Advice on ripple current - UK Vintage Radio Repair and Restoration Discussion Forum

Luxman1050 · 2nd Jul 2020, 12:16 pm

HI all can someone tell me how ripple current is worked out in basic terms. I need 330mA ripple max now data sheets showing at 100hz gives figures of 0.6 0.2 etc how do I now from that reading what the actual ripple current is. It seems all data sheets no longer give mA measurment instead your getting these 0.2 etc figures.
I know it's all to do with heat etc but say reading of 0.4 does that mean 400mA?
Cheers Chris

ms660 · 2nd Jul 2020, 12:26 pm

Multiply the ripple current that's given by the frequency correction factor...Eg: 100mA*0.4 = 40mA.

Lawrence.

Diabolical Artificer · 3rd Jul 2020, 7:26 am

Attaching the datasheet might make more sense than "0.6 0.2" which could be anything - 0.6 of the patience of a good woman, 0.2 oderosity v's wearabilty of this pair of socks I found on the floor?

Andy.

Radio Wrangler · 3rd Jul 2020, 7:54 am

Ripple current creates heat due to the ESR of the capacitor. I squared R. Simple. Heat creates temperature rise and that drives the loss of water content by vapour leaking past seals. Also simple.

Where it gets more complex is that the charging current of a capacitor is not DC, is not sinusoidal, and is a highly distorted pulse. The discharge current could be linear, could have speech/music modulation, or it could be anything.

So we retreat from the complexity and wild variety of cases, and say that because heating is involved, then it is the RMS current that is appropriate. Good, complexity simplified.

This brings in a second problem. Ordinary multimeters on AC ranges rectify the signal and multiply by a number chosen to give the RMS value if the input was a sine wave.
But the charge waveform is a long way from a sinewave, and large errors can result.

So you need to use a true-RMS meter, and you need to make sure its bandwidth is sufficient to capture the harmonics of that charging waveform.

When it comes to analysing a design, LT spice is quite decent. It has fairly thorough models of many capacitors and lots of rectifiers. You need to make your own transformer model but that's easier than it looks. It has tools for calculating the RMS values of any waveform.

David

daviddeakin · 3rd Jul 2020, 9:04 am

what MS660 said

2nd Jul 2020, 12:16 pm	#1
Luxman1050 Octode Join Date: Apr 2019 Location: Margate, Kent, UK. Posts: 1,728	Advice on ripple current HI all can someone tell me how ripple current is worked out in basic terms. I need 330mA ripple max now data sheets showing at 100hz gives figures of 0.6 0.2 etc how do I now from that reading what the actual ripple current is. It seems all data sheets no longer give mA measurment instead your getting these 0.2 etc figures. I know it's all to do with heat etc but say reading of 0.4 does that mean 400mA? Cheers Chris

2nd Jul 2020, 12:26 pm	#2
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Ad ice on ripple current Multiply the ripple current that's given by the frequency correction factor...Eg: 100mA*0.4 = 40mA. Lawrence.

3rd Jul 2020, 7:26 am	#3
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,667	Re: Advice on ripple current Attaching the datasheet might make more sense than "0.6 0.2" which could be anything - 0.6 of the patience of a good woman, 0.2 oderosity v's wearabilty of this pair of socks I found on the floor? Andy. __________________ Curiosity hasn't killed this cat...so far.

3rd Jul 2020, 7:54 am	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,896	Re: Advice on ripple current Ripple current creates heat due to the ESR of the capacitor. I squared R. Simple. Heat creates temperature rise and that drives the loss of water content by vapour leaking past seals. Also simple. Where it gets more complex is that the charging current of a capacitor is not DC, is not sinusoidal, and is a highly distorted pulse. The discharge current could be linear, could have speech/music modulation, or it could be anything. So we retreat from the complexity and wild variety of cases, and say that because heating is involved, then it is the RMS current that is appropriate. Good, complexity simplified. This brings in a second problem. Ordinary multimeters on AC ranges rectify the signal and multiply by a number chosen to give the RMS value if the input was a sine wave. But the charge waveform is a long way from a sinewave, and large errors can result. So you need to use a true-RMS meter, and you need to make sure its bandwidth is sufficient to capture the harmonics of that charging waveform. When it comes to analysing a design, LT spice is quite decent. It has fairly thorough models of many capacitors and lots of rectifiers. You need to make your own transformer model but that's easier than it looks. It has tools for calculating the RMS values of any waveform. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

3rd Jul 2020, 9:04 am	#5
daviddeakin Hexode Join Date: Apr 2007 Location: W Yorks, UK. Posts: 407	Re: Ad ice on ripple current what MS660 said Attached Thumbnails