My Dual Battery Setup- Diagram Check

[Dusty T.]

Well, here it is.

I've spent several weeks researching and thinking about how I want my next dual battery setup to be for my "new" 2002 Tacoma. I have yet to put together a parts list, but have a pretty good idea of what I will need and where to find it. Still I have questions....

Have a look at the attached diagram below showing my proposed setup. Hopefully it makes some sense. My goal here is to not only run a dual battery system, but also allow some accessories (mainly the in-dash power plugs) C.B. and stereo to be switchable between the two batteries should I choose to remove the second battery, or decide not to draw any power from it alltogether. Here, I'm using a constant-duty solenoid to isolate and connect the batteries for charging. I went with a constant duty solenoid on my last setup without a problem- but that was on a completely different vehicle. I know some floks prefer to use isolator units.

Here's where it gets interesting......
My last dual battery setup did not incorporate running the stereo and sub off of the aux battery. This time around, I am tapping into the aux battery for stereo power for both mobile and stationary use. On this setup, I am running an override switch (via an SPDT Relay). With the override switch in the ON position, the stereo "switched" signal wire can receive power without the need to have the key in the ACC or ON position. This should elliminate the risk of running the main battery down while running the radio with the engine off. Turning the override switch to the off position will allow the stereo to resume being switched by the key in ACC or ON.

Now, for the questions..... I'm certain a couple more will come around as the project progresses!

1. Charging Power:
At the most, my Tacoma has an 80A alternator. I was looking at BajaTaco's battery setup www.bajataco.com, and it doesn't appear that he upgraded the alternator with his setup. What you see on the diagram is what I will be running the most. Putting it very simply, it's basically 200W sub, and aux battery to be charged with the occasional use of a high volume air pump (30A max). There are no plans to add lights or a winch anytime in the forseable future. I would like to hook up a 1000W inverter to the aux battery someday, but that's about all I see happening. Will the alternator need upgrading, or the "Big 3" i.e. grounds, and battery cable to be upsized? I've seen some Tacomas around the boards with fridges, lights, air pumps, radios, etc and no mention of having to run a larger alternator. Where do I draw the line here?

2. The Auxiliary Battery:
I'm looking at the Optima D31T Yellow Top (75 Ah). This will be mounted in the bed (with shell) in a Taylor aluminum battery box (provided it fits!). Not mounted under the hood. I'm not planning on being able to start my engine should the main battery fail. Would a Blue Top be a better choice? Since it is in an enclosed sleeping space I do not want a battery that offgasses. Only myself!

3. Switching The Isolating Constant Duty Solenoid:
My last setup used ignition ON to connect the two batteries. Never had a problem starting- even with a low aux battery. Has this worked fine for other Tacoma owners here? I know some people hook into the "alterntor good" circuit to close the solenoid, but I have no idea where that could be located.

4. Wire Size:
This time, I'm running #2 power and ground wire between the main and auxiliary battery posts. While this will eliminate voltage drop, won't it cause the battery to charge more quickly, thus drawing more amps from the alternator and putting unneeded stress on the battery? Or is that what the alternator's internal regulator is for? Note, I'm running relatively small 80-amp Mega fuses on each end of the wire if that should make any difference. I know this probably sounds kind of dumb, but it really goes back to the alternator output.....


Thanks for reading and input/suggestions are greatly appreciated. I'm looking forward to ordering up the parts and to begin putting this together!

 

[Switch]

Well, here it is.

I've spent several weeks researching and thinking about how I want my next dual battery setup to be for my "new" 2002 Tacoma. I have yet to put together a parts list, but have a pretty good idea of what I will need and where to find it. Still I have questions....

Have a look at the attached diagram below showing my proposed setup. Hopefully it makes some sense. My goal here is to not only run a dual battery system, but also allow some accessories (mainly the in-dash power plugs) C.B. and stereo to be switchable between the two batteries should I choose to remove the second battery, or decide not to draw any power from it alltogether. Here, I'm using a constant-duty solenoid to isolate and connect the batteries for charging. I went with a constant duty solenoid on my last setup without a problem- but that was on a completely different vehicle. I know some floks prefer to use isolator units.

Here's where it gets interesting......
My last dual battery setup did not incorporate running the stereo and sub off of the aux battery. This time around, I am tapping into the aux battery for stereo power for both mobile and stationary use. On this setup, I am running an override switch (via an SPDT Relay). With the override switch in the ON position, the stereo "switched" signal wire can receive power without the need to have the key in the ACC or ON position. This should elliminate the risk of running the main battery down while running the radio with the engine off. Turning the override switch to the off position will allow the stereo to resume being switched by the key in ACC or ON.

Now, for the questions..... I'm certain a couple more will come around as the project progresses!

1. Charging Power:
At the most, my Tacoma has an 80A alternator. I was looking at BajaTaco's battery setup www.bajataco.com, and it doesn't appear that he upgraded the alternator with his setup. What you see on the diagram is what I will be running the most. Putting it very simply, it's basically 200W sub, and aux battery to be charged with the occasional use of a high volume air pump (30A max). There are no plans to add lights or a winch anytime in the forseable future. I would like to hook up a 1000W inverter to the aux battery someday, but that's about all I see happening. Will the alternator need upgrading, or the "Big 3" i.e. grounds, and battery cable to be upsized? I've seen some Tacomas around the boards with fridges, lights, air pumps, radios, etc and no mention of having to run a larger alternator. Where do I draw the line here?

2. The Auxiliary Battery:
I'm looking at the Optima D31T Yellow Top (75 Ah). This will be mounted in the bed (with shell) in a Taylor aluminum battery box (provided it fits!). Not mounted under the hood. I'm not planning on being able to start my engine should the main battery fail. Would a Blue Top be a better choice? Since it is in an enclosed sleeping space I do not want a battery that offgasses. Only myself!

3. Switching The Isolating Constant Duty Solenoid:
My last setup used ignition ON to connect the two batteries. Never had a problem starting- even with a low aux battery. Has this worked fine for other Tacoma owners here? I know some people hook into the "alterntor good" circuit to close the solenoid, but I have no idea where that could be located.

4. Wire Size:
This time, I'm running #2 power and ground wire between the main and auxiliary battery posts. While this will eliminate voltage drop, won't it cause the battery to charge more quickly, thus drawing more amps from the alternator and putting unneeded stress on the battery? Or is that what the alternator's internal regulator is for? Note, I'm running relatively small 80-amp Mega fuses on each end of the wire if that should make any difference. I know this probably sounds kind of dumb, but it really goes back to the alternator output.....

Thanks for reading and input/suggestions are greatly appreciated. I'm looking forward to ordering up the parts and to begin putting this together!

Caveat: I would not call myself an expert on dual batteries but I did a lot of reading before doing mine and it has been working fine for the past year. The write ups I did on the ttora web site include alot of links to other projects that may help you in your research (links at bottom). In general your set up seems more complicated than it needs to be given your goals. Two Odessey 1200's will fit in the stock location (I'm pretty sure two Optimas can fit the stock location too, not sure what size). Also you if run two deep cycle batteries, you can just run everything off of one battery and have the second battery just as a backup. This will greatly simplify wiring and switches - the money saved could go into two matching batteries, a better isolator, higher quality wire, and higher quality switches. If you locate the 2nd battery in the engine bay, you can use the factory ground point and it won't take up space in the bed. If you are particulary concerned about draining the battery down completely (not good for any battery) there are products that can shut off the load when the battery drains to a certain point (like this: http://www.colehersee.com/pdf/hot_feed/D-614_LowVoltageDisconnect.pdf
). I supose you already know all of this, so I'll stick to addressing your questions.

1: Charging power: The issue with a smaller alternator is that it will run at it's max output more frequently (if you drain battery down alot or have lots of auxilary stuff). So it will not last as long. Whether you need "Big 3" or not depends on the amount of current you are using at any one time. If you use more than 80A your battery will drain down while your alternator works as hard as it can.

2: Blue top: A yellowtop will do just fine. Gases are not an issue with either.

3: Switching: For various reasons I won't go into, a simple solenoid is not the best choice - there are better options on the market, all cost more money. I looked into serveral isolators before going with Hellroaring (not inexpensive). There are isolators designed to switch based on voltage levels of the respective circuits, have overide switches, and are designed for voltage sensing alternators. If you prefer solenoid based isolators, the Surepower Battery Separator 1315-200 comes to mind. Less wire, less work, better functionality.

4: If you put 2nd battery in bed, you will still get some voltage drop due to the lengh of wire needed, about .1 to .25V depending on wire length (see http://www.bcae1.com/wire.htm). Also you should be able to find out the max charging current draw from Optima's website. A good isolator will make this consideration a non-issue.

General comments:
I noticed that you plan to use a fuse block with a negative buss. That seems like extra work and wire given that there are plenty of factory ground points on the truck. Consult the the factory service manual for ground point locations.

Connecting the batteries at the negative terminals with a #2 wire would not be necesary if you had a good ground point closer to the second battery. This will also reduce voltage drop.

You don't need #2 wire to the battery selector switch if #8 is sufficent for your aux fuse block.

These links have my write ups and references: dual battery and aux fuse block, and aux switch panel:

Hope this helps, be sure to post up pics when you are done.

 

[keezer36]

If you don't have one already, here's a wire sizing chart: http://www.rbeelectronics.com/wtable.htm. Though I no longer have the reference, I know that these numbers are intentionally conservative.

My two cents is to save money using the wiring required and buy a good isolator. I too have a Hellroaring and bought their remote switch. They have a variety of diagrams for various setups. Just mind the diode configurations on the different isolators for what you want to do.
Mike at Hellroaring is good about emailing back and providing all the info you need for a successful job.

Backup configuration with parallel #4 from the backup to #1 to the starter solenoid.

Excuse the woodworking skills, one eye is lower than the other. The hole was for a switch for a harebrained idea I had before I took a good look at the diodes of the 300 isolator.

In auto position, the LED will stay on after you shut the motor off as long as you have a surface charge. A good way to gauge the condition of your battery. I set the switch in one of my blanks.

Next up is a Tripp Lite 1000W inverter.

 

[Dusty T.]

1: Charging power: The issue with a smaller alternator is that it will run at it's max output more frequently (if you drain battery down alot or have lots of auxilary stuff). So it will not last as long. Whether you need "Big 3" or not depends on the amount of current you are using at any one time. If you use more than 80A your battery will drain down while your alternator works as hard as it can.

2: Blue top: A yellowtop will do just fine. Gases are not an issue with either.

3: Switching: For various reasons I won't go into, a simple solenoid is not the best choice - there are better options on the market, all cost more money. I looked into serveral isolators before going with Hellroaring (not inexpensive). There are isolators designed to switch based on voltage levels of the respective circuits, have overide switches, and are designed for voltage sensing alternators. If you prefer solenoid based isolators, the Surepower Battery Separator 1315-200 comes to mind. Less wire, less work, better functionality.

4: If you put 2nd battery in bed, you will still get some voltage drop due to the lengh of wire needed, about .1 to .25V depending on wire length (see http://www.bcae1.com/wire.htm). Also you should be able to find out the max charging current draw from Optima's website. A good isolator will make this consideration a non-issue.

General comments:
I noticed that you plan to use a fuse block with a negative buss. That seems like extra work and wire given that there are plenty of factory ground points on the truck. Consult the the factory service manual for ground point locations.

Connecting the batteries at the negative terminals with a #2 wire would not be necesary if you had a good ground point closer to the second battery. This will also reduce voltage drop.

You don't need #2 wire to the battery selector switch if #8 is sufficent for your aux fuse block.

These links have my write ups and references: dual battery and aux fuse block, and aux switch panel:

Hope this helps, be sure to post up pics when you are done.

Hey, thanks for the links and input.

I'm am still on the fence as far as going again with a solenoid (though there were no problems with my last setup), or the isolator. I'll spend some more time looking into it, though. The Surepower sounds like a good alternative from what I researched on bajataco's site. The solenoid setup doesn't appear to be too popular with the tacoma crowd, but I really do like it's simplicity, but dislike the risk of killing BOTH batteries should the alternator fail.

Should have cited some of my sources, but I've spent the last few weeks reading through a number of the links you sent, and will most likely re-read them again! The bcae site was a great source for helping me size up wire.

I am pretty set on mounting the battery in the bed. Underhood would probably be optimal, but I just don't have the means to fab up a battery bracket. I feel silly enough as it is paying for an aluminum battery box, when I could make my own in a machine shop.

Could you clarify grounding the aux battery? From what I'm reading, it sounds like I should just ground it to the frame. I did this last time, but felt that the frame connection would corrode too easily, or come loose. That, and I would probably need to upsize the ground wire off the main battery as well. Sorry if I'm missing your point.

Back to making adjustments.

Thanks

Dusty

 

[Dave Bennett]

Great thread! :lurk:

 

[Terracoma]

Subscribed.

... Hey, pass the popcorn!

:lurk:

 

[Dusty T.]

3: Switching: For various reasons I won't go into, a simple solenoid is not the best choice - there are better options on the market, all cost more money.

I got to thinking about the above and wanted to pick your brain a bit about why the solenoid is not the optimal choice? By the way, I must give you props on your system- the workmanship looks very well done. Seeing photos of a quality finished product is always inspirational!

I've read a couple arguments both for and against using an isolator vs. a solenoid. To generalize, it seems that the isolators initiate a voltage drop to the battery being charged due to the isolator's internal diodes. Now, this doesn't seem to be the case so much with the Hellroaring unit if I read their material correctly. The advantage I see with the isolator is the ability to monitor the second battery (via LED indicator lights), start the engine off the aux battery (not a critical feature for me), and reduce the risk of running both batteries down should the alternator fail (a good feature).

Of course, the arguments I've read regarding using the solenoid is it's simplicity. Should it fail, it will simply open the circuit and isolate the battery. Now looking over my schematic, you can see I would be able to override that with the manual Blue Sea switch should the solenoid fail.... Either way, my budget isn't terribly tight since I want this system to be as trouble-free for years as possible.

In the meantime I'll read a little further on these isolator units, and make a final determination as to whether the alternator will do the trick. I guess those are my main two concerns.

Oh, and glad to see we have an audience here! :clapsmile

I'll be sure to post pics when this system is finished in the next few months!

Thanks

Dusty

 

[Switch]

I got to thinking about the above and wanted to pick your brain a bit about why the solenoid is not the optimal choice? By the way, I must give you props on your system- the workmanship looks very well done. Seeing photos of a quality finished product is always inspirational!

I've read a couple arguments both for and against using an isolator vs. a solenoid. To generalize, it seems that the isolators initiate a voltage drop to the battery being charged due to the isolator's internal diodes. Now, this doesn't seem to be the case so much with the Hellroaring unit if I read their material correctly. The advantage I see with the isolator is the ability to monitor the second battery (via LED indicator lights), start the engine off the aux battery (not a critical feature for me), and reduce the risk of running both batteries down should the alternator fail (a good feature).

Of course, the arguments I've read regarding using the solenoid is it's simplicity. Should it fail, it will simply open the circuit and isolate the battery. Now looking over my schematic, you can see I would be able to override that with the manual Blue Sea switch should the solenoid fail.... Either way, my budget isn't terribly tight since I want this system to be as trouble-free for years as possible.

In the meantime I'll read a little further on these isolator units, and make a final determination as to whether the alternator will do the trick. I guess those are my main two concerns.

Oh, and glad to see we have an audience here! :clapsmile

I'll be sure to post pics when this system is finished in the next few months!

Thanks

Dusty

Thanks, the credit goes to the guys that wrote up their projects online and Al at Arc Battery in Sausalito who helped me with selecting many of the components.

I can’t say I have my own opinions as much as I’ve relied on that of others. The reasons I went with the Hellroaring are the reasons you cited. I would have used the Surepower solenoid but it was too large to fit in the available space.

Making a dual battery mount for the stock location would not be that hard. (for an example see CNADNtacoma’s write up
http://www.ttora.com/forum/showthread.php?t=52489).
That said, one advantage of locating your battery in the bed is that you can mount larger batteries in both locations.

For grounding the #2 battery, just ground to frame. No need to run a wire back to engine bay.

BTW, I can say from experience that the painless performance fuse blocks are junk compared to the Blue Sea.

 

[ntsqd]

Some personal experience has led me to try to always share the exact same grounding point with multiple batteries. This is considerably more important when they are wired directly in parallel, but would also apply when there is some sort of key off separation. By not sharing the same grounding point there can be a small voltage drop across the two negative battery posts. In my paralleled experience this led to spontaneous charge/discharge cycles (high battery trying to raise the low battery) that ruined one battery and hurt the other. This would still be true in a key-off separated system, though of less importance.

My next dual battery system will use a Blue Sea Automatic Charge Relay (ACR). I think the CL series will work the best for me.

If they weren't $20 each I'd only use the Anchor breakers. As it is I'll likely still use them on critical circuits.

 

[keezer36]

If you have a multimeter, check continunity between the block ground point and frame where you intend to ground. If there's no resistance, there'll be no voltage drop.

 

[ntsqd]

The problem is that even a tiny difference in potential results in the see-saw self-discharge mode. Even a 10,000 Ohms resistance results in a 1.2 mA current. That's enough to do damage if the vehicle sits for periods of time.
BT,DT.

Even crossing a weld in the frame can increase the resistance significantly. Some racer types who've moved the battery to the trunk end up with slow cranking form a battery that worked fine when in the engine bay. Once they run a ground cable up to the engine the problem disappears.
I prefer to just avoid that potential problem from the start, I can find new ones without revisiting the previous ones.

 

[Dusty T.]

I
Mike at Hellroaring is good about emailing back and providing all the info you need for a successful job.

I was looking over your setup, and was wondering which model isolator are you using? I actually spoke with Mike at Hellroaring today (nice guy), and had a couple questions about which isolator would be the best for me to go with. My thoughts were running wild last night, and I thought "how about using the aux battery as BOTH a second starting battery as well?". Mike advised against this, which makes sense, since the aux battery has the potential of being drained by accessories when it may bee needed to perform, so it is NOT completely idiotproof. Mike also mentioned that I could combine both batteries should the main battery fail, and after several minutes, this should give me enough charge to start up the engine. I'd say that's good enough for me. If worse came to worse, I like bringing a 50W solar panel in the backcountry with me anyway to charge the aux battery while out for a day hike.

Now I've gone around and around between going with the solenoid and solid state isolator. The biggest plus I see with the Hellroaring (and perhaps others) is their feature which isolates both batteries automatically should the alternator fail. That's what really attracts me toward using their product.

With regards to the negative wire- I'm pretty set on running the negative cable back to the main battery. I have a slight suspicion that my old aux battery setup may have caused the radiator to prematurely corrode on my Ranger, due to the lack of proper grounding paths for my battery and some accessories (electrolysis). It's just a very slight suspicion.

What really has me paralyzed in the design/decision phase of this project, is determining what size wire and fuse combo to run to the aux battery. Since the battery will certainly be bed-mounted, #2 AWG looks like a good choice to cover the ten to twelve foot distance with minimal voltage drop. The 80 amp or smaller fuse would prevent too much current from flowing, but wouldn't it blow when trying to charge a discharged battery since #2 wire is good up to 200 amps?

Talking with Mike from Hellroaring (hopefully I'm not twisting his information around here), he recommended a smaller gauge wire, i.e. #8 as a charging wire for the aux battery. This would prevent the battery from drawing more current during its charge cycle, which could overwork my 80-amp alternator- supposing it is 80 amps. I would like to use the Optima D31T rated at 75 amp hours. I also called Optima and asked about the required amps to charge this battery should it be completely discharged. I didn't get a very direct answer, but their tech guy thought my alternator would do just fine.
Sorry if this sounds ridiculous, but I'm stumped on what size wire to go with, especially if I want to use the charging wire to also power some accessories up front in the cab without incurring too much voltage drop.

 

[keezer36]

I bought the 95300B. If your main concern is running the aux stuff and don't mind waiting for a charge if your main battery goes dead, I do believe the 95150 is the proper buy. The "A" or "B" afterwards is if the unit has the sense resistor built in (cleaner look).

No, it is not idiotproof. Hence the hole drilling in the side of my box for a BlueSea switch thinking I could get the best of both worlds until I took a good look at the diode configuration of the two different models. With the 95300, you have to run your aux stuff off the engine bay battery.

Mike told me that for a backup battery, run the negative to the engine block where the cranking battery's negative is mounted. For an aux battery, the frame is okay. This, he went on to say way due to the the higher current draw of cranking. He did add, if I had a good current path, engine to frame, I could ground to the frame for a backup configuration. So I connected a wire to the ground point on the block, crawled back to where I wanted to ground on the frame and checked continunity with my Fluke multimeter. I got zip, no resistance at all so I went with the frame. Perhaps I'm still missing something here but...Google Ohm's Law Wheel or verify with Mike. I don't think you need to go back to the engine for an aux setup but it can't hurt, that's for sure.

Fuse: Bounce this off Mike, but if I remember right, as an aux battery setup, use 8 AWG for 15-20 ft. and an 80 amp fuse. This will, of course have waiting to charge a dead cranking battery which you've said you're okay with.

When you get indirect answers from techs, it's been my experience that they just don't want to say "I don't know".

I'm not real hip on alternators, but it's my understanding that anymore they have circuit protection from being overworked.

I really recommend using Hellroaring's electrical drawings.

 

[ntsqd]

V = Volts
I = Current
R = Resistance

V = I * R

R = V/I

I = V/R

Note with this last version of the formula that a tiny resistance results in a large current.
E.G. 12 volts, 1 Ohm; 12/1 = 12 amps
but that a large resistance results in a tiny current. Seems logical.
12 volts, 10,000 Ohms; 12/10,000 = .0012 amps

However, in the case of a small resistance between two grounding points the full battery voltage would not be applied, so the current will be less than it would be if the full battery voltage were applied.

With any method that separates the batteries when the vehicle is sitting this isn't so much of an issue. It would only matter during charging and might result in one battery being slightly less charged.
In my case the OE dual battery wiring had no such separation provision.


If the 8 ga. wire will support the max charge over the distance involved, why would you need a larger cable? Do you plan to discharge that battery at rates higher than 80 amps?

 

[Switch]

If you have a multimeter, check continunity between the block ground point and frame where you intend to ground. If there's no resistance, there'll be no voltage drop.

X2 on that. If you run a #2 copper wire to a common ground point, you have the resistence of the wire to worry about. Not an issue for short lenghts but with the 2nd battery in the bed, you are talking about ~.10V drop on a +10ft wire. I'm inclined to think that the frame would offer less resistance than an #2 copper wire. MTC