KBT2 charging
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According to the builtin volt meter on my K2, my old Astron RS-20A is putting out 13.3V (which I understand to be really more like 13.5-13.6 because of voltage drop across the diode). A couple questions regarding that and the KBT2:
1. Is that adequate voltage for charging the KBT2? The battery manual calls for 13.8V. 2. Is it OK to leave the red battery switch on the back of the rig ON whenever I'm using the K2 on the power supply...in other words, am I running any risk of overcharging the battery? Or should I switch the battery off unless I'm running from (or charging up) the battery? Thanks for the input! -- 72, Ron - W5RCM / ZS1MCD Austin TX / Hermanus ZA _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hi Ron,
The proper charging voltage is 13.8 V across the battery terminals (!). To get this voltage I have to supply my K2 (sn 2894) with ~14.1 V from the power supply because of the forward votage drop caused by the diode. Looks like you either need a separate power supply for charging or even better - an adjustable one. I am using Alinco DM-330MV which has an adjustable "PRESET" function. My PRESET is set for 14.1 volts and there is a little switch on the back of the PS which activates the preset voltage when I need to charge the battery. If you supply K2 with exactly 13.8 volts at the external power supply you risk damaging the battery by undercharging it (!) especially if you run K2 at the same time which will cause the voltage to drop further. You won't overcharge the battery as long as the voltage across the battery terminals does not exceed 13.8 Volts. The SLA battery will be in "float" charge mode where the battery will self-regulate the charging current when supplied with 13.5-13.8 volts. In this mode the charging current will equal the self-discharge current and the battery can (float) stay indefinitely in a fully charged state. Less than 13.5 volts is considered "undercharge" which will decrease the capacity of the battery and will lead to "sulfation" shortening its life. More than 13.8 V is charging mode (usually at around 14.1-14.5 until the current drops to a specific level indicating fully charged battery) but if the battery is already fully charged, then it will be overcharging if you maintain higher then 13.8 voltage. Both "undercharging" and "overcharging" will damage the battery and severe "overcharging" can damage even your K2. In overcharge mode the SLA battery produces excessive amounts of hydrogen and as the pressure builds up it is vented from a special relief valve, along with corrosive fumes from the acid and the battery dries out. When severely overcharged, the battery also heats up and as it heats up will accept more current and this will make it event hotter - it's called thermal runaway and the battery will be permanently damaged and may lead to damage of your K2 - not a pretty sight. If you have an adjustable power supply you can connect a DMM across the battery terminals and start slowly increasing the voltage until your DMM reads 13.8 V. Then disconnect the DMM from the battery and connect it to the power supply and note the voltage coming from the power supply. Maintain this voltage when K2 is not in use. This will keep the battery fully charged at all times. If you are using the radio and you are transmitting for prolonged periods of time it is better to check how much the voltage drops across the battery terminals when transmitting at full power with K2 and the radio is supplied with the voltage necessary to maintain 13.8 v at the battery terminals. If at full power the voltage does not drop under 13.5 volts you don't have to turn the battery switch off. You MUST turn the battery switch off when you power your radio from an external 12 V battery - for example when mobile with the engine not running. What I usually do is to charge my battery for few days when not using K2 - every 2-3 weeks, ill leave my battery on "float" for 2-3 days and then turn the battery switch off and use my K2 as usual. 73s Andrey E. Stoev KB1FZA ----- Original Message ----- From: "Ron McDowell - W5RCM / ZS1MCD" <[hidden email]> To: <[hidden email]> Sent: Thursday, May 19, 2005 10:20 PM Subject: [Elecraft] KBT2 charging > According to the builtin volt meter on my K2, my old Astron RS-20A is > putting out 13.3V (which I understand to be really more like 13.5-13.6 > because of voltage drop across the diode). A couple questions regarding > that and the KBT2: > > 1. Is that adequate voltage for charging the KBT2? The battery manual > calls for 13.8V. > > 2. Is it OK to leave the red battery switch on the back of the rig ON > whenever I'm using the K2 on the power supply...in other words, am I > running any risk of overcharging the battery? Or should I switch the > battery off unless I'm running from (or charging up) the battery? > > Thanks for the input! > -- > 72, Ron - W5RCM / ZS1MCD > Austin TX / Hermanus ZA > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by W5RCM - Ron
Dear Ron,
One thing to remember is that the internal voltmeter function of the K2 is specified as +/- 5%. When I read this spec as I was building my K2 I thought great that seems to be reasonably accurate. When I added the KBT2 option I ended up measuring the various voltages with an accurate (1% or better) meter. I then did the calculation, 5% of 13.8v is 0.64v, in otherwords the K2 could indicate anything between 13.16v and 14.44v!! This is without taking into account the voltage drop of the diode. My measuremets showed me that the voltage at the power jack was some 0.7v higher than the K2 displayed. Having adjusted the power supply I was using to give 13.8v on the K2 display, I quickly adjusted it back - I was actually feeding the K2 with 14.5v! 72's Tim M0CZP _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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