Allan S. sent follow up queries after my response to Drake's dilemma. Allan's queries are pasted below.
Mick here: Sorry I didn't state my suggestion more clearly but, yes, in this situation the only way to know if the battery is worth trying to salvage is to pump it up nicely with a bunch of energy (meeting the battery mfr's "full charge parameters" or as close as possible)...shut off the generator & shut off the solar array...set the Tri-Metric (or other shunt based monitor) to measure "amp hours from full" & make sure the counter is starting at 0.00 amp hours from full...then impose loads on the battery bank & let it all run until the inverter shuts off due to low battery voltage. (The loads don't have to impose a steady "20 hour discharge rate" & we're not trying for laboratory accuracy. To give the battery a fair chance at proving its mettle, be sure the discharge rate is equitably chosen for the battery type & temperature, etc. To be "equitable", the servicing technician should run the test in a way that doesn't ask the battery to perform miraculously...just to perform within its design parameters.) Allan correctly states that 1.75 volts per cell is the "industry standard" discharge cut off point for lead acid batteries (@ 25 degrees C) so if the system is 48v nominal, that's 24 cells X 1.75 = 42.0 volts as the setpoint for the inverter's LBCO "low battery cutoff function". The amp-hour monitor will display the number of amp-hours that the battery was able to deliver before the inverter crashed on voltage & that value can be compared to the original rated capacity. So...although I must have muddled my explanation, Allan, the Tri-Metric type monitors can indeed measure & display the battery's amp-hour capacity. One must eliminate solar recharge during the test & any other variables such as generator run time...then there's only a battery, an inverter, some loads, and the amp-hour counting gizmo. >>An unhealthy battery will reach the failure point in a fairly short amount of time & for a fairly small amount of labor.<< A semi-healthy battery is a greater challenge because it takes longer to wring them out & the service tech may opt to educate the client on how to complete the "pump & dump" measurement after the tech leaves the site. If the client can be persuaded to install a shunt & an amp-hour meter, they'll also have better instrumentation in place to help them & their service technician down the road. Some clients will want to try an EQ charge or other measures & the ah counter will be able to display any improvements that result from those efforts...or the lack of improvements. As my Dutch solar buddy would say, "Meten is Weten": "Measuring is Knowing." A battery based energy system owner who only has a DC voltmeter is like a car owner whose only instrument is a tire pressure gauge. Definitely some clients balk at the expense & new learning required to retrofit a proper ah monitor, but better instrumentation may prove a good value to them in the long run. The Wrench List is the Bomb! Mick Abraham ---------- Forwarded message ---------- From: Sindelar Solar <al...@sindelarsolar.com> To: re-wrenches@lists.re-wrenches.org Cc: Bcc: Date: Wed, 21 Nov 2018 11:40:55 -0700 Subject: Re: [RE-wrenches] Batt Cap AGM Mick, While I fully agree on the importance of a monitor such as the TriMetric, I'm confused by some of what you've written below. A TriMet (or any similar monitor for LA) can measure amp-hours removed and replaced, but it can't measure & display the battery bank's amp-hour capacity. Only taking the time to drain the bank at a measured rate will do that, and I have yet to have a customer want to pay me to do a battery capacity test down to 1.75 vpc at the 20-hour rate - or any rate for that matter. The TriMet is set up such that the installer tells the TriMet the battery capacity. In a case such as this, what number would you program into the TM as the amp-hour capacity? How would you determine this value? Thanks, Allan -- *Allan Sindelar* al...@sindelarsolar.com NABCEP Certified PV Installation Professional New Mexico EE98J Journeyman Electrician Founder (Retired), Positive Energy, Inc. *505 780-2738 cell* Mick Abraham, Proprietor www.abrahamsolar.com Landline: 970-731-4675 Cell phone or for text messaging: 970-946-6584 ᐧ
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