Dual Battery Isolation Setup

WillnFox

WillnFox

Un-Known Member
Joined
Nov 12, 2007
Location
Saxapahaw, NC
I've got dual batteries on the Crawler that are just wired in parallel.

The snag I have is while I've got plenty of reserve to run the winch and turn the starter if my voltage goes below 12V my injectors on the Howell EFI won't fire. So my engine is left turning over with no fuel.

What I would like to do is have one battery as a "Starter" Battery, The winch, high draining Ford Taurus Fan, and other accessories will be hooked to it as well.
The other battery will run the Engine, Fuel Pump, starter realy, ect...

How do I isolate them were they can independently run and if the "starter battery" drops to 11.5V the other battery stays at 12.2V while still being charged by the same alternator?
 
Something like this:

ProMariner Multi Battery Isolators - Limited Quantity

ProMariner Multi Battery Isolators efficiently charge multiple batteries while preventing discharge, ideal for negative ground alternator systems and featuring gold-plated terminals for enhanced conductivity.
www.delcity.net www.delcity.net

The allows one alternator to charge two separate battery banks and prevents current from backfeeding from one side to the other. If the starting battery is low, you can always use a switched interconnect (or just a set of jumper cables) to tie the batteries together momentarily.
 
Take a look at the National Luna systems.
www.equipt1.com

BATTERY MANAGEMENT

Equipt Expedition Outfitters is proud to be the exclusive U.S. distributor of all National Luna products. These are the only battery systems we offer because we believe they are simply built better than the rest.
www.equipt1.com www.equipt1.com
 
EugeneTheTJ said:
Take a look at the National Luna systems.
www.equipt1.com

BATTERY MANAGEMENT

Equipt Expedition Outfitters is proud to be the exclusive U.S. distributor of all National Luna products. These are the only battery systems we offer because we believe they are simply built better than the rest.
www.equipt1.com www.equipt1.com
Click to expand...
This doesn't either.

Both of these are designed to have two batteries, but one is held as a starting battery, and the other is held as an accessory battery to provide power to coolers/lights/etc when the engine is off. When the engine is on, both batteries are connected to the alternator without any isolation or redundancy. I think it's an unlikely scenario, but if you're worried about winching with the engine running pulling the batteries down to where the vehicle wouldn't start, or if you're concerned about unequal charging when the vehicle is running, these don't address that.
 
Holy CHIT!
If they are actually SELLING those (Equipt Expedition Outfitters stuff)...I know my next career.
I mean there are industrial, 200,000 charge/discharge cycle rated, tested proven systems out here for less that do more.
And they live in harsh hot vibration environments, perfect for vehicle applciation. Just pretty up the box a bit and add a sticker and doubl the price and profit.
 
Ron said:
Holy CHIT!
If they are actually SELLING those (Equipt Expedition Outfitters stuff)...I know my next career.
I mean there are industrial, 200,000 charge/discharge cycle rated, tested proven systems out here for less that do more.
And they live in harsh hot vibration environments, perfect for vehicle applciation. Just pretty up the box a bit and add a sticker and doubl the price and profit.
Click to expand...
add the words "overland" or "expedition" and the price goes up 4x. science.
 
shawn said:
This doesn't either.

Both of these are designed to have two batteries, but one is held as a starting battery, and the other is held as an accessory battery to provide power to coolers/lights/etc when the engine is off. When the engine is on, both batteries are connected to the alternator without any isolation or redundancy. I think it's an unlikely scenario, but if you're worried about winching with the engine running pulling the batteries down to where the vehicle wouldn't start, or if you're concerned about unequal charging when the vehicle is running, these don't address that.
Click to expand...
So the isolator you linked to from DelCity keeps both banks separate, like the broverlanding stuff above, but has the added bonus of keeping them truly isolated, so one won't draw the other down?
 
orange150 said:
So the isolator you linked to from DelCity keeps both banks separate, like the broverlanding stuff above, but has the added bonus of keeping them truly isolated, so one won't draw the other down?
Click to expand...

It's basically a big ass diode/heat sink that will provide charging power to two separate battery systems with different rates of charge/charging status, etc. The typical use case would be in an RV where you had house batteries that were separate from the engine/car side of things. I used to have a massive one that came out of an ambulance.

It really just comes down to a design intent / use case problem. If you're worried about the winch or other accessories killing the battery while the engine is off, then any cheap continuous-duty solenoid will link those batteries when the engine is running. You can even do it manually with a disconnect switch.
 
Desertfox1023 said:
@snipes243 just sent me this

Smart Battery Isolators - Littelfuse

www.littelfuse.com www.littelfuse.com

Worth sharing as Its also an isolator and looks pretty turn key on the wiring
Click to expand...

This one doesn't work how you described in your original post.


This one basically wires the batteries together while running so they can charge and dissipate at the same rate assuming they both start fully charged. When the vehicle is off or is not receiving a charge, both batteries will dissipate until the "Starting battery" voltage drops below 12.7 v . At that time the isolator will disconnect the "starting battery " and you can run until the secondary battery fully dissipated. After the vehicle starts up next it will not charge the secondary battery until the "starting battery" is up to full charge. Also say somehow you winched the "starting battery" dead, a switch on the isolator can transfer power from the secondary to the "starting battery", basically jump starting the vehicle.

Also you want your starting battery to have all components needed to start the vehicle (if you separate them how's it going to start), everything else goes to Secondary battery
"Starting battery"
- Starter solenoid
- ECU
-ignition
-winch
-fuel pump

Secondary
- none essential

Also if I messed something up don't blame the ME trying to explain electrical to the EE.
 
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snipes243 said:
This one doesn't work how you described in your original post.


This one basically wires the batteries together while running so they can charge and dissipate at the same rate assuming they both start at . When the vehicle is off or is not receiving a charge, both batteries will dissipate until the "Starting battery" voltage drops below 12.7 v . At that time the isolator will disconnect the "starting battery " and you can run until the secondary battery fully dissipated. After the vehicle starts up next it will not charge the secondary battery until the "starting battery" is up to full charge. Also say somehow you winched the "starting battery" dead, a switch on the isolator can transfer power from the secondary to the "starting battery", basically jump starting the vehicle.

Also you want your starting battery to have all components needed to start the vehicle (if you separate them how's it going to start), everything else goes to Secondary battery
"Starting battery"
- Starter solenoid
- ECU
-ignition
-winch
-fuel pump

Secondary
- none essential

Also if I messed something up don't blame the ME trying to explain electrical to the EE.
Click to expand...
I believe the National Luna works exactly the same as what is described here.
 
snipes243 said:
This one doesn't work how you described in your original post.


This one basically wires the batteries together while running so they can charge and dissipate at the same rate assuming they both start fully charged. When the vehicle is off or is not receiving a charge, both batteries will dissipate until the "Starting battery" voltage drops below 12.7 v . At that time the isolator will disconnect the "starting battery " and you can run until the secondary battery fully dissipated. After the vehicle starts up next it will not charge the secondary battery until the "starting battery" is up to full charge. Also say somehow you winched the "starting battery" dead, a switch on the isolator can transfer power from the secondary to the "starting battery", basically jump starting the vehicle.

Also you want your starting battery to have all components needed to start the vehicle (if you separate them how's it going to start), everything else goes to Secondary battery
"Starting battery"
- Starter solenoid
- ECU
-ignition
-winch
-fuel pump

Secondary
- none essential

Also if I messed something up don't blame the ME trying to explain electrical to the EE.
Click to expand...

@snipes243 & @shawn

Below 12.7 though and the truck is off anyway, that or the alternator has gone bad.
I think it would still solve my problem as the goal is to just prevent the starting current from dragging the overall voltage on the rig down to low to where the fuel injectors stop triggering.
Basically I would wire it as they intended it to be used with the exception of the starter would be wired to the AUX battery. I do see a potential problem there of the starter battery not recharging until the engine battery is recharged but if the only load is the engine on the main it shouldn't drain down much. As pointed out, if I ever needed to jump the starter it would be easy to do so by (Unhooking the starter connection) and jumping it to the main battery with some cables. If I did it with one battery drained and the other full as it is now I'd just recreate my current situation
 
Desertfox1023 said:
Below 12.7 though and the truck is off anyway, that or the alternator has gone bad.
Click to expand...
A hard pull will do this, too. Our Warns will pull the battery voltage down to where the ECM thinks the alternator has failed and shuts it off.
 
shawn said:
A hard pull will do this, too. Our Warns will pull the battery voltage down to where the ECM thinks the alternator has failed and shuts it off.
Click to expand...

So you're thinking when the winch is running it will pull voltage down to where the alternator stops charging the winch battery? It's a valid concern.

That should only be temporary though and I would think that's where the override (Boost) button would be used as well.
Potential scenario would be the incab LED indicator light would shut off letting me know they've disconnected, then I know to hit the "boost" button which would lock them together for a minute.


What's your thought on how the other isolater would work?
Is it basically acting as a Diode between both the batteries and the alternator?
Would that work with my single post alternator as wouldn't it need something to regulate the field current?
 
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Desertfox1023 said:
So you're thinking when the winch is running it will pull voltage down to where the alternator stops charging the winch battery? It's a valid concern.

That should only be temporary though and I would think that's where the override (Boost) button would be used as well.
Potential scenario would be the incab LED indicator light would shut off letting me know they've disconnected, then I know to hit the "boost" button which would lock them together for a minute.


What's your thought on how the other isolater would work?
Is it basically acting as a Diode between both the batteries and the alternator?
Would that work with my single post alternator as wouldn't it need something to regulate the field current?
Click to expand...
I think you're overthinking it.

Are you actually having problems with the ECM because the battery voltage is too low? If not, just run it. You can get a second battery if you really want, but you're probably fine with one. If you get a second one, parallel it with battery #1.
 
Desertfox1023 said:
@snipes243 & @shawn

Below 12.7 though and the truck is off anyway, that or the alternator has gone bad.
I think it would still solve my problem as the goal is to just prevent the starting current from dragging the overall voltage on the rig down to low to where the fuel injectors stop triggering.
Basically I would wire it as they intended it to be used with the exception of the starter would be wired to the AUX battery. I do see a potential problem there of the starter battery not recharging until the engine battery is recharged but if the only load is the engine on the main it shouldn't drain down much. As pointed out, if I ever needed to jump the starter it would be easy to do so by (Unhooking the starter connection) and jumping it to the main battery with some cables. If I did it with one battery drained and the other full as it is now I'd just recreate my current situation
Click to expand...
If the goal is keep the voltage above 12v on startup. Why not put a gear reduction starter on it, and a full size battery. It sounds like the 2 mini batteries you have currently are not holding up. Might be time to put a real battery in the back. Also how many amps is the alternator?
 
So its happened a few times now. I've left the switch on, or lights, or just one of the batteries is weaker than the other ect...

I've got medium sized batteries wired in parallel to make one bigger battery. (I bought it this way) .

Is got a Howell TBI unit , which is a holley 650 TBI using GM injectors. If the batteries wired together are below 12V on my Guage like 11V I can hit the switch and the starter turns, pump is on (have fuel pressure Guage, ect...) but with the filter off can physically see the injectors aren't firing. Reading up this is "common" in that the injectors need 12V.

So the idea is that if I segregate the main battery to just the Engine, MSD, fuel pump, Low speed fan, it will keep the injectors firing fuel. While the other battery which is potentially drained can turn the starter while not pulling the voltage down.

I've done a simulation of this with a USB jump box and it worked. Now I just need somthing with less hassel.

The batteries are Odyssey:
www.odysseybattery.com

ODS-AGM28LMJA - ODYSSEY Battery

Whether for everyday or emergency use, today's vehicles are loaded with more electronics than would have been imaginable just a few years ago. ODYSSEY batteries have been designed to keep up with the changes. Because their plates are made of pure virgin lead (unlike the lead alloy in most...
www.odysseybattery.com

Alternator is a:
100 Amp unit
www.summitracing.com

Powermaster 8-47100 Powermaster Race Alternators | Summit Racing

Free Shipping - Powermaster Race Alternators with qualifying orders of $109. Shop Alternators and Generators at Summit Racing.
www.summitracing.com www.summitracing.com


If I'm looking at this wrong I'm open to other suggestions. The goal is to keep the threshold voltage to the Howell and MSD at 11.5v at a minimum.
 
Be aware that there is a voltage drop across the diode array of a diode-based isolator (like the one linked at DelCity), which can knock 0.5-0.6VDC off of the charge voltage, so your batteries will only charge to 0.5-0.6V less that whatever the alternator is putting out. Probably not the best solution if your injectors already don't like low voltage. There are FET-based versions of that type of isolator, with almost no voltage drop, but at higher cost.
 
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Desertfox1023 said:
So its happened a few times now. I've left the switch on, or lights, or just one of the batteries is weaker than the other ect...

I've got medium sized batteries wired in parallel to make one bigger battery. (I bought it this way) .

Is got a Howell TBI unit , which is a holley 650 TBI using GM injectors. If the batteries wired together are below 12V on my Guage like 11V I can hit the switch and the starter turns, pump is on (have fuel pressure Guage, ect...) but with the filter off can physically see the injectors aren't firing. Reading up this is "common" in that the injectors need 12V.

So the idea is that if I segregate the main battery to just the Engine, MSD, fuel pump, Low speed fan, it will keep the injectors firing fuel. While the other battery which is potentially drained can turn the starter while not pulling the voltage down.

I've done a simulation of this with a USB jump box and it worked. Now I just need somthing with less hassel.

The batteries are Odyssey:
www.odysseybattery.com

ODS-AGM28LMJA - ODYSSEY Battery

Whether for everyday or emergency use, today's vehicles are loaded with more electronics than would have been imaginable just a few years ago. ODYSSEY batteries have been designed to keep up with the changes. Because their plates are made of pure virgin lead (unlike the lead alloy in most...
www.odysseybattery.com

Alternator is a:
100 Amp unit
www.summitracing.com

Powermaster 8-47100 Powermaster Race Alternators | Summit Racing

Free Shipping - Powermaster Race Alternators with qualifying orders of $109. Shop Alternators and Generators at Summit Racing.
www.summitracing.com www.summitracing.com


If I'm looking at this wrong I'm open to other suggestions. The goal is to keep the threshold voltage to the Howell and MSD at 11.5v at a minimum.
Click to expand...
Then just do a simple isolation solenoid. Provide 12V to it when the engine is running to link the two batteries together. No smarts required.

Next time you need new batteries, get bigger ones. The 925 isn't big enough for what you're asking it to do - even with two. A single group 34 has more power than both your 925s. A single group 31 has a LOT more.
 
Bebop said:
Grab that :

www.egismobile.com

TH3 -12V Automatic Charging Relay (ACR), 160 A, Bulk

www.egismobile.com www.egismobile.com
Click to expand...

I'm not sure if anyone has looked at the datasheet for this, but it does everything needed (if I understand the problem). It's select-able to have an engine start isolation function, so that a "start" signal (from the ignition start or whatever) opens the solenoid and isolates the two batteries, and after that it works like any other automatic charging relay with voltage-based isolation/combining. Pretty cool. You can actually have one input signal to instantly open the solenoid, and another input signal to instantly close the solenoid.
So it's an automatic charging relay that also performs the functions of a diode or FET array isolator, but without any of the alternator voltage sensing or excitation issues that can happen on the isolated output side of the diode/FET arrays.

I'd definitely agree though that larger batteries can cure a lot of evils. Except the evil of weight, and often the evil of cost.
 
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I got a new odyssey PT-1500 34/74 sitting in the garage you can try. Also I would looking into a higher output 3g alternator like a 130 or 140 amp. Lots of the bronco guys have issues with the ECU dropping out when they do efi conversion when they are running the 60 and 90 amp alternators.

One other thing to look at is the ECU wired directly to the battery? Also check the grounds. ECU's will do funny things when they are not wired properly.

I know this is for Holley ECU's not the Howell but the principles are the same.
www.holley.com

EFI Wiring Tips: Proper Ground And Voltage

When installing a Holley or any EFI system to your vehicle, it's imperative to have a proper ground and voltage for the system. The internals of an ECU contain delicate microprocessors and many other components that rely on clean, sound power and ground. Here are some tips from Holley's EFI...
www.holley.com www.holley.com

 
Fabrik8 said:
I'm not sure if anyone has looked at the datasheet for this, but it does everything needed (if I understand the problem). It's select-able to have an engine start isolation function, so that a "start" signal (from the ignition start or whatever) opens the solenoid and isolates the two batteries, and after that it works like any other automatic charging relay with voltage-based isolation/combining. Pretty cool. You can actually have one input signal to instantly open the solenoid, and another input signal to instantly close the solenoid.
So it's an automatic charging relay that also performs the functions of a diode or FET array isolator, but without any of the alternator voltage sensing or excitation issues that can happen on the isolated output side of the diode/FET arrays.

I'd definitely agree though that larger batteries can cure a lot of evils. Except the evil of weight, and often the evil of cost.
Click to expand...
It's a good lil unit. That's why I shared.
It does everything on its own if you don't want to wire anything.
If you do, you can geet full manual control over it.
 
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