Battery charging problem

**Juliemac** · 08-06-2005, 07:27 AM

I have a secondary battery in the trunk thats not charging correctly.
Its fed directly from the Alt, via an 80A fuse, 30A relay (only closes when the ignition on), to the battery. The charging cable is 4GA copper.

I start the car, then turn on the system, let the car run up and away I go.
But when I stop the car and look at the battery voltage in the trunk, its only a few volts. It looks like the system is drawing from the secondary battery, but not allowing the battery to charge.

The Alt is giving out enough current (rated at 90A) and the system is drawing 10A to run the Mastero 4.5.

Its got me stumped guys. Any ideas?

**rustyboxx** · 08-06-2005, 09:09 AM

Do you have it wired up like this?

**Juliemac** · 08-06-2005, 11:19 AM

Exactly. That should work right?

**Curiosity** · 08-06-2005, 11:36 AM

Have you checked the relay and fuses?
Disconnect the battery, put a meter on the connectors and start the car. Got power?

**Juliemac** · 08-06-2005, 12:01 PM

If I run with out the computer the battery level goes up and the current on the ammeter shows normal current drain.
When running the computer, the ammeter shoes a much heavier current draw, but diminishes the secondary battery.
I am going to recheck the internal power settings and draw. I don't think I made a mistake though.

**Jcarere** · 08-06-2005, 12:14 PM

In my opinion you should have a battery isolator. That way the secondary battery is charged after the main. And if your secondary battery is drained by lets say the pc being left on, the main battery will not be dead when you try to start your car. You can get them in different sizes but these are some general ones. Ive done many setups like this in audio installs and it works great every time. http://www.jcwhitney.com/autoparts/B...+10201/c-10101

**Curiosity** · 08-06-2005, 12:15 PM

Wow. 10A doesn't seem like that much. Does the battery ever charge up full? Maybe it's going bad. If that's all good, I bet something (wire or relay) is getting hot.

**rustyboxx** · 08-06-2005, 12:44 PM

Originally Posted by Jcarere

In my opinion you should have a battery isolator. That way the secondary battery is charged after the main. And if your secondary battery is drained by lets say the pc being left on, the main battery will not be dead when you try to start your car. You can get them in different sizes but these are some general ones. Ive done many setups like this in audio installs and it works great every time. http://www.jcwhitney.com/autoparts/B...+10201/c-10101

Isn't that what the relay does? Surely the connection between the two batteries is cut off when the alternator is idle (engine off).

Julie, is the second battery in good condition?

**Juliemac** · 08-06-2005, 12:59 PM

Battery is a mid sized lawn mower battery that can withstand deep discharge.

I'll deal with it later, I am about to drive 10 hours (there and back) to get a door for my car. This winter, complete chassis strip and rewire after a nice fresh coat of paint!

**Curiosity** · 08-06-2005, 01:28 PM

I think most batteries can take a deep discharge, but the longer they stay undercharged the worse off they get. Like if it was at 6V or less for a month it would be very weak and couldn't hold much anymore.