SLA Battery charge Level
Locked
 
|
I said:
"When the battery is exactly at 13.8 volts, there would be no current." Bob, G3VVT said: "In practice found over the many systems worked on professionally this is not entirely correct. However if one monitors the battery over a longer period after the float charge period has started the battery will start to take a small charge that eventually settles on the 25 to 50 mA region for small SLA's. It all depends on the float voltage and the size of the SLA, but with a float voltage of 13.8V and a 12V SLA does definitely occur." ----------------------------------------------- Yes, I was over-simplifying it. But a battery at 13.8 Volts will not take a charge with a 13.8 Volt source. What happens I assume is that the battery discharges a bit so it is lower than 13.8 Volts, and then the trickle charge commences. -------------------------------------------------- John said: "1) The total charging time using your method would probably be longer than forcing 1.6 amps until the terminal voltage reached 14.2. But it might also be healthier for the battery." -------------------------------------------------- Yes it will take a lot longer (overnight), and not overheat the battery, but this is how the original Powersonic recommendations were in the 1990s. I imagine they have changed. --------------------------------------------------- John said: "2) If the SLA voltage got below 10.5 volts, you might initially draw more than 1.6 amps, unless your 14.39 volt power supply is limited to 1.6 amps." --------------------------------------------------- Yes this is true. But the powersonic web sight had recommendations for the amount of drain a _gell_ cell would take before it was permanently damaged. It might have been 10 or 10.5 volts. I think I chose 10.5 volts in my design, so the batteries would not suffer from over-discharging. I also monitored the voltage discharge during use so I would not damage the batteries. --------------------------------------------------- "John said: I'm in the process of building a computer-controlled (PIC-controlled) SLA charger to enter into my local QRP club's annual builders' contest next Spring...." --------------------------------------------------- This is very exciting. Please let us know about the results. If you could leave the divice in the circuit during use you could design it to warn the user when the voltage of the battery was getting near the danger point. ----------- -------------------------------------- I have had some requests for my circuit. Actually the ideas might help John in his design too. I will post the info on my website soon and let the list know. Regards, Steve, W2MY/5 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.806 / Virus Database: 548 - Release Date: 12/5/2004 _______________________________________________ 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 |
|
|
In a message dated 12/12/04 14:48:57 GMT Standard Time, [hidden email] writes: Yes, I was over-simplifying it. But a battery at 13.8 Volts will not take a charge with a 13.8 Volt source. What happens I assume is that the battery discharges a bit so it is lower than 13.8 Volts, and then the trickle charge commences. -------------------------------------------------- I still maintain that even with the supply source at 13.8V, there will be a small, but finite float current drawn by the battery and am anxious to dispel the idea that the battery will not take any current at all when on normal float service when fully charged at 13.8V. The 12V 7Ah SLA batteries I obtain surplus from security alarms are marked with their float maintenance current. It will of course depend on the actual float voltage in the alarm panel to the float current taken by the battery, but there will always be some. This factor can be used by the alarm technician in part as an indication as to the state of the battery, if it was going high impedance or had leakage across the cells. Normally the batteries are changed routinely long before this would happen. I had believed in the past that once a battery had reached it's peak charge that on the nominal float voltage for the type of battery in use the current into the battery would fall to zero. In practice was to find out over the years that it does not. Had an occasion a few years back to test this out when adding an emergency back up battery to our local low power UHF repeater. This is fed with an Advance/Gould 13.8V stabilised PSU that had been set at 13.80V. The SLA battery was nominally charged before installation and when first connected to the PSU the battery drew about 250mA for a short period then fell back slowly to a constant 25mA which was maintained from then onwards. The voltage remained at 13.80V. At this point I rest my case and beg to differ. With regard to the lowest voltage a lead acid battery should be taken to in service, in the telecom, fiber and microwave systems I was involved in maintaining, these had their LVD (low voltage disconnect) points set at 1.75V per cell. This equates to 10.5V in a 12V battery system. There are deep discharge batteries available a much higher costs, but am led to believe that a normal lead acid battery could be permanently damaged in available capacity by deep discharging. With this in mind and using normal SLA batteries, fitted 10.5V LVD devices to the two local amateur repeaters that both use 13.8V power systems. Bob, G3VVT _______________________________________________ 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 |
|
|
Gang,
The Knightlites Milliwatt 'test is coming up. Sounds like fun. Was checking out my K2 at low outputs to see if there are any problems. Got a problem. When I set the tx below about 1/2 watt I get no output. Appears to work reliably at 0.5w but not below that. Works most all the time at 0.4w. If I set it to 0.1w, which is what I'd like to use, it may work for a while. Pressing 'Tune' when set to 0.1w kills it consistantly. I can set pwr to 0.1w and press the paddles and it will (usually) continue to work for a while, then die. I haven't dug into it yet to check the ALC circuitry but am wondering if anyone else is having this problem. Did a Google which turned up nothing, so must not be too common. Even when there is no output the K2 power indicator shows 0.1 or 0.2 or 0.3 (it alternates between these) but an external meter correctly shows no output. Thanks for the BW. 73 de dave ab9ca _______________________________________________ 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 |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |