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Old 27-02-2012, 08:29   #1
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State of Batteries

Are my batteries shot or OK?
I have 1100AH bank of 4 Rolls 8D batteries. They are probably in their 5th year.

Yesterday was bright and sunny - but cold. The solar panel was topping up the battery bank and the voltmeter on the electrical panel was reading 14.2V

I decided to pull the voltage down some - give the batteries something to chew on for a while - and so turned on the 2000W inverter and plugged in a 1500 W fan heater, which drew current at about 150A.

After about 10 minutes, the inverter shut off for low voltage (10.5V).
Temperature of the battery bank started at 40F, ended at 45F.

Shortly afterwards, the voltmeter was back up to 12.3V but when the heater was turned on again, it rapidly fell to below 11V.

OK, Shot or not enough information to make a determination?

Appreciate the thoughts...
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Old 27-02-2012, 08:46   #2
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Re: State of Batteries

Bill,

Sure sounds like something is amiss, even taking account of the low temperature and of Peukert's and the relatively high load on the batteries for only 10 minutes.

You should get 10 or more years out of those Rolls batteries. It's possible they've got some capacity loss through sulfation or other mechanism (stratification, contamination, physical damage, etc.), but you don't yet have enough info to know that.

I'd look for someone who has a really good battery tester like one of the Midtronics series (which are pretty much the industry standard these days, but which cost about $600 and up on this side of the pond), and get a good reading on each battery in the bank.

If you can't find one, then you could do a real load test on each battery individually, putting a known C/20 load on the battery and seeing how long it takes to get down to about 10.5 volts. For such a test, though, you'd need to have the batteries really fully charged before beginning.

Don't know how you've been charging or maintaining them for the past 5 years, but if you haven't kept them fully charged and on float of 13.6V or so and charged at 14.8V or so and periodically equalized at 15.5V or so then it's likely there's quite a bit of sulfation of the plates.

An equalization cycle would likely help, after which you could do the capacity tests.

Bill
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Old 27-02-2012, 08:55   #3
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Re: State of Batteries

Ahoy Capn Bill,
Can you get a specific gravity tester, you can see if any cells are "sick". What solar charge controller are you using, they can have a big effect on battery health.
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Old 27-02-2012, 10:03   #4
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Re: State of Batteries

The boat is new to me - so I can't attest to the history. Since I have owned her (April 2011), she has been on a mooring, charging with 2 (130W each) solar panels through a Blue Sky Solar Boost 2512iX when not in use.

I did test the specific gravity mid year - all seemed OK. I've had to top up the levels - which I admit to not being too frequent with... yesterday I had to top up 6 of the 24 cells.

I have not run an equalization program at this point, but agree I probably should - just have to work out how!

When I picked the boat up, she had been plugged into shore power for probably 5 or 6 months and not left the dock in that time.


I'll go in search of the fancy tester - someone round here must have one!

Thanks,
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Old 27-02-2012, 10:09   #5
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Re: State of Batteries

Sounds to me like the cells are about eaten up. You need to charge the batteries all the way up at about 2 amps and then put a load tester on them with the caps off to see if they boil while under load. And to see how long a load test lasts. Which should be 1 minute or longer.


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Old 27-02-2012, 10:36   #6
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Re: State of Batteries

Rolls was quite clear with me when I purchased a set of similar batteries: Plates exposed to air will die very quickly. I purchased the special caps to prevent premature loss of electrolyte and got almost 10 years from the batteries before they wore down. I did however have to replace 2 cells that died during that time. I monitored them for fluid level once a month and was often surprised to find that there was a cell or two that were exceptions and needed electrolyte. Good luck!
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Old 27-02-2012, 11:32   #7
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Re: State of Batteries

Bill, it is hard not to take anything for granted but when it comes to batteries and voltage, you can't take anything on faith. Even your voltmeter. I wound up making a little 10V precision voltage reference gizmo after seeing the way different voltmeters displayed the same voltage, some off by 2 volts at 12.

Since your voltmeter and inverter seem to share the same opinion about low voltage, odds are that it is low. No way to tell if that's from past abuse or sulphating. No way to tell if the Blue Sky controller is really working properly. If your local water has high mineral content, that can also upset the batteries.

I would suggest looking at the options, if you can't get power to the boat, get one battery at a time ashore. If you've got a Rolls dealer around, ask them about some help. Ideally, you should be able to put a full equalization charge on each battery, then load test it, see if/what it holds, find out real battery condition. The battery distributors (not just the local auto parts store) often have fairly exotic battery testers these days that do more than plain load-and-voltage testing, and many will take a battery, place it on a proper heavy charger, try to form it up, and not just sell you new batteries.

Never hurts to ask.

Otherwise...you may be able to borrow ("rent" free) a load tester from a local auto chain like Advance or Pep. And consider buying a high capacity shore charger, to take each one ashore and put that proper full & equalization charge on it, cycle it a time or two to see if it holds a load better afterwards.

Assume nothing, verify everything. And if you do have to buy new batteries--that's the right time to make 100% sure your whole power system is set up to pamper them, and operating correctly.
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Old 27-02-2012, 12:06   #8
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Re: State of Batteries

Measure the specific gravity in each cell and report back. That will zero in on the problem much faster than anything else, and it's easy and cheap to do.
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Old 12-03-2012, 06:40   #9
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Re: State of Batteries

Got back to the boat finally and measured the specific gravities of each cell as follows:
Battery 1 - all 1320 except 2 that I had only just topped up with water.
Battery 2 - all 1320 except cell 2/2 - 1200
Battery 3 - all 1320 except 3/6: 1300
Battery 4 - all 1320 except 2 I topped up with water.

I ran a household heater via the inverter, pulling 165A. 20 minutes later, voltage fell below 10.5V and the inverter cut out. Battery temperature rose from 45F to 50F.
Within a couple minutes, voltage was back up to 12.5V

I tried plugging the shore power into the boat - but it seems the resistance in my 100' extension cable was too great - and after about 5 minutes, the GFi popped. So I can't really equalize the batteries until I'm in the water at a dock with a decent cable to work with.

My conclusion is that I have one cell that's bad (2/2) and basically everything else is OK. The 165A draw is probably a tough test - not sure how long the batteries should be able to manage it... Or am I full of mis-placed optimism?

Thanks,
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Old 12-03-2012, 07:42   #10
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Re: State of Batteries

Bill-
If you had just charged the batteries and knocked off the float charge, AFAIK you would see a specific gravity of 1.265 at 68F/20C for a brand new fully charged battery. If you are seeing 1.320 that's kinda odd, ignoring temperature compensation (are you in Mass? in the 50s? colder?) I'd suspect you're measuring float charge and that the batteries need to be recharged and let stand overnight before retesting.
That the cells are almost all the same is good, the bad cells indicate maybe that one battery will need to be replaced (or removed) and the rest retested.
Bear in mind, if your power cord and charger won't handle equalizing all four at once, it may still be feasible to move the battery cables, and just equalize one at a time, for the three good batteries, then see if #4 can be helped.
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Old 12-03-2012, 08:30   #11
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Re: State of Batteries

I assume your charger is part of an inverter/charger. Can you set it to draw less power from your cord - say 10 amps? My Victron unit allows this.

The behavior of your batteries under load (very quick decline of voltage after a full charge) is pretty normal behavior with a batteries that are on their last legs. While five years is short for Rolls, it's about average for standard deep cycle batteries. If the Rolls haven't been treated well, it's quite possible that they are done.

I'd try all of the things suggested to get the batteries back but - and I speak from experience - you don't want to go cruising without confidence in your battery bank. It may be best to replace the bank now when you can shop for good prices and have lots of time for installation rather than deal with a failure in Nantucket harbor on 4th of July weekend.

Carl
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Old 12-03-2012, 12:42   #12
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The bad news

I believe that your problem is that Rolls batteries, in general, have too high an internal resistance for use with power inverters driving microwave ovens, etc. compared to almost any other battery type pound for pound.

I have never measured a Rolls internal resistance that was "worthy" of driving heavy loads. They are, therefore, good for long light loads. This is one problem with very thick plates.

Do yourself a favor and buy a battery having known low resistance. If you buy a high quality AGM, for example, you can cut your bank size in half and get better results.
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Old 04-06-2012, 14:20   #13
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Re: State of Batteries

So finally we're on a dock and connected to a good supply of power via a proper cable... so now I can charge with the Prosine 2 inverter/charger... and I got to equalized the batteries on Saturday - maybe...

This is my first experience with wet cell batteries and therefore with equalizing too...
I started by measuring each cell with a hydrometer. It is marked from about 1100 to 1300 - which I presume is probably meant to mean 1.1 - 1.3? It's also handily marked with anything over about 1250 in green - good and below in red - bad! At last, something a bumpkin like me can understand.

Bearing in mind that I had to top up some cells first, I got hydrometer readings all over the place, with several cells at 1300+ and some at below 1200.

I don't find the Prosine very user friendly - but it said it was set for a maximum voltage during equalizing of 16V. I turned it on... and I left it on for 3 hours.

The voltage remained at 14.3V throughout the whole time (as displayed at the panel and as measured across the terminals using a voltmeter).

I had the caps open and the cells merrily bubbled along through the whole process and yes, my propane sensor went berserk!

After the three hours, I did not need to replace any fluid. I measured all the cells again and all but 2 cells topped the scale, and the two that didn't read 1300.

So... I'm not sure that I equalized anything - since the voltage never went over 14.3V. But I did get the SG up - to probably where it should be - so is that good enough?

Thanks for any assistance...
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Old 04-06-2012, 14:24   #14
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Re: State of Batteries

Fully charge batteries first then equalize.
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Old 04-06-2012, 14:27   #15
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Re: State of Batteries

Of course you DID also dip a thermometer into each cell, so you could compensate the hydrometer readings for internal battery temperature?

Funny how nobody makes a hydrometer with a thermometer built into it. Or have I just been looking in the "toy" aisles?
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