开云体育

Jim RabidWolf

While you were out last weekend we had a discussion on insertion of a moving iron amp meter between the controller and motor and were wondering what your thoughts were on the topic as far as, can it be done without upsetting the apple cart in practical sense.

Marty

I personally would install it on the input AC side.
Using a shunt and a diode bridge.
Avoid all the stuff going on with the motor control.

RC


--- In 7x12minilathe@..., "Marty N" <martyn@...> wrote:

Jim RabidWolf

While you were out last weekend we had a discussion on insertion of

a moving

iron amp meter between the controller and motor and were wondering

what your

thoughts were on the topic as far as, can it be done without

upsetting the

apple cart in practical sense.

Marty

Yep, I seem to recall suggesting the AC side. And a moving iron
meter doesn't need diodes. It's a natively RMS responding mechanism.

John


--- In 7x12minilathe@..., "r_corriveau"
<r_corriveau@...> wrote:

I personally would install it on the input AC side.
Using a shunt and a diode bridge.
Avoid all the stuff going on with the motor control.

RC


--- In 7x12minilathe@..., "Marty N" <martyn@> wrote:

Jim RabidWolf

While you were out last weekend we had a discussion on insertion

of

a moving

iron amp meter between the controller and motor and were

wondering

what your

thoughts were on the topic as far as, can it be done without

upsetting the

apple cart in practical sense.

Marty

So, do I want to use an AC or DC meter? It appears Ian was successful
with DC, but I'd think connecting to the AC line would be easier and
I'd prefer to stay away from the motor electronics. Also, wouldn't a
5A meter would be sufficient? At 120V for a 400W rated motor, it
shouldn't ever draw more than 3.5A. If it ever went over 5A I'd expect
the fuse to blow.

G'day Ed.

I respect your wish to "stay away" from the motor wiring" but is no
bigger issue than wiring into the ac side.
I used a dc meter because that was available directly from an
electronics retailer. I know ac instruments are available through the
electrical trade houses, I specify then in switchboards.
The manual for my control board expects that a dc meter will be used
when setting up the drive but allows for using an ac meter by giving a
compensation factor. If the meter is connected in the ac circuit the
manual says set the ac current a 75% of motor flc, whereas for dc it is
set to 150%. (As an experienced electrical engineer I am am uncertain
of what their wording means, is the ac to dc meter conversion factor
0.75 or .5? Its too early in the morning to dig out my text books)).

You may have noted from the above that the motor stall current is set
150% of full load current. The stall current can be up to 2 times but
this must not be exceeded. KB electronics advised me that a 1.7 factor
should be used. I have a 180V 400W motor with a full load current of
2.2 amps, my stall current setting will be 3.5 amps; thus I need a 0-5
amp meter.
If you motor is 90 volts you will need a 0-10 amp meter. For 120Vac
your motor will be a 90V unit with flc of 4.4 amps and could have a
stall current of 7 amps. You conrol board may not be able to deliver
this current. Jim Rabid may be able to advise you of what your board
can do.

As for fuse blowing, this should NEVER happen if the right size fuse is
installed AND the motor is not left on stall; when it stalls you switch
it off!
Please note that fusss are a thermal device. They do not trip the
instant the current through them exceeds their rating, this is a common
misconception. The heating energy which melts the element is
proportional to the square of the current multiplied by the time,
higher currents require less time to melt the element. At the rated
current the heating energy matches the heat the element can discipate
to its surroundings so it never gets hot enough to melt. In their
overload range circuit breakers have similar characteristics.

Hope this helps

One good gturn deserves another.
Regards,
Ian

Thanks, Ian, for the explanation. I get a catalog from
allectronics.com. They have AC and DC meters in various ranges for $12
each. I pulled my electronics and it looks like it'd be easy to add a
meter to the DC side, especially if I can connect it between the
direction switch and the motor. Does it matter if the meter is on the
+ or - side?
If I have to put it between the board and the switch, it'll be more
difficult, but there's a wiring diagram in the manual that should help
me figure out what wire to use.

I'm still a little confused on the amperage rating. Is the 400W for
the lathe or the motor? The way I see it, if an appliance, i.e., the
lathe is rated at 400W, then it'll only draw 3.3A regardless of what
DC voltage is used. (And at 150% of that, a 5A meter would be OK.)
That would mean that the motor in a '400W' lathe running at 90VDC
would be rated at 300Watts (if we ignore the power used by the
electronics.) Feel free to point out the flaws in my logic. I'm just
thinking the resolution of a 5A meter would be much better than a 10A.

Ed

G'day Ed.

UNPLUG THE LATHE FROM THE POWER BEFORE WORKING ON THE CONTROL BOX!

Putting the meter between the reversing switch and the motor means
the current reverses and the meter needle will be against the stop
when reversing, that's why I connected it between the board and the
switch. Believe me, I'm not into hard work, just outcomes.

Regarding the motor: Take the cover off (three screws at the back oh
the lathe and look at the nameplate details. It will say 90V and then
give a wattage eg 400W. This is the power of the lathe.
The power figure (400W) divided by the voltage (90V) gives you the
current at full load (flc). There are some losses, typically 10% for
a motor of this size but they can be ignored for this exercise.

Selecting a meter that can read to at least twice the flc, but not
much more, will place the full load current at 40-50% of scale for a
dc meter. This quite useable resolution. AC meters have a non linear
scale at the low end and are even more critcal to get the right range.

I used insulated male and female spade connector crimped to the wire
such that the meter can be taken out of circuit and the normal
connection rstored by connecting the respective spades. make sure you
tape over the connections afterwards with a good quality electrical
tape.

The wire connects from the + terminal of the board to the centre
terminal on the switch. I chose th cut the wire and put in the
connectors but I could have just pulled the spade connector off the +
terminal and with M & F terminals on the meter leads connected
straight in. If your board has screw terminals it is even easier, you
just need a floating screw connector (Blue Point or other)

WHAT EVER YOU DO, UNPLUG THE LATHE FROM THE POWER BEFORE WORKING ON
THE CONTROL BOX!
UNPLUG THE LATHE FROM THE POWER BEFORE WORKING ON THE CONTROL BOX!
UNPLUG THE LATHE FROM THE POWER BEFORE WORKING ON THE CONTROL BOX!
UNPLUG THE LATHE FROM THE POWER BEFORE WORKING ON THE CONTROL BOX!

One good turn deserves another.
Regards,
Ian

--- In 7x12minilathe@..., "Ed" <edo@...> wrote:

Thanks, Ian, for the explanation. I get a catalog from
allectronics.com. They have AC and DC meters in various ranges for

$12

each. I pulled my electronics and it looks like it'd be easy to add

a

meter to the DC side, especially if I can connect it between the
direction switch and the motor. Does it matter if the meter is on

the

+ or - side?
If I have to put it between the board and the switch, it'll be more
difficult, but there's a wiring diagram in the manual that should

help

me figure out what wire to use.

I'm still a little confused on the amperage rating. Is the 400W for
the lathe or the motor? The way I see it, if an appliance, i.e., the
lathe is rated at 400W, then it'll only draw 3.3A regardless of what
DC voltage is used. (And at 150% of that, a 5A meter would be OK.)
That would mean that the motor in a '400W' lathe running at 90VDC
would be rated at 300Watts (if we ignore the power used by the
electronics.) Feel free to point out the flaws in my logic. I'm

just

thinking the resolution of a 5A meter would be much better than a

10A.

Ed

Thanks again, Ian. The motor is labeled DC120V, 3A, 400W. The wiring
should be simple. The manual shows the #2 wire as + DC Out and it's a
screw terminal. I'll order a meter (and a few other parts that have
been on my list) and let you know later in the week how it goes.
Ed

Guys:

HF Micro Mill motor, 1.8 amps 110 volts or 198 watts. Board is a 150 watt board current limit 1.4 amps, 76%
Motor is billed as a 1/5th hp motor, 150 watts, that fits for full load current. Real output about advertised

HF Mini Lathe motor 3.0 amps 110 volts 330 watts, 250 watt board, current limit 2.27 amps 76%
Motor is billed as a 3/4 hp motor, 559 watts....yea? But not stalled or unregulated either, maybe ;( Real output closer to 1/3 hp. 559 watts at 110 volts would be about 5 amps (fuse) rating.

Wilton Mini Wood Lathe motor, 2.3 amps 120 volts or 276 watts or about 3/8 hp, board unmarked but billed as a 2/5 hp motor or 298 watts, pretty close to theoretical input. As the other two motor/controller set ups seem to follow a rough 76% out put to input rule, sort of, kind of maybe...This motor is likely closer to 210 watts or about .281 hp. Advertised out put seems just a shade short of theoretical.

Seems to be more ways to power factor a motor than there are manufactures (sales people). You should see the ratings some robot motor manufactures put out. Continuous power, power for 2 hours, 6 minutes, 30 seconds, momentary, stalled and on and on.

Anybody got a scope and a motor dyno? ;-)

Chris bills the F350 board as an "upgrade" to the small lathe motor which intuit suggest a 3.2 amp current limit as "extra capacity". Seems more in line with the motor name plate current anyway.

Now I know why some fit tread mill motors to these things. If you can't get the truth then just Tim Allen the thing :)

Marty

Thanks, Ian, for the explanation. I get a catalog from
allectronics.com. They have AC and DC meters in various
ranges for $12 each. I pulled my electronics and it looks
like it'd be easy to add a meter to the DC side, especially
if I can connect it between the direction switch and the
motor. Does it matter if the meter is on the
+ or - side?

The meter can go anywhere in the circuit, if you hook the + - up backwards,
you'll just get a negative reading.

If someone is planning on using digital meters, check the specs. Most of
them don't like you using the 10A range for too long, usually under 10
seconds. They're not designed to be left in permanently.

YMMV, of course. They may be happy with a couple of amps indefinitely, but
become a blob of yellow plastic on 10 amps.

Same deal for the analog ones too, the shunt can get a bit warm, but they
tend to be designed for it.

Tony

G'day Tony & Ed.

"Does it matter if the meter is on the + or - side?"
My preference is for the meter to go in the + side of the circuit so
as not to risk bypassing the current limit resistor (Horse Power
Resistor on my card) if you connect back to the wrong terminal.

NOTE: BOTH + & - CONNECTIONS ARE LIVE WITH RESPECT TO GROUND AND THE
LATHE FRAME. Treat the meter its wiring and connections as LIVE and
effectively at mains potential.

Regarding digital meters, not DVMs, I would be careful regarding the
effect of the current wave form. The lower cost units will only
measure the peak current each sampling cycle. The peak will be more
than either the average or the RMS current so the reading could be
high and so be meaningless. A digital meter needs a power supply
while an analogue meter does not.

If you connect the analogue meter the wrong polarity you will simply
reverse the needle against the stop, no harm will be done but you
will have to reverse the connections.

Hope this helps.

One good turn deserves another.
Regards,
Ian

"Does it matter if the meter is on the + or - side?"

The reason I asked was to determine whether or not I could put the
meter between the Direction Switch and the Motor. Since the switch (I
assume) reverses polarity, I now know it'll only work there in one
direction.

I convinced myself that I can get away with a 5A meter instead of ten,
but now that I see my motor is rated at 3A (regardless of voltage),
I'm looking at a 3A one with a red over-range scale.


Do you think this one would work? I think it would look pretty good
mounted in the side of the electronics box (and we all know it's all
about aesthetics.) I'd mount a SPDT switch with it to turn it off when
I'm not using it just in case it doesn't like being on for long periods.

Ed

G'day Ed.
THe meter looks nice, but whenever you are doing any heavy work it
will be reading in the uncalibrated over range area. Does MPJA have a
0-6 amp meter with over range? Minimum meter must be 0-5 amps with
over range scale.
You really want to know the stall current which can be up to two
times the nameplate current. loading the drive to just under this
gets best use fo the lathe.
To be of more than pose value the meter needs to be where you can see
it as you operate the feed screws.

Meters are designed to be left in circuit. (multimeters are not)

A switch is NOT RECOMMENDED unless it simply shorts out the meter.
The motor cicuit must not be interrupted during operation and the
spdt switch you propose would open the circuit mometarilly, enough to
harm the drive.

One good turn deserves another.
Regards,
Ian

- In 7x12minilathe@..., "Ed" <edo@...> wrote:

"Does it matter if the meter is on the + or - side?"

The reason I asked was to determine whether or not I could put the
meter between the Direction Switch and the Motor. Since the switch

(I

assume) reverses polarity, I now know it'll only work there in one
direction.

I convinced myself that I can get away with a 5A meter instead of

ten,

but now that I see my motor is rated at 3A (regardless of voltage),
I'm looking at a 3A one with a red over-range scale.


Do you think this one would work? I think it would look pretty good
mounted in the side of the electronics box (and we all know it's all
about aesthetics.) I'd mount a SPDT switch with it to turn it off

when

I'm not using it just in case it doesn't like being on for long

periods.

Ed

I can be a little thick, but I think I finally got it. Good advice on
the switch - I didn't think of the consequences flipping it while
running. Thanks, Ian.