How To Choose The Right Rectifier & Capacitor For Rectifing AC to DC
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- Опубліковано 15 лип 2024
- (Please read calculation examples below) In this video I discuss how to choose the right size & spec'd full bridge rectifier & electrolytic capacitor.
In the interests of avoiding confusing calculations please carefully study the below examples. Note in "Example 2" how the results = 200 this could easily be mistaken for 200uf. However, it is infact 200,000uf
Example 1:
10 amps x 8.3ms / 5.5volts = 15.0909 (15,0909uf)
Example 2:
10amps x 10ms /0.5volts = 200 (200,000uf)
Information provided in this video is for educational purposes only.
If you attempt to recreate/replicate anything you’ve seen in this Or any other video, you’re doing so at your own risk.
- Schematix - - Навчання та стиль
Please study the calculation examples in the video description to better understand how to read the results of any calculations you make for capacitance :)
Schematix Hi there I was wondering if how you find out the minimal voltage drop and the peak voltage after rectification.
thanks
I love your tutorials but I don't understand your capacitance formula. Result say 15.090mF but you call it 15 thousand mF. Does higher capacitance mean more voltage drop?
Raks Electric; OK, first you have to find the peak voltage after rectification. You calculate that simply by multiplying the AC output voltage of the secondary of your power transformer by the square root of 2. That gives you the peak DC voltage output of the bridge rectifier, before adding any smoothing/filter capacitors to it. (A very close example to this video would be a secondary transformer voltage of 50V X 1.4142 = approximately 70.71VDC out of your rectifier bridge.)
Then, *you* as a designer of your circuit, have to determine the "minimum acceptable voltage" that your circuit can safely or effectively operate from, which, depending on circuit design and type, can vary *significantly* , however, for *most* electronic items, if you stay within a 5-10% drop from the Peak DC output voltage of your rectifier then you should be fine. Your specific design *may* require tighter tolerances than that, but if so, that increases your required capacitance ( *and cost* ) quite significantly!
So, just for an example that's again relatively close to this video for ease of comparison, let's say that in order for your circuit to work effectively and to perform at an optimum level it needs an absolute "minimum acceptable voltage" of 65 volts DC. If you do the math, that voltage would be within about -8% of the peak DC volts out of your rectifier, so that should be just fine in most cases.
The *difference* between the peak voltage out of the rectifier and the "minimum acceptable operating voltage" for your circuit would then be the "acceptable voltage drop" that is used in the final equation for determining the required capacitance value. In this example it would be:
70.71 - 65 = 5.71V "acceptable voltage drop"
Now comes the (slightly) confusing part; This video didn't explain the discrepancies in the *units* , and *that* is why the answer is not exactly what is shown, but rather off by a factor of 1000 in each case... The (correct) formula for calculating the required capacitance is, (should be);
Circuit Current (IN AMPS) x Half Cycle Time (IN SECONDS) / Acceptable Voltage Drop (IN VOLTS) = Required Capacitance (IN FARADS)
If you use the above formula with the above shown units then your answer will always be correct... Using the above example's first Voltage calculations, and assuming (again *for example only* ) that your circuit current is 10 Amps and you are in a location that uses 60Hz frequency of AC power, like in the USA, then the correct way to use the formula is as follows;
(First calculate the last needed parameter to use in the final formula, which is the *Half Cycle* Time of a 60Hz line frequency, but calculate it in SECONDS, instead of mS, as is the error in the above video... This then equals 0.008333 Seconds.) (1/120th of a Second)
Now finally put all of your (correct unit) numbers into the correct unit formula which I showed above and you get;
10 (AMPS) x 0.008333 (SECONDS) / 5.71 (VOLTS) = 0.0146 (FARADS) of required capacitance. (Approximately anyway, due to rounding of answer)
Now, since 1 FARAD = 1,000,000 MicroFarads (or uF), then just multiply the above answer by 1,000,000 and you get the *correct* answer of 14,600 uF.
In this example's case, I would just use a 15,000 uF capacitor for a filter capacitor, which is the next largest commonly available value above the "minimum required" 14,600 uF.
The above example may seem complicated at first, but once you do it a few times with different values and for different electronic projects, you'll get the hang of it quickly. And if you always use the consistent (whole) unit formula above, and then just quickly convert your answer from Farads to MicroFarads (1/1,000,000th of a Farad), then you will *always* calculate the correct answer when doing this!
FYI, the formula in this video gives answers in MILLIFARADS (or mF) (1/1000th of a Farad), NOT MICROFARADS, (or uF) (1/1,000,000th of a Farad)!... Simply because they are using MILLISECONDS (mS) (1/1000th of a Second), rather than full Seconds... Somewhere along the line, the units got switched or dropped, (i.e. "lost in translation"), in the formula shown in the video, from the original, correct formula which I gave above... Possibly because oftentimes mF (millifarads) is commonly mistaken for uF (microfarads), simply because of the letter "m"!
Anyway, now you know the "rest of the story", LOL!... I hope this detailed explanation helps *someone* out there to better understand this at least, because knowing what is the correct size of capacitor to use to filter your AC-DC power supply is a VERY important part of proper electronic equipment design!
Accumulator1; I totally understand your confusion, however, you made the same exact (very common) mistake that this video makes, in confusing the units of mF (MILLIFARADS) and uF (MICROFARADS)... The answer actually IS 15mF, however, it is ALSO 15,000uF, because they are a ratio of 1:1000 ... The full, detailed explanation is below;
(BTW, A Higher capacitance used for the filtering of a bridge rectifier actually results in LESS of a voltage drop, not more, and therefore a higher capacitance also results in a more stable final DC output!)
Now comes the (slightly) confusing part; This video didn't explain the discrepancies in the *units* , and *that* is why the answer is not exactly what is shown, but rather off by a factor of 1000 in each case... The (correct) formula for calculating the required capacitance is, (should be);
Circuit Current (IN AMPS) x Half Cycle Time (IN SECONDS) / Acceptable Voltage Drop (IN VOLTS) = Required Capacitance (IN FARADS)
If you always use the above formula with the above shown FULL units then your answer will *always* be correct... Using this video's "Acceptable Voltage Drop" calculations for an example, and assuming (again *for example only* ) that your circuit current is also 10 Amps and you are in a location that uses 60Hz frequency of AC power, like in the USA, then the correct way to use the (correct unit) formula is as follows;
(First calculate the last needed parameter to use in the final formula, which is the *Half Cycle* Time of a 60Hz line frequency, but calculate it in SECONDS, instead of mS, as is the error in the above video... This then equals approximately 0.0083 Seconds.) (1/120th of a Second)
Now finally put all of your (correct unit) numbers into the correct unit formula which I showed above and you get;
10 (AMPS) x 0.0083 (SECONDS) / 5.5 (VOLTS) = 0.015091 (FARADS) of required capacitance. (Approximately anyway, due to rounding of numbers)
Now, since 1 FARAD = 1,000,000 MICROFarads (or uF), then just multiply the above answer by 1,000,000 and you get the *correct* answer of 15,091 uF.
In this example's case, I would just use a 15,000 uF capacitor for a filter capacitor, since it is so very close to the calculated value, and that value is the closest commonly available value. Plus, since most electrolytic type capacitors generally tend to measure slightly higher than stated anyway, especially when new, then you should be just fine!
The above example may seem complicated at first, but once you do it a few times with different values and for different electronic projects, you'll get the hang of it quickly. And if you always use the consistent (whole) unit formula above, and then just quickly convert your answer from Farads to MicroFarads (1/1,000,000th of a Farad), then you will *always* calculate the correct answer when doing this!
FYI, the formula in this video gives answers in MILLIFARADS (or mF) (1/1000th of a Farad), NOT MICROFARADS, (or uF) (1/1,000,000th of a Farad)!... Simply because they are using MILLISECONDS (mS) (1/1000th of a Second), rather than full Seconds... Somewhere along the line, the units got switched or dropped, (i.e. "lost in translation"), in the formula shown in the video, from the original, correct formula which I gave above... Possibly because oftentimes mF (millifarads) is/are quite commonly mistaken for uF (microfarads), simply because of the letter "m" being common between the two unit names! In addition, the "u" in uF isn't actually a "u" anyway, but instead it is only the closest resemblance on a common keyboard to the real unit measure, which is actually the Greek letter "mu", shown in lowercase, but to make matters even worse, that same Greek letter in Uppercase is also "M", and sometimes people state MILLIFarads as MF instead of the more proper mF!... This all results in *very much* confusion between the MICRO- and MILLI- prefixes of the FARAD capacitance unit!! (I see that mistake being made almost all the time, so it helps to understand the difference!)
Anyway, now you know the "rest of the story", LOL!... I hope this detailed explanation helps you to better understand this, because knowing what is the correct size of capacitor to use to filter your AC-DC power supply is a VERY important part of proper electronic equipment design!
JoeJ8282 thankyou very much now I understand
You are very good at explaining what can seem a complex subject. 50 years ago I was into electronics (valve amplifiers) it's been quite a struggle to bring myself up to date. I did try and tighten a connection with 240V on it whilst well earthed. Seems at 70 odd years old my heart is pretty sound. Good videos young fella me lad, greetings from the old country.
thank you. I've been trying to sort this aspect of AC-DC rectification for a number of days. YOURS was the first well explained, thorough description I've found.
Thanks, again..
GeoD
Id like to agree with this persons statement, thank you for explaning this and walking us threw how to do it! Btw popping caps can be fun I got a good chuckle outta that
I have always wondered how the capacitor value was calculated, a clear and concise explanation.
Thanks for posting this. It takes me back to basic electronics I used during my military service. Well thought out and explained. You have a new follower!
Thanks kindly for your support ;)
GREAT video! I learned a lot from it. You're video is the first I've come across that not only talks about choosing the right capacitor, but HOW to choose the correct capacitor. You do a great job in your explanation of things! Keep up the good work.
Excellent explanation and demonstration, I managed to follow every part of it, very clear and at a speed that someone like myself can follow. I will definitely watch more of your videos.
This was great. I am ok with transforming and rectification etc but was never too sure about a good capacitance selection. Now I have it. Subscribed for good clear presentation of material.
PS. Kiwis rock!
Thank you. Best explanation I have yet come across on YT!
I learned a lot here. Great video! Thank you for including an example calculation for 60Hz too that was very helpful. Now to go find a huge capacitor and pray I don't wire it up backwards. :)
The best explanation out there on this topic! Thank you!
perfect,, this is exactly I have been looking for .. you do really nice job. thanks !
You have a wonderful way of explaining
Thank you that was exactly the info I needed. Very informative, I am subscribed. Keep up the good work
Thank you this really helped me understand the calculations.
Great job all around. Quality and content.
Very informative. Thanks learned a lot on transformers and rectifiers.
Very interesting ! The method of calculating the required capacitor is very clear and easy .. thank you so much I really enjoyed your video it was a wonderful morning :)
very interesting and well descriped I am from Malta, and I really enjoy your lessons Thanks for your time
Hi Schematix, hope you're doing well! I've enjoyed the couple of videos you've posted on transformers and other power supply components.
Great videos and very well explained, cheers mate
Thank you sir. I was planning to build myself an amplifier PSU this video helped me a lot :)
Thanks for your videos Schematix, they are Excellent.
Great video. I also appreciate your humor.
Great video, thank you for the calculations
Cool I needed a refresher course on rectification and this did the Job. especially about how to determine capacitance!
These vids are the king keep them coming teacher many thanks.
Short, simple and well explained
You answered so many of my questions but show us what ur wiring up for ur example so I can see a finished setup thanks keep making videos!!!
Great job I understand more now than I ever have
Your information was a BIG help to me. Thanks
I really appreciate that you are sharing your experience worth us
I really like your content, very informative and to the point, really cool to see a fellow kiwi sharing his knowledge! :)
Thanks mate :)
Old info, bin there, done that 25 years ago.
This was so clear! Thank you! Thumbs up and suscribed!
I am so pleased that I have found your channel.
I am going to make a battery charger as I have been told that the new type solid-state chargers are not much good.
I want a charger that will charge a tractor battery, so I am looking at 4-5 Amps output current.
I can get a transformer from Jaycar, now I know what size rectifier and capacitor I need to get.
This is the stuff why i subbed to this channel, good for people like me who have to start from the beginning. :-)
Thank you so much i learn allot with this video.
Very easy to understand,thank you 👍
Excellent video!! Thanks very much
thank you very much for making the film
Excellent explanation and demonstration
Awesome explanation!!
Great video great teacher you are
Thank You for this video, well done.
These are really interesting and well explained videos. Your arithmetic at the end fired my awkwardness a bit, multiply the result by 1000 to get the microfarad result. (Because we don't say the mili word with capacitors!)
yes the cycle time input in the formula is in ms and the capacitance im mF. I specially enjoyed the definitions of a poor power supply.
Great video. To the point and well organized. Well done. Count me in as a subscriber.
Very useful.....thanks mate!
Very useful, thanks. Subbed.
God bless u, thanks for a very nice job
Thank you , really helpful
liked and enjoyed .. thank you for sharing.
Great video!
Nice vid series thanks.
Perfect, thanks.
This was so helpful. I went down to subscribe, but saw i already was. Rad
Awesome video!!!
It is such a shame you decided to stop your videos. Giving that microwave transformer 'what for' brought a smile to my face. For gawds sake keep this bloke away from a power station. However I am about to do exactly the same to a microwave transformer. I need 40V so my wire choice in amps and insulation will be a bit tight. Perhaps you could add a comment as to whether you will do any new videos. I hope you do. Happy New Year from Pomland.
Interesting, very well explained
:)
Thanks for the explanation. I don't understand frequency, farads etc.
Still very engrossing tutorial.👍🏻
Thanks. Joe
Creative video, thanks :)
By any chance have you done a full video of DC power supply using transformer and capacitors? Great video by the way. Nicely done!
Your videos are great! You've got yourself a subscriber
Thanks ;)
You've made my day ;)
Thank you sir...!!!!
Great mate.
well done !
Thanks man...🙏🙏
i want more videos on your channel, related to electrical engineering.
Hi a very explanatory video, its appreciated greatly.
The question it brings to mind is, how did you decide on the minimum acceptable voltage and for a long service life how does this acceptable voltage effect the life of the capacitor. From the data sheet I only see the recommended ripple current and not ripple voltage.
at 5:57 bridge generate 2 x VF or 33 Watts . great vid
The forward voltage drop shown at 4:24 in your video (Vf = 1.1.V) is the forward drop per diode in the bridge. The positive and negative paths through the bridge each have 2 diodes in series. You need to make allowance for double the voltage drop i.e. 2.2 volts and consequently double the power dissipation. Selection of the "right" capacitor also requires consideration of the load current. If the ripple current rating of the capacitor is inadequate it will have a short life.
Thanks
good video
A full bridge rectifier is basically four hardwired diodes .... great piece of electronic hardware ... they commonly have a hole in the middle to allow mounting on a heatsink if you are going to push its limits ....
Liked & subscribed
Good video. So the result of cap with not enough uf will not fully smooth out the current as well as a cap with the proper uf required by your calculation? Does a toroid core wrapped with copper wire, and connected to the cap, help smooth out the current even more than without it?
Great video thanks, the only slight issue is that the formula states that it equals ųF but it actually equals mF. Though in your example you had already converted it (15000 vs 15)
Nice one, I just made a comment on this too haha
uF (microfarrad) IS mF (microfarrad).
They represent the same thing.
They are the same thing.
@@googleedwardbernays6455
uF is microFarad (x10-6)
mF is milliFarad (x10-3)
@Nohr Tillman
Aaaahhhh. You are correct!! I always forget about the milliFarrad due to it not being used as the other three (u, P, N) in reference to electrolytics or in reference to capacitors. And since i am unaware of a single instance where milli has been used in terms of capacitor. My bad, homie. Thanks for correcting me
Thanks, really enjoying your vids. Building a twin power supply (2x55 watts) at the moment and bought some (probably) oversized caps because I found no suitable formula on the internet. Now I can calculate if they are sufficient.
Btw, where is the hawaii shirt from the early vids? ;-)
Lejf Diecks. Thanks for the feedback. At the moment I'm building a 900watt programmable bench power supply (Build video coming) it was a little chilly for a tropical themed shirt ;-)
Thank you for that great explnation. I have ? if i have only normal diode & i have to make BR from it with Capacitor. if I want 18V & 15A or higher, from 220 transformer. How much should be the diode & capacitor? Thank u for answering if you can.
This channel is very informative i like big, hello my dear new friend im fully watched from philippines👍🤝🙏🏼👏👇🏿👇🏿👇🏿
I have seen videos using a center-tap transformer with 2 diodes for full-wave rectifier and a single smoothing capacitor and I have seen them with the standard full-wave rectifier with the center-tap tied between 2 smoothing capacitors. Transformers are rated in power as either Watts or Volt-Amp rating which is still the same thing. So is there any one that is better for a power supply. If you have 30 volts AC at 4 Amps and after DC Rectification and Regulation - is that going to provide 15 Volts at 8 Amps?
I was gonna build a dc supply with a 1000w microwave transformer. gonna rewind it to put out around 50v I have a couple 1000v 50a bridge rectifier laying around could I just use them or would that be way overkill and have negative effects?
Can you build a simple power supply for testing a inverter compressor. Where it is not known if the compressor or inverter or both are bad.
Sir,
Excellent video! I just found what I was looking for.
But, I have few questions.
On 12-6-0-6-12 CT transformer, I'm getting 32V from first and last terminal by reading from multimeter without any load. It is the RMS right?
If it is RMS, then peak should be 45.25V. If I use a 35V capacitor, I'm getting 45V after adding capacitor. is it okay/safe?
Whats does 35V mean on that capacitor - maximum of RMS of maximum of peak?
Thanks in advance :D
Hi, any advice on the brand to choose, there are so many ! Thank you
Nice tutorial very educatioal
excellent videos keep them coming. im interested to find out how to pair a mosfet and a protection diode cause im sick of destroying mosfets lol. im running a 240vdc treadmill motor off of a 12v battery to 240vac inverter to a bridge rectifier (now i know how to match a cap for the job) to a pwm circuit with mosfet then to the motor. the motor is 100% dc not ac but the mosfets don't last long. any help would be awesome
Thanks! Plenty more videos coming! My first thought is the mosfet being adequately cooled with a heatsink? If the mosfet is exceeding the rated operation temp it's life span will be significantly reduced. Make sure you have a mosfet rated for at least 20% more current & higher voltage than what you require
👍👍
at the end when talkin about the cap blowin up, u said "it adds a little drama to ur life, but makes for a poor power supply" ..i dont Need anymore drama in my life lol i have pLENty!
How about a 3 phase windgenerator... how can I know what capasitor to use? Since its up and down on the power all the time?
Regards.
Hello, I have an ATV with no battery, just pull start which outputs AC power and I want to run a 12 V DC fan for the radiator (no other powered accessories such as lights etc.). The stator has a lighting coil that outputs 150 watts. I cannot find the wattage of the fan but I did measure the resistance and got 3.8 ohms, so I believe the wattage is about 38 through calculation. The engine manual says the lighting coil produces 32V at 2000 rpm, 50V at 3000 rpm and 67V at 4000 rpm. The motor is rated at a peak rpm of 7200 (not sure if all of this info is needed). This is a retrofit so I have not added the voltage regulator yet but I assume it will bring the voltage to 12V? With that information, can you provide guidance of which rectifier and capacitor to use? I am somewhat electrically helpless, so any assistance would be appreciated. Thanks!
I wish someone would come along and do one that is my size; 50 amp. 120 volts going into my 200 Amp rectifier and I am getting 29 volts out and I need to have at least 17.5 volts max, I have used 220uF for my filtering bank, 4 on the positive side and 4 on the neg. side as well. But I still need to be able to handle 875 Watt potential, for my power supply loading. Running an RF amplifier along with my RCI 2950 radio for my loads. Amplifier will be of a size that will not over burden my load capacity and still have some headroom to keep it running cool. So my RF Amp will be no larger than a 800 watt PEP amplifier. RMS should be well below 350-400 maybe 450 at the highest watt average for my loads.
Excellent video & tutorial. I am in the process of replacing the Bridge Rectifier in a Daiwa PS-30XMII. When I removed the faulty BR it had a 14mm brown ceramic disc capacitor across the AC terminals. I can find nothing about this on the schematic. Is the capacitor of any real value in this situation or would you recommend
fitting the new one without it please?
are you sure its cap....could be a MOV
such a cap can reduce line noise/spikes
Can someone explain? At 3:38 we are told that _"To calculate the volts after rectification multiply AC input voltage by 1.414... "_ . Why then does the calculation at 8:27 only use 70.5V for the capacitor calculation? Both the 100V (approx.) *and* the 70.5V are referred to as DC voltage "after rectification". Is this because the 100V is only a peak (as referenced in the RMS calculation), and the capacitor should be calculated based on the nominal 70.5V? Thanks for any explanation.
How do i calculate the capacitor value if the ac source is from a bicycle dynamo? Any way to make an estimate? Also, does the ready-made bridge rectifier comes with capacitor??
Can a full bridge rectifier be used as a choke in place of an inductor between a control board and a DC treadmill motor? The inductor that came with the treadmill had a bullet hole in it and was beyond repair. Also, don't know how to use a transformer as an inductor because I don't know what values would be needed. You probably have a video on inductors that I should watch. Cheers
Finally
Another option not addressed at the end is that when picking your capacitors is to just add more small capacitors rather than one big one, as long as you aren't going to exceed their voltage rating. The benefit there is that you can usually use smaller capacitors that are faster at discharging, you can often over-provision incrementally by leaving space for additional capacitors that you insert when and if your load requirements change, or for heavier duty versions of your circuit, and 2-3 smaller capacitors are usually cheaper than one big one, and if one blows you may not lose the whole bundle in the field, and you let out less magic smoke per blown cap.
Sure, in theory that works. In reality they start to clamp and self limit the amount of current output.
@@linandy1 I'm not advocating for more than a few. You see this all the time in power boards for eurorack gear where you just line up a something like 3 cheap 4700uF caps per rail rather than try to find a single capacitor.
So If I were to use in my typical electrical application an electric lawn mower for example which has an electric motor rated at 13 amps maximum with 115VAC(70.5Vdc full wave bridge rectified output with minimum 65Vdc ripple voltage varying output);
13 Max Amps x 0.00835(ms) = 0.10855
0.10855 divided by 5.5 = 19,736uF for electrolytic capacitor @75Vdc about $35 on google shopping;
would that value work for example electric lawn mower application?
So I guess my questioning would be can you use multiple compasitors to reach the compasitance you require? Like idk if that would even work in series or parallel or dose it have to be one compassitor i guess depending on the application?