Dual Battery configs - isolators, selonoids and marine switches

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Having added a Warn M8000 winch within my ARB, I've been researching throughout the forums to learn how others have set up their dual-battery configs.

And I'll freely admit...I'm still confused.

When/Why would I choose an isolator vs. a high capacity selonoid? When or where could put a marine-grade switch in the mix?

Any help on the basic concepts of the different approaches would be greatly appreciated. I'm straining to get out of the research phase and into the procurement phase to finally get something implemented.

Best Regards.
 
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Very simply, if you run both batteries in parallel with no isolator, they behave like one big battery in the way they charge and discharge in unison. Over time, they will become dis-similar and one will charge faster than the other leading to one battery passing current to the other, thus equalizing both at a lower voltage level. They will become worse as time wears on.

If you use a relay or mechanical switch to connect and disconnect batteries, the upside is simplicity and cost. Downside would be the the switch or relay is mechanical and will eventually wear out. Secondly, when you connect a fully charged battery to the discharged battery, your batteries will equalize, meaning you'll dump current from full to low battery, and this potentially large and instant current must not exceed the rating on the switch or relay....if could be north of 1,000 amps in-rush so keep that in mind.

If you go solid-state, upside is there are no moving parts, so it should outlast mechanical devices. Downside is cost...good isolators cost money, not so good ones cost more than mechanical relays and switches. When it comes to solid-state, you have to select a device based upon the current capability of the alternator. Once you decide on a current rating decide on what type of solid-state isolator is right for you. The most common are silicon or Schottky rectifier packages. These are large aluminum heat sinks with posts poking thru the top. These usually lose between .5 volts and 1.5 volts as current passes though the device. This loss manifests itself as heat which is why they have lots of aluminum surface area. Mount in vertically with airflow at it should last quite some time.

A newer style of solid-state isolators use MOSFET arrays instead of silicon or Schottky rectifiers. There are various manufacturers of these devices so you select an appropriate current rating, see what the voltage drop is at the CONTINUOUS rating, and select a device that you're comfortable with.

Generally speaking, if is has an aluminum heat sink, it does so because it gets hot, and if it gets hot, you're throwing power away.

The idea behind the solid-state isolator is that both batteries will be charged to their full potential, but the battery where you have your winch, lights, etc...can be depleted without causing your starting/running battery to discharge and feed the aux. loads.

People install a second battery for various reasons so you have to figure how you intend to use your batteries and what exactly you're trying to achieve by adding and/or isolating a second battery. Some want to charge both and deplete both. Some want to charge both and deplete one without compromising the other. Some want to charge both, run everything on one, and have the second battery as a "jumping" battery. Batteries need to be used in order to stay healthy so I find the dedicated "jumping" battery to be kind of a waste of a second battery....the idea of constantly charging it but never using it may cause the battery to be less than healthy on the rare occasion that it's needed. Again, just an opinion as you'll find many people who set things up like this.
 
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Nice overview, mobi.

I'd also add that most of the electronic isolators don't have the capacity of the mechanical switches. You may find one that can handle a starter motor, but you will have a lot of trouble finding one that can handle the 300-400 amps that a winch can draw.

You also know that a full mechanical switch will work regardless of the battery conditions. I had concerns that with one or more very low batteries, an electronic isolator might not work.

I ended up going with a combination of an automatic solenoid and a manual mechanical switch.

The point of overcharging a battery you never use is also very valid. I think it's important that you pick the right type of battery for what you're going to be doing, and have a charging strategy that fits.

In my setup, the second battery is for deep cycle while camping, for winching, and for emergency starts. I use an AGM battery, since it can hold a charge for several years if it's not used, and I only charge it when it needs it. I often go months with the second battery system totally isolated.

So far, so good.
 
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Sean;

Stay in the research mode for a while. Try to write down everything u are going to do; draw diagrams, figure what parts are required etc. For example, JCWhitney carries a USA made battery disconnect switch thats good for 500-1000 amp and it is really well made. The Hellroaring unit (http://www.hellroaring.com/) has a proven track record, as well as MOBI-ARC [which wasn't around when I did my dual batt setup].

http://homepage.mac.com/dfmorse/BattProj2/page1.html

Have fun!

...
 

Grench

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I looked around at the different automatic/isolator options before I did mine. In the end I decided to do a brute force version that requires me to choose how my system is configured on any particular day. The batteries are Optima D31A industrials bought in a matched two pack set. In general I set them as:

Day to day driving - Batteries in parallel both charge/discharge.
Camping running accesories but not the engine - Bat 1 on the house load, Bat 2 off.
Winch load1 - Batteries in parallel and engine running
Winch load2 - Bat 1 house, Bat 2 winch
Winch load3 - Bat 1 winch, Bat 2 house

When needed 24v- requiers a wrench - Bateries in serial mode for a 24volt circuit. I figured out how to do this, but haven't got the spotlights set up yet for it. If I decide this is fun, I'll likely set switches for it. Nervous though as switches set to enable this could be cross set and mess stuff up.

The advantage? I can configure it on the fly to meet pretty much any requirement. The wiring is pretty straight forward.

The disadvantage? It requires concious thought to what I'm doing and how I'm configured at the time.

YMMV
 
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tech_dog!!!!! Been searching for a set up that I want. Your set up is what I'm looking for... Got a write up?


I resently bought a box of goodies if you will but since I'm a noob.... I will need help.

Let me know...:cheers:
 
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Here's a writeup I did from my last tacoma...I plan on doing the same thing with my 80 but with two group 31 batteries :cool:

Key Components...
main battery - odyssey 1200mjt
aux battery - odyssey 1700mjt (battery specs)
mobi-arc isolator (more info here, and tech specs here)
Rockford Fosgate 1/0 cable for the (+) and 2/0 for the (-)
I only used 2/0 because we had some left overs at work
Rockford Fostgate positive battery post lugs

I'll try and keep this as organized as possible so forgive me if I ramble...

My reasons for choosing the 'perfect switch' is efficiency, reliability, and the theory behind the isolator works for my application.

Efficiency/Reliability


There are a couple ways of isolating batteries...
1. Solenoid - You can find these in your winch. Essentially they are contacts that open and close, isolating and combining your batteries, respectively. Solenoids are rated for interrupting large amounts of current that's why they are found on your winch and with battery systems. When contacts open and break excessive amounts of current a layer of oxidation builds on the current carrying contacts. This layer of oxidation creates resistance. Resistance reduces efficiency. In turn making it harder for your alternator to fully charge your batteries. Also say when you combine your batteries to winch, the battery that has to power the winch through the solenoid will waste power because of the solenoid. And I hear occassional stories of solenoid failure with winches. Maybe because it's not only electrical but mechanical as well.

2. Diodes - such as the surepower isolator. Diodes by nature waste power (watts). Typical diode isolators drop the voltage by 0.7 volts, I know it doesn't sound like much but at high currents the losses add up. Power (watts) = I (current) x E (voltage) So let's say you're winching and the winch is drawing 200 amps.
140 watts = 200 amps x 0.7 volts. What this means is at a loss of .7 volts, and 200 amps of current flowing you're wasting (losing) 140 watts. This loss of electrical energy becomes energy in the form of heat. That's why the diode type isolators are larger and have heat fins. As heat rises, the resistance rises, and excessive heat can cause premature failure.

3. MOSFETs - this is what mobi-arc uses. The electrical theory is a little too deep for me but I've actually tested my isolator to see if what they advertise is true. I didn't write down the numbers but what I did was hooked up the winch to draw current from both batteries (not how I would typically use it, I'll explain later). With a clamp on DC ammeter I measured how much current was flowing through the isolator. I think about 120 amps were going through the isolator. I then measured what the voltage was before and after the isolator and it was a difference of about .04 volts. So with the same P = IE equation that equals 120 amps x .04 volts = 4.8 watts.

Now I know it's not a whole lot of power, I think I'm just critical about it because electricity is what I deal with every day. But think about this - would 140 watts of heat or 4.8 watts of heat be easier to dissapate? Hence the reason why the perfect switch is smaller and doesn't need heat sinks. Another benefit of this type of isolator is that it's solid state, there are no moving parts = less things to break.


How it works...
I have the Single Rectifier Unit, (think direction or current flow)which isolates the main battery from the aux battery. It does NOT isolate the aux battery from the main battery.

Another way of saying this is the aux battery can and is feeding the main battery as well as everything connected to the main battery. In contrary the main battery cannot feed the aux battery.

Essentially what this means is, anything fed from your aux battery will only take power from your aux battery, your main battery will be untouched. Now anything fed from your main battery will be fed from your main battery and your aux battery via the isolator.

Now because it is designed this way, the main battery will never have a lesser charge than the aux battery. Why? Because the isolator allows the current to flow from the aux battery to the main battery, but not in the opposite direction. So it's like the aux battery is always jump starting the main battery. That's why the main battery will always have a greater charge than the aux, so it's a guarantee that I will be able to start my truck.


So here's the jist of what's connected to my aux battery..
1 fridge
multiple 12v outlets
3 lightforce lights
4 rock lights
2m
cb
air compressor
winch


All of these accessories take power from the aux battery and the aux battery only. These are the accessories that have a greater chance of draining a battery, either over long periods (fridge camping) or short one's (extensive winching).




Why don't I combine my batteries for winching?
I haven't done too much winching but after talking to many many people, one good battery is enough. I don't frequent anything too extreme and even if I did, I could always use jumper cables to combine the batteries. And if I did an extreme winch pull and killed a battery, it would be my aux battery and not my starting (main) battery.

If I did use a system that would combine the batteries and did a crazy winch pull that killed both batteries - then what? Drive around for an hour to make sure your batteries are somewhat charged. Chances are slim but I don't want to take that risk.


Now let's say you use your radio while camping a lot (which would be connected to your main battery), there's always the possiblity of killing your main battery and your aux battery. I typically don't use my radio or anything wired from the main battery, while at camp. If you do use a lot of factory wired accessories when the truck is off then this may not be the choice for you... If I do choose to listen to xm at camp I'm not afraid to because the current draw is so minimal and slow that I can catch the battery before it's too late with a voltmeter.


Whew, that was long winded. Clear as mud? I hope I helped people more than I confused people
 
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tech_dog!!!!! Been searching for a set up that I want. Your set up is what I'm looking for... Got a write up?


I resently bought a box of goodies if you will but since I'm a noob.... I will need help.

Let me know...:cheers:

The write-up is in my signature. Click on where it says "dual battery" in a different color, or go here: https://forum.ih8mud.com/showthread.php?t=93130

I've been running my dual battery setup for about a year now, and so far so good. I'm on my original everything, including the batteries, and I just got lots of juice out of battery 2 on my recent camping trip.

T.
 
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People seem to be assuming that solid state is more reliable than the switches or solenoids. That may be true of low power solid state devices, but my experience is that it's a different story with high power devices.

I don't have any data to back me up, but I'd be more inclined to trust a high quality marine switch or solenoid over a solid state device that's switching a couple hundred or more amps.

T.
 
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Jan 28, 2007
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80 in Utah, 100 in Fairbanks, AK
In the end I decided to do a brute force version that requires me to choose how my system is configured on any particular day. In general I set them as:

Day to day driving - Batteries in parallel both charge/discharge.
Camping running accesories but not the engine - Bat 1 on the house load, Bat 2 off.
Winch load1 - Batteries in parallel and engine running
Winch load2 - Bat 1 house, Bat 2 winch
Winch load3 - Bat 1 winch, Bat 2 house

The advantage? I can configure it on the fly to meet pretty much any requirement. The wiring is pretty straight forward.

YMMV

Could you share your simple wiring setup? I'm wondering how you have your switches set up to have all those options easily at hand. (I'm setting up my duals now, and am trying to figure out te best option.)

I'm also concerned about continuously charging my 2nd battery, which I will only use for house circuits (fridge, lights, electric blanket) while out camping, so I am not adverse to having a manual switch to isolate the 2nd from the alternator when not using it at all.
 
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[/INDENT]How it works...
I have the Single Rectifier Unit, (think direction or current flow)which isolates the main battery from the aux battery. It does NOT isolate the aux battery from the main battery.

Another way of saying this is the aux battery can and is feeding the main battery as well as everything connected to the main battery. In contrary the main battery cannot feed the aux battery...​


What model (amps?), and how much was the Mobi-arc rectifier? It is not listed on their web page.​
 
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I don't have any data to back me up, but I'd be more inclined to trust a high quality marine switch or solenoid over a solid state device that's switching a couple hundred or more amps.

T.

To each their own :)

My reasoning is no moving parts = less wear. But yes, everything is subject to failure.

That's the reason I went with the isolator only, not combiner. Thus no switching is involved, niether high nor low current switching.

The model I went with is a 200 amp single rectifier isolator. I think it's roughly 310 bucks. I got mine for a little cheaper because it was one of the very first production models.
 
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The model I went with is a 200 amp single rectifier isolator. I think it's roughly 310 bucks. I got mine for a little cheaper because it was one of the very first production models.

Let me be sure that I understand this...
* You paid $310 for a device that does not allow you to combine the batteries for winching.
* You paid $310 for a device that will let you run down both batteries as in the radio example you cited.
* You paid $310 for a device that will only handle 200 amps (not enough for winching even if you *could* combine batteries with it.)
* You paid $310 for an early production model and we would likely have to pay more to get this 'state of the art' device.


To each their own :)

You've got that part right.

-B-
 
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Grench

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Requested link...

Could you share your simple wiring setup? I'm wondering how you have your switches set up to have all those options easily at hand. (I'm setting up my duals now, and am trying to figure out te best option.)

I'm also concerned about continuously charging my 2nd battery, which I will only use for house circuits (fridge, lights, electric blanket) while out camping, so I am not adverse to having a manual switch to isolate the 2nd from the alternator when not using it at all.

Sure. Its in the FAQ. I'm about the 7th or so example down the list.
https://forum.ih8mud.com/showthread.php?t=104630&highlight=dual+battery+faq
 

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