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# 4 5x20mm Fuses in parallel for 4kW PSU?

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#### cupoftea

Hi,
Doing cheap-as-poss 4kW prototype of 4kW SMPS.....100VAC in, 46A.
Can we just use five 10A 5x20mm (250V) fuses in parallel, with these type of cheap holders?...

Specified holder contact resistance is higher than fuse resistance, don't expect equal current share. Paralleling fuses can work under circumstances with solder connection but not with holders.

Hi,

Fuses have a "switch off current capability".
When fuses are paralleled this value does not multiply.

Klaus

cupoftea

### cupoftea

Points: 2
Thanks, the cheapest fuses i can find which are high current ar these 15A fuses

...at 92p.....they are only 15A, so i will only be able to test up to 3.2kW, but thats a good start.

Do you think for the 22A fuse for 220VAC, which is the cheapest available here......i am having no luck on the mouser's etc......do you think i am going to have to "go to twon" and get a screw in fuse, and get the proper screw mount etc?

some 30 years ago, when I got my first engineering job,
there was a cartoon that said cost, schedule and quality.
pick 2

your "cheap as possible" is likely to have an unintended
consequence of leave quality behind

This may be wrong but it seems to me that the resistance of each fuse/holder combination will not be exactly the same. Therefore the current through each fuse will differ slightly. That means that while each fuse will carry approximately 1/5th of the overall current.
You want to carry 46A so using 5 x 10A fuses will mean that each carries 46/5 = 9.2A ON AVERAGE and assuming that the resistances are all exactly the same.
If one fuse does 'blow' then it will drive the total current through the remaining 4 fuses that will lead to each of those carrying 1/4 of the overall current which will probably blow those very quickly. In you case that means that each remaining 10A fuse will carry 46/4 = 11.5A
My guess is that having the fuses in parallel will work until one fuse blows (at just over 1/5th of the total current) and then all of the others will blow.
Susan

Nice to see the reply just above - per those comments - if you listen very carefully - for an overload - you can possibly just make out the " thu u u u u r ppp " sound as they fire off open ckt in very quick succession - as fuses are resistive they share quite well up until that point ...

I generally agree to the comments about fuse current sharing, the OP however was specifically asking about using fuses mounted in holders. In this case, you should also observe the datasheet information, see post #2.

Thanks, this is the only cheap 50A fuse in stock, but garanteed it wont be for long
...hence the search for a way to fuse with cheaper fuses in parallel........still thinking about paralleling with smaller axial leaded fuses.....yes, thanks, it does look like that cheap holder wont be of any use for pllel'ing.

for cheaper components look at asian brands
this one

Thanks for all replies,
In this doc we see two 20A fuses being used in parallel with simple fuse clips.
Do you believe they are making a mistake?

Fuse is 12.8mR each.

Fuses are ABE 020:

Fuse clips are like this: CQ-205S

My power inverter blew fuses when I touched its clips in reverse to a car battery. I opened it up and found four of the blade-type commonly available in auto stores. 30 Amp. Replacing them restored the unit to working order.

I don't know whether or which fuses were in parallel, or whether each served a different section within the circuitry.

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