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Blowing modular 10EE fuse

jwatts

Hot Rolled
Joined
Apr 19, 2006
Location
Missouri, USA
Of the three fuses next to the module I'm blowing the center fuse, one of the 2.25 amp ones. It happens after I've had the spindle running for a little while, maybe 10 minutes. I recently had the module rebuilt by Monarch so I'm hoping it's nothing in there. Any ideas where to look?
 
On my Modular schematic I do not have a 2.25 amp fuse are you sure that is the right fuse? I see a 3 amp fuse for the field. and two five amps and one 1 amp fuse.
 
Pretty sure, they are labeled on the plate above the set of three fuses. The one on the right is labeled 3 amp and the other two are labeled 2.25 amps.
 
I cannot advise you where to look not knowing what the fuse does and my manual does not have that fuse.
 
I'm not sure which is which, but my schematic lists FU1 and FU4 as 2.25 amp fuses. FU2 is 3 amp, and FU3 is 1 amp. It never struck me until now, but I converted this machine from 460V to 230V. I don't remember reading that as one of the changes that needed to be made, but is it possible that that fuse needs to be doubled now?
 
Looking at drawing 61215 dated 9/30/66 I see 3 fuses. Fu1 is on the 120 volt taps on T3 and supplies the reference voltage circuit, fixed bias circuit and the control voltage. It's referenced twice in the drawing and is 5A in both places. FU2 is in the field voltage circuit and is rated 3A. FU3 is a 1A fuse on the work light circuit across the control voltage.

I do have a schematic in the manual that shows 2 fuses on the T3 outputs, one on each leg and each being 2 1/4A (not 2 1/2A) but that really doesn't make any sense to me - the current will be the same on both legs, not split, so 2 the fuses don't add in any way I know. Maybe someone can take some time and explain that to me.
 
Looking at drawing 61215 dated 9/30/66 I see 3 fuses. Fu1 is on the 120 volt taps on T3 and supplies the reference voltage circuit, fixed bias circuit and the control voltage. It's referenced twice in the drawing and is 5A in both places. FU2 is in the field voltage circuit and is rated 3A. FU3 is a 1A fuse on the work light circuit across the control voltage.

I do have a schematic in the manual that shows 2 fuses on the T3 outputs, one on each leg and each being 2 1/4A (not 2 1/2A) but that really doesn't make any sense to me - the current will be the same on both legs, not split, so 2 the fuses don't add in any way I know. Maybe someone can take some time and explain that to me.
If the Transformer has a center tap then 2 fuses will be needed if not one is not needed.
 
No center tap on those windings and no reason for one - the point of the output is to provide 120V. If it was my lathe I'd jack up the fuses a little at a time. Not knowing the fuse type I'd just find something above the 2.25, maybe jumping immediately to 5A and be done with it as the old schematic. Both fuses have to be replaced at the same time.
 
Thanks for the suggestions. I'll get some larger fuses and give them a try.
Don't use a larger amp fuse. Fuses are protection no the problem. I had the same issue. The pin socket that hold the C3J tubes was no making good contact with the pins. It over heated and it melted the material inside. Check the pin socket connection make sure is properly fastened and secure. Use some no-ox to help if necessary.
 
Don't use a larger amp fuse. Fuses are protection no the problem. I had the same issue. The pin socket that hold the C3J tubes was no making good contact with the pins. It over heated and it melted the material inside. Check the pin socket connection make sure is properly fastened and secure. Use some no-ox to help if necessary.
Read Back he changed the machine from 440V to 220V without changing the fuse sizes.
 
Don't use a larger amp fuse. Fuses are protection no the problem. I had the same issue. The pin socket that hold the C3J tubes was no making good contact with the pins. It over heated and it melted the material inside. Check the pin socket connection make sure is properly fastened and secure. Use some no-ox to help if necessary.

Checking the C3J is a good suggestion, but the old design was for a single 5A fuse, someone changed it to 2 2.25A fuses for no good reason I can see. Maybe call Monarch and see what they suggest but going to a couple of 3A fuses wouldn't be out of line here.
 
Read Back he changed the machine from 440V to 220V without changing the fuse sizes.

This is on the T3 120V secondary. As long as the primary side was changed for the mains change he's good on the fuse size. The only thing fusey that would need changing in a 440 to 220 change would be the overloads and mains fuses if there are any in place.
 
I spoke with Tim at Monarch and he thinks that it might be an issue with the T4 transformer. I'll test that and see what happens.
 
I spoke with Tim at Monarch and he thinks that it might be an issue with the T4 transformer. I'll test that and see what happens.

Let me know the AC voltages between 31 & 32 with the controls on & off. On should be 270, I'm curious about the off voltage with the odd tapping in the schematic.

Any problem that T4 would give you is more than likely to be intermittent. If it wasn't it would probably blow the fuse immediately on engaging the drive. But anything is possible.
 
With the spindle off I get 290 V,with the spindle on it drops to 270 V. That voltage does not change with spindle speed.
 
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I replaced the capacitor associated with T4, and haven't had the problem since. I've only used it in short spurts, but so far it looks like that was the culprit.
 








 
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