How to / DIY > Generators
Solid State AVR on an ST-3 Head - Any need for it ?
BruceM:
If you're changing the bridge rectifier pre-emptively (a wise suggestion, 38ac), then consider cleaning up your the high frequency EMI by adding 4 capacitors to the bridge. The use of the piggyback spade connectors works well, or you can solder them to the base of each connector. One on each side.
This is the type of capacitor you want, with the part number on Digikey:
CMPPAC310V104K10S5
It's a thin film 310VAC rated capacitor, 0.1 uF. About $0.30 US. Similar spec parts should be available around the world.
I can't get the page to load or I'd give you link. Digikey seems to be overloaded this afternoon.
This is highly effective in reducing radio frequency noise from the ST line output. Check it with an AM radio (old regenerative tuner type with static sound between stations) before and after and you'll agree.
veggie:
BruceM
Excellent tips !
Thanks again,
Veggie
BruceM:
You're most welcome, Veggie.
Putting a 0.1 uF capacitor parallel to diodes is what's called a "snubber". It reduces the bust of high frequency EMI that occurs when diodes start and stop conduction. Sometimes a resistor and the value are specifically tuned to the circuit, but for many low frequency applications like this one, just 0.1uF works quite well.
In the case of the stock (no AVR) ST-3, these 4 capacitors (about $1.20) will reduce the high frequency EMI as much or more than a $70 dual common mode choke filter unit. A demonstration of the cost effectiveness of correcting an EMI problem at it's source (or even better by design) vs a downstream filter.
The fast switching of an AVR can also add high frequency EMI to the AC. A snubber capacitor across the excitation in/out switch may help with this, but it is best solved by design. In my own AVR, I intentionally slowed down the switching speed to limit the emissions. This works using either Mosfets or Darlington Bipolar power transistors, but requires the use of a bigger transistor that can handle the slower transistion, and often, an upgrade in heat sinking as well. In practice, you can often get huge reduction in emissions with very little or no loss of efficiency.
Most devices will tolerate this EMI on top of the AC without difficulty, but some may have problems.
mikenash:
Hey guys - thanks for the excellent advice - much appreciated
I have few chunks of finned, heat-sink alloy here out of 150kW-sized VSD/VFDs - a piece of one of them will work well. The lads here try to throw them in the scrap every time we do a clean-up but I keep saying "I'll use these one day . . ." so there we go
I will mull over all this good advice & google a few bits so I understand - especially good explanation-to-lay-idiot of the bridge rectifier, Bruce, thanks
Powdermonkey:
--- Quote from: mikenash on May 11, 2022, 08:12:30 PM ---Hey guys - thanks for the excellent advice - much appreciated
I have few chunks of finned, heat-sink alloy here out of 150kW-sized VSD/VFDs - a piece of one of them will work well. The lads here try to throw them in the scrap every time we do a clean-up but I keep saying "I'll use these one day . . ." so there we go
I will mull over all this good advice & google a few bits so I understand - especially good explanation-to-lay-idiot of the bridge rectifier, Bruce, thanks
--- End quote ---
Bruce- It seems you're a wealth of knowledge regarding power generation. As for me, I'm a gear head, and reasonably okay with the electrical side. I've got scopes, and can wrangle some basic stuff. But your knowledge is unique. Would you ever consider putting an e-book together? Drawings? Instructions?
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