LandCruiserPhil
Expedition Leader
If the vehicle is at idle and both batteries are low 12-12.6 would not be uncommon.
How to make a cheap isolated dual-battery setup for $50
- Thread starter evldave
- Start date
teotwaki
Excelsior!
That is the disadvantage with alternators: they are limited by RPMs and however their regulator is designed. That is one reason that they are labeled as being good for maintaining charge but not necessarily as good at being chargers.
dwh
Tail-End Charlie
A) Many (most?) alternators don't put out all that much, if anything at idle. You can check it again at a higher RPM, but 35a is respectable output at idle.
B) Is that 35a what is going through the batteries? Or is that everything the alternator is putting out to power the whole truck?
C) The voltage of the "12v bus" is going to be determined by the batteries.
The voltage regulator will keep the alternator turned on until the voltage of the bus rises to whatever the set point is. The voltage of the bus won't rise as long as something - like the batteries - is drawing it down. As the batteries fill up, their voltage will rise, and the voltage of the entire 12v bus will rise along with them.
So it's not like you are going to see the alternator putting out 13.8v, when the batteries are at 12.6v - when you are measuring the voltage, you are measuring the voltage of the entire 12v bus.
Southwest Chuck
Observer
........
The fastest way to figure out where to run your wire to the fuse box is a 12V detector thingamajig. Turn your key to 'ON' (don't start truck) and then start probing empty holes in her fusebox. At some point your thingamajig will light up. Write down all her locations that lit up your thingamajig and turn her OFF. Then start probing those same empty holes in her fusebox that lit up your thingamajig again. Find any empty hole in her fusebox that lit up your thingamajig when she was turned ON but got no light from your thingamajig when she was turned OFF - that's the circuit you want to use (ALL THE TIME, if you get what I'm sayin)
I'll add a suggestion here, that you take one more step. You want to find a Ignition "on" hot wire, that's true. However, I would try and find one that that is "NOT" energized when the ignition is switched to the "Accessory" position. That way your batteries are still isolated when your engine is off and the ignition is in the accessory position (to run your radio or other accessories, etc.) If you use a circuit that is hot in both the "on" and "accessory", the relay/isolator will be engaged in both positions, tying the batteries together without isolation,(and eating up power) even when the engine is off and you're kick'in back with a beer at your favorite overlook listening to some tunes.:ylsmoke:
SLO_F-250
Explorer
Quick question guys.... In the picture above he calls out a 12ga wire going to the fuse box to a fuse that is hot when the ignition is turned on. Do you simply take out the fuse, put the wire in on side then push the fuse back in?? Also does this wire have any significant power running to it? Was just wondering if I can clip it on to a hot wire under the dash? 12ga wire is fairly big so I wasn't sure. Please educate me as I have never run a wire to the fuse box.
I have everything mounted up and working but am concerned that where I attached the "ON" wire wont work due to current draw. I did test everything and it is working properly but just don't want to cause trouble down the road. Ill post a pict this evening.
THANKS GUYS!
dwh
Tail-End Charlie
Yea, that's sort of a difficult question, because every rig is different, so you have to sort of "wing it".
My truck has an "Add a Fuse" doohickey stuffed into a fuse slot that is ignition hot and feeds the solenoid:
http://www.wiringproducts.com/contents/en-us/d137_fuse_holders.html
As for the power draw of the solenoid - not much. Mine draws about an amp.
My truck has an "Add a Fuse" doohickey stuffed into a fuse slot that is ignition hot and feeds the solenoid:
http://www.wiringproducts.com/contents/en-us/d137_fuse_holders.html
As for the power draw of the solenoid - not much. Mine draws about an amp.
SLO_F-250
Explorer
Thanks for the intput. My truck has dual ignition fuses in the fuse panel under the hood. Both are 50amp. Right now I am using a wire under the truck that is hot when the ignition is turned. Just am a bit worried because the wire I am pulling from is pretty small. Maybe 8ga. Im running 12ga to the isolator.
Am I rolling the dice, or not too big of a deal? Or should I do something different? Leaving for my trip in 2 days and I doubt I can find that part anywhere, plus I need it 50amps.
SLO_F-250
Explorer
Yea, that is why I was wondering how much draw it has. Besides getting the "add a fuse" above, I took the directions as stuffing that wire into one side of the fuse connection and then putting the fuse back in. Is that seriously what some people are doing? I guess its not that off the wall.
From first post in this thread. That is what I am talking about.....
dwh
Tail-End Charlie
Well...I don't think evldave actually said to stuff the wire under a fuse...
And no, it's not recommended.
You can find a wire that is hot with the ignition, and tap off of it. If you use the same size wire or larger, then the existing fuse will protect both wires, and almost certainly be large enough to handle the extra one amp or so of extra load added by the solenoid.
G35Vortec454
Adventurer
This is a great thread.
One thing I'd like to comment on is the voltage drop of diode isolators. You can solve that problem by using an adjustable voltage regulator for your alternator and a battery sense wire to the battery, far from the alternator armature post. That way you can set the alternator to put out the proper voltage AT THE batteries.
One thing I'd like to comment on is the voltage drop of diode isolators. You can solve that problem by using an adjustable voltage regulator for your alternator and a battery sense wire to the battery, far from the alternator armature post. That way you can set the alternator to put out the proper voltage AT THE batteries.
Last edited:
Okay I have a question real quick I know most basic automotive wiring, but reading through this I had some questions. So is Isolating the batteries mostly for charging purpose? Or is it so that you don't have to rewire certain things like the Cig lighter and winch so on and so on. Because to me I would just wire them in with a separate fuse block so if I sold the truck I could just make it removable and save it for another ride.
4RunAmok
Explorer
Isolating (separating) the batteries is to protect your starting battery. You don't want to be drawing off both batteries while your vehicle is not running.
Combining the batteries while the vehicle is running is for charging both batteries. And for this, you want to use a high-amp constant duty solenoid, as opposed to a voltage reducing diode-type isolator. These diode isolators will end up reducing the charging voltage so that both batteries never receive a full charge.
To make the system simple. Run two AGM batteries, put one inside the cabin, run all your accessories on a fuse block from it, and remove it when needed. Don't forget the breakers, especially the one in the front to kill the line after you removed the rear battery.
Combining the batteries while the vehicle is running is for charging both batteries. And for this, you want to use a high-amp constant duty solenoid, as opposed to a voltage reducing diode-type isolator. These diode isolators will end up reducing the charging voltage so that both batteries never receive a full charge.
To make the system simple. Run two AGM batteries, put one inside the cabin, run all your accessories on a fuse block from it, and remove it when needed. Don't forget the breakers, especially the one in the front to kill the line after you removed the rear battery.