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Default Soft Start

Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps
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Roger
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Default Soft Start

On May 5, 7:39*pm, Roger Mills wrote:
Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps
--
Cheers,
Roger
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You can add soft start to machinery - with an inverter (I guess the
same as in your genny, just with lots of user settings on it) - but I
don't think it will reduce the current draw.

I bought an old 3-phase bandsaw, and added an inverter to that (an
Omron IIRC), and it has endless settings for things like ramping up
the Hz - and every other imaginable characteristic of power
management.

Does an excellent job, but not cheap.
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Default Soft Start

On May 5, 7:39*pm, Roger Mills wrote:
Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps
--
Cheers,
Roger
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checked.


The compressor might need and an unloading valve. ie, releases air
pressure in the compressor before it starts to reduce the start
current.
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Default Soft Start

On May 5, 7:39*pm, Roger Mills wrote:
Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?


yes

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?


well... compressors are not normally soft started, they need a good
current surge to get going in the face of high pressure. You can soft
start them, but would need to take the pressure off them until theyre
upto speed. How easy it is to arrange the additional mechanics on your
compressor I dont know.

It will also work on soft start as is if you start with an empty tank,
and switch it off once full so it doesnt try to top it up. Might or
might not be practical though.

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps


http://wiki.diyfaq.org.uk/index.php?title=Droppers


NT
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Default Soft Start

On Thu, 05 May 2011 19:39:55 +0100, Roger Mills wrote:

Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps


Does it start ok when there is no pressure in the receiver? If so then you
could add a three port solenoid operated valve between the compressor and
the receiver. The valve can vent the compressor output to atmosphere when
the motor power is removed and re-connect the compressor output to the
receiver a few seconds after the motor is powered up. It wouldn't be cheap
though.

SteveW
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Steve Walker wrote:
On Thu, 05 May 2011 19:39:55 +0100, Roger Mills wrote:

Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps


Does it start ok when there is no pressure in the receiver? If so then you
could add a three port solenoid operated valve between the compressor and
the receiver. The valve can vent the compressor output to atmosphere when
the motor power is removed and re-connect the compressor output to the
receiver a few seconds after the motor is powered up. It wouldn't be cheap
though.

SteveW

Aldi/Lidl type compressors I have seen already have a dump valve
arrangement fitted.

Bob
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Default Soft Start

On 05/05/2011 23:21, Steve Walker wrote:
On Thu, 05 May 2011 19:39:55 +0100, Roger Mills wrote:

Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

etc



Does it start ok when there is no pressure in the receiver?


Dunno - I'll try it.

If so then you
could add a three port solenoid operated valve between the compressor and
the receiver. The valve can vent the compressor output to atmosphere when
the motor power is removed and re-connect the compressor output to the
receiver a few seconds after the motor is powered up. It wouldn't be cheap
though.


An interesting solution. I'm not going to spend much money on anything
though, because it was just an experiment to see whether I could operate
it away from a mains power supply - but I have no compelling need to
actually do that.
--
Cheers,
Roger
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On 06/05/2011 08:33, Bob Minchin wrote:

Aldi/Lidl type compressors I have seen already have a dump valve
arrangement fitted.



Mine has a ring-pull valve to de-pressurise the receiver - is that what
you mean?

It *might* work with the genny if I turn it on and off manually,
completely exhausting the pressure each time - but that wouldn't be very
efficient.

In normal operation the motor is controlled by a pressure switch with
some hysteresis between on and off pressures - so it cuts out when it
gets to max pressure, and turns it on again when the pressure falls a
bit (but still way above zero).
--
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Roger
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Default Soft Start

Roger Mills wrote:
Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps


If it's a squirrel cage motor or capacitor start, then it'll take a
massive surge at start-up. The only generators I've met that will cope
have been old ones with a massive flywheel on the engine.

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Tciao for Now!

John.


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Default Soft Start

Roger Mills laid this down on his screen :
Mine has a ring-pull valve to de-pressurise the receiver - is that what you
mean?


That is a safety valve.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


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On Fri, 06 May 2011 13:53:15 +0100, Roger Mills wrote:

On 06/05/2011 08:33, Bob Minchin wrote:

Aldi/Lidl type compressors I have seen already have a dump valve
arrangement fitted.



Mine has a ring-pull valve to de-pressurise the receiver - is that what
you mean?

It *might* work with the genny if I turn it on and off manually,
completely exhausting the pressure each time - but that wouldn't be very
efficient.

In normal operation the motor is controlled by a pressure switch with
some hysteresis between on and off pressures - so it cuts out when it
gets to max pressure, and turns it on again when the pressure falls a
bit (but still way above zero).


My experience is with big process gas compressors (a small drive motor was
around 300kW, a large one 8MW!) The typical way of starting such
compressors is to remove the load either by forcing the compressor's inlet
valves to remain open or by bypassing the discharge back to the inlet. For
an air compressor, you do not need to do this, instead, you just isolate
the receiver and vent the compressor's discharge.

Don't think of the compressor and its receiver as one unit, think of of it
as a compressor feeding a receiver via a pipe. A valve in that pipe can
isolate the feed to the receiver, preventing air escaping and at the same
time vent the compressor discharge so there is no back pressure. Once the
motor is up to speed, the valve can operate, closing the vent and
reconnecting the compressor to the receiver. This will allow the normal
stop start nature of small compressors, while starting the compressor with
virtually no back pressure and therefore little load every time.

SteveW
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On Thu, 05 May 2011 22:33:21 +0100, John Rumm
wrote:

On 05/05/2011 19:39, Roger Mills wrote:

Anyone know whether it's possible to add soft start to a tool that
wasn't born with it - maybe by using some external plug-in wizardry?


Possible, certainly.

I have a Lidl compressor which, according to my power meter, takes about
750 watts[1] when running.


Probably not an ideal candidate for electrical soft starting. Chances
are it would just stall on startup.

I tried to run it today from my Honda 2kW (peak - 1.6kW continuous)
inverter-based generator, and the genny didn't want to know - presumably
because of the high start-up current.

Would a soft start help and, if so, can it be retro-fitted?


I would guess if you could find a way of unloading the motor on startup,
that alone may fix the problem. If not then you could probably
electrically soft start that, and then reload it once running.

[1] Probably 1000VA with a non-unity power factor because the indicated
current was about 4 amps


If you have a nice large none reactive load like a kettle or heater,
stick it in series with the compressor and see if it runs.

If it fails to run and doesn't trip, find a lower resistance load and
try again..

If it runs and builds to a reasonable pressure on its limited current,
then either use a pressure switch to short out a series resistor
equalish to your kettle, or a timer.

You could even do a "start run" switch configuration that you switched
through from stop to run. Use make before break contacts if you try
this route.


The surge current that trips your inverter occures when the motor is
stationary and generating no back EMF. Removing any or all of the
mechanical load is a none starter. The bare motor would trip your
inverter. Electrics is quick motors isn't.

On a final note, soft starters were available for single phase motors
when I was involved with them, they were very effective and I would
assume quite inexpensive for the load you describe.

I never saw a plug in version, but if you can grasp the basics of a
terminal driver and the terms supply and load, then you would not have
a problem.

HN






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