<html><body><span style="font-family:Verdana; color:#000000; font-size:10pt;"><div>During bulk charging, the MPPT PWM controller gives the battery all the amps it has available.</div><div><div><br></div><div>During absorption (when the "float" voltage is reached) the controller gives the battery all the amps it can accept without the battery voltage climbing further. The controller really is controlling the current (quantity of electrons) into the battery. If it did not limit/taper the amps, the battery voltage would continue to climb.</div><blockquote id="replyBlockquote" webmail="1" style="font-size: 10pt; border-left-width: 2px; border-left-style: solid; border-left-color: blue; margin-left: 8px; padding-left: 8px; font-family: verdana;"></blockquote></div><div>The PWM pulses are narrowed by the controller as the battery progresses through the absorption process. </div><div>Although the amplitude of the pulses stay the same, since the pulse width decreases, the average current flow into the battery does indeed taper off. Maybe the amps don't "technically" taper off, but the amp meter (which averages out the pulses) sure shows it happening. </div><blockquote id="replyBlockquote" webmail="1" style="border-left: 2px solid blue; margin-left: 8px; padding-left: 8px; font-size:10pt; color:black; font-family:verdana;"><div id="wmQuoteWrapper">-------- Original Message --------<br>
Subject: Re: [RE-wrenches] BZ Products Charge Controllers<br>
From: "Larry Crutcher, Starlight Solar Power Systems"<br>
<<a href="mailto:larry@starlightsolar.com">larry@starlightsolar.com</a>><br>
Date: Thu, April 11, 2013 2:32 pm<br>
To: RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>><br>
<br>
<div apple-content-edited="true"><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; border-spacing: 0px; font-size: medium;"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Hi Mark,</div><div><br></div><div>I am a real stickler about terms and I hope to always further understanding about batteries so consider this: No charge controller "tapers" charge current. The reduction in current is due to the slowing of the electrochemical process as the battery is saturated. At constant voltage, you can provide any amount of amperage to the battery but it will only absorb what it can. This is a common misconception that I hear regularly.</div><div><br></div><div>Once the battery reaches equilibrium, that is, current into the battery equals the self discharge rate, then it is in float. The process to reach float stage is called absorption stage. So I suppose we could call the two stages Bulk and Absorb/Float.</div><div><br></div><div>Larry Crutcher</div><div>Starlight Solar Power Systems</div></div></span></span><div><br></div></div></span></div></span></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline"></span> </div> <br><div><div>On Apr 11, 2013, at 9:43 AM, <a target="_blank" href="mailto:mark@hurshtown.com">mark@hurshtown.com</a> wrote:</div><br class="Apple-interchange-newline"><div><span style="font-family: Verdana; font-size: 10pt; "><div>I see what you mean by no float/3rd stage. Indeed the MPPT500 just tapers off the amps once it reaches the "float" voltage.</div><div><br></div><div>The MPPT250 however does have an undocumented(?) mode where once it thinks the battery is thoroughly charged, it only puts a brief burst of charge into the battery when the voltage sags to something like 13.8V. The first time I encountered this I thought I had a bad controller. This really does represent a form of float charge.</div><div><br></div></span></div></div><hr>_______________________________________________<br>
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