If there was no L or LC filter then the rms/ave current would be far higher than with a well filtered supply. The peltier would be far more efficient when PWMing.
-- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
You might want to add some filtering to remove some of the HF being radiated.
As long as ripple is low then rms/ave current will be close to unity. That's as good as it gets.
You can add your own inductance for a quick easy fix.
One thing to bear in mind. If you want this to work long term and use ball bearings I have come across premature failures that were explained as HF circulating currents in the stator, rotor and frame that effectively spark eroded the bearings.
If the bearings are electrically isolated then obviously this isn't going to be an issue.
-- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
========================= ===========
ct I'm working on. One of them was suggesting we control the motor with a variable voltage rather than an H-bridge to switch the current in a PWM man ner. He mentioned some high power amps to drive this, but they are class A B and so would have high losses at anything other than the maximum output.
** A class D amp would be better.
voltage to a motor?
** Absolutely for both AC and DC ( brush) motors.** However it is still constant voltage drive.
The average value of the PWM voltage is the equivalent DC drive.
.** You cannot have a large value cap across a motor using PWM drive.
a lower continuous current rather than a higher pulsed current with a duty cycle.
** Oh dear.e that work. I need to ask if we can get some better measurements to see h ow long it takes for the motor current to drop significantly when the H-bri dge removes the power connection and the reverse diode conducts.
** A few thousand Hz is usually OK for a brush motor up to a HP or so.The whining noise can be an issue.
.... Phil
==================
** No it wont, the fool is using ambiguous terms.He means smooth current not "constant current".
** The fool's posts are riddled with ambiguities. 100% has to be a dumb as soup code scribbler..... Phil
Right. An H-bridge is bidirectional, sort of a DC Variac.
Decelerating a big load can blow up the power supply. Even a modest motor and load could store hundreds of joules.
Nice summary of the situation.
onsdag den 21. oktober 2020 kl. 01.15.23 UTC+2 skrev John Larkin:
or project I'm working on. One of them was suggesting we control the motor with a variable voltage rather than an H-bridge to switch the current in a PWM manner. He mentioned some high power amps to drive this, but they are c lass AB and so would have high losses at anything other than the maximum ou tput.
ntrolled voltage to a motor? The motor is an inherently inductive load...
UT that's at audio and below. At
is capacitive...
. Rotor inerita has almost no effect on the winding. If you have burried ve rsus surface magnets, the winding inductance varies with respect to rotor o rientation, but that is another issue, relevant for the motor control algor itm
if you look at the schematic is obvious that it is a sync buck from supply to motor and a sync boost from motor to supply
Mechanical engineers dream of having a continuously-variable gear set. A lot of silly versions exist.
We can just vary the duty cycle.
onsdag den 21. oktober 2020 kl. 01.37.49 UTC+2 skrev John Larkin:
e:
lator project I'm working on. One of them was suggesting we control the mot or with a variable voltage rather than an H-bridge to switch the current in a PWM manner. He mentioned some high power amps to drive this, but they ar e class AB and so would have high losses at anything other than the maximum output.
controlled voltage to a motor? The motor is an inherently inductive load.. .
, BUT that's at audio and below. At
tia is capacitive...
ive. Rotor inerita has almost no effect on the winding. If you have burried versus surface magnets, the winding inductance varies with respect to roto r orientation, but that is another issue, relevant for the motor control al goritm
twer
ly to motor and a sync boost from motor to supply
and power can go in both directions and you can have massive peak power,
an electric car is going around the world smashing all the laps records
I like the fact that you likely know nothing about the actual problem and y et present yourself as an expert. Ok, so please tell me what pressure cons titutes "gentle"? How much air movement is required? How much power is re quired of the motor? What is the timing required?
Your remind me of me. lol
zuma-tests-north-of-york
Even more reason to mitigate the PWM impulses. We can apply any voltage we wish, but the motor determines the current. With a faster impulse rate we can at least allow the current to flow more smoothly. The RFI isn't at hu gely high frequencies at least. The current PWM rate is 500 Hz but the ind uctance of the motor prevents fast edge rates. It looks like at 10 kHz the current fluctuations will be ~1 amp AC triangle wave. I'd like to reach 20 kHz so we can't hear the noise. Right now it is very grating, not that I' ll hear much above 12 kHz. It starts falling off in one ear below 4 kHz, b ut oddly that's the one I hear better with.
-- Rick C. ++ Get 1,000 miles of free Supercharging ++ Tesla referral code - https://ts.la/richard11209
project I'm working on. One of them was suggesting we control the motor wit h a variable voltage rather than an H-bridge to switch the current in a PWM manner. He mentioned some high power amps to drive this, but they are clas s AB and so would have high losses at anything other than the maximum outpu t.
olled voltage to a motor? The motor is an inherently inductive load...
that's at audio and below. At
capacitive...
otor inerita has almost no effect on the winding. If you have burried versu s surface magnets, the winding inductance varies with respect to rotor orie ntation, but that is another issue, relevant for the motor control algoritm
Only if you don't provide for it. In our case we need very little in the w ay of deceleration. I think at the end of the back stroke the motor is rev ersed a bit to stop it without passing the limit switch (we actually have t wo slightly out of alignment as redundancy). The idea is to stop the motor before it activates the second switch so it doesn't wear. With no load th e motor current isn't very high, so it doesn't take much to stop it. Still , that current is still supplied by the PSU as the polarity is opposite onc e the H-bridge is switched. On the way down there is plenty of back pressu re to resist the motor movement.
So if the motor winding is inductive and the motor inertia appears capaciti ve, do they combine to form a resonant circuit? It would appear to be seri es, so near to zero impedance with high current, low voltage at the resonan t frequency? I imagine both the PWM and the control loop should try to avo id that frequency.
-- Rick C. --- Get 1,000 miles of free Supercharging --- Tesla referral code - https://ts.la/richard11209
Yes, bearing erosion was an emerging problem 30+ years ago when PWM motor drives for 3-phase motors were becoming plentiful.
You could do worse than look at the UK government specification:
Or the user manual for one of the units in use:
Either way the total power consumption for the whole thing is ~100W and obviously a power cut battery backup capability is essential.
Hot swapping of batteries is an optional extra useful in places where the mains is particularly dodgy.
-- Regards, Martin Brown
Sorry, you seemed to be presenting yourself as an expert, so I thought I wo uld cut through the chaff and ask you directly.
Here is a current question. When we measure air flow, we are designing for two different sensors, one measuring mass flow reported as SLM and another measuring differential pressure across an orifice where we have to do the calculations. What volume units need to be reported to and entered by the operator, SLM or absolute volume?
er=23079
Geeze, there are specs and documents about these things??? Who knew?????
Thank you. Yes, we have a battery in the system, 4 Ah which will meet the
20 minute hold up time specified somewhere. We seem to be building this to British requirements (typically IEC docs) with awareness of the US standar ds. But this is the sort of stuff that pros learn over their career and am ateurs like us struggle with figuring out.-- Rick C. --+ Get 1,000 miles of free Supercharging --+ Tesla referral code - https://ts.la/richard11209
This is reminiscent of the air for a pipe organ. With some others I have made a computer controlled small organ. Air is supplied by a weight pressing on an air column in a cilinder. I guess sometimes a patient wants to exhale, so there is time for a servo system that pulls the weight up. Even simpler is a control valve that fills the cylinder from a higher pressure oxygen tank. A fully mechanical, ultra reliable system seems possible. (That is somewhat similar to how our organ works, but we just blow air in if the air supply is low, leaving it to the weight to maintain constant pressure.) You can see the cylinder at the right in
Groetjes Albert
-- This is the first day of the end of your life. It may not kill you, but it does make your weaker. If you can't beat them, too bad. albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst
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