Maker Pro
Maker Pro

Relay contact ratings.

S

Sylvia Else

Jan 1, 1970
0
Really? You think the relay can only handle 120 VAC, just because
that's what poweres the timer circuit?

Unless you've actually pulled one apart, and determined the exact
specification of the relay, or semiconductor device, involved, it's only
safe to assume that it's specified to perform the particular task
intended for it. It may well be a part that's specified to handle higher
voltages, but it would be rash to assume that.

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
It would have to switch half the current it would on 120 VAC, and the
relays are the same for either line volktage.

You've taken one apart?

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
---
I don't care for conjecture, which is all you're offering.
---



---
That's USD 184.75, and she's in Oz, so it'd more likely be about USD
250 before she got the part in hand.

Plus, she's got an old fridge and if went belly-up shortly after
spending the money for the defroster she'd probably wind up with a new
fridge and a homeless new defroster.
---


---
Yeah, sure you would...

Why not post a schematic and some code showing how you'd propose to
implement your wily scheme, and I'll do the same proposing a strictly
hardware solution?

Game on?

OK, changed my mind, let do digital.

Let start with perhaps 4 buttons. Two to change cycles per day and two
to change durations. Three bits driving 138 (one of eight) to
indicate cycles (eight cycles should be plenty). Another three bits
to indicate durations such as 5,7,10,15,20,25,30 minutes. I doubt we
really want to defrost beyond 30 minutes anyway. So far, we can do it
with 10 port pins and 16 LEDs.

Just a quick first draft:

char cycle[8] = {1,2,3,4,5,6,7};
char duration[8] = {5,7,10,15,20,25,30};
int c_idx;
int d_idx;

while(1)
{
if(port(c_up))
c_idx++;
if(port(c_dn))
c_idx--;
if(port(d_up))
d_idx++;
if(port(d_dn))
d_idx--;

defrost_on();
delay(d_idx);
defrost_off();

delay_hrs(24/cycle[c_idx]);
}

...

Are c_idx and d_idx in non-volatile RAM? I'd prefer my fridge to
continue working, without intervention, after a power outage.

There appears to be a defrost-cycle period between each opportunity to
change the settings by one. Could take a while.

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
You've said the defrost only happens every six hours, but for how long
is the heater energized?
knowing that will allow us to determine the duty cycle of the timer
and cause it to mimic the motor timer.
It should be long enough to melt the ice and let the water drain off.
It can easily be programmable in a micro, at least during
development. Perhaps a 5 to 10 minutes range.
You don't like my numbers?
Then go with the number from commerical
defrost timer.
4 minutes to 110 minutes in 2 minutes step.
4 to 12 cycles per day.
Plus, she's got an old fridge and if went belly-up shortly after
spending the money for the defroster she'd probably wind up with a new
fridge and a homeless new defroster.
---
I would go with 2 pots + 2 A2D. adjust and time it with a micro.
Why not post a schematic and some code showing how you'd propose to
implement your wily scheme, and I'll do the same proposing a strictly
hardware solution?

OK, changed my mind, let do digital.

Let start with perhaps 4 buttons. Two to change cycles per day and two
to change durations. Three bits driving 138 (one of eight) to
indicate cycles (eight cycles should be plenty). Another three bits
to indicate durations such as 5,7,10,15,20,25,30 minutes. I doubt we
really want to defrost beyond 30 minutes anyway. So far, we can do it
with 10 port pins and 16 LEDs.

Just a quick first draft:

char cycle[8] = {1,2,3,4,5,6,7};
char duration[8] = {5,7,10,15,20,25,30};
int c_idx;
int d_idx;

while(1)
{
if(port(c_up))
c_idx++;
if(port(c_dn))
c_idx--;
if(port(d_up))
d_idx++;
if(port(d_dn))
d_idx--;

defrost_on();
delay(d_idx);
defrost_off();

delay_hrs(24/cycle[c_idx]);

}

...

Its a better idea to stop defrost cycle when the exchanger temp rises
above freezing. Otherwie you're wasting energy, and at some point the
machine will likely ice up.


NT

The 'standard' self-defrost implementation has an additional thermostat
on the cooling element, which trips open when the element reaches some
predetermined temperature (11C on mine), and closes again at some lower
temperature (0C on mine).

11C seems rather high, but I suppose it's intended to ensure that the
entire element has defrosted, not just the part near the thermostat. It
also means the thermostat need not be that accurate.

Switching the cooling back on immediately after the thermostat trips off
seems attractive, to avoid defrosting the stuff in the freezer, but I
have some misgivings about the impact on the compressor of starting when
the element is that warm.

It's not clear to me why the machine would ice up if the defrost cycle
is left running too long.

Sylvia.
 
F

F Murtz

Jan 1, 1970
0
kreed said:
I have worked on a couple of newer Australian made ones here and now
they have no relays at all in them. Other brands
might have, or older models that are being replaced.


A lot of the modern ones use butane as a refrigerant so may be they do
not want open contacts in the very remote case of leaks
 
S

Sylvia Else

Jan 1, 1970
0
On Dec 11, 5:48 pm, John Fields<[email protected]> wrote:
You've said the defrost only happens every six hours, but for how long
is the heater energized?
knowing that will allow us to determine the duty cycle of the timer
and cause it to mimic the motor timer.
It should be long enough to melt the ice and let the water drain off.
It can easily be programmable in a micro, at least during
development. Perhaps a 5 to 10 minutes range.
You don't like my numbers?
Then go with the number from commerical
defrost timer.
4 minutes to 110 minutes in 2 minutes step.
4 to 12 cycles per day.
Plus, she's got an old fridge and if went belly-up shortly after
spending the money for the defroster she'd probably wind up with a new
fridge and a homeless new defroster.
---
I would go with 2 pots + 2 A2D. adjust and time it with a micro.
Why not post a schematic and some code showing how you'd propose to
implement your wily scheme, and I'll do the same proposing a strictly
hardware solution?
OK, changed my mind, let do digital.
Let start with perhaps 4 buttons. Two to change cycles per day and two
to change durations. Three bits driving 138 (one of eight) to
indicate cycles (eight cycles should be plenty). Another three bits
to indicate durations such as 5,7,10,15,20,25,30 minutes. I doubt we
really want to defrost beyond 30 minutes anyway. So far, we can do it
with 10 port pins and 16 LEDs.
Just a quick first draft:
char cycle[8] = {1,2,3,4,5,6,7};
char duration[8] = {5,7,10,15,20,25,30};
int c_idx;
int d_idx;
while(1)
{
if(port(c_up))
c_idx++;
if(port(c_dn))
c_idx--;
if(port(d_up))
d_idx++;
if(port(d_dn))
d_idx--;
defrost_on();
delay(d_idx);
defrost_off();
delay_hrs(24/cycle[c_idx]);

Its a better idea to stop defrost cycle when the exchanger temp rises
above freezing. Otherwie you're wasting energy, and at some point the
machine will likely ice up.

The 'standard' self-defrost implementation has an additional thermostat
on the cooling element, which trips open when the element reaches some
predetermined temperature (11C on mine), and closes again at some lower
temperature (0C on mine).

11C seems rather high, but I suppose it's intended to ensure that the
entire element has defrosted, not just the part near the thermostat. It
also means the thermostat need not be that accurate.

Switching the cooling back on immediately after the thermostat trips off
seems attractive, to avoid defrosting the stuff in the freezer, but I
have some misgivings about the impact on the compressor of starting when
the element is that warm.

It's not clear to me why the machine would ice up if the defrost cycle
is left running too long.

Sylvia.


You could design a defrost system like was on the New Inventors last
year.
IIRC a resistive strip was placed in the freezer, a known voltage
passed through it periodically
and the resistance of it measured (heat causes resistance to rise, and
the more frost/ice formed on the strip
the longer it took to heat up and resistance to rise) and turn on the
defrost system only when
sufficient ice was detected.

I suppose it depends what one is trying to achieve. Clearly, it's
wasteful of energy to heat up, and then cool, an element that doesn't
have much ice on it.

On the other hand, keeping it that way means that the defrost cycle
doesn't have to take long, which is helpful is one's primary goal is to
keep the freezer compartment below a certain temperature.

Sylvia.
 
K

keithr

Jan 1, 1970
0
<OT>

FWIW, those are oft-cited misconceptions. Media drones repeat them
without understanding their basis.

The number is ~32 million, and these are people who do not have
medical insurance. That is not the same as "extremely poor access" to
care. Numerically, some 10-12 million of that figure are illegal
aliens, and most of the remainder are young people who voluntarily
choose not to buy it. Access is generally good to excellent.

60-odd % is the proportion of people who go bankrupt who, among their
other bills, also owe money to their doctors. The number whose
medical costs *caused* their bankruptcy is a small fraction.

Last, everyone can get care. There are countless medical programs for
the poor.

I personally have an acquaintance getting the full royal treatment,
for cancer, for nothing. She's better than most at working the
system, but it's there for people who need it, and seek it.

I have to say that during the time that I lived in the US, the medical
care that I received was excellent and my co-payments were less than I
pay back in Australia *BUT* I had an employer paying for my medical and
pharmacy insurance. I was never quite comfortable though that, should I
have needed expensive treatment, my HMO would have the final word on
that treatment.

At to the poor, my wife used to volunteer at the emergency room at the
local hospital she had quite a few horror stories. I did my bit to fund
the programs for the poor, 5 1/2 years of maximum social security
payments that I am not going to see a penny of.

I have a friend there who is retired (not by choice) who has to spend a
fair proportion of his income on medical insurance, and, even then, when
his wife had a bad car accident, he still had some really big bills to pay.
 
J

Jasen Betts

Jan 1, 1970
0
The 'standard' self-defrost implementation has an additional thermostat
on the cooling element, which trips open when the element reaches some
predetermined temperature (11C on mine), and closes again at some lower
temperature (0C on mine).

11C seems rather high, but I suppose it's intended to ensure that the
entire element has defrosted, not just the part near the thermostat. It
also means the thermostat need not be that accurate.

Switching the cooling back on immediately after the thermostat trips off
seems attractive, to avoid defrosting the stuff in the freezer, but I
have some misgivings about the impact on the compressor of starting when
the element is that warm.

the closer the inside temperature of the fridge is to the outside
temperatue the less work the compressor needs to do to circulate he
coolant.

a warm evaporator means the compressor's input is at a higner pressure
than normal and thus it needs to do less work to compress the gas
enough to condense in the condenser,
 
S

Sylvia Else

Jan 1, 1970
0
the closer the inside temperature of the fridge is to the outside
temperatue the less work the compressor needs to do to circulate he
coolant.

a warm evaporator means the compressor's input is at a higner pressure
than normal and thus it needs to do less work to compress the gas
enough to condense in the condenser,

From context, I assume you meant "more" in that last sentence.

The question is - does it matter? That is, will running the compressor
when the element is warm do anything more than consume some extra
electricity. I suppose it's no different from having the fridge turned
off for a while, and then turning it on, but it may have some long term
implications for the life of the compressor if it happens every six
hours. I'm speculating - I don't know.

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
I have checked a few from my junk box, any that are intended to switch
mains power and not signal
circuits have a 240v rating. Many were out of junked
US made equipment and made in Japan, Mexico or Taiwan.

As they are for the world market, I would think that most would be
rated 240v.

One Japan made one that is UL rated has an inductive rating of 5a
240VAC and 0.5a at 120VDC for inductive loads.

5A 120V and 32v for resistive loads.


The contact clearance is about 1mm.

Still, are you going to put your hand on your heart, and say that some
unknown relay in an appliance designed for 110VAC will be safe to use at
240VAC?

That aside, this subthread related to electronic defrost timers. They
may not be using electromechanical relays at all, but semiconductor
devices.

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
On 13/12/2011 9:23 AM, NT wrote:
On Dec 11, 5:48 pm, John Fields<[email protected]> wrote:
You've said the defrost only happens every six hours, but for how long
is the heater energized?
knowing that will allow us to determine the duty cycle of the timer
and cause it to mimic the motor timer.
It should be long enough to melt the ice and let the water drain off.
It can easily be programmable in a micro, at least during
development. Perhaps a 5 to 10 minutes range.
You don't like my numbers?
Then go with the number from commerical
defrost timer.
4 minutes to 110 minutes in 2 minutes step.
4 to 12 cycles per day.
Plus, she's got an old fridge and if went belly-up shortly after
spending the money for the defroster she'd probably wind up with a new
fridge and a homeless new defroster.
---
I would go with 2 pots + 2 A2D. adjust and time it with a micro.
Why not post a schematic and some code showing how you'd propose to
implement your wily scheme, and I'll do the same proposing a strictly
hardware solution?
OK, changed my mind, let do digital.
Let start with perhaps 4 buttons. Two to change cycles per day and two
to change durations. Three bits driving 138 (one of eight) to
indicate cycles (eight cycles should be plenty). Another three bits
to indicate durations such as 5,7,10,15,20,25,30 minutes. I doubt we
really want to defrost beyond 30 minutes anyway. So far, we can do it
with 10 port pins and 16 LEDs.
Just a quick first draft:
char cycle[8] = {1,2,3,4,5,6,7};
char duration[8] = {5,7,10,15,20,25,30};
int c_idx;
int d_idx;
while(1)
{
if(port(c_up))
c_idx++;
if(port(c_dn))
c_idx--;
if(port(d_up))
d_idx++;
if(port(d_dn))
d_idx--;
defrost_on();
delay(d_idx);
defrost_off();
delay_hrs(24/cycle[c_idx]);

Its a better idea to stop defrost cycle when the exchanger temp rises
above freezing. Otherwie you're wasting energy, and at some point the
machine will likely ice up.

The 'standard' self-defrost implementation has an additional thermostat
on the cooling element, which trips open when the element reaches some
predetermined temperature (11C on mine), and closes again at some lower
temperature (0C on mine).
11C seems rather high, but I suppose it's intended to ensure that the
entire element has defrosted, not just the part near the thermostat. It
also means the thermostat need not be that accurate.
Switching the cooling back on immediately after the thermostat trips off
seems attractive, to avoid defrosting the stuff in the freezer, but I
have some misgivings about the impact on the compressor of starting when
the element is that warm.
It's not clear to me why the machine would ice up if the defrost cycle
is left running too long.

You could design a defrost system like was on the New Inventors last
year.
IIRC a resistive strip was placed in the freezer, a known voltage
passed through it periodically
and the resistance of it measured (heat causes resistance to rise, and
the more frost/ice formed on the strip
the longer it took to heat up and resistance to rise) and turn on the
defrost system only when
sufficient ice was detected.

I suppose it depends what one is trying to achieve. Clearly, it's
wasteful of energy to heat up, and then cool, an element that doesn't
have much ice on it.

On the other hand, keeping it that way means that the defrost cycle
doesn't have to take long, which is helpful is one's primary goal is to
keep the freezer compartment below a certain temperature.

Sylvia.

Sound like we should wire the whole fridge with sensors. But that's
fine, thermistors are cheap. PIC32 can handle up to 16 analog
channels.

Bad idea. All that would happen would be that you'd discover that the
distribution of emperatures in the fridge are not what you'd like them
to be, but that since all you have is on/off switches for the
compressor, fan, and defrost heater, there's little you can do about it.

But if you're also adding some mechanically operated vents, and some
additional fans, then now you're talking.

Sylvia.
 
L

Les Cargill

Jan 1, 1970
0
Eveb Apple gets better, and cheaper. Your point?

Apple has chosen not to compete on price, and have had
staggering profits. Much corporate medical care
in the US also does not compete on price, if at all.

As a larger issue, when people drill
down into the details, competition as we generally
think of it rarely matters much - differences in
cost of orders of magnitude will matter while differences
of even as much as 2x will not.

But the more something is a commodity, especially
a commodity that has high volume, the more small
differences in price matter.

Medical care is a craft good, and the farthest thing
there is from a commodity. Will that change? Probably.

Specific to medical care 1) we do not have competitive
provision of medical care in the US, and 2) universal
care ala Yurp has actuarial effects very much
in favor of it.
 
J

John Doe

Jan 1, 1970
0
Phil Allison said:
"Stupider than Anyone Else"



** The 300W figure refers to DC switching - ie 10 amps at 30 volts.

The 2500VA figure refers to resistive loads and 250VAC power.

There is nothing about inductive load switching.

See the data sheet.

Fuckwit.

When did they let you out of the asylum, Philly?
Your absence was not taken for granted.
--
 
S

Sylvia Else

Jan 1, 1970
0
Interesting. Thanks.
Though on further examination, by the time you've paid the higher cost
for the chip, the postage from the UK, and either bought or made the
cable, it's considerably cheaper just to buy a programmer from a local
supplier.

http://australia.rs-online.com/web/p/microcontroller-processor/0381582/

PICAXE is probably good for people who've little or no experience in
programming, particularly at assembler code level.

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
On Thu, 15 Dec 2011 10:22:50 +1100, Sylvia Else

I did, but I've formed the view that if I were going to do this, I'd
include the thermostat as well, and choose a better point in the
thermostat hysteresis at which to start the defrost cycle, rather than
having a random relationship as is the situation now.

Sylvia.
 
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