Tracing 12v Circuits, Shorts...First Steps

[fotochop]

* '69 Safari 23 foot with

* Intellipower 30 amp Converter, functional

* new Die Hard deep cycle battery

My rig recently started blowing fuses intermittently and, being in the middle of reading "Managing 12 Volts" by Mr. Barre (good book, thanks Randy) I figured its time to start tracing my 12 volt circuits to try and zero in on the problem....

I don't have a schematic but its possible the wiring is not original to the trailer (I don't see any aluminum wiring, for example, and its possible the 69's had it orginally but a p.o. replaced it/rewired it...

I want to try and map out my own schematic particular to this trailer. I'm taking baby steps here, folks

I'm plugged into shore power, a 20 amp circuit in my garage.

Here's a photo of the fuse panel. You can see where a p.o. added a kill switch to the battery. Rig had a Univolt when I bought it and I was told to kill the battery "when it started to boil" (are there crawfish in there??) I have since upgraded to the Intellipower converter.



I'm starting out by seeking the feed wire from the converter to the fuse panel. I disconnected the wire marked "13.43" (volts dc) from the panel and took a reading: 13.43 v DC

While this wire was disconnected I read other red wires (positive, right?) and they all read "12.89", which was the same reading at the battery, which was not disconnected at this point.

Is it safe to assume my 13.43 wire is the feed from the Intellipower? That's almost the exact output reading from at the converter.

I'm more than a little confused by the added switch and lamp-cord at the fuse panel. A parallel circuit is a bit more tricky to wrap my visual-learning-brain around than a simple, circular series circuit...

I really appreciate a few electro-wizards opinions here. You can click on the picture to enlarge it if necessary..

I will update this thread as I proceed....hopefully my sleuthing will eventually point out the short/problem...

[DreamStreamr]

Rick,
Taking just one part of this (so plenty left over for more experienced ones than I):

Disconnect the 110vac to the Intellipower (kill AC power to the trailer is easiest way, unless you have a direct visual on a switch to turn off just the Intellipower). I'd rather kill power to just the Intellipower so I am sure I'm ONLY turning it off.

Then read the 13.43 circuit -- now it's zero, and you're sure it is the Intellipower because nothing else in the trailer is converting power and would be interrupted by the break in the AC power.

Good luck,

Jim

[Minno]

That's a kill swiitch for the battery? It doesn't look like it has near big enough guage wires coming out the top and bottom of the metal box. That panel looks like a jury-rigged mess. I'd strongly consider replacing the whole thing.

Chris

[Aage]

Originally Posted by Minno

That's a kill swiitch for the battery? It doesn't look like it has near big enough guage wires coming out the top and bottom of the metal box. That panel looks like a jury-rigged mess. I'd strongly consider replacing the whole thing.

Chris

And to do that, he needs to have a schematic of his actual wiring. I think that's what he's doing...

"When you don't know where you're going, any road is the right one."

[richinny]

which fuse is blowing?

[fotochop]

First it was the "13.43 volt" fuse which appears to come from Intellipower converter, then I blew the third fuse from the top after turning all the interior lights on.

(another in a series of dumb questions...): Since the Intellipower is a 30 amp unit and has two blade-type 30 amp fuses protecting against wrong battery polarity, shouldn't the Intellipower glass fuse in the fuse panel also be a 30 amp? The one that blew is a 20 amp (but formerly, probably was hooked to the Univolt). just wondering, but don't want any fires...

[richinny]

Originally Posted by fotochop

First it was the "13.43 volt" fuse which appears to come from Intellipower converter, then I blew the third fuse from the top after turning all the interior lights on.

(another in a series of dumb questions...): Since the Intellipower is a 30 amp unit and has two blade-type 30 amp fuses protecting against wrong battery polarity, shouldn't the Intellipower glass fuse in the fuse panel also be a 30 amp? The one that blew is a 20 amp (but formerly, probably was hooked to the Univolt). just wondering, but don't want any fires...

i just have some general answers.

you have a voltage drop across the "intellipower" fuse in the block. see if you can clean those clips. this can cause excessive current draw.

add up the amperage of all the items you had on when the other fuse blew. it might have exceeded the limit of the fuse.

i'll leave the other questions to the experts.

[Jammer]

The block you have the ??? on is a shunt for measuring current. The gray wires from it go to the top two fuses and should go from there to an ammeter.

The wire to the intellipower appears to be at least 10 gauge, maybe 8. If so, you can fuse it at 30 amps. You could actually fuse it for more than that but those fuse holders won't take a bigger fuse.

[Mexray]

Rick...

I'll try to shed some light on your PO's 'rats' nest, so to speak...

1. dump that 'kill' switch - it's way under rated for heavy DC amperage use...the contacts get burned quickly - they just aren't designed for DC use...If you're going to use a 'kill' switch on a DC wire to the batteries, get a quality DC rated switch, and use 8 or 6 gauge wire to keep the electrical resistance to a minimum - the larger the better, in any event don't use a smaller gauge wire than the feed wire from the batteries themselves...

2. what appears to me as a metal plate where your '??' is shown would be acting as a tie plate for the + side of the DC source - all those wires should be = to the battery POS voltage...notice all those wires feed the 'supply' side of the fuse panel, plus the black wire with the yellow terminal that apparently feed 12 volts + to the light socket at the top...

3.It appears that the wires from your batteries are the red and white heavy wires that enter from the upper RH side of your picture - is that true? You can check with your meter by removing the fuses...If so the red wire passes thru the fuse from right to left, then thru the red wire on the LH side of the fuse, down to the metal plate (in 2 above) to power that tie plate with 12 volts-POS for the other circuits via the wires running back up to the fuses...

4. The white wire from the batteries goes thru the fuse from right to left and then continues to some grounding point (or the NEG side of the converter/charger.

5. it looks like the red wire marked with the '13.43' is indeed the POS wire from the converter/charger...

6. perhaps the white wire right below the '13.43' wire is the NEG wire from the converter/charger and goes thru the fuse, then down to the same grounding point as the white wire noted in #4 above.

7. my fuse panel uses 50 amp glass fuses for the battery POS and NEG feed wires - they are noticeably larger in diameter than the other fuses and use larger fuse clips as well - I would recommend using at lease 50 amp fuses for the battery feeds...

8. It's a bit unconventional to see 'feed' wires coming from both sides of the fuse panel - all 'feeds' (or supply) wires should be on one side and the 'load' wires on the other so things don't get confused (no pun intended) when tracing problems, etc....

9. Also, I'd recommend replacing those small diameter twin lead wires with some good automotive stranded wire - I like to use at lease 10 or 12 ga wires for the accessory feeds, and larger 8 or 6 ga for the battery feeds...

10. If those wires have been in place for many years, the copper strands at the ends (where connected) become oxidized, turning brown or black in color and cause resistance in the low voltage DC circuits - I'd remove all the wires, clean the strands, or replace where possible, or even cut back the wire to get some 'new' material and use some anti-corrosion goop on the wires before sticking them back into the fuse panel with the set screws...

Hope that helps...

Ray near Lodi

[barts]

One method of debugging intermittent shorts that I like a lot is to use a 20A DC circuit breaker with wire leads and alligator clips; the kind that automatically resets itself is handiest when working alone. You also want a noise maker of some sort (Radio Shack has 'em) that will work on 12 V, also connected to the alligator clips. If the noisemaker cares, make sure to mark the clips as to polarity... now, remove the blowing fuse and connect the circuit breaker clips across the fuse holder. Turn on the circuit and start wiggling wires, etc, looking for the short. When the short trips the breaker, the noisemaker will sound, and you have an idea where the problem is. The breaker will soon reset, and then you can pin it down some more.

I once traced an intermittent fault in the wiring on my truck this way; turned out the tailgate was pinching the camper shell rear light wires, so whenever I stepped on the brakes hard the tailgate would pinch the wires and eventually caused the short... the dealer tried and couldn't find it; I drove w/ this for a day and bingo.

- Bart

[boatdoc]

Hi Rick;
Please allow me to UN-CONFUSE you first. First of all you must keep your circuitry straight. Separate AC and DC, as they are separate circuits if you disconnect the Intellipower. Your Intellipower converts AC [alternating] 115 Vac 60 Hz power to 13.5 VDC offering you converted 13.5 Volts DC [direct current power] and battery charging capability. Separate the two circuits first, by removing the Intellipower leads to the battery. Disconnect the batteries. Now you can check your 12 VDC trailer circuitry.
Using Ohm meter set to hi Ohm scale using jumper extension wire, hook up one meter lead to positive battery lead [not the battery] With all switches in off position and fuses out check the positive input lead to your fuse block. If you have continuity your lead is OK. Now switch the one lead from positive side of the fuse block to negative post on the fuse block. If continuity is present your negative lead is shorted to positive side. If no continuity between positive and negative, your input wires to fuse block are OK.
Now you need to check individual circuits in the trailer. Install appropriate fuses in the fuse block. Disconnect your meter lead from battery cable and hook it to positive side on the fuse block input. With all bulbs out of the lights and battery power still disconnected check for continuity to bulb sockets [do not forget to turn on the switches]. In this test you should have continuity only to one pin in each socket. Continuity on both sides of the socket indicates short in that circuit. Do not forget to check input into other circuits such as fans and appliances.

Next step is to remove the meter lead from positive side on the fuse block and place it on Negative side of fuse block. Repeat the tests in the sockets to make sure only one pin in the socket has continuity. Continuity on both pins indicates short to positive side. While doing this, tag all fuses so that you now in the future what they serve. If all checks OK [no shorts] replace all bulbs and reconnect appliances. Having the fused circuits tagged connect both battery leads. Install one fuse at the time and turn on any switches operating from that fuse one at the time. If the fuse blows you know which circuit is shorted by having them tagged. Repeat the process with the rest of fuses. Good luck "Boatdoc"

[fotochop]

Originally Posted by boatdoc

Hi Rick;
Please allow me to UN-CONFUSE you first. First of all you must keep your circuitry straight. Separate AC and DC, as they are separate circuits if you disconnect the Intellipower. Your Intellipower converts AC [alternating] 115 Vac 60 Hz power to 13.5 VDC offering you converted 13.5 Volts DC [direct current power] and battery charging capability. Separate the two circuits first, by removing the Intellipower leads to the battery. Disconnect the batteries. Now you can check your 12 VDC trailer circuitry.
Using Ohm meter set to hi Ohm scale using jumper extension wire, hook up one meter lead to positive battery lead [not the battery] With all switches in off position and fuses out check the positive input lead to your fuse block. If you have continuity your lead is OK. Now switch the one lead from positive side of the fuse block to negative post on the fuse block. If continuity is present your negative lead is shorted to positive side. If no continuity between positive and negative, your input wires to fuse block are OK.
Now you need to check individual circuits in the trailer. Install appropriate fuses in the fuse block. Disconnect your meter lead from battery cable and hook it to positive side on the fuse block input. With all bulbs out of the lights and battery power still disconnected check for continuity to bulb sockets [do not forget to turn on the switches]. In this test you should have continuity only to one pin in each socket. Continuity on both sides of the socket indicates short in that circuit. Do not forget to check input into other circuits such as fans and appliances.

Next step is to remove the meter lead from positive side on the fuse block and place it on Negative side of fuse block. Repeat the tests in the sockets to make sure only one pin in the socket has continuity. Continuity on both pins indicates short to positive side. While doing this, tag all fuses so that you now in the future what they serve. If all checks OK [no shorts] replace all bulbs and reconnect appliances. Having the fused circuits tagged connect both battery leads. Install one fuse at the time and turn on any switches operating from that fuse one at the time. If the fuse blows you know which circuit is shorted by having them tagged. Repeat the process with the rest of fuses. Good luck "Boatdoc"

BOATDOC YOU ROCK
Excellent summation, I am grateful to you and other contributors..I have printed out and will execute

(electro-newbs like me should print this out too..)

I have i-d'ed Converter pos & neg leads (I think) by extending multimeter leads with wire/alligator clip arrangement shown below:



above photo shows me trying to i.d. converter ground lug wire back by the fuse panel, but I got a continuity beep at a bunch of the fuses and trailer body....... normal?

and am starting a circuit map:



next step (for me, anyway) is to bypass battery switch by running a new 8ga. wire from left side of Converter pos lead at fuse panel directly to battery.. I plan to change/upgrade the battery terminal connections to wire loop and attach with wing-nuts instead of mangled old connections unless somebody says don''t do it/bad idea..

You can see I'm space-challenged back there and disconnecting (not to mention removing) the battery is quite an...adventure I'd love to move battery & install a nice new fuse panel under the gaucho but don't have time at this juncture...that'll have to go on the do do list...

[fotochop]

one more thing: I notice some people add a circuit breaker between the battery and fuse block.. Is this something I should do? 12 volts, ?? 30 amp? If so, I might simply put it where the battery switch is and up-gauge the wiring, yes?.... thanks

[boatdoc]

Hi Rick; Converter test is simpler than what you trying to do. Simply disconnect converter leads from battery and check for 13.5 -14.7 Volts output. Converter having numerous diodes is beyond your capability to test other than voltage output. Amperage output is depended on demand and it's capability. Your short which blows fuses has nothing to do with converter. Using Ohm meter you need to ring out your 12VAC wiring in the trailer. Be sure that no battery or converter power is connected to them, or you will fry the Ohm meter. You are only testing wire continuity and finding out which wire is connected to which circuit. Remember this; each circuit must have a positive lead and negative to work. For instance, If you remove bulb from it's socket the connection between positive and negative is broken and no current can flow from one wire to another. The filament inside the glass bulb enclosure is in gas environment and void of oxygen. Nothing burns without oxygen, right? The current flowing from positive side to negative when the switch is turned on flows through filament which is nothing more than resistor. The amperage flowing through that filament is converted into heat energy creating the light. Do you remember what happens when glass of the bulb cracks? The bulb's element burns out in presence of oxygen. Bulb element is made of tungsten, a very dense metal composition which will not melt unless oxygen is present or amperage flowing through it is higher than the filament can pass without burning up. Wire however will melt instantly in presence of oxygen given enough amperage flowing through it. This is why the fuses are incorporated into circuits. Fuse is normally capable to pass only a portion of amperage, of that what the wire can carry. When the load demand in the circuit exceeds fuse amp rating, the fuse burns out thus protecting wiring and final components from damage. Motors such as fan may have carbon brushes which pass the current into field windings when the switch is turned on. Others may be inductive type but they all work on the principal of current flowing from one side to the other. At this point I better leave the theory alone of how the electric motors work without burning up i oxygen atmosphere because it is too involved, and you most likely will not be repairing them. So, ring out all wires with final components disconnected. There should be no continuity between the pos. and neg. wire with final componnents disconnected. You should have continuity between both ends of each individual wire, if not the wire is broken an needs replacing. If wires checked out Ok and the fuse blows when you connect the wires to a light or a motor, that component is shorted internally. Very occasionally switches made of metal case and mounted in chassis grounded material may short out to ground and may have to be checked. Neither side of the switch posts should have continuity to ground. As I have said it does not happen very often but pending the construction of the switch it can happen. Good luck Rick. "Boatdoc"

[boatdoc]

Hi Rick; Circuit breaker in battery cables are excellent protection for your 12V DC circuitry. It protects batteries from damage by overheating in case of a serious short and protects your converter as well. Chances are you will not draw more than 30 AMP at any given time so that will be fine. Breaker in negative cable as well can protect your electrical system should overhead 230V AC wire fall on the trailer or lightning charge should pass through you trailer. Thanks "Boatdoc"

[fotochop]

- thanks, doc, converter checks out as A-OK...

- and I'm getting better at Multimeter 101...I really needed the explanation as its really not that complicated once you realize you can extend the multimeter probes with wire and clips...

- tip o' the hat to mexray, dreamstreamr, et al, barts: very clever trick with the beeping circuit breaker! guess I need to insert a self-re-setting type inline as the ones in the auto parts shop didn't seem to have any kind of re-set button...

- my rig does have a 12v circuit breaker panel up in the front dash near the "control panel"... that's 20 feet of wire away from the battery though.. the control panel mostly doesn't light up or do much of anything except manually start the water pump... its on my to-do list of things to investigate..

- if indeed that flat metal plate with the "??" in photo is a shunt that has me wondering if maybe the '69's had a crude ammeter as part of the control panel...time to dig up the owner's manual...

[garry]

That ??? is a shunt for an amp meter and the slit on the left side is the calibration ie loosen the nut and slide and re-tighten to adjust.
The meter is in series with the load in other words the meter will not be like most devices with one side to pos and the other side to neg (ground). That is why you have 2 wires for the meter one goes out to the meter and the other is the return.

[fotochop]

Originally Posted by garry

That ??? is a shunt for an amp meter and the slit on the left side is the calibration ie loosen the nut and slide and re-tighten to adjust.
The meter is in series with the load in other words the meter will not be like most devices with one side to pos and the other side to neg (ground). That is why you have 2 wires for the meter one goes out to the meter and the other is the return.

Wow, in one week I not only learned what a "shunt" is, I actually found one in my Airstream! (wouldn't have done it without you guys: props2ya) Correct me if necessary, but I believe its function is to lower a higher-amp current to a lower-percentage-or-fraction-of-itself so that you don't need a big expensive ammeter to get a readout, right?

Now if that shunt is factory-connected to a meter/readout up in the front dash control panel (tell me, Garry, you awesome-'69-owner, inquiring minds want to know!) then I wouldn't even need to know the "factor" of "lowering" the shunt is doing, I'd just need to get the dang thing working, right?

Seriously, it looks like a beautiful trailer you have there and one day mine told me it wants to look just like yours....one day.

[garry]

My schematic diagram is in MS with the AS and I am in OK so I have to guess at what is going on in your trailer.
I do have the factory amp meter on the control panel at the front of the trailer.

When you swap out the Univolt for a modern converter the amp meter has to have the old fuse panel (shunt) for the amp meter to work.

In looking at the picture of the switch does the wire from the pos side of the battery go into the switch left side and come out of the switch and go to the shunt?
Is there any other wires coming off the pos side of the battery?
Do the light colored wires come from the neg side of the battery?
Where does the black wire with yellow crimp on the right side of the shunt go?

[garry]

Sorry I did not answer you question.

You have it right on the shunt.

My theory;

You have 7 fuses from the top down.

• amp meter
• amp meter
• 12V for water pump and fans
• ground
• 12v for lights & radio
• converter to charge batteries & 12VDC to 3 & 5 above.
• ground from converter

I think you also have a power on light (light is on when plugged in) on your control panel.
Your amp meter may not work because of a missing wire that was unique to the Univolt