I made plastic fans for motors, used to meet my customers.
And a friend makes the bobbins for winding wire.
Two things to bear in mind:
'China Copper' is a cheap winding material, iron wire which is copper plated then coated with enamel.
Much cheaper than copper, okay for short duty use.
And aluminum is also used at times.
Two, the stampings are sometimes thicker than expected, and ordinary mild steel in place of electrical steel.
And some suppliers put good steel at the ends of the stack, they test okay!...
You had a higher than expected voltage on no load with the original transformer.
To avoid long term problems, use a transformer that is closer to load, the 96 VA one, the 250 VA will tend to give a higher voltage, which could damage the components inside, meaning the various coils and timer etc.
And a friend makes the bobbins for winding wire.
Two things to bear in mind:
'China Copper' is a cheap winding material, iron wire which is copper plated then coated with enamel.
Much cheaper than copper, okay for short duty use.
And aluminum is also used at times.
Two, the stampings are sometimes thicker than expected, and ordinary mild steel in place of electrical steel.
And some suppliers put good steel at the ends of the stack, they test okay!...
You had a higher than expected voltage on no load with the original transformer.
To avoid long term problems, use a transformer that is closer to load, the 96 VA one, the 250 VA will tend to give a higher voltage, which could damage the components inside, meaning the various coils and timer etc.
Recently, I checked a few transformers for IP voltage vs current wave forms and phase relationship, loaded and unloaded.
The results were pretty interesting and somewhat answered a question that has been in the back of my mind for some time WRT core magnetization level on distorted mains waveform flattened peaks.
The CRO waveform, no load, showed a significant current spike right at the 'flat top' section, phase shifted by 90 deg as expected from an inductor and looked nothing close to a sine wave.
As increasing load was applied to secondary, the current waveform increased in magnitude and whilst looking more like a facsimile of the voltage waveform at the same time pulling into phase with the voltage.
When time allows I'd like to re do this test with a few different core materials including a Toroid with grain oriented silicon steel and also fed from a true sine wave - see what the differences are.
So I am wondering whether you have some kind of severe mains waveform distortion with DC offset or asymmetry? The behavior you are reporting is only what I have found with extremely cheap or poorly designed transformers.
Do you know a Tech that has a CRO and the ability to safely look at mains current wave forms feeding primary?
PS:
a/ Did you measure the current draw or power of 96VA transformer unloaded?
b/ A good indication of when core is reaching saturation as follows: Connect transformer prim with sec unloaded to a Variac and slowly increase the voltage. Monitor the current and note there is a point where
it will rapidly increase indicating reaching saturation.
c/ I've noted that the occasional transformer, presumably using rubbish / cheap core material will draw a significant amount of current from a fairly low Prim voltage level and just get worse.
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Hmmm, I'm not sure that is correct. The 250 VA measures 24.93 VAC, no load on the secondary.
The replacement I got (not the 96 VA) measured in the 25 VAC range if I remember correctly.
I need to get a scope! The use of a scope came up with an audio related issue, maybe it's time to make that purchase.
I do have a variac and can test the 96 VA unit as suggested as well and check current on the primary side while secondary is unload.
There is some question about the power coming into my house and how clean it may be. Some of you are not in the USA so I will enlighten you about the situation here, especially in CA. There is nothing we can do to clean up, regulate or adjust voltage here. In fact, just about the only thing our power companies will respond to is downed lines or arcing and that is only to prevent getting sued if there is a fire and / or personal injury, which, here in CA, has resulted in millions of dollars in lawsuits over the years. I will have to work with whatever the power company provides.
Terry, a few questions for you:
-For measuring current I'm just using my Klein DMV in amp mode, hooking up in the circuit in series. Would a clamp on meter be a better and more accurate way of testing?
-This is completely unrelated to this issue but got be thinking. Above you mentioned an expected 90 deg shift in phase when using an inductor. Is this a hard, fast rule in electronics? Does it apply to any inductor, any application, in series, in parallel? I'm thinking about speaker crossovers and how often we see a driver in that crossover needing to be hooked up in reverse phase. Maybe I should start a new thread for this one if it isn't a simple answer!
Thanks,
Eric
I do have a variac and can test the 96 VA unit as suggested as well and check current on the primary side while secondary is unload.
There is some question about the power coming into my house and how clean it may be. Some of you are not in the USA so I will enlighten you about the situation here, especially in CA. There is nothing we can do to clean up, regulate or adjust voltage here. In fact, just about the only thing our power companies will respond to is downed lines or arcing and that is only to prevent getting sued if there is a fire and / or personal injury, which, here in CA, has resulted in millions of dollars in lawsuits over the years. I will have to work with whatever the power company provides.
Terry, a few questions for you:
-For measuring current I'm just using my Klein DMV in amp mode, hooking up in the circuit in series. Would a clamp on meter be a better and more accurate way of testing?
-This is completely unrelated to this issue but got be thinking. Above you mentioned an expected 90 deg shift in phase when using an inductor. Is this a hard, fast rule in electronics? Does it apply to any inductor, any application, in series, in parallel? I'm thinking about speaker crossovers and how often we see a driver in that crossover needing to be hooked up in reverse phase. Maybe I should start a new thread for this one if it isn't a simple answer!
Thanks,
Eric
Most meters do not have AC amps range. Those that do are on the expensive side, and bulky.
Use a digital clamp meter, or the plug in type units, as in the picture, they will tell you power factor, you may not need a scope after that.
Random image off the net, no ties to seller, in the $25 range here for decent units.
Very handy on small single phase loads.
Use a digital clamp meter, or the plug in type units, as in the picture, they will tell you power factor, you may not need a scope after that.
Random image off the net, no ties to seller, in the $25 range here for decent units.
Very handy on small single phase loads.
For the lift, a portable battery powered scope would be necessary to make safe measurements,
because it can safely float wrt ground, if rated for 600VAC or more isolation.
But it is likely you won't require this to get the lift working. A good DVM should be enough.
An inductor works according to: V = L x di/dt.
With sine waves, the inductor current lags the inductor voltage by 90 degrees, since d( sine (wt) ) / dt = cos (wt).
The cos(wt) peaks at 0 degrees, and the sine(wt) peaks at +90 degrees.
More complex circuits than an ideal inductor can have other amounts of phase shift than 90 degrees,
and then the phase shift can also vary with frequency.
https://pressbooks.online.ucf.edu/osuniversityphysics2/chapter/simple-ac-circuits/
because it can safely float wrt ground, if rated for 600VAC or more isolation.
But it is likely you won't require this to get the lift working. A good DVM should be enough.
An inductor works according to: V = L x di/dt.
With sine waves, the inductor current lags the inductor voltage by 90 degrees, since d( sine (wt) ) / dt = cos (wt).
The cos(wt) peaks at 0 degrees, and the sine(wt) peaks at +90 degrees.
More complex circuits than an ideal inductor can have other amounts of phase shift than 90 degrees,
and then the phase shift can also vary with frequency.
https://pressbooks.online.ucf.edu/osuniversityphysics2/chapter/simple-ac-circuits/
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They do, but only for pure (ideal) inductors. If you look at the model of the transformer I posted a page or two ago, you will see some inductors and some other components inside the transformer model. Together the components form a more complex phase shifting network that will in part depend on load current. Therefore if you want to measure real power going into your transformer, you would need to measure the actual phase angle.
Basically,not a simple answer.
Can you identify the variables for the equations, I'm not familiar with all:
V = Voltage
L = Inductance
x =
di =
dt =
wt =
Thanks,
Eric
V = L x di/dt
V = Voltage
L = Inductance
x = times
di = derivative of current
/dt = with respect to time
w aka "omega" = 2 times Pi times angular frequency "f"
t = time
The (wt) makes up a radian frequency x time argument for the sine or cosine function.
The di/dt is a simple bit of differential calculus, first used back in Newton's time.
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With some current steering diodes? Or let some reverse current 'charge' up the battery?
Something is really wrong with this design... not just the transformer but the entire installation.
This "system" is using almost 70 watts just doing nothing... about 1.7 Kw per day. shouldn't there we an ON/OFF switch between the 120 and the transformer?
Yep, I agree. But it was never part of the original design. If problems persist, one of the plans is to install a 3-way switch at the top and lower landing that turns the 120 on / off.
Isn't 70 VA roughly 42 watts?
I usually go back to the basic equations... P=IV. I should have used the AC equation though, which in general brings in the SQR(2). But, like the other guy said... you do need to know the power factor too because a transformer is being used... that's an inductor, huh? So, there will be a phase shift.
The fact that no ON/OFF switch is in the system might be an indication of why the parts fail so much... huh?
But, reading through the posts... I see you did decide to put a three way AC switch.