terry wrote:
On Sep 19, 8:01 pm, Jeff Wisnia
wrote:
Square Peg wrote:
Most coffee mug warmers are under-powered. One reviewer on Amazon said
that they were restricted to about 24 watts by law.
This one
http://www.amazon.com/Bunn-BCW-Warme.../B00023WAS0/re...
is made for warming the whole coffee pot. It says it's 120V/15amp.
Several of the reviews say that they use it for a single cup, but it
keeps it too hot. It only has on/off -- no temperature control.
Can I put it on a 300 watt dimmer switch like this?
http://www.amazon.com/Lutron-Electro...-300H-WH/dp/B0...
If not, is there a way to ramp the the power down as an external
thermostat?
I seriously doubt the veracity of that "120V/15 amp" rating, which I did
see listed as a "spec" on a couple of other seller's websites.
I have a Bunn coffeemaker and I just measured the current draw of the
warming plate on it at 1.05 amps. (I made sure that the main water
heating element's thermostat was OFF at that time of course.)
So, if approximately 120 watts will keep a full caraffe of coffee at
proper drinking temperature on my Bunn coffeemaker, the stand alone Bunn
warmers probably draw no more than the "built in" ones.
Thus, that 300 watt dimmer ought to do just fine after you find the
right slider setting to keep a single cup hot.
Go for it!
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.- Hide quoted text -
- Show quoted text -
My gosh how we manage to make something so complicated.
Fun, isn't it? :-)
1) Most dimmers are designed to reduce the brilliance of incandescent
lamps. They do this either by reducing the voltage, whereupon the
Voltage Squared divided by the Resistance of the load applies. (It's
not a theory btw it is "Ohm's Law" etc. And as old as the hills!) And
as noted if the voltage is reduced to half one will get one quarter
the amount of energy (heat/light or a bit of both) at the load.
BTW: Some very old style variable resistance dimmers themselves would
get hot in order to do the voltage reduction and this could be
classified as 'wasted' heat!
Don't forget the Variac type light dimmers used in some homes before the
development of the present wave chopping solid state dimmers. They
wasted far less power than those rheostat types you mention.
OR, the amount of electric power applied to the load (lamp/coffee
warmer etc.) is altered by changing the wave shape of the inputted
sine wave so that only part of it (or a reshaped wave) gets through to
the load which is then not as bright, or in this case not kept as
warm.
.
2) Since the coffee/tea warmer is most likely just some sort of
resistance heater, yes, most likely the dimmer will work fine. Just
find the right setting of the dimmer.
Also agree that any appliance that really does consume 115 volts at 15
amps (That's 1725 watts!) sounds a lot more powerful than a 'warmer'.
That's sounds more like a kettle, to 'make/brew' tea or coffee! :-)
Perahps it's designed to be used to heat up the water, drop in the tea
or coffee and then be switched off? In other words it's more of a
coffee/tea maker than a 'warmer'!
We used to make tea that way, at a work bench, by dropping a wire
wound resistor connected to 48 volts DC directly into a mug of water.
When it boiled we'd drop in the tea and after a moment or two
disconnect and remove the heater. Can't remember the wattage but it
was probably around one amp or less at 48 volts; hence V x I = 48 x 1
= 48 watts. The colour of the heater resistance was dark brown;
deepening with use. But it was quite easy to make another one if it
looked 'too unsanitary'.
Back in college in the '50s we used to cook hot dogs in our dorm rooms
by jabbing two table forks into their ends and connecting the fork
handles to line voltage with an old lamp cord.
For a while they made hot dog cooking kitchen appliances which worked on
the same principle. They held four (or maybe six) hot dogs jabbed onto
pairs of spikes which got line voltage switched onto them when a safety
cover was closed over the dogs. I haven't noticed any of that kind
advertised lately though.
For example many small floor heaters are no more than around 1500 to
1800 watts for the very reason they can then be plugged into a typical
domestic outlet! And hair dryers!
And forget all this stuff about the resistance (of the lamp or the
coffee warmer) varying with temperature; yes it does. Usually
increasing but not necessarily in a direct linear relationship with
temperature. But for practical purposes forget it. Just tiddle with
the dimmer adjustment until one finds a setting that works. After all
the amount of drink fluid will, presumably, be decreasing as it is
consumed, so we don't want to get off on the subject of a fixed amount
of kilo-calories of heat energy being applied to decreasing amount of
fluid of specific gravity X; minus the thermal mass of the container
and the rate of heat loss from that container taking into account the
ambient temp. of the room! Just sip and enjoy.
Also btw if the warmer only takes very small number of watts the
dimmer which has probably been designed and produced for a typical
incandescent desk lamp bulb of say 40 to 100 watts (maximum 300) may
be a somewhat finicky to adjust; also taking into account, as above,
the fluid will be decreasing!
Which reminds; right now have an almost full pot of Sri Lankan tea 'on
the hob'. Must go and refill this cuppa. Cheers.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.