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24vac to 115vac wiring help

Discussion in 'General Electronics Discussion' started by 95PGTTech, May 10, 2013.

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  1. 95PGTTech

    95PGTTech

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    May 10, 2013
    I would like to upgrade the fan inside my welder to a slimline computer fan as it runs awfully hot.

    The welder has a 4 wire 24VAC circuit coming off the PCB. The fan I have sitting around is a 2 wire 115VAC setup. I do not need variable speed settings just full blast all the time.

    Any tips on how to wire this or additional materials I may need?
     
  2. DuctDuck

    DuctDuck

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    Jan 26, 2013
    What about current sourcing from this 24VAC jack?

    Even if you can source an array of fans, you have to know how much airflow is going to improve (e.g.- cu.ft per min). Maybe your machine is in wrong spot!
     
  3. 95PGTTech

    95PGTTech

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    May 10, 2013
    OK to correct/clarify. The thread title should be 24vac transformer wiring help.
    Based off feedback on welder forum, bought a 24vac transformer.

    Here is the "OEM" circuitry. See RCA11 (1-4). The old fan was fried and unavailable. I am assuming the coiled wire is indicating a 24vac transformer. It appears to be the main power for the board because this is the first input after the cable coming from wall to circuit breaker to on/off switch to board.

    [​IMG]


    As I understand that, the box around both fan and transformer means it's one assembly. Unfortunately I did not inspect before tossing but the two did not appear easily disassemble-able. Therefore, the purchase of a new transformer. Ok picked up transformer. 25.2v ac 450mA. 120vac input center tapped secondary. Primary has 2 yellows. Secondary has 3 black.

    Everything I am seeing online is saying black/larger is "input" and yellow/smaller is output. That makes sense, but then how the hell do I power the fan if I'm allocating those 4 wires to the transformer? "Cheat" and steal power direct from 110vac before it ever reaches the board? I would imagine the old fan was designed for 24vac.
     
  4. DuctDuck

    DuctDuck

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    Jan 26, 2013
    10 VAs for cooling? You need more; even if a light duty machine (congratulations on your new transformer purchase; get some Leds now:p)

    Can you rig up power to the machine to get some safe voltage measurements?

    VAC sense RC10 RC5 (240VAC from outlet)

    VAC sense RC11-1 RC11-2 (possibly VAC for fan)

    VAC and VDC sense RC11-3 RC11-4 (possibly for fan speed)

    The schematic indicates to me a fan motor with speed control (e.g.-high and low). It could be possible to use a "fan" load at RC11-1 RC11-2 with out speed control but you have to evaluate those terminals. To use a "simple 110vac" fan motor on a 240vac source would require a step down to your tiny fan (really...why not match source to load?).

    ps-I have no industrial equipment repair experience and will not accept liability for what you do or anyone else does.
     
    Last edited: May 11, 2013
  5. 95PGTTech

    95PGTTech

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    May 10, 2013
    Unclear on first sentence. where are you getting the 10VA from? Yes - machine powers up fine, tested made sure I had 110vac from wall to the end of wire. Then next to the main circuit breaker. Then to the on/off switch. Finally to PCB. All these tests I used the main ground for so that checks out as well.

    This is a 110vac welder.

    Unclear to me again, sorry.

    As far as I know it has one speed (always on). There is no separate fan control on welder - when you turn on main power switch, it runs all the time full bore. That is not to say the PCB doesn't control it itself with some kind of thermostat. That's why I went with 110v fan, 110v welder.

    I'd never be enough of a bastard to hold you to it. Appreciate the help.




    Latest response on Hobart welding forum

    If that helps anyone help me.

    Here is my response.

    Unclear - the black leads and yellow leads are on the transformer itself. Currently i have 4 black coming out of the PCB (RC11-1 through RC11-4).

    Based on that picture above and your description, I think the wiring should be

    rc11-1 to fan. fan to transformer black. other transformer black to rc11-2. yellows on transformer to rc11-3 and rc11-4.

    if that is the correct idea, I am left with the following questions:
    1. what do I do with the third black wire coming off transformer
    2. wouldn't it be easier, now that it is a 110v fan, to use a simple relay to take power and ground directly after the main circuit breaker and the trigger side from the on/off switch. so anytime the switch for the welder is on the fan runs. that would simplify the transformer wiring. blacks to rc11-1 and 2 and yellows to rc11-3 and 4.
    3. Does it matter which black of the two goes to which PCB port, or the yellows? Again, nothing indicated on the wiring or instructions for transformer.

    Thanks guys, I feel like I'm getting close to an explanation of why this thing isn't working and finally fixing it.
     
  6. DuctDuck

    DuctDuck

    52
    0
    Jan 26, 2013
    Yeah, you're almost there!

    1-your small transformer is versatile; having two possible VAC levels with a center tap ground reference (25.2VAC or 12.6VAC). Omit center tap connection to pcb (cap it or cut it); check transformer for proper wires but the 25.2VAC transformer can work without all secondary side wires being connected.

    2-don't add any more parts than what you have to. A "simple" relay is controlled by a steady dc voltage (e.g.-12VDC, 5VDC,etc), specifically a control signal.

    Your goal is to connect fan and transformer as a parallel load. Transformer's primary side (high side) connects to RC11-1 RC11-2 as does the fan.

    3-nope

    Household line run gmaw/mig units have a low duty cycle (e.g.-25% implies 2.5 mins of 10 mins, but that is a quick calculation). Often 0.024 wire is the only feasible wire spool size for efficient use and that is for small beads on 22g quarter panel of an auto. When these small units get hot insides, that's it; thermal shutdown.

    All I can give you, good luck!
     
  7. 95PGTTech

    95PGTTech

    4
    0
    May 10, 2013
    Follow up -

    wired the transformer as per Tim's instructions and fixed a few other small issues while putting the welder back together. I only had time to test a small 1" long bead or so on a scrap piece but the welder functions correctly again. thanks guys!
     
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