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Tantalum follow-up

My thanks to all who responded to my 'Tantalum failures' thread.

Having looked at all the options, I intend to replace the tants with Multi Layer Ceramic Caps - probably TDK's 10uF/50V part, (always assuming of course that we can get them in the UK to the requisite spec.).

The ripple voltage with the tantalums was dominated by the I*esr product, (by a factor of around 5:1 over dV/dt), so we can get away with sigificantly less capacitance and I calculate that 100uF will be more than enough, in terms of ripple voltage and ripple current requirements.

I accept that these parts can fail quite spectacularly, due to mishandling during assembly, but we already have an array of 14 470nF surface-mount ceramics in parallel with the tantalums on the present design and have had just two failures out of around 2800 capacitors, so we can happily live with that level of reliability.

My thanks again for all the contributions.

Ted

Reply to
edward.wilson
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Hello Edward,

It depends on how much time these systems have clocked under load so far. Sometimes the caps take the ripple hit for a while and then after x number of hours you might see the failure rate run up.

Regards, Joerg

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Reply to
Joerg

Ted, as a fly on the wall during that interesting thread, can you keep this community updated on how things pan out with the changed caps?

Thanks

Reply to
budgie

Hello

Since posting this follow-up, things have moved on and it would appear that there are significant reliability problems with MLCCs that will probably preclude their use in our application.

At the moment, the most likely contender looks to be solid polymer aluminium, although I've yet to confirm that we can get these in a suitable voltage rating for our application. There's also MLPs to consider, as suggested by Mike Monett.

I'm having all sorts of problems with net access at the moment, so I've not been able to check a lot of the details on the various parts that have been suggested.

Anyway, it's Friday afternoon, my head's suffering from capacitor overload, and I'll be going home shortly and will tackle things afresh on Monday.

Once things are sorted, I will put an update on here. (By the way, if you check the original thread, you will see there have been several further posts since I posted this follow-up).

Regards

Ted

Reply to
edward.wilson
[...]

Ted, it seems quite a few people are interested in what you decide to use and why, so have a good weekend and we hope to see you again Monday.

Personally, I'd like to see if you can confirm that drilling a hole in a MLP and driving a nail through it won't affect it very much. For a warplane with shrapnel flying around, that has to be a positive attribute:)

Mike Monett

Reply to
Mike Monett

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