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Non-aero app: 120/240 AC through 24vdc switch?

 
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nuckolls.bob(at)aeroelect
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PostPosted: Thu Aug 24, 2017 6:54 am    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

At 11:14 AM 8/23/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>

Joe and Charlie,

The switch controls an electronic lamp ballast driving two 75W UVC producing. I don't know if that is inductive or resistive load. Steady state amperage is 800ma

And found this white paper(excerpt) on electronic ballasts. :

"Design Considerations for Electronic Ballasts

Inrush currents at turn-on, produced from some electronic
ballasts can cause premature relay contact failures.
These inrush currents can be much higher than those
experienced with traditional tungsten or magnetic ballast
loads because many electronic ballasts employ large
energy storage capacitors. Such capacitors can charge up
to 400V for a 277V line voltage, and will briefly draw high
current from the line to achieve this voltage.
As mentioned above, these typically short inrush currents
can climb as high as 100 times the nominal operating
levels.

ALL devices with metallic contacts have
difficulties with capacitive loads.
The majority of my experiences with
premature contact failures involved
capacitive loads.

Consider adding inrush limiting to the
switched pathway

http://tinyurl.com/yacaagsp

These are negative temperature coefficient
resistors with substantial room temperature
resistance that falls to insignificant
resistance after being allowed to warm up
under the steady state load.

I've only had occasion to use these once
on an airplane (P-180). The techs working
the experimental airplane came to my desk
complaining that the things kept 'blowing
up'. Turns out they had mounted the device
to adjacent lamp housing such that internal
heating was transferred to the housing.
The devices were not being allowed to warm up,
internal dissipation remained high and they
went into self destruction.

So be sure to mount these such that free air
is the only heat sink.

It may take a bit of fiddling to get the
optimum part . . . but this one seems
a likely starting point for your quest.

http://tinyurl.com/y92bs8ba




Bob . . .


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jonlaury



Joined: 06 Nov 2006
Posts: 336

PostPosted: Thu Aug 24, 2017 10:41 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

Thanks Bob,
Although suspicion has risen that my step-down power supply is the culprit (40a inrush), I appreciate learning about inrush current limiters for their small form and small price compared to clunky hi amperage/price relays, mechanical or solid state.

John


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PostPosted: Fri Aug 25, 2017 5:59 am    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

At 01:36 PM 8/24/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>

After further investigation, suspicion has grown about the inrush current to the power supply that I'm using.

The ballast mfgr says any inrush to the ballast is not a problem for the garden-variety installation. The thing that is different about my install is the inclusion of a step-down power supply that specs 40A inrush current...8x the switch spec of 5A.

Stay tuned
John

Okay, I've lost my mental image of the
configuration. Can you sketch and scan
a schematic of the major components along
with location of the switch?



Bob . . .


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jonlaury



Joined: 06 Nov 2006
Posts: 336

PostPosted: Sat Aug 26, 2017 9:00 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

Bob,
Here's the schematic, and late breaking...the ballast mfgr engineer informed me that the max inrush for the ballast is 101 A. Combined with the Pwr Supply's 40A inrush, rough duty for a 5A switch.

Thanks for looking at this,
John


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PostPosted: Sun Aug 27, 2017 4:38 pm    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

At 12:00 PM 8/26/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>

Bob,
Here's the schematic, and late breaking...the ballast mfgr engineer informed me that the max inrush for the ballast is 101 A. Combined with the Pwr Supply's 40A inrush, rough duty for a 5A switch.

Thanks for looking at this,
John


Okay, let's talk about 'inrush' currents.

[img]cid:.0[/img]

Here's a simple model of an inrush-energy study that will
suffice for this discussion. In reality, the model is
much more complex with features (inductances and capacitances)
combined with dynamics of the power source and timing . . .
if you close a switch at the exact instant the AC voltage
is at its peak, then MAXIMUM inrush currents can be expected.
On the other hand, if you can somehow close the switch while
the incoming voltage is zero . . . then inrush effects on
the switch will be . . . uh . . . almost zero.

I show two resistances, Rs which is the source resistance.
This component sets the maximum current that can flow if a
dead short is placed across the source. It also set the
requirements for 'interrupt current ratings' on circuit
breakers and fuses.

Then I've show a load resistance Rl which is controlled
by the configuration of your products input components,
in this case . . . a combined ballast and power supply.

The ballast mfgr has quoted a rather impressive inrush
current number . . . which is only partly significant.
Consider a range CAPACITORS sized from picofarads
to farads. The exact instant that your switch contacts
close, the inrush current will be V(applied)/Rs+Rl and
may very well be on the order of 100 amps . . . which
says NOTHING about the size of the capacitor, only that
V is applied over the total resitance for some period of
time after contact closure.

If C is picofarads, the DURATION of the inrush event is
very short, perhaps measured in picoseconds. If C is
Farads (like some of those capacitors favored by
installers of mobile gray-matter mashers) then the
duration of inrush event is orders of magnitude more
severe.

The ability of a switch to manage that event has roots
in contact mass, spring rates of closing forces and
velocity of the moving contact mass as it crashes into it's
stationary mate.

Contact bounce is an inevitable feature of ALL mechanical
switches. Further, the severity of bounce is only loosely
related to the switches pedigree. Here's a study I did
on a system with mil-spec, sealed relays that were GOING
to stick irrespective of how well the device was
built.

http://tinyurl.com/pstsggm

As you can see in this article, the sticking
wasn't even a high energy event. The relays were being
used in a situation well inside their catalog ratings . . .
but a combination of capacitance and PROPAGATION delay
down and back over a crude coaxial feed line stacked
up to offer the 'perfect low energy relay welder'.

The 100A inrush value offered by your supplier simply
acknowledges that there is some capacitive component
across the input to their product . . . but no help
for how large it might be.

Obviously, the COMBINATION of that inrush energy event
and contact bounce on your switch of choice has produced
a condition prone to sticking.

What kind of switch are we talking about? How long does
it take to produce a failure event? Have you been able to
duplicate the sticking even in a laboratory environment?
Are there a lot of fielded devices that may need
upgrading? One sure bet for fixing the problem and staying
with your existing switch is to add some electronics behind
the panel . . . perhaps a solid state relay with ZERO CROSSING
detection that reduces inrush to a minimum.

http://tinyurl.com/y7rst4a6

http://tinyurl.com/y8g8zyj9

Another possibility is to change the switch. Just a
difference in brand for the same physical switch
can make a big difference. Adding to Rl in the
inrush loop, either inrush limiter or perhaps just
a 3 ohm, 5 watt resistor (1A running current across
three ohms is 3 volts drop, 3W dissipated . . . but
a reduction in inrush MAGNITUDE by a factor of 3
or more . . . with an insignificant change in
over all performance.

Making the elegant decision demands more data. Perhaps
'scope traces on the inrush event. A study of bounce
characteristics of the switch. Better data on exactly
what the inputs to your loads look like will help.

But it seems likely that a change in brand/style
of switch is the shortest path and perhaps even
doable as a field retrofit. The elegant equation
demands a lot more 'numbers'






Bob . . .


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jonlaury



Joined: 06 Nov 2006
Posts: 336

PostPosted: Mon Aug 28, 2017 8:14 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

Bob,
A thousand thanks!

And I found your explorations and findings about the relay failures on rolll trim control boards fascinating, if for no other reason than the failure symptoms are almost identical to what I'm seeing with my product.

My switch failures are beginning to occur after about 30-60 cycles. Thinking that the sticking was purely mechanical, and acknowledging the problem to users, I suggested unplugging the machine, squirting WD40 into the pushbutton recess and cycling the switch until they got a blister on their finger, to erode/smooth the imagined rough edges of the switch internals. It either worked or customers just didn't want to talk to a crazy person any more, because very few reported a continuing problem. I even rigged up a reciprocating saw with a 'boxing glove' to wear-in the switch, as a misguided, pre-conditioning preventative.

Your analysis, with remedies, is a crescendo of angelic voices, coincident with brilliant, golden light, illuminating the path out of blasphemous tinkering to electronic righteousness. I feel cleansed. Very Happy

One more impertinent question:
In the zero-crossing relay suggested, the load side spec is 250vac (at) 2a. The steady-state ballast load is 800ma and the motor draws about 2a. Will the relay take it? or am I missing something here?

Thanks again,
John


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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Tue Aug 29, 2017 5:10 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

What if a solid state relay and a mechanical relay are connected in parallel? The solid state relay will turn on a fraction of a second prior to the mechanical contacts closing and will conduct while the mechanical contacts are bouncing. Once the mechanical contacts have stopped bouncing, then they will carry the full load.
Or use only a solid state relay rated for the current.


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PostPosted: Tue Aug 29, 2017 5:29 am    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

At 11:14 AM 8/28/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>

Bob,
A thousand thanks!

And I found your explorations and findings about the relay failures on rolll trim control boards fascinating, if for no other reason than the failure symptoms are almost identical to what I'm seeing with my product.

My switch failures are beginning to occur after about 30-60 cycles. Thinking that the sticking was purely mechanical, and acknowledging the problem to users, I suggested unplugging the machine, squirting WD40 into the pushbutton recess and cycling the switch until they got a blister on their finger, to erode/smooth the imagined rough edges of the switch internals. It either worked or customers just didn't want to talk to a crazy person any more, because very few reported a continuing problem. I even rigged up a reciprocating saw with a 'boxing glove' to wear-in the switch, as a misguided, pre-conditioning preventative.

Yup, been there . . . or at least some of
my compadres have. There was a chronic difficulty
with nuisance tripping the ov system on the
A36/B55 series aircraft . . .that stuck its
head up several times over a span of some
30 years. One attempt at a fix included taking
brand new alternators and running them at load
on a drive stand for 20 hours or so before putting
them on the airplane . . . seems the problems were
mitigated with service time.

The operative theory at the time was that QC issues
with slip ring/brush interface was root cause of
the problem. A break-in operation seemed to help.
As it turns out, the brush/slip ring interface
was a NORMAL condition that was only a trigger
for root cause.

Got to watch that same problem pop up about every
5-10 years or so. But it wasn't until my very last
service offered to the then newly amalgamated Textron,
I suggested again, that it wasn't the alternator's
fault . . . but that of the ov regulators ov
protection system.

We started a stone simple fix before my
contract ran out. At least I didn't have to
endure the machinations and pretzel twisting
it took to get one set of guts lifted out of
a regulator with a decades long, stellar track
record and installed inside the regulator enclosure for
the Beech products. i.e. a presto-changeo
creation of a form-fit-function replacement
for a regulator that had NEVER been subjected to
DO-160 study for suitability to task. A task
that we would have accomplished in mere
days back in the day . . . took nearly a year
under the 'new order'.


Quote:
Your analysis, with remedies, is a crescendo of angelic voices, coincident with brilliant, golden light, illuminating the path out of blasphemous tinkering to electronic righteousness. I feel cleansed. Very Happy

You're too kind . . . but you appreciate the
the kind of thought processes and experiments
that have to be conducted to (1) eliminate that
which does not work, (2) identify that which
does work and (3) sift all the options in quest of
the elegant solution.

That relay study on roll trim cards took about
two years as the activities had to be interleaved
with more pressing matters. And I was the only
one working on it. A 'tiger team' of similarly
thoughtful and motivated students of the physical
arts would have been very helpful. Same story with pitch
trim motor failures that plagued Beech to the tune
of $millions$ in warranty claims and lost
customer confidence.

Maybe I'll publish that paper one day . . . it's
a real zinger . . . and like the roll trim relay
studies, it took years of looking for the answers
to 'what if' and 'how about this'. Sorta like
technological whack-a-mole. Then one day, one
of the heads that popped up was the Eureka mole.


Quote:
One more impertinent question:
In the zero-crossing relay suggested, the load side spec is 250vac (at) 2a. The steady-state ballast load is 800ma and the motor draws about 2a. Will the relay take it? or am I missing something here?

Good eye. Yeah, if THAT option is attractive, you'll
need a beefier device. Maybe something like this.

http://tinyurl.com/y8bfqm5o

While on a patient transfer from Wichita today I
had a brain-fart that might be the simplest
solution. You could craft your own buffer
circuit for the switch from a triac and a couple
resistors like this.


[img]cid:.0[/img]

This could be nothing more than two resistors
soldered together with the triac, lead wires
attached and then coated in some insulating
encapsulant . . . maybe RTV, E6000 or thixotropic
epoxy. In technical terms this is known as a
"Kludge".

This would reduce stresses on your switch to mere
tens of milliamps and then only for tens of
microseconds at each re-triggering event just
after the ac wave form zero-crossing. Even if the
switch were close at the top of the wave form,
current through the switch and its series resistor
would be limited to an amp or so and again, for
tens of microseconds.

This buffer for your switch contacts raises
potential for a new failure mode. . . corrosion
over time on switch contacts causing them
to STOP conducting . . . not enough 'cleansing
current' flowing during each switch closure
to keep them free of oxides. But that risk
is generally years out into the future.


Bob . . .


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Eric Page



Joined: 15 Feb 2017
Posts: 241

PostPosted: Tue Aug 29, 2017 7:36 am    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

Quote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net (jonlaury(at)impulse.net)> In the zero-crossing relay suggested, the load side spec is 250vac (at) 2a. The steady-state ballast load is 800ma and the motor draws about 2a. Will the relay take it? or am I missing something here?


On Aug 29, 2017, at 6:29 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
Good eye. Yeah, if THAT option is attractive, you'll need a beefier device. Maybe something like this.

http://tinyurl.com/y8bfqm5o

Careful... the linked SSR is a DC-DC device. It's basically an opto-isolated MOSFET or Darlington. It might work as a rectifier, but only briefly!

For this application the output side has got to be labeled for AC, then it'll contain a triac or souce-connected N-MOSFETs.

If Jon isn't hesitant to use offshore sources for his parts, he might try these...

http://www.ebay.com/itm/112021093981

I've used a couple in mains-powered projects and had no trouble with them. They're not a brand anyone has ever heard of, but they seem to work, the price is right, and the screw terminals lend themselves to a field retrofit better than a PCB-mounted SIP package.

If heat sinking or a safety cover are desired, see...

http://www.ebay.com/itm/112159075071
and...
http://www.ebay.com/itm/112266161948

Keep in mind also that anything from China with a $0.99 price tag and a name brand like OMRON printed on it is going to be a case of blatant IP theft.

Eric
[Edited to correct spelling of Jon's name, and for formatting.]


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Eric Page



Joined: 15 Feb 2017
Posts: 241

PostPosted: Tue Aug 29, 2017 10:41 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

Upon reflection, the SSR that I linked to won't work without some redesign of the machine's circuitry, as it needs a DC input. The easiest retrofit for Jon to do would be to use an AC-AC SSR and control it with the existing switch that's already in the machine.

Here's an eBay search for parts that will work: http://preview.tinyurl.com/ybqcog6g

These SSRs are available from 10A to 100A; just change the eBay search term.

If using a known-source part is an issue, here's a Digi-Key search for AC-AC zero-cross SSRs, 5A or greater, sorted by price: http://preview.tinyurl.com/yamzd5vc

Connect as shown in the attached diagram.

Eric


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jonlaury



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Posts: 336

PostPosted: Sun Sep 03, 2017 8:20 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

[quote="Eric Page"]
Quote:


Keep in mind also that anything from China with a $0.99 price tag and a name brand like OMRON printed on it is going to be a case of blatant IP theft.


Hi Eric
Thanks for your suggestion and I did buy a lot of 3 "Omron" AC-AC SSR's from Ebay. They're labelled with Omron's logo and Made in China, $25. Probably not Omron product, right?
The question that looms large in my mind is, are they truly zero-crossing relays? Is there a way to test that function without a lot of expensive equipment? Or who would have the needed equipment so that I could have them tested?

John


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Eric Page



Joined: 15 Feb 2017
Posts: 241

PostPosted: Sun Sep 03, 2017 9:43 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

jonlaury wrote:

Hi Eric
Thanks for your suggestion and I did buy a lot of 3 "Omron" AC-AC SSR's from Ebay. They're labelled with Omron's logo and Made in China, $25. Probably not Omron product, right?
The question that looms large in my mind is, are they truly zero-crossing relays? Is there a way to test that function without a lot of expensive equipment? Or who would have the needed equipment so that I could have them tested?

John

There's probably no way to know for sure if they're genuine unless you have a known-good example to compare against. Chinese knock-off products frequently have noticeable errors or differences in printing quality or method in the part markings (i.e. the real part may be laser-etched while the knock-off is screen printed). Even this comparison isn't foolproof, as the manufacturer may produce differences between lots or between factories.

OMRON is a Japanese company, but like everyone else, they probably run -- or contract with -- factories in China.

Anyone with an oscilloscope should be able to determine if they're zero-cross SSRs by viewing the output waveform at switch-on. There is potential to destroy an oscilloscope when measuring mains voltages, so be sure that whoever does this for you knows what they're doing WRT test setup, isolation and high voltage measurement. It goes without saying that you touch ONLY the low voltage control side of the circuit during the test.

Knock-off or not, if they're marked as zero-cross SSRs, I'd be very surprised if they're not. It's a pretty trivial thing to accomplish.

If you find that they're not, the AC-AC Fotek brand parts on eBay that I linked to in my last post look like they are...

http://www.fotek.com.hk/solid/SSR-2.htm

...and anything you get from Digi-Key, Newark, Mouser, Allied, Jameco, etc. will be genuine and function as specified.

Eric


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PostPosted: Sun Sep 03, 2017 10:40 am    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

At 11:20 AM 9/3/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>

[quote="Eric Page"]
>
>
> Keep in mind also that anything from China with a $0.99 price tag and a name brand like OMRON printed on it is going to be a case of blatant IP theft.


Hi Eric
Thanks for your suggestion and I did buy a lot of 3 "Omron" AC-AC SSR's from Ebay. They're labelled with Omron's logo and Made in China, $25. Probably not Omron product, right?
The question that looms large in my mind is, are they truly zero-crossing relays? Is there a way to test that function without a lot of expensive equipment? Or who would have the needed equipment so that I could have them tested?

The SSR contains a triac (bi-directional, triggered
switch). It's the same critter I sugeseted in my po'
boy's SSR Kludge a fews posts back.

By nature, ANY AC solid state relay will be
as close to a 'zero crossing' controller as
you can get. On the upswing of each half of
an AC waveform, a network of components are arranged
to bias the TRIAC gate to the threshold of trigger.
After that time, the TRIAC becomes almost a dead
short (about 1.5v drop) and the switch can be
deemed to be "ON".

Here's a rudimentary lamp dimmer schematic:



Notice one of the devices in the trigger network
is called a DIAC . . . this is a voltage sensitive
two terminal device that 'triggers' above some
specified voltage. DIMMING is accomplished
by adjusting the resistance in the R/C network
to control DELAY in rise of the trigger volage.
The more resistance, the longer the delay. A
longer delay moves the TRIAC trigger further away
from zero crossing thus REDUCING energy fed to the
load.

Here's a rudimentary solid state AC "relay"





Here we see a little different trigger network for the
TRIAC. In this case, an LED is optically coupled to a
light sensitive DIAC such that if the LED is illuminated,
the DIAC will fire and trigger the TRIAC at the lowest
practical amplitude in the upward excursion of each
half of the AC waveform.

So technically, this relay does not close at the true
zero crossing . . . but it's very close. Within 10 volts
or so. Good enough for most applications.

These relays will work to mitigate your switch failure
issues as the current flowing in the LED loop is on the
order of 30mA or less. But you DO need a DC source of
power to energize the LED. It's only a few volts but it
does add to system complexity. You could rig a bridge
rectifier, a capacitor and a couple resistors to provide
the low energy source of DC.

But if you need to fabricate something anyhow, perhaps
the Kludge I offered earlier is the more elegant configuration.

The short answer is: You don't need to test these relays
for their zero-crossing qualities since chief complaint
is switch failure. The relays will take care of the switch
problem after you figure out how to integrate the SSR
into your design.

There are AC/AC SSR's . . . they feature TWO opto couplers
back to back so that an LED source of either polarity
will turn the SSR ON.



Bob . . .


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jonlaury



Joined: 06 Nov 2006
Posts: 336

PostPosted: Mon Sep 04, 2017 11:30 am    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote


DNA


What I absolutely love about AEL.

Thanks to both of you, Bob and Eric, for piquing my curiosity, making me stretch to expand my knowledge and skill set. The forum is in every way the embodiment of the adage, "Give a man a fish and he eats tonight. Teach him to fish...he and his family eat for a lifetime"

I've got some 47 Ω, 3A NTC thermistors I'm going to try, with the idea that I could, inexpensively, make up a bunch of low tech field-repair devices that can be installed with two wire nuts by users. For unshipped units henceforth, I plan to use the AC/AC SSR's until I can find a suitable, beefier power switch.

All good things,
John

[[/b]


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Sep 05, 2017 3:09 pm    Post subject: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

At 02:30 PM 9/4/2017, you wrote:
Quote:
--> AeroElectric-List message posted by: "jonlaury" <jonlaury(at)impulse.net>


DNA

What I absolutely love about AEL.

Thanks to both of you, Bob and Eric, for piquing my curiosity, making me stretch to expand my knowledge and skill set. The forum is in every way the embodiment of the adage, "Give a man a fish and he eats tonight. Teach him to fish...he and his family eat for a lifetime"

I've got some 47 Ω, 3A NTC thermistors I'm going to try, with the idea that I could, inexpensively, make up a bunch of low tech field-repair devices that can be installed with two wire nuts by users. For unshipped units henceforth, I plan to use the AC/AC SSR's until I can find a suitable, beefier power switch.

3A? Try to pick an NTC with (1) operating current
close to your measured running loads and (2) max
applied voltage of 120vac or greater. See
this for the nitty-gritty guidelines . . .

http://tinyurl.com/yahtoncs





Bob . . .


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jonlaury



Joined: 06 Nov 2006
Posts: 336

PostPosted: Wed Sep 06, 2017 12:00 pm    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

In the first section of the article re selecting the right ICL, I'm asked for Capacitance. But neither the ballast nor the power supply list that info on their product cut-sheets.
Is there away to deduce the capacitance from other supplied info? E.G., inrush current on PS is 40A (at) 250vac. Ballast is 100A (at) 120vac

Power Supply and Ballast data sheets attached.


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WH7-120-L datasheet.pdf
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Meanwell RS-100-24-spec.pdf
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jonlaury



Joined: 06 Nov 2006
Posts: 336

PostPosted: Wed Sep 06, 2017 12:27 pm    Post subject: Re: Non-aero app: 120/240 AC through 24vdc switch? Reply with quote

"3A?"

The steady state load is about 1A, to keep the ballast happy. There's a user selected load of 1.5A that has a 25 second cycle to open circuit. Often the selection is repeated multiple times in quick succession. So the 3A was to allow a little headroom for motor surge (Does a PM motor have a surge?) and 2.5 steady state. I installed the 3A ICL yesterday and everything seems to work fine with the ICL temp settling at about 145 deg F on my meat thermometer held on with a clothes pin.


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