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In Rush Current

ideas how to get accurate current measurements. You

case someone has so ideas.

14" long to carry the power. I "thought" is was
10 amps, and it only last for a few ms. Then the

then to 7.5 amps, then immediately back to 3.5,

Utilization at any given time.

I suspect your current spike corresponds to some extra activity. Is the internal clock speed varying, as uP's intended for mobile use often do?

Yes. You are charging the bulk bypass caps with it.

Hard to say (even if I wished to guess what "kinking off" is, but I don't want to know ;-).

power distribution wires? I did note that with the

SBC Power Terminals so I think that is a good

That's a little much for a 14 inch wire run. At those currents, heating is not really an issue, but drop may be depending on your supply tolerance and how the SBC is specified. 16 guage should be plenty big.

Is there a reason to go for the smaller wire?

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--Larry Brasfield
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Larry Brasfield
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it's on DC Converter inside so it could be it

Whew!

original motherboard specs and then looked up the 18 ga.

If the spec on your supply output voltage is enough tighter than the spec on your SBC supply requirement so that the 90 mV drop is not a problem, then I would use those

100 harnesses. And have more made up with bigger wire.

voltage drop will be much less, will I see differences

The inrush current is most likely limited by the supply rather than the wire. I would expect no real change.

computer from booting sometimes.

That seems unlikely to me. Your SBC probably has a spec on how fast the supply should come up. Be sure you meet it. Also, be sure there is no overshoot just after that initial current spike driving the supply voltage above the SBC voltage spec.

You might want to look carefully at the supply voltage waveform as it comes up. Maybe the DC-DC converter is initially putting the supply into current limit and causing a wobbly turn-on waveform rather than what the SBC designers assumed (and should have specified). You might try a higher current limit supply, experimentally, to see if that reduces the misbooting incidence.

--
--Larry Brasfield
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Larry Brasfield

I posted about a SBC P4 that randomly failed to boot (Power up) and want some ideas how to get accurate current measurements. You kind folks helped out by explaining the Shunt deal.

Since then I have taken numerous measurements and I want to share my setup in case someone has so ideas.

First, the spec of the SBC is Max. 4.5 amps on Start up, Normal 3.2 amps. I am using a 5 vdc DC COnverter located 14" away using 18 ga Instrument wire

14" long to carry the power. I "thought" is was large enough, but now I have second thoughts.

When I first power up the DC Converter, I see a small spike which is right at 10 amps, and it only last for a few ms. Then the power drops to about

1.5 amps. When the computer beeps, I jump up to 3.5 amps then to 7.5 amps, then immediately back to 3.5, then it slowly settles down to around 2 amps. Now I only have 10% Processor Utilization at any given time.

I take it, the 10 amp jump is the initial in rush current? then the 7.5 amps is a very breif spike from the SBC kinking off?

Does this mean my 18 ga is border line and I would really need 16 ga for the power distribution wires? I did note that with the 18 ga wire there is 90 millivolt drop from the DC Converter terminals to the SBC Power Terminals so I think that is a good indication I need to step up a size.

Any thoughts, Richard

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Richard

Sorry, typo, I meant that was the CPU kicking off or Starting up. The SBC has it's on DC Converter inside so it could be it starting up.

No, we just had a 100 premade harness kits made because I looked at the original motherboard specs and then looked up the 18 ga. and it seemed to be sized ok, and our other harnesses were 18 ga.

I made up a 16 ga harness to see if it helps. Besides the fact that the voltage drop will be much less, will I see differences with the inrush currents as well? I think the wire being too small and the high inrush is what keeps the computer from booting sometimes.

Richard

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Richard

It occurs to me that the modern ATX power supply has extra power supply lines. These are intended as a parallel path to supply the CPU with the extra power it needs. You may have noted the (usually) two odd power connectors coming from the power supply.

Are you using these?

Reply to
Lord Garth

No Sir,

This is an Industrial, Embedded Motherboard running a Via 667mhz on a single

5 vdc supply. We are using a Datel 18-36vdc input to 5 vdc output rated at 5.0 amps. It's 14" away from the SBC.

Richard

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