The maximum continuous total current on 9477 is 20A, but can I push it to 30A for 50ms?

[AnthonV]

The title says it all I suppose.  I am driving 32 loads at under 1A each on each of the 32 outputs of the 9477.  Not all the loads are on at one time, and each pulse is only about 50ms long.  It might happen (but improbable) that all 32 outputs need to turn on simultaneously, thus pushing the current well above the rated 20A, but only for a very short time.  

Is this ok?  I accept the answers 'yes' or 'yes, but....'

[SnowMule]

Are you out of slots on the chassis?  Seems like a 2nd 9477 and dividing the test system into two segments is probably a safer route. 

[AnthonV]

Yes all my slots are used unfortunately.

[johnsold]

What is the duty cycle? Under worst case conditions where all 32 outputs were on for 50 ms, how many of them would go off after the 50 ms and how long would they stay off before they could possibly trun on again?

What is the actual maximum current per load?  Does it vary over time? 

Lynn

[AnthonV]

Hi Lynn,
The current is fairly constant at 750mA. The duty cycle is expected to be low at around 10-15%. From your questions I am inferring that the current limit is not measured and limited by the module but is imposed by maybe the thermal limits of the common rail/tracks/pins of the module?

[johnsold]

The specifications do not say how the current limit is implemented, but my guess is that it is something like what you describe. There is probably also a limit due to the switching device on each channel but your 750 mA loads take that out of the picture.

It might survive that kind of operation but NI probably will not honor any warranty if that kills the module.  A rather expensive test.

Lynn

[AnthonV]

Thanks Lynn. I'll then continue using it as I intended.