Using shore power with bad batteries

[NEOK]

I have two batteries that only show 11v on my multimeter. I have tried to charge them up but can't get them to read above 11 volts. Is it safe to use the RV occasionally plugged into AC power until I can replace the batteries in a couple of months?

[MEXICOWANDERER]

Design of a converter *assumes* there is going to be a viable battery in circuit. Why?

A battery no only softens the shock of a load that nears (exceeds) the output capacity of the converter...

A battery also acts as a shock absorber.

The transient voltages developed by a large motor that is heavily loaded then gets stopped WITH THE CONTROL SWITCH STILL ON develops horrid transient spikes both negative and positive voltage oriented. It's bad enough when everything is working right, but when...

There is no buffer for adequate transient absorbsion (the battery)

AND

The path on the positive side remains connected and the motor field collapses due to a sudden lack of power because the converter drops off line.

BUT

The switch on the positive side remains closed (the operator wants the jack to continue working)

THE CONVERTER

Sees damaging voltage spikes. Is there enough inherent design protection against voltage foldback?

I doubt it.

This is an attempt at simplifying an answer and it is not adequate. But the essence is very valid.

It isn't that the converter merely overloads but the voltage slumps stopping the overloading of the finals. That isn't the killer. The killer is when the electric motor suddenly stalls and unloads.

[John_Joey]

NEOK wrote:
Just to clarify this issue the batteries are in a truck camper. The camper does have a furnace, refrigerator, air conditioner, water heater range and oven and four jacks. I only consider using the lights and maybe the jacks until I replace the batteries in the spring using 120v ac power.

With your rig plugged in take your meter and check your battery readings. Then Reread MEXICOWANDERER post.

[Kayteg1]

Lot depends on converter you have, but my camper dry is 4300lb and my converter will move 1 jack at the time.
No problem with other things and we use camper as guest room with battery removed.

[NEOK]

Just to clarify this issue the batteries are in a truck camper. The camper does have a furnace, refrigerator, air conditioner, water heater range and oven and four jacks. I only consider using the lights and maybe the jacks until I replace the batteries in the spring using 120v ac power.

[John_Joey]

MEXICOWANDERER wrote:
Like comparing a paycheck to a bank balance...

Check may not be nearly enough to cover an expense whereas enough money in the account (enough charge in the battery) will cover the expense. Even if the paychecks have stopped.

Took a few reads for me, but nicely done.

[DrewE]

If it's a matter of the converter not providing enough current to operate slides etc. without a battery, you could hook up the tow vehicle temporarily to the RV battery connections with jumper cables (carefully, so as not to short things out) to give the extra current. If you have a motorhome, starting the engine should activate the battery combiner circuitry to accomplish the same thing sans jumper cables.

[BFL13]

The slides and jacks would have their own wires to the house batts while the converter has another set. The converter needs a path to the slides and jacks to run them--normally where they meet at the battery posts. If you remove the batts, the converter wires do not join with the slide and jack wires unless you put them together with clamps.

The converter should be able to run the slides and jacks based on the converter's amp rating, but it may be a long way on thin wire in a particular rig so there is a voltage drop.

Our 5er with a 13 ft electric slide had no problem at all doing it with no battery and a basic Parallax 7355 amp converter on "miles" of #6 and some #8. Trimetric showed about 25 amps peak going in or out over the hump with the converter doing all the work. Lippert spec is for a 30 amp fuse, so that came out right.

I suspect many rigs that have a notice saying you need the battery is just so the converter wire and slide wire do touch each other (on the battery post)

However, there are many rigs--- so best not to say they all can do it.

[DiskDoctr]

My Cougar says to have the battery fully charged as the converter may not provide enough power to properly operate the slides.

I hadn't considered this limitation.

I was mostly concerned about one battery with a failed cell @10v, the other @12v, output is 11v.

If the cell is shorted...

@OP- what were the results of individually charging the removed batteries?

[GoPackGo]

Kayteg1 wrote:
It all depends.
Several times I had my camper park at home with no battery and had to move the slide. It will move on 40 amp converter.
Electric jacks will operate on converter one at the time, but will trip charger overload when central button is pushed.
Than when I hook up my truck and plug engine charging -it all works just fine with no battery in the camper.

Maybe the difference is that I have the 6-way leveling system . There is one pump for all the hydraulics. Lippert says it can momentarily pull more then 50 amps when retracting slides or jacks, but much less when extending them.

With this system I can't retract only one jack at a time. I can individually retract the 4 rears, one side, or the landing gear.

My converter/charger is a Progressive Dynamics 80 amp unit.

And as I stated, plugging into my truck was no help. The sustem required a functioning battery in order to work.

Like you said - it all depends.

[Almot]

Disconnecting them is safer. If you are happy with the results - do it.
The converter alone may or may not provide stable 13V, and some DC devices are sensitive to over- and under-voltage. DC circuits of propane fridge, in particular. Battery (when it works) acts like a buffer, helping converter to do the job.

[Kayteg1]

It all depends.
Several times I had my camper park at home with no battery and had to move the slide. It will move on 40 amp converter.
Electric jacks will operate on converter one at the time, but will trip charger overload when central button is pushed.
Than when I hook up my truck and plug engine charging -it all works just fine with no battery in the camper.

[MEXICOWANDERER]

Like comparing a paycheck to a bank balance...

Check may not be nearly enough to cover an expense whereas enough money in the account (enough charge in the battery) will cover the expense. Even if the paychecks have stopped.

[GoPackGo]

I had my battery go bad last summer. Here's the short version of the story.

I'm not sure what happened but all of a sudden I had a battery that was cooked, feeling very warm. I believe it developed a bad cell and the charger kept trying to bring it up to full volts. I was set up in a cg, hooked up to 50 amp power, and had to move that morning but neither the slides nor the Lippert 6-way leveling feet/landing gear would retract. Found out I had to have a working battery hooked up in order to retract the feet or for the slides to go in or out - Something to do with the large amount of electrical power required. It didn't matter that I was hooked up to good 120v. So I begged the CG folks to allow me to stay one more day until I could get a replacement battery (they were MOL booked up). I then drove 20 miles to a Walmart, got a new one, drove backed and installed it. At that point, I tried the slides and and they worked.

I should also state that all other 12v and 120v systems worked (including ac) and that I also tried plugging in to the truck - didn't work either.

This occurred last summer and things have been fine since then.

I have a 2014 Bighorn.

[rockhillmanor]

On 'most' RV's. You would have to check if yours is the same.

The fridge, and A/C, and co detector all need a constant 12v to them.

The fridge and A/C thermostats run off 12v.
(i.e. they run off your RV battery, not the shore power.)

If your coach battery has ow voltage your fridge and A/C will come on, but when they hit the temp set and shut off.....their thermostats can not turn back on again.

Detector has a 'low voltage alert'. If voltage drops from 12v they start beeping to alert you of low voltage.