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Generator vs Plugged In Puzzler


tony martin
 

I've just installed a battery monitor for my coach batteries and see a few surprises.  The first is this:  when I plug the RV into my home power, a standard 120V 20A circuit, the battery monitor detects the DC current flowing into the batteries and shows they are charging.  BUT when I plug the RV into my generator, no charging is indicated by my battery monitor.  The generator appears to be working fine as indicated by my functioning microwave and I measure 120V on the RV's power outlets via my Fluke multitester.  So, how can I see different behavior at the coach batteries if the RV's power cable is plugged into shore power vs the generator?  Does anyone know if some nominal difference in the generator's output vs standard home AC changes the charger converter's behavior?  I have the original Parallax 7345 charger converter.

Tony
08 VJ Nor Cal


Tom
 

The generator/house power should not make any difference. Does the battery voltage go higher (13.2 or more) when the Gen is running?

TomF 13NV


Don Phillipe
 

Probably a stupid question but is there any chance they could be at 100% charge by the time you got around to starting the generator and trying it?
--
Don - 2006 Navion J


Dan Booher
 

THe RVQG 3600 LP  gen set in my 2016NJ   has a flip switch style circuit breaker on the  generator.  It's below and to the right of the remote start switch  on the generator near oil fill.  Hard to see.  If that breaker is tripped/flipped  the generator will still run  but won't power your  coach.  Just something to check  if you haven't looked there.

dan 

On Mon, Sep 7, 2020 at 7:43 PM old_b4_my_time <donphillipe@...> wrote:
Probably a stupid question but is there any chance they could be at 100% charge by the time you got around to starting the generator and trying it?
--
Don - 2006 Navion J


GatorJeff
 

But, he does has power in coach.
--
Jeff S, '17 Winnebago View J, Gainesville FL


Dan Booher
 
Edited

Ah, my bad, I should reread before posting, after a day goes by. 
Is another possibility that the negative from generator is not attached to shunt?
Does the One Place show 13+volts when generator is running? Shouldnt he see a voltage increase at the batteries with his multi meter when generator is running?


tony martin
 

Thank you all for your replies.  It's true that when I have the generator running I do have power to the coach.  Installing the battery monitor makes it easy to see what's going on as far as the coach batteries go and I tried the following:

1) plugged into my home's AC power, and the battery monitor immediately indicates power flowing to the batteries
2) unplugged my house AC, plugged RV into generator receptacle, started generator and verified all coach AC circuits are live with 120 volts (as measured by multimeter), but don't see power flowing to batteries, in fact, there's an increase in the current being drawn from the batteries
3) with generator off and RV not plugged in to house AC, I started the diesel engine and immediately see power from my alternator flowing to the batteries

I cycled through these tests a few times to re-verify my observations.  My coach batteries are 2 reasonably new (purchased in March) Costco 6V GC batteries.  When plugged into the house AC the current flowing into the batteries seems to be too small, just about .25 amps or so.  And after a couple of days the battery voltage showed only about 12.6 volts.  I'm guessing there might be a problem with my converter charger.  As it's the original, and much maligned, Parallax, I think it's a good time to replace it.  I've ordered the PD 4645 and should have it in a few days.

As far as the comment about whether the generator's ground is attached to the shunt, I assume it has to be via the coach's ground wire that was originally attached directly to the battery bank.  All I did was move that ground cable to the "P" (or power) side of the shunt and then added a new short cable from the battery side of the shunt to the battery terminal.  

I still don't understand why the behavior is different when the coach is plugged in to the running generator vs my home's AC power.  Perhaps there's a slight difference in the voltage or current that's changing the converter's behavior.  Or is there some reason why there might be a signal wire from the generator to the converter, that tells the converter the generator is running?  If so, that might begin to explain the converter's different response to the different power sources.
 


David J
 

Charging at 0.25 amp and not charging are effectively the same. Within an hour or so the reading across the battery should be over 13.5 volts. So I'm with your diagnosis that the converter is not well. It is known to be picky about waveform, so not too surprising that it works a little on sinewave from the house and not on somewhat noisy output of the genset. 


Lee Haefele
 

Are you sure that the coach disconnect switch by the door is switched to ON? When AC power is applied, the green light in the switch lights, the 12V power is all on but the batteries DO NOT CHARGE unless that switch has been triggered to the on position.

Lee Haefele
10 VK Ithaca, NY


Lee Haefele
 

I have troubleshot many shunt type monitors in marine use.   All were miswired.  So, the battery negative goes to the shunt.  Nothing else can be connected to the battery negative.   Are there any other wires connected to the battery negatives and are BOTH batteries connected ONLY to the shunt?   The other side of the shunt goes to the chassis frame ground stud.  Note....   The chassis ground stud is open to road pollution, it should be disassembled, cleaned and covered and coated between conductors with any sticky grease.   I know 50 people are now going to say that grease is an insulator. I recently researched this when working with some heavily loaded 200 amp switches.   I found that electrical equipment maker Square D did tests and found no increase in resistance when grease is applied and REQUIRES their switches be greased annually.  The grease for our use does not need to be “dielectric”, it is just there to seal out moisture and pollutants like road salt.  The choice of grease gets interesting only when used for switches where there is arcing when switched.
One more thought...  If 120v AC the power wire to the charger portion of the converter had the neutral and ground wires reversed, or if the main power cord had the wires reversed,  that could give this symptom.  But, I am not sure that this is physically possible within the combined unit.  I did find this causing a non working charger, while only on generator, once on a boat.  Check the shunt wiring and switch by the door first, and determine if charging is occurring by battery voltage increase towards 14VDC, measured between the actual battery terminals,  and, clean that nasty ground stud.
Lee Haefele
10 VK, Ithaca, NY


Don Phillipe
 

Nothing should change when switching from shore/generator, so the other ideas seem moot.   It's coming from the converter it sounds like so the question sounds like what the converter is doing.   Can you disconnect the coach power wires from the front of the converter and read the voltage off the output of the converter to see what happens voltage-wise when you go to generator power?    Do any of your neighbor electronics gurus have an oscilloscope and can look at the output of the generator?
--
Don - 2006 Navion J


Don Phillipe
 

I'm not sure what your DC fuse panel looks like in your vehicle but mine has quite thick supply wires consisting of a black wire (-) and green wire (+) right on the front and to the right of the fuses.  That green wire post should read about 12.5VDC or so with no solar or shore/generator and about 13.8VDC with the short/generator power enabled.  If you don't see that voltage being the same on the green post with shore/generator the issue seems either the generator is putting out a spurious interference or spike that is tricking the converter into thinking something is wrong with the signal or a spike is saturating something in the converter or simply the converter is flaky.   It would take an oscilloscope placed on the power line to see what the waveform off the generator coil looks like and go from there.   If the two AC waveforms are near identical, then maybe a ground has come loose in the breaker box or the neutral wire broken in the converter or wiring, and the fact that the house has a convoluted path to ground via the 3rd wire or grounding wire and in contrast when removing shore power, there may no longer be a path to ground via that 3rd wire of the shore cable and thus a wiring error or a screw vibrated loose in the breaker box, when the earth ground is lost and a floating ground is assumed by switching to the non-existing ground of the tire-insulated ungrounded vehicle body, this might be a factor.   In loss of anything else to consider including a bad waveform from the generator, this ground wiring change seems the only thing that would be different and under the wild assumption the converter could be wrongly grounded to the 3rd wire instead of the neutral wire that would mean it might be powered by the shore cord and with the floating ground of the coach when generator powered, it might not have a path to neutral.
--
Don - 2006 Navion J


Ellsworth
 

To corroborate Don’s response, the author of post #11 of this thread discovered a loose ground wire at the converter which caused your symptoms (and It was getting very hot at the poor connection, which snowballs as increased temperatures increase resistance further).

So it’s worth cautiously fishing around the wire connections near the converter first to see if there’s an obviously poor connection. Using an infrared thermometer (I use a thermal camera for this) might help locate a problem connection (while the system is energized).

Ellsworth 06NJ


tony martin
 

Thanks again for your thought-provoking ideas.

Today I replaced my converter charger with the PD 4645V.  The installation wasn't too bad, but it'd sure be a lot easier if Winnebago had left an extra half inch of wire for each of those very short wires that connect the various DC circuits to the new board.  And, for some reason, the positive battery wire was also very short, requiring some creative rerouting to enable it to reach the different mounting position on the PD 4645's board.  Regardless, the installation was a success.  When plugged in to my home's AC power, voltage at the battery went up to about 14.2 volts and charging current was between 4.5 and 5-plus amps.  My old Parallax was showing about 12.5 volts and .25 amps -- barely enough to provide any charge.  Readings for my generator are comparable to those I see with my home's AC power, as I'd expect -- whereas, before, I saw no current flowing to the batteries at all when connected to my generator.  As the only changes I made were directly related to swapping the old Parallax for the new PD, my conclusion is that the Parallax was bad--though I still don't understand how/why it reacted differently to home AC power vs that from my generator.


David J
 

Congrats Tony. These converters are switch mode power supplies and very different from the legacy transformer and rectifier that we knew from the past. Unlike old linear supplies, they have no ability to handle excess power dissipation so they have elaborate protection circuits that can shut things down when they don't like the incoming waveform. We have seen laptop power supplies fail to function when connected to a generator or inverter but work fine when plugged in to sinewave AC power.


bike_for_life2003
 

Mr Martin,

Congratulations on your recent charger/converter replacement.  We also installed the PD-4645V about two years ago and it works incredibly well.  I didn't have an issue with wire length but laying on the floor for over an hour to hook the PD-4645V was something I was glad I only needed to do once. 

I do have the OEM Parallax charger/converter which was working when I removed it.  I am happy to pass along to anyone who may need one for simply the cost of postage.

-----------------------
Paul and Christine
06 View 23H in NW FL