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Can anyone help me figure out this "magnetically regulated psu". Restoration plus prop addition. — Parallax Forums

Can anyone help me figure out this "magnetically regulated psu". Restoration plus prop addition.

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??

2015-10-15%2010.51.29.jpg

Comments

  • kwinnkwinn Posts: 8,697
    edited 2015-10-23 02:41
    Sounds like a ferro-resonant transformer. They were used for regulating the incoming AC voltage. All I can recall is that they needed a specific value of capacitor and a minimum load to work properly. Perhaps one of these (http://www.relco-ritz.on.ca/, or http://www.ritz-international.com/index.php?id=116) can provide more info.
  • Acually I described it wrong the HiVolt cap is on the secondary on its own tap, not the primary. I searched that first link to no avail before ever posting anything ill look through the second. Ive done a bunch of reading on these magnet transformers and like I said the caps make sense to me but not a power resistor that eats the WHOLE load. You think calling there support would get me anywhere if I cant find anything on the International site. This is an old 70s model i painted over the year lol mine was pretty beat up but this is what im guessing a good condition looks like...

    http://www.ebay.com/itm/Ritz-Electronics-PS1001MR-Power-supply-13-8VDC-8A-magnetic-Regulated-Model-/181876173196?hash=item2a58aa298c
  • It is a ferro-resonant transformer power supply. The resistor is to help regulate the output, and to ensure the capacitor (which forms an LC tank circuit with the secondary) is safely discharged after the power is removed. While these work okay for fixed loads, they can't provide a wide range of current. They are good at rejecting incoming transients and can regulate over a larger range of input voltage than a typical transformer.
  • What do you mean they can not provide a wide range of current? So they cant easily switch from one amp to eight quickly or they just dont supply anything under eight amps in general? What if one were to have a switched power resistor network in the LC circuit?
  • If you try and draw more than the rated current, it will pull the transformer out of saturation, and the voltage will drop to near zero. So when I said wide range, I meant you can't exceed its rating, or you will get no output. If you draw less than 8 amps, much of that is going into the resistor. The resistor is part of the voltage regulation, if you change its value, you will change the output voltage. These are not well suited for general power supply use, because they need a constant load.
  • kwinnkwinn Posts: 8,697
    Acually I described it wrong the HiVolt cap is on the secondary on its own tap, not the primary. I searched that first link to no avail before ever posting anything ill look through the second. Ive done a bunch of reading on these magnet transformers and like I said the caps make sense to me but not a power resistor that eats the WHOLE load. You think calling there support would get me anywhere if I cant find anything on the International site. This is an old 70s model i painted over the year lol mine was pretty beat up but this is what im guessing a good condition looks like...

    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.
  • Ok so here is a schematic, the only thing I modified was adding an earth reference plug. I called Ritz and they told me they would see if they had a schematic around anymore, Im having a hard time figuring out what value the regulation cap is its a big metal one like a microwave the guy said it was an oil cap, my meter goes up to 40mF and it says out of range so ill have to test it a different way... if I cant get the schematic

    New%20Doc_1.jpg

    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?
  • Heater.Heater. Posts: 21,230
    Do what?

    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.
  • Yes that resistor is what is buging me soooo bad! I cant figure out what it has to do with the regulation! Ive used this puse to power a portable rc charger with and without the resistor connected, although the charger only draws 2 amps max...

    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.
  • I'm not a electronics expert, but from the bridge rectifier on that circuit looks like a simple, unregulated DC power supply. I'd guess the 13 ohm resistor is just a bleeder for that really big cap on the output. The value does seem lower that it needs to be.
  • Heater.Heater. Posts: 21,230
    RDL2004,

    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.
  • kwinnkwinn Posts: 8,697
    @rwgast, this type of transformer provides a relatively fixed output voltage over a range of input voltages. On one instrument I worked on the “nominal” 240V input at the site would vary from 195V to 260V over a 24 hour period. A ferroresonant transformer provided an output ranging from aproximately 215V to 225V with that 195V to 260V input.

    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.
  • @kwinn, AWESOME... ok so then your telling me that power resistor is just a bleed off? I guess I never thought about it being used that way because a 13.3ohm (not measured with a kelvin set up) is pretty close to the 13.8v out the psu claims, so I thought it had something to do with load sharing (for current regulation? idk guess I was overthinking) honestly, and not bleed off for the huge 47mF cap. I haven't read your link yet but I know the big oil cap on the "regulation" tap of the secondary is also pretty big because my UNI-t U71E DMM has a 40mF capacitance measurement capability, and it takes about 2 minutes ramping the analog bar graph up and and down in the mF range before it gives up and I get an OL. So why does this cap not need to be bled?
  • kwinnkwinn Posts: 8,697
    edited 2015-10-24 19:58
    I thought the resistor was connected across that capacitor. Can you draw a schematic of the windings and whatever is connected to them. Use your meter to ohm out the windings and see what is connected to what.

    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.
  • The oil cap doesn't need to be bled since it is in parallel with part of the secondary... it will self discharge thorough the transformer when the power is off. And it won't be that big value either.
  • kwinnkwinn Posts: 8,697
    This is a bit embarrassing, I see you already posted a schematic. Looks like the resistor and 47000uF capacitors are part of the output circuit, and I am guessing the "regulating capacitor" is the one on the other winding with no ratings.

    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.
  • @Kwinn, I drew a schematic above, im dont exactly know what your asking for, it shows the primary side and the two taps on the secondary. The first tap just has the cap that looks like its from a microwave(the guy on the phone said he believes it was an oil filled). The second tap has the 47mF Electrolitic parallel with the 13 ohm sand brick.
  • kwinnkwinn Posts: 8,697
    The second tap is the one you would use as the output. That would go to the input of any regulating circuits you add to it.

    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.
  • But still idea why there is a 13 ohm resistor in parallel with the output cap/plugs? I mean the things melts soldier with no load, and even using an RC charger for NiMH se to two amps!
  • kwinnkwinn Posts: 8,697
    I suspect it is there to discharge the capacitor and possibly to provide a minimum load. It is also possible that the resistance has decreased over the years due to heating. Is there a resistance value printed anywhere on it?
  • I got the original schematic from the company, the Hi voltage cap is 3.5uF 440vac, and the power resistor is suppose to be 14 ohm 20 watt. I need to measure the feedback tap but I have NO IDEA why a 440vac cap would be called for on a secondary tap..... Im guessing it must be bad if all my DMM's measure this range and display OL on this cap. I haven't had time to make a fast rising edge generator to actually test it out.
  • kwinnkwinn Posts: 8,697
    That secondary tap forms a resonant circuit at 60Hz with the 3.5uF capacitor so it needs to have a fairly high inductance. That means many turns and a high output voltage. Be careful when it is powered up.
  • kwinnkwinn Posts: 8,697
    I have a power supply built around a standard 24V center tapped transformer that I use for testing and troubleshooting. It can output unregulated 24VAC, regulated 24VDC, 12VDC, +- 0 - 15VDC, +5VDC, and +3.3VDC, but all the voltages cannot be used together at one time, so using it takes some care.

    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.
  • I actually have a 24v transformer, which Ive done the same thing too except I used those cheap ebay switchers in front of the the LDOs. This is more of for the heck of it. I acually have a nice transformer that weighs about 7lbs and maybe 5 or 6 taps ranging from 30vac to or so, I had planned on using it one day for a really nice PSU.
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