RC Model on-board regulator help please

Discussion in 'The Projects Forum' started by machasm, Oct 21, 2010.

  1. machasm

    Thread Starter New Member

    Oct 21, 2010
    2
    0
    Hi all,
    I am new to the scene here and have only a rudimentary knowledge of electronics.
    I am in need of a design for a power regulator to satisfy the following requirements
    1) Is fed from 1 or 2 input voltage sources of Li-Po 2S batteries (fully charged at 8.4V, discharged at 6.4V). So must have protection so as not to back charge either battery if 2 are used.
    2) Have a fixed 5V output capable of delivering up to 5A
    3) Have another output switchable between a) 5V b) 6V c) input voltage (bypass) and capable of up to 10A
    4) Have another output at 1.3V rated at 3A and having a momentary push switch so that this output is activated for 15 seconds (Used to power a glow plug on the model)
    5) Have LED voltage indicators of battery levels
    6) Have High visibilty LED illuminate when voltage on either pack drops below 6.4V

    I was looking a linear regulators but some of the loads means dissapating a lot of heat and also means that batteries don't last as long as I would like. Would prefer to use a switching reg if possible but if its simpler to go with a linear reg then fine.
    Any help much appreciated.
    I have attached a pic (Very basic!)
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,696
    904
    Switching is the way to go. Have you talked to the engineers at Castle Creations? You can get into problems with receiver interference, depending on what you are using for a receiver.

    Second suggestion, using diodes for dual batteries is done, but has some drawbacks too. Have you considered having a slightly more complicated management system that uses one battery, then switches to the other battery, but does not switch back?

    Do you want off the shelf suggestions or do you want to design it ground up? What are your weight and space limitations?

    John
     
  3. machasm

    Thread Starter New Member

    Oct 21, 2010
    2
    0
    Thanks for your quick reply John.
    To answer your questions I have not spoken to people at Castle creations. I realise that switching circuits do create noise and will be running these on 2.4Ghz receivers. I am not aware if there will be problems here but will have to suck it and see.

    I'm all ears if there is a better way to run off 2 sources instead of using diodes.
    I would have rather had the 2 batteries working together but am not hung up on it. Just wanted to have some sort of redundancy in case of a cell dying or leads from the pack going open circuit. It also meant that the packs could be smaller since they would only need to be half the capacity of a single larger pack.
    The prob with switching from one pack to the other is if there is a problem with pack 2 when it is switched in then there is no charge left in pack 1 to fall back on.

    Of the shelf is good but can't find anything that does all this and is still a reasonable cost.
    A custom ground up circuit would be great and might even be able to market it if any one else wants one :)

    As for weight and space limitations as light and as small as possible really.
    If I had to start somewhere I would say around 70mmX40mmX15mm but a bit bigger isnt going to break the bank. Even as long as 120mm. Weight if it could be kept down under 100grams that would be good.

    Ade.
     
  4. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
    Switching between batteries wouldn't be too hard. Detect the drop in voltage to a certain level then use MOSFETS to switch to the full battery. I hope your 100gms doesn't include the batteries, you will really be pushing it up hill I think. I know LiPo batteries are light but not that light. Can you describe what sort of model this is going into? Type of motor you will be driving?
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,696
    904
    Here is the type of backup I mentioned:
    [​IMG]

    Joe Utasi published the full construction article, PCB patterns, and schematic in the December, 1991 R/C Modeler magazine, beginning page 240 (Ultimate Battery Backup System). His article and the current EMS/Jomar product (emsjomar.com) look very similar. Unfortunately, R/C Modeler is defunct, and its current owner sells model plans only. Basically, the backup uses an ICL7673 "battery backup switch" driving a couple of other chips (DIG12-08-045) with LED's , and finally mosfets for switching. It picks the same "main" battery initially. As that battery depletes, it goes to the backup, but if the backup is bad, it switches back to the main battery. As I understand it's action, it will not keep switching back and forth as each battery regains some voltage on resting.

    If you have sufficient interest, I will scan and post the schematic. I suspect it may be overkill for your project though.

    John
     
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