Is it possible to have a second battery on the car and be able to charge it with the same alternator?

I'm interested in using the second battery to run aftermarket accessories like a DVD player, Flat screen TV, surround sound and amplifiers. I'd like to not have the car running while these accessories are running and I don't want to use the car battery to prevent having a drained battery. Just two batteries, one for the car and one for the accessories, charged with one alternator.

Yes it's quite possible - Motor Homes and RV's do it all the time. Not exactly simple - but with enought money - doable... You might look into the fourms for Motor Homes to see where they are getting the switching/control panels.

Just a thought..

Carl B.

You need a battery isolator. Here's how they work:

http://www.bcae1.com/battiso.htm

Do some research on the net. You don't need to buy a an expensive one built specifically for car audio. This is a very basic device. The battery you buy is the most important part, and I recommend a deep cycle battery for your second battery, Optima if you can afford it.

http://froogle.google.com/froogle?q=battery+isolator+car+audio&hl=en&btnG=Search

And it doesn't need to be a full size battery if space or alternator output is an issue. To that point:

http://www.carsound.com/columns/navone/nav0003.shtml

Thanks Guys, that's exactly the info I needed.

I don't know too much about this issue, but have run into it from another perspective. I bought an alternator for the conversion to an internal regulator (for my '72 240Z). I received one, a Hitachi, that looked just right except for this strange "extra" wire on the back. A friend of mine had at that time some way to connect with Hitachi, so he inquired about it with one of their service representatives, sending them pictures, etc... Seems that it was a "deep cycle" unit used for RV and marine purposes. I was told that it is a very expensive unit, but not to use it for my needs because bad bad things were likely to happen not having the deep cycle circuit and additional battery to handle the output. My friend told me that when the Hitachi rep saw the pictures the first statement was "Where the heck did you get that? They are a very limited distribution unit!"

So, I assume to do this properly with two batteries, a special deep cycle alternator would be needed. Feel free to correct me if I'm wrong..... like I said, I know very little about this, except what was passed to me from a Hitachi representative, but If anyone needs one of these alternators, I still have it on the shelf. I'm told that it is a several-hundred dollar unit... yours for what I got in it - $70.00 + shipping. I'll provide pictures if anyone wishes. Let me know if interested.

Ed, FWIW I lived aboard a boat for 16 years and multiple deep-cycle batteries and their associated equipment were pretty standard, Go to www.westmarine.com (I also worked for them for a time...good outfit)and check out their on-line catalog. They have battery combiners, isolaters, gel deep cycle batteries, switches, etc. In fact I am adding a battery cut-off switch I obtained from them as soon as I put together the rest of the parts I need to complete the project. There might even be a West Marine store near you...you can find out on their web site. Hope this helps.

Mike

One addition, look into using a capacitor or 2, at least 1 farad each. That will help to save your alternator from working so much over time! :bandit:

Jack, if you look at the date of the thread, you will see that this is from 2006. Most likely the problem is resolved.

thanks beandip, I just now am noticing that. I am a newbie here (and to forums in general) I will have to pay more attention on the dates :stupid:

Happy motoring! and great to meet you by the way

I hope the correct information was also used, there's lots of information in this thread not based on electrical theory.

Enigma is the only one in this thread with correct information regarding adding a second battery into a vehicle's electrical system.

There is no such thing as a "Deep cycle alternator". The term "Deep cycle" only pertains to batteries and thier ability to be heavily discharged and then recharged with no to little damage to the battery itself.

The alternator will only provide enough current flow to match what is being asked of it. So you can connect the smallest ATV/motorcycle battery to the largest inductrial alternator you can find, and the voltage will remain the same at the preset level (usually 14.4 on a good cold alternator charge rate).

On this above mentioned alternator that was probably used with a deep cycle battery or bank of batteries, there was probably a need to sense the charge level of the secondary batteries, so tha the alternator could adjust the output to compensate.

I would recommend a solenoid type isolator, as the diode based ones as mentioedn in the link provided by Enigma will drop the overall charge voltage by .7V (It mentions a range of .4 to .6 in the article, though it IS .7). This means that your batteries will never fully be charged. .7V might not sound like a lot but to the electical system that only uses 12 to 14V to start with, that's quite a bit.

There are smart solenoid basd isolators now that will monitor both the incoming voltage and the secondary battery voltage and will only turn on when they are close to matching.

You could set-up a system that would allow you to manual overide the monitoring side to give yourself a boost, if you found that the starting battery went dead for some reason, but the secondary battery was still charged.

I added second battery isolation to my pickup for the purpose of charging the battery in the camper. Battery isolation allows me to use stuff in the camper without killing the the truck battery. Works great.... I added a solar cell to make the solution event better.. Bottom Line... pretend you have a camper and head over to you loacl RV store.

zdisease