JCI N2 Connectors

[oldtimecontrolsguy]

Hi
I need to buy a device that will give my USB-only laptop access to N2. HVAC Pro is loaded and working.
Which is a good device to buy, the new JCI CVTPRO, S2 Innovations, or the B&B USB to RS-485? Pro's and Con's?

Thanks Everybody!

[berg2666]

S2 will be your best choice and the newest one has diagnostics. I use it more then my CVTPro.

[s2sam]

Hi
I need to buy a device that will give my USB-only laptop access to N2. HVAC Pro is loaded and working.
Which is a good device to buy, the new JCI CVTPRO, S2 Innovations, or the B&B USB to RS-485? Pro's and Con's?

Thanks Everybody!

Good day oldtimecontrolsguy,

I am biased, as we are the ones who manufacture the S2USB485 device... that being said....

The JCI CVTPro will give you N2, RS232, and Zonebus but is pricey. The CVTPro 300 is about the size of a medium-sized book, is somewhat bluky, and must be wall powered for the N2 bus. Older ones would literally burn up and the later ones I have had mixed reviews on. If you need Zonebus (you mention only N2) then this is the only game in town.

The B&B device is reasonably priced, but does not give you RS232 (this may be a non-issue, as you only mentioned you needed N2). You may need to make your own connector from N2 to the B&B connector, as the B&B connector is not the same as JCI's N2 connector. It is also USB powered.

I think that there is also a device by Digi that people like too, as well as some inexpensive Asian ones (mileage may vary on these).

Our S2USB485 device has both the N2 and RS232 interfaces in a single device, but does not do Zonebus (how's that Freddy :) ). It is USB powered, so no external power supply. It uses the same connector and is pinned to be the same as the N2 connector on JCI's N2 devices (so no cable to make, etc). It has a very well designed and hardy over-voltage protection circuit to protect the device from nasty voltages that can be present (by mistake) on the N2 bus (tested the device to withstand over 60V without issue). Many times some techs mistakenly connect the 24VAC connector to the N2 terminal thinking it was the N2 bus (on the UNT the 24VAC connector is the same type as the N2 one except it is a different color). The S2USB485 also has effectively a built-in voltmeter that can do a bunch of diagnostic tests on the N2 bus (wiring shorts, mis-wires, etc) when used with our free N2 bus diagnostic software. the S2USB485 is designed and manufactured here in Canada (not mass produced overseas) and use industrial rated components. Lastly, the S2USB485 was designed specifically for use with HVACPro and the JCI N2 bus and it is tested with this software in mind. So, if you call us with some communication issues with HVACPro, we can help you as we use HVACPro too... try that with some of the generic USB to RS485 (N2 bus) vendors :) .

Cheers,

Sam

[blackbelt3677]

S2 is definately the way to go. I have used the CVT which works but is a pain in the A__ to use. It seems like I would use it and then it will sit in my van for some length of time. then when I would need it it would take forever to get setup again. I have not had that problem with the S2 tool. Even when I worked at JCI we used the S2 tool and not the CVT. Plus if you have the external power supply hooked and plug into the zonebus you are F__ked. The S2 is USB powered. Good luck:patriot:

[skwsproul]

Lost my cvt and needed it today. I have a rs-485 to rs 232 line powered adapter. Will this work with hvac pro? I hope to find the cvt burried somewhere but till then. BTW it is B&B m#485sd9rj.

[oldtimecontrolsguy]

Great input guys! Thats what I thought. I had heard from many people, inc JCI folks, that the S2 is the way to go. Will be purchasing and hopefully recommending it!

[simux]

http://hvac-talk.com/vbb/showpost.php?p=6189442&postcount=21

[skwsproul]

http://hvac-talk.com/vbb/showpost.php?p=6189442&postcount=21

What type of controllers have you used this for? Any issues? I guess i shoulda asked that before I ordered the parts to make it but for less than $20 i will have enough to make 10 cables. Gotta love ebay.

[s2sam]

http://hvac-talk.com/vbb/showpost.php?p=6189442&postcount=21

Good day Simux,

Perhaps you should have also posted my response, as it is quite relevant.

http://hvac-talk.com/vbb/showpost.php?p=6205182&postcount=24



Originally Posted by simux View Post
I've used a direct connect cable for years... They're easy to make and it's really sweet because you can make it long enough to access controllers in the ceiling.

Materials
DB-9 connector
470 Ohm resister
3-18 Conductor shielded cable
N-2 connector
USB to Serial adapter


Db-9 Pin 5 to N2+, Db-9 Pin 2 to N2-, and DB-9 Pin 3 to ref, with a 470 ohm resistor between Pins 2 and 5.





Good day Simux,

I am glad that this has worked for you. However, it will not always work and you may have inconsistent communication in time. The reason being is that RS-232 (your serial port) uses a completely different type of electrical signaling than RS-485 (The N2 and MS/TP busses). RS-232 is voltage-level signaling where any voltages between +/- 3V are considered indeterminate (means the signal can be ignored or mis-interpretted) by the EIA-232 specification . Secondly, the voltages are referenced to the RS-232's ground pin (pin 5 on the DB-9) and are not designed for daisy chain applications, so minimal drive for loaded busses. Thirdly, the characteristic impedance of your interface is non-compliant and so as data rates increase you will find nasty communication issues.

RS-485, on the other hand, uses a differential signaling method. Here a digital signal is not related directly to its absolute voltage, but rather the voltage difference between the A and B or (N2+ and N2-) signals. Voltages differences between +/- 200mV are considered indeterminate. By this alone you can see that a voltage difference of 300mV is a valid RS-485 (N2) signal but is invalid for RS-232 because RS-232 needs at least 3V. Secondly, because RS-485 is a differential method, it is not sensitive to common-mode noise voltages that will crap out RS-232. RS-485 can be made to communicate up to 4000 feet whereas RS-232 is 50 feet. RS-485 is designed for daisy-chained applications (spec defines a minimum drive of 32 unit-loads), and has the correct characteristic impedance for higher data rates (RS-485 can communicate up to 10 Mb/s).

Anyway, you get the picture. In your case it appears that your interface works but it may not depending upon the controller, your USB/Serial adapter, your network, or your data rate.

Cheers,

Sam


Cheers,

Sam

[simux]

I've been using this direct connect cable for the last 8 years. I've used the direct connect cable on a serial port and on a usb port with a usb to serial port adapter. I've used it on Vav, VMA, UNT, DX and AHU controllers. Although I would rather use a CVT Pro and access an AHU controller through the zone bus. Probably due to the fact that you have to disconnect the N-2 wires.

[simux]

I also like being on an AHU with a CVT Pro because I can modify the AI Offsets, which you can't do with an N-2 connection. I think freddy-b mentioned this recently!!!!

[skwsproul]

Thanks. I normally use my cvt but this week could not find it, I am tearing the place up this weekend. Also have a couple sites that the service techs could get into stand alone ahu's to help save me from having to go out for easy stuff, that is why I would use the n2 cables for primarily as it would be quite pricey to set up 3 machines with the pro kits just for an occasional use.