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Resettable overload (fuse) and marring workpieces

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Pcmaker

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#1
I have a Grizzly 7x12 lathe that uses a 4amp fuse. I've had to replace it twice already. I'm looking for a way to have a "resettable" replacement for the fuse so I don't have to worry about it. I know good work practice eliminates the issue, but I still want to do it anyway.

Also, any suggestions on preventing workpiece damage when using the chuck? I keep marring the workpiece when I tighten up the chuck to secure it.
 

P. Waller

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#2
A fuse is used to protect the wiring from an over current condition, if fuses continue to open then you have another problem causing over current.

As for part holding place a softer metal between the jaws and the part, use soft jaws or make a split sleeve, for example this job required zero scratches on the tubes, it worked a charm on 25 parts.

A pvc split sleeve holding 4 1/2" OD acrylic tubes, the shoulder prevents you from pushing the sleeve through the chuck.
 

FOMOGO

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#3

markba633csi

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#4
I would feel safe going to a 5 amp fuse but no bigger than that.
Fuses typically offer faster protection for solid state circuitry than breakers, I would stick with the fuses
mark
 

RJSakowski

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#5
In viewing the manual for your lathe, something is fishy. It states that the full load current is 3 amps but it also states that you have a 3/4 hp motor. There are 746 watts in 1 hp or 560 watts required to generate 3/4 hp. At 120 volts input voltage, this would require a current of 4.66 amps. At 110 volts, the current requirement would be 5.09 amps. This doesn't even consider that motors are not are not 100% efficient, which I realize is often the case for Chinese motor ratings. However, at best. you are operating on the ragged edge with your fuse.

Fuses usually usually respond according to an i^2t curve; the square of the current times the time. A massive overload will blow the fuse almosr instantaneously while a moderate overload will require a longer period of time before it opens. Additionally, they are available with different response times. Fast blow fuses are rapid response devices whereas a slo blo fuse requires the overload to be present for a longer period of time. A stalled electric motor will cause a current spike which can blow a fast blow fuse. Try replacing with a slo blo type, if not already using one. I would also be comfortable with increasing the size to a 6 amp fuse.
 

Pcmaker

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#6
Both times, I messed up on turning and seized up the cutting tool to the workpiece, then the fuse blew.

Seems like there's another overload protection on th lathe as most of the, when something causes a seize, the power cuts off, then I just have to turn it off and back on to start the motor again.


Does voltage rating matter on a fuse? Or is that just the max allowable voltage?
 

RJSakowski

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#7
There is nothing shown in the schematic but there could be some overload protection built into the circuit board.
The fuse would more than likely be rated for 250 volts, maximum. I don't believe that you will run into any mismatch issues.

The Slo Blo fuse I mentioned before was a trademark brand of Littlefuse for their time delay fuses. Other manufacturers may call them something else.
 

Mitch Alsup

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#8
Does voltage rating matter on a fuse? Or is that just the max allowable voltage?
A fuse blows when it gets hot. The fuse gets hot due to current. Current goes way up when an induction motor is not turning.
The voltage rating is there only to prevent arcing to other points (which should not be "that close" to this fuse.)
 

P. Waller

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#9
Both times, I messed up on turning and seized up the cutting tool to the workpiece, then the fuse blew.

Seems like there's another overload protection on th lathe as most of the, when something causes a seize, the power cuts off, then I just have to turn it off and back on to start the motor again.


Does voltage rating matter on a fuse? Or is that just the max allowable voltage?
OHM's law, current is limited by resistance / voltage potential across a conductor.
Therefore a higher voltage will allow a higher current then a lower voltage in the same conductor with equal resistance.

If your tool has a condition where the resistance is lowered such as a dead short it will go over current every time.

This is one of the reasons that touching the poles of a 400 amp automotive 12 V battery does not generally kill you, your skin has a rather high resistance that limits the current. If you were to use a part of your body that has far less resistance, your tongue for instance, you may experience a whole different outcome.
Do not lick the battery in your car or other battery powered devices, the tongue has very little resistance (-:
 
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higgite

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#10
Do not lick the battery in your car or other battery powered devices, the tongue has very little resistance (-:
Whew! I saw that just in time. ;)

Tom
 

benmychree

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#11
Asian motor manufacturers seem to vastly over rate the horsepower of their motors compared to American or European manufacturers ---
 

KMoffett

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#12
Asian horses are smaller, so it takes two Asian horses to lift the same weight as one American or European horse. :)

Ken
 

Pcmaker

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#13
I was thinking of something like this:

 

benmychree

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Asian horses are smaller, so it takes two Asian horses to lift the same weight as one American or European horse. :)

Ken
That makes sense!
 

markba633csi

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#15
There should be a current limit adjustment on the board- it may be set too high- maybe check with Pete at www.olduhfguy.com
M
 

jim18655

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#16
I'd like too see someone lick both terminals on a car battery without any extensions on the posts!
 

T Bredehoft

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#17
I'd like too see someone lick both terminals on a car battery without any extensions on the posts!
No problem, one at a time.
 

tq60

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#19
Circuit breaker.

There are panel mount that go into same hole the fuse holder did.

But...

Different ones for different uses.

Fast and slow reaction.

If lathe has dc motor with variable speed then motor current can be buffered by control board.

Stick with 4 amp for now.

If you have an amp meter you can measure actual current to see.

Motor may be 1/2 hp but controller may only be 3/8 thus smaller fuse.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 

MSBriggs

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#20
If the fuse is only blowing with you seize the tool in the workpiece, the fuse is probably sized correctly. I agree with staying with the fuse rating the board came with.
 

Downunder Bob

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#21
I agree, given that electronics are involved, and the problem only happens when you stall the lathe, I would say stay with the recommended fuse. However you could include a resettable breaker of 4A and then upgrade the fuse to say 5A as a backup. That way the breaker should take care of the nuisance conditions and the fuse will protect you in case of a serious fault developing. I have done exactly this on a number of occasions, with good success.
 
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