VFD pot wiring

I'm wiring up a VFD for my son - he's WAY more lectrically challenged than myself.

I've used a 0 - 2K ohm pot many times for speed control and bought one for this job. The manual on this unit has very little info about using a pot. On chapter 2 page 11 in the lower left corner it seems to call for 3 - 5 K ohm pot

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later on in the programming section it implies using a pot to get 0 -

10 volt for speed control and using a pot is acceptable. The volt source on the unit is 10 volt. To my thinking 3K to 5K resistance won't give 0 - 10 volt from a 10 volt source.

Read Chapter 4 starting at page 32

I just asked the kid to buy me a 3K ohm resistor and mail it to me to put in series with the 0-2 Kohm pot. But this just seems wrong to me.

Can somebody explain?

karl

Reply to
Karl Townsend
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What you're calling a 0-2K pot is more properly a 2K pot. AD is suggesting that you use either a 3K or 5K (or 4.123456K) pot. The only reason not to use the 2K pot would be if the 10V power supply can't supply enough current thru a 2K load. Page 2-10 of you manual says the

10V supply is good for 10mA.

10V/2K = 5mA < 10mA

The 2K pot will be fine.

Reply to
Ned Simmons

thanks, Ned.

I'm guilty of over thinking.

Karl

Reply to
Karl Townsend

I started and deleted several response before Ned more concisely covered the issue. The whole manual is too much for me to download on dial-up.

I would double-check that the pot wiper input terminal is set to accept a 0-10V voltage instead of a 4-20mA current input, which would overload the 10V reference if you turned the pot to full speed.

jsw

Reply to
Jim Wilkins

That's almost always better than no thinking.

Reply to
Ned Simmons

"Jim Wilkins" fired this volley in news:lle017$ith $ snipped-for-privacy@dont-email.me:

HUH? A pot is a pot. We're not talking about rheostat here, Jim!

Pots don't have "input terminals". They have two outer leg connections, and a wiper.

The wiper doesn't draw _any_ current unless the input on the VFD draws it from the wiper. Unless it's a weird design, it's a voltage amplifier or an A/D on the input, and draws almost negligible current (mere micro- amps, often, but never more than a couple of mils, max. Otherwise, it would swamp the divider ratio of the pot).

Lloyd

Reply to
Lloyd E. Sponenburgh

That's true if the 4-20mA option requires an external sense resistor, but not if it switches in an internal one.

jsw

Reply to
Jim Wilkins

"Jim Wilkins" fired this volley in news:lle2ie$3q6$1 @dont-email.me:

sigh... then it's no longer a potentiomenter, Jim!

Lloyd

Reply to
Lloyd E. Sponenburgh

news:lle017$ith

connections,

Suggest use several pots and select between them via rotary drum switch...

And if you use a +10 -0- -10 power supply you can preset one or more of your pots to run in reverse.

Reply to
PrecisionmachinisT

Thanks for the tips. I had used nothing but Hitachi for many years. Now they aren't made. I can see the programming will confuse me ( I am EASILY confused)

Karl

Reply to
Karl Townsend

Lets look at the circuit.

+10v is on one side of the pot. ACM (analog common mode ??) on the other.

Note ACM is used to shield the cable to the pot. AI is the ?analog Input ?).

AI is a voltage input and wants to move from +10 to zero.

If you have a resistor in series with the pot, you will shift the pot to one side of the voltage. And the control will have a smaller range of voltage to work with.

If you have the resistor on the high end - e.g. from the +10, then your 3k will drop 10V*3K/5k or 6v.

Therefore the pot will have the range of 6V to zero volts. The range will be shortened and control will not be there.

Analog Input (AI) will be 0 (ACM) to 6v not ACM to +10V.

Buy a 3k (3.3K or up to a 5k - 4.7K pot. Use only 1 pot and no other resistors.

AI is getting a voltage reference and the pot is providing voltage from 10V to the ACM voltage.

A resistor in either leg of the resistor will bias AI to a limited range.

Mart> I'm wiring up a VFD for my son - he's WAY more lectrically challenged > than myself.

Reply to
Martin Eastburn

There is a 10V source in most VFDs. There is an input which needs a voltage somewhere between 0 and 10V for the various speeds (the higher the voltage the higher the speed, depending on configuration.

The input does not draw much current

The pot provides a way to divide that 10V down to the various voltages you need for your speeds. Your 2K pot should be more linear than the 3K or 5K pot.

Hooked across 10V, a 2K pot draws 0nly 0.05 Watts, and most of them are rated to handle 2 Watts, so no problem.

Not tonight! Too late! :-)

It is wrong. Depending on where you put it, you will either not get more than 40% of the voltage (and thus speed), or you will simply make the voltage from the pot softer to the input -- which may mean that you can't get quite to full speed, but if it works with a 5k pot, you should have no trouble with your 2K pot.

Good Luck, DoN.

Reply to
DoN. Nichols

When Jim says, "pot wiper input terminal," he means the command input (terminal AI) on the drive. Read his statement that way and it makes perfect sense.

Reply to
Ned Simmons

Thanks. I'm too busy upgrading the lightning protection on my antenna farm to download and read that manual. The monitor-end camera connectors wouldn't pass through the wall feedthru so I had to replace all the conduit with 1-1/4", and custom-machine the junction boxes to accept it. Plastic conduit turns and threads very easily but its "roundness" changes when forced onto a lathe pipe center.

When it's finished I will be able to disconnect all external cables at an indoor grounded box instead of having to run out in the rain at night.

I just found that blister-pack RCA RG-6 coax from Lowes has a manufacturing defect. The shield foil is coated on the inside and doesn't connect well to the shell. Rather than return it and hunt for more, since the length is right I cut off the ends and put on new ones which ground properly to the braid.

jsw

Reply to
Jim Wilkins

"Jim Wilkins" fired this volley in news:llfo9r$rjm$1 @dont-email.me:

Yup. Apologies, Jim.

Lloyd

Reply to
Lloyd E. Sponenburgh

Another gotcha; the 4" square grey plastic waterproof electrical boxes without openings are "Marine Outlet Boxes" whose cover screw pattern is larger than the standard for land-based (Army?) 4" boxes. Who knew that low-voltage household wiring would become such a milling machine job?

-jsw

Reply to
Jim Wilkins

I know I don't always explain things clearly, that's why I practice on people who don't sign my paycheck. jsw

Reply to
Jim Wilkins

Don't use it as a variable resistor, use it as a potentiometer. Tie one end of the winding to ground, one end to the 10 V source, and the wiper to the speed input. When turned to max, it will be zero Ohms to the 10 V, when turned to minimum it will be zero Ohms to ground.

Jon

Reply to
Jon Elson

Jon Elson fired this volley in news:J-- dndXSWdyiKubOnZ2dnUVZ snipped-for-privacy@giganews.com:

Yeah, Jon. I thrashed that one to death until I was made to understand that Jim meant, "make sure the VFD INPUT is set for 0-10V, and not 4-

20ma". Then I had to eat my words.

He had it right, I just didn't understand him.

Lloyd

Reply to
Lloyd E. Sponenburgh

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