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Tapping 12V from 24V Battery Source

Discussion in 'Power Electronics' started by CalgaryPT, Jun 11, 2019.

  1. CalgaryPT

    CalgaryPT

    19
    4
    May 7, 2017
    Hi all....

    I am building an RC Lawnmower. Most of the HD motors are wheelchair gear type and require 24V. But some of the electronics I plan to use are 12V, for example the linear actuators.

    Can I tap the series connector line between the batteries for the 12V? I think this may be how it is done on heavy equipment and trucks that use two 12V batteries to operate on 24V, but am unsure.

    What's the impact of such an arrangement if I run the 12V tap from the system when I go to charge the batteries? I'm wondering when recharging in such a situation if it would be better to either use two 12V chargers and charge each battery separately (or build a circuit that cycles one charger between the two barriers), instead of a 24V charger across the two batteries. I'm assuming the battery I tap off of will have a smaller voltage than the other after they drain.

    Not sure what chemistry I will use for the batteries, but weight is obviously a factor.

    I'd love to use this question as an excuse to buy a CAT D9 Dozer to assist in my research, but sadly (1) I live in the suburbs and (2) my wife won't let me have one.

    Pics attached....

    24v.jpg d9.jpg
     
  2. Ylli

    Ylli

    192
    34
    Jun 19, 2018
    hevans1944 likes this.
  3. CalgaryPT

    CalgaryPT

    19
    4
    May 7, 2017
    Thanks :) I have to admit originally I blew off your response when I saw the inductor and number of components on the board as I thought it looked pretty inefficient. My circuit knowledge is pretty good, but dated. So I wondered if you were to step it down why not use a linear voltage regulator and just accept the energy loss. Then I did some reading on switching regulators and see how they are much better, especially in non-noise sensitive circuit design (hope this won't be problematic in my RC system).

    Found a great explanation here: https://www.rohm.com/electronics-basics/dc-dc-converters/linear-vs-switching-regulators

    As soon as I saw the sawtooth wave I immediately figured out what was going on. I have ordered a couple of the regulators and look forward to trying them. Even if the noise proves an issue in my circuit I can go to a linear regulator easily. But I am so curious to try the switching ones (they are cheap), I thought I would try.

    So thanks for the suggestion. Just out of curiosity, do you know if the method I posted would technically work though?
     
  4. Ylli

    Ylli

    192
    34
    Jun 19, 2018
    Yes, the method you posted would work, but you would be using one battery more than the other. Depending on how much draw there is on the 12 volt tap, you may have to charge the batteries separately so that one doesn't get over/under charged. And you would probably want to rotate the batteries every once in a while (like rotating tires).
     
    CalgaryPT likes this.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    9,128
    1,841
    Nov 17, 2011
    Both issues can be remedied with one of these:
    [​IMG]
     

    Attached Files:

    • d9.jpg
      d9.jpg
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    ChosunOne and Martaine2005 like this.
  6. Martaine2005

    Martaine2005

    2,362
    623
    May 12, 2015
    Or a full size dozer and one of these....


    upload_2019-6-12_13-13-19.jpeg
     
  7. CalgaryPT

    CalgaryPT

    19
    4
    May 7, 2017
    I think the Matchbox option is the least costly of the two.
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    9,128
    1,841
    Nov 17, 2011
    With time the accumulated savings from Martin's proposal may be even higher ;)
     
    Martaine2005 and CalgaryPT like this.
  9. CalgaryPT

    CalgaryPT

    19
    4
    May 7, 2017
    Just thought I would update this post for other buck converter nubes. I ordered two but couldn't get the darn things to work. Of course the high quality documentation (i.e., NONE) that came with it was a total help. Anyways, after doing some research I discovered that buck converters only work under load—you can't just put a Fluke on the output terminals and adjust a pot to get your desired voltage. Or at least this was what solved my problem.

    P.S. When I rule this planet the penalties for poor documentation will be unnecessarily harsh and punitive.
     
    Martaine2005 likes this.
  10. Ylli

    Ylli

    192
    34
    Jun 19, 2018
    Yes, some switching supplies require a load to operate. Some do not....
     
  11. Mersama

    Mersama

    1
    0
    Jul 19, 2019
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