Voltage regulating electrolytics? - UK Vintage Radio Repair and Restoration Discussion Forum

Biggles · 4th Sep 2018, 11:30 pm

I was reading a copy of Wireless World from 1936 recently and my attention was drawn to an advert for electrolytic capacitors. It said that the capacitors would actually regulate or limit the voltage across them due to the leakage current increasing at the specified working voltage. This was a new one to me. It's as if they accepted this characteristic as a benefit. I would have thought that the capacitor could have gone into a runaway condition and eventually failed, rather than remaining at a steady value of leakage current. Surely any leakage current is accepted as a bad thing nowadays. Interesting.
Alan.

Craig Sawyers · 5th Sep 2018, 6:28 am

I have a 1938 book on Electrolytic capacitors. Section 5 is titled "Regulating Type of Wet Electrolytic Capacitors". It was a specific design that offered those enhanced leakage characteristics.

ricard · 5th Sep 2018, 8:50 am

Could it be that this effect could only be exploited in this way in wet electrolytics?

Speculating here, but could it be that the dielectric oxide was thicker in these early capacitors and thus able to withstand the abuse due to leakage more?

GMB · 5th Sep 2018, 9:34 am

All electrolytics exhibit this kind of effect, especially when the oxide layer has aged and so needs reforming. They behave a bit like zener diodes and anyone designing a reformer should bear this in mind.

Wet ones will be able to stand being in the break-down state for longer because they have loads more electrolyte than the modern kind. Electrolyte is used up in this condition.

I think this effect is only useful as a surge limiting feature. I have found that the working voltage of electrolytics rises towards the applied voltage, so while acting to limit the voltage, that voltage will also increase.

Refugee · 5th Sep 2018, 9:56 am

Surely is that not just another was of specifying a surge voltage.
If leakage was sustained for any time the capacitor would get hot and go pop.

Biggles · 5th Sep 2018, 5:11 pm

My thoughts too Refugee.
Alan.

Craig Sawyers · 5th Sep 2018, 6:03 pm

Has no-one read the page I attached to post #2?

I'm not saying it is necessarily a good idea, or that the capacitor will run really hot (up to ~10W from the graphs). All I am saying is that it seemed to be a valid design option in 1938, 80 years ago, and corresponded to the advert in WW that the OP saw in a 1936 issue.

4th Sep 2018, 11:30 pm	#1
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Voltage regulating electrolytics? I was reading a copy of Wireless World from 1936 recently and my attention was drawn to an advert for electrolytic capacitors. It said that the capacitors would actually regulate or limit the voltage across them due to the leakage current increasing at the specified working voltage. This was a new one to me. It's as if they accepted this characteristic as a benefit. I would have thought that the capacitor could have gone into a runaway condition and eventually failed, rather than remaining at a steady value of leakage current. Surely any leakage current is accepted as a bad thing nowadays. Interesting. Alan.

5th Sep 2018, 8:50 am	#3
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Voltage regulating electrolytics? Could it be that this effect could only be exploited in this way in wet electrolytics? Speculating here, but could it be that the dielectric oxide was thicker in these early capacitors and thus able to withstand the abuse due to leakage more?

5th Sep 2018, 9:34 am	#4
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: Voltage regulating electrolytics? All electrolytics exhibit this kind of effect, especially when the oxide layer has aged and so needs reforming. They behave a bit like zener diodes and anyone designing a reformer should bear this in mind. Wet ones will be able to stand being in the break-down state for longer because they have loads more electrolyte than the modern kind. Electrolyte is used up in this condition. I think this effect is only useful as a surge limiting feature. I have found that the working voltage of electrolytics rises towards the applied voltage, so while acting to limit the voltage, that voltage will also increase.

5th Sep 2018, 9:56 am	#5
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Voltage regulating electrolytics? Surely is that not just another was of specifying a surge voltage. If leakage was sustained for any time the capacitor would get hot and go pop.

5th Sep 2018, 5:11 pm	#6
Biggles Rest in Peace Join Date: Feb 2004 Location: Hexham, Northumberland, UK. Posts: 2,234	Re: Voltage regulating electrolytics? My thoughts too Refugee. Alan.

5th Sep 2018, 6:28 am	#2
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,991	Re: Voltage regulating electrolytics? I have a 1938 book on Electrolytic capacitors. Section 5 is titled "Regulating Type of Wet Electrolytic Capacitors". It was a specific design that offered those enhanced leakage characteristics. Attached Thumbnails Last edited by Craig Sawyers; 5th Sep 2018 at 6:34 am.

5th Sep 2018, 6:03 pm	#7
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,991	Re: Voltage regulating electrolytics? Has no-one read the page I attached to post #2? I'm not saying it is necessarily a good idea, or that the capacitor will run really hot (up to ~10W from the graphs). All I am saying is that it seemed to be a valid design option in 1938, 80 years ago, and corresponded to the advert in WW that the OP saw in a 1936 issue.