[robhrzic]

Can anyone tell me how to figure out what the current rating of a fuse should be for a given circuit? Should I be using a "slow blow" type or a
"fast acting" type? What is the difference?

I am trying to determine what fuse / type I need to use for my 80 VDC, 20 amp power supply (using a 56+56V 1KVA Toroidal Transformer), and what fuse / type I need to use going to each individual Gecko G320 which will be driving a Keling KL34-180-90 servo motor:

http://www.kelinginc.net/KL34-180-90.pdf

[robhrzic]

Can anyone please give me a clue?

[Al_The_Man]

Slo-Blow are generally used in circuits where there are large current surges or high inrush currents and some delay can be tolerated, otherwise using fast blow caused nuisance tripping, fast blow are often used in protecting solid state circuitry where very fast sweep through of the fuse is neccessary to save the SS device.
e.g. The input to a transformer usually calls for a slow blow as the transformer will easily handle high current momentarily, that are caused by inrush current and capacitor charging.
Al.

[robhrzic]

Thanks, Al_The_Man! Well that answers the question about what type, but can you tell me how to determine the fuse amperage needed?

[Al_The_Man]

I would start with at least under 120% of the rated current, if nuisance blowing occurs, you can always increase the rating, if solid state protection is required, closer sizing is usually preferred.
There are many different characteristics for fuses, if you go to any of the big name sites like Littlefuse, Shawmutt, Buss etc, they offer information on all the different types and assistance on sizing.
Al.

[robhrzic]

Thanks for your input Al_The_Man. I'll check out those sites to see what info I can find.