Wiring conundrum for the water heater

[routlaw]

So I am finishing up the install of a new water heater, tankless version to replace the old Suburban. Retrofitting into the Oliver is NOT an easy task but more on that later. So on the old Suburban there are 3 12 volt DC wires connected to the 12 volt terminals, red for +, blue for -, and yellow/green for ground. However when I measure the voltage across the wires with HW switch turn on, the red to blue measures only 12.2 volts but when I measure the red to green/yellow @ ground I received the full SOC of my Epoch batter which is 13. 7 ± volts. 

The new Fogatti tankless only uses two DC wires, red and black, and no AC connection at all. I am inclined to think in my case to use the red and green/yellow wire for the full DC voltage available to me. 

Can anyone explain why the red to blue wires only return a reduced voltage of 12.2 volts DC? My gut instinct is the wiring was done incorrectly at the factory build swapping the negative terminal for the ground but this is just a stab in the dark not being totally versed in DC electronics. 

Thanks and appreciate any insight on this.

[Snackchaser]

You are measuring volts with WH switch on, which means your measuring the voltage drop of the internal WH electronics.  Disconnect the red, and volts should be 13.7.  The yellow/green wire is a non-current carrying ground due to the AC aspect of the WH, so it does not see the electronics voltage drop.   All seems normal.

Cheers, Geoff

[routlaw]

I probably did not explain my situation thoroughly @Snackchaser. The old Suburban is completely out of the Oliver, AC wires are taped off and disconnected. When measuring the remaining 12 volt wires they have not been connected to anything yet. If measuring with the HW switch off, crickets, I get nothing other than small microvolts. The switch has to be turned on to obtain anything close to 12 volts +. 

So if I connect the red + wire and the blue - wire to the new Fogatti it will only receive 12.2 volts of input. That amount of DC current is not enough to effectively run the Suburban furnace based upon past experiences and it might have a negative impact on the new WH with only 12.2 volts. Or am I missing something?

Thanks 

[Snackchaser]

That is different.  I'm on jury duty lunch break, this will be quick.  The WH switch I assume is a remote switch.  It likely is a specialty switch with some resistors or such causing a voltage drop, some LEDs will do that.  Unfortunately I'm not familiar with that suburban unit.  You will probably need to replace the switch for the new WH.  Check the old switch for internal resistance with an ohm meter.  Good luck and let us know what you find

 

[routlaw]

Understood good luck with JD. The HW switch I am referring to is the one remote switch that Oliver installs on the interior not the switch at the new WH. IOW's I'm still confused. Thanks for trying though. Thus far nothing is connected to the new WH other than the propane. I am trying to figure out which wires to connect to the new WH.

Many thanks. 

[Snackchaser]

I looked at the Suburban manual, it shows a wall switch with Fault/Reset light on the blue wire.  That would cause voltage drop!  Use the green/yellow wire for negative ground, and you should be good to go.  Let us know if that’s what you have.

Cheers, Geoff

[routlaw]

After many attempts finally got the thing to work but only after I used both the blue - and green/yellow ground wires connected together and to the negative black terminal of the Fogatti WH. The device would not work using either the blue or green/yellow wires individually connected to black wires of the Fogatti.

So apparently it would be better to connect the green/yellow wire to some metal portion of the trailer, correct? I should add once operating the Fogatti worked great. 

[Geronimo John]

 

21 hours ago, routlaw said:

The new Fogatti tankless only uses two DC wires

Forgive me if I am not understanding your problem.  But here is what I am thinking:

Your Hull #70 is most likely set up like my 2018.  A hot water requires a bunch of energy.  It can get that energy from propane or 120 volt.  The switch on the unit activates the 120V AC power to heat the water.  The switch inside just activates the circuit board. Our hulls are not set up to power up hot water from the DC source.  It is not like the refergerator  that is.   

The Suburban hot water heater needs energy from three systems. 

• The 120 V lines provide alot of power to the unit if your outside switch is on to use 120V power to do the heavy lifting (heating water)
• The DC power to to the gas solenoid valve to provide propane to heat the water if you want it to do the heavy lifting.

But regardless of how you want to provide the energy to heat the water, you also must have DC to the circuit board.  Those wires are not sized to provide power to heat the water.  The DC wires are there only to provide power to the circuit board.  Put a massive load on them and one would think you would blow it's fuse.

Likely the reason your not blowing the fuse is that your new demand hot water has a sensor that will not energize it's heating coils unless the voltage is high enough to work properly.

IF THIS IS YOUR PROBLEM

Then you have a larger project than you anticipated as you'll need to run a new DC + and - to your demand hot water heater.

I sure hope I am missing the boat on this one.

GJ

[jd1923]

19 minutes ago, Geronimo John said:

… you have a larger project than you anticipated as you'll need to run a new DC + and - to your demand hot water heater.

I was thinking “new DC run” and GJ laid out the circuit logic perfectly!

See what fuse and wire gauge Fogatti specs in their documentation. I would locate a spare or empty position in the 12VDC fuse panel to do this right. The last thing you want is more inline fuses under beds! This is a  major appliance. Source wiring should start at the main +/- buses with the positive running through the fuse panel. 😎

[routlaw]

Thanks @Geronimo John and @jd1923 for the additional comments.

Clearly I have not provided adequate information regarding the install. No the Fogatti WH only uses 12 VDC to run the internal circuits, sensors etc and which also then feeds back to its remote control which is a nifty device itself. The power to heat water is only through propane and not AC and certainly not DC voltage. The wires themselves coming from the Fogatti are probably 16 AWG or 18 AWG at best and they are intended to connect to the same wires that fed the Suburban sensors circuit board, nothing more. Attaching a few photos below to illustrate (hopefully) the layout and wiring situation. 

I will be crimping those connections later on today rather than the wire nuts but used those just to make sure everything is working ok before proceeding to final installation. 

In the first photo the black and red wires represent those coming from the WH and as you can see I have red to red (+) and black to blue & green/yellow (- & GND). The new WH works fine this way oddly enough.

The next photo is the same just pulled back further to illustrate the entire enchilada a bit better

Remote below with two blue wires (non polarity) from the same wiring harness of the new WH

inside the basement where the new WH is installed using 1/4 - 20 SS screws, lock nuts and fender washers rather than the pitiful pop rivets initially used for the Suburban WH. Note this IS a two person job.

1/4-20 stainless steel screws viewed from the outside though the bottom row I used self tapping Big Timber screws into a block behind the FG wall. There simply is not access to tighten nuts and screws on the bottom row. 

Everybody knows what a locking nut looks like but just in case someone else tries this method thought might be helpful.

[jd1923]

48 minutes ago, routlaw said:

Clearly I have not provided adequate information regarding the install. No the Fogatti WH only uses 12 VDC to run the internal circuits, sensors etc and which also then feeds back to its remote control which is a nifty device itself.

Yeah Rob, my head is surely not thinking clearly this week! Yes, all you need is low-amperage wiring since power is provided by LP. Given the Suburban had a 120VAC circuit breaker, I’d still want a 12VDC fuse in the panel for your new HWH!

Also pull the original 120VAC wiring from the breaker panel, at least pull the black/hot wire off the breaker, so the other end at the HWH is dead. You’ll have a 120VAC breaker available if you need to add a new circuit for another 120VAC appliance! 😎

Great looking installation! Update us later on your experiences with the Fogatti tankless HWH!

Edited 2 hours ago by jd1923

[Snackchaser]

16 hours ago, routlaw said:

So apparently it would be better to connect the green/yellow wire to some metal portion of the trailer, correct? I should add once operating the Fogatti worked great. 

You are on the right track.  However as mentioned before, the blue wire is part of the Fault/Reset and it is grounded through the switch light as seen in the schematic.  That is causing the voltage drop you were asking about.  Don’t use the blue wire because it creates a resistive current path through the reset switch light.

The yellow/green was the intended ground wire.  It was probably grounded through the old WH chassis that’s now gone.  You are right in thinking to re-ground it.  However, I'd cap it off unused because apparently it's not be properly grounded on the switch side.  Just connect the new WH black wire directly to ground.  Only use the red wire from the switch.

The on/off switch will work for the new WH, but the reset will be disconnected and not used.  The AC side is completely separate as you know, although the AC ground might have been the original ground path for the yellow/green wire on the old units chassis.  

Having said that, isn’t the new unit controlled by a separate panel?  Is a power switch required?  I’d probably splice the red wire to bypass the switch, and blank off the switch to avoid any future confusion.

Hope that helps!

 

 

[DanielBoondock]

Note about phantom voltage drops. As mentioned it can be due to active/passive devices in the signal path, but it can also be resistance/impedance in the circuit. Case in point, the composting fan my two month old Oliver stopped working. The odd thing was my DVM measured around 3VDC at the terminal - not enough to run the computer case style fan - indicating a circuit issue. 

Jerry at support gave me a great troubleshooting list, the first of course was to check the fuse, which is fine. I didn’t suspect that as it was getting a low voltage, it’s an inline glass fuse and was unbroken. But I put the fuse back and voila - it works. There must have been a poor connection in the fuse housing which gave enough resistance for a voltage droop, so reseating it fixed the problem. 

So general advice is to check every leg of the power rail, a little corrosion or a loose connection can/will introduce resistance. 

[routlaw]

45 minutes ago, Snackchaser said:

The on/off switch will work for the new WH, but the reset will be disconnected and not used.  The AC side is completely separate as you know, although the AC ground might have been the original ground path for the yellow/green wire on the old units chassis.  

Having said that, isn’t the new unit controlled by a separate panel?  Is a power switch required?  I’d probably splice the red wire to bypass the switch, and blank off the switch to avoid any future confusion.

Hope that helps!

 

 

It does, thanks. Never knew that switch was also used as a reset. Regardless. You are correct, see photos above for pic of the control panel which works nicely. There is a power switch on the new WH which can be seen from the exterior view photo. 

You are also correct in that running the new black wire straight to ground and only connecting the red wires allows for the unit to work. Oddly enough as previously mentioned the new WH works perfectly with both the blue & yellow/green wire connected to the black wire from the WH. It will not work if using those two wires individually connected. This aspect is a mystery but clearly the two combined wires (blue, YG) create the same connection as running the WH black wire to ground. 

Given the location of the Oliver WH switch and lack of access at least on our hull it's not worth the trouble to eliminate that switch from the system but in theory yes it should be possible. Its not that big of a deal though to use, no different than years past with the old WH.

Also @jd1923 good points on eliminating the AC wires at the panel. As for fuses for 12 V DC there is a fuse located directly on the new WH and they provided an extra with the kit. I would assume this more or less suffices for a fuse inline at the panel but maybe not.