This is really helpful. It answered a bunch of questions I had but hadn't asked. People were commenting on that YouTube battery-testing video that a 100-ohm resister wouldn't be right for a D battery, but I guess it also wouldn't be right for a 9-volt. Looking at more info out there on the web -- it's a problem for me that a lot of people don't seem to know what they are doing, but they are still there, teaching the world. ;-) Thanks again, Doug. Mike On Sun, 12 May 2019, Doug Reed wrote: > Yes, the Ax-Man stores are the place to look if you don't want to ask > someone to mail it to you. I believe there are 3 or 4 stores around > town. The only stores I am familiar with are in St Paul and Fridley, but > I thought there was one more in Bloomington. > > The color code for 100 ohms is brown-black-brown. But 100 ohms is too > low for testing a 9V battery. 100 ohms is fine for testing 1.5 volt > batteries at about 15 milliamp current load which is within the > capability of all AAA or larger batteries. > > But 100 ohms will attempt to draw about 90 milliamps from a 9V battery. > Most 9V batteries are rated for 50 milliamps maximum load. Your 100 ohm > resistor will tend to suck them down so they all fail your test. For a > similar test effect, you should use a 1000 ohm resistor, perhaps even > higher, up to 3000 to 5000 ohms so the load is proportional to the > battery capability. > > So when you are looking for the resistor at Ax-Man Surplus, the 100 ohm > resistor should have Brown as the first band, black or brown or red for > the second band, and Brown again for the third band. The bands are > counted with the first band closest to one end. > > The 1000 ohm resistor would have the third band colored Red instead of > brown. Since we don't care exactly what the value is between 1000 and > 5000 ohms, the first band can be any of Brown or Red or Orange, or > Yellow, and we don't care at all about the second band color. > > And I suggest that you look for a resistor that handles one-half watt > dissipation or more. Your batteries should never approach that but the > larger physical sizes are usually less likely to break from lots of > handling. A half watt resistor is physically about 1/8" diameter and > 1/2" long with leads about 1.5" on each end. > > The size you pick isn't really critical, it is really just for ease of > handling. You will probably find multiple examples to choose from, I > just suggest you don't choose the smallest size you find. Any resistor > larger than 1/2 watt will also work of course, if that is what you find > or want. The much larger watt values usually have the resistor value > simply printed on the side. > > And of course buy more than one of each for when you break or loose one. > :-) > > Good luck. If my description isn't enough to work from, you can easily > find web pages that explain the resistor color code. And you can always > bring your voltmeter to the store and use it to check the resistor value > before you buy. Or buy a handful of different values that have brown or > red on the third band and check them at home. No matter what you choose > to do, the parts will probably cost less than the gas to get you to the > store. > > Doug Reed. > North St Paul. > > -- > Scientists say the world is made up of protons, neutrons, and electrons. > They forgot to mention MORONS. > > She had buried three husbands and at least two of them had already been dead.