battery charger, alternator, etc. and the batteries.

Look for loose and corroded connectors and connections. Look for undersized wiring. Look for improper fuses and for corrosion in fuseholders. I've even seen big battery switches with bad contacts, having a serious voltage drop across them.

If any of this sounds like Greek (or ancient Greek) to you, it might save you a lot of pain and $$$ to hire a marine electrician for an hour or so to take a quick look at your system and do some elementary troubleshooting, and then provide you with prioritized recommendations to improve things.

One of the most frequent things I've seen owners do with their malfunctioning electrical systems is jump to conclusions and take action -- like replacing batteries -- without looking at the whole picture. Often, this is just throwing good $$$ after bad.

Bill