PSU for Caiman with Pics

[UV101]

whats the height of the std cap? Can you fit a 30mm high cap in there? a 35mm would be good but I think that will be pushing it!!!

[here we go again]

whats the height of the std cap? Can you fit a 30mm high cap in there? a 35mm would be good but I think that will be pushing it!!!

From memory I think it's about 27mm - I looked at this quite a while ago now and managed to find a Panny TSUP that fitted OK.

A more elegant solution IMO is to remove the single squat 10,000u cap and replace it with 2 radial caps on their side - you'll notice on the silk screen that all the holes and tracks are already there. The research I did at the time gave me several more options - again from memory the smaller lytics can be up to 18mm dia and 25mm height - which means you can get a couple of 4700u/16v Panny FC's in there.

Actually if you are using a new linear psu you could probably get away with a lower total capacitance by using a pair of 3300u caps - with a 25V rating!! - I think I did actually buy a pair of suitable FC's and a couple of Ruby ZL's too - just never got them fitted

worth experimenting with I think but I reckon it's a better option.

[NRG]

Yes, the diode on the DC input is mainly for protection.

HI Leo, how are you doin! have you 'scoped the input and out put of the diode

[HighFidelityGuy]

Thanks for the excellent write up Martin.
I've just ordered a SuperTeddyReg board to try this out for my self.

I've been thinking about the issue of the main reservoir cap being run close to it's 16V rating and I was wondering if it would be possible to simply remove it from the equation by replacing it with a higher voltage equivalent inside the new power supply itself? Is this likely to have any negative effects?

I guess doing this will put the cap on the opposite side of the input diode D1 and fuse but that could easily be resolved if it was an issue.

Thanks.

[MartinT]

Hi Dave

I don't think you want to remove the big regulator from the circuit altogether, being close to the area of demand as it is. However, you could replace it with a smaller value higher voltage stubby cap and all would be well, the ST keeping it well topped up with clean DC. If anything, you want to ensure that there is plenty of reservoir on the input to the ST.

I am just playing on the built-in tolerances of a 16V cap by feeding it with 16V! No explosion yet...

[HighFidelityGuy]

Thanks Martin, that's a good point about keeping the cap close to the area of demand. I hadn't thought about it like that.
Ok, so like you say I could switch to a lower value higher voltage cap or as I think somebody else mentioned it would be possible to use two smaller caps. So I just need to work out which would allow the best balance.

Would using less capacitance be detrimental or wouldn't it really matter when using a big external linear supply? Also, I think I read somewhere that using two smaller caps can allow lower ESR than a single bigger cap. Is that something that could be beneficial in this application?

Many thanks.

[MartinT]

I don't think a smaller value will be detrimental in this application, especially if you can use a good quality type, e.g. Elna Silmic, Black Gate, Sanyo Os-Con etc. If you can fit two smaller caps that can work too, but check that the ESR is really better than a single larger one.

[HighFidelityGuy]

Ok, thanks Martin. I'll see what I can find.
Another option I've thought of is laying one large cap on it's side and squeezing it in that way. This would mean extending the wires down to the board though. Do you think the extra wire length would cause any issues?

Also I've noticed that the Elna cap mod calls for a few 16V caps. Do you know if these 16V caps are at risk as well?

Apologies about all the questions.

Cheers.

[MartinT]

Yes, a large reservoir lying down would be fine.

The 16V Elnas I think are all the other side of the 12V regulator, so no problem.

[fmzip]

Just curious, how much did this little project cost all said and done? Trying to weigh by options on the exact same project. Where did you end up getting the toroid from?