DC to AC inverter input capacitor question

Thread Starter

sdowney717

Joined Jul 18, 2012
648
I am going to replace the input capacitors on the 12 volt side.
They are currently some cheap china brand and are 3300 uf 16v.

I will definetly up the voltage to like 24 vdc. There 12 of these.

Would increasing the 3300uf to a higher value help with surge or be worth doing?
I have seen where some people are putting a farad or more on the DC wires going into the inverter to help with surge starts. Although if they are wider they might not fit the board. They can easily go taller about 1/2 inch. Right now they are about 1.25 inch tall and 1/2 inch wide.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
648
Since they are getting replaced, now is the time to make any changes is all.
I will likely just replace again with 3300 uf, but make them 25v.
 

alfacliff

Joined Dec 13, 2013
2,458
using higher voltage electrolytics will not make anything better, it could fail sooner due to the fact that electrolytics are made to operate at a certain volotage, and if used at a lower voltage, will fail, not enough voltage to maintain the electro chemcal reaction.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
648
I bought these Nippon, got 30 of these 25v 3300uf for about $15.
I read these are a good brand to use. NEW NOS should be fine.
they are 16mm wide and will just barely fit.
The current 16v ones are 13mm wide.

I watched a lot of inverter repair videos on youtube and 25vdc was said to be a much improved choice over 16v for a 12v inverter.

The original caps say LESR Ricon 3300uf 16v
Who knows how LESR they really are! I have been reading bad things about LESR china caps, that they aren't.
Maybe going to these higher volt ones will compensate for that?
 

OBW0549

Joined Mar 2, 2015
3,408
using higher voltage electrolytics will not make anything better, it could fail sooner due to the fact that electrolytics are made to operate at a certain volotage, and if used at a lower voltage, will fail, not enough voltage to maintain the electro chemcal reaction.
I've been in electronics for over 50 years and I've never, NEVER heard of anything like this. Got any references to back up these remarkable assertions?
 

alfacliff

Joined Dec 13, 2013
2,458
only about 50 years of experience. remember when electrolytics were marked in working volts dc, as well as maximum volts? after a number of years (less lately, someone changed the chemical mix) electrolytics used at lower voltages than they are rated start fading. in Yeasu microphones, a 1 mfd cap in series with the mic element fades to a few pf after about 5 years. a 50 volt electrolytic used at around 5 volts max. other places too, such as 12 volt supplies with caps rated at 35 volts and used at 18, fade to nothing after a few years.
 

dl324

Joined Mar 30, 2015
10,755
[snip] they are 16mm wide and will just barely fit.
The current 16v ones are 13mm wide.
When buying capacitors, you should note lead spacing, diameter, and height.
I watched a lot of inverter repair videos on youtube and 25vdc was said to be a much improved choice over 16v for a 12v inverter.
Just goes to show you can't believe everything on the internet. Everyone has a right to their opinion, but that doesn't mean it's right...

The original caps say LESR Ricon 3300uf 16v
Who knows how LESR they really are! I have been reading bad things about LESR china caps, that they aren't.
ESR will change over the life of the cap. It isn't a problem until it gets too high.
Maybe going to these higher volt ones will compensate for that?
Higher voltage rating in smaller package and unbelievably cheap prices don't necessarily increase reliability or performance.
 

OBW0549

Joined Mar 2, 2015
3,408
only about 50 years of experience. remember when electrolytics were marked in working volts dc, as well as maximum volts? after a number of years (less lately, someone changed the chemical mix) electrolytics used at lower voltages than they are rated start fading. in Yeasu microphones, a 1 mfd cap in series with the mic element fades to a few pf after about 5 years. a 50 volt electrolytic used at around 5 volts max. other places too, such as 12 volt supplies with caps rated at 35 volts and used at 18, fade to nothing after a few years.
As you wish, although this is the very first time I have ever heard anyone claim that "electrolytics used at lower voltages than they are rated start fading", or anything remotely similar. And everything I have experienced as a design engineer, and everything I have ever read, says exactly the opposite.
 

alfacliff

Joined Dec 13, 2013
2,458
then someone needs to do a failure analsys on the electrolytics. I change caps in switching power supplies and other stuff every day with the same fault, low capacitance, and usually bad ESR. usually with the rfated voltage on the cap nowhere near the voltage across it.
 

ian field

Joined Oct 27, 2012
6,539
I am going to replace the input capacitors on the 12 volt side.
They are currently some cheap china brand and are 3300 uf 16v.

I will definetly up the voltage to like 24 vdc. There 12 of these.

Would increasing the 3300uf to a higher value help with surge or be worth doing?
I have seen where some people are putting a farad or more on the DC wires going into the inverter to help with surge starts. Although if they are wider they might not fit the board. They can easily go taller about 1/2 inch. Right now they are about 1.25 inch tall and 1/2 inch wide.
If you use an aluminium electrolytic at significantly less than its rated voltage. The caustic electrolyte etches the formed oxide dielectric, this effectively reduces the distance between the plates and increases the capacitance. If you then apply the full rated voltage, the thinner dielectric will pass high leakage current until the dielectric is formed to its normal thickness - assuming it doesn't heat up and burst first.

More important parameters to 'improve' on are; temperature rating - you should be able to get 105 deg-C, and ESR which you should look for the lowest value you can find.
 

OBW0549

Joined Mar 2, 2015
3,408
then someone needs to do a failure analsys on the electrolytics.
Well, "someone" has-- namely, just about every major manufacturer of electrolytic capacitors, along with major users, has published data on capacitor reliability as well as recommendations for temperature and voltage derating.

Googling on the terms "electrolytic capacitor life vs voltage" and "electrolytic capacitor derating guidelines" brings up an ENORMOUS amount of material, none of which supports your claim that operating electrolytics at voltages below their rating reduces their life.

I change caps in switching power supplies and other stuff every day with the same fault, low capacitance, and usually bad ESR. usually with the rfated voltage on the cap nowhere near the voltage across it.
Those are the typical failure modes when aluminum electrolytics are operated at too high a temperature (which can be exacerbated by excessive ripple current), not when they are operated below their rated voltage.
 

ian field

Joined Oct 27, 2012
6,539
As you wish, although this is the very first time I have ever heard anyone claim that "electrolytics used at lower voltages than they are rated start fading", or anything remotely similar. And everything I have experienced as a design engineer, and everything I have ever read, says exactly the opposite.
The formed oxide dielectric etches thinner in the caustic electrolyte, thinner dielectric is basically less distance between the plates, which means higher capacitance.

You can subsequently form such capacitors back to their original rated values, but you have to limit the forming current to avoid overheating.
 

OBW0549

Joined Mar 2, 2015
3,408
The formed oxide dielectric etches thinner in the caustic electrolyte, thinner dielectric is basically less distance between the plates, which means higher capacitance.

You can subsequently form such capacitors back to their original rated values, but you have to limit the forming current to avoid overheating.
Agreed; and that goes double for electrolytics that have been in storage, unpowered, a long time.

Looking through my junk box, I see a Sprague 1500uF, 63V electrolytic that was manufactured back in 1978, when Jimmy Carter was president. It's never been used, never had any voltage applied to it. I wonder if it's any good...
 

ian field

Joined Oct 27, 2012
6,539
Agreed; and that goes double for electrolytics that have been in storage, unpowered, a long time.

Looking through my junk box, I see a Sprague 1500uF, 63V electrolytic that was manufactured back in 1978, when Jimmy Carter was president. It's never been used, never had any voltage applied to it. I wonder if it's any good...
My capacitor re-former was originally designed for measuring high voltage zeners - if I described its workings, that would be the end of the thread.
 
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