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.