As you may already know, Hayward added an SPST K4 relay on the newer GLX-PCB-RITE in an effort to address the Thermistor issue. For those willing to take this adventure, the schematic diagram and more on K4 relay were discussed in this thread. But if you find yourself in the market for a replacement GLX-PCB-RITE, pick the mainboard with the K4 relay on it for reliability.
NTC (Negative Temperature Coefficient) Thermistor Overview
When power is applied to a circuit with an NTC, the NTC’s resistance starts off high. After the inrush current has passed and the converter is running at steady state, the NTC heats up and its resistance drops. NTC’s limit the inrush current only when they are cold. When power is turned off and quickly on again, the NTC does not have time to cool down and will not limit the inrush current. Inrush current limiting NTC Thermistors are ideal for switching power supplies where the low impedance of the charging capacitor exposes the bridge rectifier to an excessively high current surge at turn-on.
On the older GLX-PCB-RITE mainboard without the K4 relay, the software is crippled and retrofitting a relay to bypass the thermistor is not possible without adding a delay on timer. Unless you have the latest script to flash the onboard micro-controller. Then it’s just a matter of adding a link to pull down the coil of the relay via pin15 of U5.
To replicate the Thermistor upgrade, I would recommend a 1-3 secs delay on timer to energize the relay with at least 16A or higher dry contact rating. For experimental purposes, I used the 5-30 Vdc delay off timer I bought from HK via eBay for $1.46 ea. I modified the timer to provide a 6-7 secs delay on, closest I can get from recycled parts. I connected the input from the load side of R17 which causes the voltage to drop from 19V down to 9 Vdc. The 40mA timer current load put the 2W R17 under stress and is overheating. For now, I decided to run it off from the 24V regulator via 220 ohms resistor and will observe.
Although it’s too soon to predict the reliability of the cheap timer, I can only emphasize the following;
Pros:
1. The Thermistor is immediately relieved of its duty after the inrush current has passed.
2. No more Thermistor overheating issue when chlorinating.
3. The Thermistor remains cold, thus limits the inrush current when cycling AC power.
Cons:
1. Difficult to source the appropriate least expensive timer for this purpose.
2. Low voltage timer will add more load to the onboard low voltage power supply.
3. The 5V regulator on this timer overheats and most likely to pop the mainboard 24V regulator if it failed.
4. At more than 6 Amps draw for the T-15 cell, the reliability of the 10A relay on this timer is uncertain.
5. Not an easy DIY for the vast majority.
My experiment will not end here and I am determined to modify the 100-220Vac timer that I also bought from eBay for a little over $4. This should work on a standalone with no connection to the mainboard low voltage power supply. Hence, my preferred method. More on this later…
Left DVM, is the voltage reading from the load side of the Thermistor when chlorinating. Right side DVM shows the current load from the onboard 24V, 1A linear voltage regulator. Slightly higher for the Aqua-Trol users due to the K3 relay and perhaps K4.
Shown here is the temperature of the Thermistor with the T-15 cell generating for the past 20 mins. Cannot get a straight line for accurate measurement but at least one can reference. Just imagine how much hotter it gets inside a sealed metal cabinet without ventilation.
DVM on the left shows the output voltage reading of the 24V regulator. Right side, shows the current load of the 24V regulator with the cheap timer in service. Noticed the 40mA increase with a 5Vdc relay?
The cheap timer current draw climbed to 50mA @ 13 volts, tapped from the 24V regulator output via 220 ohms.
NTC (Negative Temperature Coefficient) Thermistor Overview
When power is applied to a circuit with an NTC, the NTC’s resistance starts off high. After the inrush current has passed and the converter is running at steady state, the NTC heats up and its resistance drops. NTC’s limit the inrush current only when they are cold. When power is turned off and quickly on again, the NTC does not have time to cool down and will not limit the inrush current. Inrush current limiting NTC Thermistors are ideal for switching power supplies where the low impedance of the charging capacitor exposes the bridge rectifier to an excessively high current surge at turn-on.
On the older GLX-PCB-RITE mainboard without the K4 relay, the software is crippled and retrofitting a relay to bypass the thermistor is not possible without adding a delay on timer. Unless you have the latest script to flash the onboard micro-controller. Then it’s just a matter of adding a link to pull down the coil of the relay via pin15 of U5.
To replicate the Thermistor upgrade, I would recommend a 1-3 secs delay on timer to energize the relay with at least 16A or higher dry contact rating. For experimental purposes, I used the 5-30 Vdc delay off timer I bought from HK via eBay for $1.46 ea. I modified the timer to provide a 6-7 secs delay on, closest I can get from recycled parts. I connected the input from the load side of R17 which causes the voltage to drop from 19V down to 9 Vdc. The 40mA timer current load put the 2W R17 under stress and is overheating. For now, I decided to run it off from the 24V regulator via 220 ohms resistor and will observe.
Although it’s too soon to predict the reliability of the cheap timer, I can only emphasize the following;
Pros:
1. The Thermistor is immediately relieved of its duty after the inrush current has passed.
2. No more Thermistor overheating issue when chlorinating.
3. The Thermistor remains cold, thus limits the inrush current when cycling AC power.
Cons:
1. Difficult to source the appropriate least expensive timer for this purpose.
2. Low voltage timer will add more load to the onboard low voltage power supply.
3. The 5V regulator on this timer overheats and most likely to pop the mainboard 24V regulator if it failed.
4. At more than 6 Amps draw for the T-15 cell, the reliability of the 10A relay on this timer is uncertain.
5. Not an easy DIY for the vast majority.
My experiment will not end here and I am determined to modify the 100-220Vac timer that I also bought from eBay for a little over $4. This should work on a standalone with no connection to the mainboard low voltage power supply. Hence, my preferred method. More on this later…
Left DVM, is the voltage reading from the load side of the Thermistor when chlorinating. Right side DVM shows the current load from the onboard 24V, 1A linear voltage regulator. Slightly higher for the Aqua-Trol users due to the K3 relay and perhaps K4.
Shown here is the temperature of the Thermistor with the T-15 cell generating for the past 20 mins. Cannot get a straight line for accurate measurement but at least one can reference. Just imagine how much hotter it gets inside a sealed metal cabinet without ventilation.
DVM on the left shows the output voltage reading of the 24V regulator. Right side, shows the current load of the 24V regulator with the cheap timer in service. Noticed the 40mA increase with a 5Vdc relay?
The cheap timer current draw climbed to 50mA @ 13 volts, tapped from the 24V regulator output via 220 ohms.
