Can anyone help me figure out this "magnetically regulated psu". Restoration plus prop addition.
rwgast_logicdesign
Posts: 1,464
So I have scored a pretty beat up PSU from a ham friend it was pretty beat up but working. Im under the impression it is for automotive/industerial it is a Ritz electronics "Magnetically Regulated" 13.8v 8amp PSU.
Im currently resorting/modding the case and hand drawing the original schematic. Here is a short thread about it on the EEVBlog about the thing
http://www.eevblog.com/forum/projects/old-psu-i-like-the-case-restore-or-makes-something-new/msg753234/#msg753234
I have been doing research on magnetically regulated transformers and I understand that there is usually a capacitor on the primary side to help keep the transformer regulating right. This thing has a High Voltage cap like those found in a microwave on the primary side. The secondary side is basically a rectifier with a 44mF cap in parallel with with a 13.8ohm power resistor and banana jacks. What I dont understand is why there is a power resistor there that is basically eating up the WHOLE load when there is nothing connected to it which gets hot enough to start melting the soldier joints.... and why im seeing 15 volts across the resistor when the transformer is suppose to regulate the supply?
I love the case and I had planned on trying to make a precision power supply with multiple rails using a propelled and some high resalution ADC's/DACs I thought this may be a good platform to start from for an adjustable 12v supply I figured the magnetic side would be pre regulation and the LDO's or custom regulators would be the next step along with some filtering. Im just having a heck of a time figuring out why the output has a 4mF farad filter cap in parallel with a 13.8 ohm resistor, what is the function of the power resistor and why is the supply putting out 15 volts even with it there loading the whole thing down to the max??
Im currently resorting/modding the case and hand drawing the original schematic. Here is a short thread about it on the EEVBlog about the thing
http://www.eevblog.com/forum/projects/old-psu-i-like-the-case-restore-or-makes-something-new/msg753234/#msg753234
I have been doing research on magnetically regulated transformers and I understand that there is usually a capacitor on the primary side to help keep the transformer regulating right. This thing has a High Voltage cap like those found in a microwave on the primary side. The secondary side is basically a rectifier with a 44mF cap in parallel with with a 13.8ohm power resistor and banana jacks. What I dont understand is why there is a power resistor there that is basically eating up the WHOLE load when there is nothing connected to it which gets hot enough to start melting the soldier joints.... and why im seeing 15 volts across the resistor when the transformer is suppose to regulate the supply?
I love the case and I had planned on trying to make a precision power supply with multiple rails using a propelled and some high resalution ADC's/DACs I thought this may be a good platform to start from for an adjustable 12v supply I figured the magnetic side would be pre regulation and the LDO's or custom regulators would be the next step along with some filtering. Im just having a heck of a time figuring out why the output has a 4mF farad filter cap in parallel with a 13.8 ohm resistor, what is the function of the power resistor and why is the supply putting out 15 volts even with it there loading the whole thing down to the max??
Comments
http://www.ebay.com/itm/Ritz-Electronics-PS1001MR-Power-supply-13-8VDC-8A-magnetic-Regulated-Model-/181876173196?hash=item2a58aa298c
Not sure how much help you will get from either link. This is pretty old technology and I only replaced a couple of capacitors and resistors over the years. I have a feeling the first link is the Canadian company representing the one from the second link, or perhaps it's subsidiary. As Sapphire pointed out this type of transformer is not a good choice for a supply that can provide a wide range of current. Better to get a transformer from an inexpensive car battery charger that can supply the max current you need.
He told me that these were usually used in stores to power a bunch of car stereo head units on display, and they are actually capable of 10 amps. Im not sure in what situation you would run a constant never changing load unless it was a light? If I wanted to build a digital PSU should I just leave this guy as is and use a different transformer? I was thinking the magnetic regulation would be nice if it was filtered then followed by an LDO with pre-tracking.... I have a high quality 50v with like 12 taps, I planned to use but I figured I could get cleaner power out of this in the end?
That thing has 13 ohms across a 13 volt output. Permanently drawing 1 amp and burning 13 watts. Even without an external load? !
Nobody worried about power consumption back in the day.
If it needs to be there then im thinking maybe ill just heat sync it so the solder stops melting off the leads when unloaded and use the thing as a supply to to do things like electro plating. Ive hooked the thing up to a scope with the resistor in and did a differential reading on the outputs and i get about 14.5v and almost 1v of ripple. Im not sure what kind of ripple i get with no resistor but i still get 14.5v out so how is this even regulation? Unfourtantely the guy who designed this has passed.... so this psu is a mystery to to me. The resistor isnt even on the tap that would contain either an lc tank or just capacitor. The transformer was an inhouse design with no data sheet. I would like to take advantage of the transformer in a better way but i just cant find any good info on magnetic regulation or this psu in genral.... the the thing was CE and UL, the guy on the phone said he recalls myoutput voltage with no load being correct... so im just confused about the whole concept of this thing.... how is it any better than a regular transformer with a huge filter cap after a rectifier?
I also want to find the capacity of the huge steel oil cap, but i need to shoot something with a fast rise time at it. Does anyone know what the fastest rise time a prop can do? Is it 12ns? The only signal gen i have is the prop scope i havent measured its rise time on my siglent but im doubting is < 4ns. Im most likely going to have to order a 74ahc14 or something that has 2ns time.... although im hoping one of the various 74s chips i have will work.
Yep, schematically wise it's almost exactly the 300v power supply I built in 197...something. I have no idea if there are any "magical" properties of that transformer though. The 13 ohms I can't figure out either.
See https://en.wikipedia.org/wiki/Constant-voltage_transformer#Constant-voltage_transformer for an explanation of how they work.
If you want to build a power supply using that transformer you can do so. The 13.3 ohm resistor can be replaced with a somewhat higher value one (56 – 82 ohms or so) to discharge the capacitor when power is turned off. If you plan on high current outputs (10+ amps) then you will need a large capacitor similar to what is shown in your schematic. It should be rated at 20-25 volts minimum.
BTW, if it is an oil filled capacitor the capacitance is not that high. Typically connected to AC and 150uF or less. It may be bad and have high current leakage.
I finally dug up my old notes on these regulators, and that schematic is starting to make some sense to me. The oil filled capacitor and the winding it is connected across form a resonant circuit that does the regulating by saturating the transformer core.
That oil filled capacitor will need to be replaced with one of the correct capacitance and voltage rating if you want to have it regulate the AC voltage. An electrical supplier that handles AC motors should have motor start/run capacitors that would be suitable.
The one with the oil filled cap is the regulating winding. It also has AC on it so it does not need a resistor to discharge it.
If I were to build a power supply using that transformer I would first determine the output voltage at various current draws up to 10 amps or so. This can be done by switching various automotive bulbs across the output winding and measuring the voltage and current. If the results were good I would then add fixed and adjustable regulators to provide the output voltages I need.
Each of the regulated voltages comes from an independent little regulator board, with the +12, +5, and +3.3V modules being switchers. You could do the same for the voltages you want so if this transformer does not work out for you all you would need to replace is the transformer.