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Old 29-07-2013, 23:30   #31
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Re: Battery Capacity Access Problem

Hi again Brian,

The complexities of the lead acid cell, it's charging and discharging, voltages and SG variations are one of the reasons I feel that each battery in a bank needs to be treated as an individual. One of the things advised is to apply an equalizing chart regularly which forces the cell to gas which stirs up the electrolyte to combat stratification. If this is true then even measuring the SG, whilst probably the most practicable method of evaluating state of charge, is not completely definitive.

It is all these complexities and non quantified impacts and influences which have pushed my thinking towards recording amp hours in and out over a long term to validly evaluate the condition of the individual batteries in the bank. I would then retain those which still had a reasonable performance changing out individually only those falling below a certain criteria. What this would be I do not know yet.
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Old 30-07-2013, 05:41   #32
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Re: Battery Capacity Access Problem

Brian-This is just a nit but you have used a variation of your original assessment
Quote:
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.
a couple of times. You actually pulled 138.8 amp-hrs from your bank.

That said, we cruised the Eastern Caribbean in our trawler with a high daily usage/recharge rate with 12 Trojan T105 batteries in series/parallel. Your observation regarding your bank's operation is consistent with ours.

I also recommend that you do a carefully controlled C/20 test to ensure that the batteries have > 80% of their original capacity before heading off to the boonies.

As Gord said; the C/20 test is terminated when the bank voltage is 10.5VDC. Note that there are many pieces of rotating and electronic equipment that will not perform to specification at < 11.0VDC. However, if your bank produces 550amp-hrs when subjected to a 55A load for 20 hours with a terminal voltage of 10.5VDC, then the bank is performing correctly. Your electrical equipment may not run correctly, but your bank is performing to spec.
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Old 31-07-2013, 09:48   #33
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Originally Posted by transmitterdan View Post

Yes, that's right. But you haven't measured the charge level of your bank so you don't know what you have used. You have a huge bank so a C20 discharge is 1200/20=60A. That's about 750 watts continuously for 10 hours. After you do that then you have to let the batteries rest for several hours and check the voltage. It will probably be between 12.1 and 12.2 which is about 50% charge. Measuring the voltage with even 1A load will not give an accurate indication of charge. The resting period is very important to get an idea of state of charge using voltage.

Probably nothing happened to the other 39% because it's still in there.

In my view there is little point to a 1200AH bank unless you have at least C/10 an preferably C/5 charging capacity. For that you need minimum 120A charge source and preferably 200A charge source. That means multiple alternators, huge wire and big fuses. What good is a battery bank that lasts for 2-3 days and takes another day to recharge it? Answer: Not much.

Another point that was made earlier that is worth repeating is about recharge times. If the recharge time (12-16 hours) is longer than you are willing to wait there is a strong chance the bank will spend little time above 80% charge. This destroys almost as many batteries as over charging does.

If the SG's are good then almost certainly the batteries are working correctly. It's hard to understand what you want Trojan to do?
First off I can do without the snobish and condescending tone of this response, not all of us are are electrical engineers with your VAST inventory of knowledge.

Secondly for the benefit of everyone else I believe we have this problem resolved. I have finally heard back from Trojan and they are recommending that I A. Ignore the open circuit voltage readings that I am getting since as has been established here they are not accurate anyway and since this is a cruising boat we are living aboard and I cannot rest the batteries for the appropriate period of time because they are supporting our refrigeration and other ongoing house needs. B. Focus on the amps consumed to determine SOC and C. Confirm this with SG's taken periodically. So on Monday evening we turned our charger off and have been on batteries ever since. We have gone through just over 300 amps thus far and the batteries are doing fine with the SG's looking good. We'll continue to monitor things and will probably recharge in the 400 to 500 amp area depending on the SG's. Then it will be interesting to see how long it takes to put all this power back in.

Thanks for all of your responses.
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Old 31-07-2013, 10:15   #34
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Re: Battery Capacity Access Problem

Quote:
Originally Posted by brian.wagner View Post
First off I can do without the snobish and condescending tone of this response, not all of us are are electrical engineers with your VAST inventory of knowledge.

Secondly for the benefit of everyone else I believe we have this problem resolved. I have finally heard back from Trojan and they are recommending that I A. Ignore the open circuit voltage readings that I am getting since as has been established here they are not accurate anyway and since this is a cruising boat we are living aboard and I cannot rest the batteries for the appropriate period of time because they are supporting our refrigeration and other ongoing house needs. B. Focus on the amps consumed to determine SOC and C. Confirm this with SG's taken periodically. So on Monday evening we turned our charger off and have been on batteries ever since. We have gone through just over 300 amps thus far and the batteries are doing fine with the SG's looking good. We'll continue to monitor things and will probably recharge in the 400 to 500 amp area depending on the SG's. Then it will be interesting to see how long it takes to put all this power back in.

Thanks for all of your responses.
I think you may have taken TransmitterDan's response the wrong way. I found it straightforward and factual.
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Old 31-07-2013, 10:31   #35
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Re: Battery Capacity Access Problem

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Originally Posted by brian.wagner View Post
Thanks for all of your responses.

Sounds that Trojan told you pretty much what we told back on page 1. Most of us do hope it all works out and that you get a benefit from that large house bank.

BTW - I understand the reason for having a big bank even if your charging system can not charge at the max rate the batteries can take. It is to allow time, even if that it just between 50%-75% state of charge. But you really need to look into either a larger charging system (bigger charger with a Honda etc) or something like solar that will handle close to your normal daily use.
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Old 31-07-2013, 14:04   #36
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Re: Battery Capacity Access Problem

I have to agree with Cheechako re TransmitterDan's response, technical stuff quiet often comes across this way with no intent on the authors part to be snobish or condescending.

There are a number of reasons one may feel obliged to install a large hour amp capacity battery bank.

In my case I feel that I am not doing as much damage to the batteries if I only use 20 -25% of the available discharge, and, I like having the capacity to carry me thru a few days of overcast weather without having to resort to engine driven recharge methods, and, I don't like having to replace batteries on too short of intervals.

I recently replaced a Trojan that had been in service for seven years as part of a 4 bank installation. Before extending my spread to 4 banks I had been getting only a year, or even less out of the batteries of just one bank.

Like a lot of other stuff I am finding that battery chargers seem to have a fairly short life aboard a boat and the high ampage ones are very expensive.

Having tired of buying battery chargers I am in the process of converting an old AC transformer welder into a high ampage DC source which I will feed to my solar regulators in parallel with the solar panel supply. The conversion involves reducing the number of secondary windings to lower the output voltage of the transformer and a bank of four 60 amp diode bridges to rectify the AC output. I have a 2.2kw 240V genset to power this arrangement from. Hopefully, in my case, this will take care of the large charging system as DonL has suggested.
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Old 03-08-2013, 18:01   #37
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Re: Battery Capacity Access Problem

Thanks again for all the responses here.

I was able to access all of my usable battery capacity and still maintain good SG's so I believe that concern is resolved.

As for replacing all those amps, I have a 2500 watt inverter charger powered by a Fischer Panda 6.5 Kw generator.

What I didn't mention earlier is that I also have 325 watts of solar that pretty much keeps up with the house load during the day when the sun is out, so with all of this I now feel pretty comfortable with my setup. At some point we may add wind and I would like to beef up our alternator. Aside from that, we're pretty happy at this point.

Thanks again.
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Old 03-08-2013, 18:14   #38
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Re: Battery Capacity Access Problem

Quote:
Originally Posted by brian.wagner View Post
Thanks again guys, but I still just must be pretty dense because I can't get around the idea that if I have a 1200 amp capacity bank I should be able to take more than 138 amps out of it before it needs to be recharged. There should be 600 useable amps right? If all I'm gonna get is 11% whats the point of having the 1200 amp hour bank and what happened to the other 39%?

I realize that there is merit to what some of you are saying about the 12.29 being under load and that without the load the voltage would be higher, maybe in the 12.40 range.

Still seems screwy to me and Trojan so far hasn't been very helpful. Once they saw that my SG's were good, I haven't heard from them again.
Not screwy at all.

The simple answer is: What you take out, you simply have to put back in. All you've done by vastly enlarging your house bank is to enable you to stay at anchor without having to charge for a longer period.

But then, you still have to put it all back.

i have so much trouble understanding why this isn't such a basic concept.

Say you have a thirst, and you drink 20 ounces of water in a given period. If you have a 40 ounce glass, and you agree that you won't ever drink more than half the glass (i.e., like battery capacity), then you have to refill that 20 ounces each time you take that 20 ounce drink.

Now, enlarge that glass to 2,000 ounces. You can take a LOT more drinks without refiling. Right?

But to get back to the "filled glass", whether it's 20, 20 or 2,000 ounces, you STILL have to fill it up sometime, right?

What's so hard?
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