Forum Discussion

wmoses's avatar
wmoses
Explorer
Sep 08, 2013

Robertshaw Digital Prog Thermostat RS5110 - Opinion needed

I am interested in doing the thermostat upgrade from my Coleman-Mach thermostat:



to a digital programmable thermostat.

I need to be able to set the thermostat for 2 daily programs - awaketime and bedtime - and I want to not have to touch the thermostat regardless of the time of year or the degree of shade when I go camping. In other words, so long as the battery is powering the thermostat's brain I can set the thing and forget it.

I have already done a search on the ModMyRV site (Mod 37, Mod 100) and saw that the typical choice is a Hunter or Honeywell unit which may / may not be programmable and which does not seem to have the auto changeover feature which to me is important. I have a Hunter in my house now and have not touched it in years. I barely know how to program the darned thing now. It just works to maintain the same 2 programs, all year long.

After some searching and trying to balance cost with function (the blue display is also nice) I have come up with the Robertshaw Digital Programmable Thermostat RS5110 (Product Info) which appears to fit the bill. There are even some how-to "tutorials" on their website.

So my first question - does anyone with experience doing this upgrade have any comments to share before I buy this unit? Specifically the wiring. It would be nice to know what the wires are on the back of my thermostat are (I am not able to check myself at this time).



Also the present Coleman-Mach thermostat has 2 fan speeds and I note that some of the mods use a small toggle SPST switch to enable either fan speed to be set once it is called for by the program.

This brings me to my second question - anyone see any issues with installing such a switch on this unit?

Thanks in advance.

8 Replies

  • doughere's avatar
    doughere
    Explorer
    Sep 10, 2013
    Many digital T'stats will work fine on 12 VDC systems. We have a Honeywell TH5110D1006 stat that We've used for years. It is set up for heat only. Stat needs a new battery (2 AAA's) every year or so. The RS unit you are looking at indicates it will run on 24VAC or 3VDC (two batteries), and is suitable for mV operation(means no power will be available to run it); should work fine. If you try to use the "night light" feature, it will probably be eating batteries.

    Regards,
    Doug
  • wmoses's avatar
    wmoses
    Explorer
    Sep 10, 2013
    shepcal wrote:
    Don't want any heat at night. Bloody stat had a minimum setting of 45 and would come on several times a night. So, I'm back to manual.

    Why not turn it off at night if it was going to be below the lowest set point of 45 deg? I don't think it is a deal-breaker for me although it is a very good point. I suspect any house-based thermostat will not have a low enough minimum to suit RVers who like the "sleep cool". :)
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Sep 10, 2013
    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).
  • gotsmart's avatar
    gotsmart
    Explorer
    Sep 09, 2013
    shepcal wrote:

    ...
    Bloody stat had a minimum setting of 45 and would come on several times a night. So, I'm back to manual.

    Shep

    That's a good point. When I had my S&B house, IIRC the Honeywell CT3400 setback thermostat could not be set below 60F.

    Knowing the uppermost and lowermost temperature settings would be good criteria for a T-stat in an RV application.
  • shepcal's avatar
    shepcal
    Explorer
    Sep 09, 2013
    I've been running a Robertshaw 9600 on my heater for about 5 years now. Have had to change batteries 3 times? This isn't probably helping you much cause I have a separate stats for my AC and heater. And the 9600 is not made anymore (typical- best stat made for price and purpose- drop it???). See no problem using an aux. switch for hi and lo.

    My stat change didn't work for me as I wanted. Had it programmed to turn heat on around 8PM (while out by campfire) and shut off at 9PM. Don't want any heat at night. Bloody stat had a minimum setting of 45 and would come on several times a night. So, I'm back to manual.

    Shep
  • wmoses's avatar
    wmoses
    Explorer
    Sep 09, 2013
    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.
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Sep 08, 2013
    Gdetrailer wrote:
    wmoses wrote:
    I am interested in doing the thermostat upgrade from my Coleman-Mach thermostat:



    to a digital programmable thermostat.

    I need to be able to set the thermostat for 2 daily programs - awaketime and bedtime - and I want to not have to touch the thermostat regardless of the time of year or the degree of shade when I go camping. In other words, so long as the battery is powering the thermostat's brain I can set the thing and forget it.

    I have already done a search on the ModMyRV site (Mod 37, Mod 100) and saw that the typical choice is a Hunter or Honeywell unit which may / may not be programmable and which does not seem to have the auto changeover feature which to me is important. I have a Hunter in my house now and have not touched it in years. I barely know how to program the darned thing now. It just works to maintain the same 2 programs, all year long.

    After some searching and trying to balance cost with function (the blue display is also nice) I have come up with the Robertshaw Digital Programmable Thermostat RS5110 (Product Info) which appears to fit the bill. There are even some how-to "tutorials" on their website.

    So my first question - does anyone with experience doing this upgrade have any comments to share before I buy this unit? Specifically the wiring. It would be nice to know what the wires are on the back of my thermostat are (I am not able to check myself at this time).



    Also the present Coleman-Mach thermostat has 2 fan speeds and I note that some of the mods use a small toggle SPST switch to enable either fan speed to be set once it is called for by the program.

    This brings me to my second question - anyone see any issues with installing such a switch on this unit?

    Thanks in advance.


    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...
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    Sep 08, 2013
    wmoses wrote:
    I am interested in doing the thermostat upgrade from my Coleman-Mach thermostat:



    to a digital programmable thermostat.

    I need to be able to set the thermostat for 2 daily programs - awaketime and bedtime - and I want to not have to touch the thermostat regardless of the time of year or the degree of shade when I go camping. In other words, so long as the battery is powering the thermostat's brain I can set the thing and forget it.

    I have already done a search on the ModMyRV site (Mod 37, Mod 100) and saw that the typical choice is a Hunter or Honeywell unit which may / may not be programmable and which does not seem to have the auto changeover feature which to me is important. I have a Hunter in my house now and have not touched it in years. I barely know how to program the darned thing now. It just works to maintain the same 2 programs, all year long.

    After some searching and trying to balance cost with function (the blue display is also nice) I have come up with the Robertshaw Digital Programmable Thermostat RS5110 (Product Info) which appears to fit the bill. There are even some how-to "tutorials" on their website.

    So my first question - does anyone with experience doing this upgrade have any comments to share before I buy this unit? Specifically the wiring. It would be nice to know what the wires are on the back of my thermostat are (I am not able to check myself at this time).



    Also the present Coleman-Mach thermostat has 2 fan speeds and I note that some of the mods use a small toggle SPST switch to enable either fan speed to be set once it is called for by the program.

    This brings me to my second question - anyone see any issues with installing such a switch on this unit?

    Thanks in advance.


    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...

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