Lee, I can see that you did not proof-read your mail, or you would have caught - the two zeners are chosen so the sum of the voltages is the desired output voltage *plus* the drop of the diode at the output. For example if you want 13.5V output then the two zeners must have combined voltage of 13.5 + 0.7 = 14.2V total, which would be a 6.8V and a 7.5V zener as closest match. - the text says two 6.2V zeners, which would add up to 12.4V only, the picture shows the (more appropriate) two 6.8V zeners, adding up to 13.6V but you recommend a regular diode, so the output to the battery is still too low at approx 13.6 - 0.7 = 12.9V It is simple to step up the zener voltage by choosing a next higher value for one zener or if you already have 6.8V ones from the balancer design, to add another diode in series to the zeners so the voltage drop across the two zeners also appears at the output due to the added diode drop canceling the output diode drop, this will give you 13.6V with two 6.8V zeners
PV panel+____/\/\____________|\|___12v Battery + . . . . . . . R1 . . | . . . |/| . . . . . . . . . . _|_. . . . D1 . . . . . . . . . . \|/ D2 . . . . . . . . . . -|- . . . . . . . . . . _|_/ . . . . . . . . . .//_\ . Z1 . . . . . . . . . . .| . 6.8v . . . . . . . . . . _|_/ . . . . . . . . . .//_\ . Z2 . . . . . . . . . . .| . 6.8v PV panel-____________|___________12v Battery - Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626 Skype: cor_van_de_water XoIP +31 87 784 1130 private: cvandewater.info http://www.proxim.com -----Original Message----- From: EV [mailto:[email protected]] On Behalf Of Lee Hart via EV Sent: Monday, June 13, 2016 10:25 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] Lead Acid charging...(trickle overcharging?) Cor van de Water via EV wrote: > For many years, I have used a "take-out" UPS battery > to keep my internet, WiFi and VoIP powered through regular power > outages, always floating it to 13.5V... I can second Cor's advice. 13.5v is a good float voltage; better than the usual 13.8v you'll find in most "float" chargers. Various sources recommend different float voltages for a 12v lead-acid battery, ranging from 13.2v to 13.8v. There are lots of "feathers on the scale" to lean in one direction or another. 13.5v is a good compromise. 1. 13.2v -------- no life reduction (can last 10 years or more) best with gel cells and old batteries best during hot conditions takes a month or more to fully recharge does not equalize cells battery sits at about 80% of its capacity AGMs never fully recharge 2. 13.5v -------- long life (5 years or so) gel cells, or old "sulfated" batteries will gas continuously best during average temperatures takes a week or so to fully recharge does not equalize AGMs battery sits at about 90% of capacity 3. 13.8v -------- widely used in consumer gadgets (float chargers, UPS, etc.) life only 2-3 years best during cold conditions takes a day or so to fully recharge can equalize (slowly) battery sits at about 100% capacity > So, it appears that a simple LDO regulated at 13.5V output will allow > your solar panel to charge but avoid over-charging. > Since solar panels may go as high as 18V when there is little load, > the regulator may see just over 2 Watts of dissipation 1 hour a day > so it should have a small heatsink or be bolted to a metal piece/case > if that does not create a short circuit. > NOTE: to avoid back-feed, you might want to set the LDO to 13.8V and add > a Schottky diode after it or test that the LDO does not sink current > when input is removed or insufficient, you don't want to add an extra > drain on this battery! These solutions work fine. Here are some others. You don't need precision regulation for a float charger, so a precision regulator IC isn't strictly needed. One of the simplest is simply a resistor, two 6.2v zener diodes, and a series blocking diode. PV panel+____/\/\____________|\|___12v Battery + . . . . . . . R1 . . | . . . |/| . . . . . . . . . . _|_/ . . . D1 . . . . . . . . . .//_\ . Z1 . . . . . . . . . . .| . 6.8v . . . . . . . . . . _|_/ . . . . . . . . . .//_\ . Z2 . . . . . . . . . . .| . 6.8v PV panel-____________|___________12v Battery - D1 can be any general-purpose diode (1N4001 etc). It's there so the battery can't discharge back into the PV panel or zeners, even if you connect some higher-voltage charger to the battery. R1 is chosen to limit the peak zener current in full sun. If you are using 1 watt zeners (1N47xxx or equivalent), limit the current to about 100ma. With 5 watt zeners (1n53xx or equivalent), limit it to 500ma. Most small PV panels (1 square foot or smaller) can't deliver more than 500ma, so R1 may not even be needed. Z1 and Z2 are zener diodes. Choose them so the sum of their voltages minus 0.6v for D1 is about your desired "float" voltage. For example, (2 x 6.8v) - 0.6v = 13v. Note that zeners usually have a +/-5% tolerance, so any given 1N5342B actually ranges from 6.8-5% = 6.46v to 6.8v+5% = 7.14v. The purpose of using two in series is that you can hand-pick them to get exact the voltage you want. You can also add another forward-biased diode in series with the zeners to bump it up 0.6v. For example, if the two zeners you bought just happen to both be at exactly 6.8v (giving you 13.0v), then add another diode like D1 (1N4001 etc.) in series with the zeners to get 13.6v. -- "IC chip performance doubles every 18 months." -- Moore's law "The speed of software halves every 18 months." -- Gates' law -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
