Alternator charging house battery safely

[Ami P]

Is there a past thread detailing the tow vehicle charging the house battery setup? Is there a need for separating the charging process of the two batteries, to protect the expensive vehicle alternator/regulator? Is there a good schematic anywhere? - Thanks, Ami P

[Pete Dumbleton]

The system is quite simple -- You merely run a good wire from the Tow Vehicle battery's positive post (with a 20-30A auto-disconnect circuit breaker) to the 7-pin Bargman/Pollack trailer connector's battery (+) terminal.

Wire sizes folks have used range from #10 to #6 -- I figure as long as I am running it, the bigger the better (The less voltage loss, the truer the picture the TV charge system gets of the trailer battery -- Opinions vary on this).

If you don't have a 7-pin connector, you should install one because it will accommodate the charge lead and the brakes lead, plus an auxiliary lead for whatever.

I also ran a negative/return wire of the same size between the connector (common ground) and the battery's negative post to ensure that I had a good path, plus I made a good connection between that wire and the TV frame. Overkill, perhaps, but the return wiring has to handle ALL the returns for the various wires to the trailer.

Pin-outs for the connector wiring can be found here:

http://www.marksrv.com/wiring.htm

A Scamp trailer wiring diagram can be found here:

http://scamp.n0kfb.org/manual/index.htm

Many folks also install a cut-off relay on the charging wire, controlled by the TV ignition switch, to prevent discharging the TV battery by a trailer load (fridge) while sitting with engine off.

Separate charging systems would be the best possible way, but they would also be $$ -- Dual alternator system are available in the Marine world.

http://www.westmarine.com/webapp/wcs/store...Alternators.htm

[Ami P]

Actually, after further research, I located and installed a battery isolator. My question now: does anyone have experience with installing a good voltage regulator, that will protect the trailer battery from boil-out? The charge line is delivering 13v-14v.

[Bob D]

These folks have a bunch of interesting stuff.....................

http://www.powerstream.com/

Click on Automotive on their home page if the link doesn't take ya there.
DC-DC chargers. One sez for charging smaller batteries but might work from
running vehicle for larger. The 8 amp for $85 might be the ticket on a long haul.

Have been researching a bunch of stuff for our Cloud. Electric especially since I got my Ham license!

Bob

[Curtis F.]

I think you are worrying too much. Thousands if not millions before you have connected the TV to the TT for charging. If the altenator isn't boiling your auto battery dry, why do you think it will boil the TT battery dry? The connection should be from the TV battery and not the TV altenator. The altenators in different brands of autos charge at different voltages and amperage. Dodge and Chevy run at 13.8 volts, but the amperage in all vehicles drops as the battery approaches full charge. The same applies to the TT battery also. Additionally, the ususal wire size for the charge line is # 10 wire. It will only deliver about 8 amps and 12.8 or so volts at the end of the 20 to 30 feet wire run (Apologies to those that may take the time to look up or calculate the real numbers. It's late and I'm rambling from memory)

FYI: Battery info by Phred. If you read the paragraph "More on Charging" you will see that pushing 13.8 volts at your bsttery is not going to harm it.

I do recommend you install either a continuous duty regulator or the battery isolator as you indicated.

From experience, after 8 hours drive, the TT battery will not be fully re-charged. Especially if you have a larger refrigerator and are running on DC (recomended) while towing.

Curt

[Ami P]

Actually, it was my sailor-ex marine pilot - retired -lawyer - and -current - hog - rider - buddy who started the worry cycle. An excellent battery isolator from Northern Tool, the Industrial Battery Isolator — 120 Amp, Model# B-120A1B2E was professionally installed. With the engine running I got the following readings: TV battery 13.6 V [at] 41 AMP, TT 13.4V [at] 40 AMP. Fifteen feet of high quality 8 gauge wire was used in the TV and 16 feet in the TT. My TT battery was fully charged at 12.69V. My thought was that a float stage charger delivers 1.5 to 2 amps to a full battery and here I was getting 40 from the alternator.

[Curtis F.]

What you are seeing for Volts and Amps appear to be normal, especially if measured shortly after starting the vehicle.

You have a very good setup and should have no problems. Measuring DC electricity is not exactly like measuring the ingredients for a recipe or measuring water in a plumbing system.

The Amps reading is not the actual Amps the battery is accepting if you used a meter with contact probes. The contact probes measure something called potential. A difficult and complicated value to measure is how many Amps of that potential are being passed to the TV and TT devices that are drawing power? That number needs to be subtracted from the potiental number. More trouble than it is worth for us mere mortals to try to measure. I think if you measured with an Amp meeter that has the circular clamp that goes around the wire, you would see a much different and lower number.

Here is another good informational site explaining RV electrical systems. The 12volt Side of Life.

There are two (or more) schools of thought about how to store batteries. Some prefer to keep a "trickle charger" connected while others prefer to periodically charge the batteries. If using a trickle charger, you don't need to disconnect all loads from the battery. If not using a trickle charger, you need to disconnect all loads from the battery. I recommend the disconnect all loads and only periodically charge the battery. A healthy, fully charges battery will lose very little charge over a few weeks or a month (or several) and will not be harmed. My batteries are still at 12.5 volts after 3 months, so I will run the power cord out every couple months.

Curt

[Pete Dumbleton]

Here's the Voltage>% Charge table from 12 Volt Side of Life: