Re: PFC-30 voltage ripple

[Edward C. <ed...@la...>]

Hi Tom,

Unfortunately I think it is what makes the charger "PFC" inherently  
gives it 50Hz ripple.

1 Power drawn from the mains (single phase) must have a cos^2 ripple  
(100Hz) for it to have very high power factor (ranging from 0-200%).  
How much it buffers that ripple internally only the designer knows,  
but I would expect at least some of that to be present on the output.

2 As the charger is an non-isolated design, the -ve bus voltage will  
follow whatever is the lowest instantaneous voltage of the supply,  
either Phase or Neutral. For the half cycle that Phase is positive,  
the -ve will be the same potential (minus a diode drop) as Neutral, or  
Earth. For the half cycle where Phase is more negative than the  
Neutral/Earth the -ve bus voltage will follow the phase voltage.

This constant changing of voltage will induce small but measurable  
currents via capacitance between the non-isolated battery system and  
the surrounding earthed conductors. Running the charger off the  
isolation transformer should have reduced this effect somewhat Perhaps  
connecting the -ve battery terminal to Earth may fix some of this  
induced noise (only when the isolation transformer is present!).

You could measure the AC component of the charge current with a clamp  
meter set to AC to see what ripple is there.

Ed

On 19/10/2009, at 9:57 PM, Tom Parker wrote:

> A couple of weeks ago I blogged about the source of the noise I was
> seeing in the voltage of my battery while the PFC-30 was charging it.
>
> It turns out the charger is injecting 50Hz ripple into the battery
> voltage, which showed up on the oscilloscope. This ripple is real,
> rather than noise coupled into the BMS's ADC circuit. I got rid of  
> it by
> averaging several cycles of the 50Hz.
>
> Bob, are you seeing anything like this from your chargers? I guess
> you're taking care of this on the master side?
>
> See http://carrott.org/blog/archives/108-Charging-Noise.html
> and http://carrott.org/blog/archives/109-Noise-Silenced.html
>