How bad did I mess-up???

[rleslie]

OK, I admit that I screwed-up......royally!!!! Without going into the gruesome details, I will tell you that when I caught my mistake, my 3 month old AGMs were being fried with 15.65 volts. They got so hot that the tops of the batteries now look like waves, but don't appear to be leaking.

At the time we were on Little Shark River...a long days sail from civilization, so I figured that I would replace the batts in a few days and conserve our energy usage in the mean time. That was 2 weeks ago and the batteries are still performing as well as they did before my brain fart.

So the question is, what type of damage did I likely do to them?

Roger

[Charlie]

Here's my guess? someone with more knowledge will chine in. By heating the batteries up you have definitley melted the plastic. What you don't know is if you have melted any of the plates or messed with the chemical make up of the batterey.

Top the batteries up with distilled water. Charge the batteries and let them sit for 24 hours to equalize. Then check them with a hydrometer to see the specific gravity. If it looks ok then do a draw down test on the batteries to see how well they are doing holding a charge. From there you should have a good idea of the condition of the batteries.

If you can afford to I would just replace them b/c they may fail at an inoppurtune time.

[S/V Elusive]

Just a point - most AGMs don't have access to the cells - I believe they are sealed.

Roger? I would suggest you call the manufacturer - but you KNOW what they are going to say - :::shrug::: If it were me, I would replace them - the cost vs. peace of mind ratio is low enough. The thought of no power and/or the batteries leaking and causing damange to the boat are significant concerns.

[Intentional Drifter]

I don't mean to incur pain, but to help educate those of us with less experience -- what happened? How did it happen that you were putting so much voltage into them?

ID

[rleslie]

Without going into too much detail.....I have three battery banks and have them linked via a 3 battery bank combiner. My old shore power charger died so I replaced it with a new multi-battery bank charger. When I was hooked up to the shore power, the combiner was confusing the shore power charger (the manufacturer said it would happen). I ran a wire from the combiner to the battery bank with an ON/OFF switch so I can isolate the shore charger from the combiner.

When I was doing the re-wiring, I mistakenly ran a wire from the alternator straight to the combiner......BIG MISTAKE, because the alternator is already connected to the house bank with a dedicated wire. When I started the engine, the house bank was connected to the alternator twice. When I discovered that they were getting too much voltage, I immediately turned the ON/OFF switch to OFF and the voltage dropped. I have removed the wire from the alternator to the combiner and everything is working as it should.

Roger

[Intentional Drifter]

Ouch! I'm sorry that happened, but thank you for the details. I'm going to put that one into my little notebook.

ID

[Alan Wheeler]

You maybe fine. Firstly, the voltage is not the issue here. 15.6V is not high. Infact, the batteries were probably limiting the voltage by taking it as current. Thats basically how an unregulated charger works. The OC voltage measurement could be very high, but drops to the batteries voltage when connected. It's not about voltage or current, it's about a combination of both, equating to Power in Watts.
OK, so what would ahve been happening, is the batteries would have been over charged. They would have become very hot. But this is were the difference in a flooded and a sealed battery come into there own. flooded would have boiled the water away and left the plates dry. This would have seriousely damaged the battery. The AGM is probably OK. To find out, leave the batteries to settle and cool, unconnected for 24hrs. Then Volt test them to ensure there float voltage has remained where it is supposed to be. This will be higher than a flooded battery, so don't panic if you see 13.6V.
The next test is to see if the house banks are giving you the same cycle as they normaly did. So after the normal nights use, do you see the float voltage at ruffly the same point the next morning. If you go for a couple of days before charging, then once again, are the batteries holding up.
I suspect they are fine and will remain that way.
DON'T do it again though. AGM's don't take kindly to abuse.

Curiouse, Why the three banks???

[rleslie]

Alan

So far, they are taking/holding their charge, just as they did prior to the overheating.

leave the batteries to settle and cool, unconnected for 24hrs. Then Volt test them to ensure there float voltage has remained where it is supposed to be.
Should I disconnect them from the load, the charge source or both?

Why the three banks???
House, starter, windlass. The boat was already wired this way when we purchased her. The 3 bank combiner works fine (except when I start messing with it!!) and all banks can be used for any purpose via a manual switch.

Thanks for the help!!!
Roger

[Alan Wheeler]

As long as nothing is turned on, so nothing is being drawn from the battery, then that is fine and certainly do not have the chrager on.

Personaly, I would through the combiner over my shoulder. I don't use one. I think they are dangerouse. If you ever have a three bank charger, you do not ever need to connect any banks together. Plus, if the banks are in different places on the boat, having them connected together means unequal draws from the banks. A combiner is there as an energency only. It should only ever be used for a flat engine start problem. So normaly, it should never be used. So are you useing this combiner to charge when the engine is running??? You need a charge splitter to replace it so as equal charge is going to each bank. combining them once again means, they are not getting equal charge.

[rleslie]

Originally Posted by Alan Wheeler

problem. So are you useing this combiner to charge when the engine is running??? You need a charge splitter to replace it so as equal charge is going to each bank. combining them once again means, they are not getting equal charge.

I use the combiner for charging from the alternator and two solar panels. It is my understanding that the combiner automatically parallels the banks when charging and disconnects them when no charge is present. I don't see how that can be dangerous, especially if they can be manually connected if necessary.

combining them once again means, they are not getting equal charge.
I think that it is more likely that the banks are discharged unequally.

I have a three bank charger, but 75% of our time is spent on the hook, so I consider shore power to be an ocassional charging source. The present system is designed for charing primarily from the two 120W solar panels, secondarily from the alternator and shore power being an ocassional luxury.

Roger

[Alan Wheeler]

Arrrrh, we maybe talking two different things here. The combiner I am thinking of is a maunual swtch.
Because you have three banks seperated by distance and thus cable, the batteries will each see a slightly different load, due to resistance int he cable. Even though the cable maybe large and the resistance small, the resistance of the battery itself is even lower. So the cable loss is actually quite large compared to what the battery "see's". So you start having unequal sharing of charge. If it is an electronic combiner, which I now think you are talikg of, I presume it is also balancing the charge load. This is also something that is done in your three bank charger.

[rleslie]

Alan

As usual, you make some great points. I'm calling it a combiner, but it is actually a Xantrex PathMaker Automatic Battery Switch.

Good point on the load loss because of the wire's resistance. The house and start banks are about equal distance from the combiner , but the windlass is a much greater distance. I'll have to check that one out.

Thanks
Roger

[Rick]

Like Wheels wrote, you may determine if overhcarging resulted in excess gassing which removes water from the electrolyte via the overpressure valves built in to the batteries. This determination is done by either allowing the battery to stand without load and without a charge source, usually for 24 hours for a flooded-cell constructed battery or usually longer for gel-cell or AGM batteries. With the latter two types it takes longer to self-discharge the surface charge down to the standing voltage.

Most AGMs have a standing voltage of 12.9 V at 20-25 deg. C not to be confused with a proper float voltage of 13.6 to as high as 13.9V (more on this later if necessary). If your batteries exhibit a standing voltage higher than 13V then you most certainly have excessively gassed them. You may still get good service from them until they die a premature death from having an excessively high internal acidic content to the electrolyte which accelerates the degradation of the conductors and sometimes the active material on the plates. If you have a battery monitor there are ways to check for this.

In order to determine the standing voltage without waiting for self-discharge to reveal that do the following: Starting with a "full" battery and with a relatively small load (about 3% or less of the rated Amp-hour capacity) of current applied and a DVM (or battery monitor) to measure the terminal voltage you can log and plot (even sometimes mentally) the slope in the decrease in terminal voltage versus linear time. With a surface charge present the voltage will slope downward fairly linearly and then stabalize to one value....then STOP the discharge. Measure that voltage to obtain the standing voltage without the relatively small energy due to a surface charge present.

Please describe the symptoms that you observed in order to conclude that the PathMaker combiner "confused" your battery charger. I believe that whatever you observed is due to a poor choice in which output wires from the charger to lead to the combiner. Most multi-battery chargers will operate very well using a PathMaker combiner. One problem installation wiring error with chargers having separate voltage sense lines (either internal to the charger outputs or external to them), AND independent internal regulation for the separate outputs, is to wire more than the main (highest current rated) wire to the combiner and/or to additionally wire the auxilary battery charge lines directly to the batteries which will be combined by the PathMaker. Yeah, I've made this read in a confusing manner...let's go from here as to what kind of charger you have.

[rleslie]

Rick

We need to back-up for a minute. The over-charging and the battery charger being confused by the combiner are two seperate issues.

a) The over charging was caused by my incorrectly wiring the sub-bus (that receives the charge from the alternator and the solar panels) directly to the battery switch/combiner and to the house battery that is also wired to the battery switch/combiner.

b) The reason that I was rewiring was that Xantrex clearly states in their instructions that the multi-bank charger should not be used with a combiner/battery switch.

Anyway, the only symptom is the deformed battery cases. The batts seem to be holding a charge and discharging at the same pace as before. However, I have not brought the batteries to full charge since the mistake. We will be in a marina in a few days and I will try to get the batts to full charge, but letting them sit for 24 hours is hard to do. We're cruising and are aboard every night. Not sure that I follow the other method that you suggest.

I have a Xantrex battery monitor, but have never been able to get it to operate correctly because Xantrex's instruction on the installation were incorrect (they reluctantly admitted it). I will try to hook it up again.

Roger

[Alan Wheeler]

Roger, I am confused with the wiring issue you had. If I understand you correctly, you figure the two wires from Alternator have caused the issue. I see no reason why. Could you elaberate on this further as I must not understand something here.