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Old 08-24-2009, 07:21 AM   #15
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Based on the schematic that Azflycaster put up, the shunt has four connections.
1 to the battery neg through a fuse
2 to the neg load
3 and 4 to the ammeter.

The top picture shows the shunt 1 and 2 both connected to the ground bar which will bypass the shunt. Remove the big wire going to the neg side of the battery from the ground bar and run it straight from the shunt (to a fuse) then to the battery.

Also make sure the shunt is insulated (do not mount it to anything conductive).

Will
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Old 08-24-2009, 12:02 PM   #16
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Stingray, First off you need to do some due diligence ... Google capacitor and look at some of the pictures. They come in all shapes and sizes. But the discussion of capacitors is irrelevant to getting your ammeter working.
You also need to Google series and parallel circuits ... so you can see pictures and understand the terminology. Your Mag light is an example. You pop in 2 AAs ... the + of one battery contacts the - of the other. The 2 batteries are in series. My Dodge turbodiesel has 2 honking 12 volt batteries in the engine bay ... the + of one is connect to the + of the other and - of both go to chassis ground. This is parallel. Other examples of series and parallel in an Airstream is the fuse is in series to protect the circuit ... the tail lights and clearance lights are in parallel on one circuit.
I don't know how to do pictures yet so can't help you there.
If I could see a diagram I could tell you where to put the shunt.
Give me 2 months and I will be able to tell you all about rv power but now I am days away from picking up my first trailer, and this is all I can do with the info at hand.


Quote:
Originally Posted by StingrayL82 View Post
Okay, Bob, I'm tracking what you and Richard are saying. The only thing I can add to this mystery is that there are no capacitors (as I recognize them) on this Univolt. I have two Univolts, one from 1970 and the other from a later model, possibly 1980's....the newer Univolt has three recognizable capacitors....the 1970's Univolt has a 2"x3" circuit board, and the solder is crystalized.

So, as I understand it, my updated pics should be correct, with the exception of what attaches to the back of the shunt...I know that, when the panel was attached to the Univolt, the solid metal wire attached to the back of the shunt, completing the circuit and allowing the ammeter gauge to read amperage....so the million dollar question now is, what attaches in place of the transformer solid metal wire in the back of the shunt?

on edit: Feel free to save the pics, black out what I wrote, and correct my mistakes. That brass shunt, by the way, is completely separate and independent of the fuse portion of the panel. It is in no way attached to the fuses.
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Old 08-24-2009, 12:13 PM   #17
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Ignore this!!! I don't know what I'm talking about!!!


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Originally Posted by Xbob2 View Post
Excuse me but you are mistaken. Though I am an RV noob the old 12v fuse panel in these pictures has NO ground or 12 v negative connections on it. The top bolt is the 12v + distribution from the battery or power supply. The black wire comes from a pole of a power on/off switch. the bottom left and center bolts are the in and out of the ammeter shunt.
By contrast, the first picture in the thread of the new fuse panel there is a 12v dc - buss on the right side of the panel.
In the picture of the transformer you are looking at a power supply. 120 AC goes into the transformer and 12v ac comes out of it, is connected to the diodes on the heat sink. (The round thingies) The diodes are half of a rectifier circuit. Thats something that changes AC to DC. The other half of the circuit that isn't shown in the picture is a pair of capacitors. This can be used to charge a battery or power 12v equipment or both.
After all that, that doesn't help you get your ammeter working. You were half right in your wiring ... the ammeter gauge connects to the small terminals of the shunt but you might of had the wires reversed.
The large bolts "interrupt" the hot wire of circuit you want to measure.
The range of your gauge tells you how many amps your shunt can take.
This is where my lack of RV systems knowledge fails you ... I don't have clue where you put the shunt!
Can someone else step up?
Bob
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Old 08-24-2009, 05:32 PM   #18
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Quote:
Originally Posted by meadowlm View Post
Based on the schematic that Azflycaster put up, the shunt has four connections.
1 to the battery neg through a fuse
2 to the neg load
3 and 4 to the ammeter.

The top picture shows the shunt 1 and 2 both connected to the ground bar which will bypass the shunt. Remove the big wire going to the neg side of the battery from the ground bar and run it straight from the shunt (to a fuse) then to the battery.

Also make sure the shunt is insulated (do not mount it to anything conductive).

Will
Hey Will, now I'm really confused. The shunt appears to be connected directly between the lugs that feed the positive and negative battery cables on my '73 Univolt. See picture attached. Is that correct? Keep in mind I have no idea how an ammeter works, other than it measures draw on the battery (in this case).


Well, I can't get the picture to upload for some reason, I'll try that a little later.
Jim
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Old 08-24-2009, 05:46 PM   #19
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Try again...
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Old 08-24-2009, 08:54 PM   #20
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I thought the ammeter was supposed to tell you how many amps you were hooked up to...


Crap....
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Old 08-24-2009, 09:00 PM   #21
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By the way, Bob, thanks for the schooling on electricity, I really do appreciate it.

One of my soldiers has a father who is a Master Electrician. He is coming in to town next week, so he's going to take a look at the Univolt fuse panel and figure something out.

I was looking through my 1971 Owner's Manual and the 1972 Service Manual (since there is none for 1971)...figures that they'd change the design of the frickin' Univolt in 1972...the diagram looks like yours, Jim.
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Old 08-24-2009, 09:04 PM   #22
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Sarge, I'm talking about the meter that measures the DC amperage on the batteries, NOT the shore power draw. Did I miss something? Maybe I need to go back and reread the thread.

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Old 08-24-2009, 09:07 PM   #23
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I'll dig thru my shop manual for the '73's and check the diagrams. Unfortunately, my scanner is done right now, so I won't be able to post a scan if you need it for a week or so.

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Old 08-24-2009, 09:23 PM   #24
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having trouble attaching my image

some one double check me, but here is how I would do it
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Old 08-24-2009, 09:26 PM   #25
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No, I think we're talking about the same thing, just that I was extremely mistaken. The little gauge on the Central Control Panel that says, "Ammeter"....I thought that measured shore power. So that brings me to my next question...what the hell is the point of having it? I already have that "Good Fair Poor" battery indicator, which doesn't really work worth a crap anyway....I really dislike retro-engineering stuff, just to make it work. If it weren't for the fact that Univolts are notorious for boiling batteries, I'd consider getting mine rebuilt and just putting it in and being done with it. The hum actually puts me to sleep...that's what having barracks next to the flightline does for you.
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Old 08-24-2009, 09:32 PM   #26
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I just read this on WikiAnswers...ding ding ding, the light finally went on:

"There are two main wires that normally come off the battery, one extremely large one that feeds the starter, and one reasonably thick wire (usually around 10 ga) that feeds everything else in the car.

A classic style ammeter runs in series with the battery wire that feeds everything else in the car. It samples which way the current is flowing and how much current is flowing. If the alternator is pushing current into the battery (charging the battery) the gauge reads positive. If current is flowing out of the battery, it should read negative, and usually means that your charging system is not keeping up with the electrical demands.
Since the classical ammeter is hooked up in series, it involves very thick wire (like 10 ga) to be routed all the way to the ammeter in the cockpit of your car. With all that current flowing through the ammeter, a short circuit on the ammeter in the cockpit can be fairly dramatic, and some classic car guys avoid ammeters for the possibiilty of causing a fire.
There are also ammeters out there that have an external shunt. An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parrallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to)."

Now it makes perfect sense to me.
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Old 08-24-2009, 11:05 PM   #27
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The resistance of the shunt, btw, is 0.6 ohms.

Now if I only knew what the hell that meant....

Oh well, at least I know how to measure it.
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Old 08-25-2009, 06:42 AM   #28
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ammeters

The answer from wiki is correct. The only differences are that the ammeter they are talking about has an internal shunt and it is in the positive wire. We are talking about an external shunt and the negative wire.

Look back at the diagram Azflycaster posted.
the top left lug of the shunt goes to a fuse and then to #3 (battery negative)
the top right lug of the shunt goes to #8 the negative load.
the bottom connections on the shunt are the ammeter.

all of the current must go through the shunt or it wont be measured.

Will
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