fuse burning frequently in Allen Bradly 1769-FB2(power supply unit).

naag_slet · Apr 13, 2010

Hi to All,
This is naag,

i have only allen bradly L32 CPU (compact logix)attached with 1769-FB2(power supply unit)here my problem is
fuse(6.3amps 250v rating)on the 1769-FB2(power supply unit) is burining frequently,i checke dby replacing the 5No's of same rating fuse still everyone is burning..
Then i removed the PLCL32E from the 1769-FB2(power supply unit)and checked again by replacing the fuse,still same problem...fuse blowing out.

awaiting on how to fix the problem and if possible repair the power supply unit...atleast where could be the problem???

is any method to overcome from the problem for time being as plant is so far from here to travel..

Thanks in advance.
Naag.

frankh · Apr 13, 2010

A Fuse With A Different Curve

Hi Naag,

Do you use the fuse that is listed by Allen Bradly for the 1769-FB2?

If you do, and the fuse still blows frequently, you could try a different kind of fuse.

A fuse that has got another curve, one that reacts slower to the surging current.

rdrast · Apr 13, 2010

Does it burn out instantly? or after some time of service?
What is the incoming power to the plant like? You might want to go with a filter or UPS ahead of the PLC.

As of the last 5 years here, we don't use AC powered supplies for the PLCs at all, we specify everything now with 24VDC only. That makes for a much more reliable and inexpensive UPS system.

naag_slet · Apr 13, 2010

Actually i am using 1769-FB2 and its rated input is 24vdc only,
fuse is blowing instantly after replacing with new one(same rating and same company of original fuse)

Note:3 phase 415v ac supply is converting TO 24VDC from the PSU(TELEMECHANIC POWER SUPPLY UNIT WITH INBUILT SURGE SUPRESSOR))and this 24v dc is connected to 1769-FB2.

Then what could be the problem.

mordred · Apr 13, 2010

if it burns out instantly it sounds like a dead short to ground. Disconnect any unnessary devices an try it. try the PSU by itself no processor then processor then I/O cards..whichever card you add and causes it to pop will help eliminate where the problem may be

naag_slet · Apr 13, 2010

Hi to All,
Actually i have remove all the attached module from this power suplly including plc cpu also,now it is alone and still fuse is getting blow out...

where could be the problem....?

Mickey · Apr 14, 2010

naag_slet said:
Hi to All,
Actually i have remove all the attached module from this power suplly including plc cpu also,now it is alone and still fuse is getting blow out...

where could be the problem....?

I'm going out on a limb here, I would say its a bad power supply.

Eric Nelson · Apr 14, 2010

Mickey said:
I'm going out on a limb here, I would say its a bad power supply.

I think it's a pretty sturdy limb you're venturing out on... :nodi:

-Eric

naag_slet · Apr 14, 2010

Hi Eric,
i realy did not got meaning on your message..

mordred · Apr 14, 2010

hes saying the power supply probably has a ground short in it as its whats popping the fuses if that is the only load after the fuse

AFASHLUM · Apr 14, 2010

Hi every one.
From all the discussion I read above, I believe the short cct is inside the P. Supply, by shorted DIODE or some PIN is touching in the wrong place of the p. Supply. So, I suggest that you check carefully all the Diodes specially of the power ones and let us know also how this started in the first place?.
Abdu.

fuse burning frequently in Allen Bradly 1769-FB2(power supply unit).

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