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-48 Volt DC vs -72 Volt DC

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pontifex

pontifex

Lifer
What is the reason that you would use 1 over the other? this applies to power supplies in servers.

I can't seem to find any info regarding what the difference is.
 
-48V is a widely used standard for telecoms equipment for many years. Most telecoms facilities will have -48V battery banks, making it a useful source for ancillary equipment.

Can't say I've ever heard of 72V backup power.

The new thing with servers is +350V DC power, especially in high density datacentres. Low currents, and no inverter losses for on-line UPS systems, and no rectifier/PFC losses in the PC PSUs.
 
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With 48v you need to find 4 good batteries at the junk yard.
With 72v you need to find 6 good batteries at the junk yard.

What kind of server uses DC?
 
Back when Moby Dick was a minnow and inwas working for Fujitsu in St. Loowey, ALL telco/data equipment ran from 48VDC with a positive ground. I've never seen a 72v system in the wilds.
 
mikeford said:
With 48v you need to find 4 good batteries at the junk yard.
With 72v you need to find 6 good batteries at the junk yard.

What kind of server uses DC?
Click to expand...

Ultimately, almost EVERYTHING uses DC. Except radio. And more often than not, radio generates its AC signal from a DC source.


True story.
 
-48V is still used a lot. Never heard of -72 standard.

Personally I'd love to see -48V more standard for PSUs, it would make power backup easier if you could just hook the batteries straight to it and then a rectifier for the batteries set to float. Rectifiers are hard to find though. There's ebay, and that's about it. Basically the PSU internally has to rectify to DC anyway so it would just be the thing of having a point in the SMPS process that can accept 48v and then there would be terminals in addition to the regular AC plug. I wonder how hard it would be to modify a PSU to use 48v actually...
 
I deal with support for session border controllers for VOIP so dealing with telco stuff. Some of our products can use -72v power supplies.
 
mikeford said:
With 48v you need to find 4 good batteries at the junk yard.
With 72v you need to find 6 good batteries at the junk yard.

What kind of server uses DC?
Click to expand...

All of the major brands have optional DC supplies. Often the SANs and switch gear will also.
 
Leros said:
Why are we talking negative volts?
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Traditionally phone systems attached battery + to ground, same as the positive ground cars from the 30's and 40's. Positive ground cars operate at -6 or -12 volts, for example. Voltage is referenced to ground.
 
imagoon said:
Traditionally phone systems attached battery + to ground, same as the positive ground cars from the 30's and 40's. Positive ground cars operate at -6 or -12 volts, for example. Voltage is referenced to ground.
Click to expand...

Yep the positive is connected to ground. I believe this has to do with helping to prevent corrosion in the phone lines. Not 100% sure how that works, guess the negative side wont corrode as easily or something. What gets real fun is some data circuits use 100 or so volts. That's always a surprise when you go to touch that on the MDF. 😛 Ring voltage is like 170vac too, and it's a lower frequency. Don't squish your face against the terminal block when reaching in for a wire. 100 pairs... decent chance of a phone call coming in. 😱
 
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Actually I need to buy some steppers and servos, they sound like fun to play with. I already have an arduino I could use to drive them. You can also play music on a stepper motor, then again you can do it on a regular DC motor too. I imagine even on an AC motor it would work.
 
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