OK, more progress...

Here is the new location for the Pathmaker battery controller. Below it is a battery energy gauge that reads like a fuel gauge. It can be switched between the main and aux. batteries.



I made a cover for the controller out of....... ...OMG!...a tackle box! Hey, don't laugh too hard... it works great! The box dimensions were just perfect. Although it was a twin sided box with lots of little dividers, so I had to cut the back half of the box off, and remove the dividers. Here is a pic with the lid open...



If you look at the carpet where it meets the plastic wall, there is a step in the line of the carpet, just below and to the left of the battery gauge. That is where the original bench seat used to take a 90 degree turn to the floor. I extended the bench for my speakers and the fridge/freeze. I'll post more pics in the other thread "ice cream in the desert"

 

It is true that with the battery isolator the alternator will only sense the voltage of the primary battery. When the main battery is fully charged the alternator will turn off... it will turn back on when the battery voltage drops. When the truck is running, the alternator will turn on and off frequently. The truck requires power (spark plugs, lights, radio, etc) and it will drain the battery, and the alternator turns on occasionally to fill the battery back up. The more loads (lights, etc), the longer the alternator will stay on versus staying off. Now think of the second battery as just another "load" on the alternator. When the alternator turns on (because the main battery voltage is low), then it sends current to the lights, engine, and the second battery. If you have a nice big cable from the isolator to the second battery, then the second battery will have a very low resistance (a very large load) and it will consume lots of power (imagine it like a 500 watt light bulb). Now since you, presumably, have the same alternator as when you only had one battery, the alternator will now need to be ON more often than before (because the second battery needs power, just like adding lots of lights, which requires the alternator to stay on more often). Now, as the second battery fills up (voltage increases) the voltage difference between the alternator and the 2nd battery decreases, which in turn (ohm's law) decreases the current going to the second battery. As this current goes down (a smaller load), the 1st battery fills up faster and the alternator doesn't turn on as long as when the 2nd battery was empty. This process keeps going and going until the 2nd battery is full (its voltage matches the alternator's output voltage), and then finally the 2nd battery is no longer a 'load' on the alternator.

Alternative, one could build a very simple circuit that would compare the voltage of the two batteries and then provide the lower of the two voltages to the alternator. Once I finally get my dual batteries installed (I have the isolator installed, the aux battery box welded, the cables ran, I just need to move the wire from the alt to the isolator and then put the 2nd battery under the truck, oh and then rewire my lights, 400watt stereo, 600watt inverter and auxillary 12volt plugs to the 2nd battery) I will start measuring the voltages of the two batteries and see how well the second battery stays charged. I am getting a mean-green 130 amp alternator (should be here tomorrow), so hopefully that will keep the second battery full.

Brad

 

Great post Brad - thanks. Good luck with your setup! I would love to get one of those mean greens.

 

UPDATE August 3, 2004:

Optima replaced the first battery that I bought (from batteriesrus.com on eBay) which apparently was a lemon. (The battery is a D31T yellow top) It would not take a charge. Since having this new battery, I have done numerous trips and drained it good, and it is working just fine. The stock alternator charges it up just fine and the dual battery system is working great (it's been about a year now). A friend just told me that he found the Optima group 31 battery (blue top) at Sams club for about $150 (FYI).

This battery doesn't have the greatest amp-hour capacity (75 A/H), but it is extremely durable. This part is what I have read/been told: It doesn't care at what rate you charge it, or how much/often you drain it, therefore it is much more forgiving and faster charging than a conventional deep cycle. This part I know from personal experience: This battery has an incredible resistance to vibration, and the case is super tough - I had the battery come loose in Mexico and shift up against the fan shroud - a huge gouge developed in the case and didn't even phase the battery. A regular plastic case would have busted and caused me big trouble. That made the battery worth a lot more to me right there.

 

Thanks for the update, always good to hear how things are going. Are you referring to Optima vs. other brands here? Or the Optima Blue-top vs. Yellow top?

(I ended up with a blue-top myself, I think it was like $130-140 at Costco)


Thanks,
Jim

 

Jim, I was referring to the Optima vs. other batteries. As far as I can tell, the only difference between the blue top and the yellow top is the color of the plastic on the top of the case. They both have different options for terminal posts depending on which model you get, but from what I see on the specs, they are the same battery as far as internal construction goes.

Also, the Blue top you mentioned for $130-$140 is probably the regular sized battery? The Group 31 is pretty big and weighs 75 lbs.

 

Thanks for keeping us posted. How that fridge been working during the summer?

 

The fridge continues to amaze me. A couple of weeks ago, we decided to go and camp up on top of one of the mountains really close to our house. We weren't even planning on using the fridge, but at the last minute we decided to stop and get some oatmeal stout for dinner. So I just turned the fridge on when we left the house. The thermo said it was 97 degrees inside the fridge. We stopped at the store and got a few bottles (that's all we put in there besides a small neck pillow to take up a little volume) and when we got to camp the fridge was already at about 40 degrees. That was only about 25 mins. from when we left the house! (disclaimer: numbers are approximate - it was over 2 weeks ago and my memory sucks )

 

What brand of fridge is it? Where did you get it?

 

It is made by some company who also makes the ARB fridges. So it is exactly the same as the ARB fridges.

 

Baja has the Norcold. We found a 3 fridge deal a year or so ago, for some damaged units, I think the cost was $250 plus shipping. When we got them they looked to big, but for desert exploring, big seems to be a plus.

When the whole deal came up. It looked like a deal "that was to go to be true" and I wondered if we where going to get burned for the $$s, but the deal worked out.

 

Yea, it worked out GOOD!

Mt Goat, here is the write-up on my fridge...

http://bajataco.com/fridge/fridge1.html

 

Thanks, that's great. Do they make some smaller ones too?

 

Yes, there are about 3 basic sizes. Here are a few links.


http://www.norcold.com/portable.cfm

http://www.arbusa.com
click on products, then Freezer Fridge.

There are also other makes, but the prices are all close.

 

UPDATE 6-13-05:

The system is still working really well. Almost 2 years now, and lots of field testing. Just took the truck to the Sierra Madre in Mexico recently for 2 weeks, and ran the fridge almost full-time (except when sleeping at night) for the entire 2 weeks at about 34 degrees F. Also used the camp shower, radios, lights, etc. and even fired up the elec. blanket one night. Everything is working sooooo good! I am a happy man!

I did an article on the dual battery setup

 

TEST

Man, I just added a post to the end of this thread, with an update and pic, and it's gone.

Weird, I just switched from "hybrid" dispaly mode, to "linear" and now they show up. I guess I don't have the modes figured out yet.

 

Anyone know of anyone who has been able to work a similar setup under the hood of a 2nd gen 4Runner? I'd love to do the dual batteries without putting one inside the vehicle somewhere.

Ed

 

Roger put his under the truck: http://www.4crawler.com/4x4/CheapTri...atteries.shtml

 

Thanks for posting an update. Been 2 years??

 

You're welcome! Not quite 2 years, about 7 weeks shy.