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post #1 of 5 (permalink) Old 2019-07-03, 09:14 AM Thread Starter
 
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Ring Pro Doorbell

Hi, I suspect I know the answer but I thought I would get a second opinion. I have an existing hardwired doorbell (2007 construction). From a multi-meter voltage from the transformer is 20V. Issue I have is that the doorbell is wired with cat-3 24/2 wire. I do not know how many VA the transformer is providing (cannot see any markings on transformer) but I suspect not too many given the size of the wire.

Ring tech services responded (very quickly I might add) to a question with the following statement. "The power requirements needed for Ring Doorbell Pro is 16-24 volts AC. The transformer itself has an indicator of how many voltages per contacts. The two wires on your Ring doorbell should be connected to the 16V contact and the other wire to the 24 V contact or 30 V. If your transformer is only up to 20V this will make it under powered."

I am a bit confused with his reply but my basic question is will the low-voltage wiring (24/2) be sufficient to provide power to the ring doorbell or will it draw too many VA? The Ring website support page shows a wiring diagram with a recommended 16V-30VA transformer.

Running a new wire is not practical based on house design.

Thanks in advance, Jason
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post #2 of 5 (permalink) Old 2019-07-03, 12:05 PM
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Quote:
From a multi-meter voltage from the transformer is 20V.
This is quite likely a 16V transformer. The nominal V (voltage) and volt-amps (VA) should be marked on the transformer itself. VA is similar to watts (W) but measured differently.

The Ring service response makes little sense. I suspect they used V instead of VA in some places and the connection instructions are misleading.

The Ring units appear to require 16V and 30VA. Slightly over 30VA will be fine. Under 30VA could cause issues. It should be marked on the transformer or be available by searching for the make and model number.

If the VA cannot be determined, I would consider replacing it. One way to determine if the transformer VA is adequate is to measure the transformer voltage while in use. If it falls below 16V, it needs replacing. A temporary drop below 16V but still above 12V caused by a door chime should not be an issue. Another concern would be excessive transformer heat while in use. If it's too hot to touch, creates fumes or intermittently stops working then disconnect the power ASAP and replace it. If replacing, use a current limiting transformer designed for doorbell use, rated at 16V and at least 30VA. Other types of transformers could cause issues.

24/2 wiring will be adequate provided the correct current limiting doorbell transformer is used. The doorbell will not draw more VA than it needs.
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post #3 of 5 (permalink) Old 2019-07-06, 07:53 PM
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Ring FAQ sez Transformer needs to provide 16-24 VAC with a total capacity of 30 VA (i.e. Watts)...so total Current Draw is under 2 Amps. Resistance of AWG24 is about 2.6-ohms/100-ft....so if Ring is 50-ft away from Transformer, the Total Resistance (there and back) would be about 2.6-ohms....corresponding to a negligible voltage drop of only about 5.2 Volts.

I see that 10 VA [way too wimpy] is very common in Replacement Door Bell Transformers....so if you are unsure about YOUR unmarked Transformer (mine aren't marked either), then you might want to upgrade to either of fol. which are compatible:
https://www.amazon.com/Newhouse-Hard.../dp/B07HKQ4GC3 [Meets min. rqmts: 16-VAC with 30-VA]
https://www.amazon.com/FCHO-Thermost.../dp/B07PCRHP4Q [Enough for OTHER devices: 24-VAC with 40-VA]

Ring Video Pro Manual Download:
https://support.ring.com/hc/en-us/ar...o-Doorbell-Pro

Ring provides alternative wiring diagrams, depending on how complicated you want to make your situation:
https://support.ring.com/hc/en-us/ar...bell-Pro-Setup
https://support.ring.com/hc/en-us/ar...o-Doorbell-Pro

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #4 of 5 (permalink) Old 2019-07-08, 08:40 AM Thread Starter
 
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Hmm - that is interesting. So your analysis shows that (assuming the transformer is supplying the correct voltage) that the cat 3 24/2 wire should work just fine? The run is less than 50 feet each way.


There are no markings on the transformer itself. I think I will swap it out just in case.
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post #5 of 5 (permalink) Old 2019-07-08, 03:03 PM
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Most doorbell transformers have a fairly high internal impedance in order to prevent excessive current draw in the event of a short circuit. They usually also have a thermal cut off to prevent damage from overheating. They supply a higher than stated voltage at no load in order to compensate for internal voltage drop at full load. Any calculations for voltage drop need to factor in the internal transformer impedance.

Note: Impedance (for AC) is similar to resistance (for DC) but is typically higher due to the effects of reactance in AC circuits.
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