Yes, a slim Liquid Heat Exchanger (LHX) can be attached to the rear of QSI 500/600 Series camera bodies to increase the cooling. 500 Series cameras will typically achieve up to 45°C below the temperature of the circulating fluid. 600 Series cameras will achieve up 52°C below the temperature of the circulating fluid.
The LHX includes two quick release-connectors designed for 1/4" inside diameter tubing. 1/4" i.d. clear vinyl tubing works great.
The LHX works best with a low flow rate of approximately 2 gallons per hour (gph). QSI also sells a small pump and 25' of tubing. Any small fountain, aquarium or lab pump will work fine. Small fountain pumps and clear vinyl tubing are widely available at most hardware stores.
Extra quick-release connectors for a second cooling setup can be ordered directly from McMaster-Carr:
Submersing the pump in a 5-gallon bucket of water works well. Over the course of the night, cooling the camera will only raise the temperature of 5 gallons of water by a few degrees.
Generally you won't need to cool the water to achieve your desired set point. On very warm nights, you can throw a 7 lb. bag of ice into the bucket to slightly lower the temperature of the water.
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Be careful not to cool the water below the dew point. In high humidity situations, common in the southeastern U.S. for instance, the dew point may be very close to the air temperature. The entire back of the camera acts as a large heat sink. With standard air cooling, the temperature of the body will always be above the dew point. With chilled water, it's possible to drive the temperature of the camera below the dew point, potentially causing condensation.
Fill the tubing with water by submersing it in the water before starting to cycle it through the LHX. A small pump may not be able to "lift" the water through empty tubing, but it will cycle the water through the tubing just fine.
The fans can be turned off when using liquid cooling, but if you do so, be sure to turn them back on before running the camera with standard air cooling.