wmoses wrote:
Gdetrailer wrote:
Not sure if that T-stat is going to work very well on 12V.
Per the spec chart "24V AC with battery back-up OR 3.0V DC" it looks like the T-Stat uses the 24V AC coming from furnace transformer as the MAIN supply. The battery serves as BACKUP in case of power outages or long calls for HEAT on the furnace line (when T-stat calls for heat it basically shorts out the power the T-stat sneaks from the furnace).
I doubt that the life of the battery will be long if you don't have 24V AC coming from the furnace or T-stat may not even function correctly...
Just my hunch...
Hmmmm.... Looking at Mod 37 referenced in my initial post, I see
"Some residential thermostats use 24 VAC to power them. But if they have the battery backup feature, they can be used for RV 12-volt systems."
I am hoping that this in fact the case.
THAT is a quote from someone who has EXPERIMENTED with a FEW digital T-stats, not ALL digital T-stats.
Not ALL digital T-stats FUNCTION the same way when it comes to powering them. ALL digital T-stats have some sort of "power backup" which can be a large capacitor or a small rechargeable battery or even plain off the shelf replaceable dry cell.
NONE of the HOME DIGITAL T-STATS were EVER DESIGNED to be used on ANY 12V system. That IS a FACT that you can take to the bank on.
MODERN DAY HOME heating and A/C systems use 24V AC (some old, old systems used "millivolt" T-stats which ran off the voltage developed by the thermocouple on the furnace), NOT 12V DC so it is EXTREMELY IMPORTANT to find a T-STAT which SOLELY DEPENDS ON DRYCELLS to "operate". Not ALL home T-stats do this.
My suggestion is if your heart is SET on using this T-stat then TRY IT, worst comes to worst it won't work and you take it back for a refund. If it works then keep it.
My point was the way the manufacturer spec read it was 24V with battery "backup" so to me it is very questionable if it would work.
As someone also pointed out, most if not all digital T-stats have a LOW TEMP CUTOFF point where they will not even turn on the furnace nor go below that temp. I have one in my garage which doesn't go below 45 degrees and if the temp is BELOW 40 degrees it WILL NOT turn the furnace on. I have to hold my hand over the T-stat to "warm" it up to fake the stat into firing the furnace (I only heat the garage when I am working in it).
Another point to think about, SOME digital T-stats may not have a LOW BATTERY CUTOFF. In other words if the battery dies the T-stat may not shut off the furnace. This is important to consider especially if you are attempting to keep your temps down, drycells get weaker the colder they get.
I ran into that with a digital T-stat, came home from work one winter day with the house at 95+ degrees and the furnace still going :E The T-stat battery died while it was calling for heat and LOCKED UP the output (used solid state relays).
