I am building a twin air pump for a pond, powered by a 50W PV system with charge controller connected to a DIY fused DC consumer unit. I have a project box with two switches - each switch goes to a pre-made (fan controller) LM317 linear adjustable voltage regulator, each going to a simple DC motor. The idea is to have each pump independently switched and adjustable but running off one 12V output from the consumer unit - because it will be attached to a single timer.
When tested on separate outputs on the consumer unit, they worked fine, but when I forked them at the point of entry into the project box (before the switches of course) they worked erratically for a few seconds during adjustment. After a while the potentiometers 'died open' allowing full speed only. There was no visible sign of damage to each circuit board however.
I've now obtained another pair of these regulator circuits - but before risking them again is there a best practice method of protection here? My initial thoughts were a diode on each (+) between where the line forks and the switch and/or diodes on the line between each regulator and motor. I have 1N4001 silicon diodes and SB560 Schottky diodes available. Are diodes enough or is there something else needed here?
2x Mini toggle SPST switches. Rated 5A @ 125VAC / 2A @ 250VAC.
2x RF-370 Mini motor pump. Rated 12V. Suited 5V-12V. Rated current 250mA
2x DC Linear Converter LM317 Down Voltage Regulator Board 'XH-M137 v5'. Adjustable: 3V-15V. Input: 3.25V-15V. Output: 1.25V-13V. Output current: 5-1500mA. This consists of the 12v +- input, 2 5-band resistors (can't read them against the blue), 1 zero ohm resistor, 2 tiny brown disc capacitors labelled '102', the LM317T chip & heatsink, a B10K pot, tiny red LED, and 2 fan outputs (1 goes to +- wires for the motor, the other is a 3 pin socket for a PC fan which is not used). Schematic at http://img01.cp.aliimg.com/imgextra/i2/199304554/T2mq7tXkdXXXXXXXXX_!!199304554.jpg
My solar setup outputs around 12V and can deliver up to around 3A. The output this pump unit will be connected to is protected with a 1A blade fuse.
UPDATE 26/05/17: Having now blown these LMs- I've obtained a couple of 1803BK PWM controllers instead which appear to be better quality than the LM317s. I'm unable to get a schematic of these but I can tell you the spec (the large cap says 25v 100uF and the pot is 100K ohm if that helps):
Model: 1803BK - Ver2.0 201505 Input 1.8V-15VDC Max output: 30W Max output current: 2A Self-recovery fuse (2A) Duty cycle 0-100% (built in switch)
The updated question now is, should I still apply the advice given below (1N4001 diode and 1000uF capacitor per controller) for this new setup? Also, as I have switches before the controllers, is it safe to leave them turned up before switching on - or would the sudden jolt of voltage/drawn current be damaging? I really don't want to blow these somewhat cute 1803s.