Shopsmith Forums

In normal circumstances when you turn off a PowerPro the motor isn't even running. There must be some energy released from the switching power supply though.

JPG wrote: ↑Fri Jul 16, 2021 11:19 pm Not sure what switching the power pro power on/off effect occurs. Likely less 'kick' than an induction motor.

Having spent my entire career as an Electronics Tech, I've torn down and repaired more electronic/mechanical devices than most people have ever seen the insides of.
I haven't seen a schematic for a PowerPro, but if it is like other electronic devices, the power switch doesn't actually switch the motor on and off like the old Shopsmith mechanical motors. The PowerPro power switch likely simply tells the electronics what needs to be done with a low voltage, low current signal to make the motor run or stop. In this case, the heavy load that was on the power switches of the old Shopsmiths is no longer there. The old mechanical system puts the entire current flow for the motor onto the switch and with time and use, the contacts will arc, burn, and fail.
With the PowerPro, there should be almost no current flow through the power switch to do that. In that case, the switch should no longer be a source of failure very often. Low voltage switching of this type does lend to another problem where there isn't sufficient voltage on them, so occasionally you see intermittent issues due to not having enough voltage to "make the trip" across the contacts, but it should be far less often than on a switch that handles the 120v line.
I don't expect to see switch failures on the PowerPro. The weak link here will be the electronics behind the switch as it has to handle the switching job, and as we see, this is the type of failures the PowerPro is showing up with.

Yes, with electronic motor drives, the switch doesn’t see the motor inductance as a direct load. It’s usually switching the current to a DC power supply, which is a basically a capacitor bank with some sort of rectifier in front of it. So there’s no inductive load on the switch, nor the attendant high-voltage arcing at turnoff.

But … if the power supply has a simple “dumb” (non-power-factor-correcting) rectifier, you can get huge inrush currents into the (discharged) capacitor bank when the power switch closes. (This can also lead to arcing and wear, as switch contacts tend to bounce a bit upon closing). So for a PowerPro, I suspect that it would be better to wire the switch contacts in parallel, so that each one is carrying less current.

The 'traditional' power switch on the PowerPro is more of an Off/Standby switch, though not labeled as such. It switches both input power lines. PowerPro is dual voltage so neutral is not a given. It turns the power supply, processor, and display on. Compared to a conventional headstock, I rarely turn mine off and frequently leave it on for days at a time. When I was a new user, I turned it off by accident way more often than on purpose. Pushbuttons on the control panel, though labeled On/Off, provide a Run/Stop function to apply or remove motor power (via the software and electronics).

- David

What pray tell is a "Power-Factor-Correcting rectifier"?

JPG wrote: ↑Sat Jul 17, 2021 8:52 am What pray tell is a "Power-Factor-Correcting rectifier"?

A rectifier, when properly installed, corrects the power factor.

https://www.vishay.com/docs/88868/anpfc.pdf

JPG wrote: ↑Sat Jul 17, 2021 8:52 am What pray tell is a "Power-Factor-Correcting rectifier"?

It’s basically a rectifier circuit with solid-state switches that allow the designer to control when, within the AC cycle, conduction is allowed. The goal is generally to create a reasonable approximation to a resistive load. I’ve never designed one myself. I’ve simply seen components intended for various circuit topologies, such as the one that Dusty referenced.

I think the term "rectifier" is being used a little loosely here. When I think of a rectifier, I think of a single diode or a diode bridge. In fairness, what is discussed in the application note that Dusty posted is an AC-DC switched mode power supply (SMPS)...more specifically a Boost converter with active power factor correction (PFC). There is 1 rectifier inside this SMPS in the app note. In fact the app note points out that the "rectifier" by itself has a degraded power factor, but this SMPS has active PFC to improve it. Maybe I am nitpicking here though?

Welcome to the new Power Electronics Forum, everyone!

RFGuy, as with many things in electrical engineering, I suspect that that terminology usage varies between device manufacturers. But a quick Google search confirmed that the IXYS Semiconductor (for one) does indeed use the term "rectifier" for complete PFC rectifier modules.

In any case, the following application note from IXYS contains a good overview of PFC rectifier topologies, for anyone who is interested (that being probably just JPG ).

Rectifiers with Power Factor Correction

BuckeyeDennis wrote: ↑Sat Jul 17, 2021 12:11 pm Welcome to the new Power Electronics Forum, everyone!

RFGuy, as with many things in electrical engineering, I suspect that that terminology usage varies between device manufacturers. But a quick Google search confirmed that the IXYS Semiconductor (for one) does indeed use the term "rectifier" for complete PFC rectifier modules.

In any case, the following application note from IXYS contains a good overview of PFC rectifier topologies, for anyone who is interested (that being probably just JPG ).

Rectifiers with Power Factor Correction

Yeah, sorry to start a new debate...Being an IC guy, I guess I deal more at the component/circuit level than at the board/module level. Looks life "rectifier" can mean many different things. Hearing discussion about a diode (rectifier) having PFC just doesn't make any sense to me, whereas a power management system (any type) having PFC makes perfect sense to me. I was just more questioning the semantics with the word choice, but then again there are always differences in term use even across the same industry. We can now resume today's regularly scheduled program...sorry for the distraction.