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Lm317 battery charger

Discussion in 'General Electronics Chat' started by baxterdmutt, Dec 21, 2016.

  1. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Here's the LTspice simulation of a fairly simple and accurate circuit that lights an LED at the desired charge voltage.
    It uses an inexpensive TL431 as both a voltage reference and a comparator.
    The pot U2 adjusts the trip voltage (set here for 14V).
    If you know the voltage you want then you can use a fixed resistor for R2. The trip point is where the voltage at the U1 input reaches 2.5V.

    upload_2017-1-11_12-11-55.png
     

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  2. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi there spec, and ST, and later Carl,

    Well thank you that is very nice of you to say. I try to explain things so that almost anyone can understand. It takes little more effort but i think it is worthwhile to be able to transfer knowledge to other individuals which can not only benefit but then transfer that knowledge to others as well.

    I could have mentioned a couple other little things too.

    For one, i had used my Mastech power supply (30v, 10amps max) to charge Lead Acid batteries because it has the two basic settings neeeed: voltage, and current limit. I simply set the voltage to some level like 14.2v, then set the current to a low value like 100ma, then connect the battery, then raise the current limit until it reaches whatever is good for the battery like 1A or 5 amps (i never do little batteries always quite large) The current limit LED lights up to tell me the current is being limited and the readout tells me it is 5 amps, then after a time as the battery charges, the current limit LED goes out and the voltage LED comes out to tell me that the voltage is now being regulated at the set point of 14.2v, and the readout tells me it is 14.2v which i also check with a trusted meter. The current limit is not that critical, i can be 4 amsp to 6 amps or even less than that, while the voltage i like to get more accurate. So it is just a matter of setting up the power supply, connecting to the battery correctly, then adjusting the current limit. It is very important not to connect the battery backwards though or the power supply will blow up. I had it blow out ones on my so i installed a protection circuit, but that's another story.

    Second, some LA charge regimens are slightly different than what i described. What they do is they limit the time the battery has to charge at some nominal current once the voltage has reached the set point such as 14.2v or so. Once it reaches that, they cut back on the voltage too, reducing it to maybe 13.8v and that is called the "float" charge. That is intended for long term charging where the person operating the charger might not be around and so they cant turn the charger off once it reaches some low value in current. So the charge in this case would start out with limited current like 140ma, then ast the voltage got to 14.2v or close to that it would actually reduce the voltage set point to 13.8v and then that would be the end of it.
    The 13.8v is also sometimes called the "maintenance" charge, but is not needed unless you need the battery to be up and ready at some random time such as with a UPS system where you never know when the electric will go out because of power line failure.

    For myself, i am always around when i charge any kind of battery as i never let the battery alone for even 5 minutes when charging because that is the highest probability in time for some nasty problem to occur. This is especially true for the lithium group type batteries like Li-ion.

    If you think nothing can go wrong, then it most certainly will :)
    Do a search and see what happened to Samsung when they had many of their phone's blow up because of the Li=ion battery. The latest story is that the battery compartment was designed too small so that the battery was too confined and did not have enough room to expand when charging or getting warm. It cost them 10 billion dollars because all of them had to be recalled. No official report from Samsung yet, but it does make sense that the battery needs room to expand or else it compresses in on itself and punctures the separator material.

    Good luck with yours :)

    ST:
    Yes, that was an interesting story that i myself thought could never happen.
    It is even more interesting that NASA had put out a paper some years before that which stated that they would ONLY use metric units from then on out. Whoever used English units did not read that paper apparently.
    It's so amazing what could go wrong even with people who must be so well educated. For some really amazing stories, read into the near miss nuclear disasters that occurred in the US over the past maybe 40 years. You wont believe what could go wrong when you build a weapon that could potentially kill 10 million people in one shot, and what is even more amazing is they might even be YOUR OWN people in YOUR OWN country because something went very wrong. In particular, check out the disaster in Damascus, Arkansas around 1980 ish where it took days just to find the warhead after the explosion.

    Carl:
    I love those little 431 chips. Used them in several things over the past years.
     
    Last edited: Jan 11, 2017
  3. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Yup, they're cheap, make a fairly accurate programmable zener, and can also be used as a comparator with an accurate built-in reference voltage.
     
  4. dave

    Dave New Member

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  5. baxterdmutt

    baxterdmutt Member

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    That should work for me.
    Thanks.
     
  6. baxterdmutt

    baxterdmutt Member

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    Thanks, you probably won't believe it but that's how I do mine. It just won't work for the application I need it for. I somehow figured out how to charge them like that but was never really sure if that was correct. I feel good now!
     
  7. schmitt trigger

    schmitt trigger Active Member

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    Mr Al, many comments;

    -Yes, I've read Eric Schlosser's book, "Command and Control" which describes in harrowing detail the Damascus incident and others. Here is the Amazon link:
    https://www.amazon.com/dp/B00CDBZ6N...TF8&colid=1WUCBTK9E9C4A&coliid=I3FOIXP2GW98WJ

    -The three-stage charging system is a must for hi reliability standby systems with large and expensive battery banks. Unitrode, which became TI, had a wonderful but expensive analog IC, the UC3909, to implement the proper charging algorithm. It is obsolete now.
    But you are absolutely correct, a two-stage system satisfies the vast majority of the users.

    -The TL431 has long been a favorite of mine, Not many people understand that it is actually an opamp with a reference. Clever designers have used it in many applications.
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Yeah that looks like an interesting book. I might have to read that one.

    I like the 431 too because of the same reasons you guys do, the only improvement i would like to see is a lower internal voltage reference.
     
  9. crutschow

    crutschow Well-Known Member Most Helpful Member

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    I agree.
    There are a lot of references with a 1.2V output and it would be desirable to have a 431 type circuit with that reference voltage.
     
  10. alec_t

    alec_t Well-Known Member Most Helpful Member

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    How about the ZR431L?
     

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