On Tue, Mar 28, 2006 at 09:22:22PM -0800, George Gillburg wrote: | I like the EDR-2 from ElectroDynamics. I've been using one for | better than 10 years and I've never found a better unit, imho. Here is a | link: | | http://www.electrodynam.com/cgi-local/SoftCart.exe/new/EDR-2/index.shtml?L+scstore+prnw1066ffd6e1d6+1148846929
They shouldn't have included a picture, since that suggests that you could save a whole lot of money by making it yourself -- and you can. Go to Harbor Freight Tools. Buy a $3 digital multimeter. (It might be $4 this week. But if it's $10, wait a week or two and come back.) Buy 5 more while you're at it, so you can make some ESVs for your friends too and so you can have some around the house, in the flight box, etc. They have a few different models of their budget multimeter, and it would be more convenient if you could get the version with the seperate on/off switch (rather than the `off' position on the dial.) Do some math ... you've got 5 volts, want 250 mA current flow ... so that's about 20 ohms. (Oops, I did the math for you.) Go to Radio Shack, and buy some 20 ohm resistors. If you plan on leaving your ESV connected for any length of time (like to cycle batteries), get a resistor rated for two watts or more, if not, any 20 ohm resistor will work. Even the exact value of the resistor doesn't matter -- anything in the ballpark of 20 to 30 ohms will give good results, but you might want to go on the higher end if you're testing tiny HLG packs, and on the smaller end if you want to test bigger subC packs. Solder the resister into parallel with the test leads. Cut off the probes, and solder it to a plug that fits your favorite battery connector. Voila! Granted, the EDR-2 looks like it has a few different plugs to use, and I don't know what's in that box (perhaps a constant current flow circuit? Adjustable current flows?) but one you make yourself will be almost as good, and around 85% cheaper. And as always, ESVs are easily fooled when used to determine the condition of your battery. If you take a fully discharged battery and charge it at 1C for two minutes, the ESV will probably lead you to believe that it's almost full, when it fact it probably won't last ten minutes in flight. ESV stands for `enhanced scale voltmeter.' That term doesn't really apply to digital multimeters like this, and doesn't talk about the resistor to add a load, so perhaps I should just say `battery tester'. -- Doug McLaren, [EMAIL PROTECTED] Speak softly and carry a +5 Sword. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
