PSU for multiple N2's

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venkatbo
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PSU for multiple N2's

Unread post by venkatbo » Fri Apr 19, 2019 12:27 am

'am looking to power my N2 stack with one of these Mean Wells: LRS-350-15 (15v, 23A):
https://www.jameco.com/z/LRS-350-15-MEA ... 19815.html

I think I know the answer, but just want to check...
There's a blurb in the N2 page - "Power: ... up to 25Watts"...
  • Is it safe to assume that the N2's power protection circuitry will protect the N2 against unnecessary draws, even if the PSU can supply it ?
  • Is there a max current/wattage it can withstand, beyond which it will cease to function?

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Re: PSU for multiple N2's

Unread post by mad_ady » Fri Apr 19, 2019 5:54 am

That's the power draw, the psu is more than enough

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Re: PSU for multiple N2's

Unread post by venkatbo » Fri Apr 19, 2019 6:28 am

True... my concern was the statement... "upto 25watts"...

Would that imply that, if "higher wattage" was made available to the N2, the N2 could be harmed somehow, and thereby not advisable, or some such... ie., was the power protection circuitry designed for only 25watts max...

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Re: PSU for multiple N2's

Unread post by OverSun » Fri Apr 19, 2019 7:12 am

Voltage is the pressure that is being applied, amperage is a diameter of the pipe an a rough analogy.
If pressure applied is more than designed, then receiving side is going to have trouble. If a diameter of incoming pipe is bigger than needed (keeping in mind the pressure is still going to be same) that wouldn't make any difference, the receiving side is still going to get the amount it needs and not more.

PS. watts are volts * ampers.

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Re: PSU for multiple N2's

Unread post by odroid » Fri Apr 19, 2019 8:39 am

N2 consumed less than 15Watt when we ran full CPU+GPU intensive loads.
So I think you can connect around 20 N2 boards to the PSU if there is no USB device connected.

But you have to use thick and short DC power cables to minimize voltage drops and power loss.

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Re: PSU for multiple N2's

Unread post by hominoid » Fri Apr 19, 2019 8:50 am

You Don't say how many N2's are in your stack...15V x 23A = 345W potential x 80% = 276W / 25W = 11.04 Odroid N2's power it could. Make sure you calculate for the correct wire size and voltage drop for the length of connections. I try to stay at 2% or less. This is very important and will cause damage if not correct!

Edit: @odroid beat me to it :)

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Re: PSU for multiple N2's

Unread post by hominoid » Fri Apr 19, 2019 10:12 am

One other thing to keep in mind is the efficiency power curve. I noticed this power supply is rated at 86% efficiency typical. They don't show an efficiency power curve but in a lot of designs that is only realized (the typical efficiency) in the middle of the power range. In this case it would be around 172 watts. It may not be in the middle of the power range either based on the design and In some designs the efficiency can fall off dramatically on either side of the typical efficiency point. It's not unusual to see a drop of 5-15% efficiency in power supplies. For a computer cluster that is going to be running long periods of time this can be costly and very inefficient. Just another point to consider in choosing the right power supply. It would be better if they showed a power curve so you knew how to size it from an efficiency stand point. You might want to contact the supplier or manufacturer and ask.
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Re: PSU for multiple N2's

Unread post by venkatbo » Fri Apr 19, 2019 12:39 pm

Thanks for all the tips. Plan is to setup a small lab setup with 3 each, XU4/C2/N2, a H2, a Cshell2 w 2x2tb Hdds, and 2 8-port switches, and a few stepdown xformers. Think the the psu can handle it. just wondering if i need to add some fuses to protect the devices.

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