Difficulty booting a PC (Intel NUC) using a lab Power Supply (Korad KA3005P) - Page 1
Forum section: electronics / beginners

author: spayno
author_rank: Newbie
timestamp: October 09, 2015, 05:43:07 am
content: Hello! Can I have some help with something?I'd appreciate your thoughts on if a bench power supply should be able to substitute for a 19V 3A dedicated AC->DC adaptor when connected to a PC.Here is what I tried:I have an Intel 34010WYK NUC PC which is usually powered by a 19V 3.42A AC->DC adaptor.To do some experiments, I tried to power this device using my Korad KA3005P power supply at 19V which I believe can deliver up to 5A at 30V.I expected that the Korad should be able to power this NUC without problem.What actually happens is that the NUC resets during boot. It gets to the boot loader, drawing less than 1 Amp at 19V and then the resets at the point where the lowest level boot hands off to the Linux boot and I'm guessing mounts the external devices, so draws more power. When this happens the Korad power supply jumps around from 19V down to some low voltage, beeps and then eventually goes back up to 19V.I tried inserting a dc-dc regulator and also tried increasing the wire guage of the connectors. Neither changed the above behaviour.Is it reasonable to expect the power supply to substitute here? or does it point to a problem with the power supply? Or...Thanks in advance

author: nbritton
author_rank: Frequent Contributor
timestamp: October 09, 2015, 06:47:00 am
content: It sounds like the NUC is drawing more current then the Korad can supply. If it's spinning up the hard drive and queuing up the cpu I can see it temporaraily causing a current surge of several amps. The i3-4010U processor by itself has a 15W TDP. When the current spikes the voltage on the rail proabably drops to compensate, thus resetting the computer.Try buffering the output with the largest capacitor you have.

author: Kappes Buur
author_rank: Regular Contributor
timestamp: October 09, 2015, 06:54:53 am
content: Depends on when you got the power supply.See

author: spayno
author_rank: Newbie
timestamp: October 09, 2015, 10:38:03 pm
content: @nbritton. Thanks. I'l try the capacitor idea. I've got a 3200 uF and a bunch of 400uF that I could hook up in parallel.@nbritton and @kappes. Thanks. I'm suspicious of the Korad power supply because of that review. But I'm now thinking it's plausible for a circuit to want to draw more faster than the Korad can provide without dropping Voltage for some critical period of time. A bit counter intuitive to me because I originally thought any lab supply, including the Korad, would always outperform the brick. And perhaps lab>>brick is unreasonable. A lab supply might just not be able to handle the spikes that the brick does.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: October 09, 2015, 10:56:41 pm
content: Most lab power supplies have very little capacitance on their output, otherwise the current limiting function will not work too well as the capacitor will store charge that the current limit cannot control.The bricks however, normally have lots of capacitance to filter the output and keep it clean.Do you have a scope? You could connect the scope to the output of the supply and set it to trigger on a downward slope to see how the power supply is dropping out. Add some capacitance and try again, add more and keep checking to see how much you need. Use it as a learning experience to see how much capacitance you need and what the effects are.

author: Delta
author_rank: Super Contributor
timestamp: October 09, 2015, 11:03:50 pm
content: Is your current limit wound right up?(I've been bitten by that embarrassing one before! 😠)

author: Nerull
author_rank: Frequent Contributor
timestamp: October 09, 2015, 11:37:49 pm
content: Its not an uncommon issue - many devices have a large spike in current at power up, which will cause a lab psu's current limit to trip. The brick won't care about this momentary spike. My mobile ham radio won't power up on my hp 3A power supply, even though it draws about half an amp normally. (not transmitting, of course)

author: spayno
author_rank: Newbie
timestamp: October 10, 2015, 07:47:34 am
content: Adding caps got me further into the boot. I don't know what is triggering first:if the low voltage is resetting the NUC orif it's the current sensor on the power supply cutting out.I find @nerull's explanation appealing, that a brick is more insensitive to current spikethanks @PTR_1275, it does make sense that a lab power supply would want to be more dynamic and capacitors would slow that down.@Delta, yeah the current was wound up to 5.1A. I tried it with 5.1A and OverCurrentProtection enabled and disabled OCP. I think no OCP got further.Moving forwards I think I'm not going to use this power supply with the device. I don't think it's a good match.

author: The Magic Rabbit
author_rank: Regular Contributor
timestamp: October 10, 2015, 01:13:01 pm
content: I do laptop and PC repairs. I can tell you now that 19V 3A is constant - in reality you can draw sometimes up to 10A at 19V without issue, but only for very short periods of a few ms. It's enough to kick on a few drives, check for PnP devices, reset the power management, etc. though.Sent from my XT1039 using Tapatalk

author: free_electron
author_rank: Super Contributor
timestamp: October 10, 2015, 01:23:11 pm
content: Lab power supply current regulation reacts fast. While on those bricks there is no current regulation. So the nuc draws so e peak current the lab power supply can not give, or reacts to , where the brick doesnt care...You often hear : Atx supplies are not lab supplies, but that is also true in reverse ...Same goes for those bricks.