E-meters, We Love to Hate it! [RE-wrenches]

Tue Nov 21 16:43:40 EST 2000

Richard (and all),
    There's a "right-brain" balance thought I want to put out here that in
implicit but unstated in your posting.  It's in this part: "I watch the
ampere-hour figures in relation to battery volts and battery current.... I
check this against the ampere-hour count on the three meters and reset the
meters if necessary. "  You and Windy and some other well-respected souls
are "grandpa wrenches", from the days when there was no industry, and every
system included home-made parts.  The users were real pioneers, who were
themselves tech-heads,involved in their systems, nursing them along, living
well.
    I'm a "second-generation wrench", coming along when there's an
(admittedly immature and imperfect) industry.  My job is more selecting,
combining, and installing existing manufactured stuff than making it on a
lathe or soldering bench.  My customer base is different, too, especially in
Santa Fe, New Mexico.  Solar has a strong history here, in many forms, and
my average customer isn't a tech-head.  It's an average person who has seen
or heard enough by now to want an "off-grid passive solar straw-bale with
infloor radiant heat".  OK, only a few have that whole-enchilada view, but
my point is that it's critical that we install systems that take care of
themselves as much as possible.  Our average customer will never relate
amp-hour figures to battery volts, unless we're doing phone support with
them at the time.  And it's also why we ALWAYS include a good
monitor-generally a Tri-Met-in the system.
Allan at Positive Energy
-----Original Message-----
From: Richard Perez, Home Power magazine <richard.perez at homepower.com>
To: RE-wrenches at topica.com <RE-wrenches at topica.com>
Date: Tuesday, November 21, 2000 12:38 PM
Subject: Re: E-meters, We Love to Hate it! [RE-wrenches]


>Hello Wrenches
>
>These battery ampere-hour meters are essentially electron counters.
>The determination of when a battery is "fully" recharged is very
>difficult. Sometimes these meters go astray.
>
>The efficiency figure delivered by the amp-hour meter is coulombic
>efficiency, not energy efficiency. Since all batteries require
>several volts higher to recharge than they deliver on discharge, the
>energy efficiency is far lower than the coulombic efficiency. Energy
>efficiency in a L-A batt in good condition is between 82 and 88% for
>shallow cycle service such as encountered in a well designed PV
>system..
>
>I often see 98% and 99% efficiency figures from our E-Meters here.
>These high readings occur mostly during the summer when the battery
>is receiving gobs of overcharge and the nighttime discharge cycles
>are shallow, less than 8% DOD.
>
>Peukert's Equation is a mathematical description of an "average" L-A
>batt's ability to store charge (coulombs). This equation doesn't
>directly include factors such as self-discharge, cell impedance, and
>temperature. All factors which radically effect battery efficiency.
>
>In the case of the E-Meter, regular discharge cycles below 10% DOD
>are necessary for efficiency recalcs. The efficiency figure radically
>effects ampere-hour counting as the input amps are scaled based on
>efficiency. It's easy to see why these meters give erratic
>measurements during periods when the battery is not regularly fully
>recharged and also given a fair amount of over charge (about 5 to 10%
>of the capacity).
>
>I think that these meters deliver GREAT service and value for the
>$200 that they cost.
>
>We have both the E-Meter and the Tri-Metric running side by side in
>the same system. Our 24 Volt system also has a Heart/Cruising Link
>2000 two channel amp-hour meter. These three meters almost never
>agree exactly, but they are generally in the same neighborhood. They
>more closely agree when the batteries have been fully charged
>routinely.
>
>I watch the ampere-hour figures in relation to battery volts and
>battery current. We have our 24 Volt system (twenty L-16s) set pretty
>hot with voltage regulation at 29.5 VDC. Since our batts are in a
>heated box, they are always within a few degrees of 77 degrees F (25
>degrees C), so temperature is not a factor here. When the charge
>current drops to about 17 amps (C/100) at 29.5 VDC, I know that the
>battery is within a few percent of being totally recharged. I check
>this against the ampere-hour count on the three meters and reset the
>meters if necessary. The only time I see big differences between the
>meters (and reality) is when the battery is cycled deeply and not
>fully recharged for a week or more.
>
>I totally agree with Spark's comment on noise and the E-Meter. If
>there is RFI or even if there is a PWM charge controller, the E-Meter
>will give bogus ampere reading which will effect the ampere-hour
>count. The Tri-Metrics are much more noise immune.
>
>Hope this helps.
>
>Richard
>
>At 08:55 -0800 11/21/00, R. Sparks Scott wrote:
>> List;
>>
>> Recently, on another list I belong to, someone made the (outrageous)
>>statement that it required 2Ah of charging to replace 1Ah of consumption
>>from a battery bank. I made the retort that my E-meter is displaying a CEF
>>of 99%, and that it seems like I see almost exact Ah for Ah equivalents
>>when charging, i.e., a 45 Ah discharge being charged at 15 A usually takes
>>exactly three hours to full.
>> Got out the E-meter manual and did a quick study on Peukert's Equation,
>>and how CEF is calculated. OK, so CEF as displayed isn't actually the
>>batteries overall efficiency, but the logrithmic calculation of discharge
>>rate applied to charging.
>> So....If I'm seeing Ah consumption being replaced at 99% of
>>the charging
>>current (as calculated by the E-meter, and by direct observation), what is
>>the actual battery efficiency? Sounds to me like 99% of what goes in as a
>>charge comes out and is delivered to the load.
>> About the only thing I can think of that is that efficient is the
>>government's ability to waste my tax dollars. I smell a rat. Anybody care
>>to comment? Richard, you're the Battery Miester here.....
>>
>> -S
>>
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>------------------------------------
>Richard Perez
>Home Power
>PO Box 520, Ashland, OR 97520  USA
>Tele: 530-475-3179
>FAX: 530-475-0836
>Subscriptions: 800-707-6585
>mailto:richard.perez at homepower.com
>Web: http://www.homepower.com
>
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>
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>
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> RE-wrenches-unsubscribe at topica.com
>
>To check out the other RE-Wrench participants:
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>
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>
>For info contact list moderator by email:
> michael.welch at homepower.com
>
>___________________________________________________________
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>

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For info contact list moderator by email:
 michael.welch at homepower.com

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