I have a hydroponic baseboard heat system in my home (just bought home
in June and house was built in 1988) that is regulated by the old Mears
analog (2 wire NI 120/240 Vac) thermostat. I have 3 zones therefore 3
thermostats. I wish to replace these with digital programmable models.
I have measured 122 Volts at .68 amps at the wires coming into the
thermostats. I have been unable to locate a thermostat that can run on
this low power. Most have a 1 amp (250 W) minimum power rating.
Besides changing my wiring to a low-voltage system, is there a solution
to my problem other than just keeping analog thermos in place?
You are misinterpreting this. What you just measured is that your
existing thermostats draw 0.68 amps of current. Your house electricity
is right about 120V, as it should be, and this is irrelevant for your
If you put your new 1-amp rated thermostat on, it will draw whatever
current it needs to function. The 1-amp rating is telling you that it
will pull something around 1-amp or less. Probably right around 0.68
amps would be my guess, actually. It is a "minimum power rating",
because it is telling you that your wires had better be able to handle
a minimum of 1-amp, otherwise it might be unsafe. You can't measure
current capacity in the way that you are doing. What you do instead is
look at the wiring and make sure it is large enough (and installed
properly) to handle up to 1-amp.
[ I'd be real surprised to find any 120V wiring in a house that is
rated anywhere near as low as 1-amp, but don't take my word on that. ]
I removed the thermostat and used an amp/volt meter on the wires coming
out of the wall. That is where I am measuring .68 amps and 122 volts.
I had previously installed a Honeywell line-voltage thermo that was
rated at 2 Amp minimum and it gave me a low power indicator and was not
able to switch on the heat although the display functioned perfectly.
At any rate, the battery operated LUX ELV1 will work according to LUX
tech support so I believe I have found my solution.
I appreciate very much that you took your time to try to help me.
If you have the ends of two wires, you can't possibly be measuring
amps. So either you are completely confused, or I have completely
misunderstood what you are talking about. Amps are what you get when
electricity travels through things. If there is no _thing_, then there
are no amps. What you said is basically the same as me saying "I walked
out to the road in front of my house with a meter and measured 35mph
coming out of the road." It just don't make sense.
What you likelly have is not 122 volts. What you have is 12V. There is
a transformer in your basement that converts from 122 volts down to 12.
Now, this transformer is only capable of putting out a certain number
of amps, maybe just 1 or probably even less (I really don't know -- but
it is certainly down in the range of a few tens or hundreds of
milli-amp, and not more than say 1-amp). When you put your "2-amp"
thermostat on, it tries to pull too much electricity through the thing.
What ends up happening is that the transformer can't keep up, and could
overheat and ruin itself. In these cases you might see the voltage drop
below 12V, and you would inteed get a "low power" indicator. Of course,
you won't see any such drop when there is no thermostat connected.
Alternatively, is it that you only have a _single_ wire, which you are
measuring the current as it is travelling through the wire? In that
case you could be trying to wire something in series (where I mean
_really_ in series, electrically, not as many people use the word).
Which is bad.
Or I could just be completely off my rocker. (Admittedly, I haven't
slept in a bit.)
The "thingy" is my TENMA Digital Amp/Voltmeter. :) So, yes, I am
accurately measuring the current and voltage running through my system.
One wire is the load and one is the line. I also have a copper ground
No, I do not have a low voltage 12 V system. I have the
"old-fashioned" 120 Vac line-voltage system. No transformers
I have a 2 wire with a ground. The wires are thick - much thicker than
those on a 12V line.
Ok, I'm probably wrong and confused, and I don't know what you are
measuring. In my defense, you don't seem to know what you are measuring
Obviously I don't know how these line voltage themostats work. But I
suppose it is reasonable that they _are_ placed in series with the
load. And you are measuring the AMPs by just touching the two probes to
your two wires, and so are measuring the current that would pass
through your heating elements in the full ON position. I would be a
little nervous about having 10 amps or more go through the little
multimeter probe wires that I would be holding, and I know my
multimeter would blow its fuse if I tried that anyway.
The other poster is probably right, that your thermostat is going to
borrow some power using a current division circuit, and that this
requires at least a certain low resistance (and so high amps) for the
heating element. But that you are measuring 0.68 amps seems odd to me,
because an electric heater would use 5, 10, or more amps, no?. I don't
know what a hydroponic baseboard heater is (unless you are using an
electric heater to grow plants in water, that is). Is this some fancy
hot water system with electronic valves (that need .68 amps to
It should be obvious that I am not going to be able to help you here,
but I am curious all the same.
The current measurement confuses me too.
I went looking on the web.
Looks to me like this is what he is talking about but it is nothing but a
If so the ELV1 looks like a direct replacement.
As for the Honeywell, all I can think of is that it might have been for a
240 volt system.
My best guess would be that the load the stat runs has something to do with
how the stat is powered. The stat "robs" power off the line voltage when the
heating load is off. In other words it runs a small amount of power through
the heating element constantly to power the stat. Enough to power the stat,
but not enough to produce any heat. If the resistance is too high there will
not be enough electrical power trickling through the system to allow the
stat to work.
Your other post backs up my theory because the stat's low power indicator
was lit up when connected to a too small of load, (heating element).
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