Building 4.3 - is there a difference between 25v and 10v caps? can I use 25v for both?


 
L

Louis P

New member
Hello!

Been lurking for a while and LOVE this community. I'm planning on building v4.3 very shortly, and not being an electronics expert, I was wondering if I could use 25v caps for both the 10v and 25v 100uF listed in the bill of material. I would assume yes, but wanted to be sure.

Thanks!
Louis
 
With caps higher voltage is always acceptable, but higher voltage caps can be larger, so you need to make sure they will physically fit in the spot and lead spacing will work.
 
I just tested and the 100uF 25V (the biggest capacitor in the standard BOM) fits when used in all 4 capacitor holes and would be suitable for use in all of them. The lead spacing holes for our 100uF/10V and 47u/25V are 2.5mm, so the spacing is actually for the larger 25V capacitor already. I used the wrong footprint when I designed the 4.0 HeaterMeter, it should be 2.0mm lead spacing, but it is close enough that I never revisited it.

But also to confirm what Ralph said, you can always use a higher voltage rated capacitor (i.e. 25V instead of 10V), and in our case we can even use a 100uF in place of the 47uF (and would actually be better for voltage mode output).
 
Bryan Mayland said:
I just tested and the 100uF 25V (the biggest capacitor in the standard BOM) fits when used in all 4 capacitor holes and would be suitable for use in all of them. The lead spacing holes for our 100uF/10V and 47u/25V are 2.5mm, so the spacing is actually for the larger 25V capacitor already. I used the wrong footprint when I designed the 4.0 HeaterMeter, it should be 2.0mm lead spacing, but it is close enough that I never revisited it.

But also to confirm what Ralph said, you can always use a higher voltage rated capacitor (i.e. 25V instead of 10V), and in our case we can even use a 100uF in place of the 47uF (and would actually be better for voltage mode output).
Click to expand...

Thanks Bryan! And especially for that last piece of info, as I'm doing my BOM and noticed that neither Mouser nor Digikey have the 47uF in stock. I have found a Panasonic one which I think could fit the bill (here). Since the original 47uF cap in the parts list was the DD series of Nichicon (I assume smaller height, at 7mm based on what I could understand of the spec sheet), I thought this Panasonic (same 7mm height, but 6.5mm instead of 5mm diameter) would fit physically, although the electrical specs seem a bit different.

If I understand correctly, you're saying I could even use a 100uF instead of the 47uF, so that's great! Just wondering how much of a gamble that would be given that I'm not sure anyone ever used that value :rolleyes:

Thanks again!
 
Correct, you can just use another 100uF instead of the 47uF. The reason the 47uF one is in the schematic is for pulse output mode where, in conjunction with the spec'd blower, had juuuuuust the right balance between smoothing the output to quiet the blower and not being too large that you lose the ability to run the blower at low speed.

That's rarely used these days since the default voltage output mode provides much better control across the entire blower output range. When used in voltage mode, the larger the capacitor the better (up to a point, obviously).

Ironically, the only people that are probably using pulse output mode are those who are driving SSR, where removing the capacitor entirely would provide a cleaner output signal.
 
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