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Old 27-07-2013, 00:25   #1
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Battery Capacity Access Problem

Hi,

I have a 1200 amp house bank that consists of 10 Trojan 6V golf cart batteries that are one year old wired in series and in parallel. The bank is recharged with a 2500 watt charger/inverter powered by a 6.5 Kw Fischer Panda generator when away from shore power, in addition to the stock 80 amp Yanmar alternator (undersized I know). The system is monitored by a Xantrex Link Pro. We have a separate start battery for the engine and generator. We have been cruising for a year now and the problem we have is that we are unable to access most of this battery capacity.

For example the other day we did a simulated night sail. I first made sure the bank was fully charged. The voltage on the bank was at 13.50 but to make sure we took specific gravity readings and all 30 cells were within the manufacturers specs as fully charged. We then turned shore power off and turned on our instruments, running lights etc in addition to normal house loads like refrigeration. We did not use any interior lighting. At that point we were pulling 14 to 16 amps out of the bank. As I said the bank was at 13.50 volts when we began and eight hours later the bank was at 12.29 and over that period we had pulled 138.8 amps out of the battery bank.

My question is, since this is a 1200 hour bank should we not have somewhere in the area of 600 usable amps in these batteries before the voltage drops to the point where it needs to be recharged? These are good quality batteries. Every indication is that they are being properly charged by our 2500 watt Xantrex Charger/Inverter. We are quite careful about making sure they are watered when needed and never fall below the recommended 50% charge, in fact they never get anywhere near that if one does the math. We do equalize the bank periodically but nothing seems to solve this problem and it is making me crazy.

We intend to spend the winter at anchor in the Bahamas but I really want to get this problem solved before we go. The boat is a 2003 Hunter 426. If anyone has any suggestions or thoughts I would greatly appreciate it.

Thanks.
Brian
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Old 27-07-2013, 01:02   #2
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Re: Battery Capacity Access Problem

Since the real battery gurus have not replied yet, let me humbly take a stab at this: Trojan makes excellent batteries. If you are not getting the performance you should, I would suspect your methodology before the batteries. According to the chart in the Trojan users manual, at 12.29v, your bank is about 35% down. (50% is 12.10v) Trojan cautions that open circuit voltage measurements are the least reliable method of determining state of charge. Did you wait the recommended 6 to 24 hours battery idle state before measuring the voltage? Were you still pulling the normal load when you read 12.29v? Also, I would verify the voltage at the shunt terminals is the same as what the Link Pro displays. There could be unwanted resistance in the Link Pro shunt sense wires. I would also recommend talking directly with Trojan about the issue. Their tech support has always been helpful to me.
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Old 27-07-2013, 01:03   #3
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Re: Battery Capacity Access Problem

Hi Brian, I am told that the voltage range for 12V lead acid batteries is 11.7V discharged to 12.6V fully charged and what you see above 12.6V in a fully charged battery is actually "surface charge" which will draw down fairly quickly once the battery is placed under load. If this is true then your batteries performance is not actually to bad.
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Old 27-07-2013, 03:18   #4
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Re: Battery Capacity Access Problem

Greetings and welcome aboard the CF, Brian.
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Old 27-07-2013, 03:39   #5
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Re: Battery Capacity Access Problem

Welcome to the forum Brian.

The need to recharge the batteries at 12.3v is only valid when the batteries have been sitting with no charge, or discharge for a long time. (It is a resting battery voltage). Even then it is a crude measurement that needs to adjusted for temperature and battery type.

12.3v does sound a little lower than I would have expected for the parameters you have described (15A discharge on a 1200AHr battery bank @ 88% SOC), but it is not far out. Often the voltmeter is slightly miscalibrated or it is measuring slightly lower because it is reading some voltage drop in the wiring.

If you are concerned a capacity test is next step. Some electrical experts recommend a test like this once a year, but it is hard on the batteries.
At 1 year old the batteries would have to very abused to be in poor shape.
Some voltage measurements at the battery while charging would also confirm they are being correctly charged. In theory SG measurements are better, but it is easy to make erroneous reading when doing this and confirming the correct charging voltage profile is a good double check that the batteries are being charged correctly.

Also remember when charging via the generator you are probably stopping at around 80% SOC (the final 20% is very slow). So you only have 360AHrs before the battries are down to 50%. If your average draw sailing is 15A you will need to run the generator every 24Hrs.

Finally, 15A is large average draw for your sized boat. Some simple power conservation steps would be worthwhile, if this is your average draw sailing.
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Old 27-07-2013, 05:32   #6
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Re: Battery Capacity Access Problem

You cant tell if its fully charged when you are still charging on shore power. So the 13.5 was wrong.

8 hours at 16 amps/hour load on 1200 amp hours is probably not too bad. Thats a huge load.

The 12.29 was that under any load whatsoever? You must take off all loads before that voltage is relevant. With ALL loads off I go down to 12.24v but with my max load on (4 amps) that will show as 12.15


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Old 27-07-2013, 05:38   #7
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Re: Battery Capacity Access Problem

1200AH 1 year old batteries that have been sitting on the charger all the time probably aren't close to their capacity yet. Batteries need to be cycled a few times before they get to their ratings. Run them though some cycles (ie use them a while) then recharge and equalize and see how they perform then.

And yes that voltage doesn't mean too much if it was a 14 amp load reading, what was the specific gravity at the 12.29V?
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Old 27-07-2013, 08:21   #8
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Re: Battery Capacity Access Problem

12.3V under a long-term 15A load sounds fine to me. What did the voltage do when you turned off the loads? If it went back up, then everything is working like it should. Did it fall rather steadily to this voltage and then stayed there for a long time? If so, then that sounds OK and you are reaching into your capacity like normal.

BTW, 15A steady load is a lot when nothing but instruments, nav lights and reefer is on. When you add the autopilot when underway, that is going to add another 5-10A. Do you know where the power draw is coming from? Sounds like the navigation lights from your description. Maybe LED's are in your future?

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Old 27-07-2013, 08:37   #9
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Re: Battery Capacity Access Problem

Google "Breaking in New Batteries" just discussed on this or manybe another forum. Maine Sail did a nice writeup, could be on Sailnet, I know I've written about it on our C34 message board:

Breaking in New Wet Cell Batteries: "Breaking In" New Wet Cell Batteries

Good luck.

PS - I don't think you have a problem.
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Old 27-07-2013, 09:13   #10
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Re: Battery Capacity Access Problem

When we installed our last set of T105's, I asked Trojan about the Ample Power "break in" method and they specifically said not to do it, and to just let the batteries cycle through a couple of discharge/recharge periods of normal use to get them to capacity.

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Old 27-07-2013, 10:18   #11
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Re: Battery Capacity Access Problem

Thanks for all the replies. On our house draw - Hunter installed amp hog appliances on this boat. We have a frig and separate freezer that together draw around 10 amps. This combined with the fact that they are front loading and not real well insulated translates to a lot of run time. They work well though and I don't want to spend the money to replace them so I am going to have to live with the draw.

I think I am going to run this simulated sail again and with the some of the suggestions made here and see what this looks like. I appreciate all of your advice.
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Old 27-07-2013, 10:45   #12
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Re: Battery Capacity Access Problem

You didnt mention if the 12.30 is under load or not.

I dont think simulations ever work. Go away for a weekend and test with beer.
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Old 27-07-2013, 11:01   #13
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Re: Battery Capacity Access Problem

Quote:
Originally Posted by RaymondR View Post
Hi Brian, I am told that the voltage range for 12V lead acid batteries is 11.7V discharged to 12.6V fully charged and what you see above 12.6V in a fully charged battery is actually "surface charge" which will draw down fairly quickly once the battery is placed under load. If this is true then your batteries performance is not actually to bad.
Yep.
OP: at anchor you wont be drawing all that amperage. (if I understood your test) However, fora 1200 amp hour bank .... it does seem like it drew down rather a lot. The reality is though, you need to recharge alot every day. Typically I needed to do about 100-120 amp hours per day... mostly due to refrigeration.
One of the fallacies of a huge battery bank is that ...sure.. you should have more reserve to start with, but you have two choices: replenish that reserve daily, or end up having a bank that is down 300-400+ amp hours and now it will take forever to recharge somehow!
Once I realized this, I started having a much smaller bank of batteries to Buy, Maintain and recharge. You only need a bank big enough to supply that 125 amphours a day without damaging the batteries. All else is excess weight.
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Old 27-07-2013, 14:45   #14
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Re: Battery Capacity Access Problem

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Originally Posted by MarkJ View Post
You didnt mention if the 12.30 is under load or not.

I dont think simulations ever work. Go away for a weekend and test with beer.
So do I pour the beer into the batteries? - wait, that would be a waste of good beer.
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Old 27-07-2013, 16:57   #15
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Re: Battery Capacity Access Problem

do a c20 test at the dock. best and only way to fully test battery cap.
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