Cj18a mini lathe

[Ron LadenParticipant @ronladen17547]

Steve, Having had no electrical problems with my CJ18 I never dabbled into the electrics so dont have much experience with it. I,m sure Anthony will answer your questions though having fitted the same control unit and having it work well on his machine.

Good luck with it, if it does the job at £20 thats a real winner.

 

Edited By Ron Laden on 03/05/2022 07:43:14

[Steve LangParticipant @stevelang11304]

Thanks Ron, I have bit the bullet and ordered one, lol

[Ketan SwaliParticipant @ketanswali79440]

Posted by Anthony Knights on 02/05/2022 13:04:36:

The motor on my Clarke CL300 lathe is a 180volt DC permanent magnet brushed motor, rated at 350(chinese) watts.The control unit shown is rated at 500 (chinese) watts and works fine on my lathe.

Just need to clarify…with respect, the figures stated are Clarke watts, rather than Chinese watts. Its a machine manufactured for Clarke, and the figures stated are those as specifically required to be stated by Clarke on their machine…. as manufacturer of the machine. the sub-contract manufacturer has followed Clarke's requirements – instructions. Clarke can choose what they want to be specified – input/output or some other watts, but I can confirm that the stated figures are not the ones speified by the sub-contract Chinese factory.

Ketan at ARC

[Steve LangParticipant @stevelang11304]

Thanks

[SillyOldDufferModerator @sillyoldduffer]

Posted by Anthony Knights on 02/05/2022 13:04:36:

The motor on my Clarke CL300 lathe is a 180volt DC permanent magnet brushed motor, rated at 350(chinese) watts.The control unit shown is rated at 500 (chinese) watts and works fine on my lathe. There is an internal adjustment for the output voltage. I fitted the pcb in the original lathe control box. While this voids any warrentry, for £20, I thought it was worth the risk. This is only a temporary measure as I already have a 3phase half horse power motor with inverter which I am in the process of fitting now. Keeping the lathe running with this cheap control box enables me to make the bits necessary for the conversion. Interestingly, the 1/2 HP motor is physically twice the size of the DC motor and they are both in the 350watt range (1hp=746 watts). It must be the difference between Chinese and British watts.

There's absolutely no difference between Chinese and British watts!

Confusion arises because it's not always clear what's being measured, which can be exploited by salesmen, and I suspect most motor users don't understand how the number of watts consumed by a motor varies with load. It's complicated, and is best understood by looking at a graph, like this example:

If you think a 500W motor is a 500W motor in all circumstances you are wrong, wrong, wrong. In the example above, a DC motor:

• The motor is rated at 48V and 350A. It's a 16.8kW motor (input watts)
• The power supply should produce 350A continuous, but note the motor actually draws 377A at 2500rpm. The designer should overrate this motor's power supply by at least 10%, but providing a 400A supply doesn't mean the motor is magically able to take 19.2kW input without overheating.
• The 16.8 kW input only occurs at just under 4000rpm, and it coincides with the motor's peak output, which is 19.75HP (about 14.7kW)
• All bets are off when the motor is run at any speed other than just under 4000rpm. At about 1800rpm, the output is only 10HP (7.46kW), and the output also drops to 10HP at 7000rpm.
• The graph is drawn for whatever the manufacturer considers normal operation. The actual maximum input and output powers that can be taken are only limited by the motor's ability to get rid of the heat without melting the insulation. If the motor works in bursts and has time to cool off, it can deliver much more power than when operated continuously. This is why hobby machines tend to be fitted with physically smaller motors than the industrial equivalent. The expectation is that hobby machines will be worked relatively lightly and in short bursts. It's easier to overload a hobby motor with long hard cutting than an industrial motor.
• The graph doesn't show what happens toi input and output power during an accident. Worst case, if the motor is stalled, the output watts spike, then drop to zero, while the input watts go through the roof, potentially damaging the motor and blowing the power supply up unless it's clever enough to shut down, or has a fast-acting fuse.

Simply put:

• when choosing a lathe, the owner wants to be told output watts, but salesmen like to quote input watts because it's a bigger number. They're also prone to not mention the power is only expected to be taken in short bursts. Unless otherwise stated in the specification, hobby machine owners are wise to assume their motor has a low duty cycle, that is it can do hard work but only in short bursts with time allowed to cool down. Heavy handed owners should note electric motors can and will exceed it their ratings, and this risks popping the power supply.
• when choosing a power supply to match a motor, the owner needs to know the motor's input watts; knowing the output doesn't help much. The power supply should provide at least the input stated on the motor plate, plus an overload allowance. Most of the time, hobby lathe power supplies are run well under their maximum, so the allowance can be low, keeping costs down. But if you're a heavy handed accident-prone operator in a busy workshop, it would pay to allow more, say 30% more than the motor plate. But in doing this, remember a big power supply is more likely to burn out the motor and cook the machine's wiring than a small one.

If the size of the motor and power supply on a hobby lathe are a constant worry in your workshop, you probably have the wrong machine. What's needed is either a bigger hobby lathe, or a professional machine rated for continuous hard work. Don't expect a lightly built hobby machine to last long doing piece-rate production work! Although capable of accurate work, hobby machines aren't go-faster metal munchers!

Dave

[Anthony KnightsParticipant @anthonyknights16741]

Posted by SillyOldDuffer on 03/05/2022 12:56:57:.

There's absolutely no difference between Chinese and British watts!

I am quite aware of that. The purpose of the "Chinese watts" quip was to highlight the different ways people specify equipment. This point has been very well stated by S.O.D. in his treatise above. We've had the same thing with amplifiers and loudspeaker (Peak versus Average versus RMS etc) and just about every other piece of electrical kit you can think of.

I dug the lathes old motor housing out of the "might come in handy" box and have found that despite the written lathe specification, the actual motor plate states 250watts.

Shown here is the old motor housing in front of the half HP 3phase motor which I am hoping to fit, as just about everyone on this site sings the praises of the 3phase inverter plus motor.

[Dave HalfordParticipant @davehalford22513]

Posted by Anthony Knights on 04/05/2022 11:08:45:

Posted by SillyOldDuffer on 03/05/2022 12:56:57:.

There's absolutely no difference between Chinese and British watts!

I am quite aware of that. The purpose of the "Chinese watts" quip was to highlight the different ways people specify equipment. This point has been very well stated by S.O.D. in his treatise above. We've had the same thing with amplifiers and loudspeaker (Peak versus Average versus RMS etc) and just about every other piece of electrical kit you can think of.

Not to forget the pinnacle of rubbish that is Watts PMPO.

[Steve LangParticipant @stevelang11304]

I have now purchased a variable dc speed controller but it has no reverse switch, but I have a new reverse switch that I purchased this week,

Can anyone tell me how to wire this in line onto my new controller,

[Steve LangParticipant @stevelang11304]

[Ketan SwaliParticipant @ketanswali79440]

Steve,

Cant help you directly with an answer. Perhaps Anthony may be able to assist.

The last time the C3-181 switch was discussed was on 15 April 2015. on following thread. Perhapsthis may give you some assistance.

Ketan at ARC

[Steve LangParticipant @stevelang11304]

Thanks

[Anthony KnightsParticipant @anthonyknights16741]

As I said in a previous post, I fitted the control pcb in the lathes original control box. This was so I could use the existing emergency stop and reverse switches. The diagram is below, with the reversing switch on the left. The contacts are shown in the centre off position.

My reversing switch is a 3 position (centre off) toggle switch, while yours is rotary. The same connections apply. If the switch come without documentation you may have to meter the connections out to determine the correct ones to use. The centre off position is to stop you switching directly from foreward to reverse, although I always switch the power off before operating it anyway. Please note, I did not use the PW terminals on the control pcb. There does not appear to be any form of feedback with this board, so expect a reduction in speed when you load the machine. I can live with that in view of the difference in price between this controller and the expensive "proper "one.

Hope this helps.

Best wishes Anthony

[Steve LangParticipant @stevelang11304]

Hi Anthony

Think I understand diagram lol,

Can ask what is the small dotted line just before the switch,

And do you mean just leave the pw as it is, open,

Thanks again

[Anthony KnightsParticipant @anthonyknights16741]

Hi Steve. The dotted line is a drawing convention to indicate that the two switch contacts are mechanically linked and operate together. NB lines which cross WITHOUT a dot are not electrically connected. I wasn't sure what the PW connections were for and the controller works OK with no connection to them. Just leave them open.

Regards Anthony

[SillyOldDufferModerator @sillyoldduffer]

I believe the PW contacts are for an optional emergency off switch. The switch is normally open, closing it cuts the power.

If I was fitting one, I'd ignore PW and use the lathe's existing NVR/Emergency Stop Switch as described by Anthony.

Dave

[Steve LangParticipant @stevelang11304]

Thanks for that

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