Using shore power with bad batteries

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.

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.

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.

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.

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.

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.

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.

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?

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.

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.