From owner-qrp-l@Lehigh.EDU Tue Jan 20 22:01:34 1998 Received: from fidoii.CC.lehigh.EDU (fidoii.CC.lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.8.5/8.8.5) with ESMTP id WAA07093 for ; Tue, 20 Jan 1998 22:01:33 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <12535-18730>; Tue, 20 Jan 1998 22:00:51 -0500 Received: from nss4.cc.Lehigh.EDU ([128.180.1.13]) by fidoii.cc.Lehigh.EDU with ESMTP id <12448-51240>; Tue, 20 Jan 1998 21:57:04 -0500 Received: from reg.seresc.k12.nh.us (reg.seresc.k12.nh.us [199.92.100.100]) by nss4.cc.Lehigh.EDU (8.8.8/8.8.5) with ESMTP id VAA113790 for ; Tue, 20 Jan 1998 21:57:00 -0500 Received: from jadepro.jadeprod.com ([199.92.99.51]) by reg.seresc.k12.nh.us (8.7.5/8.6.11) with SMTP id VAA17146; Tue, 20 Jan 1998 21:57:39 -0500 Date: Tue, 20 Jan 98 21:13:24 PST Reply-To: jadepro@jadeprod.com Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: Jade Account To: "Low Power Amateur Radio Discussion" Subject: Re: preventing destruction of gel cell? MIME-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=us-ascii X-To: Arjen.Raateland@vyh.fi, qrp-l@Lehigh.EDU X-PRIORITY: 3 (Normal) X-Mailer: Chameleon 4.6.5, TCP/IP for Windows, NetManage Inc. X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Message-Id: <98Jan20.220051-0500est.12535-18730+186@fidoii.cc.Lehigh.EDU> Status: RO Hi Arjen: I'm posting this to the list as well as yourself because you ask some very good questions, some of the best I have seen in a while. Your questions follow, and my answers are indicated by **** The schematic we are discussing is at: http://www.jadeprod.com/lovolt.html >Hello Dennis, >Thanks for the tip. I looked at the schematic and printed it. I assume >the relay is non-latching. Correct? ****Correct >What happens if the charger is in overcharge mode? The relay draws >current from the battery and so the charging current will never drop low >enough to end the overcharging state? ****If the battery is large, the 30 MA that the relay draws will affect the shutoff point somewhat, but this is not critical. If the battery is small, the the current is a significant factor. In this case the etch was layed out with several jumpers that are not shown in the schematic on the WEB page. A jumper "W4" can be used to change the cutoff current point, or if needed the overcharge region can be avoided althogether. Unitrode suggests that a timer can be used instead, the signal is available on pin 9 to control this. >I had this kind of problem when I used a LED and LM3914 voltage >indicator on a 2Ah battery being charged in O/C mode. It wouldn't go >back to float mode, because the LED circuit would keep the current draw >above the limit of 1/10th or what was it again. **** The current, known as Ioct is equal to 0.025V divided by the value of the sense resistance. In our controller this would be 0.5 Ohms for the 1/2A mode and 0.25 Ohms for the 1A mode; which means 50MA for the 1/2A and 100MA for the 1A mode. A battery in good shape will usually be well under these numbers when floating. As they age I have seen this current increase. >Perhaps O/C mode is not allowed with this protection circuit. **** See previous. >Using the trickle output is neat, but the protection doesn't work when >the charger isn't connected, I suppose. ****In this case the protection (reverse battery) is still there because of the PTC device. The Low Voltage protection still works too because diode D9 keeps the circuit alive until the relay drops out. >What would you say about a latching relay and a comparator circuit with >an external buffer stage coupling to the latching relay via a 1000 microF >cap and some hysteresis? Not my own idea, but it would be a separate >unit altogether and should be easy to apply. The latching relay is the >hard part for me. ****I'm not quite certain I know what you mean, but I suspect you could make it work. As others have suggested, a diode to prevent reverse discharge will keep the charger from drawing the battery down. Of course this means you have to increase the charger output to compensate for the diode drop. As far as the load (radio?) is concerned, put a DC powered relay in series with the radio power. Run the relay from an AC powered supply (Wal Wort?). Wire the relay so that it holds itself on. Use a few diodes to create an "OR" circuit that will keep the relay on when the AC power is there or if the battery is up enough. When the AC power goes away, the relay will stay on as long as the battery is up. When the battery starts to drop, the relay will drop and disconnect the radio. You may want some resistance in series with the relay winding to make sure it drops out at around 11 volts. ****This is just one possibility, there are many others. That is why I added so much circuitry to our battery controller series, these problems seem simple to solve at first, after all, it is only a battery charger. However, when one really looks at the problems involved, they are not easily solved. There are a number of less expensive controllers around but for around the clock "unattended" service they may not be adequate. >cheerio. >-- >Arjen Raateland >Finnish Environment Institute Once again, great questions Arjen, it is wonderful to see folks thinking about the technology. That is the joy of this list. Seeing all the problems with the power grid here in the Northeast USA this winter should send a message to us all to make sure we're "ready", you never know when those batteries could be needed. 72' Dennis, K1YPP ------------------------------------------------------------------------------ Jane Blanchard, KA1FUN, President -- Dennis Blanchard, K1YPP, Chief Engineer Phone: 603-329-6995 (Telephone hours 4 to 10 PM EST) Jade FAX: 603-329-4499 Products, Orders: 800-523-3776 Inc. e-mail: jadepro@jadeprod.com US Mail: Jade Products, Inc PO Box 368 East Hampstead, NH 03826-0368 See our Web Page: http://www.jadeprod.com/ ------------------------------------------------------------------------------