Low Voltage from a fully charged house battery

[DLB]

Back at testing today, Monday

One of the positive cables from the battery goes to an Auto reset 50 amp mini breaker, then to a "Battery Disconnect" then to the 12 volt Distribution panel. There is a cable from the power converter which joins the 50 amp mini breaker.

With no shore power, to create the maximum continuous load, i had all led lights on, both vent fans (bathroom and bed room) on, and with the furnace running. I then checked the voltage at each side of the devices in the circuit. The voltage were measure between each device and the battery negative terminal or ground. This is what I found:

Battery positive terminal: 12.23 v measured under load

50 Amp mini Breaker: battery side 12.17 V
50 Amp mini Breaker: outlet side 12.08 v
voltage loss across mini breaker : 0.09 v

Battery Disconnect: inlet 12.06 v
Battery Disconnect: outlet 12.04 v
voltage loss across disconnect : 0.02 v

12 Distribution panel : 11.91 v

JimD .... Are these that these voltage drops OK or are any indicative of a resistant connection?

[JimD]

With that much load I would say the voltage drops are OK. There will always be a bit of a drop as nothing is perfect as far as being resistance free. A circuit breaker or fuse will have a little resistance so it can sense current flow and react as needed.

So overall with everything running you are only losing 0.3 volts total from the battery to the distribution center. I could live with that.

Now is the time to get the battery up to capacity so it can hold a decent voltage over a period of time. Give it a good charge and then see how quickly it drops with a load. If you can, swap in a different battery to compare with. You may need a new battery. Repeated drops below 12.1 or so volts will hurt its capacity to supply current.

[JimD]

I forgot to mention....Very good troubleshooting on your part!!! That was one heck of a load to pull all at once and it appears the original problem may have been the bad ground. Now all you need is a good battery supply.

[chrisvandette]

Hello
I think you have it wrong

I looked at my dielectric grease bottle and it says it improves electrical connections

So it does not impede electricity

Dielectric grease it used on all electrical connections just to keep moisture out and improve electricity movement

Most web articles are wrong

This info was direct from my dielectric grease bottle

Permatex part # 22066

[ed767]

Wow - had a similar problem with the fridge DC control wire having unexplainable low voltage. I ran a parallel wire from a good source at the furnace and the problem went away. Lost a lot of hours of stress on that one. Surprising they use such crappy components....

To the OP - you might want to install a battery monitor like the Victron 712 - I can see current flows when turning on/off individual components, super useful for tracking down electrical issues and ensuring things are doing what they are supposed to do.

[JimD]

Originally Posted by ed767

Wow - had a similar problem with the fridge DC control wire having unexplainable low voltage. I ran a parallel wire from a good source at the furnace and the problem went away. Lost a lot of hours of stress on that one. Surprising they use such crappy components....

I thought I was the only lucky one with low voltage to the fridge. If you look at page 1 of this post you will see I had the same problem it appears that you had.

[ed767]

JimD - sorry, I meant to mention you, I noticed your problem, crazy how many different things I thought it was, so many phone calls, testing this, testing that - in the end a bad wire or connector somewhere unknown (never found it...)

[jclen]

[QUOTE=JimD;899249]This sounds like a resistance of some sort in the system. It doesn't take much of a resistance for a high current device to drop dead when running. Troubleshooting is actually not that difficult (of course that is said through the eyes of an experienced electronic field tech).

Here is an example of something I encountered in my 2017 Greyhawk. I have a constant display of my battery and never let it get critical. Overnight my fridge will go into a low voltage error even though my battery was showing above 12.2 volts. The fridge was not suppose to go into this error until the voltage was in the low 11s.

Simple test was to measure the voltage at the fridge. When it was turned off I was getting basically the same reading as my battery gauge. But when I turned it on, the reading dropped to about a full volt less than battery. According to the Jayco wiring diagram for my unit, the fridge was fed power using 16 gauge wire. There is no way I should have been losing a full volt with the length of wire going to the fridge. It was not pulling enough current to drop that much voltage across a wire.

Looking at Jayco's method of wiring I found they like to use Scotch Lok connectors. I am guessing they spliced the wire run and that was causing my voltage drop. My fix was simple - I just piggy backed 2 new wires to the fridge right across the old wires. The 12 volt positive was tied in at the fuse panel and the ground was tied in at the chassis ground connection.

Problem solved, no more voltage drop and error condition. Now, in your case you are probably fighting the same type of problem but probably not due to a spliced cable. Since it is affecting multiple items, the common denominator is the main feed to the distribution panel. This can also include the chassis ground connection as that is also part of the power feed.

What you need to do is take some voltage readings at various points to see when the voltage drop is occurring. With the rig running completely off the battery only, measure right across the battery. Now try one of your devices that won't work under battery. The voltage at the battery should remain mostly stable (may drop a few tenths depending on how big the load is). If it drops dramatically your battery is bad or the connections to it are crap. Take the same reading at your fuse panel and see if it drops a few volts under load. If there is a resistance in the line the voltage will drop under load. The more the resistance, the more voltage you will lose and the worse your devices will operate.

Assuming the voltage is dropping by the time it reaches the fuse panel, you now have to look at things inline with the power feed. The first thing I would do is remove the chassis ground connector and sand/grind/file or whatever it takes to get a clean bare metal connection. No paint or crud between the connector and chassis ground, period.

With the ground being good you can focus on the positive feed to the panel. Assuming it goes though a fuse or breaker plus possibly a disconnect relay, you now take voltage readings at these items. You can measure it in one of 2 ways - from the connection to ground or right across the item. With a fuse or breaker if you measure across the connections you should measure zero volts meaning you are not losing voltage across it. If you measure anything, there is resistance and you need to replace it. If you measure from the connection to ground, you first measure from one connector to ground and then the other. Both readings should be near battery battery voltage you measured previously. If one side reads good but the other does not, you have resistance so just replace it.
I had a bad scotchlock that stopped my heater and a/c from working. Took it to get repaired and while diagnosing the problem the tech bumped the wire and it kicked on. Easy splice fixed it.

[Bill Johnson]

Originally Posted by DLB

I have a problem with my 12 volt electrical system when running on the house battery alone. The lights dim , the awning will not extend and the generator cannot be started, all symptoms of low house battery voltage.

All 12 volt systems work when connected to shore power, or with the generator running. With the Ford engine running, the lights, frig etc work.

I had the house battery load tested checked out ok. Still thinking it was the battery, I had a new one installed and the problem was still there.

The three stage converter is working as it should with up to 14.45 volts measured at the battery.

Looking for help. Cant understand why the 12 volts system will not work with a fully charged house battery.

Here is the electrical schematic drawing for the 30X, hoping it may be helpful.

My ground fell off the frame, Jayco uses Ground Clip, Bonding Lug and a selftapping screw that broke. If you can weld or put a bolt through the frame. Put the wires in a lug, crimp it and use heat shrink tubing. Put the lug on the bolt and tighten the nut down

[Markomyt1]

Great troubleshooting!

This is what you need:

https://www.amazon.com/Gardner-Bende...1576963&sr=8-1

Protects the connection, but allows conductivity.

-Mark-

[Jab55]

When we were on our first trip I would get the DC low message on the fridge. It was pretty consistent even though the battery was new and had good voltage. I knew I was going to upgrade the electrical so I put off troubleshooting until I finished the upgrades. I ended up putting 2 really big batteries in the lower compartment and 2 solar panels and a 2K watt inverter. That pretty much resolved the issue because we have tons of capacity....although I think I still get the error when I'm running a big 12V draw like the microwave on the inverter. I'm going to check the Fridge 12 volt wiring and probably add another wire.... I love the RV but the wiring is substandard in my opinion. The wires feeding the original 1000 watt inverter were way too small and way to long. I installed new much larger and shorter wires from the batteries to the inverter...

[ed767]

Jab55 - I found an easy spot to get clean 12VDC connections at the furnace just below, easy to snake wires up through the existing fridge penetration. It's worked perfectly well for about a year since I made the change, never an issue. Good luck.

[Jab55]

Thanks Ed. I was going to thank you for your post about the fix...but I didn't have your info when I was writing my post. SO Thank you.

[DLB]

I would like to thank everyone for their help in trying to resolve the "low voltage" issue when running on house battery.

I replaced my original battery with a new one. I repeated the "line" or "power" voltage tests on the items in the line to the DC Distribution panel and found no significant voltage drop. When trying to operate significant loads, on battery only, such as Slide motors or furnace , lights would still dim or slide would only try to move. Still the same problem.

I then replaced all copper set screw grounding lugs with new copper lugs similar to Gardner Bender Copper Mechanical. There are four lugs on two bolts connected to the frame.
Lugshttps://www.globalindustrial.ca/p/electrical/Wire-Connectors/Lugs/copper-mechanical-lug-10-14-awg-2-pk
I cut off the ordinal copper lugs, striped the copper wires, cleaned up any corrosion with a wire wheel on a drill motor and connected the new lugs to the frame. used OX-Gard , Anti-Oxy Compound by Gardner Bender (as suggested by Mark (Markomyt1). This is a conductive silicon grease with zinc. Still no improvement.

Next I had an RV service technician look at the unit, and after 2 1/2 hours, he found.... a bad battery ground wire crimped connection to the frame. He replaced the the crimped copper connection and all issues disappeared. I had perviously cleaned the connection to the frame, ie removed all corrosion from the frame and filled the crimped confection surfaces to bar copper, but the problem was corrosion inside the crimped connector, impossible to identify by sight. The technician found the issue by connecting the battery negative terminal to the frame with a "Booster cable" in addition to the normal cable. When he connected the booster cable to the frame and battery all the issues disappeared. I will remember this trick, to rule out a battery ground resistive connection.

Sorry for not providing an update sooner. I have been on the road heading to Victoria BC for the winter as soon as the electrical problem was addressed.

Thanks everyone.

[RetiredOne]

Originally Posted by DLB

Next I had an RV service technician look at the unit, and after 2 1/2 hours, he found.... a bad battery ground wire crimped connection to the frame. He replaced the the crimped copper connection and all issues disappeared.

I will remember this trick, to rule out a battery ground resistive connection.

Glad you figured it out. Guess who thought it was a bad ground issue in post #2?

Originally Posted by RetiredOne

Hmmm, since you're getting some power, but not enough to power up those items, first place I would check is the ground connection of the battery to the frame. Make sure it's clean, attached well, and not corroded.

Oh, look at that, it was me.... What do I win?

[JFlightRisk]

Thanks for updating your post. We always like to hear when an issue is resolved. Happy trails!

[pconroy]

Originally Posted by RetiredOne

Oh, look at that, it was me.... What do I win?

Gold star.
Enduring gratitude.
Icy cold brewski.

[ed767]

Also glad to hear you worked it out.

Recently, I noticed during a test that my new lithium battery negative terminal got hot under a heavy load from the inverter. Not good.

By just replacing the battery cable to the negative terminal the issue went away. I couldn’t see any issue in the “bad” cable either.

Good info for people to remember. Thanks for sharing!

[RogerR]

a loose, dirty or corroded connection gets hot. Sometimes the corrosion is not apparent or the cable end may be warped and not as tight as it seems. I always clean my connections every spring as I assemble them. I also clean my tail light connections every spring.