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Old 25-10-2010, 07:22   #1
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Wet Cell Charging Voltage

US Battery is a pretty reputable company for 6V Golf Cart batteries. I use them, as do many others. Mine are 3 years old, and starting to lose their capacity. When I first bought them, I wrote US battery and asked what the charging levels should be. This is what I received, and is still what they state on their web site:

"US Battery's bulk charging voltage recommendation for a 12 volt battery is 15.5 volts (2.583 vpc x 6) with a maximum charge current of 20-25 amps per parallel leg (60-75 amps for 3 sets in parallel). Your charge voltage settings of 14.4 &14.65 volts will tend to undercharge the batteries if they are deeply discharged on a regular basis."

Now, we are in the Caribbean, often with higher temps, so here is their temp modification from their site:

"Reduce voltage by .028 per cell for every 10F over 80F".

So, assuming our temp is about 90F, the voltage on a regular basis they want me to charge the batteries to is 15.3.

I a 3-stage cycle, the volatage would be brought up to 15.3, and the amps slowly decreased while the voltage stays a 15.3 during the "acceptance" stage.

Wow, that seems crazy to me. I dont even think Xantrex charges will do this except in Equalize Mode.... I guess I was hoping to get more like 5 years of full time cruising from these, but doesn't look like it. We liveaboard full time, on the hook, never discharge > 50%, and also rarely bring them to total full charge as it has to be done with our engine. I am wondering if its due to undercharging (we bring ours to about 14.7 as often as possible, but they only touch >15 during an equalize a few times a year).

What are people's thoughts/comments on this....

Thanks
Mark

PS I have read a few other comments by people with 6V batteries and their respective manufacturers also sometimes state > 15 V to normal/regular charging....
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Old 25-10-2010, 07:29   #2
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They are correct despite what many folks apparently think. The key ingredient here is internal temperature which wasn't mentioned. As long as you have a good way of monitoring battery temp to regulate voltage, you can't go wrong.
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Old 25-10-2010, 07:44   #3
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My BZ solar charge controller has a battery temperature sensor for that very thing
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Old 25-10-2010, 07:50   #4
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Originally Posted by kiltym View Post
What are people's thoughts/comments on this....
This differs from Trojan's recommendation.

Trojan Battery Company
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Old 25-10-2010, 07:57   #5
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15.5 volts is equalization charge. That voltage is too high for normal charging.
14.4 volts is correct for normal charging.
Equalization charging should be done for 2 hoours or so once every month.
At 15.5 water will gas off and need to be replentished.
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Old 25-10-2010, 08:39   #6
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What Trojan recommends and what USBattery recommends are different. Since all wet cell chemistry is equivalent, you can deduce how critical charge voltage really is when two reputable companies differ. A lot of the discussion about what constitutes a proper charge voltage is based on myth, old generalities and perception. It's all about temperature sensors.
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Old 25-10-2010, 08:40   #7
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You do not mention whether you check your specific gravity on a maintance schedule. SG numbers will tell you when a cell needs equalized. I think your charging method is contributing to a lower SG and therefore more frequent equalization is needed.
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Old 25-10-2010, 08:44   #8
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They also said you only need to reach those voltages if you have deep discharges on a regular basis.
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Old 25-10-2010, 12:49   #9
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Thanks for all the thoughts. Here is some more info.

We do have a temp sensor on the batteries for the AC Batter charger as well as our Solar charger. I realize temp is important and is why I made sure to purchase chargers/controllers with a temperature sensor.

I also understand that as the battery temp increases, the voltage does not need to be brought up as high as it does when they are "cold".

I dont quite think a statement like " It's all about temperature sensors." is quite correct though. The temp sensor compensates for increase temperature, but if the baseline is 15.5, even when heated your going to be in the very high 14's. And based on a 14.5 top end voltage, you would be around 14. So, temp is important, but you need the "baseline" to work from. S/V Illusion, perhaps what you are stating is the 15.5 is correct, but then needs to be adjusted for temps? Still seems pretty high, no?


All that being said, I still think most chargers will not bring the battery voltage up > 15 in a normal charge cycle. I have never seen a charger spec that would do, or recommends this, yet, battery companies are stating this is the correct charge. Perhaps that are meaning it on a very deep discharge basis (like all the way down), but I would not think that the top voltage you would want to bring the batteries too would be effected by this.

I too have read, and seen that 14.5 or so is right place for wet cell batteries. However, if the manufacturer is stating this is wrong, I would hope they know more than me.

I know all the results of equalizing batteries and such, and how to do it, and make sure its done safely.

The only issue/question I have is why would a battery manufacturer (and its more then just US Battery, Interstate says similar (but maybe its the same batteries)) state the charge cycle should go to 15.5 every time, if its just plain wrong. Somethings doesn't add up to me.

Even Trojan is stating 14.8, which is also above what people here seem to think is correct.

Mark
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Old 25-10-2010, 12:58   #10
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They also said you only need to reach those voltages if you have deep discharges on a regular basis.
I am not sure which "They" you are referring to, but here is what US Battery says on their site:

"Typically, charge at C/10 amperes, (where C = the 20 hour capacity of the system expressed in Ampere Hours) until the battery voltage rises to 2.583 Volts per cell (i.e. 7.75 volts for a 6V battery). Hold this voltage constant for 2 to 4 hours, and stop charging. A similar method would be to charge at the following upper limits and terminate the charge when the time limit is reached:

- Charge Current = C / 10 Amperes
- Charge Voltage = 2.583 Volts per Cell
- Charge Time = 10 Hours

Battery Temp Adjustment - reduce the voltage by .028 Volts per cell for every 10F above 80F, increase by the same amount for temperatures below 80F"


Note, the interesting thing also mentioned here is there is not mention of 3-stage charging, but I would assume they just ignore "float" and the acceptance is the 2-4 hours at 15.5V for a 12V battery bank.
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Old 25-10-2010, 14:11   #11
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my volt meter when the solar regulator was charging was around 14.5 v -14.8 my batteries are 200 amp wet cell and i just changed them after 7 years of service 2.5 years as liveaboard if your only getting 3 years life out of these batteries on your vessel something is not right ! ps- how often were you topping up the fluid levels in your batteries? cheers andy
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Old 25-10-2010, 14:39   #12
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One of the primary causes for reduce service life of lead acid (flooded, AGM or Gel) batteries is not fully charging them on a regular basis. If this full charge is not accomplished, the batteries WILL sulfate and capacity will be lost.

I have never heard of taking a lead acid battery to such voltage levels except to equalize. If the mfgr. is correct, and how can we mere mortals contradict the MFGR, then your batteries are losing capacity through sulfation caused by two modes; insufficient absorption voltage, and the aforementioned failure to fully charge them on a regular basis.

I advise my clients that the "regular basis" comment needs to be tempered with operational considerations but should be accomplished about every ten cycles at the most. More often is better for the batteries, not so much for the iron that has to run for a long time to provide the full charge.

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Old 25-10-2010, 14:40   #13
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ps- how often were you topping up the fluid levels in your batteries? cheers andy
The batteries were checked about every 2-3 months, topped up about every 6 months. Never was any plating exposed when I topped them up, thats for sure, not even close. They are kept full, no doubt about it.
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Old 25-10-2010, 15:46   #14
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Interesting discussion.

I'd just add the following points:

1. Flooded battery chemistries DO in fact differ; one variable is the lead antimony content; there are others.

2. 15.75 volts on a regular basis is higher than any other reference I've seen, and much higher than battery chargers and alternator regulators are set for -- except for equalizing, as mentioned above.

3. It may be that most manufacturers of batteries, chargers and regulators wish to avoid any liability by limiting the finishing voltages to levels which won't boil a healthy battery. I don't know this for a fact, but it's possible. When the voltage climbs much above 15VDC for a 6-cell flooded battery, the electrolyte begins to bubble vigorously.

4. Internal heat is certainly a danger, as excessive heat can cause the plates to buckle and short out. If you were a charger manufacturer or a regulator manufacturer you'd not likely want to open yourself to the possibility of lawsuits based on using a too-high-voltage charging regime.

5. Temp sensors are great...when they work properly. Unfortunately, that's not all the time....not even close. Great variability in new temp sensors has been documented, both under-reading (VERY DANGEROUS) and over-reading (leaving your batteries under-charged).

6. In my personal experience and testing, flooded golf-cart batteries which are kept fully charged (14.8V absorption level) but not often deep-cycled will begin to show significant (more than 20%) reduction in storage capacity after about five years. The deterioration in capacity begins much earlier. At six years you may have a battery with about 70% capacity remaining. These are very rough ball-park figures. Note that for many sailors, a battery with 70% remaining capacity is still "good". Therefore, I'd treat with extreme caution statements like, "my batteries lasted 8 years and are still good".

Like many things on a boat, with batteries "your mileage will vary". If you were to stop and think about all the variables contributing to the current state of health of your batteries, you'd wonder how we are able to even come up with ballpark estimates :-)

Bill
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Old 25-10-2010, 16:21   #15
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What Trojan recommends and what USBattery recommends are different. Since all wet cell chemistry is equivalent, you can deduce how critical charge voltage really is when two reputable companies differ. A lot of the discussion about what constitutes a proper charge voltage is based on myth, old generalities and perception. It's all about temperature sensors.


So I should read the manual for a model a Ford and use that totake care of my Honda because a car is a car, wet cells are not all the same, they have differing lead chems, acid conc., and more
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