High Current Regulator Problem

Discussion in 'Homework Help' started by gunvald, Jan 29, 2015.

  1. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    I've been trying to this on my breadboard hoping to get more current from my lead acid battery of 12V 4Ah and I can't get it to work.. The current draw is much higher when I directly connect it to the battery(about 1.3A) than when it is connected in the circuit(1.07A ~ 1.17A).. I want to amplify the current to suffice the needed optimum input for a 60W Peltier(TEC-12706).. Can you recommend me any other circuit that can output a constant 5A and can supply at least 2~3 60W Peltier.. Thank you in advance.. Any help will be greatly appreciated..
     
    • HCR.jpg
      HCR.jpg
      File size:
      15.3 KB
      Views:
      78
  2. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    A linear regulator can only regulate voltage, it can't increase the current (current out ≈ current in). It's output current would be expected to be less than the battery directly connected, since that regulators maximum output voltage is about 4V less than the battery voltage.

    Did you measure the battery voltage when it is directly connected to the TEC?

    If you draw 15A from your battery it will last less than a quarter hour.
    You need a bigger battery.
     
    gunvald likes this.
  3. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    I did measure the voltage on the battery and it's about 11.78V.. How can i draw the needed current on the battery? I can't seem to figure out how it works, I even tried connecting a 2.5Ohms resistor in series with the peltier and still get 1.3A.. Thank you again.

    P.S I'm not very knowledgeable in electronics, hoping for your very kind consideration in assisting me.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    That is very poor current booster for the LM317. Do you want me to show you one that is recommended by TI/National (the maker of the LM317)?
     
    gunvald likes this.
  5. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    Yes please, I would appreciate it very much. Thank you.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I looked at the specs for this cooler, and I cannot see any reason to use a voltage regulator between a 12V SLA battery and the cooler. A fully-charged SLA will be about 12.8V initially, and you should stop discharging it when its voltage falls to about 11.5V. During this time, the cooler will operate just fine, even as the voltage drops between these two values. No regulator is required.

    Now, as pointed out earlier, a 4Ah battery will run this cooler less than 40min before the battery needs recharging...
     
    gunvald likes this.
  7. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    I have two 12V 4Ah lead acid battery.. I need at least 12V and 5A that can run two 60W Peltier.
     
  8. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    My problem is that the battery only supplies 1.3A.. how do I pull the 5A from it? Thanks.
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    The reason that your battery only puts out 1.3A is because it is totally discharged, and needs charging. Or the battery has been sitting around discharged for months to years, and is now worthless. When in storage, a lead-acid battery needs first to be fully-charged before being put in storage, and then to be periodically recharged (at least once a month to replace the charge lost due to self-discharge). If you do not do this, you permanently damage the battery, and might just as well recycle it and get a new one...

    A fresh fully-charged 4Ah 12V SLA would put out a peak current of >~20A (but not for very long)!
     
    gunvald likes this.
  10. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    Thank you very much, I will now start charging the battery and see if I can pull out the current needed..can you still teach me how to boost current though? and is it still okay to use a discharged SLA(discharged it to 10.5V :()? I didn't know that it's not suppose to go down below 11.5V.

    Once again, Thank you very much for helping me out..:)
     
  11. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    You need to in series with an 0.22 Ω/5W for each E of 2N3055.
     
    gunvald likes this.
  12. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    I will try it, thank you :)
     
  13. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    As I previously noted your circuit cannot "boost"the current.
    It can regulate or limit the current but not increase it over what the battery will give all by itself.
     
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    And since that regulator is worthless, and the TS doesn't need a regulator in the first place, then this suggestion is worthless, too.
     
  15. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Read the article on taking care of SLA batteries at Battery University.

    The only way to "boost current" is to get a larger battery, or wire smaller ones (of the same type) in parallel.
     
  16. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    Something that he should do then he have to do, otherwise when he solve the battery problem, we can't make sure when the 2n3055 will be damaged.
     
  17. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    I'm back and still got the same problem.. I managed to charge this battery to 13.5V (dunno if it can go higher).. I got a little boost of current after charging.. From 1.3A ~ 1.8A.. but I still can't get the required 5A to maximize the peltier's cooling.. I also measured the voltage again going to the peltier and found that it's only about 10.1V.. is it possible that my battery is defective?.. I hope you continue guiding and helping me with my problem.. Thank you.
     
  18. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Battery is shot. Replace it. If it was still good, after charging, it should deliver a peak current > 20A. That fact that it does not means it has been left sitting uncharged too long, or it was previously incorrectly charged.
     
    gunvald likes this.
  19. gunvald

    Thread Starter New Member

    Oct 16, 2013
    15
    0
    Is there no other possibilities that affects it? ex. Peltier itself.. it is rated at 60W yet it draws only 1.3A ~ 1.8A.. I also tried supplying it directly from a wall adaptor rated 12V @ 5A but when I connect the ammeter in series, the peltier draws only 2A max.. And is it safe to use a 12V @ 12A adaptor for the supply? Thanks again.
     
  20. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    If the voltage at the Peltier is less than the supply voltage then there's a voltage drop between the two.
    What size and length wires are you using to connect it?
    Note that the ammeter itself has some resistance.
     
Loading...