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

[dwh]

Only a bad batteries end up venting, and they vent a harmless gas, especially in the non airtight space of a car.

Wrong.

Any non-sealed battery vents whenever it is being charged. Sealed batteries only vent when they are *over*charged and the safety valve opens up.

What a lead-acid battery vents is hydrogen. Hydrogen burns FAST. So fast, you could call it an explosion:



Ever heard of a car battery exploding? That's why.


And to answer another question from higher up - hydrogen is lighter than air, so it has to vent upwards.

 

[dwh]

 

[gunnermoose]

Switch questions?

Great write up. One of the most informative electrical write ups I have read. I can basically fix anything mechanical, but electricity is something I have always stayed away from. I get the basic install of everything but the switch. Maybe I missed it-

-What type of switch is used?
-How is it wired; which post goes where?

 

[dlichterman]

Great write up. One of the most informative electrical write ups I have read. I can basically fix anything mechanical, but electricity is something I have always stayed away from. I get the basic install of everything but the switch. Maybe I missed it-

-What type of switch is used?
-How is it wired; which post goes where?

Are you asking about adding a switch to control the solenoid manually?

I just picked up a normal rocker switch. Since the current is <1a going to the solenoid it is fine.

 

[gunnermoose]

Hooking up fully isolated, fully automatic, with manual bypass starting, house, and trailer batteries (whew!)

This is only for the most experienc...meh, that's a load of crap...this is really easy!!!!! I have basically this same setup in my truck and I did the whole thing drunk!

I am referencing the in dash switch.

 

[dlichterman]

I am referencing the in dash switch.

Ah, yeah that diagram is a little confusing. The solenoid will probably have 2 poles - you connect ground to one and positive to the other. All you need to do for the switch it put it in the middle of that...somewhere.

 

[4RunAmok]

That diagram is VERY confusing. What it's missing is a line drawn from the switch to a power source and an inline fuse graphic.

Essentially what you want to do is provide 12 volts to the solenoid from TWO SOURCES.

Source 1 would be an ACCESSORY 12 volt source. Why Accessory? Because 12 volts from an Accessory source is CUT OFF when the key is turned all the way to the START position, but has 12 volts while in the ON position (engine running). This is an easy way to achieve "START ISOLATION". Make sure you add an inline fuse, 3 to 5 amp, where you tap the Accessory wire.

Source 1 may optionally be run to an IGNITION source, this will provide 12 volts to the solenoid during START and ON key positions. Again, make sure you add an inline fuse, 3 to 5 amp, where you tap the Ignition wire.

Source 2 would be a wire directly from a constant 12 volt source (like directly from the battery, usually the AUX battery) to a MOMENTARY SPST Switch which then leads to the solenoid. Why a momentary switch? So you don't accidentally leave your batteries paired and walk away for a week to return to two dead batteries. Again, make sure you add an inline fuse, 3 to 5 amp, where you tap the battery. In case the main battery dies, the purpose of grabbing the 12 volt source at your AUX battery is so that you have a good 12 volts to operate the solenoid to pair the batteries so that you may jump your main battery. If both batteries are dead, then you have a whole other problem! Haha!

 

[4RunAmok]

Ah, yeah that diagram is a little confusing. The solenoid will probably have 2 poles - you connect ground to one and positive to the other. All you need to do for the switch it put it in the middle of that...somewhere.

Most of the solenoids shown in these diagrams are grounded through the shell of the solenoid. Which means the mounting bracket shouldn't be mounted to plastic or insulated surfaces. If you do that, you have to run a ground wire from one of the mounting bracket legs to a solid ground or directly to the battery.

 

[dlichterman]

Most of the solenoids shown in these diagrams are grounded through the shell of the solenoid. Which means the mounting bracket shouldn't be mounted to plastic or insulated surfaces. If you do that, you have to run a ground wire from one of the mounting bracket legs to a solid ground or directly to the battery.

Mine had 2 sets, one for the current and one for the power.

 

[4RunAmok]

Most of the solenoids shown in these diagrams are grounded through the shell of the solenoid...............

Emphasis added

 

[4RunAmok]

Short and easy, it doesn't matter how you get power to the solenoid's positive post of the magnetic coil, one source or ten, so long as each wire is fused. The common practices are outlined in my post where I try to explain what's missing from the diagram.

 

[evldave]

I am referencing the in dash switch.

Sorry for the confusing diagram, I was drunk when I made it

The switch can be either momentary or regular on/off switch. It is a 'backup' so that you can manually close the isolator and make both batteries work together (great for starting your truck or your Pinto).

Many solenoids (including the high-current solenoids I reference in this thread), have two BIG posts (for the main wires to your two batteries) and then two small posts, one that goes to power one that goes to ground (these can be smaller wires, and has been noted, should be fused). Ideally you would make an 'automagic' setup that engages the solenoid when you start the truck (in the START position)...that's what the fusebox connection is for....the switch is for manually engaging things...

ok, so that was rambling...here's direct answer to your question: Go to Radio Crack and buy some smaller power wire (with combined red/black wire) get something like 22 gauge, 18 would be better. Get a flip switch - make it one of those cool aircraft switches with the big red cover!!

Run the small Radio Crack wire (with two wires) from the cab to the solenoid. In the engine compartment connect the red wire (with a small fuse) to one of the two batteries (preferably whichever battery will likely be the fully charged battery when you run your other battery down). Then connect the black wire to the 'power' of the solenoid - this will be the same post you connect the wire to that you also connected to your fusebox (if you have two small posts, the other post should go to ground).

Go back into the cab and then connect the red/black wire to the switch in the cab, one wire to each post on the switch.

Once this is all hooked up, when you flip the switch, you'll be combining your two batteries (because one of the batteries is actually powering the solenoid to connect the two batteries). Assuming you have a solenoid on PEDs (big and strong enough to handle starting current, but not so big as to arouse suspicion of cheating ), you will be able to 'self-jump' your truck.

Hopefully that helps

edit: As an fyi, I have not bothered with a switch - instead I use a mini-jumper cable (see post #99)...instead of using the switch, I just temporarily jump from within the engine compartment - I connect one end of the jumper to the 'fully charged' battery, the other end to the positive post...I recently hosed my starting battery and this helped me get it started a couple times in an emergency.

CHEERS!

 

[VanIsle_Greg]

edit: As an fyi, I have not bothered with a switch - instead I use a mini-jumper cable (see post #99)...instead of using the switch, I just temporarily jump from within the engine compartment - I connect one end of the jumper to the 'fully charged' battery, the other end to the positive post...I recently hosed my starting battery and this helped me get it started a couple times in an emergency.

CHEERS!

This thread just keeps on givin! That last bit is golden! I still need to get a second battery in the XJ, and this is the trick I plan on using. Good info as always, posted while drunk or not! lol

 

[Cole]

Wrong.

Any non-sealed battery vents whenever it is being charged. Sealed batteries only vent when they are *over*charged and the safety valve opens up.

What a lead-acid battery vents is hydrogen. Hydrogen burns FAST. So fast, you could call it an explosion:




Ever heard of a car battery exploding? That's why.


And to answer another question from higher up - hydrogen is lighter than air, so it has to vent upwards.

No, in 40 years of being a gear head I've never heard of a single incident of a car battery exploding.

If you read the whole quote, I was saying that only a bad/over charge battery would went enough in the NON airtight space of a car to be an issue. MILLIONS of cars for DECADES have the batteries installed INSIDE the passenger compartment.

As a matter of fact, the highest production car on the planet, ever, has the batter under the rear seat behind the driver! Produced that way from the 1940s to the 1980s.

Is there always the 1 in a million exception? Sure! So its "Possible" but the "probability" of an issue, especially with modern batteries, is extremely low.

 

[crawler#976]

Ya'll think to much, and $50.00 is too much money...

http://www.solar-electric.com/blseabaswon3.html?gclid=CIef3q3I-rgCFS_ZQgodTxkAGg

Get it done for under $30.00. When we want to isolate the fridge, it's as simple as turning off the switch. The Power Wagon 12K winch really likes having 2100 amps available when needed, and this switch can handle the load when the batteries are combined. The Group 65 Diehard Platinum under the hood and Group 31M in the bed are combined with 2/0 welding cable - no isolator, nothing fancy, just a big switch that can handle up to 600A for 5 minutes, 350A continuous load. We've had no trouble with this for years now, and I never expect to. As an old Coasty, I've seen these switches used for years in the marine environment.

Mark