Should I Build 500 or 51X?

[amarten]

A) This is my first thread, I apologize if it's not in the right spot. I definitely read the rules, but I couldn't find any better place to ask a simple question like this one.

B) I'm a student building a 500 or 51X series rack for a class project, and I'm trying to get the most long term use out of the money I'm about to spend. I plan to have these racks for a long long time. The ~$1200 that I'm spending for the rack/PSU/my first two modules is pretty much all the available spending money I have, so I want to be absolutely sure I do this right.

C) So, from this moment in time, which format would I get the most use out of for the future? 500 series or 51X?
I see a bunch of DIY modules that I want to build, and many of them are for either 500/51X. I'm going to be building one of the racks from classicapi.com. According to him, I can't put more than 11 VPR modules and 11 51X modules on the PSU he specs for his racks. So, I would be stuck at 11 modules of 500 series, and 11 modules of 51X. I'm fearing that I won't find enough 51X modules running off of 24V to fill the 11 spaces, and will end up with empty useless spaces, as I can't have more than 11 VPR modules.

This confuses me though. Wouldn't the only determining factor for how many modules I can have in a rack be the current consumption of each module?
If that's true, then why am I only able to have 11 VPR modules? Would it not make sense that I could have more than 11 VPR modules running so long as they ran well below the 130mA per module spec, allowing the 24V modules to eat up whatever they needed?

I get myself turned around. Any direction at all would be great. Even direction toward the right board for this post would be good.

 

[dmp]

You can use 500 in 51x.
So, I think 51x is preferable.
If you look up the pinouts, you see that 51x has the exact same card edge connections as 500, but adds the +/-24v pins at the end

so I want to be absolutely sure I do this right.

Then DIY might not be for you...  it's a learn as you go sort of thing 

 

[qmp audio]

I'm currently running 8 51x modules and 14 VPR modules with 1 capi PSU with no issues... and is still below the 16v current limits of using 1 power supply.
Please note though that i measured the draw of my modules to ensure I was within the spec of the PSU.

 

[okgb]

I was going to say you could make one half and half , but it would be a waste of psu unless you scaled back, so
there's more standard modules for 500 , but more possibility & potential for 51x
can't go wrong either way but 51x covers your bases