I’m trying to sort out the information I read about batteries in parallel and in series, and the dangers associated with each setting.
Tell me if I got it right (I hope I’m not completely wrong…) :
In series:
Voltage differences cause reverse charging (cells with lower voltage are reverse charged)
Flashlight will sometimes stop working because of low voltage
Not dangerous with primary cells (charge current is limited to what one cell can provide; cells that are reversed charged aren’t dangerous?)
Dangerous with unprotected rechargeable cells (unstable at lower voltages? problem only with li-ions?)
Protected cells generally prevent reverse charging (will shut down the protected cell and stop current flow; but if current flow is high, protection may fail)
In parallel:
Voltage differences cause charging (voltage will continuously strive to be equated across cells by charging the cells with lower voltage)
Flashlight will have lower runtime because of internal charging
Dangerous with primary cells (may leak, catch fire or explode?)
Dangerous with respect to the number of charging cells vs the number of cells being charged (the larger the ratio the bigger the danger because of larger potential charge current)
Protected cells alleviate the danger by limiting charge and discharge currents (but if current flow is high, protection may fail)
For both:
Bigger voltage differences - more dangerous
Capacity differences don’t matter at first, but discharge rate differences cause differences in voltage later on
Different cell chemistries affect charge rates so may be dangerous
Cell protection alleviates problems? (allows only forward current and limits charge rate)
And a question - what is the upper limit of voltage difference that is considered to be “not dangerous”? Is it chemistry / protection dependent? In general up to 0.2V max difference and same chemistry is okay?
Oh dear ! Primaries or CR123 are or were the main cause of flame outs , people would mix depleted cells with fresh ones and turn their flashlights into pipe bombs ...
This is still quite possibly the main issue with Li-ion .. Voltage variation = Buy a Multi meter ..
Also high performance flashlights running 2 or 3 or 4 batteries means more vigilance ..
Im amazed more incidents are not being reported , which sais something about how safe these batteries are for non safe batteries ..
Takes a fair bit of abuse and bad luck ( ignorance ) to get an explosion .
I’d say it depends on current flow between batteries, which is higher with higher voltage difference and lower internal resistance.
Of course, at zero int. resistance for both batteries, any difference in voltage would cause infinite current.
With two batteries, V1 and Rint1 and V2 and Rint2, in parallel, the loop current is (V1-V2)/(Rint1 + Rint2).
Nicads are capable of enormous short circuit current and so you’d have to be especially careful with these.
Don’t forget the danger of forgetting if you have two cells in a parallel battery holder that you need the holder or you may will likely poof something - amazing how we sometimes learn the hard way.
So 0.2V difference with pessimistic 0.02 ohm resistance for IMR gives about 5A which is 2-3C, and with “standard” li-ions with 0.05 ohm it would be 2A which with 18650 is less than 1C.
Is it too much for these cells? I believe the charge current would drop quite rapidly with the voltage change, so the danger would be for a very short time?
No offense taken. Some people take the time to make absolutely sure that everything in their lives is as perfect and fool proof as possible. Lights, cars, power tools, the house, the yard, whatever you like, they make sure everything is exact. Nothing wrong in that. Making yourself feel comfortable and secure about what you are doing and using, is the right thing to do. It's just that everyone has a different comfort, (or discomfort) level about things.
That said, I personally, would think using a meter to test the voltage of cells would be common sense, unless I relied on others, (like manufacturing companies in some other country half a world away), to take care of my personal safety, whether it be batteries or my car, etc. etc.
Please re-read the added emphasis. If you have a stacking parallel holder and forget the holder, it becomes series - and poof (assuming the driver isn’t designed for series in the first place).
Because that’s how batteries get charged. A source with higher voltage potential is connected to a cell with lover voltage potential. The disparity in voltage potential causes current flow which charges the low voltage cell.
The low voltage cell doesn’t have any way to know it’s in parallel with another higher voltage cell rather than a charger - the two voltage sources look identical to it.
That’s a good question.
Heat kills electrical devices over time but high current can quickly melt a small wire. House wiring insulation lifetime sort of follows an I squared R relationship at some currents and some elapsed times but the chemistry of cells is quite different.
Also, the internal R probably depends on the state of charge and whether the cell is being charged or discharged. This seems to be true of car batteries.
Ideally, after making many measurements on many cells you maybe could come up with a voltage difference that does not ‘significantly’ shorten battery life for almost all of the cells on the market.
+1 I would have to agree, Ignorance is a very common reason for people getting injured or even killed. It is always better to perform the Checks and Balances to insure your own Safety and the Safety of those around you. That is why the Manufacturers and Experts issue these warnings in the first place, to insure your Safety. As i am New to this hobby I was completely unaware of the issues with Litium Batteries till reading this Forum, and i am Thankful for the People who give of their Time and Knowledge to advise people of the correct and Safe Methods of handling these Issues, to hopefully avoid Hazards like these. They may Save a Life/s. Luckily there is more good advice on this Forum than there is bad.
How do you know what the 'green light' signifies, if you've never tested it? Some chargers have been known to overcharge cells, after all.
Nobody ever has a cell go bad...until they do. Your green light will not alert you to any number of signs that a cell is on the way out.
Is it likely to happen? No, especially if you only use single-cell lights. Is it prudent for those of us who use high current multi-cell lights? Definitely.
Going back to the car/tire analogy, checking one's tires is prudent. You can't tell if a tire is safely inflated by looking at it, and under-inflation causes heat to build up - ultimately causing a blowout. With the downside being so great, I deem it worthwhile to check both my tires and my rechargeable cells.
For other uses, see Ignorance (disambiguation).
Ignorance (Definition)
Ignorance is a state of being uninformed (lack of knowledge).[1] The word ignorant is an adjective describing a person in the state of being unaware and is often used as an insult to describe individuals who deliberately ignore or disregard important information or facts. Ignoramus is commonly used in the US, the UK, and Ireland as a term for someone who is willfully ignorant.
Ignorance is distinguished from stupidity, although both can lead to “unwise” acts.
Consequences of Ignorance
Individuals with superficial knowledge of a topic or subject may be worse off than people who know absolutely nothing. As Charles Darwin observed, “ignorance more frequently begets confidence than does knowledge.”[4]
Ignorance can stifle learning, in that a person who falsely believes he or she is knowledgeable will not seek out clarification of his or her beliefs, but rather rely on his or her ignorant position. He or she may also reject valid but contrary information, neither realizing its importance nor understanding it. This concept is elucidated in Justin Kruger’s and David Dunning’s work, “Unskilled and Unaware of It: How Difficulties in Recognizing One’s Own Incompetence Lead to Inflated Self-Assessments,” otherwise known as the Dunning–Kruger effect.
_
This is not written to be an Insult, it is a Request.
Please let the people who are trying to Learn (like myself), do so without trying to confuse them with Personal Opinions. If you do not wish to learn from a thread such as this then that is your choice. But why must you try and Derail it with Negative Comments or at best unhelpful ones. There are a lot of Good and Knowledgable people on this Forum trying to help the People who are wanting to Learn with Good Advice. It does not help those with the Knowledge who are trying to Teach in any way to have someone Trivialise the Good Work and the Advice they give, as though they are wasting their time. They are trying to make this a Safe Hobby for all of the New people and old alike, who want to Listen and Learn. I don’t know what your reasons were for joining this Forum, but the reason i chose to join and follow this Forum was to Learn and maybe one day be in a position to Help Others, through what i have learned, as i’m sure did many others. This type of Topic is one that should be based on Fact, Not Opinion or based around Luck. I am usually capable of telling the difference between Good and Bad Advice, but others may not have that same Luxury and need Guidance.
I would also ask that you give some consideration to changing the Slogan at the bottom of your comments (I was told as a boy to never let anything get on top of me - So I apologize profusely in regards to your daughter). I don’t know if you are a father or not, but i am, with 4 Daughters. So i find this Slogan to be at best Offensive and in Very Poor Taste, especially for a Public Forum that seems to have many Young Members. Lead by Example.
For those of you who do Give of Your Own Time to Research and share the Knowledge, i sincerely thank you all for the Good Work You do and the Effort and Your Time You put in to make this a Safe and Enjoyable Hobby (Addiction) for all. And be assured many people do read and Appreciate your Efforts.
You are the People that make this Forum.
Cheers
After reading both comments, I find Toph’s to be mildly obnoxious (what with the definition of Ignorance) but otherwise genuine and reasonable. I JJ Findlayson’s to be hostile, and threatening. I also see foul language, which is against forum rules. I suggest you both avoid each other for a while and calm down.
In the interest of seeing this thread continue as it was, it was one that i was very interested in, i will make no further comment other than this so it can continue without interruption as a result of my comments or retorts to them. I have said what i thought needed to be said and hope that it does not halt your discussion there, as that would be a shame. I thought that my comment might have met with some sort of common sense reaction. I was obviously mistaken. The definition of ignorance was only displayed as a referance as to the meaning of the word, as the meaning seemed to be in question and it was relevent to both the Topic and the Comments made. I made sure to state that it was not meant as an insult and kept the Definition separate to the comment i made. It was not meant to be obnoxious. I was also not the only one to comment on the persons statements. I also tried to put in such a way that it was not Inflammatory, i had to Google the word Troll.
I am a 52 yo, father of 4 Girls and i am just concerned when i think that someone could be injured (especially young people) as a result of such bad advice on a thread that was made to Educate about Safety. Anyway thank you for listening, Sorry for the interruption and i will sit on the side without comment and hopefully keep learning. Thank You for Your Understanding.
Back to the thread’s topic - what of what I wrote in the opening post is correct and what is not?
(besides what old4570 has already corrected regarding CR123 in series)
And how much do protection circuits help to alleviate the dangers of running batteries in series or in parallel?