Rockwell Maintenance Manual – Coolant
The cooling fluid is a mixture of de-ionized water, ethylene glycol, and special corrosion inhibitors. De-ionized water has been purified of most ionized solids and has very low conductivity. The ethylene glycol is a high purity type which is iron &chloride free and also has low conductivity. The inhibitors do not contribute to conductivity and are unique for thermal fluid blends.
Water is an active solvent and gathers contaminants from everything it contacts. In nature, ionized solids such as Sodium (Na+), Calcium(Ca+2) and chloride (Cl-) are stripped from rocks and soil by water.
Also found in water are organic molecules from decaying debris,bacteria and microbes that normally grow in water, and dissolved ionized gases such as chlorine (Cl2) and carbon dioxide (CO2).
Conductivity is primarily the result of ionized solids and gases in water. The other materials in water contribute very little to electric current flow. When a voltage is impressed on water, current flows by using the ionic molecules as stepping stones for the current. Most Bacteria and organic materials offer few stepping stones for current,so if the ionized solids and gases are removed, the water becomes relatively non-conductive.
Dissolved ionized solids and gases can be removed by using ion exchange resins. Such resins attract ions in the water replacing them with H+ and OH- ions, which ultimately join to form water. Ion Exchange resins are synthetic polymers with several ion exchange sites attached to the surface. The ion exchange resins gradually losetheir effectiveness and need to be replaced or recharged. NOTE: Do not recycle the de-ionizing cartridge because it has beencontaminated by ethylene glycol and would contaminate the recycling facility.
If straight ethylene glycol (EG) is used because the pre-blended coolant is not available, it is imperative that high purity iron & chloridefree EG be used.In addition,de-ionized water may be added to the system for top up. Distilled Water can only be used when no de-ionized water is available, and only when there is no other alternative to run the drive. Please note that using distilled water will significantly reduce the life of the ion exchange cartridge (use up resin), reduce the life of mesh filters (foul filters), and reduce the life of the coolant solution itself.
Coolant Solution Expiry Date (1-2 years)
The coolant mixture constantly scrubs carbon dioxide from air lowering the coolant’s pH level. This change in pH is slow but decreases steadily over time and cannot be adjusted. When the coolant mixture becomes more acidic, it also becomes very corrosive. To minimize the negative influence of lowering pH, a specialized inhibitor was formulated into all coolant mixtures. The corrosion inhibitor is important and recommended. Not only does the inhibitor protect metal surfaces within the fluid loop, it also helps protect the metal housing the VFD is contained in should a leak occur.
Normal operating pH of Coolant -10C, Coolant -45C, and Coolant -55C is between 6 and 8. After six months of drive operation, the pH can drop as low as 5 and after one-two years, the pH of the Coolant can be as low as 3.5 – 4.5, or lower. This is very acidic and very corrosive to metal in particular. There is no way to buffer the pH back to 6 – 8 without drastically increasing the conductivity of the coolant. Buffering the pH would compromise the drives conductivity control and likely shut down the drive.
Dumping and refilling PowerFlex 7000 Liquid Cooled (‘C’ Frame) Medium Voltage AC Drives with Coolant -10C, Coolant -45C, or Coolant -55C (Part #80025-784-81, 80025-784-51, 80025-784-91) brings the pH back in the 6 – 8 range helping to protect pump seals, control valves, copper piping, rubber tubing, PVC plumbing and all other materials the coolant comes in contact with including the housing should a leak occur.
We recommend the PowerFlex 7000 units be flushed and refilled with new Coolant at least once every 1-2 years (min-max) to prevent possible drive down time.
Maintaining Coolant Ratio
Mixing pure ethylene glycol and de-ionized water produces the coolant used as the cooling medium in the liquid-cooled PowerFlex 7000 Medium Voltage ‘C’ Frame drive. It is possible to blend your own coolant. However, we have found it is more operator friendly to purchase the three commercially available coolant blends depending on required freezing point, Coolant -10C, Coolant -45C, and Coolant -55C (Part #80025-784-81, 80025-784-51, 80025-784-91). This has the added benefit of preventing cross-contamination when blending in unclean containers, maintains corrosion inhibitor concentration, and does not require testing.
Special Note: For those who wish to blend their own coolant, make sure you have clean containers and pre-rinse them with de-ionized water first before blending to prevent cross-contamination.
During operation, the concentration of pure ethylene glycol and de-ionized water may change due to fluid leakage or evaporation; therefore, the freezing point of the coolant may not be correct. The following instructions are required for those who wish to blend their own coolant to correct the freezing point of the coolant mixture.
- Glycol and battery tester (Part No. 80025-862-01)
- De-ionized water, 19-litre (5-gallon) container(Part # 80025-784-60)
- Pure ethylene glycol, 19-litre (5-gallon) container(Part # 80025-784-61)
- Measure and record the reservoir coolant freeze point using the Glycol and Battery Tester.
- If the freezing point of the coolant is at -45°C (-50°F) ±2°C,correction is not required.
- If correction is required, then follow the remaining steps.
- Water freezes at 0°C (32°F) and pure ethylene freezes at -13°C(8.6°F), but mixtures of the two freezes at lower temperatures.For example, a 50/50 mixture by weight of ethylene glycol and water freezes at -36°C (-33°F). The addition of ethylene glycol to the mixture will lower the freezing point. Adjust the freeze temperature of the coolant mixture to -45°C (-50°F) using this method.
- Add either substance in small quantities and measure the freezing temperature after each addition until desired freezing temperature is achieved.
I M P O R T A N T
It is better to have more water than glycol in the
mixture because water is a better thermal
conductor than glycol.
There are two possible causes of water loss in the drive:
Evaporation – Up to 99.5% of liquid lost to evaporation is water because of the chemical properties of the substances in the mixture.
Leaks – Glycol and water are lost proportionally depending on the concentration of the substances in the mixture. For example, if the mixture is 60% glycol and 40% water, then any leakage will contain the same proportions of the liquids.
To rectify the problem, add small quantities of water. Measure the freeze temperature of the coolant after each addition and continue adding until the desired freezing temperature is achieved.