OTS DCDC module overcurrent trip behaviour? - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: March 06, 2020, 09:48:35 pm
content: Hi,The output overcurrent limit for the Vicor BCM4414xG0F4440yzz DCDC module is stated as 42A to 70A. Do you know what happens when this level is breached? The datasheet doesn’t say..We wonder if it latches off?..Or maybe it turns off for a certain amount of time, then re-trys?..or maybe it clamps its output current to 42A?BCM4414… module datasheet:http://www.vicorpower.com/documents/datasheets/ds_BCM4414xG0F4440yzz.pdf

author: Siwastaja
author_rank: Super Contributor
timestamp: March 08, 2020, 01:01:08 pm
content: You could guess that "auto restart time" "Start up into a persistent fault condition" means all types of fault conditions.So it would give short pulses (3.6ms typical "LO-Side Overcurrent Response Time Constant") every 900..1100ms.This is what many (most?) power supplies do: implement a hickup-style retrying mechanism, which has low enough duty cycle so that no significant heating happens in the shorted (or almost-shorted) output, but removing the short fixes things without requiring upstream power cycling.Buy one and test it to verify the assumption.

author: ogden
author_rank: Super Contributor
timestamp: March 08, 2020, 01:30:58 pm
content: Quote from: Siwastaja on March 08, 2020, 01:01:08 pmIt is not even assumption, but expected behavior specified in the datasheet. Timing diagram (on page 13) agree with what you say.

author: ocset
author_rank: Super Contributor
timestamp: March 08, 2020, 05:34:07 pm
content: QuoteThanks, but on page 13 it shows the response to a “short circuit”…not an “Overcurrent”. Short circuit is at 55A…overcurrent is at 42A (42A-70A).It’s the response to “overcurrent” that we are querying....ie overcurrent at 42A.Its worrying because our max I(out) is 39.5A, and overcurrent is 42A…….and we don’t yet know if there are load transients which could make us go into the 42A region

author: ogden
author_rank: Super Contributor
timestamp: March 08, 2020, 06:27:42 pm
content: Quote from: treez on March 08, 2020, 05:34:07 pmIf consumption of your device can reach 39.5A, it is bad idea to use supply with 42A overcurrent treshold. You need better margins than few percent.

author: ocset
author_rank: Super Contributor
timestamp: March 09, 2020, 05:53:11 am
content: Thanks i agree, though the alternative is far far more pricey if we use the vicor modules in the way we plan...i wish we knew what would happen if that 42A threshold got breached?This thread shows our setuphttps://www.eevblog.com/forum/renewable-energy/dcdc-module-has-unusual-input-filter-requirements/…..the alternative is to use a “Unit” of one vicor BCM, module feeding just 3 vicor DCM modules……..and then use 13 of these units…that’s an extra £2700

author: ogden
author_rank: Super Contributor
timestamp: March 09, 2020, 04:05:00 pm
content: Quote from: treez on March 09, 2020, 05:53:11 am1) Try to consult manufacturer rather than public forum full of "sofa experts" ? 2) Buy one supply and test?

author: Siwastaja
author_rank: Super Contributor
timestamp: March 09, 2020, 05:21:53 pm
content: 42A being theminimumvalue, I don't see an issue. That's exactly why datasheets have those min/typ/max tables, it's very likely close to the typical, and the idea is they kinda guarantee it won't be outside [min, max]. So as long as you are truly certain your maximum being 39.5A, I'd go on and trust that number.You are below the maximum rated continuous current of 40A, and this isn't in the absolute maximum section. The spec should hold if the product is of decent quality.But if you expect exceeding the rated 40.0A, even briefly, you could expect to see hickuping in action, i.e., it could turn off for 900..1100ms before auto-retrying.

author: ogden
author_rank: Super Contributor
timestamp: March 09, 2020, 08:06:21 pm
content: Quote from: Siwastaja on March 09, 2020, 05:21:53 pmThey are not certain:Quote from: treez on March 08, 2020, 05:34:07 pm@treez can correct me, but to me it looks like 39.5A is nominal current, not max current. If we add some +/-10% "error margin window", then we get overlap with supply overcurrent limits. Anyway gamble to run so slim margins can be fine for hobby/DIY projects, but I am afraid that this is not the case, right?