Running a Submersible Aquarium Pump

Thanks. Now I would have courage to connect it.

Are you using this pump just to exchange water occasionally? ...I ask because this pump is not recommended for continuous use over 24 hrs...

https://www.amazon.com/XCSOURCE-JT-500-Submersible-Immersible-TE484/dp/B01GH82NQ2

Thanks. This is the pump. I would not have to run it more than five minutes at a time.

I used to build all of my power supplies. Get a 7812 voltage regulator connected between the DC rectified, filtered output and the pump. Make sure the regulator is tightly fastened to a good heat sink with thermal grease to enable good heat conduction.

http://www.ti.com/lit/ds/symlink/lm340.pdf

https://www.instructables.com/id/Make-a-simple-12-volt-power-supply/

While I like your circuit I wish to draw your attention to the fact the 7812 voltage regulator is only rated at 1amp and many I have used fold back on the current before they reach 1amp. A better option is to use an LM317 adjustable voltage regulator which will deliver 1.5amps and as a bonus you can make the resistor network variable on the adjustment terminal to change the output voltage. As suggested put a fuse in the primary and secondary side of the transformer. Primary fuse to protect the transformer and the secondary fuse to protect against a diode shorting and burning the secondary up. Now some may scoff at the thought of a diode failing but I have seen it many times and they don't always go open circuit or short circuit some become a bidirectional resistance of low value.

There are other voltage regulators in the LM series or even use buck boost regulators where the DC voltage from your rectifier circuit can be transformed to give a stable 12V DC and a current limit can be set. Buck Boost regulator circuits can be had for less than $5 from Hoing Kong.

A point to remember is that 12V AC when rectified and filtered with a capacitor will have AC RMS voltage * 1.414 (peak ) - forward voltage drop of the diode 5408s. An AVo just isn't up to the mark of modern digital voltmeters where you can measure the forward voltage drop by selecting the position on the dial.

As for AVOs I used to repair them in the long gone past and they were robust, models 7, 8 etc and even VTVM, vacuum tube volt meters but now I just stick to using Fluke multimeters, not quite as forgiving as the old wire wound resistors of the AVOs but well fused.

Thanks. I shall try to get a LM 317 circuit.

Thanks for the good suggestion. I did want to buy a ready made power supply. Those which were available in the market though rated as 12V 1.5 Amps DC output actually did not supply more than 500 mA (Labelled as China made). So decided to DIY. More over I have already ordered 12V 5W DC power supply from Ali Express. But that would consume at least two months I think. When purchasing the pump power supply was not in their list.

I=P/E. a 12V 5W power supply can only 5/12 of an Amp ≈417mA.

To supply 12V at 1.5A, you need a supply rated at at least 18W.

I presume what you are calling an avometer is the same device I knew as a VOM (Volt-Ohm-milliAmmeter). If it can only measure up to 250mA, then it has significant internal resistance when measuring current. That resistance would limit the current that could be provided by the power supply, so your statement that the supply rated at 1.5 Amps could only provide 500MA is probably mistaken.

A couple of things here... If the supply can supply more-than-neccessary current, and you are worried about the higher voltage, you can always use a half-wave rectifier. If you use a half-wave on both sides of the center-tap, and you still have a high voltage problem, try only side of the tap. And don't forget to remember the difference between no-load voltage and full-load voltage. You didn't say how you took your readings. Maybe with a load, the voltage will come down to spec.You might not really need a full-wave recti-fryer.

Thanks. I took the reading on open circuit voltage i.e. without any load. If I use only one side of the tap, don't you think that current would be less than 1.2 A? I have not tried yet. I shall remember "the voltage will come down to spec".

Several factors interplay with each other. Some are more dominant than others, depending on which is being adjusted. Even tho some other values might change, it might not be significant. You have to check the ratings on all of your parts to see if all remain in spec.

If you have time to play around with it, it's not so bad. Otherwise, It might be better to find the right one already made.

Available options: 1) Full-wave on both sides w/tap @12vdc 2) Half-wave on both sides w/tap @12vdc 3) Full-wave on one side w/tap @12vdc 4) Half-wave on one side with tap @ 12vdc.

If none of those options work for you, I have a big box full of "power bricks". I'm retired and don't need them any more. I've got a variety of sizes.

The current drawn will depend on the pump motor.

The output from you FW bridge agrees with calculated value of 1.4 P to P. AC is normal rated RMS,which is Root Means Square,which is an equivalent amount of power as DC of the same voltage.Peak to peak voltage is 1.4 times RMS voltage,and capacitors store the highest voltage applied,so you output voltage will be higher than the RMS of the transformer. The internal resistance of the motor will determine the amount of current draw.The only advantage in a larger transformer would be a cooler running transformer. I agree with the other posters:Buy a ready made regulated power supply,or use the one provided. IMHO: I prefer the KISS system myself.I am too old to be wasting my time building what I can buy.It interferes with my beer-thirty schedule.