Shared Power Supply Protection

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Tizio
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Shared Power Supply Protection

Post by Tizio »

I am thinking of using a single 5V 80A power supply to provide power to up to 20 Odroid XU4 and I would like to make extra sure that the system is protected from failure.

For example I would like to ensure that:
1. if the power supply fails the voltage applied to an Odroid cannot exceed a threshold (5.2V? 5.3V?)
2. if an Odroid fails the current drawn by the Odroid cannot exceed a threshold (4A+?)
3. anything else?

Any suggestions on which type of electronic components would be best suited for this purpose?

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Re: Shared Power Supply Protection

Post by L67GS »

I'd be concerned that with so many on there they may experience voltage drop. It would be a good idea to put a little volt meter on it, like a cheap panel mount one.
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Tizio (Sat Aug 07, 2021 11:32 pm)

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Re: Shared Power Supply Protection

Post by rooted »

Personally I would just go with XP Power but you would need three VFT150PS05 as they don't make 5v 80A supplies, to me I would rather spread the load.

That would cost around $180, or a single Mean Well PSP-600-5 would cost around $130.

I know you are asking a different question but due to complexity and cost I would go with top tier power supplies and rely on them without additional protection.
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Tizio (Mon Aug 09, 2021 4:26 pm)

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Re: Shared Power Supply Protection

Post by odroid »

1. Do not exceed 5.25V.
2. Over-current protection IC TPS259251 on the XU4 board limits 5Amp.

You have to use at least AWG-18 grade DC cables something like this to minimize voltage drops.
https://www.hardkernel.com/shop/dc-plug ... bly-5-5mm/
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Tizio (Mon Aug 09, 2021 4:26 pm)

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Re: Shared Power Supply Protection

Post by L67GS »

Cost effectively the HK power supply is $5.50, would be $110 total. Not as cool as a big rail system but certainly safer in the end and positively compatible.

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Re: Shared Power Supply Protection

Post by mad_ady »

Well, I think 20 PSUs are bound to be less efficient than one big one...
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Tizio (Tue Aug 10, 2021 10:45 pm)

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Re: Shared Power Supply Protection

Post by rooted »

mad_ady wrote:Well, I think 20 PSUs are bound to be less efficient than one big one...
I wouldn't use 20 different supplies but having one point of failure which takes down the entire stack isn't ideal IMO.

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Re: Shared Power Supply Protection

Post by Tizio »

Thanks for the replies :)

Yes, this is the concern I have. I am looking into setting up my first system step by step, learning as I go along. I bought a Mean Well UHP-500-5 power supply and on setting it up and testing its output it occurred to me that with a single power supply the problem of single point of failure may need to be addressed.

Cable wise I am thinking of up to 5 x AWG 10 (pair of) cables connected with ring crimp terminals to the power supply, each splitting into up to 4 x AWG 18 (pair of) cables. With an MC1 cluster, the splitting would be closer to the MC1.

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Re: Shared Power Supply Protection

Post by rooted »

Since you already purchased the supply I would wire a good power cord to the supply and get a UPS to put between it an the mains to protect from surges, brownouts, etc.

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Re: Shared Power Supply Protection

Post by mctom »

I have a setup with 6x RasPi4 and 2x XU4, all fed from a single 5V source (MeanWell RS-150-5 IIRC).
The trouble with low voltages is extreme current, which as outlined before, need extra thick wire. Mind you, my apartment has 16A circuit braker, so for any higher current than that you'll need much thicker cables than you have in your walls.
In order to distribute power to my SBCs, I have built two boards:

For RasPis - PiStackMon, that enables me to power them via screw terminals rather than wimpy USB ports. But that's not your concern.
For distributing power among SBCs, a simple board with screw terminals and holes for two brass M4 screws, where I screw in the thick wires with input power. Also, a bunch of bulk capacitors to mitigate problems with transient current spikes.
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At this point, it's not a great idea to make short circuit anywhere - you may weld metal pieces together with this setup. Tried that, do not recommend.

Also, I'd recommend getting ammeter instead of voltmeter - that's at least a meaningful load gauge.
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Re: Shared Power Supply Protection

Post by rooted »

I don't know if Pi are like Odroid but if you power it through the GPIO you lose the built in protection.
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Tizio (Tue Aug 10, 2021 10:45 pm)

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Re: Shared Power Supply Protection

Post by mctom »

Polyfuse is one of many features of PiStackMon. ;)
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Re: Shared Power Supply Protection

Post by Tizio »

So my understanding now is that the overcurrent the protection is already on the odroids side and the overvoltage protection is already on the power supply side, so that the main concern should be about protecting the power supply from the mains rather than protecting the power supply and the odroids from each other.

However, if e.g. the power supply did not have overvoltage protection or if the odroids built in current protection was bypassed, then for what I can see at the moment the way to add that protection would be through fuses for overcurrent and through a crowbar circuit for overvoltage.

But it's not as straightforward as I thought it would be, especially with crowbar protection and the likes, to find something on the market to just purchase and plug in, which seems to suggest that this type of protection is not something for which there is a strong market demand for.

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Re: Shared Power Supply Protection

Post by mctom »

I guess you are overthinking a simple matter really.
The input of XU4 is protected by this bad boy:
scrn-2021-08-22-14-42-21.png
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This circuit protects against:
- ~5A overcurrent
- Overvoltage up to 20V
- Protects itself against overheating, so it may be assumed very reliable.

So failures of XU4 boards will never propagate to other boards.
UHP-500-5 has its own overvoltage protection that trips at 6.75V max, so no need to worry about that either.

Just hook it all together and enjoy.
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Re: Shared Power Supply Protection

Post by mctom »

Also, a crowbar for 100A PSU is not a feasible option. You'd be better off with some sort of high side sub-1mR MOSFET switch, or a car starter relay, along with simple logic to detect overvoltage.
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