Control Board VAC to VDC Problem

Discussion in 'The Projects Forum' started by swen, Aug 1, 2014.

  1. swen

    Thread Starter New Member

    Aug 1, 2014
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    Hello, I am troubleshooting a driveway gate operating system. It runs on 24 volts (2 12-volt batteries in series). It runs on a transformer that converts 110 VAC to 24 VAC. Then the control board converts the 24 VAC to 24 VDC to keep the batteries charged. My problem is that the batteries are not getting charged. I discovered that the control board power going to the batteries is only 20 VDC, and it should be at least 25 VDC or so to charge the batteries.
    Could someone possibly be able to describe what to look for on the board that might be the problem?

    [​IMG]
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I'm guessing the IC mounted on the big heatsink next to the 'Battery low' LED could be a regulator for the charging. What are the markings on it?
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Looks to be Elite Miracle One Part ID Q223.
     
  4. swen

    Thread Starter New Member

    Aug 1, 2014
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    Here's a closeup of that.
    [​IMG]
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It's a 7812 +12v regulator that supplies the main 12v rail for all the relays etc.

    That toroid next the 7812 and caps and a small (hard to see, next to blue trimpot top photo) heatsink look to be a SMPS, probably a buck SMPS IC for battery charging?

    That blue trimpot is likely to be an adjuster for float charging voltage.

    Of course, if the battery has one or more shorted cells (common in old SLA batteries) the circuit might be perfect and the reason for the 20v on the battery terminals is the faulty battery. Did you measure the charging voltage with no battery connected?
     
  6. swen

    Thread Starter New Member

    Aug 1, 2014
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    I've already gone through two sets of brand-new 12-volt batteries (4 batteries). Could it be as easy as adjusting that trimpot? I can sure try it & see, but don't want to make anything worse....
    I get 20 VDC with and without battery connected.
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
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    Make sure the batteries are fully charged when installed.
     
  8. gagwd

    New Member

    Aug 2, 2014
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    It would be nice to know the starting point that prompted the repair. Has this board been out of service for sometime? The reason for the question is a concern that the charging voltage is far enough out of spec for open circuit output that the pot may not bring it back, but farther still I would not anticipate that the charger could stray that far away without reason. Is it 20V because someone already tried adjusting it and left it in the wrong position?

    Regarding the type of SMPS I would not expect it to be a buck if the input to the charging circuit is 24V. However before any assumptions are made it wouldbe a good idea to find the active device(s) for the charger circuit. Can you post a picture front and back of the board in the area of the torriod after you confirm that the charger output originates from circuitry in very close proximity to the torroid?
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What's the component near the 7812, marked 'VR1' ? Does 'VR' denote 'voltage regulator' or 'variable resistor' ?
     
  10. swen

    Thread Starter New Member

    Aug 1, 2014
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    I'm not sure the control board ever worked. I bought the system on ebay (internal batteries included) and it sat for at least a year before I installed it. But I made sure it operated the gate arms right after buying it, and I kept the batteries charged via the transformer now and then before install. But as soon as I installed the system the batteries were dead. So I bought two "lawnmower" batteries and ran the gate without problem with these external batteries for about 3 months. But not with the transformer. Instead, I ran it with a solar panel installed per the gate manufacturer's manual. The panel puts out 37 vdc and I've since read that overcharging can damage board and/or batteries, so that could have been the start of the problem. Then I installed 2 new internal batteries and ran off the transformer. Those batteries lasted about 6 days; that's when I discovered that the board doesn't put out enough voltage.
     
  11. swen

    Thread Starter New Member

    Aug 1, 2014
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    The charger output is on the lower LEFT corner of the board; not very close to the toroid and trimpot discussed above. I can post pics later if that helps.
     
  12. swen

    Thread Starter New Member

    Aug 1, 2014
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  13. swen

    Thread Starter New Member

    Aug 1, 2014
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  14. swen

    Thread Starter New Member

    Aug 1, 2014
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    No more responses for awhile, but since Wifey gets annoyed having to open the gates by hand, I tried adjusting that trimpot. 1/4 clockwise gave me 24 VDC. Another nudge to 25 VDC and I installed the board and it is working. Internal battery that was at 20 V is now operating the gates at 24 V. My only concern is whether I had damaged the control board with the solar panel and whether the board will soon be going up in flames.
     
  15. to3metalcan

    Member

    Jul 20, 2014
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    Well, just to check the obvious...anything getting hot? (careful about the heatsinks...sometimes in smps circuits, they're live!)
     
  16. THE_RB

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    Feb 11, 2008
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    Thanks for posting the bottom of the board. That little heatsink I mentioned seems to have a 8pin DIP IC under it, I'm thinking it's likely to be a MC34063 SMPS buck IC.

    All should be fine re the board and the solar panel. Assuming the solar panel did not put out enough current to charge the batteries significantly above their normal voltage it won't damage the 34063 IC, they will just share the current as needed.

    The correct float voltage for a 24v SLA battery is 13.7v *2 or 27.4v. You should adjust that with no battery connected, to make sure it is right at 27.4v.
    :)
     
  17. swen

    Thread Starter New Member

    Aug 1, 2014
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    Thanks! So far, still working fine.
    Question: I plan to re-hook-up the solar panel. I bought a solar panel battery regulator charger controller to prevent overcharging the batteries. The specs say it will cut power when it reaches 27.4 - 28.8 V. That ok?
     
  18. THE_RB

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    Why bother? Assuming the miracle board is always powered up (which it generally would be) then it will keep the batteries charged to float all the time.

    The only time the solar is needed or will do anything at all is when there is a blackout, which is what the batteries are for. And the blackout would have to happen during the middle 5 hours of the day or the solar would still be useless.
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    Consider yourself lucky that Wifey appreciates your spending sooo much time on AAC for her benefit.:)
     
  20. swen

    Thread Starter New Member

    Aug 1, 2014
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    No, I'm not going to leave it on transformer. I'd have to bury conduit underground 18" deep for about 100 feet to do that. It's temporarily on extension cord.
     
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