Dual Battery Setups! Let's see them! Multiple Batteries Thread!

Thanks!
Unfortunately not. No build thread.

 

Not too comfortable modifying anything under the hood to this extent myself. Does anyone know of a place in the Los Angeles or Bakersfield areas that could handle the install?

 

Has anyone install a D.C. To D.C. Charger to optimize battery charge to 100% especially for the auxiliary battery. Newer vehicles that is more fuel-efficient run the alternators at 13.8 V when you really need 14.8 to charge a battery probably. Any thoughts on this.

 

First point to make. It's always the case that a lead acid battery has specific states during a charge profile that must be met.

Normally cars provide a constant voltage around 14.4V, which is not really a true bulk, absorption or float. The battery voltage is never tapered so it's allowed as much current as it wants initially, like bulk, and current tapers in absorption only as its internal resistance increases. Ideally during absorption the voltage also tapers down to float as the battery state of charge increases, where the battery can sit indefinitely.

This is the problem with 1-stage dumb chargers, you never really achieve 100% but at the same time may be too high to let sit for prolonged periods. Since you need a higher bulk voltage to force the current and a longer float period to really charge a battery (e.g. the 3-stages). If they were to use a higher voltage (14.8V usually) for a true bulk then it would tend to overcharge the battery and cause them to boil on a highway road trip. So they picked a voltage that won't hurt too much to leave on it for hours while still returning as much energy as possible as quickly as possible.

To prolong your battery(s) life you should consider doing a good charge once in a while no matter what kind of alternator your vehicle has. What I do is about once a month I put my batteries on a good overnight charge using a smart charger. Mine is a Minn Kota MK106D. If you don't over time your battery capacity slowly degrades. When it's brand new a full charge 100% point is what it is (measured as open circuit voltage, amp-hours, cranking amps, etc). If you always just take it to 95% state of charge then it's new full point isn't the original 100% anymore. This slow decline in condition continues down until the battery fails.

Not saying doing a good charge means your battery never fails, but it will increase its useful life. There's no reason a lead acid battery should only last 3 or 4 years chemically. Some battery banks can last a decade when the conditions are more controlled and good charging is done (marine, solar systems, etc). In our cars batteries are subjected to temperature extremes, mechanical shock, hard discharges (starting, winching, slow drain by the ECU, fridge) so they aren't going to last as long even with perfect charging. But by doing periodic maintenance charges you might get an extra year or two from a battery. I usually get about 6 or so useful years from a Red Top. The Odysseys I have now are only a year or so old, so lifespan remains to be seen.

Now seeing 13.8V in a car means you're using a smart alternator. What is going on is the car knows the battery is done charging as much as it going to and it's OK to roll back the alternator to a float voltage instead of normal charging. The theory behind this is you save a little bit of energy and thereby reduce the amount of drag the alternator puts on the engine. This is small relatively speaking but when you've squeezed efficiency in other places a few percent here and there starts to add up.

Do a lot of cars have them now? I don't know but I don't really keep up. I'd guess the high efficiency cars probably do and possibly high end cars. Do the new Tacomas do this? Also keep in mind that it's possible that a particular new car doesn't have a lead acid battery, so the charging parameters and profile might be changed for LiFePO4 or other chemistry. I think for cost most cars still come with lead acid, though. It's hard to beat them for the energy density vs. cost. Plus they are highly recyclable so the materials are renewable, so to speak.

The smart alternator/regulator technology has existed for a few years. Balmar, for example, makes all different kinds of regulators to do this and some that can retrofit existing alternators to do multistage charging.

http://www.balmar.net/?page_id=15145

Either way, in the case of a smart alternator you probably wouldn't want to indiscriminately parallel the aux battery to the one that the ECU or smart regulator is using to set alternator status. Although depending on what the logic is doing it may see the multiple batteries lumped and still decide to go into float only when both are charged. Hard to say without knowing the logic. It may be sensing terminal voltage, current in/out, etc. If the system is measuring the current to the battery then it would not adjust for the second battery. If it's reading bus voltage it may not care when you add the second battery and as long as there's not much voltage difference between the two then it will correctly stay in the state to charge both well enough.

So my $0.02 to your question, if you have a smart alternator then you probably are right to be careful about just randomly adding a dual battery.

You could add a battery-to-battery charger as you mention, to compensate for the dip in alternator voltage. But the problem with this is during the period when the alternator is rolled back it also won't be making much power so even if you boost the voltage it may still not source the necessary current to really do bulk or absorption. The only advantage to this is that if you boost the voltage at least the aux battery wouldn't try to equalize down, so it won't get any lower in charge and may slowly recharge.

Or it may be fine, it will fully recharge. Depends on how much energy is available from the charging system. Running the battery-to-battery may also force the smart alternator to go back up based on the system load. It would need to do this anyway if you have a high drain on, seat warmers, headlights, etc.

Another problem is if you're using an voltage-sensing isolating relay it may try to disconnect when the alternator goes into float or it may just confuse it such that it oscillates between open and closed.

I think if your truck has a smart alternator then you need to really go back to the drawing board, possibly adding a second alternator that you control for your aux/house battery. Or trick the ECU into staying at 14.4V while you charge the aux battery (be that directly on the alternator bus or with a battery-to-battery charger).

 

Speaking of voltage sensing/isolating relays, I have been manually separating (putting the ML-ACR switch into the off position) before doing a maintenance charge. Charging each Northstar individually overnight with a smart charger (CTEK MUS 4.3). I am wondering if it is necessary to do them individually to get the best out of the charger and battery life.

The information you've added to this thread is great BTW.

 

Using a smaller charger (such as my MK106D or your CTEK) I keep them isolated.

Usually my MK106D will only take 15 or 30 minutes to get to the flashing green light "fully charged" status and I figure that's good enough. It got across a 6A/14.8V bulk and moved through the 14.4V absorption taper to 13.4V float. After this the charger will sit for 24 hours at float, turn off and then go to solid green.

I start with the aux battery, get it to flashing green, move it to the starting battery and let it sit at float overnight. My reasoning is it's actually more abused I think. It has to do the high drain starting but also is constantly under trickle discharge from the ECU and the other little things. So it's always being forced to go up, down, a little here, a lot there. The profile is erratic.

The aux battery only gets the same small discharge and gets connected and disconnected based on my AL-MCR. Things are just more consistent and less stressful on it. It doesn't see the starter cranking impulses, the noise from the alternator is smoothed by the time relay closes.

I notice the starting battery also tends to be the one that falls faster to its stable voltage after a charge. When they were new both my Odysseys would stabilize around 12.85V (which is excellent) after a few hours off the charger. The aux still does seem to settle not far from that but my starting one has started to relax between 12.65V and 12.75V after a few hours. So I think it's wearing out faster. Now this is with it still in my truck, so I need to isolate it from the parasitic loads to really know for sure.

Whether it matters or not to charge both at the same time, I couldn't say. It probably doesn't make much difference since this is what happens in your truck. I think what you'd want to do is make sure the bulk charge current that the charger can do meets the combination of the two (or more) you have parallel. IOW, the battery manufacturers give a number that is considered the minimum for bulk, usually in some proportion to capacity (designed 'C').

It's typically 0.2C, 0.4C or something similar. This means my 6A charger will meet the minimum for a 30 A-hr battery at a 0.2C rate. My PC1400 actually want 24A to meet their 0.4C requirement ideally, so I'm already starving it technically. But I'm not charging a dead battery but conditioning one from a mostly already charged state, so I'm not too concerned. However I don't want to push it by asking it to do two at the same time.

 

Sounds like I should continue to do the maintenance charging with the batteries separated since my CTEK charger will only do 4.3 amps maximum. Thanks for the feedback.

 

Charging them isolated is probably the safer option but honestly that you do a maintenance charge at all is good even if they are parallel.

 

I had noticed that the battery monitor was showing the starting battery settling at lower voltage than the house battery. They used to settle equally when they were new. So I am hoping that the desulphating cycle the CTEK unit does will help with this. The batteries are identical in capacity and age (about 11 months).

Your comments earlier suggest that the starting battery is also more vulnerable to this so I am hopeful I can get it back to where the house battery still is.

 

You should try taking the starting battery off the load and checking it. I need to do that, too. It won't really relax to its true happy place if the parasitic loads (ECU, alarm, etc) stay on it. I don't like losing my radio presets so I'm just lazy. Ideally you should also do the conditioning charge and relaxation at room temp (25 degrees C). "Hey honey, don't touch the battery charging in the kitchen until tomorrow evening. Thanks, you're the best!"

 

Ha. This made me

I'll try pulling it so see where it settles at. Thanks.

 

So everyone is Agreeing getting a DC to DC charger to optimize the auxiliary battery charge is a waste of money. before commenting view this link http://www.australiandirect.com.au/ultimate-dual-battery-education-video

 

Maybe a time link to what you're pushing for since it's an hour long. 13:10 strats the DC-DC talk.
https://youtu.be/Z9c1hVXBggk?t=793

 

@orafrith, 66 minutes? Can you summarize your rational for adding a DC-to-DC converter for us? Are you sure you need one? You'd need to consider total power available before a DC-to-DC conversion is even useful. The main benefit to adding one would be the ability to run a proper 3-stage charger with it and thus the need to define your task here. BTW, I'm not saying you couldn't use one but you'd first usually need to have either a smart alternator or solar/wind as potential charging sources that you're trying to control. Does the new Tacoma have a smart alternator? In a normal dumb alternator system their usefulness is more limited and IMO maybe over complicating things.

 

I'm trying to put in a dual system in my '01 Tacoma SR5 to supply some electricity to the bed for heating/lighting, making the bed into a sleeping/storage platform setup. I had a few questions that I haven't been able to answer in doing research on here/the web general.

How much is the cost to do this type of project?
Is it possible to put the Aux battery in the bed? What conditions make that less/more possible? If I do put it back there, should I worry about it being where we're sleeping? Would I need a tray to store it in?
What type of Aux battery should I be using? Marine/deepcycle?
What isolator do people recommend?
I'm trying to do the total build for less than $500, do you think this is possible?

 

How much is the cost to do this type of project?

Depends on how elaborate you want to make it.

Is it possible to put the Aux battery in the bed?

Yes.

What conditions make that less/more possible?

Just running the proper gauge wire for your application.

If I do put it back there, should I worry about it being where we're sleeping?

Not really a concern for the most part.

Would I need a tray to store it in?

Would probably be a good idea.

What type of Aux battery should I be using? Marine/deepcycle?

You can use just about any type. Really depend on what you want to do with it. You can even use the more expensive LiPo batteries, but they require different chargers.

What isolator do people recommend?

There are many good options from the very simple starter solenoid to solar charge controllers. Again, it depends how complex a setup you want/need for your application.

I'm trying to do the total build for less than $500, do you think this is possible?

Yes.

 

Would you or anyone else be able to point me in the direction of a supplier I could find all/most of the things I'd need for this? either that or a parts list, as of right now I've got:
Aux battery
Aux battery tray/box
Cables
Isolater (synonymous with a solenoid?)


I'd also like to be able to power a heating blanket off of the battery, is it possible to wire an outlet to the battery?

Sorry for all the questions, I've never done anything like this before.

 

I was poking around 'cause I was thinking that, too. I saw a 12V one on Amazon that consumed 4.6A but I couldn't say how that compares heat-wise to household ones. My guess is it would be pretty small since that's only 55W. The ones for your house are probably a lot higher than this. A group 34 deep cycle is usually about 65 A-hr so it would discharge it in about 14 hours.

 

Totally agree. As it is a fridge consumes about 2A when running and my Engel runs maybe 50% duty cycle (so about 1 A-hr) when it's hot, so I get about two days normally from the battery. I'd invest in good sleeping bags. Zero power consumed and you have back-up way to stay warm if your truck breaks down or you get stuck out in the winter.

 

Hmmmm.
I would do this. My Aux Optima 27F yellow top should be able to manage 6 hours of 4.6A draw.

I do have a Mr Buddy Heater, but always leery of CO2 - probably unwarranted worry.