How to make a cheap isolated dual-battery setup for $50

[4RunAmok]

If you are using a solenoid as stated in the beginning of the thread and had, for some reason, a dead house battery. Once started, wouldn't the system want to equalize the batteries causing a rapid drain from the start battery, perhaps overloading the system, assuming 4ga wire, 200A solenoid with 120A ANL fuses?

What would be the merits of a battery isolator like this?
View attachment 192437

Sorry if this has been asked and answered, I missed it.

There are no merits to an isolator of this type. These are Diode isolators, which will reduce voltage coming from the alternator/charging source, and neither battery will ever receive a full charge as a result.

What you mention about pairing the batteries when the aux battery is very low is a real situation, which is why you would want to use your accessory wire to engage the solenoid and NOT your ignition wire. The result is "Start Isolation". Accessory loses power when the key is in the start position, thus separating the batteries during start up. And regarding the aux battery being very low, that's why you want a large fuse and large wire.

 

[evldave]

I have my solenoid engaged in the IGN position, not ACC. This is so when I start the truck, both batteries are engaged.

I have had my aux battery down below 4v and haven't had enough current draw when joining the batteries to be an issue (but again, they are 2ga wires).

Using ACC prevents you from self jumping unless you use a small wire to manually engage the solenoid. Ultimately either way works

Sent from my HTC One X using Tapatalk

 

[dwh]

If you are using a solenoid as stated in the beginning of the thread and had, for some reason, a dead house battery. Once started, wouldn't the system want to equalize the batteries causing a rapid drain from the start battery, perhaps overloading the system, assuming 4ga wire, 200A solenoid with 120A ANL fuses?

Nope. Here's the explanation:

http://www.smartgauge.co.uk/nosurge2.html

 

[4RunAmok]

That explanation conflicts with my own real life experience.

Our situation was this:
3 Aux batteries, 8D 1440CCA, drained to 10.8 volts with by a Magnum 2500 watt inverter running a dometic air conditioner.

at 10.8 volts, a low voltage disconnect shut down the system.

The vehicle was started, and the ACR sensing voltage from the 280 amp alternator, paired the alternator to the aux batteries.

This blew the 150 amp Blue Sea breaker in our power distribution block.







As a result, we now use a 300 amp breaker, and 0 Gauge wire from the ACR to the alternator.

 

[davesteve]

My Take on Isolators

Just read all 28 pages and was wondering how many more times 4RunAmok is going to have to say,

"Don't Buy Those SQUARE ISOLATOR BOXES!!" :drool:

I agree. Not worth the trouble. Read these instructions for a diode SS isolator and it will turn you off the whole project:
http://www.cooperindustries.com/con...sources/instructions/BUS_CBT_INST_180012q.pdf

What I got from all this, is that I don't want a $50 set up. Sorry :elkgrin:
I want a set up that will:

-- Be a dual battery system that is linked for charging and is unlinked for discharging.
--Automatically determine what does what and when. If the aux battery is low-charge it. If both are low-charge both. Isolate when needed and combine when needed. Regulates the voltage across connected batteries. etc. Kicks on at #volts and kicks off at #volts.
--Facilitate a solar panel or two w/ a charge controller.
--Will provide a monitor system for both batteries in the cab that can be instantly accessed.
--Have a linking feature for self-jumping without opening the hood.
--Be EASY to install. No splicing into ignition circuits or messing with UBEC and running wires to alternators, etc. A "no-no" according to GM bulletin no. 08-08-45-004C. Which basically says, "Don't hack into some factory circuits or you are asking for trouble."

So the cheapest thing I could find that would meet that criteria is the T Max system from Westin:
http://www.carid.com/universal-winc...&cagpspn=pla&gclid=CO6TlKmezLsCFYQ7OgodDD0Aaw

$115-$150....... depending where you shop.......... I will gladly pay the additional $65 to get those extra's. Especially when the set up is as easy as this:

http://farm9.staticflickr.com/8428/7687698530_0df8d0b337_b.jpg

The 200 amp fuses in that diagram are unnecessary IMO. (not a factory diagram)

 

[fireball]

I've got a t max waiting to be installed in my dual battery setup. And two 200amp fuses. Curious why you say they are not needed.

 

[crismateski]

I've got a t max waiting to be installed in my dual battery setup. And two 200amp fuses. Curious why you say they are not needed.

I just got the Tmax for christmas. Hoping to start the install this weekend, but it will probably be a bit before I pick up the battery. As for the fuse / breaker always use protection

 

[4RunAmok]

I've got a t max waiting to be installed in my dual battery setup. And two 200amp fuses. Curious why you say they are not needed.

The fuses, 200 amp or whatever, are ABSOLUTELY necessary! AT BOTH ends. Typically a fuse or breaker within 18" of each battery! WHY?

WHAT IF something pinches the cable anywhere between the two batteries? If you only have a fuse/breaker at one end, it will pop when the cable shorts. But the cable will still be connected to a battery at the other end and continue shorting, causing a fire.

If you have a fuse/breaker at both ends, when a short happens anywhere in the cable, both ends will pop, rendering the short unpowered.

Leave this out, you are only asking for trouble.

 

[4RunAmok]

Just read all 28 pages and was wondering how many more times 4RunAmok is going to have to say,

"Don't Buy Those SQUARE ISOLATOR BOXES!!" :drool:

Thanks for noticing!

I agree. Not worth the trouble. Read these instructions for a diode SS isolator and it will turn you off the whole project:
http://www.cooperindustries.com/con...sources/instructions/BUS_CBT_INST_180012q.pdf

What I got from all this, is that I don't want a $50 set up. Sorry :elkgrin:
I want a set up that will:

-- Be a dual battery system that is linked for charging and is unlinked for discharging.
--Automatically determine what does what and when. If the aux battery is low-charge it. If both are low-charge both. Isolate when needed and combine when needed. Regulates the voltage across connected batteries. etc. Kicks on at #volts and kicks off at #volts.
--Facilitate a solar panel or two w/ a charge controller.
--Will provide a monitor system for both batteries in the cab that can be instantly accessed.
--Have a linking feature for self-jumping without opening the hood.
--Be EASY to install. No splicing into ignition circuits or messing with UBEC and running wires to alternators, etc. A "no-no" according to GM bulletin no. 08-08-45-004C. Which basically says, "Don't hack into some factory circuits or you are asking for trouble."

So the cheapest thing I could find that would meet that criteria is the T Max system from Westin:
http://www.carid.com/universal-winc...&cagpspn=pla&gclid=CO6TlKmezLsCFYQ7OgodDD0Aaw

$115-$150....... depending where you shop.......... I will gladly pay the additional $65 to get those extra's. Especially when the set up is as easy as this:

The 200 amp fuses in that diagram are unnecessary IMO. (not a factory diagram)

See my previous post reply regarding fuse protection...

As for easy to install without tapping into ignition circuits, short of an Automatic Charging Relay, a-la Blue Sea 7622 ($180~ retail), I don't see how you will pull this one off. How else will the system know that the vehicle is running? We install mission critical systems in Emergency vehicles all the time tapping into the ignition circuit. The trick is to make sure you use a fuse at your tap point. This way if something happens on your add-on side, it pops that fuse, protecting the factory wiring. Blah blah blah on the GM Bulletin, we do it on GM's Chevy Tahoes and Caprices, Ford Police Interceptors, Dodge Chargers, and specialty vehicles all day long. It's how you protect the factory circuit that is the key.

I am genuinely curious here. I'd like to see what you come up with to combine the batteries, control charging, etc. Your list of wants is ambitious, but not impossible. But also nowhere near the price range you mentioned. Just the piece that controls combining based on voltage, an automatic charging relay, is going to cost more than your high estimate. Most accurate monitoring panels cost a hefty penny as well (example: http://www.powerwerx.com/digital-meters/digital-instrument-dc-voltmeter.html)...

The cheapest solution is a constant duty high amp solenoid. The question is how you control it; manually with a switch or automatically via intelligent circuitry or an ignition tap.

Please don't take what I'm saying as discouragement or criticism, it is based on my real-life experience that I employ at my job Monday through Friday. I don't know everything, and if you have a way to pull off your want list within the price range you mention, I really do want to know how!

 

[kjp1969]

So I have a two-step variation on this thread- a dual battery system for about $12 or less.

1. Tap into the trailer battery charge lead at your 7-pin trailer plug (if equipped)
2. Run it to your aux battery.
3. Run your accessory circuit from the aux battery.

The charge lead is already switched to engine-on, and is designed to charge a trailer battery.
The $12 comes from the cost of the wire that you need to tap into that charging circuit.

*Some say* that the trailer battery charging circuit isn't designed to, and won't, charge a fully discharged battery. That may or may not be true; our trailer batteries (2 @ 6v golf cart batteries) get charged pretty well when we are towing our travel trailer from campsite to campsite. But assuming that it's true, do you ever really need to charge a battery from a full discharge? Don't you really just have to top it up between stops?

Anyway, I'm going to try my own Kool-aid and build a setup to power my Edgestar fridge using this type of circuit. I'll use this 26ah battery powered from the trailer battery charge circuit. http://www.amazon.com/gp/product/B002L9AN4G/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
I'll post up how it works. It obviously won't be useful for self-jump starting, but I'm betting that if the fridge isn't sapping the main battery, there won't be much need.

So I did this, for our recent 3200 mile road trip from SoCal to Houston and back. The goal was to run an Edgestar fridge while driving and parked overnight, and run our electronics chargers and other 110v accessories. I mounted two 25ah SLA batteries in parallel in a plastic battery box (not the best choice of batteries, but what I had on hand), and installed 2 12v outlets and an inverter. For charging, I ran 10ga wire to a 7-pin plug trailer plug and plugged it into the trailer hitch. When driving, the alternator provided power to the whole system and charged the batteries. When the engine was off, the batteries powered the fridge just fine for 24 hrs at a time. Granted, ambient temps ranged from 30F to 65F, so performance in warm weather will likely be different. Still, it worked and I'll leave it alone to see how it does over time. For longevity I'll either upgrade the battery or see what a solar panel will do.

 

[Xterabl]

Thanks for the idea and update, Kevin.
Just FYI: My Edgestar 43 qt will go about 1.5 days without starting the rig, in warm weather (70-85 deg. F), before depleting the battery to below starting power.

 

[evldave]

Adding an extra wire won't likely make much of a difference. The rate your 2nd battery will charge is more based on the power your alternator provides and how much the 2nd battery needs, and less on the size of the wire you use (as long as you are using a large enough wire).

You can verify this by using an ammeter, or...next time you get to a point where your 2nd battery is discharged, using just the single wire, run your truck at higher idle (in park/neutral). By running the truck at higher idle, your alternator can generate MORE POWER Feel the single wire - is it HOT? If it is, your 2nd battery is 'pulling' more current than the wire can handle (and so the wire is acting like a resistor). Adding a 2nd wire (or a larger separate single wire) will help - and in fact I would highly recommend that! (to prevent it someday melting and shorting out).

10GA is usually pretty solid for using as a charge wire in situations like this. If it was a longer run (say to the rear of your truck, or to a trailer) then a larger wire might help.

 

[dino2000]

assuming i have chosen and installed my dual battery system ( all I have so far is a bettery), id like to install some charge ports and a cig socket for fridge in the back of my RRC.
what gauge of wire would I run from the battery up front to a fuse block out back for this application? any recco for fuse block?

Thanks in advance, Dino

 

[dlichterman]

assuming i have chosen and installed my dual battery system ( all I have so far is a bettery), id like to install some charge ports and a cig socket for fridge in the back of my RRC.
what gauge of wire would I run from the battery up front to a fuse block out back for this application? any recco for fuse block?

Thanks in advance, Dino

How many amps do you plan to run and how long of a run are factors in this.

You can use a table such as this to figure out the gauge.

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

 

[Dan Grec]

I have some other goodies for inside; a time delay relay to trip the charging solenoid a set time after starting the vehicle, and a digital display to monitor the batteries.

Can you please post some details/pics on both of these?
I would really like a time-delay on the solenoid so it doesn't start charging the 2nd battery until the engine has warmed up.

Thanks,
-Dan