Re: [Elecraft] KX3 Please evaluate LiFePo4 battery/charger choice, UPDATE
That is very reassuring information, Fred, thank you. So I understand you are using two fuses, one for each pole. What amp rating? My PCM includes overcurrent discharge protection at 42A with a protection delay time of 20 ms. Does that sound like it has the fuse built in? 73, Arno K7RNO __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] KX3 Please evaluate LiFePo4 battery/charger choice, UPDATE
On 11/22/2013 11:00 AM, Arno Dienhart wrote: So I understand you are using two fuses, one for each pole. What amp rating? Yes, I put a fuse in each lead. They're 5A fast-blow, they're supposed to open in less than 2ms. I decided to tolerate the tiny increase in resistance for the protection. I used the blade type automotive fuses, they make a really good, low resistance contact in the holder. My PCM includes overcurrent discharge protection at 42A with a protection delay time of 20 ms. Does that sound like it has the fuse built in? Yes, it does, and it probably will reset once the overcurrent condition is removed. Many of these packs that are capable of dangerous discharge currents seem to have them these days. LiFePO4 batteries like to be stored at less than full charge ... around 2/3 - 3/4 or so. My charger has a storage cycle on it that charges to full and then discharges to 2/3, keeping the cells balanced. 73, Fred K6DGW - Northern California Contest Club - CU in the 2014 Cal QSO Party 4-5 Oct 2014 - www.cqp.org __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] KX3 Please evaluate LiFePo4 battery/charger choice, UPDATE
On 11/21/2013 4:26 PM, Arno Dienhart wrote: When I hooked it up to the KX3 in RX (170mA draw), it started showing 13.5V and rapidly sunk to 13.1V within five minutes. Now, after ten minutes, it seems to have settled at 12.9V. Is this normal for such a battery, to have such a large difference between no load and small load? And also, is it normal for the Voltage do go down quite rapidly during the first few minutes? Yes and yes. That's what my A123 pack does. Right after a full charge, voltage is about 14.8/9 no load, and 14.1 or so with K2 receive load [~270mA]. It drops fairly quickly [minutes] to 12.8 or so. It will stay there or very close, dropping to perhaps 12.2/1 under full TX load, until near full discharge. At that point, the voltage falls very fast, resembling the glide angle of a brick. I charted mine using the K2 in RX as a load since it is constant, but will trip out on low voltage before discharging the pack too far. Incidentally, the internal resistance of an LiFePO4 pack is extremely low and they'll deliver 20-30C or more into a short circuit, so don't do that to them. :-)) I recommend fusing the power leads close to the battery and using fast-blow fuses. It will add a little resistance in your power leads, but it's a lot better than smoke. With two fuses, my stable RX voltage starts at about 12.8, and on TX [5W, ~1.7A depending on band] goes to about 12.1V. I'm fairly certain that is drop in the power cable and fuses. Radio works super. And, FWIW: I've never gotten my pack below about 30%. Made 30 CW Q's on W5N/RO-015 on day 1 and 27 on W5T/DE-003 on day 2 and it was at 30% when we got back to Mike's in El Paso that night. Really remarkable batteries! I'll run it down, verify that the under-discharge protection works, and then charge it again for a longer time to make sure balancing sets in and does its magic, if needed. I'm no battery chemistry expert, but I don't think running them down, like NiCd's, [except maybe to check the protection as you say] is necessary or desirable. I do know they like to be stored at around 2/3 charge, my charger has a mode to do that. 73, Fred K6DGW - Northern California Contest Club - CU in the 2014 Cal QSO Party 4-5 Oct 2014 - www.cqp.org __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
[Elecraft] KX3 Please evaluate LiFePo4 battery/charger choice, UPDATE
Thank you all for your help and suggestions. I wanted to stay small and lightweight, so I stayed with my original 3 Ah LFP from Bioenno. It arrived today in the mail, a very nicely covered pack (thin but firm, fully enclosed rectangle package, not just an open shrink tube over some cells). Anderson power poles already installed on battery and charger, so all an instant fit. It came with 14V on my external meter and charged up to 15.4V. When I hooked it up to the KX3 in RX (170mA draw), it started showing 13.5V and rapidly sunk to 13.1V within five minutes. Now, after ten minutes, it seems to have settled at 12.9V. Is this normal for such a battery, to have such a large difference between no load and small load? And also, is it normal for the Voltage do go down quite rapidly during the first few minutes? I'll run it down, verify that the under-discharge protection works, and then charge it again for a longer time to make sure balancing sets in and does its magic, if needed. Thank you for sharing your advice. 73 de Arno, K7RNO __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
