L&R Cleaning Machines

[Plato]

27 minutes ago, jdm said:

Maybe a PhD doesn't, but people of practical experience do. As mentioned, 50 or 60 Ohm is little for any "power application".

Nonsense. 

[jdm]

4 minutes ago, Plato said:

Nonsense. 

Not when one obeys both Ohm and Joule laws 

https://ohmslawcalculator.com/ohms-law-calculator

[Plato]

1 hour ago, jdm said:

Not when one obeys both Ohm and Joule laws 

https://ohmslawcalculator.com/ohms-law-calculator

It all depends on the motor. The rheostat just controls the current running through it. What if the 800ohm rheostat was set to 60ohms? It more to do with the power rating of the rheostat.

Do you really use the internet to calculate ohm's law?

[Plato]

Is this the motor?

If so, it'll draw 0.5A from a max voltage of 120V.

60ohms isn't enough to alter the speed too much. 800ohm would work but a min of 240ohm would do the job... ensure that the rheostat can handle a minimum of 0.5A.

[jdm]

2 hours ago, Plato said:

Do you really use the internet to calculate ohm's law?

I was trying to help you verify the following: at mains voltage, 60 ohm is too little to "control"

I see now you have written that yourself, so finally, all is good.

[LittleWatchShop]

Controlling the speed of a motor with a rheostat, is crude, but is simple and effective in this application.  The speed of the motor will be determined by at least three three things: 1) the series resistance, 2) AC mains voltage, and 3) the load on the motor (the viscosity of the fluid where the basket is spinning, and the mass of the basket).  For this application, nobody cares about the precision of the speed, but you certainly care that the speed is not too fast at the lowest setting...and you care that you can get the motor running fast enough at least by full travel of the knob (rheostat)...thus my reasoning that 60 ohms was probably too small.

Is 800 ohms too large?  A simple application of ohms law is not going to be much help for at least the reason that the load on the motor will have a significant impact on the speed.  What I have observed is this:

I get what I think is optimal motor speed (with basket immersed in the cleaning solution) when my knob is turned to about half scale.  That would give about 400 ohms in series with the motor at the speed I am comfortable with.  For this reason--my experimental results--I posit that 60 ohms is probably too small.

There is a fourth aspect that determines the speed of the motor (beyond the three listed above).  That is the motor itself!!  It appears (scanning the internet) that these cleaning machines have various motors on them.  Perhaps L&R changed the motor over the years, or some of these machines have been repaired using different motors.  The motor on my machine does not appear to be an original "stock" motor.  Thus a new variable to consider. 

Now to the schematics (where my skills where questioned).

The L&R schematic appears to properly wire the heater in series with the heater switch although the heater switch is drawn as a "push-button" style which it is not.  But I am not gonna get my panties in a wad over that because, hey, it was 1960.  The IEEE probably had not established the standard symbols for schematics by then.  The L&R schematic properly shows a SPDT switch used to control the direction of the motor. The L&R schematic is fine, but there are no values listed for components.

The hand drawn schematic is problematic.  The heater is an 84 ohm resistor in parallel with the pilot light.  The L&R schematic shows the correct way to wire the heater--the hand-drawn schematic does not.  The resistor in my machine is 236 ohms as measured.  In addition, I have a spare resistor that my Dad had purchased for future repairs.  It is labeled 220 ohms and is identical in shape, size, color to the one in my machine.  In the hand-drawn schematic, there is no switch to control the direction, and the notation indicates that the motor used comes from a "milkshake" machine.  Will the hand-drawn schematic work.  Yup...probably so.  My guess is that the "designer" took the rheostat and motor from a milkshake machine...thus the low value of resistance.  But, we cannot really know.

At the end of the day, I stick with my view that 60 ohms is too small and that, depending on the motor, a better value is closer to 800.  This is trivial to verify by @SonnyBurnettwith the expense of a few components.

[LittleWatchShop]

1 minute ago, LittleWatchShop said:

My guess is that the "designer" took the rheostat and motor from a milkshake machine...thus the low value of resistance. 

I say this because the viscosity of a milkshake is far greater than that of cleaning solution, so the motor must be more powerful.  A more powerful motor draws more current, so the "stock" rheostat in an L&R machine would have a resistance that was too high.  So, the "designer" of the hand-drawn schematic realized this and swapped the rheostat when he swapped the motors.

[Plato]

6 minutes ago, LittleWatchShop said:

Now to the schematics (where my skills where questioned).

Sorry, I didn't mean to offend. I felt I was being critised too, the 60ohms was measured by @SonnyBurnett and 50 ohms was on that diagram I found on the nawcc website.

I underestimated the power of the motor - I'm assuming I've found the correct one.

[JohnR725]

Somebody else I think already mentioned this but what about getting rid of the resistor altogether and using some form of solid-state speed control? It doesn't even have to be that complicated I've seen people using light dimmers to control their lathe motors. The same lathe motors that look really similar to the motor on the cleaning machine.

[LittleWatchShop]

28 minutes ago, JohnR725 said:

The same lathe motors that look really similar to the motor on the cleaning machine.

Cleaning machine motor is much less powerful than lathe motor, but I agree that a PWM controller would work just fine...or perhaps even better, and there is plenty of room under the housing to install one--they are not very big.

[Nibbler]

Something like this:

https://www.amazon.com/HiLetgo-Control-Regulator-50-220V-Adjustable/dp/B00LODGP2E?ref_=ast_sto_dp

Matt

 

[LittleWatchShop]

7 minutes ago, Nibbler said:

Something like this:

https://www.amazon.com/HiLetgo-Control-Regulator-50-220V-Adjustable/dp/B00LODGP2E?ref_=ast_sto_dp

Matt

 

This is triac based rather than pwm, but it should work fine.

 

[jdm]

4 minutes ago, LittleWatchShop said:

This is triac based rather than pwm, 

I was to say that, we all know that in any good Chinese product description there are two or three nice words that may relate to the item or its purpose, but do not actually describe it.

[Tore]

1 hour ago, Nibbler said:

Something like this:

https://www.amazon.com/HiLetgo-Control-Regulator-50-220V-Adjustable/dp/B00LODGP2E?ref_=ast_sto_dp

Matt

 

This controlregulator works just fine at my lathe motor(sewing machine motor) 85w.

 

[SonnyBurnett]

On 11/27/2021 at 2:52 PM, jdm said:

Why. That would be another case of unjustified fears of a danger that scientifically doesn't exist when exposure to the harmful substance non-existent, as when asbestos is firs and solid, and in a minuscole amount. One needs years of continuous exposition to fibers to get in danger of developing lung cancer.

Thanks for all the information I will try to answer everything.  The machine is at work and I'm off for deer season but I can run up to get it for details if needed.

jdm:  I agree I have asbestos siding on my 1922 cape cod house.  As long as it doesn't become fibrous in the air to breathe and you don't lick it, it wont hurt you.  Just have it encapsulated with a special paint and you're good to go.

Edited November 29, 2021 by SonnyBurnett

[SonnyBurnett]

23 hours ago, HectorLooi said:

Even a PhD won't be able to tell the correct value for the rheostat with the limited information given. 

The value would depend on the internal resistance of the motor used in the machine. I'm sure the motor must have changed over the decades of production.

But 50 ohms does seem a little low.

The motor seems to be original to the machine.  It's an L&R Precision 115V at 75 cycles at 60 watts

 

13 hours ago, Plato said:

Is this the motor?

If so, it'll draw 0.5A from a max voltage of 120V.

60ohms isn't enough to alter the speed too much. 800ohm would work but a min of 240ohm would do the job... ensure that the rheostat can handle a minimum of 0.5A.

YES that is the EXACT motor on my machine

Edited November 29, 2021 by SonnyBurnett

[SonnyBurnett]

13 hours ago, Plato said:

Is this the motor?

If so, it'll draw 0.5A from a max voltage of 120V.

60ohms isn't enough to alter the speed too much. 800ohm would work but a min of 240ohm would do the job... ensure that the rheostat can handle a minimum of 0.5A.

The one suggested to me by Dave was a , (RWA) A-29418-500 ohm, 50 watt, 0.25 amp. Type R-50. 2-1/4" diameter body, 1-3/8" behind panel depth. 1/4" diameter x 1/2" long round shaft.

As you stated the amperage of the motor is double for what this is rated for, so is there another from surplussales that I can use? 

[HectorLooi]

i would just clean up the original rheostat, improve on any potential insulation problems, do an earth leakage test and see how it goes.

[HectorLooi]

I was just thinking about the asbestos issue... I don't think I've ever seen asbestos used in a potentiometer. Asbestos is usually used in heat insulation applications, while a high power wirewound potentiometer might get warm, it shouldn't require asbestos.

[LittleWatchShop]

11 hours ago, SonnyBurnett said:

The one suggested to me by Dave was a , (RWA) A-29418-500 ohm, 50 watt, 0.25 amp. Type R-50. 2-1/4" diameter body, 1-3/8" behind panel depth. 1/4" diameter x 1/2" long round shaft.

As you stated the amperage of the motor is double for what this is rated for, so is there another from surplussales that I can use? 

If those dimensions fit mechanically, buy it and install it.  It will work fine.  The motor current is rated at full speed at some (unknown) load.  You will never run it full speed.  You will be fine.

At lowest setting of R=500.  IR drop at 0.5 amp is 250 volts.  Cannot happen

At middle setting of R=250.  IR drop at 0.5 amp is 125 volts.  Cannot happen

At 80% setting of R=100. IR drop at 0.5 amps is 50 volts.  That leaves 70 volts across the motor.  The motor will not be running at full power at that point.

These are overly simplified calculations, but they satisfy me that you will be fine with that rheostat.

 

edit: and Dave has been around the block a few times, so I would trust his guidance!

Edited November 29, 2021 by LittleWatchShop

[SonnyBurnett]

2 hours ago, LittleWatchShop said:

If those dimensions fit mechanically, buy it and install it.  It will work fine.  The motor current is rated at full speed at some (unknown) load.  You will never run it full speed.  You will be fine.

At lowest setting of R=500.  IR drop at 0.5 amp is 250 volts.  Cannot happen

At middle setting of R=250.  IR drop at 0.5 amp is 125 volts.  Cannot happen

At 80% setting of R=100. IR drop at 0.5 amps is 50 volts.  That leaves 70 volts across the motor.  The motor will not be running at full power at that point.

These are overly simplified calculations, but they satisfy me that you will be fine with that rheostat.

 

edit: and Dave has been around the block a few times, so I would trust his guidance!

I've known Dave a long time.  When I first started into watches he helped me take apart and put back together my first practice pocket watch.

[LittleWatchShop]

1 hour ago, SonnyBurnett said:

I've known Dave a long time.  When I first started into watches he helped me take apart and put back together my first practice pocket watch.

If you proceed with that rheostat, be sure to report back to the forum on your progress!!

[SonnyBurnett]

11 hours ago, LittleWatchShop said:

If you proceed with that rheostat, be sure to report back to the forum on your progress!!

I'll get it ordered and get it in as soon as I get back to work.  I'm off for deer season this week.

[SonnyBurnett]

Okay I got the part ordered.  When it gets here I'll start on the machine.

[jdm]

Non horological, off-topic content has been split to another topic.