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Voltage regulation/current limitation?

pinnopinno Posts: 45,289
edited May 2015 in The cake stop
Now I could purchase a Voltage regulation unit but might there be an easier way?

Here is the rough flow:

Petrol generator 240v AC > Trip switches > Control box for a baling machine.

The baler has a control box. Current is split, primarily to 2 circuits (A and B)
A. 240v > 110v via a transformer for the conveyor
B. 240v > 24v via another transformer.

The solenoid actuators and system/start controls work off a 24v supply.

This is the weak point. The system is quite content working off anything down to 175v (roughly) but as there are multiple things connected to the baler; lights, 2nd conveyor, the current to the control box fluctuates.

So there are fluctuations in the current. The 24v transformer is sensitive to a power surge. This happens when both conveyors are stopped. A big power surge can cook it.
I wondered if I can deploy an in line resistor to the 240v power supply to the 24v transformer to cap the current into it, or is that a little simplistic?

Specs for the 24v transformer:
Input: 100 - 240v @ 50-60hz, amps
Output: 24v DC, 0.6 amps

seanoconn - gruagach craic!


  • sungodsungod Posts: 14,341
    that omron thing is not a transformer, it's a switchmode power supply, according to the datasheet it has some basic input protection but it's clearly not enough for your application

    it's a voltage surge that's zapping it, an inline resistor large enough to protect it wouldn't allow the power supply to work

    an olde linear psu might be more robust, but i'm assuming you'd rather not get into that sort of modification

    you can add an ac surge suppressor on the input side of the psu

    industrial ones can be quite pricey, may be cheaper to use a domestic one designed to protect a home computer etc. - though i'm wondering what the surge energy is, you need something chunky enough to survive
    my bike - faster than god's and twice as shiny
  • pinnopinno Posts: 45,289
    Cheers SG.

    I looked at this:

    Except the operating current is between 220 and 240v. Would it work under currents less than 220v?

    I measured the current at the input to the control box into the baler when the whole system was under full load - i.e Lights (strip lighting) and 2 conveyors. It was 175v.
    At minimal load, the current is a steady output of 218 to 222v from the generator. I set the governor so that under minimum load, the revs were limited to preserve engine life and because the sudden rise of engine speed under immediate low load. cooked the Omron switchmode* (*yes, you are quite correct).
    The conveyor, which is linked to the baler has a sensor. When the sensor light is broken, the conveyor stops. The other conveyor is manually operated. Under most conditions, one or both are running.
    When the baler ejects, (activated by the solenoid actuator - hydraulic switch), the baler is using 0 current.
    If at this point, both conveyors stop by coincidence simultaneously (either manually or automatically), there is a power surge.
    I can only presume that the power surge is 222 - 175 = 47v max. Too much for our mate Omron.
    seanoconn - gruagach craic!
  • sungodsungod Posts: 14,341
    if there're heavy motors being started/stopped by mechanical switching there can be substantial voltage spikes generated, these can be high energy, dumb stuff survives them, but active electronics such as the omron thing will not be so tolerant

    it is also possible that the power supply is using a dual-range input circuit (basically it kicks-in a voltage doubler if the ac is in the low range), i've seen these fooled by wide voltage swings (bang), which'd also match the generator surge idea

    that suppressor will work with lower voltages, it imposes an upper limit on spike voltage, for this type it's probably around 400v peak but it won't help if the cause is the voltage swing of the generator


    tbh i'd be tempted to look for a dumb linear power supply with a wide input range
    my bike - faster than god's and twice as shiny
  • pinnopinno Posts: 45,289
    Do you think something like this would do? Or is the 30 milli amp trip speed too slow?

    seanoconn - gruagach craic!
  • sungodsungod Posts: 14,341
    not sure what that is, but it looks like a leakage detector which would not give the omron protection
    my bike - faster than god's and twice as shiny
  • pinnopinno Posts: 45,289
    sungod wrote:
    not sure what that is, but it looks like a leakage detector which would not give the omron protection

    Bad photo. It is a surge protector.
    seanoconn - gruagach craic!
  • sungodsungod Posts: 14,341
    you can try, but like i said, if it really is an isssue with the input autoranging in the omron this won't help
    my bike - faster than god's and twice as shiny
  • pinnopinno Posts: 45,289
    All I need is something to limit the current into the Omron.
    Now I have the governor sorted on the genny, it would only be a once in a blue moon event that the current exceeds 240v. It has survived many power surges before but the genny is not a device that you can control 100%.

    The problem may occur when demand is suddenly reduced and the RPM momentarily goes too high before the generator balances out.
    seanoconn - gruagach craic!
  • sungodsungod Posts: 14,341
    yes but how can it be limited? like i said, a simple resistor is no good, so you need t identify the cause before working out the options

    the thing i'm concerned about is this:

    i assume the omron uses a voltage doubler on the input side to provide basic autoranging over a wide ac range

    the voltage is normally low enough to cause the omron to operate on it's low range, the internal multiplier is active

    when the generator is unloaded the ac rises for at least a few cycles

    this causes the ormon to go bang as the doubled voltage on the input side rises far above safe operating before the doubler can cut out

    an ac surge supressor will not provide any protection if this is the cause, it will only limit at a far higher voltage than needed for failure (it will protct against spikes, but that's a different failure mode)

    by all means try the suppressor, but be aware it may not be the answer

    if the doubler is the failure mode, you'd need an ac regulator, that gets expensive, which is why i thought using a robust linear supply may work out better - for the power involved it'd be straightforward to design a linear one with adequte margin or even get a secondhand one on ebay and tweak it for what's needed - or even use a linear supply to drop the voltage to, say, 30v, then use a dc-dc convertor with a wide input range to get the desired 15v
    my bike - faster than god's and twice as shiny
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