12v issue! Need pointers fast!

[dustyone]

Check them. Oops

[JimBob46]

Good trouble shooting technique, sounds like it may be a poor design drawing very close to 15 amps on a 15 amp circuit. Since it is a 5 month old camper it should still be under warranty, maybe you can persuade the dealer to check out the problem and if no other problems are found put the refer on a separate circuit?

Maybe the manufacturer thought it was a good idea to put the lights on the same circuit as the refer, but IMHO it would have been a better idea to give it it's own circuit.

Remember fuses are SAFETY devices.

[ODH]

4 lights and a RV fridge are no where near a 15 amp draw if everything is working properly. The fact that the circuit will operate with a 20 amp fuze installed tells you that the present short can not draw enough amperage to blow a 20 amp fuze. The next time you move the short could get better or worse. Find the short. Do not mask the problem by changing to LED bulbs.

[vsheetz]

Short = a lot of current draw... A short circuit that pops a 15a fuse will highly likely pop a 20a fuse.

As these are likely lights often used, good to change them to LED anyway for dry camping, being green, etc. If perchance changing to LED does not mitigate the issue nothing lost.

[mel s]

Originally Posted by vsheetz

Change out the light bulbs for LED bulbs. They pull maybe 10-20% of what current the incandescence bulbs consume. That should relieve the circuit overload and you can go back to a 15a fuse.

vsheetz

[Permadirt]

As the debate goes, "odh" is right and "the matrix" is wrong. Get a dc ammeter and turn all that stuff on. See how many amps it is drawing. Figure what to do after that.....

[ODH]

Short = a lot of current draw... A short circuit that pops a 15a fuse will highly likely pop a 20a fuse

No. A short is defined as an unintended path to ground. The amount of current that will flow down that path is determined by the resistance of the path. Connect the positive terminal of your battery to ground with a 2 ft long 4 gauge wire and you will get lots of amps (at least for a little while). Connect the positive terminal of your battery to ground with a 10K ohm resister and you will get 0.0012 amps. Both of these conditions are a short. If the OP has a short, the path appears to have a resistance of approximately 1.2 ohm, which would result in an additional 10 amps flowing through the circuit. This would blow a 15 amp fuse but not blow a 20 amp fuse.

With regards to LED lighting. They are a great idea. I have 27 in my TT. Every light bulb in the TT including the fridge and cook-top fan. They are not however a fix for a circuit with a short. The short needs to be found, corrected and then a change to LED bulbs can be made.

Would it be a good idea to have the fridge on its own fuse? Yes. It would be ideal if every single electrical item in the TT was on its own dedicated circuit. This would increase the usability of the TT but drive up the cost. Would I design a TT with the fridge and several light fixtures on the same circuit? No. I want the fridge to always work. I can get along without a light or two if that circuit develops a problem.

[YC1]

4 bulbs at 2.5 amps, more if the voltage is higher equals 10 amps, now add the unknown refer amps and you indeed can be right on the edge of or over 15 amps.

Of course I do not have your bulbs on my lab bench to measure their current draw but if they are standard automotive type bulbs I have indeed measured those.

I certainly would not want my refer on a circuit that close to its limits.

I highly suspect a service center will be reluctant to make any changes if the fuse does not pop for them.

Once again, with 40 years of electronics servicing on vehicles of every flavor and owning a repair center I would not hesitate to change the interior heat producing current hogs out to LED's. If you boondock at all you will thank us.

[ODH]

4 bulbs at 2.5 amps, more if the voltage is higher equals 10 amps

The 921 wedge base incandescent light bulb (standard in most TT) draws 1.4 amp at 12.8 vdc. Times 4 equals 5.6 amps. No where near the 15 amp fuse limit. The fridge control board draws a fraction of an amp and the interior light draws 1.4 amps when the door is open. The fact that the OP made 10 trips with this TT with no problems indicates that something has changed. The most likely change is a short. I find it hard to believe the number of people who are advising the OP to just ignore the problem and mask it for now with LED bulbs. If he had a flat tire would you suggest he just pump the tire back up and head across the desert? A short has the potential to start a fire. All it takes is a few amps through a small piece of metal next to something flammable.

[Dodgey]

As per my post I am in total agreement with ODH, younhave a fault, get it fixed. At the risk of causing upset, there are professionals and then those that actually understand what they are talking about.
Last RV, side lights (and markers) went out blown fuse. Did I upgrade the 15 amp fuse to test, NO, I replaced with a 10 amp for testing. Isolating and testing circuit by circuit was the plan starting with the front markers, simply because adjacent the fuse box was a cable marked front markers. Appearing ok, testing, and disconnected tryed the lights and sure enough blew the fuse. Now we'd had the RV 2 years but I remembered the previous owner had had a rear marker replaced, light bulb moment, pun intended Flipped the lense off and I just knew what the professional had done. Those fittings have the pin of the bulb as ground, or negative, over here it's typically the other way round. Very obvious as there is a strip of connector from the pin to the screw mounting. Pulled the fitting, made sure it was isolated from the body and switched on, fuse fine and metered to confirm reversed polarity. Somehow it took 3 years to ground but that was all it was, a pro with no real grasp of the topic.
Current RV, over voltage alarm on dash shortly after, those puns keep coming A security device had been professionally installed as an insurance requirement. Relay box spliced in to two particular wires, approx. 30 amp capacity wires, wires on relay box, 5 amp if that, supprise supprise, confused ecu thought flat battery so turned the altenator charge up to full, rectified and back to normal, thankfully no lasting damage, a professional again

Don't fudge, fix.

[twinboat]

In some stubborn short circuit issues, I used to jump in an auto reset circuit breaker.

As the breaker was tripping on and off, I would feel around for the hotter wires. That would lead me to the short.

[J Birder]

Originally Posted by TheMatrix

Not true.
P=I x V
If you lower the voltage the amps increase to compensate to keep the power the same as the unit will pull a certain power rating.

However, I do agree with your point about the short.

As a retired electronics engineer, I am telling you that you are giving out incorrect advice. Your formula is correct, but the wrong formula for the application. What you say is true for a motor driven device that wants to draw constant power. The lights and fridge are resistive loads. The formula that applies is Ohm's law I=V/R. When the voltage drops, the current drops also.

Additionally, since the OP is asking about problems in his 12V system, neither the size nor length of the any extension cord used to plug him in is likely to have any relationship to his problem.

Joel

[YC1]

We cannot assume you have specific lights. We can only guess based on years of experience. Without a picture of the fixtures and the actual bulb number it is speculation at best.

If ODH is right about the current draw of one of those bulbs, how can one assume they are single bulb fixtures.

And you cannot assume the voltage is 12.8 . It is probably around 13.5-14 volts. I know, not a lot of difference but if this thing is on the ragged edge, just a few tenths of a volt could take the fuse over the edge.

We do Not know if on the previous trips that he had all of the lights on. We do not know if he had shoreline hookups which would take the voltage to the upper limits.

IF it is an intermittent short, then these can be a real pain to sort out and as suggested by one of our highly talented long time contributors suggests, a resettable fuse/breaker can easily be inserted in place of the fuse.

My voltmeter is calling me. I love to get my hands on these types of issues.



There are some highly qualified people here and are tying to make some excellent suggestions.

[rarebear.nm]

I agree with Dodgey and ODH. If the OP made 10 trips with no issues then one trip fuse blows he most likely has a short somewhere. Shorts need to be fixed both for fire safety and battery drain. Many RV fires are caused by 12 volt shorts, don't ignore them- fix them! When I use or find a wire nut on a RV I will always apply a few wraps of electrical tape around the nut and down onto the wire, keeps them from backing off while bouncing down the road. It could also be a wire that was not punched down well onto some type of terminal or connector. I'd also look for a strand(s) of braided wire not being contained in some junction. Not knowing if the RV is wood or metal framed, I'd also consider a wire that has rubbed insulation through and is shorting against something that is grounded. I've seen nails/screws that penetrated a cable and in time has started to short between hot and ground.

I would also replace the lights with LED bulbs after the problem is fixed and move the frig to its own circuit. Gotta keep the beer cold.

Some RV professionals really know what they are doing and the underlying technology, some other have managed to pass a test. I worked on a 5th where a professional RV shop had replaced the springs. I was able to remove the shackle bolts and a couple u-bolt nuts with my fingers! Chose your professionals with care.