current capability of W1/W2 on NEST 3rd gen learning tstat?

[rny1nestcom]

how much current can a nest 3rd gen learning thermostat supply on W1 or W2 terminals?

i need to supply 150ma to control a relay on a Dual Fuel implementation when the heat pump switches off and needs to turn on a 3 zone baseboard heating system

[CoolingWizard]

@rny1nestcom ,

if what you have is a dual fuel system that is to say that you have an electric heat pump and you have a gas boiler driving baseboard heat. in a dual fuel system there’s plenty of current available. It’s not that the thermostat supplies the current but the actual equipment supplies the current. So in your particular case, the air handler that’s supporting your heat pump would connect its power wire to the RC input terminal of the thermostat and the gas boiler would put its input power on the RH. The W1 wire would go to the boiler, and you would not need to use W2 since you have no auxiliary heat. Now if your boiler comes with a two stage gas valve, then you wouldn’t be able to use W2, but you’ll have to define it as stage two gas heat. 

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AC Cooling Wizard

[rny1nestcom]

Cooling Wizard 

thanks, i got it; i think i mis-stated the question - let me try it this way:

1. when the 3rd gen switches off the heat pump [let's say the crossover from heat pump to baseboard is say 40deg],  it passes a signal to a TACO ZVC403 to allow thermostats for the 3 baseboard zones to exercise control for the temp settings of their zones

2. i need to energize a 3-pole SPST relay [NO contacts] with each pole in series with that zone's thermostat circuit; the current required to flip all 3 poles is about 150ma

so the question should have been ...can the 3rd gen 'PASS" a constant 150ma to this relay to allow the 3 zone valve thermostats to exercise baseboard control of their zones,,,?

i kept looking at the specs on the NEST 3rd gen, says 24volts, but doesn't mention the current capability. And you are correct, it isn't what the 3rd gen can 'PROVIDE' but i should have said what can it 'PASS". 

So am i correct in saying that it can 'PASS' what it needs to turn on the relay since there is plenty available from the  HVAC system? [the relay is an RIBL3C 3-pole SPST relay]

i am new at this. If this was wood, i would measure 3x but cut once. Since the NEST stuff is expensive, i though I'd ask first before just trying it. I thought about not using the relay, but that would mean basically tying the 3rd gen to all the 3 zone thermostats in parallel - bad idea - loss of independence; i think each circuit needs its' segregation.

really thanks for answering,

Ron

[CoolingWizard]

@rny1nestcom,

The Google Nest Learning Thermostat 3rd generation typically handles 200 mA of constant current flow when charging. There’s no reason to believe that the back plate can’t handle a constant 150 mA on any other path, such as W1 

It sounds to me like you’re going to set up the nest thermostat as a dual fuel heating system. And you’re gonna pick a specific temperature at which the system switches from heat pump heat to gas boiler baseboard heat? Is that correct? In other words, you will have no auxiliary heat for the heat pump 

AC Cooling Wizard

[MilesSummers]

I want to ask similar one, any help?

[CoolingWizard]

@MilesSummers ,

What is your specific question?

AC Cooling Wizard