Is a diode needed for dual battery setup if I want two options to bridge?

[4BY4ADV]

Probably not the best way to phrase the question.

I’ve got a dual optima setup and a battery isolator. 12v to the isolator bridges the two batteries in order to charge the secondary while driving.

I’m about to put in a solid state 8 switch panel and one in the many switch labels gave me an idea. Why not have a second way to bridge the batteries? Push a switch to send 12v from the first battery to the isolator and bridge the two when I’m not driving.

I wouldn’t do it often, but there have been times when I haven’t had enough sunlight one day for my solar panel to keep the second battery topped off, and I don’t want my fridge to shut off. I’d press the switch to use my primary as a bit of reserve power.

I’m not worried about getting stranded. I’ve got a buddy with me in most camping trips and I also bring a portable jumper.

So in wiring this, should I use diodes on both 12v power in to the isolator to prevent power going “backwards”? More worried about frying my new solid state switch.

 

[mrblaine]

Probably not the best way to phrase the question.

I’ve got a dual optima setup and a battery isolator. 12v to the isolator bridges the two batteries in order to charge the secondary while driving.

I’m about to put in a solid state 8 switch panel and one in the many switch labels gave me an idea. Why not have a second way to bridge the batteries? Push a switch to send 12v from the first battery to the isolator and bridge the two when I’m not driving.

I wouldn’t do it often, but there have been times when I haven’t had enough sunlight one day for my solar panel to keep the second battery topped off, and I don’t want my fridge to shut off. I’d press the switch to use my primary as a bit of reserve power.

I’m not worried about getting stranded. I’ve got a buddy with me in most camping trips and I also bring a portable jumper.

So in wiring this, should I use diodes on both 12v power in to the isolator to prevent power going “backwards”? More worried about frying my new solid state switch.

I'm not a fan of diode isolators. I much prefer the mechanical solenoid style with voltage sense. They charge up the house battery first, then when a threshold is reached, the solenoid closes and charges the aux. When you key off, both batteries will run down to the discharge threshold then the solenoid opens and the draw is only on the aux. so you can't run down the house battery below the ability to start the vehicle. The sense circuit has a small delay in it to prevent the bell effect on charge.

 

[WSS]

This is the cleanest and has the least voltage drop I have used. Very small when compared to a solenoid and isolater type setup

https://www.hellroaring.com/bic95300B.php
This kit finishes it off nice and clean:

https://www.hellroaring.com/remote.php

 

[dbbd1]

On those few occasions, why not just use the portable jumper to charge up the battery for your fridge?

 

[4BY4ADV]

I'm not a fan of diode isolators. I much prefer the mechanical solenoid style with voltage sense. They charge up the house battery first, then when a threshold is reached, the solenoid closes and charges the aux. When you key off, both batteries will run down to the discharge threshold then the solenoid opens and the draw is only on the aux. so you can't run down the house battery below the ability to start the vehicle. The sense circuit has a small delay in it to prevent the bell effect on charge.

First let my clarify. Diodes would not be for charging. The isolator is a solenoid. One of those 200amp ones that uses a 12v signal (when vehicle is on) to charge both batteries. Then when off, separates them.

The 12v signal is basically an accessory power signal. I was thinking of using the switch to be a second accessory power source to trigger the solenoid to link the two batteries. So it would be what you are saying… but not intelligent. Either running the vehicle or my switch button would trigger them to be in parallel… vehicle and switch off would isolate them.

I DO however like what you are saying with having them automatically stay in parallel until a specific voltage drop. What isolator does that? If we’re talking redarc… or similar, I’d rather not drop tons of money if I can have a manual switch like what I’m talking about. The diode was just to prevent current from flowing back to the switch panel whenever the vehicle is running. So think 1-way 12V trigger.

On those few occasions, why not just use the portable jumper to charge up the battery for your fridge?

The jumper is one of those tiny lithium batteries. It starts the Jeep no problem, but would not work well charging a battery or powering a fridge.

 

[4BY4ADV]

This is the cleanest and has the least voltage drop I have used. Very small when compared to a solenoid and isolater type setup

https://www.hellroaring.com/bic95300B.php
This kit finishes it off nice and clean:

https://www.hellroaring.com/remote.php

So that would be a second battery just as a backup to start the vehicle, isolated from the primary that would possibly see too deep of a discharge. There is however mention and a link to the 95150 that would be for my situation.

Looking at what the 95150 does, I don’t see any benefits to swapping from how I currently bridge/isolate the batteries. But maybe I’m missing something?

 

[C.J. Roberts]

I don't know about modern electronics, but the way it used to be done is a battery isolator that charges both batteries. The two batteries can be wired with a Ford style starter relay, so that when one, usually the primary, battery went dead, you could use the secondary to start the vehicle, which would charge the primary.
The primary was a standard vehicle battery, the secondary was a deep cycle.

 

[WSS]

So that would be a second battery just as a backup to start the vehicle, isolated from the primary that would possibly see too deep of a discharge. There is however mention and a link to the 95150 that would be for my situation.

Looking at what the 95150 does, I don’t see any benefits to swapping from how I currently bridge/isolate the batteries. But maybe I’m missing something?

The main benefit is the secondary gets a full charge. With a diode type isolator, there is a voltage loss, meaning if your main battery is fully charged at 13.6v, then the secondary will top out at 13.1, or what ever the diode loss is for a particular isolator. Check the voltage on both your batts at rest and you will see the variance.

Aside from the loss, there is the solid state switching as opposed to mechanical switching. The size of the unit was a big bonus for me on my current TJ.

When winching or using a heavy load, you can combine both to help with low voltage heat problems. Another issue I have had twice is dead main batt from the key coming out of the ignition when it is not in the "OFF" position. My son is good at starting it up once a week but sometimes is in a hurry to turn it off and get onto others things LOL. Luckily the odyessy batts are pretty tough. I flip the switch and it starts right up. I can flip it right back and both batts still get charged.

 

[4BY4ADV]

So dual battery setup works and I've been using it for over a year.

The question is in relation to having a secondary trigger for the isolator to bridge the batteries. I'll just order a diode off Amazon just for safe measure.

 

[4BY4ADV]

The main benefit is the secondary gets a full charge. With a diode type isolator, there is a voltage loss, meaning if your main battery is fully charged at 13.6v, then the secondary will top out at 13.1, or what ever the diode loss is for a particular isolator. Check the voltage on both your batts at rest and you will see the variance.

Aside from the loss, there is the solid state switching as opposed to mechanical switching. The size of the unit was a big bonus for me on my current TJ.

When winching or using a heavy load, you can combine both to help with low voltage heat problems.

I'm not using a diode to isolate the batteries. I was just asking for advice on whether a diode would be best when adding a second trigger to the current solenoid style battery isolator.

I'm able to charge my secondary to the same voltage as the first.

 

[WSS]

I'm not using a diode to isolate the batteries. I was just asking for advice on whether a diode would be best when adding a second trigger to the current solenoid style battery isolator.

I'm able to charge my secondary to the same voltage as the first.

My bad, I was answering your question about benefits. I have no clue what the answer is. I’m sure someone with knowledge will step up.

 

[psrivats]

I'm not a fan of diode isolators. I much prefer the mechanical solenoid style with voltage sense. They charge up the house battery first, then when a threshold is reached, the solenoid closes and charges the aux. When you key off, both batteries will run down to the discharge threshold then the solenoid opens and the draw is only on the aux. so you can't run down the house battery below the ability to start the vehicle. The sense circuit has a small delay in it to prevent the bell effect on charge.

That sounds like a really well thought out setup for dual batteries. I had done some research a couple years ago but kind of dropped the idea entirely. Out of curiosity, do you build this yourself Blaine, or do you use a kit from somewhere?

 

[4BY4ADV]

My bad, I was answering your question about benefits. I have no clue what the answer is. I’m sure someone with knowledge will step up.

No worries! I'm all about discussion and learning new things.

I'll answer your edited question anyway... since someone it may pose useful for someone in the future.

Dual battery setup:
Two Optima Blue tops stacked.
Both are grounded together to the chassis.
The starting battery is used as normal... positive to the normal engine/accessories/etc.
Second battery positive to my power distribution block to my router, fridge/freezer, lights, CB, and anything else that I might want to run off of house power.

Both batteries have a 2 or maybe 4 gauge power cable running to battery isolator. The isolator has a separate power/ground. Power to the separate terminal causes the solenoid to close and both batteries are then in parallel. This power line is connected to an accessory power line. So any time I turn the key, the second battery is bridged to the primary, and they charge via the alternator together.

My original question was about using a solid state switch panel (knock off version of SwitchPros) as another option/way to send a 12v signal to connect the batteries in parallel. This would be any time I want to extend the life of my fridge/internet/lights/etc and I'm not worried about draining both batteries and being stranded. I'll verify I have jumper cables and a buddy or that my jumper pack is fully charged.

I've had a few times where I didn't get enough sun one day or something was wrong with my solar panel and having use of the starting battery to keep the fridge going another couple hours would have been huge.

So at this point, I'm going to add a 12v 20amp diode to the additional 12v feed to the isolator from my switch panel as a safety measure.

 

[mrblaine]

That sounds like a really well thought out setup for dual batteries. I had done some research a couple years ago but kind of dropped the idea entirely. Out of curiosity, do you build this yourself Blaine, or do you use a kit from somewhere?

Neither, I just paid attention to how Lance wired up the camper to charge the camper batteries off of the truck without running down the truck batteries. They use the Sure Power 1315 to do it.

 

[4BY4ADV]

Neither, I just paid attention to how Lance wired up the camper to charge the camper batteries off of the truck without running down the truck batteries. They use the Sure Power 1315 to do it.

Just looked this up. Looks like it really just an automatic version of what I have. No need to run a signal wire to power the solenoid.

IF you could program it, and have the disconnect voltage lower than the 12.7volts.... It would be pretty cool. Set it to isolate the two slightly above the voltage needed to start the Jeep and you could power accessories while camping longer. But with a disconnect voltage at 13.2volts... it wouldn't help in a scenario like I'm in.

Good info regardless though!

 

[afitzray97]

Check out marine stuff. These are used all the time to run a dedicated start battery and a second battery for accessories. Use a battery rated as combo for both start and deep cycle for your second battery.
https://www.bepmarine.com/en/Products/Battery-Management/Voltage-Sensing-Relays

 

[macleanflood]

Redarc? Might as well just do a battery management system.

-Mac

 

[mrblaine]

Just looked this up. Looks like it really just an automatic version of what I have. No need to run a signal wire to power the solenoid.

IF you could program it, and have the disconnect voltage lower than the 12.7volts.... It would be pretty cool. Set it to isolate the two slightly above the voltage needed to start the Jeep and you could power accessories while camping longer. But with a disconnect voltage at 13.2volts... it wouldn't help in a scenario like I'm in.

Good info regardless though!

They have a combine to start version as well.

 

[NskLJ]

First let my clarify. Diodes would not be for charging. The isolator is a solenoid. One of those 200amp ones that uses a 12v signal (when vehicle is on) to charge both batteries. Then when off, separates them.

The 12v signal is basically an accessory power signal. I was thinking of using the switch to be a second accessory power source to trigger the solenoid to link the two batteries. So it would be what you are saying… but not intelligent. Either running the vehicle or my switch button would trigger them to be in parallel… vehicle and switch off would isolate them.

I DO however like what you are saying with having them automatically stay in parallel until a specific voltage drop. What isolator does that? If we’re talking redarc… or similar, I’d rather not drop tons of money if I can have a manual switch like what I’m talking about. The diode was just to prevent current from flowing back to the switch panel whenever the vehicle is running. So think 1-way 12V trigger.


The jumper is one of those tiny lithium batteries. It starts the Jeep no problem, but would not work well charging a battery or powering a fridge.

If you are going the solenoid route, make sure it is the continuous duty version not just a starter solenoid. Cole Hersee has them in different amp ratings.
https://www.amazon.com/dp/B0064MX7US/?tag=wranglerorg-20

 

[NskLJ]

First let my clarify. Diodes would not be for charging. The isolator is a solenoid. One of those 200amp ones that uses a 12v signal (when vehicle is on) to charge both batteries. Then when off, separates them.

The 12v signal is basically an accessory power signal. I was thinking of using the switch to be a second accessory power source to trigger the solenoid to link the two batteries. So it would be what you are saying… but not intelligent. Either running the vehicle or my switch button would trigger them to be in parallel… vehicle and switch off would isolate them.

I DO however like what you are saying with having them automatically stay in parallel until a specific voltage drop. What isolator does that? If we’re talking redarc… or similar, I’d rather not drop tons of money if I can have a manual switch like what I’m talking about. The diode was just to prevent current from flowing back to the switch panel whenever the vehicle is running. So think 1-way 12V trigger.


The jumper is one of those tiny lithium batteries. It starts the Jeep no problem, but would not work well charging a battery or powering a fridge.

My motor home has a momentary switch on the dash to connect the house batteries to the engine battery in case the engine battery is low and I need to start it. The charge solenoid is wired to the accessory position so does not get power when starting. The momentary switch bypasses this to apply power when starting. You could install a on/off/ momentary switch to do what you want, my concern and why I would not do that is the switch could be left on and drain all the batteries. With me the only time this would happen is when I forgot the jumper and my buddies went ahead and “I’ll catch up”
https://www.etrailer.com/Accessorie...ttLS4QqAhJQW5JxXYxl3aw6pSAtu2JQhoCy18QAvD_BwE