Onoff Posted October 12, 2021 Posted October 12, 2021 Playing with an old lathe here and the main contactor cum NVR switch has burnt out. A weird thing I've never seen is the contactor coil has two windings? I've seen motor brake coils with two windings where one winding excites the brake then ms later it gets the full wallop to release but never seen a contactor like it. Contactors are pre 1948 when British Klockner were sold.
markc Posted October 12, 2021 Posted October 12, 2021 Could be separate pull-in and run windings? But then there would be a spare aux contact to cut the pull-in circuit. plus not usual on smaller machines, even old ones 1
ProDave Posted October 12, 2021 Posted October 12, 2021 Since you will be replacing the contactor, does it matter that the old one had 2 coils? I don't think I have ever seen a lathe that can run in reverse. Why?
markc Posted October 12, 2021 Posted October 12, 2021 Running a lathe in reverse is good for manual boring so you can see the cut on the inside but away from you without leaning over the tool post 1
Onoff Posted October 12, 2021 Author Posted October 12, 2021 On 12/10/2021 at 15:19, ProDave said: Since you will be replacing the contactor, does it matter that the old one had 2 coils? I don't think I have ever seen a lathe that can run in reverse. Why? Expand Just interested more than anything. They're big lumps too. Fully strippable. 415V coils. Burnt to a crisp. Can't access the motor terminal box without moving the lathe. Measured nom 6 Ohm between each phase at the overload. IR was circa 2M Ohm each phase to earth. In a damp old shed!
SteamyTea Posted October 12, 2021 Posted October 12, 2021 Run a lathe in reverse for LH thread cutting.
Onoff Posted October 12, 2021 Author Posted October 12, 2021 (edited) On 12/10/2021 at 14:51, markc said: Could be separate pull-in and run windings? But then there would be a spare aux contact to cut the pull-in circuit. plus not usual on smaller machines, even old ones Expand The hold on contact is on 1 & 2 isn't it on that RH contactor? Drops out if the o'load trips or you press stop. Or a power failure. Edited October 12, 2021 by Onoff
ProDave Posted October 12, 2021 Posted October 12, 2021 On 12/10/2021 at 15:28, SteamyTea said: Run a lathe in reverse for LH thread cutting. Expand Not when I did my machining, you ran the spindle the same way, just mechanically reversed the feed shaft. Agree on internal boring being a good idea to run the spindle backwards. 1
markc Posted October 12, 2021 Posted October 12, 2021 Is there just one contractor doing forward and reverse? There were some odd centre off units that had a push pull action so they did do forward and reverse but would also bounce to momentarily energise the other direction like an insta brake effect
JFDIY Posted October 12, 2021 Posted October 12, 2021 Although shown diagrammatically as above is it possible that one contactor switches two phases for reverse. My lathe has reverse, but a separate mechanical switch to flip the windings. Run lathe backwards with rear toolpost or for parting off with upside down tool, stops it digging in. 1
SteamyTea Posted October 12, 2021 Posted October 12, 2021 On 12/10/2021 at 15:31, ProDave said: Not when I did my machining, you ran the spindle the same way, just mechanically reversed the feed shaft. Expand Not if you use a large tap.
markc Posted October 12, 2021 Posted October 12, 2021 On 12/10/2021 at 15:44, SteamyTea said: Not if you use a large tap. Expand And a pair of stilsons as a tap wrench so when it get hold the jaws will release and let go lol
Onoff Posted October 12, 2021 Author Posted October 12, 2021 Two separate contactors for fwd/rev. Then the main contactor set up as an NVR. I think what I thought was a separate winding on the main contactor is just a secondary little coil to energise the pilot light "P/L". Then the fwd and reverse contactors have a small set of NC auxiliary contacts. They're just used to break the feed to the other contactors coil. Just going to chuck in 3 modern contactors I think, retain the original overload (unless I can find another). The existing coils are all 415VAC. I'll either use 230 or 48VAC coils and a small control trannie if necessary. The fwd/rev is a proper (you can see it sloshing about) mercury switch. Keeps the grey matter ticking over. No star / delta on this..... It's being run off a dodgy phase converter. 1
Onoff Posted October 13, 2021 Author Posted October 13, 2021 Just spent 10 minutes at the lathe owners with the voltmeter. Turned the phase converter on. Left the lathe off. L1 to L2 - 430V L2 to L3 - 430V L1 to L3 - 0V L1 to earth - 0V L2 to earth (machine body) - 430V ? L3 to earth - 0V He did say he may have wired it wrong... Didn't go any further as just finished a Marston's Pedigree.
SteamyTea Posted October 13, 2021 Posted October 13, 2021 On 13/10/2021 at 17:23, Onoff said: Didn't go any further as just finished a Marston's Pedigree. Expand Do a couple more and it will become very easy to do, once.
Onoff Posted October 13, 2021 Author Posted October 13, 2021 On 13/10/2021 at 18:10, SteamyTea said: Do a couple more and it will become very easy to do, once. Expand More tempting than you know at the moment... ?
ProDave Posted October 13, 2021 Posted October 13, 2021 Get him a proper variable speed drive. Or a single phase motor for the lathe.
scottishjohn Posted October 13, 2021 Posted October 13, 2021 On 12/10/2021 at 15:28, SteamyTea said: Run a lathe in reverse for LH thread cutting. Expand also for using a parting off tool attached on back of the saddle saves fitting it on every time you want to part off while still having your normal turning tool on the other side of the saddle
Onoff Posted October 13, 2021 Author Posted October 13, 2021 On 13/10/2021 at 18:51, ProDave said: Get him a proper variable speed drive. Or a single phase motor for the lathe. Expand Bit pricey a single to 3-phase vsd for this as it is. The motor I don't believe is dual voltage so doesn't offer the option to run 220v delta. Pity as single phase 220 to three phase 220 are comparatively cheap.
Onoff Posted October 15, 2021 Author Posted October 15, 2021 How does the boost button on a phase converter work anyone? Brings other caps in? The above results suggest I've lost a phase. It won't start on the fwd/rev switch but will get going if you press the boost button. Now I know a 3P motor shouldn't start with just two "real" phases present but will run albeit a bit crap on 2 once it's turning. Wondering if the boost does something odd to start it turning. First thing is to check the voltages properly. Hoping to have another look this weekend.
SteamyTea Posted October 15, 2021 Posted October 15, 2021 (edited) On 15/10/2021 at 19:03, Onoff said: How does the boost button on a phase converter work anyone? Brings other caps in Expand Bypasses the thermal fuse? Edited October 15, 2021 by SteamyTea
dpmiller Posted October 15, 2021 Posted October 15, 2021 Boost is higher voltage at same frequency I think. Like a torque assist 1
Onoff Posted October 16, 2021 Author Posted October 16, 2021 Just been back... sober... Definitely between one phase to earth I'm getting 430VAC: Where the phase converter connects to the commando socket: JB at the back of the lathe: Took the lathe out of the equation and checked again. Same results. Said he's never changed the lead on the converter. As much as anything it's a case of redoing terminations, sleeving/marking and tidying as I go.
dpmiller Posted October 16, 2021 Posted October 16, 2021 Delving into the converter is your next stop. What variety is it, transistorised or rotary?
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