Charging TM batteries with jumper cables

[T and C]

Folks,

I have the usual problem that so many threads discuss: Running the referigerator on DC power while towing runs the TM batteries down. The suggested fixes that I have read about are well beyond my knowledge of electrical repair.

I currently have neither a generator nor solar panels. I have read on these boards that it would take 2-3 hours to charge the batteries by running the TV motor while parked.

What if you just connect the TV battery directly to the TM batteries with jumper cables and then run the motor?

Tom

[scrubjaysnest]

This is one of those to many variables questions. Like what are the TM batteries state of charge when you begin. When on DC the norcold refrig draws between 12 to 14 amps per the manual. In reality it will depend on the battery and its state of charge. If we assume 12 amps, and a fully charged battery at start, and the typical group 27 deep cycle marine battery (12 volt). A 50% discharge of the battery will occur in about 4 hours. That's theory, in my experience the battery usually lasts about two hours if the TV is hooked and running. The battery will be discharged somewhere around 70 to 90%. This is another big variable which depends on the TV. If you stop for a meal the refrig is quite capable of total battery discharge in an hour. Again a lot of variables.

Back to the 50% discharge assumption when you arrive at the CG.
Using jumper cables could bring the battery back up in a 1/2 hour, best case, or more likely an hour or more. Your initial charge rate is quite high but once the battery reaches about 70 to 80% charge the rate drops way off and this is where it becomes difficult to determine.

If you haven't done so look at this link:

http://www.marxrv.com/12volt/12volt.htm

This is the The 12 volt Side of life. It is mentioned in other threads on the TM site.
I'm sure that others here will be glad to give their thoughts and experiences.

Maybe Philip, link to his thread http://www.trailmanorowners.com/foru...ad.php?t=10986, with his 2 gauge mode, since it is closer to some jumper cables has some insight.



Another thought: build a generator from an alternator and lawn mower engine, there are several web site that describe how to do this. This link is just one:

http://theepicenter.com/tow082099.html

[Joesjunk]

Thanks for the link scrubjaysnest. A bunch of good info there.

[ShrimpBurrito]

Originally Posted by T and C

Folks,

I have the usual problem that so many threads discuss: Running the referigerator on DC power while towing runs the TM batteries down. The suggested fixes that I have read about are well beyond my knowledge of electrical repair.

Tom -

First, you may not have a problem at all. Some vehicles have inadequately sized wiring or poor connections in the wiring harness for the towing circuit such that it results in the poor performance you noted -- i.e. the TM battery discharges while underway with the fridge on DC. But some vehicles, particularly larger ones where towing is more the norm, that is not the case. That is easy to do with a multimeter, which are cheap and easy to use. If you don't know how to use one, we can teach you. But obviously, you can also tell if you have a problem if your battery is drained upon reaching camp, and it sounds like that is what is happening to you.

Originally Posted by T and C

I have read on these boards that it would take 2-3 hours to charge the batteries by running the TV motor while parked.

A Group 24 battery, which I believe it what new TMs are sold with (but I'm not sure), has a capacity of roughly 80 Ah. When my batteries are discharged and I connect my TV with its factory wiring, they initially charge at a rate of about 6 amps. If you wait till your lights are dim, your battery is probably discharged to about 30%, which means you need to restore 56 Ah back to the battery to bring it back to full charge. The charging process is only about 90% efficient at best, so even with 6 amps going to the battery, only about 5.5 amps gets absorbed by the battery. 56 Ah / 5.5 A = 10 hours to recharge the battery, but it will actually take longer than that for the reason scrubjay mentioned. Bottom line: this is a silly way to charge your battery.

Originally Posted by T and C

What if you just connect the TV battery directly to the TM batteries with jumper cables and then run the motor?

You could do this, but it's still going to take you a couple of hours. Again, not a good solution.

IMHO, by far the cheapest and easiest way to extend battery life is to replace your incandescent lights with LEDs. At $20-$25/each, you can replace the 4-5 lights you use the most for about $100, and if you do that, you will probably rarely ever have to use anything but an LED light.

Here's another solution:
http://www.trailmanorowners.com/foru...ad.php?t=10587

It will cost you a few hundred bucks, but installation is fairly simple (hook up 5 or so wires and screw the box to the wall) and you don't need to run any new wires. You will need a multimeter to do it though.

But I would do the LEDs first.

Dave

[Wavery]

I second Dave's comments. Charging the battery from an idling TV engine is not only inefficient, it is dangerous.

I have a Honda 2000 "Quiet" generator. It's an expensive "Battery charger" but it has other (obvious) benefits.

However, I installed 160W solar panel array and I don't even bother bringing the generator camping anymore. It not only resolved the towing issue, it resolved all of the issues with battery charging and electrical consumption while camping.

The cost of the (DIY) installation was around $650 (Honda generator was $1,000). We use all the electric that we want (no LED lights) and never even think about electric anymore. The panels are even sufficient for mostly cloudy days when combined with 2, 6V batteries (additional $300). The other benefit is that you don't put any fuel in them and they add re-sale value to the camper. We could camp for 6 months and never be concerned about the batteries.

[Barb&Tim]

Originally Posted by T and C

Folks,

I have the usual problem that so many threads discuss: Running the referigerator on DC power while towing runs the TM batteries down. The suggested fixes that I have read about are well beyond my knowledge of electrical repair.

I currently have neither a generator nor solar panels. I have read on these boards that it would take 2-3 hours to charge the batteries by running the TV motor while parked.

What if you just connect the TV battery directly to the TM batteries with jumper cables and then run the motor?

Tom

Tom, just a thought, Have you verified with a voltmeter that you are actually getting a voltage from the charge line coming from the TV to the battery on the TM?

My TV, a GMC, came from the factory without a fuse for that so i had to get one.

Tim

[Wavery]

Originally Posted by Barb&Tim

Tom, just a thought, Have you verified with a voltmeter that you are actually getting a voltage from the charge line coming from the TV to the battery on the TM?

My TV, a GMC, came from the factory without a fuse for that so i had to get one.

Tim

That's good point. I notice that both of tour TVs are Fords. Ford requires a Trailer relay in the main fuse box, under the hood. Check your Owner's Manual for the relay position.

[Bill]

My Fords (Explorers) have come from the factory with all fuses, relays, etc, as part of the factory tow package. I can't speak directly to your Fords, but I'd be surprised if the answer is different. Still, as B&T and Wayne have said, it is an easy thing to check.

For what it is worth, charging with jumper cables won't work particularly well, dangerous or not. And sadly, putting in really large wire to the TM, with the goal of decreasing voltage drop to increase charge rate, won't be particularly effective beyond #8 or so wire. If anyone is interested in a techie explanation, PM me, but we go through this about once a year and it is not real helpful to repeat it again. My apologies for that.

Bill

[Wavery]

Originally Posted by Bill

My Fords (Explorers) have come from the factory with all fuses, relays, etc, as part of the factory tow package. I can't speak directly to your Fords, but I'd be surprised if the answer is different. Still, as B&T and Wayne have said, it is an easy thing to check.

For what it is worth, charging with jumper cables won't work particularly well, dangerous or not. And sadly, putting in really large wire to the TM, with the goal of decreasing voltage drop to increase charge rate, won't be particularly effective beyond #8 or so wire. If anyone is interested in a techie explanation, PM me, but we go through this about once a year and it is not real helpful to repeat it again. My apologies for that.

Bill

When my brother got his '04 Expedition (new) the relay was in a plastic bag in the glove-box with instructions.

I'll tell you one thing, that fuse panel lid under the hood was a bear to get open .