ammeter for trailer plug

[hallmont]

Hi out there,
I tow a 5th wheel Alpen Lite with an 06 SD . As the truck dosn't have an ammeter I want to moniter the electrical current going to the trailer Batteries via the plug. Has anyone put an ammeter in an 06 or has ideas about doing it.
thanks

[drcampbell]

It's no different than installing any other ammeter. Cut the wire supplying power to the trailer and connect each of the two cut ends to the ammeter.

[T_Bone]

Hi HM, Welcome To The Forums [img]/ubbthreads/images/graemlins/biggrin.gif[/img]

I bought a clamp on inline ampmeter made by Reliance trailer parts. You don't have to cut the wires. Have no idea if it actually works as I never used a clamp on "DC" ampmeter, about 1-1/2" round. It was designed specificly for electric brake use.




[img]/ubbthreads/images/graemlins/smokin.gif[/img]

[johnmart]

I had a problem a few years back where I was running a 12V refrigerator while traveling and the trailer battery would discharge even though the truck had a 100 amp alternator. I used a multimeter back at the trailer battery to see what was getting back there. As I remember, very little current actually went to the battery from the truck charging system due to resistance in the small wire that was installed in the truck wiring harness. I ran a 10 gauge wire back from the truck battery to the connector and felt that my trailer batteries stayed up better. But I also stopped running the 12V refrig.

If you have a multimeter capable of reading amperage, you might want to check current at the trailer battery first before installing a meter at the front of the system that may read more current than you are actually putting into the intended battery. Some percentage of the current going in at the front of a small wire may be just heating the atmosphere.

[drcampbell]

There may be a voltage drop from one end of a long, thin wire to the other, and that is often responsible for trailer batteries not getting enough juice to remain properly charged, but the current in a wire is the same no matter where you measure it.

[johnmart]

I stand corrected. [img]/ubbthreads/images/graemlins/blush.gif[/img]

[BuilderBob]

There are many ways to measure current, I will mention a "current shunt" and a Millivolt meter.
Very accurate, very cheap, but you need expertise, search the web for more info

[kiteflyer]

What problem are you trying to solve? Are you concerned about low charging voltage for the trailer batteries?

Here is the resistance of different gauge of wire

8 gauge is about .00640 ohms per foot or about .022404 ohms from truck batteries to the trailer batteries*
10 gauge is about .001018 ohms per foot or about .03563 ohms from truck batteries to the trailer batteries*
12 gauge is about .00158 ohms per foot or about .05558 ohms from truck batteries to the trailer batteries*

*On my truck/trailer combination there is about 35 feet from the truck batteries to the trailer batteries.

Those resistances don’t sound very high how every when you run some current (amps) through the wire you end up with a voltage drop. Here are some typical voltage drops:


For 10 amps the voltage drops are as follows:
12 gauge wire .56 volts
10 gauge wire .36 volts
8 gauge wire .22 volts

For 20 amps the voltage drops are as follows:
12 gauge wire .83 volts
10 gauge wire .53 volts
8 gauge wire .34 volts

For 30 amps the voltage drops are as follows:
12 gauge wire 1.67 volts
10 gauge wire 1.07 volts
8 gauge wire .67 volts

For 40 amps the voltage drops are as follows:
12 gauge wire 2.22 volts
10 gauge wire 1.43 volts
8 gauge wire .90 volts

The resistance losses do not include any connection resistance losses like the trailer connector or splices.

If you look at the voltage drops they can be significant. If you trying to charge the trailer batteries at 40 amps with 12 gauge charge wire the batteries will only see 12.28 volts if the alternator is outputting 14.5 volts. At 12.24 volts the battery is only charged to 50% and we wonder why we drive all day only to find the trailer batteries dead at the end of the day.

If I were you I would take some voltage measurements to see what the voltage at the trailer batteries under different conditions. Do you have a digital voltmeter? If you do, this is that I would do. Start with measuring the voltage at the trailer batteries with everything in the trailer turned off and the trailer disconnected from the truck and shore power. The will be a base line for further measurements. Then I would turn all the equipment in the trailer and take a second measurement. This will provide an idea of the condition of the batteries. Next I would connect the truck and retake the measurements with the truck running. Also take the truck battery voltage at the battery. Compare the trailer battery voltage and truck voltage. How big is the drop. That’s the problem you need to solve. The truck running with the trailer turned on would give you a ballpark on the type of charge voltage the trailer batteries sees while traveling.

I don’t know what size the factory wiring is but it probability not that big. On my truck/trailer setup I ran a separate charge wire from the batteries to the trailer connector. I put a relay in so when the truck is off it separates the truck and trailer. I then replaced the trailer wiring from the connector to the trailer batteries. I used 8-gauge wire to reduce the voltage drops. This helped keep the trailer batteries charged while traveling. [img]/ubbthreads/images/graemlins/smile.gif[/img]

[drcampbell]

Plus the resistance and voltage drop of the ground return path.

[kiteflyer]

Good point. I redid the ground circuit also. I ran new wiring from the truck batteries to the trailer batteries. I also spent time cleaning the connector and plug for the trailer wiring harness. They were pretty bad. I have round pins and used valve grind compound to clean it up. The compound was water-soluble, so after I was done cleaning I rinsed with water and dried. This was a good general upgrade and the time well spent. Although I have an older truck, I can’t imagine that the wiring in the new trucks is significantly bigger wire gauge.

[Larry M]

[ QUOTE ]
Hi out there,
I tow a 5th wheel Alpen Lite with an 06 SD . As the truck dosn't have an ammeter I want to moniter the electrical current going to the trailer Batteries via the plug. Has anyone put an ammeter in an 06 or has ideas about doing it.
thanks

[/ QUOTE ]

I monitor both the amperage to my trailer brakes with <font color="red"> THIS</font> (don't bother looking that meter is no longer made [img]/ubbthreads/images/graemlins/frown.gif[/img] ) and the trailer battery charging current using <font color="red"> THIS</font> (That meter is a 1940's/50's Simpson panel type meter).

The reason for the trailer brake ammeter is that I use a vintage (read that as really, really old ... early 1970's) brake controller <font color="red"> HERE</font>. It ain't fancy, but since I've been using it for over 30 years I really like it. That meter also tells me if I have broken a wire either to just a single wheel or even an entire axle which has happened to me more than once in the 25 years that I have owned my current trailer. In many, many cases I never use my trailer brakes or keep the amperage under around 6amps (1/2 power since each magnet draws around 3amps) ... this really extends the life of the trailer brakes and the need to adjust them. I have the old star type Dexter axles and just try and get thosed turned (especially the electric magnet surface) or purchase replacement drums [img]/ubbthreads/images/graemlins/shocked.gif[/img]. I need upgraded axles and wheels tires since I intend to die before I replace my TT. [img]/ubbthreads/images/graemlins/wink.gif[/img]

That second meter is a shunted MA meter that I calibrated to 30 amps and made a new face plate for it. I pulled my factory trailer charge wire from my 7 pin plug and used that as power for my aux backup lights. I then ran a dedicated 30 amp circuit using 8 gauge wire to a 30 amp relay which is controlled by one of those illuminated rocker switches in that second link and from the relay output thru the meter and then back to the 7 pin plug. I think the stock charge wire is like a 10 or 12 since I could just barely get my 8 gauge in the plug. I made this setup since I have four batteries in my trailer on three completely independent circuits (two 6V T-105s) and two 12 V Group 31s on the A-frame. The two 12V deep cycles are not wired in parallel, but are controlled via relays to provide power from either or both (i.e. in parallel) to my main 12 V trailer power. I did this because I like to draw down the batteries some before charging them and be able to charge them independently of each other and not in a parallel system. I have a charging console in my trailer along with two 10 Amp automatic deep cycle chargers that I can select two of the three battery systems to charge at any one time. On my charger console I also have two switches where I can select to either use my two 110V chargers or the vehicle charge ckt and if on the vehicle charge ckt option another switch to charge either the pair of Trojans or both of the 12V deep cycles. This charging ckt for the deep cycles is run thru a dual battery diode system. I know this all sounds complicated, but the reason for all the controls on the vehicle charging ckt is that since I don't run that circuit to the two 12V batteries in parallel, but thru that dual battery diode system, I don't like to have that system constantly trying to charge my batteries since the voltage losses from the wire and especially those diodes doesn't really provide a good charge voltage. So while on the road if I can't get the charge current via the vehicle trailer charge circuit up above 5 amps, I don't turn it on and I will turn it off when it gets down to under 5 amps. This helps to keep down the boiling off of the water in the batteries due to insufficient charge voltage and has significantly increased the useful life of my trailer batteries probably by two times.

Yes I'm a meter/monitoring freak [img]/ubbthreads/images/graemlins/crazy.gif[/img] and I even moniter the shore power input 110 voltage/freq/amperage, but also the 12V and amperage draw when on batteries. Again that 12V amperage draw for the trailer is an excellent indicator of problems, etc. I used to also have a meter in the trailer to see the trailer charge amperage when on shore power, but took that meter out when I installed my two deep cycle chargers that have a small meter on them indicating the amperage charge rate.

Larry

[drcampbell]

[ QUOTE ]
Yes I'm a meter/monitoring freak [img]/ubbthreads/images/graemlins/crazy.gif[/img] and I even monitor the shore power input 110 voltage/freq/amperage, ...
Larry

[/ QUOTE ]

You are pursuing getting some professional help for that, right?

[hallmont]

Thanks for all the helpful hints and suggestions. I ran an #10 wire from the battery to the plug and put the ammeter in the drivers " glove compartment" so it would not look like a blivit and I could check it at will. Thanks again,
Monty Hall