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Hi Guys need help with a charger circuit please

Discussion in 'Repairing Electronics' started by Dr Bob, Sep 7, 2013.

  1. Dr Bob

    Dr Bob Member

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    Indeed! I wonder if there are anymore we aren't aware of yet. I was just looking at the LTspice, I haven't used it before, when I load your circuit it says it hasn't got a symbol for the LM324 is there a repository somewhere like the Protel 99 circuit libraries used to be?

    Edit: Just noticed on your sim cicuit you have a reference voltage of 1.86 that precision reg is programmable and measures 3v with my digital meter.


    Edit: oh! I found the LM324 it's the LT1014
     
    Last edited: Sep 10, 2013
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Glad you've got LTspice. Great fun for 'what if ....' experiments without frying real components! Bit of a steep learning curve but the F1 help is good (albeit a tad concise sometimes). Right-click on almost anything to change its properties. Run the sim then click on a wire/node to plot voltage. Click on a component to plot current. Alt-Click to plot power.
    Sorry, I didn't post the model file for the LM324 but you can download loads of models (including the LM324) from the free zipped libraries at the Yahoo LTSpice User Group.
    After unzipping, just put/copy the required .lib or .sub file into your LTspiceIV/lib/sub folder and put/copy the associated .sym file into the relevant LTspiceIV/lib/sym folder. Best NOT to keep your own work files (.asc) in the LTspice folders.
    A left-over from playing with some values. Right click on the symbol to edit it to ~3.0 (the TL431 is programmed to give a nominal 3.08).
    That will do nicely (indeed many opamp/comparator models will do for our purpose).
     
  3. Dr Bob

    Dr Bob Member

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    Thanks Alec, any further thoughts about the bottom circuit or have you had enough now? It will be quite some time before I'm good enough with the sim to use it in anger :D
     
  4. dave

    Dave New Member

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  5. Dr Bob

    Dr Bob Member

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    I can't create a yahoo account to go on the Yahoo LTspice User Group as their registration demands a mobile number and I don't have a mobile phone, I think demanding a phone number on the internet pretty abysmal
     
  6. alec_t

    alec_t Well-Known Member Most Helpful Member

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    I haven't played further with the sim of the IC2 part. I would hazard a guess it may have been intended originally to start the charging whenever battery voltage dropped below 13.2V; but the sim shows charging starts now above 2.6V. The schematic may be from an early prototype rather than the present charger?
    As for Yahoo requiring a mobile number that's an absurd invasion of privacy. I'll have to check that I can still get into my account (which I signed up to without a mobile number).
     
  7. Dr Bob

    Dr Bob Member

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    Ok Alec thanks, I'm working with the sim, if I discover anything interesting I will post.
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Where is the schematic?
     
  9. Dr Bob

    Dr Bob Member

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    On the first post on page one? Nope! it would appear they have lost all my attachments while messing with the forum! Hang on mate I will try and put it back

    Edit: well when I edited post one it said the pdf was attached but it wouldn't show it until I uploaded it again, but now it shows two of them ?
     
    Last edited: Sep 12, 2013
  10. Dr Bob

    Dr Bob Member

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    Alec, I have done some work on the sim, added more of the circuit so I could study the timings etc and I find this circuit acts pretty much the same as the charger, just play with the battery voltage to see the different comparators trip, changing the voltage of the gate drive just changes the charge current as in the real circuit I have it giving about 3 amps similar to the low mode.

    I see the top circuit trips and stops the charging at around 14 volts ish, the bottom circuit is strange and only trips if the battery voltage is about 2 volts or lower, yet as I said before if you completely disconnect the battery and put a capacitor between the leads it will charge it? I still can't really see a sensible purpose for the bottom circuit??

    I feel the voltage on the battery is a key part of the circuit and the circuit did not start to behave like the real charger until I included the battery and output fet.

    Please give me any observations, I checked all the values and found that C9 is 22uf not 220uf and as was said before R6 is 1k6
     

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  11. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Your observations completely agree with mine. I had previously run my sim as a DC analysis, sweeping the battery voltage from 0V to 15.6V (the theoretical bridge output). I didn't include caps in my sim because I assumed they were to damp transients around the on/off switching points. I now think they are in circuit to smoothe the opamp outputs, to hold them up during the mains zero-crossings, when the bridge output drops to zero.
    Your sim shows FET current starts rising at ~ 3.6V gate voltage, consistent with the turn-on spec for the chosen FET.
    We're agreed: the bottom part of the circuit has no clear purpose.
     
  12. Dr Bob

    Dr Bob Member

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    Hi Alec. Thanks for having a look. Unless! I just had a moment of clarity, is it output protection? if the FET goes short circuit the drain line will go to zero and the charging circuit will shut down, hmmm wouldn't stop a high current flow from the bridge through the battery but the fuse should blow though.
    if the fet went open circuit it wouldn't matter as it wouldn't then draw a very hight current.
     
  13. alec_t

    alec_t Well-Known Member Most Helpful Member

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    It would be nice if that happened, but I don't see how shut-down could occur. If the FET fails short-circuit its gate voltage will have no effect and control is lost.
     
  14. Dr Bob

    Dr Bob Member

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    Maybe he who designed it never thought of that :D
     
  15. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Thanks for posting the schematic. I hope we dont loose any of these attachments with the forum changeover.

    It looks a bit more complex than i had hoped :)
     
  16. alec_t

    alec_t Well-Known Member Most Helpful Member

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    There are three situations in which the bottom circuit can turn off the FET :-
    1) If a short-circuit occurs across the battery terminals,
    2) If the batttery is connected with the wrong polarity.
    3) If the battery voltage is below 2.6V.

    Perhaps that's its mission in life :)
     
  17. Dr Bob

    Dr Bob Member

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    Welcom Mr AI it was fairly expensive and despite the make appears to be very good, the beauty of it is that you can leave the charger attached to a battery to maintain it without damaging it.

    Hi Alec, thoroughly enjoyed going through this with you mate and thank you for taking the time to help me and introducing me to LTspice, which is the dogs! I think you have it there mate, the connecting the battery the wrong way round one, notice there is a "Reverse" LED up near the bridge, so they obviously thought of it and I think that would be the major function of the bottom circuit.

    Last thing. I understood that when charging a battery 15.5 ish will take it to 100% charge and then if the charger stays connected it needs to drop to a lower maintenance voltage, I don't see anything in this circuit which will do that do you? Or doesn't this one need to as it switches off completely between top ups?
     
  18. alec_t

    alec_t Well-Known Member Most Helpful Member

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    No. It just shuts off at 14.4V, waits until the battery volts drop to ~12V, then turns on again and so on. No trickle charge at a lower maintenance voltage.
     
  19. Dr Bob

    Dr Bob Member

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    Ah good, thanks Alec. I have been a bit quiet because I thought I would check out the bottom right regulation circuit, in the "Low" mode it works fine but in the "High" mode there seems to be no regulation and it draws 60 amps or more only dropping as the battery charges.
    I have checked all the components on the real board the only change is R39 which is physically 5k6 not 5k1 the circuit won't work at all with 5k1 oh! and r37* 1m5 isn't fitted.
    I have also checked the switch is connected as per the circuit and it is, so I am pulling m hair out again :D it works until c3 charges up and then stops as the output of U7 goes low, if it can't recover from going low how can it regulate?

    Edit: Ahh I think it's something to do with the fet I am using not matching the correct one, well part of it anyway, but I can't find a 60N06 I think it's gate voltage is lower than the one I was using, I have been trying different ones and getting better results but not regulating yet
     

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    Last edited: Sep 13, 2013
  20. alec_t

    alec_t Well-Known Member Most Helpful Member

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    I've run my own sim of just the bottom quarter of the charger cct. Results agree with yours: current is regulated by the FET on the 'low' setting but not on the 'fast' setting. On 'fast', charge current is limited only by the sum of the resistances of the transformer secondary, the bridge diodes, the FET's Rdson and the battery. So charging occurs with 100Hz current pulses whose amplitude decreases as battery voltage increases.
     
  21. Dr Bob

    Dr Bob Member

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    Morning Alec, thanks for that, do you think it's meant to be like that, or did they make a mistake in the reg circuit?
    Oh! would you have a look for me to see if there is a 60n06 in the components on yahoo please?
     

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