Wikipedia:Reference desk/Archives/Science/2018 August 20

= August 20 =

Ni-MH batteries
I use rechargeable Ni-MH batteries in my GPS unit. I am aware that these slowly lose their charge when not in use. For this reason I charge a few the night before I need them. They are all getting rather old, and I know that after a few years they die completely, but when I take them out of the charger they all give a reading of about 1.2 volts on my multimeter. However when I put them in my Garmin GPS (Oregon 450) the battery level indicator shows some of them fully charged but others as empty or part charged. What is the battery level indicator measuring that the voltmeter is not?--Shantavira|feed me 09:11, 20 August 2018 (UTC)
 * A voltmeter is not a good way to show either charge state or cell health in NiMH cells. I'm curious though as to what the GPS is doing to judge the batteries like this. It has two AAs and I've not seen a consumer device like this which showed individual cell health before. Also, to do that, it usually requires a long-term relation to that particular identifiable cell, specfically by watching its behaviour during charging.
 * To charge my 18650 LiPo cells (a useless format, best avoided) I use a VC4 charger. This is a useful charger and does NiMH too.  I like it because it has a seemingly accurate per-cell charge meter. I also have a discharge tester (cheap thing, based on an Arduino and a big load resistor). The ratios of the charge capacity vs. rated capacity, and the charge capacity vs discharge capacity are a pretty good guide to cell health and aging. Much better, albeit more awkward, than any instantaneous measure with a voltmeter. Andy Dingley (talk) 09:47, 20 August 2018 (UTC)
 * My Garmin Etrex GPS unit takes two AA cells. I never intended to use anything but rechargeable Ni-Mh, but found that the unit shut down due to low battery after a disappointingly short time. The conclusion I came to was that it was meant to be used with 1.5V cells such as carbon (full charge 1.6V, a total of 3.2V), and my two Ni-Mh cells at 2.4V fully charged were already way down the discharge curve at switch-on, so the flat battery shutdown occurred far too soon. Akld guy (talk) 10:37, 20 August 2018 (UTC)
 * I have a few bits of kit like that (although not GPS). I've refitted them with simple DC-DC converter modules to raise the battery voltage. These are now in the couple-of-bucks range direct from China. Andy Dingley (talk) 10:41, 20 August 2018 (UTC)

Thank you both. The unit has a settings option: System > battery type > rechargeable Ni-MH, but as you say even the "fully charged" ones don't last long and I have to take at least a few spares with me when I go out.--Shantavira|feed me 14:41, 20 August 2018 (UTC)
 * One option would be some new, high quality, NiMH. I only buy the good ones now (any lesser uses can use up my old ones) and those have a reliable 2,000 mAh capacity, and negligible storage losses.  This is also why I don't waste effort on 18650s. Apart from the utter junk and counterfeits, that's the same capacity / volume as any 18650 I can afford, and without all the drawbacks. Andy Dingley (talk) 15:32, 20 August 2018 (UTC)
 * I've had the same problem with older NiMH cells, especially in recent GPSr models and in cameras. I find that new 2900 mAh NiMH cells last most of the day, even in newer models, and last more than a day in old eTrex models.  As Andy says above, perhaps it is time to buy new?  Your battery level indicator is measuring voltage under load conditions, probably with a significant startup current drain.    Dbfirs  18:41, 20 August 2018 (UTC)

Characteristics of common wasps and bees
This list states that yellow jackets and paper wasps (among honey bees and bumblebees) supposedly are not attracted by light at night (except this appears near their nests). However, as I can clearly testify – not only from my very personal painful (in both senses) experience –, this is simply wrong! Wasps, yellow jackets, hornets etc are indeed attracted by light, and I guess at least some of you can agree and tell a thing or two about that phenomenon… Also, the sting pain intensity is rated with 2.0, equally for a honey and a bumblebee sting, but with "2.x" for yellow jackets and European hornets, which I find hard to believe, as bee venom is said to be far stronger than wasp and even more so than hornet venom. Finally, the article calls wasps' (in the broader sense) nests "hives", which I consider incorrect, too, as in my view, the term hive is only to be applied when speaking of bees. But, as I am probably not sufficiently competent in this field, what would the experts say?--Neufund (talk) 22:59, 20 August 2018 (UTC)
 * But how do you know they were attracted by the light, rather than something else which just happened to be in the same place? Andy Dingley (talk) 23:21, 20 August 2018 (UTC)
 * The sting indices in the article were unreferenced, and "The Sting of the Wild" by Justin O. Schmidt lists yellow jackets at 2, the same as honey bees and bumble bees, but does not mention European hornets as far as I can see. The article has now been corrected in regards to yellow jackets.--Wikimedes (talk) 04:53, 21 August 2018 (UTC)


 * You're quite right as regards photophilia--some social wasps are attracted to light in a darkened environment. While most such species are diurnal by nature, they are efficacious workers, and in the peak of summer will sometimes push the limits of nightfall during forays for food and other nest resources, making the ability to navigate after dark a valuable if infrequently used ability--some species of hornet and yellow jacket also regularly hunt at night, though there may not be any such species native to where you live, depending where you are, as such species are an exception to the general rules governing social wasp activity levels (more broadly, nocturnal behaviour is quite common amongst the larger array of wasp species).


 * For almost all species of insect which display an attraction to artificial light sources, the individual in question is not actually "drawn to" the object in question as a matter of "wanting" to be near it--rather, the behaviour is a consequence of their normal means of navigation being thwarted by the light source. Nocturnal animals which rely upon light as their primary modality for navigation use the stars and moon to orient themselves.  These celestial objects are so far away as to be functional fixed as regards the insect's movements in any given moment, but this is not so with a light that is mere feet away, so the hapless creature ends up flying in circles or in other no-productive paths around that object, confused by its actual vs. apparent position as a navigational point.  Note that in some cases, the insect may utilizing polarized light, though either variation can result in the short-circuit of the evolved navigational strategy.


 * As to "hives", you're correct that this is less common than "nests" as the go-to label in most areas, but you'll hear both with frequency, and neither is a formal, set clinical term. Most researchers doing entomological research of eusocial Hymenoptera species will refer to the collective as the "colony", and may do so when referring to the actual structure of the nest itself or the kin-group/superorganism. Sn<b style="color: #99d5fe;">o</b><b style="color: #b2dffe;">w</b> <b style="color: #d4143a">let's rap</b> 15:31, 21 August 2018 (UTC)