Hi Guys
I am using a 240 V to 24 V transformer.
I then put this through a GBPC1204 - Bridge Rectifier Diode, Single, 400 V, 12 A, Module, 1.1 V
I then filter the output with a 4700 uF cap to run a led light bar.
When I measure the current from the 24 AC I measure 2.8 amps.. but when I measure the DC I only measure 1.7 amps
Can someone explain why ..and also if there is way to reduce the current on the 24 volts AC
Thanks
Nick

 

You've observed a common characteristic (but not well known) of a rectifier-capacitor supply.
The RMS current from a transformer into a rectifier-capacitor is always much higher than the average DC output current due to the high peak currents drawn from the transformer at the peaks of the sine wave to charge the capacitor to near the peak voltage.
Typically there's near a 2:1 difference in the two current values, which is why you need to derate the transformer about 50% for a given DC output current.

One way to make the two currents about equal is to use a large inductor in series with the bridge output to smooth the large peak currents.
But the expense and size of such a large inductor precludes it being commonly used for that purpose.
It's cheaper to just use a larger transformer.

 

See

 

You've observed a common characteristic (but not well known) of a rectifier-capacitor supply.
The RMS current from a transformer into a rectifier-capacitor is always much higher than the average DC output current due to the high peak currents drawn from the transformer at the peaks of the sine wave to charge the capacitor to near the peak voltage.
Typically there's near a 2:1 difference in the two current values, which is why you need to derate the transformer about 50% for a given DC output current.

One way to make the two currents about equal is to use a large inductor in series with the transformer output to smooth the large peak currents.
But the expense and size of such a large inductor precludes it being commonly used for that purpose.
It's cheaper to just use a larger transformer.

Hi Thanks for explaining that

 

See
View attachment 137564

Thank you for that
If I go straight from the rectifier to the led with no cap I guess the Ac current should be less.? I will go and try it. I know the led works but not as bright . I know the DCV is only about 22-24V

 

For a resistive load, the current will decrease. In order to calculate everything correctly, you need information about the LED lamp circuit. Is the current stabilized? Or a simple resistive power circuit for LEDs?

 

For a resistive load, the current will decrease. In order to calculate everything correctly, you need information about the LED lamp circuit. Is the current stabilized? Or a simple resistive power circuit for LEDs?View attachment 137566

Hi
all I know from the manufacturer is
POWER 60 Watts
LED CHIP 5W Watt High Intensity CREE
CURRENT DRAW 3.8A @ 12v, 1.9A @ 24v
VOLTAGE 9 to 32v
RAW LUMENS 5,400LM

I also have tested without the cap and the light works ok .. I know it would be a pretty dirty wave but works ok but not as bright with the cap

 

I do not advise you to feed the driver circuit not filtered by power. It can collapse. Those. it is a matter of chance (luck).

 

I do not advise you to feed the driver circuit not filtered by power. It can collapse. Those. it is a matter of chance (luck).

thanks I will leave the cap in the circuit then