Battery Drain When Travelling - Power Converter Issue?

[YNPKing]

Originally Posted by Padgett

There are other threads but the 3-way fridge takes 2x to 3x the power of a compressor fridge and is a real power drain, around 180W regardless of voltage. You would be better off from a capacity standpoint running on propane rather than battery

Power from the TV really depends more on the TV wiring to the Bargman & altermator capacity than anything. Mine appears to have a 10 gauge wire on a 30A fuse and a 160A alternator. My experience is that you need at least 140A (under 100A is Not Engough particularly with lights on, 120A is marginal) rated alternator to be able to charge effectively at low engine rpm. (My Interstate cruise is under 2,000 rpm)

Thanks for the reply. Yes, I only run the refrigerator on DC when traveling.

We both have a Jeep GC although a different year. My Trailer Tow Group IV includes a 220-amp alternator and the schematic shows a 30-amp fuse so I assume we have the same 10-gauge wiring in the TV. I checked the pins on the Bargman with a volt meter and there is power.

The TM schematic shows 12-Gauge wiring to the WF-8955 converter and 10-Gauge wiring to the battery.

In my reading, some other sites indicate that RV trailer wiring is only capable of a few amps and cannot really charge a trailer battery but TM may be different. Any further thoughts would be appreciated on how to determine if the battery is able to get 16 amps to offset running the fan and refrigerator?

[Padgett]

See the tables (scroll down) here. 12 gauge is capable of a bit over 20A even at 60C. 10ga just has lower resistivity.

[ShrimpBurrito]

Originally Posted by YNPKing

Thanks for the reply. Yes, I only run the refrigerator on DC when traveling.

We both have a Jeep GC although a different year. My Trailer Tow Group IV includes a 220-amp alternator and the schematic shows a 30-amp fuse so I assume we have the same 10-gauge wiring in the TV. I checked the pins on the Bargman with a volt meter and there is power.

The TM schematic shows 12-Gauge wiring to the WF-8955 converter and 10-Gauge wiring to the battery.

In my reading, some other sites indicate that RV trailer wiring is only capable of a few amps and cannot really charge a trailer battery but TM may be different. Any further thoughts would be appreciated on how to determine if the battery is able to get 16 amps to offset running the fan and refrigerator?

This is a common problem, and the search engine will turn up a number of threads on the topic. TM's are not unique -- they have the problem just like everyone else. The solution is to run heavy wire -- think welding cable size -- for as long as possible between the alternator and the TM battery. Like 2-gauge or 4-gauge wire, and you need 2 runs -- one for positive and another for ground. And that gets expensive very fast, which is why RV and car manufacturers don't do it. Most RV'ers camp with hookups, so battery drain isn't an issue.

FYI, my fridge draws about 10 amps, and the fan another 0.5 amp.

To solve this problem, I installed a DC-input battery charger in the TM that is powered by the TV, as described in the second link below. So either you do that, or like a few other folks have done here, install bigger wire. Those are the only options for getting more current to the TM.

Check out these threads:
http://www.trailmanorowners.com/foru...ead.php?t=8268
http://www.trailmanorowners.com/foru...ad.php?t=10587

Dave

[ZekenSpider]

To add my two cents;

Remember there are two conductor paths involved in the battery charging process, either one can limit charging current due to resistance. The first path to consider is the conductor size and the Bargman connector. Both have resistance to current, and the higher the current, the more the resistance. The second path to consider is the return "ground" frame, the ground to frame terminals, the Bargman ground and the frame grounds in the TV. The net total resistance of both paths is what limits battery charging current.

All that has been said by others is generally correct, but remember that the battery will not accept a charge if the input voltage is not at least around 1 volt greater than the terminal voltage. In other words, it takes about 13.2 VDC to begin to flow current into a charged battery. Typically an alternator will produce about 14.3 VDC in the engine compartment. Also, typically, there is at least 1 volt lost in the total resistance of the conductors to and from the battery and the engine compartment.

You would think that "OK 14.3 is greater than 13.2 so there should be flow into the battery". What is being ignored is the voltage drop in the conductor paths to the battery. As flow (current) to the battery begins, the voltage drop goes up. The more the flow, the more is the voltage drop. The problem is wire (or conductor)size and or frame grounding or both.

Typically, assuming a 40 foot path from the engine compartment to the rear of the TM and a sound ground return to the alternator;

A 10 amp current through a 14 gage wire will cause a 2.06VDC drop at the battery.

A 10 amp current through a 12 gage wire will cause a 1.30VDC drop at the battery.

A 10 amp current through a 10 gage wire will cause a 0.86VDC drop at the battery.

A 10 amp current through an 8 gage wire will cause a 0.51VDC drop at the battery.

Jerry



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[Padgett]

Well sorta but that 40 foot number is a little extreme, more like 25-30 for a 2720. In my case about 10 feet of #10 for my TV and 20 feet of #12 in the TM or about .87 - call it 1v drop at about 20A (less at 5A). Also the converter is about 5' in front of the battery so that is where the load (fridge, fan) is going to be. Things get a little complicated from there but in the long run the batteries will equalize and the TV will charge the TM, the only issue is at what rate ?

Now what I really want to know is what is that delta winged thingie behind the blackbird ?

[ShrimpBurrito]

Originally Posted by ZekenSpider

Typically, assuming a 40 foot path from the engine compartment to the rear of the TM and a sound ground return to the alternator;

A 10 amp current through a 14 gage wire will cause a 2.06VDC drop at the battery.

A 10 amp current through a 12 gage wire will cause a 1.30VDC drop at the battery.

A 10 amp current through a 10 gage wire will cause a 0.86VDC drop at the battery.

A 10 amp current through an 8 gage wire will cause a 0.51VDC drop at the battery.

Jerry

Great post, Jerry. I should have pointed out in my post that when I approached this problem, I was not simply trying to supply enough current to the TM to run the fridge (and fan). I wanted to do that, of course, but on top of that, I also wanted to have the capacity to charge the TM battery at a decent rate (like 5-10 amps). So I needed to be able to deliver 15-20 amps to the TM battery, so that's where I was getting my 2 gauge wire recommendation from. As your post implies, if the goal is only to supply the fridge with enough power so it doesn't drain the TM battery, then 2 gauge is certainly not necessary.

Originally Posted by Padgett

Well sorta but that 40 foot number is a little extreme, more like 25-30 for a 2720. In my case about 10 feet of #10 for my TV and 20 feet of #12 in the TM or about .87 - call it 1v drop at about 20A (less at 5A). Also the converter is about 5' in front of the battery so that is where the load (fridge, fan) is going to be.

Actually, as Jerry pointed out, you need to run TWO conductors if you want to minimize resistance. So if you have 10 feet in your TV, and 20 feet in the TM, like you said, that's 30 feet, but that's only for ONE conductor. If you only replace or add to ONE conductor, that will certainly help. You just have to run the math to determine whether it helps enough for what you're trying to achieve.

Dave

[Padgett]

The return is through the skin of the TM, the white ground wire in the Bargman, and the frame of the TV. Usually the resistivity of the ground is low enough to be ignored.

Battery cables in the TV are usually much larger (0 or 00) because a starter may pull over 100 amps and you want as little drop as possible. For a front engine/rear battery (weight distribution) vehicle I hve seen 000 or 0000 used. The TM does not need that much.

The only unknown is any circuitry that might exist between the 12v input to the WFC converter and the battery connection though from the booklet it appears to be a direct connection.

[ZekenSpider]

Originally Posted by Padgett

Well sorta but that 40 foot number is a little extreme, more like 25-30 for a 2720. In my case about 10 feet of #10 for my TV and 20 feet of #12 in the TM or about .87 - call it 1v drop at about 20A (less at 5A). Also the converter is about 5' in front of the battery so that is where the load (fridge, fan) is going to be. Things get a little complicated from there but in the long run the batteries will equalize and the TV will charge the TM, the only issue is at what rate ?

Now what I really want to know is what is that delta winged thingie behind the blackbird ?

First things first.

Using the attached voltage drop calculator (assuming it works for you after downloaded...I have had trouble getting it to work after e-mailing it to others) AND ignoring the likely losses through the Bargman (which can be substantial...depending on condition) AND ignoring losses caused by poor ground return, we get the following voltage drop at the battery with 14.3 supplied by the TV:

For 20 Amps through 20 ft. of #12....VD = 1.3 V
For 20 Amps through 10 ft. of #10....VD = 0.41 V
Total VD = 1.71 V. Therefore 14.3 - 1.71 = 12.59 V at the battery terminals.

For 5 Amps through 20 ft. of #12....VD = 0.32 V
For 5 Amps through 10 ft. of #10....VD = 0.10 V
Total VD = 0.42 V. Therefore 14.3 - 0.42 = 13.88 V at the battery terminals.

This tells me that your combined wiring should charge the battery fully (over time because you are only putting(at the most)about 65 Amp Hours into a nominal 120 AH battery). If you have any loads turned on in the TM (which you always do), the charging takes longer or may not occur at all. If you have a refrig on plus the fan, you will only get the battery up to about 50 to 60 % charge.

Remember a fully charged battery reads about 12.7 V and a dangerously low battery reads about 12.0 V. It takes about an additional 0.7 V to force charging current into the battery.

Now, about the delta winged thingie.

It is a drone that is actually perched on top of the blackbird and was launched from it. Google "D-21" where you will find much information. I was the ramjet engine flight test engineer for the "D" and wrote some articles about it that you will find on Leland Haynes web page regarding the M-21/D-21 program. It was a long time ago in a far away place.

Jerry

[Padgett]

Except that is allowing for the return also: =IF($B$7>0,($B$6*C$19*$B$5*2/$B$7),"") b7-# conductors, b6-amps, c19-ohms/ft, b5-length

E=IR Since b7=1 (solid core) we can drop that factor

Voltage loss a single conductor for 20 ft of #12 at 20A is .65v 10ft of #10 is .20v = .85v

Agree the Bargman must be spiffy both for the 12v and the ground (cannot rely on trailer to hitch ball).

Bottom line: Charge the battery before you leave and rely on the TV just to maintain the charge. I also carry a generator if not guarenteed power.

ps in another lifetime at the swamp in the 70s one of the interesting questions was "If the A-12 was retired and F-12 cancelled, why were we still building J58s ?"

[YNPKing]

Great discussion, thank you. I decided to supply this additional information (particularly, in light of the discussion on VD) to see if it alters your thoughts on charging the batteries while traveling with the fan and Dometic RM2354B refrigerator running on DC.

Given the following:
TV: 2014 Jeep GC alternator 220-amp; TM: 2014 TM 2417 Sport; Bargman to WFCO WF-8955PEC converter is ~20ft @ #12 wire (per schematic); converter to (2) 6V Lifeline AGM batteries is ~10ft @ #10 wire; Dometic ~halfway between converter and batteries.

Batteries tested with voltmeter:
13.03V - Pulled out of TM, fully charged (several days), rested 2 days (No surface charge). It actually took 2 days to remove the surface charge.

TM cables tested w/o batteries:
12.71V - w/ Bargman connected; Jeep off
14.16V - w/ Bargman connected; Jeep idling
14.18V - w/ Bargman connected; slight rev of engine

Batteries connected in TM:
12.99V - w/o Bargman
12.91V - w/ Bargman; Jeep off (reverse current flowing to Jeep?)
13.00V to 13.83 - w/ Bargman; Jeep idling (interesting, as I watched the voltmeter climb in .01V increments until it stopped; no dramatic jumps)

Dan