Shopsmith Forums

JPG40504 wrote:Knowing Volts and Amps yields Watts ONLY if a DC circuit.

A true Wattmeter is a four terminal device which simultaneously measures Volts and Amps, and historically used a thermocouple device to indicate Watts.

Add to that the typical Multimeter has a average responding analog meter movement. Digital meters are lord only knows what.

Like that other quick responding smart alec said(sorta), do not confuse DC rules with AC rules.

Also only pure resistance follows those DC rules.

A multimeter is a DC device. It may 'measure' AC stuff, but converts it to DC then measures the 'result'.

Are you sure about that?

http://www.rapidtables.com/convert/elec ... o-watt.htm

JPG40504 wrote:You gots a multimeter that measures Watts?:rolleyes:

I doubt that but if one knows voltage and current, the consumed wattage is easily calculated. Power(in watts) equals Current(in amps) multiplied by Voltage(in volts). P=IE

So I guess my Mark V, which draws approximately 7 amps with 120 volts ac applied, must be consuming 840 watts of power???

JPG40504 wrote:Knowing Volts and Amps yields Watts ONLY if a DC circuit.

A true Wattmeter is a four terminal device which simultaneously measures Volts and Amps, and historically used a thermocouple device to indicate Watts.

Add to that the typical Multimeter has a average responding analog meter movement. Digital meters are lord only knows what.

Like that other quick responding smart alec said(sorta), do not confuse DC rules with AC rules.

Also only pure resistance follows those DC rules.

A multimeter is a DC device. It may 'measure' AC stuff, but converts it to DC then measures the 'result'.

I'd bet that they are analog meters with an "analog to digital converter" driving the display.

dusty wrote:I doubt that but if one knows voltage and current, the consumed wattage is easily calculated. Power(in watts) equals Current(in amps) multiplied by Voltage(in volts). P=IE

So I guess my Mark V, which draws approximately 7 amps with 120 volts ac applied, must be consuming 840 watts of power???

Ok, I understood PIE. I like pie.

heathicus wrote:

Happens a lot when one 'ducks'.

dusty wrote:So I guess my Mark V, which draws approximately 7 amps with 120 volts ac applied, must be consuming 840 watts of power???

I think you are right. There are 746 watts per horsepower (if the manufacturer doesn't overstate their HP rating). The motor is 1 & 1/8 so it should consume 839.25 watts.

joshh wrote:I think you are right. There are 746 watts per horsepower (if the manufacturer doesn't overstate their HP rating). The motor is 1 & 1/8 so it should consume 839.25 watts.

I'm just going to chime in on this dead horse after being off the grid all weekend.

Like anything that carries or converts power, what goes in does not equal what comes out so 839.25 is the minimum and impossible in the real world. But you're not producing 1 1/8 hp constantly, only when under enough load to draw that kind of power to maintain rpm's.

frank81 wrote:I'm just going to chime in on this dead horse after being off the grid all weekend.

Like anything that carries or converts power, what goes in does not equal what comes out so 839.25 is the minimum and impossible in the real world. But you're not producing 1 1/8 hp constantly, only when under enough load to draw that kind of power to maintain rpm's.

I just have to chime in on the "Dead Horse" theme. I have a few different version of this theme but like this one the best. I would send a different version to my management each time they tried to resuscitate an idea or project that had been some what unsuccessful in the past.

Dakota tribal wisdom says that when you discover you are riding a dead horse, the best strategy is to dismount.
However, in business we often try other strategies with dead horses, including the following:
1. Buying a stronger whip.
2. Changing riders.
3. Saying things like "This is the way we always have ridden this horse."
4. Appointing a committee to study the horse.
5. Arranging to visit other sites to see how they ride dead horses.
6. Increasing the standards to qualify as a dead horse rider.
7. Appointing a tiger team to revive the dead horse.
8. Pass legislation declaring that "This horse is not dead."
9. Unilaterally declaring, "no horse is too dead to beat."
10. Blaming the horse's parents.
11. Providing additional funding to increase the horse's performance.
12. Do a Cost Analysis Study to see if contractors can ride the horse cheaper.
13. Declare the horse is "better, faster and cheaper" dead.
14. Revisit the performance requirements for horses.
15. Promote the dead horse to a supervisory position.


OK I'm a meter junkie. I have:

• Simpson 260 analog for those things that only an analog meter so well. I bought this one on eBay after I broke the case on my 30 year old Radio Shack meter.
• Fluke designed for automotive work I don't remember the model. With the right adapter it can measure ignition pulses. Has a tachometer function and other automotive specific functions. You can get all sorts of probes for a Fluke.
• Several free Harbor Freight that let me keep a meter in places I would not normally have a meter. Like my motorcycle tool kit. This saved my butt a couple of times. I have one in my desk drawer at work.
• Radio Shack Digital that was very expensive when I bought it new but only comes out now when I need a continuity checker I can hear. It's kind of strange has automatic ranging that I never quite got used to.
• A tiny credit card size meter I carried around in my computer tool kit when I did that sort of work.
• A clamp on amp meter that also serves as a voltmeter.
• An old school analog engine analyzer that is essentially a specialized multimeter. I can set up points and do several engine diagnostic tests with it.
• A wireless meter for working with AC. It finds hot wires inside a wall. Very handy at times.
• Kill-a-Watt - not a multimeter but since someone brought up watts. Measures power usage in kilowatt hours.
• Three battery testers.

I never realized there were so many until I started making a list.

I only have one Shopsmith.