Second battery prob..

**BuNNy-RaBBiT** · 11-07-2005, 10:51 AM

Hello, i`ve got a second battery that sits in the truck and powers my pc.
When the engine is of the second battery is not connected to the primary one.
Here`s my prob: when i start my pc on the second battery with the engine not running it works fine, when i start my car it stil works fine but when i turn the switch for connecting my second battery with the dynamo, the music falls out and the 7" sceen goes off and on again 1 time.

How do i solve this prob?

Its conected like this:

Greets,
Bunny

**EsKALad** · 11-07-2005, 10:54 AM

maybe you should just get a battery isolater and put it in line from battery1 to batter2 and get rid of the switch.

**BuNNy-RaBBiT** · 11-07-2005, 11:02 AM

I could use a Diode to get rid of the switch but when i do that i would draw power from the main battery, and thats not what i want.

A Battery Isolator would be perfect but those things are to expensive.

**Nicorolla** · 11-07-2005, 12:43 PM

what's happening is when you connect the second battery there's a big surge of current going thru the battery with less potential (voltage). This could be dangerous. You need a isolator or you have to leave both batteries connected together at all times (before you do that, charge both batteries to their full capacity).

in details, the battery has a very low internal resistance, therefor if one battery has (for example) 12v and the other has 14, thats a diffrence of 2volts. and since current always travels to the path of least resistance, that 2 volts will flow thru the other battery. To give you an idea of how much current is going thru, say ur battery has an internal resistance of 0.1 ohms. That makes ur current 2 / 0.1 = 20 Amps. The bigger the diffrence and the lower the resistance, the higher your current surge will be.

**BuNNy-RaBBiT** · 11-07-2005, 01:55 PM

Originally Posted by Nicorolla

what's happening is when you connect the second battery there's a big surge of current going thru the battery with less potential (voltage). This could be dangerous. You need a isolator or you have to leave both batteries connected together at all times (before you do that, charge both batteries to their full capacity).

in details, the battery has a very low internal resistance, therefor if one battery has (for example) 12v and the other has 14, thats a diffrence of 2volts. and since current always travels to the path of least resistance, that 2 volts will flow thru the other battery. To give you an idea of how much current is going thru, say ur battery has an internal resistance of 0.1 ohms. That makes ur current 2 / 0.1 = 20 Amps. The bigger the diffrence and the lower the resistance, the higher your current surge will be.

Ok thanks that clears up.
I connected both fully charged battery`s, and put a diode between the two, now the second battery get`s charged but cant give power to the other battery so it will last longer.
The only draw is that the first battery gives power to the second one so it will eventualy be drawn emty

.

**1629dill** · 11-07-2005, 02:29 PM

I had the same problem on my boat and found a Battery Isolator - 70 AMP/2 Bank for $57.99 at West Marine that solved the problem. It is cheap protection for the electrical system of your car. Take a look.
http://www.westmarine.com/webapp/wcs...01/12106/544/9

**Nicorolla** · 11-07-2005, 06:18 PM

Originally Posted by BuNNy-RaBBiT

Ok thanks that clears up.
I connected both fully charged battery`s, and put a diode between the two, now the second battery get`s charged but cant give power to the other battery so it will last longer.
The only draw is that the first battery gives power to the second one so it will eventualy be drawn emty

.

it shouldn't happen, when the second battery recieves power, it will store (charge) most of it and eventualy come into equilibrium with the first battery, at that point the first battery will stop feeding the second battery because the potential is exactly the same therefor there will be no path for current to flow