Re: [CAD_CAM_EDM_DRO] Fuse Ratings for Drive protection

Always problematic trying to protect drives with fuses. Fuses are
fundamentally fairly slow devices and their characteristics show that they
will take a long time to blow when the current is say 50% above their rated
value and a relatively short time to blow (maybe a tenth of a second) when
the current is say five times the rated value. Hence the electronics in the
drive is most unlikely to be protected by a fuse. The purpose of the fuse is
to protect against short circuits to reduce the risk of fire and further
damage. Fuses are normally fitted on the primary side of the transformer
feeding the drive but here again this can become problematic as the inrush
current when the transformer is switched on can result in high currents and
the fuse failing. The other question to consider is the size of the wiring
and the protection that the fuse will offer (ie will the fuse blow or the
wiring fail? - properly rated the latter). Secondary fusing can also be
employed but again the current to the rectifier and smoothing capaitor is
very peaky and fuses can fail unexpectedly on the peak of the pulse.

On a 3.5A drive I would start with a 5Amp fuse and expect that I may have to
increase it if it blows unexpectedly. I would use 10Amp rated wiring.

Regards Peter

---- Original Message -----
From: <xylotex@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, January 01, 2003 6:07 PM
Subject: [CAD_CAM_EDM_DRO] Fuse Ratings for Drive protection

> Hi All,
>
> Thanks for all the help on Three Phase etc. I have a new question
> regarding protecting motor drives with fuses (stepper or servo). How
> does one decide on the proper rating for a fuse? (max current then up
> to next standard fuse level)? How does one figure in the voltage
> rating of the fuse along with the amp rating of the fuse, i.e. if I
> have a max of 3.5Amps at 24-28 Volts, what size fuse should I use?
>
> I'll give "Thanks in Advance" now so I don't clutter up the
> archives with a separate thanks in the future.
>
> Jeff
> http://www.xylotex.com
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>
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