[Q] Using a DVM to check batteries?... - Page 1
Forum section: electronics / general

author: rbid
author_rank: Newbie
timestamp: December 22, 2012, 12:58:40 pm
content: Hello,I'm new here...One of my hobbies is High Speed Photography that use a lot of AA batteries for the different flashguns (which require at least 1.5V and not the 1.2 rechargeable ones).Before I start a session, I use my DVM to check their voltage, but lately I have read that that is not enough, that some load is required in order to test the charge of a battery .Can someone explain this in more detail?Thanks in advance.Have a happy holidays and a prosperous EEVBlog new year.--- Ricky Marek.

author: nukie
author_rank: Frequent Contributor
timestamp: December 22, 2012, 01:17:37 pm
content: ztsinc.com buy it, it works with reasonable accuracy. Don't buy fake ones from eBay they don't have enough battery profiles in the fake firmware.

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2012, 01:25:21 pm
content: Checking a battery voltage does not tell much about how much current it can deliver to the load ( flashgun) when it is in use. As a battery ages the internal resistance increases, and this appears as a voltage drop across the terminals when you draw power from it. You need to check the voltage drop when it is supplying a load, ideally smilar to the load it will be expected to support. Thus if you draw 2A from the cell ( typical flash gun during charge) you want the cell voltage to be above the voltage where the flash gun stops working.

author: rbid
author_rank: Newbie
timestamp: December 22, 2012, 01:34:33 pm
content: Great... that is, it could be by testing the current that goes through a resistor used as a load and not only the voltage.... this could be also done with a DVMNow, if someone is selling this as a product, I guess I can do it also using a simple Arduino board with the correct firmware and build a "sensor" that would be check the battery charge.. now, just need the correct electronics to do it...

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2012, 01:50:27 pm
content: Simple battery tester has a resistor that provides a load, and a meter to show the voltage across it, with a scale marked at the top in green ( good) a small spot in yellow ( fair) and the bottom in red (fail) as a simple guide.

author: rbid
author_rank: Newbie
timestamp: December 22, 2012, 01:55:38 pm
content: Quote from: SeanB on December 22, 2012, 01:50:27 pmTrue, that was why I was thinking to use the DVM I haveQuote from: rbid on December 22, 2012, 01:34:33 pmJust found this after asking uncle Google about this item:Measuring Battery Capacity With an Arduinowhich is overkill to my needs, but gave me the idea how I can check the healtines of a battery using the hardware I already have... (Arduino Due, LCD and breadbords)Happy holidays and a prosperous eevblog year.--- Ricky Marek.

author: Unknown
author_rank: Unknown
timestamp: December 22, 2012, 02:15:51 pm
content: Quote from: rbid on December 22, 2012, 12:58:40 pmMost flash guns draw a lot of current during recharging. Battery life of alkaline cells tends to be quite pathetic under these conditions, since output impedance increases as it is discharged. NiMH performs much better because of the much lower output impedance. Even an almost empty alkaline cell will have an open terminal voltage of about 1.5 V without load, but the voltage will be much lower under heavy load. The supposedly lower voltage NiMH batteries can have a higher voltage under heavy load. Primary lithium cells have an excellent battery life, but are quite expensive.

author: tom66
author_rank: Super Contributor
timestamp: December 22, 2012, 04:01:26 pm
content: Your conclusion that 1.5V alkalines are better seems incorrect. At 1 amp, an alkaline essential "becomes" a 1.2V battery, whereas a NiMH will rarely budge.http://www.batteryshowdown.com/graphs/1000mA/Duracell-Plus-Power.pngIt only lasts 10 minutes >1.2V.But even under low drain...http://www.batteryshowdown.com/graphs/200mA/Duracell-Plus-Power.pngMore than half of the battery's life is spent under 1.2V.A Ni-MH will begin life at 1.45V, very rapidly drop to 1.3V, then slowly drop through 1.2V and then will be considered dead at around 0.7~0.9V which will occur rapidly.