Exactly. Products designed to SAE standards and OEM standards will be hardened against all sorts of things, including 24V applied to 12V products, reverse DC polarity, alternator load-dump transients, etc. Products generally available to consumers will generally not be designed to those requirements as it adds significant cost.
The general answer to the sine wave vs square wave question is that the square wave (the inverter industry calls it “modified sine wave”) is generally compatible with most loads. There are a few types of loads that get a bit hotter due to the steep rising edges of the waveform, and years ago there used to be some types of transformerless battery chargers (for portable tools, phones, and the like) that would actually fail, but we haven’t seen anything like that in a long long time. Jim Eichner, P.Eng. Compliance Engineering Manager Xantrex Technology Inc. e-mail: [email protected] web: www.xantrex.com <http://www.xantrex.com/> Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. From: [email protected] [mailto:[email protected]] On Behalf Of Doug Smith Sent: Monday, January 19, 2009 12:40 PM To: Price, Edward Cc: [email protected] Subject: Re: Cigarette socket in vehicles Hi Ed and the group, In addition to the 12/14 Volt question there are a few other points to consider. 1) pretty big fast transients from loads like the starter motor 2) load dump conditions (battery becomes disconnected when engine is running) where the alternator drives the voltage way above the normal ~14 Volts for a time. This is more common that you might think, these days caused by lead-free battery clamps failing. (Lead free battery clamps strikes me as a very bad idea and does not accomplish anything compared to the battery itself and the real source of lead from cars, the wheel weights flinging off wheels.) I have observed first hand one of these clamps failing during use and immediately replaced both clamps with nice lead ones. Automotive electronics are designed to withstand load dump conditions but your electronics may not be. Doug Price, Edward wrote: ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, January 19, 2009 6:37 AM To: Scott Xe Cc: [email protected] Subject: Re: Cigarette socket in vehicles Hello Scott, In the case of 12V accessories to plug in normally they have a regulator installed to prevent the overvoltage. Thank you. Rob Kado EMC Engineer - Module Laboratory Operations Chrysler Initial assumptions can be deceiving. I recently bought a Magellan GPS. It operates on 5 VDC, and came equipped with an external "cigarette socket" adapter. I assumed the cheapest, that there was a little resistor inside the adapter, or just possibly a cheap linear regulator. On taking the adapter apart (yes, I tend to do things like that), I was quite surprised to find a little 2 custom IC switching converter, with input inductors, filter capacitors and a hefty input overvoltage clamp. The input voltage range was not specified, but it seems likely to be capable of 24 VDC operation. Ed Price [email protected] <blocked::mailto:[email protected]> WB6WSN NARTE Certified EMC Engineer Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 Military & Avionics EMC Is Our Specialty - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
