which value fuse is needed for primary

[nazirdigi]

pls help,
which value fuse is needed for primary?
I have 10a transformer.

[madtecchy]

Hi Nazirdigi.

What votage are the secondries of the said transfomer? Also is it a torroid or EI type. And what type of load do you expect the circuit connected to it to draw? Regards Ian

[nazirdigi]

Originally Posted by madtecchy

Hi Nazirdigi.

What votage are the secondries of the said transfomer? Also is it a torroid or EI type. And what type of load do you expect the circuit connected to it to draw? Regards Ian

hi madtecchy,
my transformer is 230ac primary and secondary 55ac,0,55ac dual supply 10ampere and EI core.
thanks for the reply.

[AndrewT]

Fuse value = VA / Voltage = 550 / 230 ~ 2.5Aac
This close rated fuse will only survive a few, or less, power start ups.

If you want to direct on line start an inductive load eg. motor or transformer, you need
fuse value = 3 * VA / Voltage ~ 7Aac.
Try T5A and see how many start ups it can pass without blowing. If too few then try T6A and repeat experiment. Fuses do fatigue, too many high load peaks and the wire deteriorates and eventually says "enough".

If you want to go to the safer option of using close rated fusing then you must fit some form of soft start and depending on the capacitor input filter may also need some form of slow charging.
After you have fitted all these start up current limiting measures you may find that your average demand from the 550VA transformer will allow reliable starting and running with an even lower value fuse. Try F2.5A or T2A or even T1.6A

edit:
oops, just realised that 55+55Vac @ 10Aac per winding is a mighty big EI. Is it really 1100VA?

[nazirdigi]

Originally Posted by AndrewT

Fuse value = VA / Voltage = 550 / 230 ~ 2.5Aac
This close rated fuse will only survive a few, or less, power start ups.

If you want to direct on line start an inductive load eg. motor or transformer, you need
fuse value = 3 * VA / Voltage ~ 7Aac.
Try T5A and see how many start ups it can pass without blowing. If too few then try T6A and repeat experiment. Fuses do fatigue, too many high load peaks and the wire deteriorates and eventually says "enough".

If you want to go to the safer option of using close rated fusing then you must fit some form of soft start and depending on the capacitor input filter may also need some form of slow charging.
After you have fitted all these start up current limiting measures you may find that your average demand from the 550VA transformer will allow reliable starting and running with an even lower value fuse. Try F2.5A or T2A or even T1.6A

edit:
oops, just realised that 55+55Vac @ 10Aac per winding is a mighty big EI. Is it really 1100VA?

thanks for the reply andrewt,
yes it is 1100va.

[AndrewT]

Double all the fuse value suggestions in my reply.

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