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Hi, I bought a MB356 bridge rectifier rated at 600V at 35A. I will be running it at 230Vrms at about 20A, my question is what power this will be dissipating,
Thanks
If you are using it with a capacitor filter to generate DC then the peak currents are significantly higher than 20A, so from the data sheet, figure about an average 1V drop per diode. For two diodes conducting at any one time, this would give an average dissipation of about 40W for the module, at 20A output.
You would want a heat-sink to keep the module below 70C for reasonable reliability at that power level. Make sure you use a good thermal grease between the module and the heat-sink.
Sorry I must have worded it wrong. Yes the rectifier will be running at 4.6kVA but I mean when in operation it will heat up, I want to know the heat dissipated (in watts) when in operation, I cannot find anything on datasheet.
Joepage, it's easy to figure out for yourself, you need to find out what the forward voltage drop of the diodes are at the current you'll be running them at. If they drop .6 volts at 20 amps the current will be going through two of them at any given time, so you'd have a total voltage drop of 1.2 volts., at 20 amps that's 24 watts for the unit.
Thank you Carl but nope. Ron totally missed the real question. The swoosh Ron heard was the sound of it going over his head. It was like yep, load power is... Never catching dissipation in the process.
I checked the datasheet and it's 1.1V per diode at the full rating.
At 20A the drop will be 1V per diode which is 2V in total giving a total loss of 40W.
In reality it'll be a bit more complicated, the loss will be higher during the peak and less when the current is near zero.
If the load is a large capacitor when the current will be drawn in pulses which will increase the losses. If it's a resistor or a power factor corrected load it'll be less.
I'm guessing if you design for half again as much power dissipation as full load under all temperature conditions you should be okay. That's a decent amount of power dissipation though, I have soldering irons that don't put out that much. Definitely heat sink and fan.
Well known the semi-conductor burns down quickly by an over-current it is a really short while. The resistor must probably have to reduce an impulse while the capacitor does charg.
The smaller the capacitor value the lower the power dissipation in any one diode.
Here are some measurements using 1N4001 diodes in a bridge and a sine input with zero source resistance, and adjusting the peak of the sine for each measurement to achieve a 10v average dc output voltage into a 10 ohm load (1 amp average output current), with various capacitor values:
This shows the average power PER diode (multiply times 4 for the entire bridge).
For example, with 1000uf cap and 1 amp output the power dissipated was 0.657 watts per diode.
With 2000uf cap and 1 amp output the power dissipated was 0.714 watts per diode.
Extrapolating and taking into account the ratio of device parameter to circuit parameter:
2000uf, 362mw
so that would mean at 20 amps we would see about 7.24 watts per diode, or about 30 watts for the entire bridge
with a 2000uf cap. With a 4000uf cap maybe around 32 watts.
That's a significant amount of power and yes requires a heat sink.
I dont think someone read my first post, 4600W through a little 15W resistor will equal a huge boom. I understand what you mean about the resistor though. @ dvinchy
There will be a 350V 4500uF capacitor on the end of the bridge rectifier, I will use a relay, resirs. The resistors charge the capacitors to a high voltage and then a relay turns on afterwards for the high power. No timing relay would equal a huge surge current when turned on.
40W does seem mighty large.Im making something that runs at 2.5kW or 5kW, it will mainly be running at 11A or 22A, it may spike at 25A. I dont think 50W should be too much of a problem, most of my setup is water-cooled anyway so cooling shouldnt be a problem.
I dont think someone read my first post, 4600W through a little 15W resistor will equal a huge boom. I understand what you mean about the resistor though.
Hi, I bought a MB356 bridge rectifier rated at 600V at 35A. I will be running it at 230Vrms at about 20A, my question is what power this will be dissipating,
Thanks
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