The method Dave showed is the simplest and least expensive solution - other approaches are possible as well, such as diversion regulation with a dump load via a solid-state relay for example.
In most utility back-up applications, this simple "on-off" approach is acceptable as the loads will be consuming most or all of the output of the grid-tie inverter and some of the batteries power during a power outage. The control of the relay is simply to prevent an over-voltage condition for the batteries - not precise recharging regulation. This is acceptable on an AC coupled back-up system since the battery will be properly recharged by the OutBack's built-in battery charger once the grid has returned. For off-grid AC coupled applications - I would advise using a more sophisticated approach to controlling the battery recharging process by using a dump control system. This also puts the excess power produced by the system to a good use - such as space or water heating. If you would like more information or assistance with these types of applications, contact myself or OutBack's application engineers & technical support people. Christopher Christopher Freitas Director of Research and Development OutBack Power Systems, Inc. [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> Tel 360 435 6030 Cell 360 202 4239 19009 62nd Ave NE Arlington WA 98223 USA www.outbackpower.com <http://www.outbackpower.com/> ________________________________ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of mick abraham Sent: Wednesday, November 05, 2008 9:39 AM To: [EMAIL PROTECTED]; RE-wrenches Subject: Re: [RE-wrenches] AC coupling Dave Katz sent a drawing which breaks the AC connection between grid-tie inverter and battery based inverters when the battery voltage is high. I've seen similar sketches from others. Thanks as always, Dave...but it seems that in this arrangement the amperage to the battery is either 100% on or 100% off, with no finely tapering pulse width modulation as is commonly preferred for a good finish charge. On/off hysteresis would be relatively slow just as in the days of Trace C-30 type charge controllers. Is there a "shift to float voltage" with this simple setup? What about temperature compensation? Those are not accusations, just questions because I'm unsure whether the Outback auxiliary control output manages using those factors. If the battery lifetime suffers because of rough management at the end of charge, that's a hidden cost which reduces the appeal of using a simple AC relay. "Pulse width modulated" diversion into a dump load may be better for the battery (especially with float mode and temperature compensation)...but that requires a controller, dump resistor, & circuit for relatively high amperage DC at the battery voltage, so there goes part of the cost benefit of AC coupling. One must weigh the cost of fancy charge control methods against the cost of possible battery degradation using the simple method in Dave's drawing. The battery degradation cost (if any) is difficult to predict, and may vary from one installation to another. If the AC loads during the daytime are big relative to the array size, the battery may only be receiving a trickle charge anyway. Mick Abraham, Proprietor www.abrahamsolar.com <http://www.abrahamsolar.com/> Voice: 970-731-4675 ________________________________ _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org <http://www.members.re-wrenches.org/> ------- End of Original Message ------- MESSAGE CONFIDENTIALITY NOTICE: This message (including attachments) is covered by the Electronic Communication Privacy Act, 18 U.S.C. sections 2510-2521, is confidential, and may also be protected by attorney-client or other privilege. If you believe that it has been sent to you in error, please do not read it. If you are not the intended recipient,you are hereby notified that any retention, dissemination, distribution, or copying of this communication is strictly prohibited. Please reply to the sender that you have received the message in error, then delete it. Thank you.
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