FWC battery low on arrival

[remithoren]

GOING CAMPING
Charged the camper battery and fridge all day Friday via 110 house power.
Left on trip.
Set fridge to batt to hold cold on our trip to Monterey.
When we got to campground that evening (after 3 hour drive) the camper battery was reading low voltage. (I thought maybe the draw was so huge that the truck did not get the chance to top up the camper battery)

Switched the fridge to propane and we have lanterns so no real worry here, however when we drove back home Sunday (4 hours) the battery appararantly did not charge. Hooked up the 110 cord and it was back up in two hours.

Has anyone had experience with checking on this?

The obvious problem appears to be no charging between truck battery and camper battery. I have the optima battery in the FWC. Checked the connection between the truck battery and camper battery. No disconnects here.

When I installed my camper the previous owner and I hooked up the 'separater' in the truck cab properly and it's my understanding that this device prevents the truck battery from discharging when the camper battery is down.

Any suggestions from anyone on how to troubleshoot this?
thanx!

 

[chnlisle]

I have the opposite problem. The batt charges just fine on engine power but zippo on 110.

 

[Mark W. Ingalls]

The obvious problem appears to be no charging between truck battery and camper battery. I have the optima battery in the FWC. Checked the connection between the truck battery and camper battery. No disconnects here.



Any suggestions from anyone on how to troubleshoot this?
thanx!

Get yourself a digital multimeter. Cry once-- spend the money for a good one.

Now go around and check the voltage of different 'nodes' to see if you get a result you would expect. If you don't know what to expect, there is no shortage of experienced automotive electric techs on this forum, so post a question.

Good luck.

 

[John D]

Remithoren,

Your post reads like you have the isolator reversed. Obviously, I can’t say from here. A digital volt Ohm meter is more or less standard test equipment these days, but you need a good one that will not go crazy around an alternator. I would buy a Fluke brand meter.

The basic idea is to establish a fully charged resting voltage, and find out if the charging system raises the voltage a minimum of one volt above the resting voltage at all times.

Specifically, for a 12 volt battery and charging system, 1) Determine the resting voltage of the battery fully charged. To do this, it is necessary to start with a fully charge battery. Use an independent charger, such the 110 volt unit mentioned. After charging, disconnect everything from the battery and allow it to stabilize for a couple of hours. 2) If practical, measure the specific gravity of the electrolyte in each cell which should be between 1.26 and 1.28. 3) Measure the resting voltage of the fully charged battery, which should be about 12.6 volts. Now find out if the charging system is able to provide at least 1 volt above the resting voltage of the fully charged battery. Following is one good method.

Install the battery and connect it to the system. Securely connect the volt meter directly to the positive and negative terminals of the 12 volt battery. The meter should read the same resting voltage as if the battery were disconnected. If it reads a bit lower while connected, there is a resistance in the circuit that may discharge the battery. After resolving that issue, start the engine. This engages the charging system. Idle at 1,500 RPM. The voltage across the battery in question should now read about 14.6 volts with no load on the electrical system. Next, turn on all the various accessories powered by the battery. With the battery and charging system electrically under load, the minimum voltage should be 1 volt above the resting voltage, about 13.6+ volts.

Battery isolators may interfere with achieving the needed voltages. Honestly, I don’t like isolators for this very reason. I prefer heavy duty manual switches typically found on dual battery yacht systems. John D.

 

[LAWNMOWERMAN]

I just got back from a 2 week trip and ran my fridge on propane the whole way.I probably used not much more than a 1/3 of a tank.When I was in higher elevation areas I had to be carefull not to freeze stuff even on the lowest setting.I tried running it on 12volt when I first got my camper almost 4 years ago and was not happy.It seems to work much better on propane.

 

[remithoren]

FWC battery not charging from Truck Battery

Good info.

Bought voltmeter tested all. Was a break in the wire from isolator to FWC connection. Repaired and all working fine. Sometimes it's the most obvious that is easiest to fix. I agree that a boat type three way battery selector would be a good choice. (Batt 1, Batt 2, All)

 

[Mark W. Ingalls]

On the bright side, you now have a very important piece of diagnostic equipment in inventory!

Pack it in the truck whenever you go...

 

[Pete D]

If you put in a manual switch, be sure that it can't switch your truck battery off from the truck's charging system while the engine is running or you may do damage to alternator/voltage regulator.

Although a disconnect was found in this situation keep in mind that sometimes, plugging a somewhat discharged battery overnight to the converter isn't enough to fully charge the battery; depends on the state of the battery and the output of the converter.

Also, sometimes the truck charging system can't replace the energy consumed by a fridge in 12VDC mode plus charge the TC battery. Again, depends on the components, state of charge of truck and TC battery, how cold the fridge was starting out and how hot the ambient temperatures are.

Just stuf to consider for everyone.

 

[Jack]

The standard battery separator in our Eagle not only protects the car battery from being discharged , it also PREVENTS the camper battery from being charged if the it is TOO low! We installed a bypass switch that allows us to bypass the battery disconnect switch so the car alternator will charge the camper battery regardless.

 

[brett13]

Glad to hear you found the problem so quickly.

For those who might have recently installed the camper, I couldn't get a charge to the camper and couldn't figure out why. Turned out that the wire that ran from the truck to the bed was zip-tied too tight to the undercarriage. The first time I took it off road, the twisting of the bed pulled the ground loose from the plug. Took forever to find until I used the multimeter to check the plug's connections. Will never travel without the multimeter now. And I added lots of slack underneath.

 

[brett13]

Voltage Question

I finally got around to fixing the problem in the previous post (happened on my last trip, so I never got around to recharging it). Also bought a trickle charger ("slow charge 1.5A). I put the trickle charger on for a few days and the batter went from 5.9v back up to 13.4v. My question is shouldn't a fully charged battery at rest be 14.4v? It says something on the battery like 13.2-13.6v for float charge and 14.0-14.4v for cycle charge (or vice versa, I can't remember now).

I'm wondering if it will only truly "top off" to 14.4 from the alternator and not the trickler charger? Thoughts?

ps. Its not on the truck during the winter, so I can't really charge it off the truck.

 

[John D]

Specific gravity of battery electrolyte is a measure of the state of charge, as is the resting voltage of the battery. A fully charged lead acid battery in your camper or truck will have a resting voltage of about 12.5 to 12.8 volts, more or less. The reason for the lack of precision in these numbers is intentional because a lead acid battery is more like a living organism than a purely mechanical device. You engineers and technicians will be driven nuts if you expect a lead acid battery to act in a predictable straight line fashion. Batteries just don’t act like gear heads think they should, so don’t get excited about them, just adapt.

For a 12 volt lead acid battery to be charged, the charging circuit needs a voltage of 1 volt above the resting voltage. Usually, we set this at about 13.8 volts with a voltage regulator. Charging with voltages between 14 and 15 will charge the battery faster. Assuming a steady voltage, a battery also charges faster when heavily discharged, which is animal behavior. Generally, the higher the charging voltage above resting voltage, the more excess heat is generated inside the battery and the more the electrolyte is likely to vaporize and be lost. When electrolyte is boiled off, the plates may be uncovered, causing damage. It does not take much heat to damage an animal. This whole subject is actually rocket science complicated.

Batteries and charging systems are not simple subjects, yet people continue to try and simplify them with unhappy results. I repeat here, the best way to set up a starting/house dual battery system is with manual switches, 1, 2, All, Off, or with independent dual alterternator setups with a completely independent charging system for each battery (I have heard of, but never seen a true twin circuit alternator. I do not know if they work and I bet they are more expensive than simple twin alternator setups.).

My personal answer to this problem, after putting up with dual battery systems over many years, is to illuminate the house battery through conservation of electricity using innovations such as LEDs and paying attention to electrical use. Once the house battery is illuminated, the flat battery at the outset of a camping season is illiminated.