Specific gravity test is overdue. The battery mfg should have float voltage recommendations. Rough area is 41v for 36v nominal pack.
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-------- Original message -------- From: john j casey <jjcrmc verizon net> Date: 5/17/17 11:52 AM (GMT-05:00) To: noaddress drmm net Cc: elec-trak cosmos phy tufts edu Subject: Re: (ET) E-15 not getting out of first speed
Would a specific gravity test be in order? Cheers, jack
On May 17, 2017, at 1:03 AM, David Roden wrote:
> On 17 May 2017 at 0:35, Briggs, Michael wrote: > >> I'm wondering if I'm just not charging long enough. I'm using a Landis >> charge controller. > > I would definitely try bypassing it. That said, if it's been undercharging > the battery for some months or years, the damage to the battery (hard or > permanent sulfation) is probably long since done. > > A sulfated battery will have a lower on-charge maximum voltage, lower > operating voltage, and reduced capacity. These phenomena aren't reversible > in any meaningful way; the damage is permanent. > > I already suggested measuring your batteries' voltage under load (while > driving the tractor and perhaps mowing). I don't see any other way you can > determine whether they can maintain enough voltage to run the tractor > properly without connecting a voltmeter to them and reading it under load. > Sorry, but "they can hold a charge well enough to mow for a while" doesn't > really tell us anything of value here. > > As for measuring their capacity, the easiest and cheapest (if approximate) > way I've found requires a 12v inverter, preferably with a capacity of at > least 1000 Watts; an AC powered analog clock with hands (check garage sales > and thrift stores); and a 120v load of some kind. > > The ideal load will put a 75 amp load on the battery, because then you can > compare the battery's actual measured capacity to its factory reserve > capacity specification. For a golf car battery, reserve capacity is > normally stated in minutes of operation at a constant 75 amps until the > battery falls to 5.25v under load. > > Most cheap inverters are around 70-85% efficient when running at around 2/3 > load. Let's take 80% as a reasonable approximation. If you have a really > good inverter with higher efficiency, just plug that value into the math > that follows. > > This is not lab equipment and the actual current and voltage will vary over > the test, but remember, I said this is an approximation! At an average of > 12v, an average 75 amp avg load will be an average 900 watts from the > battery. Allow for 80% efficiency and you get 0.8 * 900 == 720 watts of AC > load to put on the inverter output. This can be approximated pretty well > with three 250 Watt incandescent light bulbs. > > If all you have at hand is a small (< 1000W) inverter, you can still do this > measurement, but then you have to convert to amp-hours and adjust for > Peukert capacity. It's just a little more time and a little more math. > > Connect the inverter to a pair of charged 6v batteries in series. Set the > clock to 12:00:00 and plug it into the inverter, along with the lights. Let > 'er rip. > > When the batteries are effectively flat (around 10.5 volts under load), your > inverter should automatically shut down. You may have to keep an eye on it, > though, because some inverters will start up again when the battery voltage > rises after a rest, throwing off the test. > > When the lights go off and the clock stops, read the hours and minutes of > reserve capacity from the clock. Assuming you used 750W of lights, convert > to minutes and compare to the batteries' factory specification. Typical > golf car batteries' RCs are 105 to 125 minutes. A battery is considered > spent when its capacity is below 80% of specification. > > > David Roden - Akron, Ohio, USA > > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > Note: mail sent to the "etpost" address will not reach me. To send > me a private message, please use the address shown at the bottom > of this page : http://www.evdl.org/help/ > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > > > > > _______________________________________________ > Elec-trak mailing list > Elec-trak cosmos phy tufts edu > https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
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