Outback RSI J4 pins

MJSullivan56

So I have my Outback Radian GS4048A/FM100 system set up for module-level shutdown. I'm using an Outback RSI as the exterior switch that the fire department can use to shutdown my PV modules from afar. So far so good. I plan on using the J4 pins to flag the RSI LEDs being in the "Solar Off" mode. The J4 pins are a simple dry contact. I am using 75 feet of 18/8 cable to communicate back and forth between the RSI and the FM100. I am also using a 12Vdc relay as an intermediary (see attached diagram). I have measured 0.0 Ohms at the relay for the NO circuit (when closed, of course). But at the RSI -- 75 feet away -- I measure 2.0 Ohms, which is not surprising.

My question: For a dry contact is that going to be a problem?

Thanks
Michael

BB.

Do you know the voltage (signal) levels (zero/one) and current of the controller?

For example, if you plan on a 0.1 amp (or less) signal:

V=I*R
Voltage drop = 0.1 amps * 2 Ohms = 0.2 volt drop

Typical signalling voltage is probably either 5 or 12 volts... A (for example) 0.2 volt drop should not be an issue.

Do you have the possibility of lightning in your area? Long signalling wires can be an issue... Placing inside metal conduit for shielding (or using shielded cabling) could be a help.

-Bill

MJSullivan56

It is a dry contact. No voltage involved at all. Basically, the relay closes the NO circuit when it detects when someone switches the RSI to "Solar Off".

So the question remains: for a dry contact, is 2 Ohms too much resistance? Or will it see it as "completing the circuit"? Or is this something only an engineer familiar with the Outback RSI can answer?

Thanks!
M

mike95490

Try it and see.  Or wait for an OB rep to get back to you

BB.

"Dry Contact" just means that the source is a set of relay contacts--No power/sense circuit.

https://www.electrical4u.com/dry-contacts/ (nice/detailed explanation)

The "destination" or "receiver" of the contacts needs to send out power and receive the relay state back...

Looking at the manual for J4:

https://www.solar-electric.com/lib/wind-sun/ics_plus_manual.pdf

Appears to be a 24 VDC signal/receiver circuit. I would guess the loop current would be between 0.001 to 0.040 amps (1-40 mAmps). With 2 ohms of wiring resistance:

• V=I*R
• V=0.001 amps * 2.0 Ohms = 0.024 volt "wiring drop"
• V=0.040 amps * 2.0 Ohms = 0.080 volt "wiring drop"

Both are pretty insignificant to a 24 VDC powered sensing circuit... If the voltage drop was >~5 VDC--Then I might worry.

If you had the hardware, you could always use a current meter to measure the J4 current by "shorting" with a DMM set to current mode and see what Amperage you measure if you don't get an answer from Outback.

The above is based on the assumption that the "detection circuit" was electronic.

If the circuit was the coil for a relay--Then worst case draw could be something like 3-6 Watts (typical guess):

• P=V*I; I=P/V
• I = 6 watts / 24 volts = 0.25 Amps "relay control current"
• V=I*R= 0.25 Amps * 2 Ohms = 0.5 Volt wiring drop

The unit has 30 volt @ <2 Amp rated contacts.... But even a "6 Watt" relay coil load is appears not to be an issue with 2x75 feet (round trip) of 18 AWG cable.

From what I can guess--Don't see any major issue here.

-Bill