Keeping battery charged on travel trailer

I'm running a 2000 Tacoma, pulling a 16' Scamp.

My problem, in a nutshell, is that I want to run my TT's refrigerator on DC while I'm traveling. The fridge pulls 10A. After a six-hour travel day, the TT battery is seriously down. Lights may work, but I can't run the furnace, which gets uncomfortable in fall traveling.

I think I've narrowed the issue down to the entry in my truck manual that says "Charging capacity, 5A max". If that means what I think it means, then I'll never keep up with the draw on the trailer battery.

I have seen this or similar problems discussed in some older threads in this forum, and some interesting solutions were mentioned, but without enough detail that I would know how to implement them.

One that I saw was to take the charge wire to the trailer directly off the alternator (currently I have it connected to the +terminal of the truck battery). Since the alternator produces around 60A, that should be plenty of juice, but I have a couple of questions about it: 1) which wire from the alternator? How would I know I'm not going to fry the alt or cause some other undesirable result?
2) is there some way of controlling the current? Would it control itself? 60A directly into the battery would boil it dry, wouldn't it?

The other solution was to use a "DC to DC booster". The idea seemed to be that somehow it could provide power that is still 12V but at higher amperage. I have searched and have not located a device for automotive use that would do this.

I would love to hear from the original posters or anyone who knows about these solutions and how to do them. I've done a lot of my own wiring, and I'm not totally ignorant about auto electrical, but I guess I'm too ignorant to figure this out.

Thanks,
RandyTac

 

Solar panels on the trailer with a charge controller. A couple flexible 100W panels can be affixed non-permanently pretty easily with either gorilla tape, or eternabond tape.

I'm going to end up doing that on my a-frame eventually.

 

I'd guess the max current that can be supplied to a trailer through the plug.

 

That's my interpretation. Does anyone know different?

 

Yes, it's a 7-pin. I have a 12 ga wire from the battery post to the plug-in socket.

What I think happens is, the 5A charge maintenance current goes first to the pickup battery, and whatever is left over goes to the trailer battery. My understanding of this may be a little simplistic.

RandyTac

 

Hi, SOSC,

What you say makes a lot of sense. I'm only deterred from fully believing it by the "Charging capacity 5A max" in my owner's manual. What does that mean? Why is it there? Why does my perceived experience so fully line up with that limitation? Do you know for a fact that the alternator's full output is available to whatever may need it? There's no regulation on that?

But, you may be right, so let's look at what happens within the trailer. The hot (black) wire from the truck connects directly into the whole hot wire network within the trailer. That includes the + side of the battery, and also includes the converter unit. So, whatever amperage is available from the truck is available to whatever needs it in the trailer. Or so my simple mind suggests. In my case, those needs are limited to running the refrigerator and maintaining the charge on the trailer battery. An additional piece of info that may or may not be relevant - the fridge is powered off the converter. Does that affect the equation in some way? I'm not sure. And I realize this is not an RV site, so it may not be an appropriate question for this forum.

RandyTac

 

Even without the fridge, that trailer battery isn't going to build much of charge just using the 12 to gauge wiring that's part of the 7 pin wiring loom. Without the fridge, you'd be lucky to arrive at the campground with the trailer battery showing 12.5 volts.

Voltage drop occurs at the end of long wire runs whenever there is a high amp current draw. The amount of voltage drop depends on the gauge of the wire and its distance from the battery. - There may be as much a 10% voltage drop with 20 foot of 12 gauge wiring when there is 10 amp draw. -

So, when that fridge kicks in - you may only be showing 11 to 11.5 volts at the terminals of the trailer battery - under load. Keep in mind that the wire run essentially begins at the truck battery - so, it may be a 20 foot length of wire. Bottom line, when you arrive at your campground, the trailer battery might be down below 11.9 volts, if you use the fridge.

https://www.bluesea.com/resources/1437

If you want to arrive at your campsite with a fully topped off trailer battery, i.e. 12.7 to 12.9 volts of charge, when running that sized fridge - you'll need to run a 6 gauge wire all the way to the positive terminal of the truck battery, plus another 6 gauge wire to the frame of the truck. Then utilize a charging apparatus at the trailer that boosts the charging voltage to between 13.7 to 14.5 volts - depending on the level of charge in the trailer battery.

CTEK 40-186 D250SA 5-Step, Automatic DUAL 12 V 20 A Battery Charger

https://www.amazon.com/CTEK-56-677-Automatic-Battery-Charger/dp/B005LBCVL4

Be sure to locate a heavy duty fuse as close to the truck battery as possible - and - maybe an isolation relay similar to what's shown on the Blue Sea web site, if you go the CTEK route.

 

The easiest solution is to utilize a Yeti style 60 quart cooler. It'll let you keep the wiring the way it is now.

 

Thanks OldandSlow!

I appreciate that information. It closely matches a posting I found in the RV Forum, except that guy was using a Redarc charger (Australian made). Same principle. Pretty expensive solution. Of course Yetis ain't cheap, either!

I'm gaining a lot of education about how this all works or doesn't work. I understand now why it won't work the way I'm doing it. Another solution I've seen on the Scamp forum involves solar, which might have some other benefits as well. I haven't got far enough on that to determine costs and feasibility.

RandyTac

 

Let's start simple and go from there. Are you actually getting voltage through the plug and to the camper? Just because you're plugged in doesn't mean you have charge. Just because you have charge to the plug means it's getting to the battery. Plugged in and truck running you should be seeing 13+ at the trailer battery.

When your truck is running, it's not drawing from the battery anymore, it's running off the alt. The alt also replaces the charge used to start the truck, after that it doesn't do much. In stock trim there is plenty of capacity to run the truck and maintain the trailer unless you're running some severe lights or sound system.


What fridge are you running? Most draw 2 to 4 amps, not 10.

12v 12ga wiring maxes at 8a over 20 feet. You don't need 6ga unless you're drawing about 30a. You can pull more than 8 but then heat becomes an issue.

The 5a max is lkely referring to the fuse rating on the truck but I don't have the specs, trailers are wired to run normal v and a found available in most trucks. 5a should be more than adequate unless you're towing a grow operation.

Are you also running the furnace while you drive?

The simplest solution to this issue is to make sure you're cold before you hit the road, turn off or at least adjust the thermostat for minimum usqge, and then keep the door closed. Once you're set back up, drop the Temps again.

 

Hi Indy,

The answers I can supply are:
I have measured and know that I have a live connection from the truck to the trailer battery. I have even seen that, when not running the fridge, the truck will gradually restore the trailer battery. Just not fast enough.

I have 12 ga wire from the truck battery to the junction box inside the front of the trailer. From there to the fridge may be 14 ga. I need to verify that. Others are telling me that, even if it was 12 ga all the way, I will have significant voltage drop just from the wiring.

The refrigerator is a Dometic 2202. The specs call the DC element a 125W. The confirmation is that I have measured 10A going through it.

When I'm driving, the propane tanks are turned off, so, no I'm not running the furnace. To me this is a safety issue. Some users have urged running the fridge on propane while on the road. I have resisted.

Your final paragraph is what a lot of people recommend. Maybe my fridge is inadequately insulated, but I have seen the inside temp start out at 35 deg. and end up at 60 after six hours driving on a warm day. Thus the importance of being able to run the fridge on DC. The alternative seems to be to buy a Yeti.

Any other ideas are more than welcome.

RandyTac

 

Thanks, SOSC,

I appreciate your looking out for me. I have been in that forum and have seen the string you referenced, but I need to go back and follow it on out. I think there's some good information there.

Regards,
RandyTac

 

What's the voltage at the battery with the truck running? What is the amp draw at the battery with the fridge on and with it off? You might have some other parasitic drain going on besides the fridge.

Voltage drop between the battery and fridge shouldn't affect your battery capacity. A dc booster cam raise voltage and sacrifice amps, or raise amps and sacrifice voltage, it can't do both.

Speaking of your battery, what kind, capacity, how old etc?


My last camper would run the blower with the propane off, we had to make sure it was actually turned off at the furnace.

 

Not really a solution for you if you want to run the fridge while traveling but here's what I do.....

Plug in at home several days before the trip and place several water bottles in the freezer and drinks in the fridge. Turn it up to max cold to freeze the water. The day before trip I load the fridge and freezer with food. After I'm hitched up and ready to roll I unplug, turn off the fridge, and move frozen bottles from the freezer to the fridge. Food stays cold for 8+ hours that way and I don't have to run the fridge while driving.

 

Thanks, Indy,

I have done some of those measurements, but I didn't write them down. There was a clear progression of voltage drop from the truck battery to the connector on the truck side, to the battery on the trailer, to the connection to the fridge. But my impression from other posters here is that all that is normal. I'm pretty confident there's no parasitic drain. The battery is good for a long time if I'm not running the fridge.

The battery is a year old, NAPA deep cycle. I'd have to take it out of the box to see what the capacity is. Memory suggests it's around 100 AH.

I have been investigating DC boosters. They're a little spendy, and all say I need to upgrade the wiring to either 6 ot 8 ga, depending on who you ask, all the way from the Tacoma battery back to the booster inside the trailer. Which has lead me to wonder if I wouldn't go a ways toward solving the issue just with the wiring upgrade.

RandyTac

 

A wiring upgrade is going to give you by far the biggest bang for the buck. The wire in the truck, on paper, does everything you need. X wire over y feet is good for z volts. But a lot can go wrong from a to b. Running fresh copper can eliminate the problem. Going straight from the battery post is pretty much just as good as straight from the alt. Just make sure you have clean connections and fuse it properly.

When I first started learning basic electrical I found thinking in terms of plumbing made the most sense to me. Voltage is volume, amps is pressure. Your battery is a big tub of water that is constantly being filled by your alternator. It's not obiously But in thought it works.

Increasing wire size works like going to a larger pipe running out of the tub. More water can flow through a 1" pipe than a 1/4". And if I crimp off that 1", less water will flow but with greater pressure, think of a garden hose when you put your thumb over the end. If your second water tub is running out of water, you want to increase the feeder pipe. Bumping pressure up may speed up the water flowing in to the 2nd tub, but less water will actually be going in.

I have installed 2 accessory fuse blocks straight off the battery withat least 4ga on all my offroad vehicles. 1 block is relay controlled so only on whe the truck is on, the 2nd alwqys on. They're cheap at 4 or 5 bucks and make adding circuits pretty simple and letting you fuse appropriately. The alternator makes all the volts and amps you will need, no expensive booster needed.

.

 

I think there's a good chance you're right, from everything I've read (and I've read a lot on this subject by now). However, I'm about decided I'm going to address by installing about 200W of solar on the trailer. That should be enough to keep up with the drain from the refrigerator, but has the added benefit of keeping the battery up when I'm boondocking, which I do quite a bit.

Thanks to everyone involved for inputs, thoughts, opinions, and yes, even facts on this topic.

RandyTac

 

Does your reefer run on propane too? If so run it on gas and solar to recharge the 12v system for the lights and fresh water pump.

 

Can you run the fridge on propane? It's not as efficient as battery, but it will keep it cold.

 

It's been my experience that running a fridge on propane lasts WAY longer than 12V.

a DC to DC booster like what you want does not exist because it is magic. lol

Other options are to add a solar charger to your trailer and leave it connected 24/7