Stray/Phantom Voltage

[richard5933]

I've got a 12v water pump in the wet bay. It is fed by three different 12v+ feeds, one from each of the three switches upstairs (bathroom, kitchen, & cockpit).

There is an LED indicator light on the dash which lights when there is power to the water pump. Helpful because we like to turn off the pump any time we leave the bus, and this indicator is on our visual checklist as we go out the door.

Recently we've noticed a very faint glow of the indicator at all times. It might have been there for a while, but we just noticed it. So today I did some testing. I separated all the feeds, and found a few mV on each of them. Since they all go through the main wiring loom where both 120v and 12v live lines feed, I wasn't surprised to see this.

Here's where it gets weird...When I measure with the three feeds together, with all three switches in the 'off' position, I get 0.9v from them. I then pulled the fuse from the two rear switches and disconnected the wire going to the front switch at the switch. Still got 0.9v at the point all three join together to feed the water pump.

Is it possible to have this much stray voltage transmitted just by having the wires run through the loom?

My concern with all this is the result of having that phantom voltage going to the water pump all the time. My immediate solution will be to install a relay in the circuit. The coil in the relay will be triggered by the current water pump switches, and I'll run a new 12v+ feed directly from the fuse panel to the switch side of the relay. This should isolate the pump from any of the stray voltage floating around in the switches. Probably should have had a relay in there from the start, but that's not how things came to me.

Still would like to learn more about this and figure out where the stray voltage is coming from.

Any thoughts?

[sstgermain]

There is usually a "pump controller" that those switches go to and there is an output that goes to the pump. The controller allows you to turn on the pump from different locations. That unit might be going bad. They are fairly inexpensive.

[dickandlois]

Richard, By chance is the LED indicator still lighting?

The voltage reading is real close to the voltage one would read on a old geranium diode, leakage voltage.

The only location that would have something that old, would be the charging circuit for 12 volt battery circuit originally installed in the Perkins battery charging system and you have or are using a different system to charge the battery. 

Rich.

[richard5933]

15 minutes ago, sstgermain said:

There is usually a "pump controller" that those switches go to and there is an output that goes to the pump. The controller allows you to turn on the pump from different locations. That unit might be going bad. They are fairly inexpensive.

Custom Coach didn't install anything like this - all the switches go directly to the pump. That's why I was going to install a relay, but a latching control sounds like it would be better. Thanks for the suggestion.

[dickandlois]

4 minutes ago, richard5933 said:

Custom Coach didn't install anything like this - all the switches go directly to the pump. That's why I was going to install a relay, but a latching control sounds like it would be better. Thanks for the suggestion.

Richard, the latching relay referenced to do come in different current ratings. So you will need the current requierment of the current pump or maybe a larger one . if you are considering an upgrade in the water pump in the future.

Rich.

[richard5933]

11 minutes ago, DickandLois said:

Richard, the latching relay referenced to do come in different current ratings. So you will need the current requierment of the current pump or maybe a larger one . if you are considering an upgrade in the water pump in the future.

Rich.

Yup - I noticed that when I went to research the controller. The most common ones are 10-amp, which would work but not provide much head room. I ordered a 15-amp controller so that I have room for a larger pump in the future.

Good thought about the charging circuit. There is one in the old Kohler generator but it's switched off right now. Of course, that doesn't mean that there isn't a failed part in there causing the phantom voltage. The main battery chargers right now are Progress Dynamics modern multi-stage chargers, so they are unlikely culprits.

My guess is that the whole thing has something to do with all the 120v and 12vdc wiring sharing conduits, chases, and terminal blocks. A gift from Custom Coach that just keeps on giving. Slowly working to remedy that whenever I'm doing improvements and upgrades.

[dickandlois]

Richard, what is causing a steady 0.09 volts is a sticking point for me. If everything is disconnected then the meter would read a varying volt caused by the alternating voltage inducing the varying voltage induced into the long wiring used to power the 12 volt pump.

With only Vacuum tubes, resistors and capacitors to work with our ancestors made some amassing strides in developing a modern world. DC voltages where supplied by using vacuum tube diodes or DC generators before the advent of any solid state  items.

Rich. 

 

[kaypsmith]

I am wondering, when you set meter to AC, do you see any voltage, if so how much?

[richard5933]

4 hours ago, kaypsmith said:

I am wondering, when you set meter to AC, do you see any voltage, if so how much?

That's a great thought. Custom Coach did some weird things, one of them being using bonded neutral/ground. Even more weird was then using the 120v neutral as a ground source for some of the 12v circuits. I thought that I had identified and corrected all those, but maybe I missed one.

[kaypsmith]

The 120 V ac sure needs to be completely isolated from chassis ground for several reasons including just getting a tingle to becoming lethal if a person touches that metal skin on the side of the coach. Also LED lights and 12 volt dc devices can misbehave. Even the generator should not be bonded to chassis, it should be mounted in rubber with the ground strap bonded to the transfer switch and the ac circuit should have an isolated ground bus to and through the transfer switch. Richard, I realize that you already know this, but added for the reason of making others reading the post aware. Good luck finding the problem.

[richard5933]

I've ordered an Intellitec 15-amp water pump controller. I've got the wiring diagram downloaded from one of the sites online.

I have a few questions, and hope someone can help. It appears that the controller uses momentary switches to control the water pump. Push the momentary switch once and the pump turns on, push it again and it turns off. Is this correct? It appears that I can have as many momentary switches connected in parallel to accomplish this, which means I'll use two. The switch currently in the cockpit panel only has one conductor going to it, so I'll re-purpose that to trigger an indicator lamp on the dash for the water pump since I don't really need to control the water pump from the dash (there is a switch in the bathroom and in the kitchen).

I've currently got one 12v+ wire going from the fuse block to each of the switches. The switches then sends 12v+ to the water pump. If I understand correctly, this will need to be changed. The switches will now provide a ground to the controller, so I need to change out my on-off rockers for momentary switches, and then wire them to provide a ground source.  I'm planning to add an additional conductor for this ground wire, and then use the existing conductor to send 12v+ back to indicator lamps which I'll mount next to the switches.

It seems that I'll also need to run a 12v+ supply line directly from the fuse block to the water pump. Should be no problem. The current ground wire going to the pump will be disconnected and will be replaced by the ground wire coming from the newly-installed Intellitec controller.

Do I have this generally correct?

[dickandlois]

Richard.

Push the momentary switch once and the pump turns on, push it again and it turns off. Is this correct? Yes !

I hate to admit it but have not worked on or replaced any of the latching relays for the water pumps in years, but it sure sounds like you have a handle on converting the system. The system works very well and is quit robust. The one thing that will do them in is over current and the wrong sized wire for the current load that supplies voltage to the module when it is turned on.

Rich.

 

[richard5933]

Thanks Rich. I'll post a followup once the parts all come in and I've got things installed. It will be nice to be able to turn the pump on from either bathroom or kitchen, regardless of where it was turned on. I'll add an additional switch in the wet bay for convenience as well.

[richard5933]

Rich - Any idea why the Intellitec 15-amp latching controller says it's only for use on water pumps with at least a 5 amp current draw? I understood the controller to be a simple latching relay which was triggered to switch on-off by momentary switch.

Since our pump has a pressure switch built in, once it reaches pressure there will be zero current draw. Same for any modern pump. I understand putting a max load rating on the controller, but why the minimum especially since nearly all pumps will have zero load lots of the time.

What am I missing on this?

[richard5933]

Wrap-up/Update...

I got the Intellitec water pump controller yesterday and today I installed it.Took a bit of finagling to get all the wiring run, but it's in and works. Only missing piece is the proper connector to plug into the controller - I'm still waiting for that so for now I'm using the terminals wrapped in heat shrink tubing. I used a terminal block for the switches to connect through and another for the indicator lamps. Made for a cleaner install, I think.

I've got a switch w/indicator light now in the bathroom and kitchen, as well as an indicator over the dash visible from the door (so we can check pump status without having to go inside). I also installed a switch w/indicator in the wet bay for convenience.

Overall I like using the controller better than how it was before. Pump can now be turned on/off from any switch, regardless of where it was turned on. Also, the switches are carrying only a ground conductor so there is less risk. The 12v+ runs directly between the fuse block and the pump on a 12ga wire.

The phantom/stray voltage was largely corrected by moving some of the 12v wiring away from the 120v, and whatever remaining few milliamps won't matter to the pump now that there is the latching relay in between.

Thanks to all for the help and for the suggestion about the pump controller.

[manholt]

Nice work! 

[kaypsmith]

Nice work Richard! Those switching relays do work well, nice thing is, you can use as many momentary switches as you may like to control them. This is the same system that is used in many industrial installations for emergency shutoff purposes.

[richard5933]

What's odd is how hard it was to find the harness to connect to the thing. The controller itself was easy to find, but the harness took some effort. Hopefully the company I ordered from will ship promptly.

I suppose that most people never need to replace the harness connector, just the controller. The harness connectors are probably sold only to manufacturers. I could have called Intellitec, but it seemed that my only time to sit and do the research recently is nights and weekends.