Crown V-Rack "120v" vs "208" volt settings

T

TJ Cornish

Graduate
Jan 13, 2011
1,263
1
0
St. Paul, MN
I've used a Crown VRack a couple times now, and am at a loss to understand why they opted to put in a power selector switch. In "208v" mode, each of the three amps in the rack are fed phase to phase, so the amps each receive 208 v. In "120v" mode, the amps are fed from phase to neutral.

The guy who owns the VRacks that I rent occasionally has asked if I have 208v power available, otherwise he'll set the switch to 120v mode. The amps have a universal power supply, and take 100 - 240v without needing to switch anything.

The VRack is powered by an L21-30, which requires 208v power anyway, so there's really no "120v" mode short of making up an illegal cheater adapter with 3 Edison plugs to an L21-30R, so why would you ever want to be in "120v" mode? If you only had 120v power, you'd be far better off unplugging the C19 cabling from the back and using external cables rather than bodging the distro.

The only thing I can think of is behavior if you lose a phase - in 208v mode 2 amps go down, in 120v mode, you only lose 1 amp; the flip side is that if you lose the neutral, all 3 amps are floating. That seems like a pretty weak reason to not always use 208v mode.


Any VRack aficionados know the real story? What am I missing?
 
Last edited:
TJ Cornish said:
I've used a Crown VRack a couple times now, and am at a loss to understand why they opted to put in a power selector switch. In "208v" mode, each of the three amps in the rack are fed phase to phase, so the amps each receive 208 v. In "120v" mode, the amps are fed from phase to neutral.

The guy who owns the VRacks that I rent occasionally has asked if I have 208v power available, otherwise he'll set the switch to 120v mode. The amps have a universal power supply, and take 100 - 240v without needing to switch anything.

The VRack is powered by an L21-30, which requires 208v power anyway, so there's really no "120v" mode short of making up an illegal cheater adapter with 3 Edison plugs to an L21-30R, so why would you ever want to be in "120v" mode? If you only had 120v power, you'd be far better off unplugging the C19 cabling from the back and using external cables rather than bodging the distro.

The only thing I can think of is behavior if you lose a phase - in 208v mode 2 amps go down, in 120v mode, you only lose 1 amp; the flip side is that if you lose the neutral, all 3 amps are floating. That seems like a pretty weak reason to not always use 208v mode.


Any VRack aficionados know the real story? What am I missing?
Click to expand...

In 208v mode you don't need a neutral, so less conductors and cheaper power distribution

Sent from my SCH-I545
 
Re: Crown V-Rack "120v" vs "208" volt settings

Silas Pradetto said:
In 208v mode you don't need a neutral, so less conductors and cheaper power distribution

Sent from my SCH-I545
Click to expand...
You're preaching to the choir about the value of running the amps from phase to phase, but the L21-30 connector (and possibly the network switch inside the rack) still requires a neutral, so that's not it.
 
Re: Crown V-Rack "120v" vs "208" volt settings

TJ Cornish said:
You're preaching to the choir about the value of running the amps from phase to phase, but the L21-30 connector (and possibly the network switch inside the rack) still requires a neutral, so that's not it.
Click to expand...

Think "single (split) phase" and "three phase" rather than 120v / 208v.

BTW, I thought the V-Racks had CEE-form power inlets... those are what I recall seeing.
 
Re: Crown V-Rack "120v" vs "208" volt settings

Tim McCulloch said:
Think "single (split) phase" and "three phase" rather than 120v / 208v.

BTW, I thought the V-Racks had CEE-form power inlets... those are what I recall seeing.
Click to expand...
You know me well enough to know that I understand 3-phase power distribution.

V-Racks have CEE-Form in and L21-30 in, selectable by another switch. Doesn't matter though - both are 5-wire connectors.

I just re-read the manual, and I understand the "what", but I still don't understand the "why".

Manual is here: http://www.google.com/url?sa=t&rct=...o4HYBA&usg=AFQjCNHoBAshxL6Y1Ngxpzz0qEB0hUHhKw

if anyone wants a look.
 
Re: Crown V-Rack "120v" vs "208" volt settings

TJ Cornish said:
You're preaching to the choir about the value of running the amps from phase to phase, but the L21-30 connector (and possibly the network switch inside the rack) still requires a neutral, so that's not it.
Click to expand...

Since these racks are set up for international use, I guarantee the switch is auto-ranging and can run phase to phase as well. Just because a connector has 5 wires does not mean they all need to be used, either.
 
Re: Crown V-Rack "120v" vs "208" volt settings

Silas Pradetto said:
Since these racks are set up for international use, I guarantee the switch is auto-ranging and can run phase to phase as well. Just because a connector has 5 wires does not mean they all need to be used, either.
Click to expand...
The switch is not auto-ranging; it's a 5-position manual selector switch that you need to take the Speakon output panel off to get to. The positions are P-P L21-30 in, P-N L21-30 in, P-P CEE-Form in, P-N Cee-Form in, and OFF. The OFF position is equally confusing - not sure what value that has, since you have to remove screws to get there.

As to not populating all the wires - you could make an argument that an L21-30P to L14-30R adapter cable is acceptable, but it is ABSOLUTELY NOT acceptable to leave out the neutral wire to an L21-30R. The whole point of the different plug serieses (seri??) is to prevent different mismatched electrical systems from being interconnected. How do you keep Joe Stage Hand from picking up your "special L21-30 cable with no neutral for V-Rack use only" and using that to feed your stage stringers or your video world breakouts?


Edit: Oops - you meant network switch. Yes, the switch probably has a universal voltage wall wart. I'll have to peek inside the one I'm using this weekend to see if it's wired P-N, but that's my guess.
 
Re: Crown V-Rack "120v" vs "208" volt settings

Along the lines of Tim's post, suppose you are going into a venue with a V-Rack and a three phase distro and the venue only has split phase power. If the show was low-key enough - think small classical jazz show, talking heads with speakers on sticks, etc. - you could jump two legs together at the distro and make things happen if you were running 120V leg-neutral. Not so much with things set for 208V leg-leg. I know this is not ideal and understand very clearly the concept of overloading the neutral in this situation. However, we have racks with three PLM10000Q 120V amps in them wired to L21-30's, and on occasion, we will do this if the situation is not going to come close to overloading anything.

Obviously you're not going to do this if you're doing a metal show with all three amps on sub duty.

YMMV.

Regards,

Brian
 
Re: Crown V-Rack "120v" vs "208" volt settings

Brian Ingwell said:
Along the lines of Tim's post, suppose you are going into a venue with a V-Rack and a three phase distro and the venue only has split phase power. If the show was low-key enough - think small classical jazz show, talking heads with speakers on sticks, etc. - you could jump two legs together at the distro and make things happen if you were running 120V leg-neutral. Not so much with things set for 208V leg-leg. I know this is not ideal and understand very clearly the concept of overloading the neutral in this situation. However, we have racks with three PLM10000Q 120V amps in them wired to L21-30's, and on occasion, we will do this if the situation is not going to come close to overloading anything.

Obviously you're not going to do this if you're doing a metal show with all three amps on sub duty.

YMMV.

Regards,

Brian
Click to expand...
That's a possible use case, but as you mention is against code and/or dangerous. It seems to me that if the availability of 3-phase power was a concern, maybe V-Racks aren't a great choice. A local company I work with from time to time has standardized on 2-phase/split phase down-level distribution (from 3-phase main distros), which makes a lot of sense to me. A switchable distro like this one: http://www.leprecon.com/productfiles/PwrDis.280061B.pdf can handle both 3-phase and split-phase input and still light up all the receptacles if you are using L14-series.
 
Re: Crown V-Rack "120v" vs "208" volt settings

Helge Dr. Bentsen said:
IIRC the switch PSU is auto-ranging.

We use the P_P L21-30 mode when running them at our old style 3-phase power here (230V P-P, no neutral) and P-N CEE when we run on the new 3-phase( 380V P-P, 230 P-N)
Click to expand...
This is the only thing that makes sense to me - when you need to go P-N to get the voltage within range of the devices. Perhaps this switching function in the US is just an artifact of international use. FYI, our mid-voltage 3-phase system is 480v P-P, 277V P-N, which is illegal to use on the L21-30 connector, and the 277v P-N voltage is too high for the ITechs anyway.
 
Re: Crown V-Rack "120v" vs "208" volt settings

Did they say why? Triac dimmers can cause noise on the neutral wire, but I'm not familiar with any issues P-P - should be as good quality as P-N, just at a higher voltage.
 
Re: Crown V-Rack "120v" vs "208" volt settings

Helge Dr. Bentsen said:
IIRC the switch PSU is auto-ranging.

We use the P_P L21-30 mode when running them at our old style 3-phase power here (230V P-P, no neutral) and P-N CEE when we run on the new 3-phase( 380V P-P, 230 P-N)
Click to expand...

Good point. You could run a Vrack on 3 phase Delta in P-P mode. Of course you couldn't run anything else in the rig, but...
 
Re: Crown V-Rack "120v" vs "208" volt settings

TJ Cornish said:
Did they say why? Triac dimmers can cause noise on the neutral wire, but I'm not familiar with any issues P-P - should be as good quality as P-N, just at a higher voltage.
Click to expand...

No, but the newest manual states:
Never try to reproduce a 230 V circuit connecting an LA8 or LA8US to two live wires of a 120 V three-phase circuit.
Click to expand...
 
Re: Crown V-Rack "120v" vs "208" volt settings

Jens Bacher said:
No, but the newest manual states:
Click to expand...
I'm unfamiliar with that amp, but it appears to be a non-universal power supply - there are specific versions for US and Europe. Two phases of US 3-phase power is 208 volts, which may be a little low for an amp designed for 230 volt operation, which is I suspect the issue. ITechs are different - they can take 100-240v 50/60Hz and auto-switch, and therefore are perfectly happy P-P and P-N in a US system, hence the choice in the V-Rack.
 
Re: Crown V-Rack "120v" vs "208" volt settings

One thing I like about the CEE P-N running at 380V is that you can run 4 amp racks on a single breaker (32A). Cleans up your cabling system, one 32A drop to each side of the stage, link all the racks and off you go :)
Of all the factory specified amp racks I´ve used, I like the V-Racks best.

The AES over network cable-solution is also pretty sweet.
 
Re: Crown V-Rack "120v" vs "208" volt settings

David Sturzenbecher said:
Fun fact, the 12000V Racks have AES over the network cable just between the racks. The 4x3500's have AES over the network cable all the way to the amps. It's what the Vdrive is i guess.
Click to expand...


I´ve only used V-Racks with 12000HD going AES into rack 1 by using the AES input and just network cables all the way from there. No need to patch anything in the remaining racks as long as the AES stream selector switch is in the correct setting on all racks. And you have to go input to output on your network. If you´re only doing control, you can go input to input or output to output.
 
Top Bottom