Since I have a flowrate of 4.4LPM in my actual setup with a Eheim 1250 (corresponding to a head of 1.8m), with a Johnson CO30 or CM30 in the same setup I should have a theoretical flowrate of more than 20 LPM (following the P-Q curves of both pumps).
Therefore I'd liked to be able to control the flowrate in my cooling setup (see also previous post), so I developped this simple schematic of a variable power supply for Johnson CM10, CM30, CO30, (or other) 12V DC pumps not exceeding 2.5 Amp of current draw:
It's based on National's LM350 3 Amp voltage regulator (bigger brother of the 1 Amp LM317).
The LM350 comes in two possible packages:
- LM350T: plastic TO220
- LM350K: metallic T03
Both versions have the same specs but the thermal resistance of the K-version is a lot lower (due to the metallic housing).
Also the K-version is more expensive (about 9.00$ vs 2.40$ here in Belgium) than the T-version. Both versions can be used in the schematic.
The LM350 must be mounted on a heatsink for heat dissipation.
R1, potmeter P1 and trimpot P2 have been calculated to obtain roughly an output voltage of 7 to 13V (fine tuning of the voltage range is done by P2):
Vout = Vref x (1+((P1+P2)/R1)) , where Vref=1.25V
Mains voltage is transformed to 2x 12V through a 30W (toroidal) transformer and rectified by D1 & D2. Those diodes can be any 3 Amp minimum diodes. C1 & C2 are for smoothing and spike suppression of the rectified voltage. C1 can be any electrolytic capacitor of 2200µF or more, and a voltage of 25V or more.
F1 is the by Johnson Pump advised (slow blow) fuse.
C3 (1µF Tantalium capacitor) is added for increased output stability.
R2 and the LED on the output give a visual indication of the presence of voltage to the pump. If omitted, R2 and the LED should be replaced by a 1K resistor to ensure a minimal load current (minimum 5mA) on the LM350 when the pump is disconnected.
The primary of the transformer is connected to the SPDT contact of a 12V coil relay to switch the pump's PSU together with the PC's PSU.
S2 can be closed to power the pump without the PC's PSU powered on (for leak testing).
I have almost all components available, except for the transformer and the LM350 regulator.
I will do some tests with my two CO30P7 Johnson pumps from Surplus Center under different load conditions, also to measure the max dissipated power of the LM350 and calculate the needed heatsink.
CD
