Bizarre electrical issue

[Janss]

I have a built in digital clock in my motorhome by the bed. It seems whenever I turn on the gas furnace, it affects this clock. After the furnace starts running, the clock sounds one long beep and the time changes. This morning the display showed 0:02. Then awhile later it showed 52:08. Just weird. The clock display is fine before the furnace gets turned on. I'm plugged in to shore power.

Any ideas?

[Janss]

Very interesting wa8yxm!

Harvard...I'll have to check the result of resetting the clock while the furnace is running, i.e. if the time stays correct. Don't remember if the furnace was still running the other morning when I reset the clock.

[wa8yxm]

Janss wrote:
wa8yxm...I have a digital multimeter. Your previous post mentioned "analog multimeter". Why analog?

Ah, this is where I get to show off 🙂 (I studied electronics and engineering)

Digital meters have what is called a Sampling rate. That means they update every slice of time (Say every second or 10 times a second) the reading does not change fast enough to follow the dip in voltage and what's worse your eyes only refresh about 1/30th of a second at best (Proof, watch TV, you are seeing 30 still pictures every second, not a smoothly moving picture but 30 stills a second, at 25 (PAL standard) you may notice flicker)

The analog meter will not properly display the lowest voltage either, BUT the needle will move instantly, and you will see that movement, for your eyes respond to movement very fast.

So you have two choices when looking for a short term "Dip" a fast analog meter will show the presence of a DIP, which a Digital may well miss completly. Or a 'scope which will properly display the DIP in real time since the "needle" (Trace) moves at the speed of light.

But scopes are expensive

[Harvard]

Another thought! What is the layout of the RV relative to the three items?

1. The clock,
2. The furnace, and
3. The breaker panel.

Does it look like it would be easier to run the clock power wires to the breaker panel or easier to run the clock wires to the furnace?

[Harvard]

Not to spoil the fun but it is probably voltage spikes that are upsetting the clock as opposed to a steady low voltage problem.

In other words, can the clock be demonstrated to perform like a clock when the furnace is in a steady run mode.

[2oldman]

Janss wrote:
I don't know where to touch the black and red needles of the multimeter onto to check the voltage.

where the wires connect

[Janss]

2oldman...Thank you for the learning encouragement. I don't believe this would be a battery problem. It has been going on for the 4 or so years we've had the motorhome, and we've gotten new batteries in that time.

wa8yxm...I have a digital multimeter. Your previous post mentioned "analog multimeter". Why analog? The clock is a panel built in to a little wood sort of cabinet. I have to unscrew 4 screws to get to the back of it. Clock does have "Display on/off" toggle switch. I don't know where to touch the black and red needles of the multimeter onto to check the voltage. I assume I would do that live (with clock on) while my spouse turns on the furnace?

beemerphile1...Good idea! As I noted before, I'm not too concerned about this issue. But I like a good puzzle, and this is just that. Unfortunately I'm not too handy at working this kind of puzzle, compared to, say, a word puzzle. 🙂

[beemerphile1]

Hang a picture over the clock and go camping. :B

[wa8yxm]

Better to measure the voltage at the clock

IF the clock is on the furnace fuse (i did not think of that earlier)

Moving it to the bedside light circuit might fix it.

I have other fixes too but they cost money.

[2oldman]

Janss wrote:
Okay, this is getting too complicated for me now. I'm not good with electrical stuff.

Can you measure the voltage of a battery after turning off the converter for 1/2 hour or so? That's by far the easiest of all this, and in my opinion has a good chance of being the problem.

You can get better at electrical stuff. It takes a bit of effort and time, but it's well worth it as this isn't going to be your last electrical issue.

[Janss]

Okay, this is getting too complicated for me now. I'm not good with electrical stuff. Thanks for the additional comments though. With more research, I found out my house 12v panel is circuit breakers, not fuses...push to reset if they pop out. Maybe someone is familiar with these Winnebago panels. Seems like you have to unscrew the panel to get behind it to do anything with these breakers (other than reset). Even looking at the wiring diagrams I found online, I cannot figure out the connection to the alarm clock. Of course, I know nothing about wiring diagrams.

Anyway, this is a pretty insignificant problem in the great scheme of life.

[Harvard]

Any current changes in the supply negative of one device will have an unwanted effect in the other two devices. IMO

[Harvard]

The clock may be sharing the same DC POSITIVE and NEGATIVE wires as the furnace. The clock should be getting DC power from the DC distribution source with its own + and - wires and not be hanging downstream from the furnace.

PS: It is the NEGATIVE wire that is the real culprit as it may be in a ground loop configuration when it shares the DC NEGATIVE wire with the furnace.

[2oldman]

wa8yxm wrote:
It can happen the voltage will drop (Can happen.. WILL HAPPEN) and it may drop below the clock's cut off voltage, causing the BEEP, and weird action.

I'm going with that. I'm also suggesting you check the condition of your house battery.

[Janss]

Thanks so much for those ideas. Sounds logical that the clock might be on the same fuse as the furnace. There is not a separate 12v fuse labeled "clock" on the house 12v panel.

If that turns out to be the case, then I suppose the situation is not so weird afterall 🙂