Wire Size for trailer batteries?

[cracker39]

Ok...Thanks. I'll sit back and watch the dialogue unfold...And learn.

[cracker39]

I only got as far as the first question...how is it going to charge? First, I am basing this on every small boat I have ever owned that used an electric trolling motor. I have a battery that is connected only to the trolling motor and the boat is on the water...no ground wire except to the motor. When I charge the battery, I just hook up a battery charger to the battery. My camping trailer is the same. There are no connections to my tow vehicle for the trailer electrical system. It appears that your question is based on charging from the tow vehicle, and I am not doing that. I will only charge from the converter/charger when hooked up to shore power or from a separate float charger at home.

Now, about the trailer stop/tail lights:

In the paragraph above, I am not talking about my trailer tail/stop lights which are connected to the tow vehicle via 5 wires to the connector at the rear bumper of my tow vehicle (1 tail/marker, 2 stop, 3 right turn, 4 left turn, 5 ground). They too are NOT grounded to my trailer chassis, the same as with my boat trailer. The boat trailer lights are on a removable bar that I clamp to my boat for traveling to and from the water. I remove it and put in the truck while fishing. The boat is isolated from the trailer frame by wood and carpeting...NO connection to the trailer at all and they work. I have a ground wire connected to the metal bar and the lights, and routed back to the tow vehicle through one of the wires, where it grounds on the tow vehicle itself. This works just fine. It is the same as having all of the trailer tail/stop lights on my tow vehicle, and not on the trailer. The trailer lights are actually a part of the tow vehicle electrical system as they are totally isolated electrically from the trailer.

I may not be an electrician, but when it comes to trailer tail/stop lights, I have been wiring them for years with no problems. Wiring an electrical system in a camping trailer IS new to me and I have much to learn. I've learned a lot from both of you (George, Powderburn), and I appreciate all of the information. But, from time to time, either of you will throw in a question or comment that muddies what I read earlier. I hope I learned enough now to do what is right, so I am going to ignore the part about charging. I'll just ground everything to the chassis of the trailer except for my tail/stop lights which I am keeping totally isolated and separate.

[GeorgeTelford]

hah

For several reasons I do not use a standard vehicle alternator to charge.

1. Alternators are basically power supplies and do not charge a battery properly, about 65-70% full is the most you will get from standard alternator charging.

2 and perhaps worst is that say you run a decent charger and properly charge the battery, any journy you make will discharge the house battery down to the same level as the starter battery.

Because you should never discharge a house battery below 50% say you start with a 100 Ah battery if its charged to 65% take away the 50% not to be used and you end up with 15 miserable amps

I agree though that all elec systems should be grounded mains and ultra low voltage battery systems.

Here is some info

http://www.caravanandmotorhomebooks.com/books/motorhome_electrics_caravans_too.htm


Here is a test I did to prove that a fully charged battery lost some AH when connected to an alternator system

From fully charged at 12.93v (measured 12 hours after coming off the Sterling charger) connected bulb, it took 6 hours and 17 mins to reach 12.2v (ie flicking over backwards and forwards from 12.3v)

It was then fully recharged on the Sterling, allowed 13 hours to settle the voltage, reading was 12.94v flash 12.93v, the engine on the iveco was started, then I connected the battery using a good solid cable as before and drove this morning for 1 hour 14 mins, as soon as I got back it was connected to the same bulb (55w halogen) connected at 12 : 12 today, it started flashing between 12.3 and 12.2 at 5 : 37 PM today

Same battery, same full charge by Sterling, only difference 1 hour 14 mins of extra "charging" as knocked off 52 mins off usable power !!

The Sterling charger is a top quality 30A 4 stage inteligent charger, which also acts as a power supply on hook up/shorepower, made for marine use it will accept input power from 80 to 440v and 40 to 400hz so will work from any power supply in any country.

If I was ever going to charge via a vehicle I would add a smart regulator to the alternator and a split charge diode so the 2 systems stayed completely isolated.

And I would still ground all equipment and metal work, its the safest way, I would never use it as a feed though for the reasons already stated.

[GeorgeTelford]

Hi Cracker

Ignore all the theory stuff after, I did say to ignore, just ground battery and mains.

Good to see that you dont use vehicle charging.

[cracker39]

Hi Cracker

Ignore all the theory stuff after, I did say to ignore, just ground battery and mains.

Good to see that you dont use vehicle charging.

I think I will be doing that...by "Mains", I presume you mean both the shore power incoming and the converter/charger, which must be grounded according to a wiring picture of it that I have.

I've considered hooking up a wire from my vehicle to charge the trailer battery, using an isolator, but have never done it and don't think I ever will. I don't plan on ever being out so long without shore power that I'd run the two trailer batteries down too low. As I mentioned before, I will use two group 24 deep cycle batteries rather than a single 27 or heavier one. That should give me enough power for a long weekend without charging.

[GeorgeTelford]

Hi Powderburn

Depends on your definition of charging, a max of 70% leaving only 20 % useable as never seemed a good charge to me, although some people do get by with this tiny amount of power.

The alternator as never been a good charger, it was never meant to be one, its a power supply that puts a tiny charge in a battery.

A properly charged battery will give much better service in terms of ah Available (100% charge gives 50 AH available thats 2.5 times more power) and years longer service too.


Its been done for years, but its not a good system. But you have a choice 15 to 20 amps if you charge via standard alternator or 50 Amps from same battery if you charge properly.