++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Thu, 12 Apr 2001 23:44:46 -0600 From: Kevin Ferguson Subject: Re:[Elecraft] NiMh Batteries > > > NiMH cells get extremely hot if > you continue charging at rates above C/10 {rated capacity in Ma divided by >10} after they have peaked. Safe if solar cell capacity does not exceed this [Kevin Ferguson] The same is true of NiCads. BTW, both NiMH and NiCad may be routinely discharged to near 0% capacity without degradation. Any type (even deep discharge) of lead acid has trouble if routinely discharged below 50%. So if you routinely run your batteries down, then SLA weighs about 2X NiCad, and 3X NiMH for same "long term useful capacity". A _single_ NiMH or NiCad cell may be safely sischarged to zero volts. The problem comes with series strings, where the first cell to discharge may be _reverse_ charged by the others in the string...that can be bad, and is the reason that cells are matched for capacity in high performance applications (much as elecraft sorts the xtals for our rigs). I actually had to take large amounts of experimental data on SLA batteries at a previous job. The manufacturers say that discharge should not proceed below 10.5 V (for a 12 nominal Volt battery). According to my measurements, the battery was about 95% discharged when it got down that far. If you routinely discharge to such low voltage, you should anticipate that the battery will have reduced life. The downside is that Neither NiMH nor NiCAD likes "float" service (continual charge) Also, Lead-acid is better suited to Solar applications as its power-out/power-in effiency is much higher than other common types. NiMH are great if you can charge them from AC line just before use (or a day or two)...but they have an even higher self-discharge than LA If you like SLA batterys, you can do much better than the commonly available Power-Sonic gell cells. (Sonnenschein are nearly as bad a P-S, but venting is more reliable, IME)Panasonic, and Eagle-Pitcher both make "starved electrolyte" versions of the popular gell-cell batteries. These offer a lot of advantages....higher permissable charge& discharge rates, No "break in" needed. ~20% more capacity, Less likely to leak acid on over-charge (not theory, but personal experience talking here) The Gates cells, and large (car sized) Optima & Concord batteries are other examples of starved-electrolyte technology. Starved electrolyte is still Lead-acid chemestry, but with a couple of twists in the way it is done...especially WRT gelled-electrolyte construction. If there is interest, I can eleaborate on this. 73-ko0b +++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sat, 14 Apr 2001 16:33:36 -0600 From: Kevin Ferguson Subject: [Elecraft] More on SLA Batteries This turned into a real book, had no idea it would be so long when I started out. It is worth reading, even if you like the stock battery just fine, because I found a $20 source for replacements when I was doing some research for this. I know, I know: Lots of hams have been using lots of gell-cells for many years with nary a trouble....Follow all the rules, and you will be fine. But thier are other batteries that offer a degree of insurance, and some other advantages as well. This posting is about my experience with the difference between gelled-electrolyte (gell-cells) batterys, and so called AGM (_A_bsorbed _G_lass _M_at...basically a fibreglass sponge full of acid, has the same no-spill feature of gell battery) So you don't have to take my word for it, here is a URL for a company that sells both kinds.... http://www.windsun.com/Batteries/Battery_FAQ.htm This URL discusses batteries from the viewpoint of wind/solar/micro-hydro storage. Though we use smaller batteries, hams are concerned about a lot of the same issues. Of particular interest is the distinction between gelled-electrolyte, and AGM construction. Also If you are into off-roading, you know that the Optima battery is held in high regard for it's ability to run winches without complaint. Optima is a AGM design. Specifications for the elecraft supplied PS1229 battery may be found at: http://www.power-sonic.com/ There is no information given on the type of construction used. I have seen several Power-Sonic batterie split open and leaking gelled acid. I would be very supprised if they have moved to AGM construction, and think they would be bragging about it if they had. So why did I bother to learn all this stuff? Several years ago, I was involved in the design/installation/support of an electronic system that used a (nominal) 6Ah 12V battery as a sort of built-in UPS. Over several years, we built the systems using first Sonnenschein batteries, then Panasonic, Power-Sonic, and Finally Eagle-Picher batteries. With several hundred systems in the field, operating 24/7, many in "armpit" countries with unreliable power, I saw perhaps 50 or so battery failures. Also, as a sailplane pilot somewhat knowlageable about "electroniking" I see a number of failed batterys used to power aircraft radios and instruments. Most of these batteries are of the same size...roughly twice the capacity of the K2 internal battery. One very important consideration, that I have not seen in print, is that when overcharged, Gelled electrolyte batteries tend to first swell, then split open, and leak gelled-acid. I have seen both Sonnenschein batteries, and Power-Sonic do this. (These are the only two gell batterys we used) I do not feel comfortable having such a potential "acid bomb" in my radio, and certainly not in my airplane. Many of the pilots ignore my cautions, and continue with the gell-cells, as they are easier to find. I only wish I had pictures of those ruined electronic devices to use to convince them. Let me be perfectly clear that in all these cases, the acid leakage was due to overcharging, due either to component failure, or mis-adjustment of "float" voltage. I never saw a Gell-Cell fail catistrophically except due to overcharging. If a cell were to short, though, the remaining cells would be subjected to exessive voltage, even when the charger works properly. Yes this is abusive service, and against the battery manufactuer's reccomendation. Still, the two brands of AGM batteries I have used in the same systems & service, never did leak. We had several cases where the AGM battery lost its ability to hold charge due to too-high a float voltage, but did not leak. This is a much more graceful failure mode. Let me amplify the manufacturer's recommendation: DO NOT OVERCHARGE GELL-CELLS. It may be wise to anticipate component failure and build in some sort of over-voltage protection cercuit. If this is a crowbar circuit, make darned sure there is a fuse and/or diode between the crowbar device and the battery....On a power-supply, the crowbar shorts the output, and blows the fuse, no problem. On a charger, The battery could keep current flowing for a long time, cooking wires, starting fires, etc. A protection circuit is no good if it causes a larger problem than it protects from. Don't leave your K2 charging for extended periods. I'm not sure why the AGM doesn't split and leak: here are my guesses: Gas bubbles from overcharging "foam" the gell, and can't recombine because they are immobilized in t the gell. I think the AGM construction lets the gas move to whatever is used to catalyze the recombination cycle, thus avoiding over pressure. It may also be that the AGM battery is able to vent the pressure (they have safety vents built-in). The Power-Sonic battery did not have any vents. The Sonnenschein batteries did have vents, but still swelled and split. Perhaps the gell plugs up the vents? I never saw any evidence that the AGM batterys allowed any acid to come out thier vents. I fully admit that my evidence is purely anicdotal, and only includes 2 brands of each type of battery. Perhaps I rush to conclusion, but the evidence was compelling and convincing enough for me. Here is a URL for cross-referencing batteries by size. The PS1229 is not listed, but it is the same size as the PS1226 which _is_ listed. http://www.telesound.co.nz/battery_crossrefs.htm Interestingly the PS1229 has a noticeably higher rating than any of the other batteries with the same dimensions. This makes me suspicious. The others range from 1.9-2.3 Ah. This may be specsmanship. It may be due to extreamly thin plates (bad for durability). Maybe if you leave the vents out, you have more room for lead and acid. Interestingly, Power-Sonic offers batteries of the same exact size with published ratings of 2.0,2.6 and 2.9Ah. also very interesting is that in the sizes I am most familiar with Power-Sonic's gell-cell is rated 6Ah, and the AGMs of the same size are rated 7.2 & 7.7 Ah...hmmm? I actual service,even if these ratings are accurate, you may get more operating time from an AGM battery than a gell battery. If you operate for 1 hr.each day, then the larger rated gell battery may offer more operating time. If you want to do all you operating on the _same_ day, then you might actually get more Ah from the lower rated battery. As the battery is discharged the acid next to the plates is converted to water. The gell tends to immobilize the electrolyte, and you may have to allow the battery to "rest" a few hours so that the acid can diffuse back into contact with the plates. The AGM construction allows the acid to flow much more freely, and so AGM batterys do not suffer from this effect. So where do I get an AGM battery? I know for a fact that Eagle-Picher, Panasonic and Yuasa use AGM construction in the following batterys which according to thier dimensions should fit in the K2: Yuasa NP2.3-12 rated capacity 2.3 Ah E-P CF12V1.5 1.5 Ah* Panasonic LCR12V2.2P 2.2 Ah *The CF12V1.5 is slightly smaller (physically) than the others. It is the nearest fit EP makes. Of these, I brands, I would recommend the Panasonic, because I know that it uses starved electrolyte chemestry, in addition to being AGM. (More on that below) I have also had very good experience with this brand in the 7.2 Ah size. I have also had good experience with Hawker (Gates) Genasis batterys, (Who invented starved electrolyte concept) but they make nothing close to fitting in a K2 This place: http://www.batterystation.com/gelcell.htm Has a good price on the Yuasa, and also the Power-Sonic if you want to stick with that. ($20, take yer pick) Allied Electronics carries the Panasonic and E-P lines. The panasonic is cat. no. 884-0551 In my searching, I came across several other brands, but I could not determine if they are AGM design. UBC makes the UB1222, Portalc the PE12V2.2 I mentioned "starved electrolyte" above. Basically this means that there is not enough acid in the battery to completely convert the lead on the plates...the battery turns ALL the acid to water before it can be discharged deep enough to seriously damage it. Deep discharge erodes the plates of conventional batterys. There is some chemical "trick" needed in order to make the battery accept a charge when t he electrolyte is fully depleted, and I'm not sure exactly what it is, but it seems to work well. I think Gates/Hawker may have patents on this. That is way more than enough for one posting - -73- ko0b +++++++++++++++++++++++ To: elecraft at mailman.qth.net Date: Mon, 4 Feb 2002 13:24:16 -0600 From: n4so at juno.com Subject: [Elecraft] Panasonic Sealed Lead Acid batteries 2.3aH battery packs for external use with K1 or K2 Panasonic cellular and camcorder replacement batteries or battery pack Digi-Key catalog page 776, part nr. P179-ND 2.3aH at 12 volts, fully charged no load at 13.35 volts Digi-Key has the matching terminal clip (the clip is special to camcorder battery packs) Terminal clip for trickle charging= P260-ND Mating connector for Clip P260 = P261-ND The terminal clip is a fast disconnect clip for the camcorder battery pack. Power-Sonic has a battery charger for Sealed lead acid batteries, which will charge the Panasonic camcorder battery pack. Mouser part number 547-PSC12500A 12 Volts at .50 A which is a wall-mount plug-in unit at about $38. Attach the Digi-Key Terminal Clip and you are ready for charging. Ken Brown-N4SO Mobile, AL EM50tk Elecraft K1 at 5 watts/4 ele. yagi Keylite Kit keyer +++++++++++++++++++++++++ Date: Tue, 02 Jul 2002 19:54:21 -0600 From: "James R. Duffey" To: , Subject: [Elecraft] Gel Cells in the K-2 (and other battery powered rigs) Jeff - Your battery failure may be related to undercharging. To float charg= e a Gel-Cell, the battery should have 13.6 V to 13.8 V applied, limited to a current of 0.1 C or less, where C is is the amp hour (AH) rating of the battery. Many battery manufacturers print the exact float voltage on the side of the battery. It usually varies from 13.6 to 13.8 Volts. You should measure the voltage at the battery terminals (not the input to the K-2) and adjust it to the correct value. Too little voltage is as bad as too much. Don't take the stock answer of 14.0 V at the input of the K-2 as gospel, measure it at the battery. The ideal voltage for trickle charging a battery is that voltage where the current to a fully charged battery is zero. If th= e current is positive, the battery is being overcharged, and if it is less than zero, the battery is being undercharged, that is, the battery is supplying curent to the charger Overcharging a battery is as bad as undercharging it. Ideally, one would limit your charging of the Gel-Cell to 14 Hours at at a time at the 0.1 C level. If you can't rig up a timer, you might want to plug in the charger when you operate and unplug it when you stop, or a day later. This will increase your battery life over leaving it connected all the time. Fully charging a Gel-Cell is difficult. Triple charging is recommended; the battery is charged at constant current until an end point voltage of 14.4 V to 14.8 V is achieved. This can be done safely at 0.1 C, many batteries can be charged at 0.3 C, some batteries tell what this maximum level is on the side. After this voltage is reached, one switches to a constant voltage at 14.4 to 14.8 V, depending on the battery (check the side again), and it continues to charge until the current drops. After the current has dropped, the conventional trickle charge at 13.6 to 13.8 V kicks in. The Unitrode=A03906 IC charges batteries this way. A circuit using this triple charge method was in the handbooks for years. Again, voltages should be measured at the battery terminals, not at the input to the K-2. A compromise between the two techniques achieves better charging than the trickle charge, but is not as complicated as the triple charge. A conventional voltage regualtor (such as the LM317) can be configured as a constant current charger by connecting a resistor between the output and th= e reference leg. The battery is charged with this constant current source. Th= e voltage of the battery, which is roughly the same as the output voltage of the charger is measured, and when the desired voltage is reached (14.4 to 14.8) an SCR is triggered. The SCR is in series with a potentiometer in the reference leg to ground. The potentiometer is set so that the voltage from the charger is the trickle voltage, 13.6 V to 13.8 V. Either of these two schemes should maintain the battery so that it is usefu= l for hundreds of charge/discharge cycles. That is several years of typical Ham use. If you get less, either you or the manufacturer are doing something wrong. The capacity of Gel-Cells depends on the discharge rate. Usually the rated capacity is based on a 20 hour diecharge. So the 2.7 AH gel cell in the K-2 will only have the full 2.7 AH of capacity when discharged at an average current of 135 mA. Depending on the battery and the discharge rate, the capacity drops to 1/2 to 2/3 of the rated capacity at a 10 Hr discharge rate, and less at higher discharge rates. So if you draw 270 mA out of the battery (I seem to recall that this is the average current draw for a K-2 running at 5 W with a 50% duty cycle on CW), you can expect far less than the 10 hours that the 2.7 AH rating would indicate, perhaps as few as 5 hours or so. At 15 W, I would expect a very short life indeed for the internal K-2 gel-cell. I have gel-cells that are over 5 years old with hundreds of cycles on them that still take and keep a full charge. You should be able to do as well. I hope that this helps somebody. Sorry for the rambling. - Dr. Megacycle KK6MC/5 --=20 James R. Duffey KK6MC/5 Cedar Crest, NM DM65 +++++++++++++++++++