CONIFER SOLAR CONSULTING

Jon Klima, Owner
360 Trout Lane, PO Box 23, Guffey, CO 80820
Phone: 719 479-2281,  Email: jon.klima@gmail.com
In business for 37 years

 

• Article 14 - March, 1995

 

Programmable Differential Temperature Controllers #1©

 

This is the first in a series of several articles that will summarize the programming capabilities of most of the differential temperature controllers used in the Colorado area. Programming may be as simple as installing a third SAS-3 sensor with a Heliotrope DTT -80 to add high limit protection or as complex as setting the 16 DIP switches (two banks of eight switches) on the Independent Energy C-100-P2. Although most programming is simple and taken for granted as "being built in and fixed", the features will never-the-1ess be pointed out. In most cases, the service technician can make the decision as to whether or not the programming should be used.

 

The information contained within these articles is taken 'from product literature I have collected over the years and I believe it to be accurate. In this issue of the COSEIA newsletter, we look at the Dencor, Dynatech, HI2/Hawthorne, and Honeywell controllers. Next time, we will examine the Heliotrope, Independent Energy, and Johnson brands of controllers.

 

Dencor (5 K ohm thermistor) Model 912 and 913, air system controller. This controller is used to control: 1 heating storage, 2. Heating the house from storage, and 3. Heating the house from the collectors. Use point temperature (the temperature that the storage or collector must be at to provide heat to the house) is selected by a jumper or by use of an external resistor.

 

Dynatech SC30 (10 K ohm thermistor). High limit is programmable with a high limit adjustment pot. Models SC30-COl, C04, C05, C06, and C07 are programmable for recirculation freeze protection with appropriate sensors. Models SC30-C08, C09 Cl0, C11, C12, and C14 have a drain valve output. Drain protection at high limit is available on the SC30-C11, C12, and C14 models. Appropriate normally closed snap switch sensors are required to make these options operate.

 

Dynatech SC90 (3 K ohm or 10 K ohm thermistor, depending upon model number). High limit is programmable with a high limit adjustment pot. The SC90 is programmable for recirculation freeze protection with appropriate sensors. Drain valve models were also manufactured. SC90 models with model numbers SC90-C03-- use 3 K ohm sensors and those with SC90-ClO-- model numbers use 10 K ohm sensors.

 

Novan used a lot of Dynatech SC30 controller boards in their control systems and these occasionally show up in Independent Energy C-30 boxes. It is easy to see which board is installed on the solar system. The true C-30 has red LEDs for the power ON and power output indicators. The SC30 has green LEDs for those indicators. Most of the Novan SC30s were manufactured with the ON position of the ON-OFF-AUTO switch disabled, i.e., when the switch is placed in the ON position, it in reality is still in the AUTO mode.

 

HI2/Hawthorne (10 k ohm thermistor). Hawthorne was bought out by HI2 in the early '80s. Most model numbers remained unchanged, but there were a few changes. Drain down and recirculation freeze protection is incorporated by use of appropriate snap switches. Drain down freeze protection is available with the H-1506-C and H-1513-C models using the H-1522 frost sensor (contacts open on temperature fall at 38° F, +l0° F, -1° F), yellow/black leads. Recirculation is available with the H-1503-B and -C, H-1510-B and -C, H-1603-S and -H, and H-1610-B and -H models using the H-1521 frost sensor (contacts open on temperature rise at 38° F,+10° F,-1° F, yellow/yellow leads). By using either the H-1515 (165° F, red/red leads), H-1516 (150° F, org/org leads), or H-1517 (185° F, red/org leads) high limit sensors, high limit shut down can be achieved. These sensors are all open on temperature rise at the given set point +/- 10° F.

 

Honeywell R7412A-F (C773A-D sensor, platinum film PTC sensor). Model R7412A only provides the basic ON-OFF temperature differential function by energizing/de-energizing an internal relay.

 

Model R7412B provides the basic ON-OFF temperature differential function as in the R7412A plus freeze (recirculation) protection by energizing the internal relay.

 

Model R7412C provides the basic ON-OFF temperature differential function as in the R7412A plus freeze protection by providing a signal to energize an external relay.

 

Model R7412D provides the basic ON-OFF temperature differential function as in the R7412A plus over temperature protection by de-energizing the internal relay.

 

Model R7412E provides the basic ON-OFP temperature differential function as in the R7412A plus over temperature protection, by providing a signal to energize an external relay.

 

Model R7412F provides the features of all of the above models. The ON-OFF differentials are factory set at 18° F and 3° F respectively. Plug in resistors(R-ON and R-OFF) can be substituted for the factory installed resistors to change these values to anywhere from -10° F to 40° F (Table 1, pg 7 of the Honeywell R7412 product literature).

 

Freeze protection is set at the factory at either 37° F, 42° F, or 47° F and is not adjustable for the B and C models. The R7412F is field adjustable to one of these settings by installing a 48.7 K ohm resistor at the R40 resistor position for 47° F, a 110 K ohm resistor for 42° F, or leaving R40 open for a 37° F setting. The freeze differential in all cases is 3° F.

 

Over temperature protection is factory set at 5° F increments from 140° F to 190° F and is not adjustable for the D and E models. The R7412F is field adjustable by changing the OT1 (R41) and OT2 (R26) resistors (Table 2, pg 8 of the Honeywell R7412 product literature). The over temperature differential in all cases is 10° F.

 

The R7412F can be changed to any of the other models (A - E) by cutting various combinations of the CR9 - CR12 diodes (Table 3, pg 8 of the Honeywell R7412 product literature).

 

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