Electronics Advice

[CB]

I have a dead TP Link Homeplug adapter.

This video

points to a suspect capacitor and on inspection I find that this capacitor on my unit has failed (top of the can has burst open).

Now I need a 1500UF 6.3V Capacitor.

I drive past Maplin twice a day and they can supply either a 1000UF or

2200UF for less than a quid.

RS can supply exactly the right component for less than a quid plus GBP4.95 for postage and packing.

CPC Farnell can supply exactly the right component for less than a quid but the minimum order is GBP5.00

Does anyone know how critical these things usually are, could I get away with either 1000UF or 2200UF from Maplin (and if so which would be best) or do I really need to load up my basket with GBP4.50 worth of junk from Farnell in order to get exactly the right component?

Any help appreciated.

Thanks. Chris.

[sintv]

If you have space the 2200 & 1000 in series would give you 1600. If not always go for the higher value. I repaired mine n I seem to remember there wasn't much space inside

[dennis]

Take it back for a refund.

[LumpHammer]

According to the Wikipedia article at

electrolytic capacitors typically have a tolerance of +/- 20%, so the exact value may not be critical.

[newshound]

I'd use the big one if it fits, the small one if it doesn't. I would not expect it to make much difference (it is probably smoothing the power supply rail).

[fred]

In article , CB writes

You should only use a capacitor that has been designed or is suitable for use in switched mode power supplies. These will have a high ripple current rating, low Effective Series Resistance (ESR) and Effective Series Inductance (ESL). You should also choose a 105degC rated device (rather than 85deg) as it will have longer life. The value itself is not that critical but using a grossly larger capacitor may affect the stability of the supply design.

If you're not confident to make your own choice then post the part numbers of the components you have researched and we can give you some further advice.

[Andrew Gabriel]

That rating can only be the PSU output smoothing capacitor.

Both will probably work fine, the 2200uF being slightly better, but if the 1000uF fits better in the available space, go for that.

The other thing to check is the operating temperature. Standard electrolytics are 85C, high temperature ones are 105C. Running over temperature will reduce the rated life, but within these limits, either will work.

Also, in case you didn't know, these capacitors are polarity sensitive and must be put in the right way around.

[fred]

In article , sintv writes

A series connected capacitor pair can never have an effective value greater than that of the lowest valued component. The combination you describe would result in a value of 687.5uF, from (C1xC2)/(C1+C2).

[CB]

Well the one that has come out is 1500UF 6.3V, "Lelon"? (I asume that this is the manufacturer) RXY105C H105M. Length 15mm Dia 10 mm.

The potential replacements are Farnell

(Exact Replacement).

Maplin 2200UF

or Maplin 1000UF

Although noting a comment made in another reply it is very crowded in there and physical size is as important as electrical properties. I can see from the Farnell website that theirs will fit, the Maplin site does not give physical sizes.

[alan_m]

Or from CPC/farnell (slightly better spec)

The can size may be larger for higher the operating voltage so the 25V volt versions from Maplin could be physically larger.

Don't forget CPC have a catalogue full of useless gadgets you can order for christmas presents to make up your order value :)

[Tim Watts]

Buy it from CPC and buy some batteries to make up the difference - CPC's alkalines are cheaper than most other places IME.

[fred]

That's absolutely fine, full spec quoted and boxes ticked for ripple, impedance and frequency, Panasonic is a quality component. Note that the min order is 5 off and that the price is + VAT. One consolation on the

5quid + vat min order on CPC is that there's a good chance you'll find a wanted filler to make up the order value. Patch or audio cables being a good example.

If you can physically fit a 10V or higher rated one from the same range then do so as it will improve reliability.

In the absence of a quoted spec I'd suggest that these will only be suitable for audio applications and not switch mode. Also, even an audio cap with a 25V rating will likely be oversize.

As mentioned elsewhere, watch the polarity, the wide band on the cap is negative and may be matched by a filled half circle on the board silk screen or they may mark the positive pole with a simple plus. Push the cap right down to keep the leads short.

Feel free to punt any others that you want to check.

Good luck.

[fred]

Well spotted and MOQ is only one for that one so prob enough cash left from the fiver to buy a one of their worthless Christmas trinkets ;-)

[meow2222]

2200uF is better than 1000uF, the latter might prove barely adequate.

FWIW 105C & greater voltage rated caps last longer, but more volts = more size, which you dont have.

You can get such caps out of a fair percentage of scrap electronic items, why pay & wait.

NT

[Martin Brown]

I suspect you actually want a high ripple type for the switched mode supply (especially based on your description of how it failed). Maplin will stock pretty ropey ones that are not rated for higher currents.

I confess I am a bit surprised that they can cook their capacitors as it isn't a particularly high power device ISTR

Worth seeing if Rapidonline will do one or five for a better price.

You need to be able to physically fit the component in and it needs to be the right sort to survive the environment. Not all electrolytic capacitors are happy in switched mode supplies (and blow their tops).

Tolerances of capacitors are such +/-20% that anything in the

1000-2200uF range ought to work OK but it also needs to be able to cope with the ripple current in the PSU design as well.

[John Rumm]

Yup, my recapping cap of choice...

[Ian Jackson]

In message , sintv writes

Beware of connecting electrolytics in series unless you also add a (high-value) resistor in parallel with each to equalise the DC voltage across them - especially if the rated working voltage of either is less than the total voltage across them both. This is because electrolytics have a slight DC leakage current (hopefully only a few microamps), and you could end up with the DC voltage across one capacitor exceeding its rating.

For example, if you have a 20V DC voltage across a 1000uF, 25V capacitor, and the capacitor fails, you could replace it with two 2000uF in series. However, make sure that neither voltage rating is lower than

25V (say 15V). If it is, and their leakage currents are unequal, without the resistors you could have (say) 16V across one capacitor and 5V across the other. Adding across each a high value resistor - but low enough to pass enough current to swamp the leakage current - will ensure that the voltage across each capacitor is close to a safe 12.5V.

[CB]

Thanks to all who responded - Its looks like CPC/Farnell with some fillers to make up the order.

Thanks again.

Chris

[fred]

You're welcome.

I only noticed after responding that the rubycon cap is longer at 20mm c/f the 16mm on the panny, may be ok or may not.

[meow2222]

No, 1000uF cap can not be assumed to have enough capacitance. There's a reason they went up to 1500 in such a tight space.

NT