Electrical Questions for a camping cargo trailer

[texasdog]

First - let me say that I am in awe of what is posted on this forum. My god!! You guys are awesome. I have skimmed through all the reading material - I will go back and look at it much more closely here over the next week or so as there is a lot of good info in there. As a result of what I have read so far - I have made some decisions about what to do. However, I still have some questions - and I know they may be answered in the standard reading material - but I want to ask some anyway to help me get started. I hope I'm not too lame.

So - I am building a camping/cargo trailer and I want it to have some electrical functions. I've done some research, come to some preliminary conclusions and I want to check my results and get some info from people in the know. It has been a while since General Physics II, so please bear with me (:

First - information about my tow vehicle. I have a 2007 Jeep Wrangler Unlimited Sahara. It came from the factory with a tow package, including a 4 pin adapter. Because my existing trailer has a 6 pin, I modified the Jeep to have a 4 pin and a 6 pin adapter (although 2 of the pins on the 6 pin are not connected to anything). However, I want the full enchilada for this tow trailer, I went ahead and got the pricey Mopar 7 pin adapter kit that plugs into the brake lights and has additional leads for the battery (+|-) and blue cable for the electric brake controller. I have a question about how this works to charge the batteries in the trailer. I have verified with my multimeter that the positive pin on the 7 pin adapter is hot, even with the engine off. My questions here are:

a). My understanding is that SOMEWHERE there is a diode that prevents juice from the trailer from flowing back to the Jeep. Is this a standard thing? Is this part of the 7-pin kit, or does the jeep already have it or what? Details, please. Second part of this - if I hook up a hot wire to the 6 pin adapter I put on the Jeep already, does it also have this diode and offer the same protection, or do I need to put one in-line, or what?

b). My understanding is that the purpose of this hot wire is to charge up the trailer batteries when the Jeep is rolling along. However, I've been told that the current flowing through this wire is just a trickle and doesn't really do a whole lot for charging up batteries. Is this true? If it is, then why bother with it at all? Looking at the wire in the 7-pin harness, it looks to be about a 12ga wire - nothing too special. Some have told me that if I want to do things right, to run a real cable, like a winch power cable, from the Jeep's battery to the trailer, to get high current flow. Your thoughts? FWIW, I will probably run high amp cables from the battery to the back bumper anyway, just so I can hook up a hitch-mounted winch back there if necessary. I wasn't planning on doing that soon, but if it will be helpful for my trailer stuff - I need to know (:

c). I have verified with my multi-meter that this hot pin is hot, even when the Jeep is off. Anything connected to it is going to suck power when the Jeep is off. So, with this 7-pin config, do I need to connect this hot wire to a battery isolator in the trailer, which is then connected to the trailer batteries, so that I do not run the Jeep dry?


Second - my understanding of the trailer electrical universe is:
Trailer's tail/stop/turn/reverse/marker lights will be powered from the Jeep. When the Jeep's come on, the trailer's will come on.
Trailer's electric brakes will be powered from the Jeep.
Everything else on the trailer will be powered by the trailer's batteries.


Third - DC power vs AC power. I had planned on putting an inverter in the trailer's electrical system, so that I could run a few standard electric things if needed - but people have been telling me I would be better off using an inverter directly with the Jeep if needed, and use its battery, rather than the trailer's battery. Does this make sense to anyone? I fail to see the logic here.


Fourth - my camping electrical needs are pretty modest. I am not building something to sleep in. I am building a camping cargo trailer - much like an AT Horizon (http://www.adventuretrailers.com/horizon.html). Its purpose is to give me some cargo security when camping with a soft top Jeep, allow me to carry more stuff, and reduce the overhead hassle of packing/unpacking camping gear (I can leave it in the trailer ready to go). I could unload everything and sleep in it if I really had to for some reason, or I could sleep on top of it - but that's not really its purpose. It's a cargo trailer (:

So, I do not anticipate using any fridges, microwaves, TVs or any of that kind of stuff. I'm really more interested in things like having some cargo bay lights so I can see when loading/unloading something from the trailer, being able to light up my camp site so I can see what I am doing, running a 12v air pump of some kind (inflatable kyack or something), running the wife's hair dryer or coffee pot, charging up a laptop or digital camera, iPod, maybe running wife's blender (margaritas), and other such stuff. I suppose it might be nice to run a heater of some kind into my tent, but there are propane solutions for that kind of thing. Pretty easy to throw another propane bottle in the trailer if needed. I might go camping in a hot spot one day - maybe - are there propane based A/C units for a tent? (: Anyway - my electrical needs are fairly modest I think. However, I would like to be able to be off-grid for 2 weeks at a time - completely self-sustaining - so I need to make sure whatever system I end up with can usually go the distance.


So - given all of that - some questions/issues are:

1). I had a question about 12v or 24v - but I see now that the answer for me is a 12v system - unless someone can convince me otherwise.

2). Inverters - so, I know that to live my dream here, I need an inverter. I know there are the sine wave ones and the square wave ones - and that the sine wave ones are twice as much and up (everything else being equal). Research seems to indicate that for my purpose, the square wave ones are fine. One question I have is how much to buy? Is 1000w enough? Is 2000w overkill? Maybe 500w is enough. I know it depends on what I am using at any particular time - but assuming the electrical use is really more in the "support" category rather than the "I can't go camping unless I have all the comforts of home category" - what do you think? Anything else I should know about inverters? What about the install in Jeep vs. Trailer question? What if I might want to run some 20A VAC power tools on occasion, like a chop saw or table saw? Does that change the picture at all?

3). I had been thinking of an Optima Yellowtop or Bluetop - but battery store says they are really low amp-hour batteries and that I would be better off with a pair of 6v golf car batteries. Space is not a problem for me - I can fit 4 of these golf cart batteries if I want to. My current thought is to start with 2 of them in series and design my trailer to take 2 more in parallel, so that I can easily add them later if needed. That would give me a nice 12v system, with decent amp-hours. Thoughts/comments on this approach?

4). I plan to have a master on/off switch for the trailer electrical. If I do go with 2 6 volt golf cart batteries, and want to add two later, should I use a selector switch so that I can go with batteries 1+2 (12v), 3+4 (12v), or 1+2+3+4 (24v)?? I've read some things like putting it in 24 volt mode can be good if you are connected to hard-line power and charging up. Any thoughts here? I realize that if I put it into 24v mode, I need to not use any of my power, since it will all be 12v rated stuff.

5). If my understanding of the battery isolator is correct, then I will be using one, so that I can isolate the Jeep's battery (via the charging pin) from the trailer system, so that if I manage to drain the trailer's batteries, I don't whack the Jeep next. Is this going to introduce conflict with the battery selector switch and/or solar panel (keep reading), or anything else I'm doing? Thoughts? Anything I should know?

6). I'm planning on having something in the way of a switch panel for the trailer. It will have switches to turn on/off various lights or things on the trailer, a volt meter, maybe an ammeter (is an ammeter a complete waste of my time here?), a remote panel (on/off) for the inverter (I've seen them out there), and maybe some other things. I'll also have a fuse box for a few things. Any thoughts for useful things to add?

7). I've considered the addition of an "unbreakable" solar panel - either permanently mounted to the top of the trailer, or stored and deployed as necessary. I know I need a charge controller so that it doesn't overcharge the batteries, but does the use of a switch selectable 12v/24v system conflict with this idea in some way? I am thinking of "plumbing" for a solar charger up front, but I will probably not add it until later. Anything I need to know here?

8). I might want to power an air compressor off this system - to maybe pump up a tire, or inflate one of those inflatable kayaks or rafts or something. Is that going to be too much load for the scope of what I'm talking about here? Should I just stick with the little 12v ones rather than using a regular one via an inverter?

9). I figure a good electrical system in this trailer is better than hauling along a generator (which I'd have to buy) of some kind. If I am saving money on a generator, it can be reasonable to spend more on the electrical system for the trailer. Although, eventually, I am sure I will buy a generator.

10). I want to end up with what meets my needs - but I don't want to blow more money that I need to either. This trailer is already over budget. It's likely that something like the solar panel is something that I would add later - but I want it to be easy to do that later too. I'll probably add a second set of golf cart batteries too - and I want to make that easy in the future.

11). Any chance of running power tools, such as table saw, chop saw, etc. off such a system? They all seem to pull 20A of 110VAC. Could be useful for cabin building.

12). What do I need to know about making the trailer so can I charge up the batteries via "shore" power at an RV site, or at home or what not? I know they use a 30A or 50A power line, but what else should I know here - in terms of how it inputs into my electrical system, dangers, tips, etc.?

I think that's about it. Hope to get the experts on this stuff to pitch in (:

Thanks in advance!
td

[prohandyman]

Wow...Do you type for a living by chance? I'm walking out the door, and will have to re-read this again when I can sit down for awhile. My mind wont let me comprehend that much in one sitting!

[bobhenry]

And the correct use of punctuation and spelling. That much verbage and no typos.

Kudos to you !

If you love your power tools don't try and run them on an inverter. Brown out to a brush motor is a big problem. If you are running saws and such noise is probably not a problem invest in the generator for the cabin building.

Heating element appliances such as coffee pots larger microwaves and electric skillets are difficult to operate successfully on a limited inverter.

You are camping arn't you. If you are that tied to the grid maybe you should have the power company set you a temporary electric pole whereever you camp.

[mechmagcn]

Boy, a lot of questions and info to digest from one post.
First let's address the Jeep; don't power an inverter from the vehicle unless you want to have it running anytime that the inverter is being used (you don't want to be out in the boonies with a dead starting battery (also, inverters should be powered from deep cycle batteries and not from a starting battery)
Next let's talk about inverters. If you want to power things like a hair dryer or coffee pot, the inverter will have to output more wattage that the appliance is rated for (ie: most hair dryers are rated at 1000 to 1200 watts, most coffee makers are rated at around 1500 watts) so you will be looking at an inverter of at least 2000 watts. Modified or true sine wave, it depends on what you plan to run. If running any sort of electronics, use a true sine wave, most other appliances and tools will accept the modified wave of the cheaper inverters. And forget running an air conditioner from the inverter unless you are going to carry a trailer load of batteries.
For charging purposes, The charge wire from the Jeep will not be sufficient. Run at least a 8 gauge wire to the rear of the vehicle (I prefer to run at least #4 welding cable) and use a continuous duty solenoid (powered when the ignition is on) to prevent running the battery down on the vehicle. I use the solenoid instead of an isolator to prevent the voltage loss through the diodes of the isolator. This will be marginal at best to charge the batteries unless you upgrade the alternator on your vehicle.
Batteries, for the loads that you are wanting to run, go ahead and buy at least 4 of the best 6V deep cycle batteries that are available.
I really don't understand the part about the switches except for using a master switch to disconnect the batteries, it really sounds like you are trying to make the system much more complicated than it needs to be.
For practical purposes, I would recommend you buy one of the "quiet" inverter/generators in the range of 2000 watts to power your needs.
I know that this is not what you wanted to hear, but living off grid does take some planning and it is a compromise between how deep your pockets are and what luxuries you can do without.

[brian_bp]

1). I had a question about 12v or 24v - but I see now that the answer for me is a 12v system - unless someone can convince me otherwise.

Yes, 12V. If someone changes your mind, find someone else to change it back!

[brian_bp]

Fourth - my camping electrical needs are pretty modest...

...running the wife's hair dryer or coffee pot...

...I would like to be able to be off-grid for 2 weeks at a time - completely self-sustaining...

Running heating appliances, and doing much of anything for two weeks, are certainly not "modest" requirements. Heat the water for the coffee with propane, and discover the joy of natural air drying.

11). Any chance of running power tools, such as table saw, chop saw, etc. off such a system? They all seem to pull 20A of 110VAC. Could be useful for cabin building.

Not without either adding a generator, or carrying a huge array solar panels (several square yards), or running the Jeep a lot as a really inefficient and expensive generator set. I would ditch the idea of a AC-powered air compressor, too.

[brian_bp]

3). I had been thinking of an Optima Yellowtop or Bluetop - but battery store says they are really low amp-hour batteries and that I would be better off with a pair of 6v golf car batteries. Space is not a problem for me - I can fit 4 of these golf cart batteries if I want to. My current thought is to start with 2 of them in series and design my trailer to take 2 more in parallel, so that I can easily add them later if needed. That would give me a nice 12v system, with decent amp-hours. Thoughts/comments on this approach?

If you had a realistic idea of capacity requirements, expressed as amp-hours (A-h) at 12V, you could look at the capacity of batteries and make a suitable choice.

A Group-34 sized Optima (e.g. D34 or D34M) has about 55 A-h capacity. A pair of the most common golf cart batteries (e.g. Trojan GC2 T-105) have about 225 A-h capacity. Although these two specific batteries use somewhat different technology, the bigger difference is sheer size - that's 43 lb of Optima versus 124 lb of golf cart batteries. That's a bit like comparing a small gas car to a diesel one-ton pickup... it's not just about gas versus diesel - the size is wildly different.

For long-term camping without services, the two to four big battery scheme is suitable... but to put this in perspective, most regular RVs - including 30-foot trailers and motorhomes - don't have that much battery.

[brian_bp]

4). I plan to have a master on/off switch for the trailer electrical. If I do go with 2 6 volt golf cart batteries, and want to add two later, should I use a selector switch so that I can go with batteries 1+2 (12v), 3+4 (12v), or 1+2+3+4 (24v)?? I've read some things like putting it in 24 volt mode can be good if you are connected to hard-line power and charging up. Any thoughts here? I realize that if I put it into 24v mode, I need to not use any of my power, since it will all be 12v rated stuff.

Connecting all batteries in series has some advantages... if they are always connected that way. Charging them in series and discharging (using) them in parallel doesn't sound like a good idea to me at all, since the advantage of series operation is that each battery handles exactly the same current: they would get equally charged but perhaps unequally discharged.

There's little reason to run anything but the complete array of batteries. If one fails in the four-battery system, you need to disconnect it and likely (depending on configuration) the one it is in series with, but that can be a manual cable removal operation, or use of simple disconnect switches on the batteries, rather than any kind of selector switch.

[brian_bp]

12). What do I need to know about making the trailer so can I charge up the batteries via "shore" power at an RV site, or at home or what not? I know they use a 30A or 50A power line, but what else should I know here - in terms of how it inputs into my electrical system, dangers, tips, etc.?

The purpose of large RV power services (which are indeed a single 30A circuit, or two 50A circuits in one cable) is to be able to run a lot of stuff at the same time. Since that much power is not going to be available while camping (assuming the intention is to generally camp without shore power), I don't think there's any point in setting up either the trailer to use it or the house to supply it.

Even the huge proposed 4-battery setup would have a total capacity of about 450 A-h at 12V. Since batteries should be charged slowly, even a 20-hour charge is fast enough to charge between trips; the rated capacities are based on a 20-hour discharge, and faster means more energy loss, whether charging or discharging. 450 A-h over 20 hours is an average 22.5 amp charging rate. 22.5 amps (or, say, 30 A peak) at 12V is within the capacity of an ordinary charger (i.e. one you can buy at WalMart) that only uses a few hundred watts - ideally a charger which puts out 30A at 14 V (to charge) only needs 420 watts of input power... or 3.5 A from a 120V AC power circuit. Even with less than perfect charger efficiency, any old household outlet on a 15A circuit is fine to run the charger.

I had a welding outlet in my garage, and changed the socket to match the 50A RV standard to power a large trailer which we had at the house for a while and wanted fully functional. With a suitable extension, I had power at the trailer and didn't need to have an additional outlet outside. I never bothered doing anything like that for my small travel trailer (even though it is wired for 30A RV service), since an ordinary extension cord from the house on a typical outside convenience outlet is enough for lights and power tools while working on the trailer, and a charger for its battery.

[madjack]

...let me add one more VERY IMPORTANT thing for your consideration...there is a 10 fold increase in AMPERAGE when going from DC TO AC...that AC power tool that pulls 15 to 20 amps worth of 120VAC power will need 150 to 200 AMPS of 12VDC power to work...that hair dryer or coffee maker that uses 10 to 15 AMPS of 120VAC will need 100 to 150 AMPS of 12VDC...a 720watt 120VAC microwave that draws 6AMPS of 120VAC will need 60AMPS of 12DCV...so along with a MASSIVE battery bank, you will need MASSIVE wiring along with a 2000watt inverter to run them...are ya gettin' my drift here...running those types of items are not practical with just battery power...get a 2000watt gasoline generator or learn to do without them....
madjack

p.s. 4, 6V golf cart batteries will run you 1000+ bucks, that is more than the best 2000w generator made........MJ

[texasdog]

All:

Thanks for your replies! Please keep them coming (:

Some response to your comments - posts 2 through well..doesn’t look like the posts here are numbered. OK, response to all of the posts above this one (:

Thanks for the writing compliments. It’s one of the few things I do semi-well (:

General comment – I think people may have misunderstood where I am coming from here. I have never gone camping with any kind of camper or trailer before, let alone any electrical power of any kind, beyond what comes with a stock vehicle. So for me, there is no “getting used to doing without” here. When camping, I’ve never done WITH (: My over-eagerness that you may be sensing is just me knowing nothing about making a trailer with electrical capability of some kind and trying to find out what the limits are, what’s reasonable/realistic, what isn’t, etc. I gave you my “wish list” – not necessary my must have list. I am not “that tied” to the grid when camping. Last place I went camping there was not so much as an electrical socket for at least 100 miles in any direction. I’ve lived in a cabin with no water, phone or electricity for three years – so doing without luxuries isn’t as hard for me as my original post may have made it sound. So – that said – on with the rest of the responses. (:

OK – so power tools and air compressors running off batteries is out. Same for 110VAC coffee pot (I don’t even drink coffee by the way) or hair dryer (I can only WISH I had some hair to dry). If it doesn’t come with a 12v plug, more or less forget about it – with the exception of charging up electronics. Got it (:

No inverter on the Jeep – keep it on the trailer, and even then, only use it when I need to. Based on all this advice, I’ll set my inverter budget at $100 and get whatever is available at that price point.

The charge wire from the Jeep is worthless for charging batteries. Got it. So what do they put it on there for? Here I was all excited to use it and it’s worthless. Damn. Can I do anything productive with it? In the meantime, I’ll run a winch cable and the solenoid – do you have a link for the “continuous duty solenoid” you suggest? What exactly IS a solenoid anyway? I’m not sure an upgraded alternator is available for my Jeep, but I can check around.

From what I’m hearing, it sounds like starting off with two 6v golf cart batteries is a good way to go. Local place wants about $300 for a pair of them. The brand is “Werker” and the owner of the place (BatteriesPlus) swears by these things. He says that compared with a yellowtop or bluetop, they have way better amp-hours. Size/weight isn’t really an issue for me – I’ve got plenty of both. I don’t want to piss away money, but it sounds like I will not be – too much – as long as these batteries are not complete crap. What say you? (: I’m a bit concerned about the one reply that indicated 4 such batteries would be $1000. That makes it $500 for two, and local place wants $300 for two. Are they likely to be complete crap??

OK – so I don’t need to concern myself with “RV Power” – I can just charge up my batteries with a standard battery charger. Does anyone disagree with this? Is there anything special I should know about charging up these 6v golf cart batteries connected together as a 12v system? I have a battery charger, but you know, it’s a cheap one and it works, but I’ve had it for 10 years. Maybe I should get a new one – to leave in the trailer so I can leave my other one in the garage. Any recommendations, or will any ole cheap one do?

Thanks to all – I appreciate your feedback. Always willing to hear more (:

Cheers!
Td

[madjack]

...some more thoughts...a 10ga wire from your tow vehicle will carry around 40 amps...fuse it for 30 and hook it up...I have done this with no problems several times...you need to find a switched circuit on your fuse box...most newer vehicles willl have one, or get a continuous duty relay so that the charge wire is not hooked up when the motor is switched off...of course you can manually disconnect the charge wire(iff'n you remember too)...this is what I have done in the past...as far as the cost of the batteries...I just did a quick google search and came up with a price of 250/per...what you can find locally is what you can find and not necessarily better or worse...Trojans and Lifeline are considered the cream of the crop but there are many others out there...as far as charging with a regular charger, I just don't know...with the heavy amperage available in a setup like this, I don't know if a regular charger will work...the only experience I have had with a golf cart was one that used 3, 8V batteries to give 24v and obviously used a special charger...others may have better info on this and more research may be needed......
madjack

p.s. a continuous duty solenoid should available from an auto parts house like NAPA...if not got www.waytekwire.com and enter "continuous duty solenoid" in their search window...a solenoid is a relay...just like the starter on your Jeep...the starter solenoid is an "intermittent" duty model...it gets juice from the switch and energizes the starter cable...a continuous duty model gets juice from the switch but stays engaged to flow energy down the cable to your battery on a CONTINUOUS basis......MJ

p.p.s. if a regular charger is sufficient, you should invest in a good "3stage" charger...your batteries will thank you....MJ

p.p.p.s. http://www.batterymart.com/p-battery-te ... arger.html is a charger I have recommended in the past...it is actually a 4 stage charger, however it only has an output of 5A and you might want something with more power...by the way www.batterymart.com is a good place to shop/compare/find quality products at a fiar price.....MJ

[brian_bp]

A lot of people use and/or recommend "golf cart batteries". There's actually nothing special about them at all, except that they are common and therefore likely available at a reasonable price. Batteries of other size formats and voltages of the same type and from the same manufacturer will work just as well, weigh about the same, and take about the same amount of space. The converse of that is that when comparing two golf cart batteries of the same size, but from different manufacturers, they will likely be different in cost and quality.

So what should a golf cart battery cost? That's like asking what a steak would cost, without specifying the cut or quality.

Compared to actual golf cart use, occasional camping doesn't sound like a very demanding application. Personally, I doubt it's worth paying for the best.

BatteriesPlus says that Werker Batteries are a house brand of theirs, but other retailers sell them as well. House brands in anything are often a good deal, but are sort of unknowns. They could be anything, and could change at any time, but at least the seller is willing put their own name on them.

Even within the Werker models sold by BatteriesPlus and labeled for golf carts, there are different types (flooded and gel) and different capacities... so "6V Werker golf cart battery" still doesn't say enough to really know exactly what you're getting or whether the price is reasonable.