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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Batteries don't stay charged
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Thread: Batteries don't stay charged Reply to Thread
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Topic Review (Newest First)
10-08-2013 09:19 PM
Mechsmith
Re: Batteries don't stay charged

Yes the old batteries pass the test but they do not achieve a high enough voltage to reduce the rate of charge. Eventually one of the cells or batteries will show up as hot (warm to the touch) or with a dry cell or all cells dry.

I always replace all the batteries in a bank as one bad one will kill the rest. (Or at least reduce the voltage to the lowest)

I feel that this is a bit hard on an engine driven alternator.
10-08-2013 07:51 PM
travlineasy
Re: Batteries don't stay charged

I have 4 Trojans, all of which are new. A few months ago, only two were new and the same thing happened. While the old batteries still tested good, they seemed to charge constantly, even when there was nothing turned on and the SG reading was 1.275 or higher. After replacing the old ones with new, the problem ceased to exist. The manufacturer didn't have an answer for me, but now I no longer worry about overcharging with the solar system.

Cheers,

Gary
10-08-2013 07:24 PM
Omatako
Re: Batteries don't stay charged

Maybe off topic for the OP's post but while we're all here, Mainesail, maybe you can give me a tiny piece of advice.

I have 280w of solar array working through a charge controller and it all appears to work pretty well. But . . . .

I topped all my batteries up (6 x Trojan T105) about three weeks ago and when I went aboard last weekend, I checked the batteries again and they were all dry (water below the plate tops).

What is puzzling is that my batteries were at a 13.2v state of charge (SoC) when I left the boat 3 weeks ago and everything was turned off. Incoming charge was about 7 amps, reduced due to high SoC. The solar array and a wind gen (also on a charge controller) are wired through the 1-2-All switch which was left in All position. Wind gen was switched off because I didn't believe it needed to be running.

Is this a sign that the batteries are reaching the end of life? They are about 7 years old. Even with a low water level, the battery monitor still showed about 13.5 volts. I topped the batteries up again and then ran everything (fridge, lights, radios) for the whole weekend with no problem, SoC still right up there.

Your advice would be of value.
10-08-2013 12:38 PM
Maine Sail
Re: Batteries don't stay charged

Quote:
Originally Posted by BubbleheadMd View Post
Ah, ok. Thanks for the tip. I bought an inexpensive panel, and it says it has a diode, so I kind of took it for granted that most of them have it. I guess not.

A lot of smaller panels do have them but with the Chinese el-cheapos there are no guarantees. Many larger panels only have bypass diodes which are different from blocking diodes.


From Kyocera:

10. BLOCKING DIODES
Blocking diodes are typically placed between the battery and the PV module output to prevent battery discharge at night. Kyocera modules are made of polycrystalline cells with high electrical “back flow” resistance to nighttime battery discharging. As a result, KYOCERA modules do not contain a blocking diode when shipped from the factory. Most PV charge regulators do have a nighttime disconnect feature, however.



Kyocera assumes you will be using a controller thus only ships with bypass diodes which are not the same as blocking diodes.
10-08-2013 12:32 PM
BubbleheadMd
Re: Batteries don't stay charged

Quote:
Originally Posted by Maine Sail View Post
There are many, many, many el-cheapo solar panels out there with no blocking diodes in them. If using them without a controller they can become a load.. Many panel makers figure you will be using a solar controller so not all panels come with blocking diodes..
Ah, ok. Thanks for the tip. I bought an inexpensive panel, and it says it has a diode, so I kind of took it for granted that most of them have it. I guess not.

10-08-2013 11:52 AM
travlineasy
Re: Batteries don't stay charged

Using the volt meter, set the switch to amps. Disconnect the positive terminal of the battery, and connect the voltmeter between the battery cable and the battery terminal. If you have any reading at all, you have something draining your batteries.

If you do get some sort of reading, the next step is isolate the problem. This can be as easy as turning off all the panel switches until the reading goes to zero amps, or as complex as disconnecting wires one at a time until there is no reading. Most of the time it's an easy fix.

Be sure to check the batteries with a hydrometer. Each cell should read 1.275 and all cells should read equally.If one cell reads a bit lower than all the others, this is a good indication that the better is headed for the scrap heap. And if your battery switch in on 2 when they discharge, this indicates that one is dragging the other down and is in the process of going south.

I found that my explosive gas sniffer was dragging down the batteries of my son's boat. There was no on/off switch on the sniffer, and he didn't have a solar panel. Didn't take more than a few days to really drag down the batteries.

I've never seen a solar panel that did NOT have a blocking diode - not even the cheap ones they sell for charging through a cigarette lighter connection. I don't believe the solar panel is part of the problem.

Hope this helps,

Gary
10-08-2013 10:42 AM
geronimo69
Batteries don't stay charged

Thanks, I did buy a voltmeter to start the preliminary tests on batts. I bought the boat over the summer and not quite sure the age of the batteries. I'll follow up later after checking batts. Thx guys.
10-08-2013 10:34 AM
Maine Sail
Re: Batteries don't stay charged

Quote:
Originally Posted by BubbleheadMd View Post

3. No, the solar panel doesn't act as a "load" on cloudy days, it simply doesn't produce any output. Also, most panels have a diode to prevent current from flowing back to them. If the diode is damaged...maybe, but unlikely.
There are many, many, many el-cheapo solar panels out there with no blocking diodes in them. If using them without a controller they can become a load.. Many panel makers figure you will be using a solar controller so not all panels come with blocking diodes..
10-08-2013 10:24 AM
BubbleheadMd
Re: Batteries don't stay charged

The following possibilities may be at play here:

1. Your batteries are old, and have greatly reduced capacity.
2. You have a short or hidden load somewhere, draining the batteries.

3. No, the solar panel doesn't act as a "load" on cloudy days, it simply doesn't produce any output. Also, most panels have a diode to prevent current from flowing back to them. If the diode is damaged...maybe, but unlikely.

4. Shore power is not relevant to the state of your batteries unless you have an onboard charger. Is the charger on or off when you connect shore power?

Buy a cheap voltmeter or multi-meter. Set it for Volts (DC) or VDC.
With the engine off, but with the switch ON, observe the battery voltage.

Is the voltage dropping?

Now, set the battery switch to OFF. Does the voltage continue dropping?

Next, with a fresh charge on the battery(s), turn on a couple of lights.
Does the voltage drop precipitously?

Try cranking the engnie.
Does the voltage crash?

The answer to these questions will help determine if you have a short, or if your batteries are toast.
10-08-2013 10:21 AM
Maine Sail
Re: Batteries don't stay charged

Quote:
Originally Posted by geronimo69 View Post
I have a solar charger on bat 1. When I start engine, I switch the panel to ALL so that I can charge both bats. When I raise the sails and turn off the engine, I usually dont turn off the switch to the batteries. If i dont, the bats are struggling to get the engine started. Do you think this is an alternator issue or does the solar panel reverse charge the batteries when cloudy or dark out?

Side question, does being connected to shore power have any affect on charging the batts?
The short answer is we don't have enough information to tell you anything.

*What wattage is your panel?
*What size battery is it feeding?
*Does it have a controller?
*Does it have blocking diodes?
*How is the solar panel wired in?
*Where is it placed on deck?
*How big, in Ah's, are the battery banks?
*Have the batteries been tested/how old?
*How big is the bank you are paralleling it with?
*How is your shore charger wired?
*What turns on your shore charger?
*Have you checked the voltage AT THE BATTERY TERMINALS with the engine both OFF and RUNNING?
*Same with the shore charger?
*What is the voltage difference with the engine OFF and ON?
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