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obelisk 01-05-2012 02:37 PM

Battery Equalization Amperage
 
My batteries have been on a float charge for the better part of a year while I have been in the States and need to be equalized. They are not holding their voltage as they used to. I have never really equalized them before and it has not been a problem but now it is time.

I have read a lot about it but one main question still escapes me: what amperage? Nigel calder says 3-5% of the amp hour rating of the battery. Is that the combined amp hour rating of my battery bank (408ah) or of each individual battery (136ah)?

I will continuously monitor the temp. of the electrolyte and follow all the other steps. 12-20 amps sounds like a lot to be cramming in with the batteries fully charged.

Thanks.

btrayfors 01-05-2012 02:45 PM

I assume you're talking about flooded batteries.

The batteries will take what they'll take...period. So long as you control the VOLTAGE (to, say 15.5VDC to start), the batteries' internal resistance will determine the maximum amperage.

For reference, I recently tried to restore/revive a pair of 8-year old T-105 Trojans which were down to about 30% capacity. I fed them 15.5VDC, increasing to 16.5VDC as we went along. They took about 20 amps.

By the way, as far as I could tell, there was no loss of electrolyte even though these puppies were bubbling pretty good for upwards of 36 hours total.

Bill

Maine Sail 01-05-2012 02:52 PM

Quote:

Originally Posted by obelisk (Post 813574)
My batteries have been on a float charge for the better part of a year while I have been in the States and need to be equalized. They are not holding their voltage as they used to. I have never really equalized them before and it has not been a problem but now it is time.

I have read a lot about it but one main question still escapes me: what amperage? Nigel calder says 3-5% of the amp hour rating of the battery. Is that the combined amp hour rating of my battery bank (408ah) or of each individual battery (136ah)?

I will continuously monitor the temp. of the electrolyte and follow all the other steps. 12-20 amps sounds like a lot to be cramming in with the batteries fully charged.

Thanks.

If your charger has an equalization feature it should handle this automatically. Most good quality chargers will not even go into an EQ mode until the bank has been sufficiently fully charged. At that point the increased EQ voltage is driving the "acceptance" higher than at float voltages. The battery ultimately decides what the amperage output of the charge will be at a given voltage.

I would not equalize your batteries as a bank if they've "never been done".. Personally I only equalize individual batteries, or series pairs of 6V, but I do it mostly in my shop, on the bench, where I can monitor them for temp, SG, odor, uneven cells etc... Split them out and do them one at a time while being their to monitor temp and SG.

You have no way to control the "current" with most marine chargers other than to change the voltage, as you do with an EQ mode. Start with fully charged batteries and you'll be fine.

Leaving batteries on constant float can still lead to stratification and sulfation. As an example a 125 Ah battery at 13.5V on my bench charger, a Xantrex TruCharge (Not a great unit but does what I need in the shop), is seeing just 0.02A - 0.035A to maintain that 13.5V while in float. Many a boater has assumed this charger just shuts off in float because their battery monitor simply does not have the resolution to read those currents. It doesn't turn off it just pumps out what the battery needs to maintain that float voltage which in the case of the 125Ah battery on it now is about 0.02A - 0.04A...

You're simply not moving enough electrolyte at that amperage or voltage to prevent stratification. This is why many newer, and actually "smart-er" chargers revert to a periodic absorption voltage to get the electrolyte moving again. I see plenty of batteries left on "float" die and it's simply because the electrolyte can still stratify which can lead to plate damage.

EDIT: I see Bill and I answered at the same time saying basically the same thing....

btrayfors 01-05-2012 04:36 PM

Yes, I agree with Maine 100% on this.

And, the batteries I was trying to revive experimentally are a perfect example of what he said. They lived their 8 years as a power source for my radios in my home. They were on an Iota DLS-45/IQ4 smart charger with a float voltage of 13.6VDC 24/7. They obviously didn't move around much, but were stationary at my radio shack location.

Occasionally, they'd get a healthy draw of 90A with my 12V 500 watt HF amplifier on, but the charger was on at the same time so they really didn't get much of a workout unless we lost power....a relatively rare occurrence.

Sometimes, not often, I'd "exercise" them by pulling the plug on the battery charger for a day or two, and using the radios entirely from the batteries.

During equalization, the batteries bubbled vigorously and got warm, but not hot. You could feel the warmth on their sides, but not really at their terminals. There was no noticeable loss of electrolyte. These batteries, like all of my T-105s, have WaterMiser caps.

Conclusion: Despite being on a 13.6VDC float charge 95% of the time, they nevertheless aged and lost capacity (most likely through stratification and sulfation) over those years. I removed them from service about six months ago when they were down to about 45% capacity (as measured by a Midtronics tester) and were losing it fast.

A couple of weeks ago when I tried to revive them, they were at about 30-35% of original capacity. After several days of jolting them pretty good with a healthy equalization charge of 16.5VDC @ about 20 amps, they still tested about 35% capacity, so no improvement there.

There was a sort of "improvement" though: the cell bubbling was more uniform (one cell barely bubbled at all when I began the treatment) and the pair now holds a charge much better than before, i.e., the self-discharge rate is much less. However, their capacity didn't really improve.

I did do a real (direct) capacity test with them, however, putting a 12 amp load on them. They delivered just over 70AH in a 6-hour period before falling to 10.0VDC under load, which is consistent with my earlier estimate of 30-35% capacity. A new T-105 pair, broken in, would have gone almost 20 hours before dropping that low.

FWIW,

Bill

obelisk 01-05-2012 06:12 PM

unfortunately, i have been in the US and away from Chile for some time, working, and unable to properly tend to the batteries. I have a Balmar ARS-5 charger that does not have an equalization setting but I do have an equalization setting on my SolarBoost 2000e solar charge controller or access to an independent mobile adjustable charger.

If i may get straight to the point: I can adjust the voltage, but is 12-20 amps too much to be putting into a a 408ah battery bank during equalization as long as I monitor the temp and stop charging and cool down when the electrolyte nears 118deg F?

notawriter 01-07-2012 02:10 PM

Maybe Iíve got the science wrong, but Iím confused by the answers to the original posterís question. My understanding is that a battery in need of recharging is not a traditional load which will simply draw the amps it requires. I also think that charge generators (for example wind and engine alternators) actually push electrons down the wire and thus "dump" resistors are often part of the system. Do battery chargers have electronics which accomplish this and prevent the battery from ďacceptingĒ too much charge too fast?

btrayfors 01-07-2012 03:56 PM

A battery has a certain (and variable) internal resistance. The value of this resistance depends on several things, most notably:

1. the type and chemical composition of the battery (flooded, AGM, gelled lead-acid);

2. the state-of-charge (SOC) of that battery -- the lower the SOC the less internal resistance the battery;

3. the ambient temperature and internal temperature of the battery; and

4. the condition of the battery -- as batteries age and deteriorate, their internal resistance changes.

Now, think about Ohms Law. In any active electrical circuit, amperage = voltage divided by resistance (I = E/R). As resistance increases such as when a battery moves toward a higher SOC, then current (amperage) decreases accordingly.

It's the battery, not the charging source, which determines how much amperage will flow, assuming the same voltage being provided.

If, for example, a battery is accepting 25 amps @ 14.2 volts from a 50-amp charger, it would accept exactly the same amperage from any charging source -- battery charger, wind generator, solar panels, etc. if they were to be controlled at 14.2 volts.

The only way to "push" more amps into the battery would be to increase the voltage.

Wind generators have "dump" resistors because they need to be kept under load, even when no further charging is required. You can't just break the circuit, because you'll blow them out. Therefore, you have either to physically stop their rotation or divert their output, e.g., to "dump resistors" (preferably to a useful one like a 12VDC heating coil in the hot water heater).

Solar panels are different: their circuits can be interrupted without damage by a simple switch.

However, both wind generators and solar panels -- as well as all other charging sources of any decent capacity -- require a good regulator to control their voltage levels. Why? Ohms Law, as explained above.

Hope this helps a bit.

Bill

obelisk 01-07-2012 11:00 PM

so, the batteries themselves will dictate how many amps they receive during equalization?

I have separated my three batteries and am equalizing them separately so that I can retain use of the boat's electrical system in the meantime. my battery charger is currently (no pun intended) putting in 10A at 14.3V into my 136AH flooded deep cycle battery. I have set the voltage to 14.8, the max setting. It is not the desired 15.5, so I will just have to continue the process longer. Will the amps continue to drop as the voltage comes up to the target and the SG rises?

Maine Sail 01-07-2012 11:19 PM

Quote:

Originally Posted by obelisk (Post 814400)
so, the batteries themselves will dictate how many amps they receive during equalization?

I have separated my three batteries and am equalizing them separately so that I can retain use of the boat's electrical system in the meantime. my battery charger is currently (no pun intended) putting in 10A at 14.3V into my 136AH flooded deep cycle battery. I have set the voltage to 14.8, the max setting. It is not the desired 15.5, so I will just have to continue the process longer. Will the amps continue to drop as the voltage comes up to the target and the SG rises?

Yes the current will drop. You should see under 2% of capacity acceptance when the batteries are mostly full. The last bit takes a long while and with healthy batteries you can get them to under 1% acceptance at around 14.4V so slightly higher at 14.8V..

obelisk 01-07-2012 11:59 PM

hmm, am i being fooled by my battery monitor? it reads 100% and has since beginning equalization and the charger is still putting in almost 10A.


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