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Ventilation blocking factor used for safety approval etc.?

Working on a design where the electronics gets a bit hot.

Safety margin for insulation temperature is being calculated.

This part of the design is directly influenced by the enclosure ventilation.

Trying to find source for a design rule for a ventilation blocking factor as the vents are expected to "fur-up" during the life of the product and also to give the design a bit of margin.

Questions to sci.electronics.design group is:

What ventilation blocking factor is used during for example, equipment safety approval testing or does the test limits take into account a fall off in ventilation efficiency with time?

regards

Louiiv

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Reply to
Louiiv
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Why not measure the temperature at the hot point and have a thermal shut down and warning light?

Reply to
Raveninghorde

I believe that's the only method a test lab would accept. Unless maybe, just maybe, they'll let it fly if there is a rigorously enforced maintenance schedule that includes this vent.

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Regards, Joerg

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Reply to
Joerg

Thanks for the replies.

Even with thermal shutdown cct. the test houses need to perform the test to some standard.

Looking for info on if they test with some of the ventilation blocked to simulate a single fault or the effect of performance drop.

regards

Louiiv

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Reply to
Louiiv

I can only tell you for medical, EN60601. I've never seen them test with blocked vents but of course they do their water pour tests and the artificial finger thingie. But: They do go through your docs and want to see the hazard analysis, with rather intense scrutiny on anything that is connected to mains or looks like high power. Occasionally they came back with a question, including thermal stuff. Then we told them about the thermal lock-out described on pages 97 or somewhere and everybody was happy.

If you have a thermal shutdown with warning in there, what would be your concern regarding failing the agency cert?

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Regards, Joerg

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Reply to
Joerg

A bit off topic, The book "hot air rises and heat sinks" by Tony Kordyban is a fun read. Oh I think he had a web site...

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I think there is some sort of discussion/forum? Perhaps you could ask the question there.

George H.

Reply to
George Herold

In general, the standards for professional equipment only require that special ventilation requirements be layed out plainly in the installation instructions; the warning 'consult installation guidelines' must be written on the equipment labelling, when this is the case.

Be advised that single fault abnormal limits must not be exceeded when 'ventilation' or thermal limiters fail (air movers stalled, vents blocked or sensors open/short).

For consumer audio ( ...go figure ) the normal thermal rises are recorded in a standard shelf or 'corner' that severely restricts airflow in the immediate viscinity of the DUT (...for UL, anyways). The units are run with 'typical' loading under those conditions, not 'rated'.

RL

Reply to
legg

It would probably be more effective to call a test house and discuss it.

Reply to
JosephKK

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