Hey folks!
First post... please be gentle. I know very little about electronics theory or design and have a project to complete quickly and for which I'd be willing to pay.
First, the background. I'll try to be quick and summarize the current situation. If you're scratching your head.. it's probably because "I didn't know that at the time". LOL I've been catching up today!
I have a WaterFurnace, circa '91, that has a DC control board (I didn't know that at the time). The furnace wasn't working so I called my heating contractor. He told me the thermostat was done and I needed a new one. He had one in the truck (not the right one, but one that would do for the present) and wired it in. I got a quote for the right one, shopped around and picked up one locally. I wired it in last night and things start working.
Well, mostly. The instructions were unclear about a couple of things and I don't know why the call for service light comes on briefly when he unit switches off, so I call my contractor back for a looksee and verification. He says it's all wired correctly and confirms that it's supplying 24VAC to the terminals.
In the meantime, I called Waterfurnace to get some info and they tell me about the DC board in my old model and that I need a DC thermostat (of which, only one manufacturer still makes them and boy - are they pricey!) My contractor verified the DC board's presence and neither he nor the guys at Waterfurnace know why it's operating (but they both said that's the reason for the sporadic "call for service" indicators).
Anyway... all that backstory to come to this. I don't want to install an ugly DC stat with absolutely no features when I can use a nice modern one instead. Not unless I absolutely have to be dragged, kicking and screaming, into acceptance. I have plans for down the road, which include installing a Honeywell VisioPro IAQ to control the furnace, the VanEE and a humidifier down the road, all while eliminating wall clutter.
The specs for the original (dead) thermostat indicate:
Power Requirement: 18-30VAC, 10ma
Control Outputs: 15ma @ 22VDC max.
And the specs for the White Rodgers indicate an input of 24VAC from the transformer. I've been told that the thermostat steals power from the transformer hookup and converts it to DC for its own internal use. I've also been told that the thermostat relays are mechanical - switching whatever is put through them.
The first thought that comes to mind then, is converting the 24VAC from the transformer to 22VDC at 15ma (max).
the other thought that comes to mind, is to leave the 24VAC in place and convert the signals from the thermostat from 24VAC to 22VDC before connecting to the furnace.
Not sure what's easier, but it seems the latter approach - delivering what would be expected - would be the safer one. There would be up to 6 converters required, including the fault indicator.
What do you think?
First post... please be gentle. I know very little about electronics theory or design and have a project to complete quickly and for which I'd be willing to pay.
First, the background. I'll try to be quick and summarize the current situation. If you're scratching your head.. it's probably because "I didn't know that at the time". LOL I've been catching up today!
I have a WaterFurnace, circa '91, that has a DC control board (I didn't know that at the time). The furnace wasn't working so I called my heating contractor. He told me the thermostat was done and I needed a new one. He had one in the truck (not the right one, but one that would do for the present) and wired it in. I got a quote for the right one, shopped around and picked up one locally. I wired it in last night and things start working.
Well, mostly. The instructions were unclear about a couple of things and I don't know why the call for service light comes on briefly when he unit switches off, so I call my contractor back for a looksee and verification. He says it's all wired correctly and confirms that it's supplying 24VAC to the terminals.
In the meantime, I called Waterfurnace to get some info and they tell me about the DC board in my old model and that I need a DC thermostat (of which, only one manufacturer still makes them and boy - are they pricey!) My contractor verified the DC board's presence and neither he nor the guys at Waterfurnace know why it's operating (but they both said that's the reason for the sporadic "call for service" indicators).
Anyway... all that backstory to come to this. I don't want to install an ugly DC stat with absolutely no features when I can use a nice modern one instead. Not unless I absolutely have to be dragged, kicking and screaming, into acceptance. I have plans for down the road, which include installing a Honeywell VisioPro IAQ to control the furnace, the VanEE and a humidifier down the road, all while eliminating wall clutter.
The specs for the original (dead) thermostat indicate:
Power Requirement: 18-30VAC, 10ma
Control Outputs: 15ma @ 22VDC max.
And the specs for the White Rodgers indicate an input of 24VAC from the transformer. I've been told that the thermostat steals power from the transformer hookup and converts it to DC for its own internal use. I've also been told that the thermostat relays are mechanical - switching whatever is put through them.
The first thought that comes to mind then, is converting the 24VAC from the transformer to 22VDC at 15ma (max).
the other thought that comes to mind, is to leave the 24VAC in place and convert the signals from the thermostat from 24VAC to 22VDC before connecting to the furnace.
Not sure what's easier, but it seems the latter approach - delivering what would be expected - would be the safer one. There would be up to 6 converters required, including the fault indicator.
What do you think?