One of the heat systems in my house is electric powered hydronic heat.
I'm using a water heater, which is sufficient for my needs. Time-of-use
electricity makes it cheaper than propane, nights and weekends.
I'd like to do something a bit more sophisticated than my current
control system, which is a day/hour timer switch. Can anyone suggest
something which ideally would be:
1. Computer controlled (PC is OK, others are OK too)
2. Capable of driving a 30A 240VAC relay
3. Capable of taking temperature readings from several inputs
to determine if the relay needs to be on or off
4. Reasonable cost
Basically, a smart controller that knows about time and return water
temperature, and turns on the heat when it's got access to cheap
electricity and when the floor is cool enough to need it.
Suggestions of vendors, or specific products, or even homebrew solutions
are most welcome.
Dave Hinz
> 1. Computer controlled (PC is OK, others are OK too)
> 2. Capable of driving a 30A 240VAC relay
> 3. Capable of taking temperature readings from several inputs
> to determine if the relay needs to be on or off
> 4. Reasonable cost
> Basically, a smart controller that knows about time and return water
> temperature, and turns on the heat when it's got access to cheap
> electricity and when the floor is cool enough to need it.
Boy, that is a tough combination. programmable thermostat is the
closest "cheap" solution that comes to mind. But for full-blown
homebrew computer control...
For temperature, use Dallas/Maxim DS1820 temperature sensors. They are
direct to digital, and can be hooked up with a bunch of them on a simple
twisted-pair bus (ground plus combined power and signal and optional
seperate power). aag.com.mx (iirc) and peter h anderson sell ways to
get them hooked up to your computer. (Dallas did a "weather station"
promotion a few years ago, that is what I have, and now AAG sells the
current version.)
Then connect some solid-state relays (SSRs) to the parallel port. You
need ones which take a fairly low trigger current (15ma is a stretch,
try to find lower) at 5volts, ideally a range such as 3v-12v. I watch
the surplus places such as allelectronics.com, bgmicro.com, etc and have
found some good deals. I'm using some two-pole, 240vac @ 40amp relays
that were about $15/ea. I put two relays in a dual-gang metal box with
two duplex outlets (split) on top. I mount an rj45 on the box for the
control input, and have a few feet of 12ga pigtal with a plug for input
power. The line from the computer plugs into the rj45 and then I have
four individually switched outlets.
(SSRs need a heatsink, and the closer to operate to their max current
ratings, the more heatsink they need. Mine are rated at 40amps, and I
have four of them per 20amp circuit, they are mounted to a metal
electrical box and never seem to get warm.)
See computerchristmas.com and the many other similar sites for how to
connect to the computer. It isn't hard. The standard parallel port has
8 data bits and 4 control bits for output (5 bits of input), and you
just wire those outputs to the control inputs on the relays. For added
safety, use a resistor in series to limit the current (330ohm to 470ohm
should be very safe, but might not allow enough trigger current). I
took two network cables, cut them in half, and wired them into a plug
for the parallel port so that I have three four-bit output plugs, and
one input plug.
Distance between the computer and the relays might be a factor. My
relays only need 3v on the trigger to switch, and I have run them thru
about 30ft of cat-5 (8 meter cable plugged into the relay box, rj45
coupler, 1 meter cable into parallel port) without problem.
Now find or write the software. (That's a whole 'nother topic!)
I estimate cost as:
$10-$20 for dallas 1-wire bus interface
$2-$5 per DS18s20
$15-$20 per two-pole relay
plus incidentals (cables, connectors, boxes, etc)
plus computer (w/ rs232 or usb for 1-wire, and parallel for relays)
plus software
You could eliminate the 1-wire bus interface, and just connect the
DS18s20's to the parallel port inputs. But then software has to do all
the bit-banging directly, it's a pain and I don't know if any software
out there supports that.
sdb
--
Wanted: Omnibook 800 & accessories, cheap, working or not
sdbuse1 on mailhost bigfoot.com
Whatever for? The PC alone will waist more energy than a well insulated
tank!
I mean come on we do our banking and such with a computer now
...............but why would someone want to wake up and find out that the
water is frooze because the PC frooze?
Sylvan Butler wrote:
> > 1. Computer controlled (PC is OK, others are OK too)
> > 2. Capable of driving a 30A 240VAC relay
> > 3. Capable of taking temperature readings from several inputs
> > to determine if the relay needs to be on or off
> > 4. Reasonable cost
> >
> > Basically, a smart controller that knows about time and return water
> > temperature, and turns on the heat when it's got access to cheap
> > electricity and when the floor is cool enough to need it.
> Boy, that is a tough combination. programmable thermostat is the
> closest "cheap" solution that comes to mind. But for full-blown
> homebrew computer control...
> For temperature, use Dallas/Maxim DS1820 temperature sensors. They are
> direct to digital, and can be hooked up with a bunch of them on a simple
> twisted-pair bus (ground plus combined power and signal and optional
> seperate power). aag.com.mx (iirc) and peter h anderson sell ways to
> get them hooked up to your computer. (Dallas did a "weather station"
> promotion a few years ago, that is what I have, and now AAG sells the
> current version.)
> Then connect some solid-state relays (SSRs) to the parallel port. You
> need ones which take a fairly low trigger current (15ma is a stretch,
> try to find lower) at 5volts, ideally a range such as 3v-12v. I watch
> the surplus places such as allelectronics.com, bgmicro.com, etc and have
> found some good deals. I'm using some two-pole, 240vac @ 40amp relays
> that were about $15/ea. I put two relays in a dual-gang metal box with
> two duplex outlets (split) on top. I mount an rj45 on the box for the
> control input, and have a few feet of 12ga pigtal with a plug for input
> power. The line from the computer plugs into the rj45 and then I have
> four individually switched outlets.
> (SSRs need a heatsink, and the closer to operate to their max current
> ratings, the more heatsink they need. Mine are rated at 40amps, and I
> have four of them per 20amp circuit, they are mounted to a metal
> electrical box and never seem to get warm.)
> See computerchristmas.com and the many other similar sites for how to
> connect to the computer. It isn't hard. The standard parallel port has
> 8 data bits and 4 control bits for output (5 bits of input), and you
> just wire those outputs to the control inputs on the relays. For added
> safety, use a resistor in series to limit the current (330ohm to 470ohm
> should be very safe, but might not allow enough trigger current). I
> took two network cables, cut them in half, and wired them into a plug
> for the parallel port so that I have three four-bit output plugs, and
> one input plug.
> Distance between the computer and the relays might be a factor. My
> relays only need 3v on the trigger to switch, and I have run them thru
> about 30ft of cat-5 (8 meter cable plugged into the relay box, rj45
> coupler, 1 meter cable into parallel port) without problem.
> Now find or write the software. (That's a whole 'nother topic!)
> I estimate cost as:
> $10-$20 for dallas 1-wire bus interface
> $2-$5 per DS18s20
> $15-$20 per two-pole relay
> plus incidentals (cables, connectors, boxes, etc)
> plus computer (w/ rs232 or usb for 1-wire, and parallel for relays)
> plus software
> You could eliminate the 1-wire bus interface, and just connect the
> DS18s20's to the parallel port inputs. But then software has to do all
> the bit-banging directly, it's a pain and I don't know if any software
> out there supports that.
> sdb
> --
> Wanted: Omnibook 800 & accessories, cheap, working or not
> sdbuse1 on mailhost bigfoot.com
Yes, this is probably a job for a PIC.
Anthony
Thomson Tim wrote:
> Whatever for? The PC alone will waist more energy than a well insulated
> tank!
> I mean come on we do our banking and such with a computer now
> ...............but why would someone want to wake up and find out that the
> water is frooze because the PC frooze?
>
>>
>>>1. Computer controlled (PC is OK, others are OK too)
>>>2. Capable of driving a 30A 240VAC relay
>>>3. Capable of taking temperature readings from several inputs
>>> to determine if the relay needs to be on or off
>>>4. Reasonable cost
...
XML site map
> 2. Capable of driving a 30A 240VAC relay
> 3. Capable of taking temperature readings from several inputs
> to determine if the relay needs to be on or off
> 4. Reasonable cost
> Basically, a smart controller that knows about time and return water
> temperature, and turns on the heat when it's got access to cheap
> electricity and when the floor is cool enough to need it.