its to run a small air pump but a regular 12v supply is to little
Transformerless supplies are sometimes used in things that have no external "user" connections, like plug-in remote controlled power sockets.
They are normally used for very low power devices.
For one to work, the impedance of the "voltage dropping" components must be matched to the maximum load current, and there must be a load to always take that current, or the output voltage will rise to the same as the input voltage.
With a typical tiny bit of electronics, the permanent load can just be a small zener diode, to take the excess current.
Your 12V air compressor probably takes 5 - 10A.
That means the stabilising "load" would have to take more that 10A to prevent the voltage rising above the 12V range.
And the series impedance has to be such that 10A is passed through the rectifier to the load all the time.
The 120W shunt regulator will cost at least $10 and run very hot, needing a lot of cooling.
The total series impedance to pass 10A from 110V will be around 10 ohms. Doing that with a resistor would dissipate another Watts as heat; basically an 1KW electric heater element.
Using a capacitor in place of a resistor, you would need a 270uF 250V AC rated one.
Something like this:
Find many great new & used options and get the best deals for 270uF-324uF Start Capacitor BMI 250VAC motor pump dryer fan induction 270-324uF at the best online prices at eBay! Free shipping for many products!
As you would be using a bridge rec, you should actually use four of those to keep it a balanced circuit, so two in parallel connected from each AC input to the bridge rec.
You would end up with something massive, weighing possibly around 10 - 20lb, costing at least a couple of hundred dollars, that wastes large amounts of power and heat, & is also lethally dangerous.
Or you just buy a proper transformer, or pay about $20 for a complete, ready built, 12V DC power unit.
In other words, "transformerless" power supplies are totally impractical for anything other than trivial loads.
Thanks for the input guys. I have several okd cores i can rewind for an isolation/reducing transformer. They are just simply quite heavy. 15lbs at least. I had only hoped a transformerless would have been much lighter but after 10+hours of tinkering, yall are correct. Its useless. As for the drain, im not sure. Its not so much a pump as a fan. For blowing up air mattresses and pools. Its the perfect size for my needs and i have plenty of dc motors to replace the once inside should it inevitably burn out. So i propose this question: should i go with a full wave bridge rectifier or is there another preferred way to do it?
You seem a bit confused?, a 'bridge rectifier' and a 'full wave rectifier' aren't the same thing. A bridge is
ONE TYPE of full wave rectifier, and is just called a 'bridge rectifier' - a 'full wave rectifier' would normally refer to a twin diode one, along with a dual winding secondary.
Your question is also fairly meaningless, yes you should go for a full wave rectifier, of either type depending on what transformer you use (either single or dual winding) - or if you use a switch-mode design, you just need a single diode, as full wave isn't required (but that's a
MUCH more complicated design).
Your earlier comment makes no sense either.
a regular 12v supply is to little and its intended 12v car battery is to strong
A correctly specified 'regular' 12V supply would be fine, as would a 12V car battery - why would you imagine it would be 'too strong'?.
First though you need to find out what you actually need, and a good way to do that would be to use a car battery to power it, and monitor the current it takes - assuming it's less than 10A you should be OK with most multimeters, as they normally have at least a 10A range.
My apologies for the confusing questions. Been a bit busy with to much and was responding in a rush. I did try using caps with resistors to build a capacitive potential divider? It worked just fine to dim a bulb or run an ac motor slowly but did nothing when i attemped to rectify to dc. Multimeter showed dc output but didnt run even a small dc motor. Dangers aside i dont plan to try doing it this way so ill rewind a transform. But curious me wants to know if a core can be built or is it best to just rewrap an existing core?
Why not just buy a transformer? - you talk about reliability, and then plan reducing it by rewinding an old transformer.
But I refer you to post #12, you need to find out what power you require for it first before you either rewind, or buy one.
Nothing is written on the casing of the fan or serial information other than the sn of the model but has no results online other than typical use and price. Granted its designed to run directly off of a 12v x*-amp car battery but theres no solid information on the motor other than dont run longer than 10 minutes. Ive used a: 12v 1.5 and 2 amp adapter and it runs meh. Sure itll blow air but nothing usable. Ive also used a 19.5v 1amp adapter and ran slightly better. Along with a 6v 1amp and it was the same as the 12s. A car battery will run it to the point of a leaf blower but as i stated thats just to strong. I can likely be wrong but it seems a higher voltage and a modest 1 to 2 amps seems great. Just the need for the greater voltage has put me outside of what im able to buy at the moment.
Hello all. I could use some help understanding bridge rectifiers. I’m repairing an Allen and Heath ZedR16 PSU and am slowly understanding most of the circuit. I’ve never worked on an SMPS before. Can I expect the same DC voltage (around 80VDC from 120VAC) to be present with different rectifiers? Specifically, the circuit has a 2KBP206, would a KBP208 have the same DC output and can I safely replace it? The data sheet seems to have their max input voltage as the main difference. Forward voltage is 1.1V on both rectifiers.
I actually don’t think it needs replacing as it tests fine but the question is just more for my learning. Awake and pondering bridge rectifiers… haha. I guess if both rectifier’s forward voltage is the same then they should put out the same DC voltage correct? Is there other factors that need to be considered other than max voltage?
Another question for anyone familiar with SMPS power supplies, but can I safely power up the unit without the mosfet (f8nk100z or stp5nb100fp) and controller chip (UCan) installed to check voltages? I would like to make sure the controller isn’t getting too much voltage at VCC before I install it.
Not sure if I’m allowed to upload the schematic to this site but I can if it’s permitted. I’m pretty wary of uploading things I don’t have copyright to.
Thanks
Ryan
Another question for anyone familiar with SMPS power supplies, but can I safely power up the unit without the mosfet (f8nk100z or stp5nb100fp) and controller chip (UCan) installed to check voltages? I would like to make sure the controller isn’t getting too much voltage at VCC before I install it.
That won't do much of anything. The UC will, at best, be in some "hiccup mode", since it supplies itself from the main switching transformer, once it starts up. And if it's "getting too much voltage at VCC", it WILL let you know about its own discomfort by going "poof", long before you have time to probe anything.
Speaking of which, you'll wanna be VERY careful poking around the mains-input / primary area. AC isn't all that bad, but i still wouldn't recommend it. And high-voltage DC with a fat(ish) reservoir electrolytic won't be fun either.
If anything, using a series bulb tester (with an old-school ~100W tungsten filament bulb; nothing else will work) would do a lot more good.
https://www.bristolwatch.com/load_lamp.htm