There's nothing inherently unsafe about non-isolated supplies; like any high-voltage project, you have to be careful about keeping everything properly insulated and follow minimum-spacing rules carefully.
The most-dangerous item in a high-current supply is the electrolytic cap. You *must* handle all of these concerns - Extra margin for voltage-rating. I use 450V (500V when possible) caps for ~200V supplies. Higher voltage ratings also reduce leakage current. Caps designed for solar-energy inverters are perfect because they come in high-voltage + high temp + high ripple-current. - Be very conservative with rms ripple-current, because it directly affects self-heating. Obviously you dont want any warm components near your capacitors. Remember: Lifetime is dramatically impacted by temperature. - You must have a discharge resistor; I even put a flashing neon bulb across my large caps to indicate they have dangerous voltage. Larger resistance values take longer to discharge, but they reduce wasted energy (heat) - Series fusing. In case the cap fails, you want to blow a fuse, not the cap. The fuse must be a small as possible, and dont forget the RMS charging current is not sinusiodal. BTW, this fuse is for the cap; it's in-addition to the fuse at the AC input. - Charging-current needs to be limited during power-up. For the 1.5 amp supply, a 1500uF cap will have 10 volts of ripple at 50Hz when using a full-wave rectifier. I'd suggest a series charging resistor of about 200 ohms to charge at power-on, then 'shorting' the resistor with a relay after charging is done. - Surge protection at the AC input. I always have a fuse on both AC lines, then a varistor and 0.01uF capacitor (for filtering hash noise if it's present). If your current is 'low' (which isn't the case in this design), adding series resistance to create an RC filter is a big help, and furthermore the resistors will act as secondary fuses if you pick low-enough wattage. - Reverse-polarity protection diode. If you dont use a bridge rectifier, be sure to put a protection diode across the cap. BTW, a bridge-rectifier gives you reverse-polarity protection down to 1.4V, whereas a single diode is 0.7V. Polarized electrolytics caps can be damaged with as little as 1 volt of reverse voltage, so you may want to add the diode even if a bridge rectifier is used. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/e8b4859e-9374-43ad-b851-18bcb467d305%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
