Newbie questions on batteries - Page 1
Forum section: electronics / beginners

author: Trinity
author_rank: Contributor
timestamp: January 24, 2011, 06:52:45 am
content: I have two simple newbie questions about batteries...1. How do you measure how much life is left on a battery? Either in amp-hours, or rough percentage of it's normal capacity?2. If you have a rechargable battery, but are unable to find any spec sheets on it, how can you determine the correct voltage and current to charge it with?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 24, 2011, 07:00:17 am
content: Before you get in there , electrical specs etc etc ..First you must identify the type : chemistry typeIf you say the type , we have the first starting point ,so to find and the rest answers.

author: tyblu
author_rank: Frequent Contributor
timestamp: January 24, 2011, 07:16:19 am
content: For #2, you can't, not without characterizing it. What I would do if I absolutely had to charge it would be to guess a capacity based on chemicals and size, then charge at 0.1C and monitor temperature. If temperature rise changes dramatically, stop charging. If cell voltage peaks, (drops 10mV-20mV or more), stop charging. Discharge and characterize, identify, then recharge properly.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 24, 2011, 07:22:20 am
content: i'm no expert at this but let me try and be corrected:Q1: How do you measure how much life is left on a battery?A1: it depends on what device you are putting it into. some device will shut down at say 1V (for 1.5V alkaline), and some at much lower V, so... it varies.Q2: If you have a rechargable battery, but are unable to find any spec sheets on it, how can you determine the correct voltage and current to charge it with?A2: first you need to know whats the battery normal operating voltage, without it i cannot answer. but if you do, i suggest charging at a little bit higher than normal volt, say 0.01-0.1C current (i stand to be corrected on this), but still, as Kiri and tyblu stated, you need to know what battery's type,volt and capacity.

author: Trinity
author_rank: Contributor
timestamp: January 24, 2011, 02:38:37 pm
content: Okay, so your replies would suggest that if you know the chemicals and amp-hour capacity, you can both measure how much life is left, as well as determine the correct voltage and current to charge it with. Am I interpreting that correctly?If I am, then I would guess the recharge specs would largely be a matter of looking up some baseline reference, or finding a spec sheet for a battery of similar specs, figuring that would be close enough?But then, I would still like to know how you would properly determine how much charge is remaining. Pick any type of battery you want - standard alkaline AA, or lithium coin cell, and give me an example?

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 24, 2011, 03:23:48 pm
content: yes, you interpret it correctlyyes, that should be close enoughas tyblu stated, characterize the battery. different battery different characteristic.mostly charge remaining based on remaining voltage of the battery. lower tha voltage, lower the charge.note: our admin Dave has just release a video to answer your question, download and watch it carefully.do it for me and then teach me. i cannot download the video anymore

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 24, 2011, 09:29:55 pm
content: Quote from: Trinity on January 24, 2011, 02:38:37 pmThat's an easy task today, that we havethetool !!https://www.eevblog.com/forum/index.php?topic=448.msg6650#msg6650(click on the pictures for larger ones )

author: Zero999
author_rank: Super Contributor
timestamp: January 24, 2011, 09:54:19 pm
content: One thing you should never do is connect your multementer, set to measure current, directly across the battery. If it's a good meter, the fuse will blow, if it's a cheap and nasty piece of crap, it will melt and catch fire.Always ensure the meter is set to measure voltage before connecting it across the battery. The correct way to measure current is to connect the meter in series with the device you want to measure. A standard multimeter will not directly measure the capacity or maximum output current of the battery.

author: Trinity
author_rank: Contributor
timestamp: January 25, 2011, 12:17:14 am
content: Quote from: shafri on January 24, 2011, 03:23:48 pmThe video doesn't actually answer my questions.

author: Jimmy
author_rank: Regular Contributor
timestamp: January 25, 2011, 08:01:10 am
content: Mesaure the voltage and use the datasheet to determine how much power left

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 25, 2011, 08:17:16 am
content: Quote from: Hero999 on January 24, 2011, 09:54:19 pmAre you drinking something ?Or if you have a point .. can you become more specific, of what type of battery you have in mind ?Because currently with standard alkaline AA, or lithium coin cell , no one had archive of what you are saying !!

author: Zero999
author_rank: Super Contributor
timestamp: January 25, 2011, 05:59:50 pm
content: Yes I know, it's unlikely that will happen with a low energy source but it's better just to tell a nubie never do something rather than writing pages of crap about maximum short circuit current and leaky batteries.Even small batteries can be dangerous NiCads can provide enough current to melt LED leads. I remember burning a hole in my thumb when connecting an LED to a NiCad when the insulation around one end of the cell failed causing the lead to short circuit the cell and glow bright orange. Fortunately the skin on my thumb was very thick to it didn't hurt too much, I smelled the skin burning before I could feel it.There's no hard and fast rule, just don't short circuit a battery.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 25, 2011, 06:10:38 pm
content: so you are typing it Hero... the long way. so did Kiri. so do i!

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 25, 2011, 08:55:13 pm
content: Quote from: Hero999 on January 25, 2011, 05:59:50 pmWell I strongly disagree with this tactic , no matter if he is a noob or not.because , when we will talk about 220 , usually the voice tones gets wild , and if we speak about 1000 volts , some people get easily mad.And they act that way because of terror , that some one implanted it to them.And so such scare tactics , has no room in public places.