Battery drains while towing trailer

[chicknnhead]

So i have a 76 dodge class C, 360 v8, basically 1 ton van chassis
I use my rig about 5 time a year, 3 of those trips are 5-6 hours long
on the other 2 trips they are a little over and hour long, one of which is at night

On the night trip i pull a 6x10 trailer.

I'm getting to my issue bare with me..lol

So on any of these trips i can run the lights no issue.

Now on my night trip pulling the trailer is about 1 hour & 40 mins long. about an hour into it i have to pull over and shut the lights off and let the rig run for about 15mins then the battery is charged. and i can continue on the other 40 mins. it seems the draw on the trailer lights is to much and the battery get sucked down.

I went to auto zone and told them i have a 1976 1 ton dodge van and the battery i have is the biggest they list, but the battery just seems small in size.

I know some of the winnie owners on the road pull things with lights.
Finally my question is this
what are you guys  doing for batteries

[DaveVA78Chieftain]

My bet is that you have a bad diode in the alternator or a bad wiring connection.
I would have the alternator checked to insure it can produce the rated current unless you know how to do that and have tools.
If that is ok, then you may have a bad wiring connection.  JKountz had a simular problem where the fuzible link for the circuit that supplied the sense voltage back to the regulator was partially opened (only a couple of strands of wire remained connected).  This resulted in a incorrect battery voltage sense such that the alternator never put out full current.  Check all wiring connections from alternator B+ to starter relay to battery.  And connections from starter relay to ignition switch back regulator.

Dave

[chicknnhead]

Dave, thanks for the reply
I understand what you are saying. but wouldn't it do it when i'm not towing a trailer or when I'm just running the lights during the day
which in both those cases the battery stays charged.

can you have too many 12volt lights on one battery? where the alternator won't be able to keep up?
would a bigger battery solve this issue?

[DaveVA78Chieftain]

Think like this
You have a nice size water pump able to put out 300 gallons per minute.    You have a restriction in the pipe that only allows you to flow 150 gallons per minute even if the on/off valve is fully open.  During normal service (i.e lights and major loads off) that 150 is fine.  When you need more (i.e. lights on) that 150 gallons just will not cut the mustard.
Your 76 chassis should have at least a 60 amp alternator which is more than enough to pull the load your talking about.  The restriction in this case is either a bad diode in the alternator (1/3 power loss), a bad wiring connection (improper voltage sense), or a defective regulator limiting the amount of voltage/current to the alternator field circuit.

Dave

[chicknnhead]

OK, now i see what you are saying.

let me start testing