Charging From The Tow Vehicle - Good Idea or Not?

[mrchuc]

I just took delivery of a new Little Guy 4-Wide Platform TD. I ordered it with a deep cycle battery and wiring for 12 volts in the TD. It is also set up to charge from the tow vehicle while driving.

I am new to all this and so I read everything I could in sdtripper2's index related to batteries. That was a BIG help. To keep the battery in good condition, I ordered the Battery Tender Plus.

One thing confused me though. In one of the posts, it was stated that having the battery hooked up to the tow vehicle is not a good idea. As I remember it, the writer said that if I start out on a trip with a fully charged battery (as mine will be having been tended by the Battery Tender Plus), that I will actually lose charge as I drive and that I will arrive with only 70% charge. That would not be good at all.

1. Does that seem correct?
2. If so, should I disconnect the charging wire (or put a switch on it to keep it off when not needed)?
3. Also, if so, is there something I can do to use the tow vehicle's power to keep the TD's battery topped off correctly.

Finally, can someone enlighten me on why this is or is not true?

Thanks, everyone, for making this forum such a great resource.

[Dale M.]

Regardless if somebody wrote a fully charged battery will only have a 70% charge after some "drive time", what are your priorities.... To have a charged batter or a dead battery.... It really is not significant if you camp in a location with shore power and can charge battery upon arrival (if discharge while driving is true) If you primitive camp (no shore power) the vehicle charging is probably a must...

Bottom line is you have power and can use it.... Sometime we get to specific on the details and loose the whole picture, TO HAVE FUN TD CAMPING...

Also consider new electrical systems in most vehicles have ability to create enough voltage and amperage to keep most battery systems at full charge (float voltages 13.5 to 14 volts) so why worry about it...

In most cases these details are just a stress creator that takes the fun out of the TD experience..

Only thing I would recommend is have some sort of isolation (either relay or diode) between vehicle and TD battery so when car charging system is off the batteries are disconnected from each other so one "system" can not put a drain on other system...

Dale

[Alphacarina]

One thing confused me though. In one of the posts, it was stated that having the battery hooked up to the tow vehicle is not a good idea. As I remember it, the writer said that if I start out on a trip with a fully charged battery (as mine will be having been tended by the Battery Tender Plus), that I will actually lose charge as I drive and that I will arrive with only 70% charge. That would not be good at all.

1. Does that seem correct?
2. If so, should I disconnect the charging wire (or put a switch on it to keep it off when not needed)?
3. Also, if so, is there something I can do to use the tow vehicle's power to keep the TD's battery topped off correctly

1.) - No, that's not true. If you have it connected to your vehicle battery as you drive, both batteries will stay topped up because the car's alternator will keep them at 14 volts as long as the engine is running

2.) - Yes, you want to disconnect the two batteries when the engine isn't running. The best way to do this is with an ACR (Automatic Combining Relay). The ACR checks the voltage on the car battery and when it goes above 13, it connects the tear battery to the car battery so both get charged. When the voltage falls below 13 (which means the alternator is no longer charging . . . . because the engine is no longer running) it disconnects the two

3.) - Yes, when combined with an ACR, you'll always have a fully charged battery in the tear. You should have a fuse in the wire between the car's battery and the ACR and then another fuse near the tear battery so that any shorts in the teardrop connection won't harm either the tear or the car

Do a Google search for 'Blue Sea ACR' and you'll find them for sale several places

http://www.marine.com/product_info.php/products_id/29608

There's one for $65

Don

[Gerdo]

I have my TD charging off my TV. I have a solenoid in line to ios the batteries whar the TV is not running. I also have a switch in line to turn off the solenoid. My TD battery cutoff also disconnects the power line from my TV. This way I can charge or not charge when I want to. Works great.

[Phil & Ningning]

I was thinking about this charging dilemma recently. If you use a relay to isolate your batteries and trigger it from the ignition system, it will disconnect the trailer battery when the ignition is turned off. The problem is if you try to start the car when the trailer battery is low. The discharged auxillary battery will then load the system such that the vehicle battery may not have enough voltage to start the engine effectively, thereby defeating the purpose of the whole thing. In that case, there is also possibility of excessive current draw from the trailer battery by the starter, which could blow fuses or even overheat the wiring if not fused. In my view, it is just as important to isolate the batteries during starting as when the engine is not running.

For this reason, I triggered my relay from the accessory circuit in the truck. In modern cars, the accessory circuit is deenergized during engine starting. I suppose if I was sitting still, just listening to the radio with the engine off it could drain the trailer battery a bit, but I pretty much never do that.

Phil

[tonyj]

More people have died from discussing this issue than any other discussion on this forum.

Let the fisticuffs begin.

[len19070]

More people have died from discussing this issue than any other discussion on this forum.

Let the fisticuffs begin.

HOW TRUE!

This to me is a no brainer.

The RV industry has been doing this successfully for Decades.

Automobile Manufactures Ford, GM & Dodge sell vehicles set up to do this from the factory.

Every Major RV manufactures build trailers that are set up to do this.

Honestly! This is not a hair brained idea thought up by somebody with no practical experience.

If you charge from your vehicle while you drive..YOU NEVER HAVE TO WORRY ABOUT HAVING A CHARGED BATTERY.

Happy Trails

Len

[Alphacarina]

If you charge from your vehicle while you drive..YOU NEVER HAVE TO WORRY ABOUT HAVING A CHARGED BATTERY

Actually, that should read "You never have to worry about having a discharged battery" - Charged batteries are never a 'worry'

Don

[mrchuc]

Okay, I probably shouldn't have asked if charging from the tow vehicle was a good idea. Of course, having the towing vehicle be able to charge the tear's battery is a good idea. What I really wanted to know is what is the best way to charge from the tow vehicle (just leave it like it is, install other items in the circuit, etc.) AND are there times that unhooking the charging circuit is a good idea.

For example, in the thread I read earlier (which I can't find now, sorry) the situation was a stay of more that one day where shore power is not available. He claimed that disconnecting the charging circuiit on the way to the camp allowed him to arrive with 100% battery charge and that his battery lasted longer when he did this than when he left the charging circuit hooked up while traveling. No one challenged this information at the time (but I don't think anyone supported it either.) That's why I wanted to know more.

I admit that even though I have fooled around with electricity and electronics for most of my life, rechargeable batteries (lead-acid in particular) are a mystery to me. I really just want to do a good job of maintaining my tear's battery so it will live long and prosper (and so I will have power to turn on a light so I can see to get up in the middle of the night like I often have to at my age.

The advantage of gasoline over electricity, of course, is that you can easily see how much gas is left by glancing at the gas gauge. Knowing how much electricity is left in the battery (and how much of that is safe to use without hurting your battery) seems like a lot harder question to answer.

Apparently this has already been cussed and discussed. Sorry if I am going over plowed ground. Please know, I did read literally dozens and dozens (and dozens and dozens) of old posts on this subject and I found myself still having questions.

[Gerdo]

Here is a charge/voltage chart. http://tnttt.com/viewtopic.php?t=9009

[Alphacarina]

Measuring battery capacity just by measuring the battery voltage is a hit or miss proposition at best

For one, the measurement must be done with the battery at rest (not being either charged or discharged) for an hour or so to mean ANYTHING, and even then, it doesn't tell you how many more hours of use you have left

The advantage of gasoline over electricity, of course, is that you can easily see how much gas is left by glancing at the gas gauge. Knowing how much electricity is left in the battery (and how much of that is safe to use without hurting your battery) seems like a lot harder question to answer

Yes, a true 'gas gauge' for your battery is a lot harder to do - It takes lots of electronics and computer power to do it, but they do make such a thing, if you're really interested

ebay clicky

This unit has a shunt which mounts in the negative battery lead and it measures all power going into and out of the battery, so it knows when the battery is 100% full and it then does an 'electrical countdown' of every 'drop' of electricity you use from the battery and can give you an accurate percentage of what you've used . . . . and how much is left

It does lots of other neat things too. It's easy to install and program, even for a novice. I've installed probably 25 of these on sailboats and had a more elaborate version on my own boat for several years and can heartily recommend them. If knowing where you stand on the 'battery gauge' is important to you, this is a 'must have'

Don

[mrchuc]

It does lots of other neat things too. It's easy to install and program, even for a novice. I've installed probably 25 of these on sailboats and had a more elaborate version on my own boat for several years and can heartily recommend them. If knowing where you stand on the 'battery gauge' is important to you, this is a 'must have'
Don

Wow! I am glad to know there is such a thing. Kind of restores my faith in electrical science. I was beginning to think that lead-acid batteries were magic.

I would love to own one of those instruments, but if the price of the one you showed us is typical, I will not be able to justify the expense. I don't think it is overpriced considering what it does. But at this point it would be a nice luxury rather than a necessity.

Thanks for the info!

[Alphacarina]

That's a pretty good price for the single battery version - Here's a well used one and it's up to $140 with a day to go

ebay clicky

They've been around for about 10 years - The dual battery version we all used on sailboats also functions as a computer controlled alternator voltage regulator and it sells for over $600

http://www.consumersmarine.com/modperl/product/details.cgi?r=view&i=830014&aID=41E&cID=FROOGLE

The matching computer controlled inverter/battery charger to go with it is about another grand

Compared to sailboats, teardrops are a really affordable way to travel

Don

[Dale M.]

More than you ever wanted to know about "storage batteries"....

http://www.batteryfaq.org/

Dale

[Mary K]

Awa...this is boring yall. Can yall disagree on something? I was hoping for some entertainment.

Mk

PS Good info though.