> Typically batteries are only considered at their end of life until they > only test at 50% of original labeled capacity.
A rough guess for a marine deep cycle battery is that during a Reserve Capacity test if the under load voltage drops to 11v at less that half the run time the battery has less than 50% of the original capacity. > There is no need to go full discharge. If the battery is in known good shape you can extrapolate the capacity from a partial discharge. A defective battery may still work correctly and follow a normal discharge curve for a while, then rapidly it's voltage will fall off. Sort of like the "Discharge curve of SLA batteries" from here: http://www.steveduncan.net/html/discharge_testing_slas.html Testing those three batteries for 15 minutes would yield similar results, but only one battery has full capacity. Which is what you are saying with your junk batteries. So in some cases going to full discharge may make sense. Michael Brown Windburn C&C 30-1 From: Josh Muckley <muckl...@gmail.com> There is no need to go full discharge. The voltage and capacity properties of a lead-acid battery have a near linear relationship so a 50% discharge is fine for testing. That should be 11.6v. All of this is just a comparison. A brand new battery might show +/- 10% of the labeled rating. That doesn't mean that you got a good or bad battery. It's just an indication of how difficult it is to accurately measure the capacity. Typically batteries are only considered at their end of life until they only test at 50% of original labeled capacity. Capacity tests really are most powerful as a trending and comparison measurement rather than a go/no-go. I've successfully used 100Ah batteries that measured at only 7Ah. I know they are junk but keep them around for various workbench projects. I've even used them to successfully start my spare marine diesel sitting in the garage. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Feb 7, 2017 5:09 PM, "Michael Brown via CnC-List" <cnc-list@cnc-list.com> wrote: > If you have the original battery Reserve Capacity specs it is an > acceptable quick test > to see if the battery is good but maybe worn or at end of life. > > If possible test the battery(s) individually, Charge fully, bring battery > to around 80F and > time how long it will sustain a 25 amp load before reaching 10.5v. Note > that takes the > battery to almost complete discharge and may significantly shorten it's > life. If the voltage > gets to 11.0v and the time is less than half the RC spec there is not much > to be gained > testing further, the battery is worn out. > > The 10.5v sounds pretty bad but that is an under load voltage and is > different from an > at rest voltage. > > Michael Brown > Windburn > C&C 30-1 > > > > _______________________________________________ > > This list is supported by the generous donations of our members. If you > wish to make a contribution to offset our costs, please go to: > https://www.paypal.me/stumurray > > All Contributions are greatly appreciated! > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://cnc-list.com/pipermail/cnc-list_cnc-list.com/attachments/20170207/5b985121/attachment-0001.html> ------------------------------ Message: 4 Date: Tue, 7 Feb 2017 17:44:53 -0600 From: Frederick G Street <f...@postaudio.net> To: cnc-list@cnc-list.com Subject: Re: Stus-List Battery test Message-ID: <31218ecf-62be-4a0e-83ec-552d052b5...@postaudio.net> Content-Type: text/plain; charset="utf-8" I think I?ll stick with my Midtronics conductive tester; good, accurate results on the health of my golf-cart and start batteries, it only takes a minute, and no chance of starting things on fire? :^) Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^( > On Feb 7, 2017, at 4:52 PM, Josh Muckley via CnC-List <cnc-list@cnc-list.com> > wrote: > > There is no need to go full discharge. The voltage and capacity properties > of a lead-acid battery have a near linear relationship so a 50% discharge is > fine for testing. That should be 11.6v. All of this is just a comparison. > A brand new battery might show +/- 10% of the labeled rating. That doesn't > mean that you got a good or bad battery. It's just an indication of how > difficult it is to accurately measure the capacity. Typically batteries are > only considered at their end of life until they only test at 50% of original > labeled capacity. Capacity tests really are most powerful as a trending and > comparison measurement rather than a go/no-go. I've successfully used 100Ah > batteries that measured at only 7Ah. I know they are junk but keep them > around for various workbench projects. I've even used them to successfully > start my spare marine diesel sitting in the garage. > > Josh Muckley > S/V Sea Hawk > 1989 C&C 37+ > Solomons, MD -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://cnc-list.com/pipermail/cnc-list_cnc-list.com/attachments/20170207/77e0f58a/attachment-0001.html> ------------------------------ Message: 5 Date: Tue, 7 Feb 2017 19:53:46 -0500 From: "Rick Brass" <rickbr...@earthlink.net> To: <cnc-list@cnc-list.com> Subject: Re: Stus-List Battery test Message-ID: <00a101d281a5$cdfc32d0$69f49870$@earthlink.net> Content-Type: text/plain; charset="us-ascii" Joe; Not to be argumentative, but the Amp Hour rating for a battery is by definition based on the current the battery will provide that results in it being fully discharged over 20 hours. For a typical 12 volt group 27 or 31 battery in the 100 AH range, that's about 5 amps of current. For a 4D or 8D you might be in the in the 10A range. For a set of 4 GC5 golf cart batteries wired to be a 12v bank at 480AH, maybe 24A. Deep cycle batteries typically have the AH rating on the label. So you could take the total of the AH ratings for the bank you want to test (My house bank happens to be 4x115=460AH when new. ) divide by 20 and get the current flow that you want to use as to measure your AH capacity. Then discharge the battery to 50% as you suggest (about 10 hours, give or take a bit) and you can calculate the AH capacity you have. Regarding your suggestion to use a 20A discharge rate, by definition the Reserve Capacity of a battery is the number of minutes that a battery will deliver 25 amps of current before being fully discharged. That's because a typical automobile uses about 25A of current to run the ignition, lights, wipers, and other essential systems (not the air conditioner, GPS, or stereo). The reserve Capacity is intended to tell you how long you have to get to the mechanic after you have a failed alternator or a broken alternator belt. A typical BCI 27 automotive battery with about 100AH rating would typically have something like 160 minutes reserve capacity. 25Ax2.67hr=66.75AH - far less than the AH rating of the battery because of Peukert's Law and the impact of discharging at the higher rate. AmpHour capacity and Reserve Capacity are not the same thing The real AH capacity of a battery bank decreases over time; with each discharge/charge cycle of the battery the capacity decreases slightly. I already indicated in a earlier post that my house bank (460AH when installed in 2010) is down to about 400AH based on the information from my LinkLite. Len, you indicated that your boat already has a Link battery monitor. If you fully charge the battery, "synchronize" the monitor, open the circuit from the solar panels to take them out of the system, and then wait a few hours you can get the information needed to calculate the total AH capacity of the bank when you "synchronized" the meter. You just need the total for amp hours used and the percentage of capacity remaining to do the arithmetic. I wonder why you are looking for another method? Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Della Barba, Joe via CnC-List Sent: Tuesday, February 07, 2017 10:15 AM To: 'cnc-list@cnc-list.com' <cnc-list@cnc-list.com> Cc: Della Barba, Joe <joe.della.ba...@ssa.gov> Subject: Re: Stus-List Battery test Easy cheap way. If you have accurate volt and amp meters, a 20 amp (or near enough) load applied for enough time to drain the batteries 50%*. You should see 12.2 for wet cells and 12.3 or so for gel/agm. Light loads like 1-5 amps and heavy loads like 50-100 amps both will be inaccurate because of Peukert's law. This law deals with the fact that a 100 AH battery can supply 100 amps for 1 hour or 1 amp for 100 hours in theory, but in practice 1 amp will last longer than 100 hours and 100 amps won't make the full hour. 20 amps is a good value for these tests. * (AH capacity of batteries/load in amps) /2 = time in hours for 50% discharge From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Russ & Melody via CnC-List Sent: Tuesday, February 07, 2017 00:41 To: cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> Cc: Russ & Melody <russ...@telus.net <mailto:russ...@telus.net> > Subject: Re: Stus-List Battery test Hi Len, If you're 100 percent full and have a coffee in your hand, may I suggest some advice from Bobby... and words I live by. Don't warry. Be Happy. Cheers, Russ Sweet 35 mk-1 At 07:28 PM 06/02/2017, you wrote: I think the CBA would work well so far from the little reading I have done. I have four 6 volt deep cycle batteries for my house bank and a Link monitor. I also have a simple analogue load tester. The problem is the solar panel masks any shortfall in the bank by fully charging usually before I make coffee in the morning. The house bank isn't quite as full on a rainy day and everything works but I would like to know how well. I probably should just leave it alone but if the bank is 100% charged but at 50% amp hour capacity I want to know. Len -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://cnc-list.com/pipermail/cnc-list_cnc-list.com/attachments/20170207/523a7d85/attachment.html> ------------------------------ Subject: Digest Footer _______________________________________________ CnC-List mailing list CnC-List@cnc-list.com http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com ------------------------------ End of CnC-List Digest, Vol 133, Issue 23 *****************************************
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