From owner-freebsd-questions@freebsd.org Tue Aug 9 16:22:54 2016 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 5206DBB37F8 for ; Tue, 9 Aug 2016 16:22:54 +0000 (UTC) (envelope-from freebsd@qeng-ho.org) Received: from bede.qeng-ho.org (bede.qeng-ho.org [217.155.128.241]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "fileserver.home.qeng-ho.org", Issuer "fileserver.home.qeng-ho.org" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id EB29C1D28 for ; Tue, 9 Aug 2016 16:22:53 +0000 (UTC) (envelope-from freebsd@qeng-ho.org) Received: from arthur.home.qeng-ho.org (arthur.home.qeng-ho.org [172.23.1.2]) by bede.home.qeng-ho.org (8.15.2/8.15.2) with ESMTP id u79GMjE4066291; Tue, 9 Aug 2016 17:22:45 +0100 (BST) (envelope-from freebsd@qeng-ho.org) Subject: Re: Power consumption tuning To: RW , freebsd-questions@freebsd.org References: <20160809172345.312117ac@e733> <20160809165640.5aa087c2@gumby.homeunix.com> From: Arthur Chance Message-ID: <8fd8eccc-aef7-eeaa-9851-b8ed03a6bfd8@qeng-ho.org> Date: Tue, 9 Aug 2016 17:22:45 +0100 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <20160809165640.5aa087c2@gumby.homeunix.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Aug 2016 16:22:54 -0000 On 09/08/2016 16:56, RW via freebsd-questions wrote: > On Tue, 09 Aug 2016 17:03:36 +0200 > Solène Rapenne wrote: > > >> Buying a device to measure the power consumption is also a good idea, >> so you can check your changes. >> It costs around 12€. Example >> http://www.ecvv.com/product/1000019919.html > > A lot of those cheap power meters will work with simple loads like > heaters or fridges, but are very inaccurate with computers. I have one > and I've heard a lot of bad reports about them. Clip-on type meters you get for measuring mostly whole house consumption don't handle reactive loads (basically anything with a motor) well and measure high. All the plug in ones I've tried work well enough, 1-2% variation between units on realistic loads, near enough to the readings of the industrial grade load monitoring I have on all my power circuits at home(*), but they can fail in time if mistreated. They also can be not very good with harmonic power but modern switch mode power supplies are supposed to keep that to a minimum. (*) Long story short: my wife's an energy consultant, advises both government and industry and helps energy conservation charities, and if it measures electrical power we've either got or tested at least one, often more. -- Schrödinger's cat had 18 half lives.