30 amp in-line fuse continually blows

[ian_c]

Boy do I need some help! Every time I try to extend the landing gear on our 5th wheel when hitching or unhitching the 30 amp inline fuse blows after a few seconds.

We had this problem a few years ago, were told that our house batteries weren't charged and, after charging them at a gas station everything worked well. For a time.

On our current trip all was well until last week in Zion. We'd been on the road for about 5 weeks. All of a sudden we started blowing fuses again. The "charge" indicator on the rig panel read "fully charged" but we could not raise the trailer.
I finally caved in and bought a new pair of 6v Deep Cycle Interstate GC2's in Kanab.

This morning we hitched up without problem but when trying to raise the trailer to unhitch the fuse blew after 20 seconds. It then continued to blow after about 10 seconds on each attempt. (Fortunately I stocked up on 30 amp fuses!)
I have NO idea what's going on here. Any suggestions are appreciated. I even put a coat of white lithium grease on the landing gear in case they were dragging.

Best wishes to all!
Ian

[MEXICOWANDERER]

I does hope the poster a few notches above meant direct current and not alternating current. The entire slide-out and landing gear designs for RVs are a cruel joke IMHO.

I did a total rewire on a fifth wheel (using a helper's labor) a few months ago. Upgraded to 6 gauge wire, 200-amp reversible contactor. Owner's Comment...

"Goes in and out twice as fast as when brand new".

[john_bet]

Glad you got your problem fixed. For my self I only operate my landing gear and slide pump after I have plugged into the park power or home power and disconnected the truck pig tail. No reason really except that my converter is a 55 amp output one. Just feel better about doing it that way. JMHO.

[ian_c]

For those interested, the final solution to my fuse-blowing problem was a new motor. I have had no problems since I installed it. The voltage across the terminals was 13-something but I have a pretty basic volt-ohmmeter.
THank you so much for all your suggestions!
Ian
PS and if you're interested check out my new problem under "Overflowing toilet!"

[mkirsch]

Don't bother having the motor "checked." Replace it.

"Checking" involves some RV dealership employee performing a visual inspection. If the motor is not visibly smashed, does not have smoke pouring out, is not oozing any fluids, does not smell funny, they will declare that it is perfectly fine and send you on your way.

You can't tell if there's a problem by just looking at the outside of something. It would cost more, and take far longer, to properly analyze the motor and repair (if repairable) than to simply replace it and be done with it.

Those motors are inadequate to begin with. You are slowly burning the windings out of them from day 1. Over time the motor will slowly degrade until it can't produce enough power, and stalls lifting the trailer. Stalling is what's causing the fuse to blow.

[Chris_Bryant]

I would also look at the fuse holder- glass fuses particularly, but even blade fuses.

[edbehnke]

had to replace with a larger fuse....good luck.

throughout forums you read about 5th wheelers upgrading to a 50 or 80 amp fuse.

[myredracer]

MEXICOWANDERER wrote:
it is common for an AC motor to draw more amperage with low voltage - impossible for this to happen with a brush type DC motor UNLESS

Muy incorrecto-mundo... With an AC motor, the output goes down with lower voltage and varies as the square of the voltage too. (EE 101) Motors take a bigger and bigger hit as voltage drops. At say 50% of rated voltage, output drops to 25% (1/2 x 1/2) and current to 50% (using ohms law I=P/E). AC units are an exception however and current goes up.

No idea on the OP's issue tho... Maybe try disconnecting wires at the motor and see if fuse still blows? Found this on another RV forum: When a DC motor runs, it creates "back electromotive force" or "back EMF." This back EMF limits the currrent flow through the motor. If the motor stalls, the back EMF goes away and the stall current will increase above the running current. If the system isn't designed for this, the stall current can blow the fuse. I've never dealt with slideouts, so I don't know if they are set up with a limit switch that kills the power at end-of-travel or if they're designed to stall out at end of travel. If it's the former, the limit switches may not be making up and the motor is stalling at end-of-travel and pulling enough current to blow the fuse. Maybe this can happen on landing gear too?

[time2roll]

Just for fun please post the battery voltage and the change when the button is pushed.
Do you get the same result going up or down?

[ian_c]

Wow! So many ideas! I will try to comment on the ones where I’m sure I’m on solid ground.
1) The batteries are installed correctly – just as RoyB’s diagram indicates.
2) I have lubed the leg screws.
3) I have manually lowered the leg screws when the rig was on the truck and I could sense no binding.
4) The fuse only blows when extending. (So far…)
5) I’m using 30 amp fuses because that’s what was there originally.
6) The connections on the battery terminals are clean.
7) To the best of my knowledge the landing gear is the ONLY item on that fuse.
But…
1) I don’t know how to tell if my converter (inverter?) is charging the house batteries.
2) I have a volt-ohm meter but my understanding is that will only read voltage potential across the terminals, not amperage.
So…
I’m going to check the leg screws again but everything you folks have said suggests a problem with the motor. I don’t have the knowledge to check it myself but I’ll be in Page, AZ in several days and I think I can get it checked there..
HUGE thanks yous to everyone
Ian

[azrving]

dougrainer wrote:

rjxj wrote:

dougrainer wrote:
1. Install a 30 amp auto reset Circuit breaker. CHEAPER than replacing fuses.
2. I(F you are positive that the ONLY item on that 30 amp fuse is the landing gear, then the motor is probably defective. IF you have other 12 volt items on that fuse then the accumulated amp draw may be blowing the 30 amp fuse. Doug

The only problem with auto reset circuit breakers is that some designs will weld the tips and take out the harness. I'm speaking of the clicker style that is basically a metal arm that heats up and pops open. When a fault occurs and they sit and cycle over and over and can end up welding the tips. Just mentioning it. The only breaker I would use would be a manual reset. If it pops maybe it's a one time thing, if it does it again find the problem.

Well, I have 36 years of working with and seeing Auto reset Circuit breakers in action. NEVER had a problem with what you state. Possible? Yes, but never had it happen where the Auto CB welded closed and that caused a burned harness. Doug

I know. I spent 40 plus years on lift trucks etc and seen them used in many areas. Normally they fail open but maybe the ones we had trouble with were from you know where. We had a fleet of cheesy Motrec personnel carriers that the drivers kept taking the fuses out of to prevent others from using them. One of our guys had the idea of wiring in auto reset breakers. Problem solved until they had a solenoid or or component fail. Then the breaker sat there and clicked on and off until it welded and smoked the harness. It was in more recent years so it's probably like the propane regulators and other junk that we are getting. We were constantly complaining to management to order oem potentiometers and other components as the failure rate was very high. But but....they were saving money! I'm sure you know that story.

[dougrainer]

rjxj wrote:

dougrainer wrote:
1. Install a 30 amp auto reset Circuit breaker. CHEAPER than replacing fuses.
2. I(F you are positive that the ONLY item on that 30 amp fuse is the landing gear, then the motor is probably defective. IF you have other 12 volt items on that fuse then the accumulated amp draw may be blowing the 30 amp fuse. Doug

The only problem with auto reset circuit breakers is that some designs will weld the tips and take out the harness. I'm speaking of the clicker style that is basically a metal arm that heats up and pops open. When a fault occurs and they sit and cycle over and over and can end up welding the tips. Just mentioning it. The only breaker I would use would be a manual reset. If it pops maybe it's a one time thing, if it does it again find the problem.

Well, I have 36 years of working with and seeing Auto reset Circuit breakers in action. NEVER had a problem with what you state. Possible? Yes, but never had it happen where the Auto CB welded closed and that caused a burned harness. Doug

[RoyB]

I am always leary about things when someone says they just installed some new batteries...

They are so easy to installed wrong... Especially two 6VDC BAtteries in series...

Be sure to take a good look at the battery cases where the POLARITY words and symbols are printed on the new batteries... Then make sure you have followed something like this google image...

Not installing correctly will blow the in-line 30AMP fuse in addition to the two REVERSE POLARITY fuses...



Roy Ken

[enblethen]

Bad leg screw is why I asked if he had lubed it.

[donn0128]

Since landing gear motors are DC not AC. You have only four choices. Low voltage=high amperage, corroded connection, bad motor, or bad leg screw. My bet is bad screw causing a lot of excess drag on the motor.