ytsestef said:
I am very confused as to what deviations from the parts jakob is suggesting are acceptable.
I live in Greece and would rather order the parts from some european store (the most decent I found is farnell), but I can't seem to find EXACTLY all the parts. Let's take for example the bridge rectifier. Jakob suggests 1A/50V minimum and Kev has chosen 1,2A/400V. Was the "minimum" referring to voltage or amperes? Then is the following 1,5A/50V one ok?
http://export.farnell.com/multicomp/am150/bridge-rectifier-1-5a-50v/dp/9381422
Welcome ytsestef.
Voltage rating requirement for your bridge rectifier is not related to any published BOM but to the transformer that
you intend to use. From Jakob's schematic this is a 5VA 2x15V or 2x18V transformer to make this gssl work without the need of additional heatsinks for the voltage regulators.
(If a build plan for your gssl also includes additional circuits like a turbo circuit, sidechainfilter(s), optical gimmicks, cigarretlighters or whatever, this 5VA rating might need to be increased for these currents.)
Anyway, this maybe 2x15V transformer is wired with secondaries in series, giving a center tap at the junction in the middle (so a 30V center tapped transformer will also fit). This voltage is AC, but for the diodes inside your bridge rectifier the value of interest is AC peak voltage, so multiply this 30V by sqr(2), giving 42.4V pk. Your mains line voltage is not a constant and might vary by +/-10%, depending on location or mood of a generator for an open air venue, that also will show up on the transformers secondary. Adding this for a high mains scenatio by factor 1.1 for +10%, voltage will be 46.7V pk. This 2x15V or 30VCT number from catalog or transformer attached sticker is the secondary voltage under load condition and might be 20% higher unloaded. Adding this by factor 1.2 for +20%, your rectifier has to stand 56V pk for a worst case scenario, 50V for a less conservative calculation might do. A 2x18V or 36VCT transformer might need a rectifier rated for at least 67V, so next higher standard value would be 80V or 100V. Rule of thumb is, double transformers secondary voltage for your rectifiers voltage rating. A 400V part probably will cost the same.
Again current rating requirement for your bridge rectifier is not related to any published BOM but to the transformer that
you intend to use.
Switching your gssl on, the empty capacitors after this bridge rectifier will nearly represent a short and draw all current, your transformer can deliver for some AC cycles. A 5VA transformer will deliver less current than a 10VA, 15VA or even a 30VA transformer that some members here used for whatever reason to build their compressor and your bridge rectifier has to stand this current. Just use the highest rating that fits the pcb. Difference in cost between a overspecced part and a close fit will be cents if any.
For the gssl rectifiers pcb footprint and maybe farnell, have a look at
1497585 for a 400V/2A part is 0.77€ in singles (same cost for a 50V, 100V, 200V or 600V type).
Your quote
9381422 for a 50V/1.5A part is only 0.42€, but has a 5 pcs min.order.
(last digits order number after the slash for farnell in Greece is probably the same as here)
