Mini lathe blown fuses and Motor overheating

There seems to be a misunderstanding regarding the performance of cartridge/wire fuses and their rupture time. A quick blow fuse will run indefinitely at its rated amperage, which one would expect. However when the current rises above the rated value the fuse it does not immediately rupture. In fact, worst case figures, at 2 times the rated current it can take a fuse in excess 6 seconds to rupture and at 3 times the rated current it can take 0.4 seconds. The energy passed during this time is frequently enough to damage a semiconductor component.

Fuses are not there to protect the components or equipment but to limit the energy drawn by the device in order to:

a) To limit the current drawn so it does not damage the house wiring and potentially start a fire.

b) But primarily to ensure that the energy provider's cabling is not compromised.

Hope this helps.

Martin

?

That is the job of the Supply fuse which has a wire seal and is fitted just befor the meter not the job of the consumer unit.

regards Martin

Martin

That is just the first fuse in the supply chain in the property which is then normally broken down into lower current circuits but it is the final safeguard. Yes I totally agree that it is sealed, is the responsibility of the energy provider and is there to protect the incoming supply.

As I had stated that I was looking at Fast Blow fuses I purposely did not include the Consumer Unit or any other fuse in the circuit and was giving just a general description as to the rationale re the fusing system and their purpose.

Cheers

Martin

Hi Apologies to all for wrong link

Eric

It's actually the last fuse in the energy suppliers cabling and ensures that whatever the householder does they cannot overload the incoming cables.

So we can agree then that any downstream fuses are not there to protect the energy suppliers cables.

best regards Martin

oh ok thanks for the tip. I will have a look for some of those

Yes it is the last fuse that the energy supplier is responsible for but it is, as I said, the 1st fuse 'in the supply chain in the property' .

Cheers

Martin

The small fuse hopefully saves the motion control.Otherwise the Triac is burned. But you see this with the bulb test.

Werner

This seems to have wandered away from Davids Lathe Problem -

Just to re-iterate for Davids sake: The control board is a Pulse Width Modulation controller and DC power supply, providing something like 200VDC. The DC supply powers the motor, and is switched by the controller - varying pulse width controls the motor speed.

As mentioned by other members, the motor can be tested by connecting across a 12V car battery - it should turn fairly slowly - if it does, chances are it is OK.

Also as mentioned, the controller board can be tested with a 100 Watt incandescent filament bulb - connect it in place of the motor, and it should be possible to vary its brilliance using the motor speed potentiometer. If its on Full, and uncontrollable, chances are the output devices (there are various types) on the controller board are short - circuit - this is a common fault, but can be repaired relatively inexpensively with the appropriate skills. The alternative is a replacement board at about 120 Pounds. Arc Euro Trade is a good source (no connection) for spare boards and motors - look at their web-site.

Hope this helps a bit, David

If you need a motor or control board, Amadeal sell these and most other parts for their CJ18A mini lathe. ( I think this will be the same as your 618 lathe. There are photos of the motor and control board on their website.

Stuart

I found the parts I need its for my exact model the only down side is waiting 2 weeks to a month for delivery but I guess thats the price you pay. I had to order a bulb on ebay especially for this test as all my bulbs are smart bulbs so I just have to wait for that before I do the test. I will keep you updated.

Edited By Neil Wyatt on 29/08/2020 21:51:49

***UPDATE*** So the motor definitely has a short. I will do the bulb test later today when I get back and I will find out if I need to buy a new circuit too 😒

Sorry guys for the late Update but I have confirmed the short in the motor. Did the 180 degree test on the commutator and got an average of 30 ohms on most of the contacts then it dropped to 20 ohms then went right down to 9 ohms on one or two of them so I have ordered a rotor for my motor.

The circuit was then tested with the bulb method and I confirmed that the circuit is operating correctly, no issues. The bulb got brighter as I turned up the pot and duller as I turned it down . It turns off when the pot clicks to zero.

So thats good news for me it spares me the extra £50 cost for a new circuit so its just the motor. Have to wait a couple weeks for delivery but I don't mind that.

Edited By Neil Wyatt on 05/09/2020 16:02:29

Good!

Looks like you are on the way to sorting it! So shouldn't be too long b efore you are up and running again.

Howard