Battery Charging

I am looking at a TM (used) but whether I buy it depends on finances. I did not know much about them until reading this thread. I am impressed.
I have one thing to add here though.
I have never had a TT or TM but I have seen street rods with trunk mounted batteries and that relates to trailer mounted batteries.
If you run #4 gauge wire from your TV using a battery isolator you will keep each battery charging as needed only. Using #4 wire prevents voltage drop. Voltage drop will cause amperage rise in direct rate and that will cause problems.
#4 wire is big, but workable. Run it through the inside of the TV or through pvc under the TV. Water and corrosion causes problems under there. I have heard #4 audio cable is more flexible than other types but expensive. If you go to a welding supply store and buy #4 for welding, the price is right.
This way, when your alternator puts out the 14.8 volts it is set for, you will get a good 12 (or more) to the TM battery.

[Bill]

My experience has been different. I found that if I ran the refrigerator on battery while towing, neither of my Explorers would keep the battery charged on either of my TMs. A little investigation showed that in each of the Explorers, the trailer battery charge line included several snap-together connectors, and some stretches of small-diameter wire between the battery and the Bargman connector. To solve the problem, I installed a parallel run of flexible #10 wire for both +12VDC and ground, directly from the alternator to the rear bumper. It was interrupted only by a circuit breaker and a relay (for isolation), both of which had bolted connectors. From then on, no problem.

Street rods typically have high-compression engines. In order to crank it over, the starter motor requires a very high current. If the battery is far away (in the trunk, for instance), then very large cables, such as #4, are needed. But there is no comparable demand in a TM.

Just my experience.

Bill

[Wavery]

Originally Posted by Bill

My experience has been different. I found that if I ran the refrigerator on battery while towing, neither of my Explorers would keep the battery charged on either of my TMs. A little investigation showed that in each of the Explorers, the trailer battery charge line included several snap-together connectors, and some stretches of small-diameter wire between the battery and the Bargman connector. To solve the problem, I installed a parallel run of flexible #10 wire for both +12VDC and ground, directly from the alternator to the rear bumper. It was interrupted only by a circuit breaker and a relay (for isolation), both of which had bolted connectors. From then on, no problem.

Street rods typically have high-compression engines. In order to crank it over, the starter motor requires a very high current. If the battery is far away (in the trunk, for instance), then very large cables, such as #4, are needed. But there is no comparable demand in a TM.

Just my experience.

Bill

This is exactly right. Where our TM's may demand as much as 20A while towing with the fridge on and trailer battery charging, a starter on a 12:1 compression ratio 454 cu in engine may pull 500A+. If the batteries have a 12' run each way (24' round trip), that engine better start pretty quickly or that #4 wire will soon melt. I would think that "00" battery cable would be in order.

10g wire works quite well if there are not a lot of connectors involved. It's the connectors (and the corrosion there-in) that cause a lot of resistance.

I have both a 2002 Chevy 1500HD and 2008 GMC 2500HD, both factory equipped with the towing package.

If I leave home with the pair of group 24 RV/Marine batteries charged and the TM fridge already cold and running on 12 volts on setting 5, when I arrive in camp 3 hours later the fridge is still very cold and my batteries are both fully charged.

I have no idea what the wire size is on the trucks, nor how many connectors there are. I do know that there is a 40 amp fuse under the hood for the charge line to the trailer.

[ZekenSpider]

Originally Posted by PopBeavers

I have both a 2002 Chevy 1500HD and 2008 GMC 2500HD, both factory equipped with the towing package.

If I leave home with the pair of group 24 RV/Marine batteries charged and the TM fridge already cold and running on 12 volts on setting 5, when I arrive in camp 3 hours later the fridge is still very cold and my batteries are both fully charged.

I have no idea what the wire size is on the trucks, nor how many connectors there are. I do know that there is a 40 amp fuse under the hood for the charge line to the trailer.

That has been essentially what I have seen with my 2004 Chev Suburban 1500 and the 3326 until I installed a Tri-metric battery monitor. We have always started with a loaded, cold refrig set on 5 and always arrived with the refrig still cold and the TM monitor saying the battery is "good".

Now (with the Tri-metric) I see the battery (a single Group 27) has lost about 6% after a 2 hour tow but I have never noticed the loss because we always connect shore power as soon as we arrive at campsite or back home.

Looking into it last week(just to see what was actually happening) I set up the TM so I could measure current and voltage at various points in the charge circuit with the TM on battery only and then with the TV connected and running.

I have the factory trailer wiring package on the Suburban with the standard 40 amp fuse, the standard 7 wire Bargman connectors and a 12 ft long Bargman cable into the 3326. That cable terminates in the the refrig cabinet (outside, bottom vent space).

I started with a fully charged Group 27 (rated at 160 volt-amp capacity when loaded at 15 amps). With the refrig and the fan on, the Tri-metric display said battery at 100%, 12.65 volts and -10.7 amps (leaving the TM battery). I then connected the Bargman cable to the TV with the engine running.

At this point the Tri-metric read 99%, 12.60 volts and -5.6 amps indicating that some of the refrig current was being supplied by the TV. I measured the TV battery voltage as 13.73 and using a DC clamp-on ammeter, I read 5.1 amps in the TV wiring harness near the hitch.

Exploring the wiring further I found the Bargman cable termination in the TM refrig cabinet was easy to get to and also provided easy access to the refrig terminals, the wires feeding the TM battery and the wires coming back to the refrig from the TM battery buss fuse panel. Measuring voltages and currents at this location I found 13.3 volts at 5.1 amps on the Bargman cable (#10 wires) and 11.6 volts at 10 amps on the refrig DC supply terminals. Here I also confirmed the TM battery was supplying 5.6 amps.

The 13.73 volts at the TV battery minus the 13.3 volts in the TM meant I was losing 0.43 volts in the total wiring from the TV battery to the TM cable termination in the refrig cabinet. The current in this wiring was 5.1 amps. About normal for a two wire #10 circuit running 15 ft.

I also noticed the TM battery charging and refrig supply wires were #12 and ran at least 18 ft back to the battery in the rear storage and at least another 15 feet from the DC fuse panel forward to the refrig.

Left in this condition, the TM battery was slowly discharging at a rate of approximately 5 amps-hours/hour or over 3%/hour. On an eight hour trip the battery would be down to about 75%. Since I never checked it before, I would never have noticed it be cause it would recharge over night when I plugged into shore power.

For me and this particular TM (2010 3326) it's an easy fix. Since I have the Bargman cable right next to the refrig DC terminals I will connect it directly to the refrig as well as leave the existing connections. That will remove the refrig load from the TM battery, supply the refrig from the TV (when towing) and provide an additional set of #12 wires for charging the TM battery. All of the wires are already fused properly.

I'll be trying this idea out on our trip to Pismo Beach so will let you know how it works out.

Jerry

[ShrimpBurrito]

I would bet there are alot more people being "power negative" at the TM battery while towing with the fridge on DC than perhaps is represented here because many folks don't realize it due to the fact they rely on the battery status LEDs to determine battery charge. If they checked with an ammeter, I would not be surprised if many, if not most setups, are power negative.

Of course, if you are driving on trips that are only a few hours long and you hook up to shore power upon reaching your destination, then being power negative isn't a big deal. Generally, it's only relevant when you are dry camping.

Dave

[Keith Wire]

Jerry,

I realize that alternators don't exhibit the same problems that the old generators used to (ie @ idle RPM they almost generated so little it wouldn't charge a battery). But, there is still a difference from idle to say 2000 RPM...

So the question is, what RPM was the Suburban running at?

Keith

[ZekenSpider]

Originally Posted by Keith Wire

Jerry,

I realize that alternators don't exhibit the same problems that the old generators used to (ie @ idle RPM they almost generated so little it wouldn't charge a battery). But, there is still a difference from idle to say 2000 RPM...

So the question is, what RPM was the Suburban running at?

Keith

As I recall the tach said 800 but it would move up to 1000 when the AC compressor cycled. The important thing for the test was the Suburban battery voltage stayed steady at 13.73 (if my DVM is accurate) regardless of the RPM.

We had just finished a 2 hour daytime drive so the battery was topped off and the voltage regulator had cranked the alternator output down to it's minimum.

I just looked at the Suburban again and right after start-up the RPM is 1,100 to 1,200 and the battery voltage went up to 14.3 for a few minutes then dropped to 13.8. Within 5 min. the RPM dropped to 800 and the voltage remained at 13.8. My testing in the previous post was done over a 15 min. period with the TV battery voltage at a steady 13.73.

Jerry

[ZekenSpider]

Originally Posted by ShrimpBurrito

I would bet there are alot more people being "power negative" at the TM battery while towing with the fridge on DC than perhaps is represented here because many folks don't realize it due to the fact they rely on the battery status LEDs to determine battery charge. If they checked with an ammeter, I would not be surprised if many, if not most setups, are power negative.

Of course, if you are driving on trips that are only a few hours long and you hook up to shore power upon reaching your destination, then being power negative isn't a big deal. Generally, it's only relevant when you are dry camping.

Dave

I think you are "right on" with that statement. Most of us are "power negative" by the time we stop to setup. It's still better (safer) to use 12 VDC refrigeration than propane. The only time it becomes an issue is if you need a full charge for dry camping.

I know the on board solar systems can help make up the difference but only if you are traveling in the full sun.

Jerry

[ThePair]

There is a whole thread about adding a DC-DC charger to the TM to alleviate the problem as well.