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 35 years

 

• Article 24 - July/August 1997

 

Programmable Differential Controllers©

 

This is the ninth in a series of articles that will summarize the programming capabilities of most of the differential temperature controllers used in the Colorado area. This article will examine the Apollo 44, Apollo 88, Webb 990 and Webb Systemizer III controllers. The Apollo 44 and Webb 990 contain the same circuit design and both use 30 K ohm thermistor sensors. The Apollo 88 controller requires 10 K ohm thermistor sensors. The Webb Systemizer III uses a negative temperature coefficient sensor that is close to 21.5 K ohms at 77° F. However, this sensor does not follow the same resistance versus temperature curve as would a 21.5 K ohm thermistor. Since this sensor is next to impossible to find, an alternate approach is to use a 30 K ohm sensor in combination with two resistors as shown below. This two resistor network will allow a 30 K ohm thermistor sensor to closely track the original 21.5 K ohm sensor (within about ±6° F) over a reasonable operating range from 68° F to 176° F. Outside of these limits the tracking error increases.

 

 

The Apollo 44, Apollo 88, and Webb 990 programming features are all similar, except for the "-NF" (no frills) model which only incorporates adjustable (0° to 50° F) ON-OFF differential temperature capabilities. The II -A" models contain only one relay, the K1 relay. This relay energizes and de-energizes when the turn ON and OFF differentials (adjustable, 0° to 50° F) are reached. The relay also activates when the freeze protection point (adjustable, 39° to 50° F) is reached by the collector sensor. This freeze protection function of the K1 relay may be disabled by cutting the J4 jumper in the Apollo 44 and Webb 990 or the K1-FP jumper in the Apollo 88. The K1 relay will de-energize when the over-temperature protection set point (adjustable, 70° to 180° F with the Apollo 44 and Webb 990 and 60° to 180° F with the Apollo 88) is reached by the storage sensor. This over-temperature protection function of the K1 relay may be disabled by cutting the J2 jumper in the Apollo 44 and Webb 990 or the K1-Hi Limit jumper in the Apollo 88. Operation of the K1 relay may also be manually controlled by the OFF-AUTO-ON switch in the Apollo 44 and Webb 990.

 

The Apollo 44, Apollo 88, and Webb 990 II -"B" models are a model A unit plus a second relay, K2 . During normal operation, the K2 relay will be energized. K2 will de-energize when the freeze protection set point is reached by the collector sensor. This dropout of the K2 relay at the freeze protection set point may be disabled by cutting the J3 jumper in the Apollo 44 and Webb 990 or the K2-FP jumper in the Apollo 88. K2 will also de-energize when the over-temperature protection set point is reached by the storage sensor. This function may be disabled by cutting the J1 jumper in the Apollo 44 and Webb 990 or the K2-Hi Limit jumper in the Apollo 88. The K2 relay is not affected by the position of the OFF-AUTO-ON switch in the Apollo 44 and Webb 990.

 

The Apollo 44, and Webb 990 II -"C" models (note, there isn't an Apollo 88C model) are a model B unit plus a third relay, K3. During normal operation, the K3 relay will be de-energized. This relay will energize when the over-temperature set point is reached by the storage sensor. The K3 relay is not affected by the position of the OFF-AUTO-ON switch.

 

All Apollo 44, Apollo 88, and Webb 990 models contain W-R terminals that can accept an OPEN / CLOSED switch to either break or make the circuit to the K1 (differential temperature) relay. The OFF-AUTO-ON switch does not affect any of the LED function indicators on the Apollo 44 or Webb 990 models. The ON-OFF switch on the Apollo 88 controllers controls DC power used to power the circuitry of the controller and the relays. With this switch in the OFF position, the entire controller will be disabled and both relays will be de-energized.

 

The only programming capabilities in the Webb Systemizer III deal with set points for the domestic hot water, room temperature (heat provided by solar) and room temperature (heat provided by auxiliary heat).

 

If I've made a mistake or have left out some important information, or you otherwise take exception to what I have written, please write to me (c/o CoSEIA or to my address listed in the CoSEIA membership directory) and we will include your comments in the next newsletter.

 

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