> On 24 May 2017, at 15:20, Richard Fjeld <rpfj...@outlook.com> wrote: > > I had bought a balance charger and a voltage monitor, and low voltage alarms, > but I have made battery packs that wouldn’t be practical to attach a monitor > to. Example, I have an old Kenwood hand-held that hasn’t had a battery pack > for years. Now, for a few dollars, I had made a battery pack for it. > > I also have CREE flashlights made for the 18650, and 14500 batteries. There > is no way to monitor the voltage in this application. I tested one yesterday > and found it was down to 2.0 volts.
There are LiIons out there (18650 and maybe also 14500) that have built-in protections against all sorts of things, including both under- and overvoltage. That can significantly reduce various risks associated with them. There are a few downsides: - They can be longer, might not fit in all equipment - They can have current-limits, typically not a problem with flashlights, but can be with higher power radios (a few amps is certainly fine, I’d expect no issues for QRP). - They can appear “dead” if the voltage ever drops too low. About the last part… Sorry if it’s been already mentioned in this thread, but LiIons can become more dangerous if they stay completely depleted for a long time. Best for storage of regular LiIons is probably around 3.6V, but if you have a choice between fully charged or fully depleted, go with the fully charged. > (Also being marketed today, are packs to jump-start cars and trucks. That > will be interesting!) > > This thread has made gel-cells look pretty good to me again. There’s a lot of different chemistries when it comes to LiIon batteries, and they each have different tradeoffs. If you’d like to gain a little bit in safety, consider IMR, INR or NCR batteries. They are intrinsically a bit less scary than some of the other chemistries, like ICR. Googling a battery will typically lead you to a data sheet about this kind of information. Not only is it harder to get an incident from these, but the incident would be less severe as well. All of those batteries operate with the same voltage range, but the mentioned types typically have a bit less capacity (for an 186500, that might be 2000 - 3000mAh, where ICR can be up towards 3400mAh). Those batteries can often provide more current safely though, and can also have less of a voltage drop. That in turn, means you won’t get to battery low as fast (caused by the voltage having dropped low enough). Bottom line to that is that at higher currents (couple of amps and up) you might get similar real runtime from a 3000mAh IMR battery, as from a 3400mAh ICR battery. Then there’s LiFePo4. These have a different (lower) voltage range, and you’d need a charger with specific support for them. That used to be a problem, but it’s not anymore. You can find chargers in all price ranges for these. They are a lot safer than other Li-chemistries, and they’ll survive something like 10 times the number of cycles (ballpark of 2000 vs 200). They can often support a higher current, they’re more forgiving on overcharging, and so on and so forth. You’re paying the same tradeoff as the other chemistries though, with less energy density, but better safety and higher current. They do have another property that makes them really nice for radios though, which is a fairly flat discharge curve, spending most of their time around 3.2V. Four of them in series would give you about 12.8V for most of the discharge, a much better voltage for our needs, than “regular” LiIon which would be between 9.9V and 12.6V for a 3-cell, or 13.2V and 16.8V for a 4-cell battery. Yeah, Li-batteries can be scary, but so can any other high concentration of energy. If you pick your cells carefully, protect them physically and electrically (charging, usage, fuse, etc), keep a watchful eye on them (temperature? signs of damage?), then you can greatly reduce any risk, even to a lower level than the LiPo you probably have in your cellphone. Personally I’m probably going to go with 18650 or 26650 LiFePo4 batteries, two packs of 4S1P. Just haven’t decided yet if I want a read made pack, or if I want to set the pack up myself. The latter would probably allow for easier removal of the cells, to charge them externally. For those of you in Europe, nkon.nl is a trusted supplier with good prices (though currently not shipping to Norway last I checked).. 73, Terje Elde / LB8KH ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
