emiller233
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Isnt that 91Adc for the output amperage? I am trying to find the maximum input amperage at 480 VAC so I can have all my currents for a list. our UL certifying agent wants a report on every device
Transformer current calculation help for In-rush and current consumption
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Isnt that 91Adc for the output amperage? I am trying to find the maximum input amperage at 480 VAC so I can have all my currents for a list. our UL certifying agent wants a report on every device
How about this formula:
AC amps = (DC watts)/(Vac x 1.732 x PF x Efficiency)
I get 56.4 amperes AC input at 480VAC using Vin = 480VAC; Amps dc = 91A; Vdc = 330VDC; PF = 0.8; Efficiency = 80%
From the spec sheet
eff 0.87
pf 0.69
min v for rated output 30000 w/330 vdc is 396 vac
30000/330 = 90.91 rounded to 91 A dc (same as spec sheet)
30000/(1.732 x 396 x 0.87 x 0.69) = 72.86 rounded to 73 A ac
at 480 his i may be < 73 A ac
30000/(0.87 x 0.69) / (1.732 x 480) = 60.11 A ac
50 kva either way, I would still use a 75 kva, run cooler
I'm not sure if i is linear with a solid state convertor???
emiller233
Senior Member
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- pittsburgh, pa
this forum is awesome! I've read many helpful articles on here, but never had to post anything until now...
thanks for all of the help!!!!
thanks for all of the help!!!!
The 73Aac comes the relationship between the DC and AC currents. So 91Adc results in 73Aac. Assuming reasonably smooth DC which it ought to be in this application.
The 91Adc is simply from the 30kW and 330Vdc.
What would be useful to know is what converter topography is being employed. That might answer some of the apparent anomalies.
The 91 dc output is not proportional to the i input of 73 ac
the unit is rated/regulated 330 vdc 30000 w or 91 A dc regardless of the input voltage
ac input range per the spec sheet is 396 to 528 vac
so same rated dc output over that range
input kva = 30000/(0.87 x 0.69) = 50 kva
and since pf and eff are ~ constant per spec sheet
so for various vac input the corresponding i ac input
396 73 A
480 60 A
528 55 A
approximately
the unit is rated/regulated 330 vdc 30000 w or 91 A dc regardless of the input voltage
ac input range per the spec sheet is 396 to 528 vac
so same rated dc output over that range
input kva = 30000/(0.87 x 0.69) = 50 kva
and since pf and eff are ~ constant per spec sheet
so for various vac input the corresponding i ac input
396 73 A
480 60 A
528 55 A
approximately
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I could see some nonlinearity in the conversion between RMS AC amps and average (mean) DC amps, but not enough to worry about.
And it does not sound like there would be any constant magnetizing current term if it is just a rectifier.
I agree, output amps will be proportional to input amps, just have to make assumptions about the filtering if any to figure out what that constant is.
And it does not sound like there would be any constant magnetizing current term if it is just a rectifier.
I agree, output amps will be proportional to input amps, just have to make assumptions about the filtering if any to figure out what that constant is.
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"The 91 dc output is not proportional to the i input of 73 a"
is what you said.
That's incorrect and the point I was addressing.
But, let's leave at that before one of the mods intervenes.
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- Retired PV System Designer
You rang?
It seems clear to me that the output DC voltage is not necessarily proportional to the input AC voltage, given the spec.
But there would have to be some pretty interesting circuitry inside to make the output current not proportional to the input current, at least for a given voltage.
If the proposal is that the constant of proportionality as you vary the DC load is a function of input voltage, I can see how that could happen.
You are both right, and therefore both wrong.
It seems clear to me that the output DC voltage is not necessarily proportional to the input AC voltage, given the spec.
But there would have to be some pretty interesting circuitry inside to make the output current not proportional to the input current, at least for a given voltage.
If the proposal is that the constant of proportionality as you vary the DC load is a function of input voltage, I can see how that could happen.
You are both right, and therefore both wrong.
Misunderstood your post
dc i out is not proportional to input i
dc i is constant
ac i input varies with voltage as I illustrated
input kva is constant
voltage varies for rated output per the spec sheet
therrfore so must current since kva = sqrt3 x v x i
if v goes up i must go down for kva (and pf and eff) to be constant
we can disagree yet show respect
where does the sqrt2/3 come from? How is it derived?
i know for a diode rectifier 3 ph
Vdc = 3 x sqrt2 x Vll ac rms / Pi = 1.35 Vll rms
if Vll rms = 480
Vdc = 650 dc or +/- 325 vdc
single ph 2 sqrt2 / Pi = 0.90
so for 120 vac ~ 108 vdc
You rang?
It seems clear to me that the output DC voltage is not necessarily proportional to the input AC voltage, given the spec.
But there would have to be some pretty interesting circuitry inside to make the output current not proportional to the input current, at least for a given voltage.
If the proposal is that the constant of proportionality as you vary the DC load is a function of input voltage, I can see how that could happen.
You are both right, and therefore both wrong.
look at the spec
the dc output v is held to a tight tolerance over the spec input range
pretty worthless dc power supply if it didn't
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I agree. (Depending, of course, for what purpose the DC supply is intended.)look at the spec
the dc output v is held to a tight tolerance over the spec input range
pretty worthless dc power supply if it didn't
And I do not see anything about that that contradicts what I said.
I can definitely see that for a regulated supply with a buck or boost converter the input current can vary as a function of input voltage for a constant output current. Or if dissipative linear regulation is are (however unlikely that is in such a large supply) the input current could be strictly proportional to output current over a wide range of input voltage.
Line regulation at rated load
voltage mode w/sensing wire
nominal input voltage +/- 10%
440/480 or 396-528 (rated operating range)
Rated dc v is +/- 0.01% of full scale
for 330 vdc +/- 33 mV
that is tight
better be for $20k lol
so v dc is constant over a varying input v of 396-528 vac for a constant load
so i dc is constant
since eff and pf are constant and v vac varies i input must vary (inversely) for a constant output
voltage mode w/sensing wire
nominal input voltage +/- 10%
440/480 or 396-528 (rated operating range)
Rated dc v is +/- 0.01% of full scale
for 330 vdc +/- 33 mV
that is tight
better be for $20k lol
so v dc is constant over a varying input v of 396-528 vac for a constant load
so i dc is constant
since eff and pf are constant and v vac varies i input must vary (inversely) for a constant output
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- Retired PV System Designer
:thumbsup:
Well stated and leaving no ambiguity about what you are referring to.
Well stated and leaving no ambiguity about what you are referring to.
:thumbsup:
Well stated and leaving no ambiguity about what you are referring to.
are you 'taking a piss'?
lol
Besoeker will know what that means lol
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No, I was being quite serious.
Your last post was a refreshing finish to a warm but not yet heated exchange where both posters were right but were talking at cross purposes about different things.
When I am 'taking a piss' it will look like this.
:angel:
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