Dual Battery System (1 Viewer)

[xplorerlc200]

I am in Southern Arizona and have a 2019 - LC200 with what I thought would be a pretty good Dual Battery Setup. The main objective was to be able to power the ARB Classic Series II 63QT Fridge utilizing the Transit Bag, ARB Lights which are rarely used, a winch which has yet to be used and a few small accessories such as USB Plugs in the rear and not put any stress on the Starter Battery. I am using 8 Gauge Wire for my Fridge and 8 Gauge Wire for the Blue Sea System Fuse Block in the Rear. I am using the OEM Panasonic Battery for the Starter Battery and an Odyssey Extreme Group 35 - 35-PC1400 for my Auxiliary Battery. The two batteries are linked with a REDARC BCDC1240D.

Everything appears to be functioning well and there are no error codes. I have tried setting the ARB Fridge Battery Monitor on Low and Medium settings and the bottom line is that I am lucky if I can get the Fridge to run for 24 Hours without the Odyssey Battery being complexly drained.

My mind keeps swirling with the following thoughts and I wanted to reach out to get some opinions:

1. Maybe this is how things are due to using a Medium Sized Auxiliary Battery? - 20 Hr - AH - 65 and 10 Hr - Ah - 55

2. Maybe this is how things are being that it is over 100 Degrees every day and when the Truck is simply sitting during the day, it is baking inside at 120+ Degrees.

3. Maybe this is how things are being that I have a very short commute to work - 6 miles and the Truck sits all day and then gets driven 6 miles home at the end of the day?

4. I have the Fridge set to 37 Degrees and leave it on 24/7. Maybe this is too much?

5. Should I have used a BCDC1225D instead? From reading the Odyssey Battery literature, they suggest that their batteries should be charged at 40A so the BCDC1240D seemed like a logical choice. I should mention that I am using Profile A on the BCDC1240D - Maximum Voltage is 14.6V. This seems to align with what both REDARC and Odyssey recommend.

6. Should I try to use the OEM Battery Location - Group 31 as my Auxiliary Battery Location and use the Group 35 Battery area as my Starter Battery? - I have been advised by a very reputable Off-Road Store not to go this route.

7. Should I integrate a small Solar Panel on the Roof? If so, which one should I use?

8. Should I be running a three battery system with a dedicated battery in the rear for the fridge? This doesn't seem ideal to me, but I am throwing out all thoughts.

Maybe everything is just fine and this is how things are when you live in the 100+ Degree climate and only drive 12 miles a day. It should be noted that even on the days that I drive a little further, I roughly see the same results.

One other thing I should mention is that I Hard Wired a NOCO GENIUS2D to the Odyssey so it could charge at night, but that seems to be worthless. What do I know, but 2A just does not seem to be enough.

One more thing to mention is that I have put a meter on both batteries and they both read as Good.

On a final note and completely different topic, my Winch is hooked up to the Auxiliary/Odyssey Battery. As stated above, the Winch has never been used so no strain has been put on the Auxiliary/Odyssey Battery. I have heard differing opinions on whether or not the Winch should be hooked up to the Starter or Auxiliary Battery. Your thoughts?

I appreciate all input and look forward to your responses.

 

[sdnative]

A few different things going on here.

That fridge will draw about 5A when the compressor is running. I have the 50qt with transit bag and on a 70-75 deg day it will run about a 20% duty cycle (compressor running 20% of the time). So that will add up to ~1 Ah every hour or 24Ah per day. If it is very hot, the compressor will run more than 20% of the time so the Ah could be significantly more.

Your battery is rated at 65Ah (20hr) , but only about 50% of that is actually usable due to the high Peukert exponent associated with lead acid batteries, so realistically you will get about 35Ah until it is considered discharged.

Based on these two conditions it could very well be reasonable that you are getting 24 hours out of the fully charged battery before it is discharged.

I think the BCDC1225D would be better suited for that battery, but the 1240D should work if you already have it.

I have seen people switch the starting battery to the PS and put a group 31 on the DS. This would be a good way to go if you are planning on running two LA batteries to power your fridge and house loads under those conditions for more than a day at a time.

 

[spressomon]

Per above: You need more charging ability than your alternator can provide given you only drive 12-miles a day. And you need more battery storage capacity to provide enough amps to run your fridge...longer than 24-hours or however long you sit w/o charging batteries.

I'm old school and don't know a thing about the smart alternator/electrical systems apart of modern vehicles but swapping batteries to get a Group31 for aux battery system needs sounds like a no brainer.

Invest in a real dual output battery charger & maintainer. I use this one (V1 for 10-years or more...) and it works great for keeping my Odyssey batteries in tip-top shape: Powermania Turbo M220 (V3) 20 Amp 2-Bank - https://www.defender.com/product.jsp?id=6856789 For AGM, you can't rely on the alternator to get them to 100% capacity...etc. I'd wager your not getting your Odyssey AGM much north of 50% given your 12-mile daily charge regiment. Even for longer drives the best you will typically see is 80% ala the alternator.

Solar could be an answer for providing more current generating capacity but many variables to consider...the first being how much direct sun do you see on a consistent basis? What do you have on the roof now? Consider Merlin semi-flex panel if it has to be mounted atop an RTT for example. Otherwise go glass mono...about $1/watt these days. Get a Victron Smart controller to be the brains between the PV panel and the battery (charge & maintain algorithms provided for most any type of battery including LA, AGM, LFP, etc.). The Victron MPPT controller works for portable set-up. I'm not up on the REDARC unit but see it too functions as a solar controller...

A 3rd battery, 75-100Ah LFP, could be a good strategy to consider for powering the fridge. A Battleborn 100Ah has a BMS that cuts charge to the LFP if too cold (typically ~ 32F). That would provide 80A of current on a regular basis assuming you deploy a different charging strategy than 12-miles/day from the alternator.

The problem with most DC-DC chargers: Before current is pushed to the aux battery/batteries the house battery needs to be fully/near fully charged (at least that is how my Sterling operates). So, using your 12-mile commute as the example, I doubt your main/starting battery is getting to 90/100% SOC to allow much current to push to your aux/Odyssey. What is the resting voltage of your Odyssey after your commute (wait an hour or so before measuring)?

 

[FrazzledHunter]

A few different things going on here.

That fridge will draw about 5A when the compressor is running. I have the 50qt with transit bag and on a 70-75 deg day it will run about a 20% duty cycle (compressor running 20% of the time). So that will add up to ~1 Ah every hour or 24Ah per day. If it is very hot, the compressor will run more than 20% of the time so the Ah could be significantly more.

Your battery is rated at 65Ah (20hr) , but only about 50% of that is actually usable due to the high Peukert exponent associated with lead acid batteries, so realistically you will get about 35Ah until it is considered discharged.

Based on these two conditions it could very well be reasonable that you are getting 24 hours out of the fully charged battery before it is discharged.

I think the BCDC1225D would be better suited for that battery, but the 1240D should work if you already have it.

I have seen people switch the starting battery to the PS and put a group 31 on the DS. This would be a good way to go if you are planning on running two LA batteries to power your fridge and house loads under those conditions for more than a day at a time.

Why do you think the 1225D would be better suited? Is it perhaps different charging rates?

I have the REDARC 1225D and Odyssey 35-PC1400 battery combo. I recall reading that using the 1240D wasn't recommended for this as the 1240D could charge it too fast generating excessive heat. Sorry I can't find my source for that recommendation at the moment.

 

[e9999]

(I'm assuming your starter battery does not drain into the house one with engine off)

Seems normal to me. Big fridge, high temps, smallish house battery, little recharge time. Can't beat thermodynamics, sadly...
You need more energy from somewhere.

 

[sdnative]

Why do you think the 1225D would be better suited? Is it perhaps different charging rates?

I have the REDARC 1225D and Odyssey 35-PC1400 battery combo. I recall reading that using the 1240D wasn't recommended for this as the 1240D could charge it too fast generating excessive heat. Sorry I can't find my source for that recommendation at the moment.

Too much charge current will generate heat and create a less efficient charge (lower energy density). The Peukert exponent is a significant factor here for LA I believe, much less so for LFP. There are curves, at least for lithium chemistries, that show the effect of charge C-rate on energy density.

I would stay under 0.4C or even 0.33C with LA. You can go up to 0.5C and sometimes 1.0C with lithium chemistries.

The 1225 should be good for batteries up to 100Ah, which is pretty much all automotive batteries up to group 31.

 

[FrazzledHunter]

Too much charge current will generate heat and create a less efficient charge (lower energy density). The Peukert exponent is a significant factor here for LA I believe, much less so for LFP. There are curves, at least for lithium chemistries, that show the effect of charge C-rate on energy density.

I would stay under 0.4C or even 0.33C with LA. You can go up to 0.5C and sometimes 1.0C with lithium chemistries.

The 1225 should be good for batteries up to 100Ah, which is pretty much all automotive batteries up to group 31.

Thanks I thought heat was at least part of the issue. I was all set to get the 1240D because, well, bigger is better right?

These sources also discuss the recommended charger. REDARC recommends the 1225D over the 1240D based on battery size but doesn't say exactly why. The other article mentions that the battery can be harmed. I'm not sure just how hot an AGM battery would have to get before it's damaged, however.

"The size of BCDC you choose to install will depend on the size of the auxiliary battery(s). For a single auxiliary battery (75 to 200Ah) REDARC recommends installing a BCDC1225, where as if your auxiliary battery bank is 200Ah or larger REDARC recommends installing a BCDC1240."

BCDC1225 or BCDC1240 | REDARC Electronics - https://www.redarc.com.au/forum/discussion/244/bcdc1225-or-bcdc1240

"Sometimes the biggest and angriest charger you can get your hands on isn’t always the best, and this simple mistake is killing your batteries by pushing too many amps into them… without you even realising!"
How to stop killing your batteries! - Pat Callinan's 4X4 Adventures - https://mr4x4.com.au/how-to-stop-killing-your-batteries/

 

[xplorerlc200]

A few different things going on here.

That fridge will draw about 5A when the compressor is running. I have the 50qt with transit bag and on a 70-75 deg day it will run about a 20% duty cycle (compressor running 20% of the time). So that will add up to ~1 Ah every hour or 24Ah per day. If it is very hot, the compressor will run more than 20% of the time so the Ah could be significantly more.

Your battery is rated at 65Ah (20hr) , but only about 50% of that is actually usable due to the high Peukert exponent associated with lead acid batteries, so realistically you will get about 35Ah until it is considered discharged.

Based on these two conditions it could very well be reasonable that you are getting 24 hours out of the fully charged battery before it is discharged.

I think the BCDC1225D would be better suited for that battery, but the 1240D should work if you already have it.

I have seen people switch the starting battery to the PS and put a group 31 on the DS. This would be a good way to go if you are planning on running two LA batteries to power your fridge and house loads under those conditions for more than a day at a time.

Per above: You need more charging ability than your alternator can provide given you only drive 12-miles a day. And you need more battery storage capacity to provide enough amps to run your fridge...longer than 24-hours or however long you sit w/o charging batteries.

I'm old school and don't know a thing about the smart alternator/electrical systems apart of modern vehicles but swapping batteries to get a Group31 for aux battery system needs sounds like a no brainer.

Invest in a real dual output battery charger & maintainer. I use this one (V1 for 10-years or more...) and it works great for keeping my Odyssey batteries in tip-top shape: Powermania Turbo M220 (V3) 20 Amp 2-Bank - https://www.defender.com/product.jsp?id=6856789 For AGM, you can't rely on the alternator to get them to 100% capacity...etc. I'd wager your not getting your Odyssey AGM much north of 50% given your 12-mile daily charge regiment. Even for longer drives the best you will typically see is 80% ala the alternator.

Solar could be an answer for providing more current generating capacity but many variables to consider...the first being how much direct sun do you see on a consistent basis? What do you have on the roof now? Consider Merlin semi-flex panel if it has to be mounted atop an RTT for example. Otherwise go glass mono...about $1/watt these days. Get a Victron Smart controller to be the brains between the PV panel and the battery (charge & maintain algorithms provided for most any type of battery including LA, AGM, LFP, etc.). The Victron MPPT controller works for portable set-up. I'm not up on the REDARC unit but see it too functions as a solar controller...

A 3rd battery, 75-100Ah LFP, could be a good strategy to consider for powering the fridge. A Battleborn 100Ah has a BMS that cuts charge to the LFP if too cold (typically ~ 32F). That would provide 80A of current on a regular basis assuming you deploy a different charging strategy than 12-miles/day from the alternator.

The problem with most DC-DC chargers: Before current is pushed to the aux battery/batteries the house battery needs to be fully/near fully charged (at least that is how my Sterling operates). So, using your 12-mile commute as the example, I doubt your main/starting battery is getting to 90/100% SOC to allow much current to push to your aux/Odyssey. What is the resting voltage of your Odyssey after your commute (wait an hour or so before measuring)?

I definitely agree with many of your comments. In reading through the ARB Manual, they advise not using a High Output Charger on the House battery that powers the fridge as it could cause some issues. I was advised that I could try a 10A Charger on the Starter Battery which would then flow the energy through the BC1240D and charge the House Battery. I did try that today and it did charge both batteries.

 

[xplorerlc200]

Why do you think the 1225D would be better suited? Is it perhaps different charging rates?

I have the REDARC 1225D and Odyssey 35-PC1400 battery combo. I recall reading that using the 1240D wasn't recommended for this as the 1240D could charge it too fast generating excessive heat. Sorry I can't find my source for that recommendation at the moment.

I was thinking the BCDC1225D would be better suited as it will charge more slowly. I have read the same material you have and REDARC absolutely recommends the BCDC1225D for anything under 100Ah. Interestingly enough, I called REDARC today as they have a US Number that transfers the call to Australia and they advised that although the BCDC1225D may be the best alternative, that is not an absolute answer. What the gentleman told me, was that it really depends on what the Battery manufacturer advises the battery can accept. To further that point, he mentioned that Optima batteries can take a 40A charge and based on them being able to accept that charge and the BCDC1240D would be a better alternative if you are driving less as you can charge the battery faster. When the conversation was over I walked away that the best charger was based on what a battery can take.

 

[xplorerlc200]

At this point, I have come away with two conclusions:

1. The vehicle is simply not being driven enough. In addition, the Arizona Heat doesn't help.

2. The BCDC1240D is overkill and most likely not the right Battery Charger for the job. In addition, the battery may be more efficient with using a BCDC1225D. I will work on ordering a BCDC1225D and then sell the BCDC1240D. Is there anyone out there that would like to buy it?

I welcome any more suggestions and feedback and would still welcome your input on whether the winch should be hooked up to the Starter Battery or House Battery?

Thanks again for your help.

 

[FrazzledHunter]

I was thinking the BCDC1225D would be better suited as it will charge more slowly. I have read the same material you have and REDARC absolutely recommends the BCDC1225D for anything under 100Ah. Interestingly enough, I called REDARC today as they have a US Number that transfers the call to Australia and they advised that although the BCDC1225D may be the best alternative, that is not an absolute answer. What the gentleman told me, was that it really depends on what the Battery manufacturer advises the battery can accept. To further that point, he mentioned that Optima batteries can take a 40A charge and based on them being able to accept that charge and the BCDC1240D would be a better alternative if you are driving less as you can charge the battery faster. When the conversation was over I walked away that the best charger was based on what a battery can take.

Very interesting. I imagined our use-case to be drawing the battery down at a remote area and then driving for hours and hours or needing the battery for a jump start. I ended up kind of throwing up my hands as this seems to be a gray area. So I went with what was recommended which was the 1225D but really wasn't satisfied that I understood the whole story. I'm still not sure I do LOL.

 

[xplorerlc200]

Very interesting. I imagined our use-case to be drawing the battery down at a remote area and then driving for hours and hours or needing the battery for a jump start. I ended up kind of throwing up my hands as this seems to be a gray area. So I went with what was recommended which was the 1225D but really wasn't satisfied that I understood the whole story. I'm still not sure I do LOL.

Interestingly enough, it now appears that the BCDC1225D may not be the answer and may not even be the best solution for Odyssey Batteries.

One thing I neglected to mention was that over the past few weeks, I tried contacting Odyssey Battery in the United States to ask about the best charging method and unfortunately, I never received a response. From looking at the Odyssey website again this evening, getting increasingly frustrated with the situation and knowing that several Odyssey batteries are sold and used in Australia, I decided to send an e-mail early this evening to the Australian Office of Odyssey/EnerSys to get some clarification on what charging amperage they recommended for their Odyssey batteries. Within an hour I received the response shown in the attached photo.

At this point, I truly believe I just need to start driving more.

 

[LandLocked93]

1) The biggest reason to run a BCDC is to overcome the voltage loss encountered when running a smallish wire intended to carry respectable current over a distance. Move your second battery (or add a third, much larger batt) to the rear of the truck and connect the RedArc (in the rear) between the it and the start bat. I recommend replacing the 2 8ga with a single 2ga, but you can use the 2 8ga as single run too just fine. Run the fuse block and fridge to the rear battery. (make sure it's a sealed batt)

2) As you know, a BCDC operates only at alternator voltage. Get a solar panel and MPPT controller for autonomous and segmented power generation. It's not much in terms of your load, but scavenging power without thinking about it will add up and help in cases of little driving.

3) Power storage (and conservation) is the key to long runtimes. Consider a 200Ahr D4 size AGM battery in the rear. Meets your current and future needs. Be sure to strap'er in real good.

 

[e9999]

yes, a smaller wire will incur higher voltage drop for a given current. But it's not like it won't let you charge things fully. Eventually, the voltages at the source and load battery will come close when the load battery is fully charged because the current is now low so the voltage drop becomes negligible. So -aside from potential wire overheating issues which are important but can be avoided- the smaller wires will basically make the charging process longer but if time is not of the essence then it's no big deal to use a smaller wire, you can still charge things fully.

 

[LandLocked93]

yes, a smaller wire will incur higher voltage drop for a given current. But it's not like it won't let you charge things fully. Eventually, the voltages at the source and load battery will come close when the load battery is fully charged because the current is now low so the voltage drop becomes negligible. So -aside from potential wire overheating issues which are important but can be avoided- the smaller wires will basically make the charging process longer but if time is not of the essence then it's no big deal to use a smaller wire, you can still charge things fully.

Right.
Tho I submit that it's relatively critical. The smart alt in a 2019 LC will see a higher voltage on one end and function in that knowledge.
The other end (truck rear) will see a lower voltage as a result, from the start. And then see less and less current supply as the alt sees less load. All the while the two are 1.5v disparate.
The Redarc compensates for that by presenting a suitable load to its charge source and providing a suitable charge to its load souce (rear batt) regardless of flux in either, w/i the parameters of the selected charge profile.

 

[e9999]

^ for this to work well (If I understand you correctly), the Redarc would have to know what the voltage is at the load (at the end of the wire). How does it do that? Is there a sensor? Or do you have to have the charger right next to the load with short thick wires (in which case there is no need for any special compensation)?

 

[LandLocked93]

^ for this to work well (If I understand you correctly), the Redarc would have to know what the voltage is at the load (at the end of the wire). How does it do that? Is there a sensor? Or do you have to have the charger right next to the load with short thick wires (in which case there is no need for any special compensation)?

Copy. The Redarc is connected to the load (by 'load' I mean the battery being charged), and using it's charge profiles knows the status of charge and how much current and at what voltage is needed to charge the batt to full.
It then varies the load presented to its charge source (alt) to maintain the current level it (RedArc) deems necessary to completely charge it's load (second batt).
The alternator sees only the load (or lack thereof in terms of current flo) presented to it by the RedArc. As the second batt charges, the alt sees none of it and reacts only to what the RedArc 'tells it to do' based on the RedArcs presented load to it.
Essentially, the alt sees a constant load regardless of charge state of the second batt, until the RedArc presents a 'full batt' charge state to the alt. (basically raising the circuit voltage as seen by the alt, and the alt lowering the current flow as a result)
Yes, Redarc recommends putting the unit as close to the charge (load) battery as possible.
Once there is a batt in the rear (edit:along with the RedArc), the distance to devices (in the rear) is much less obviously and both voltage drop and current loss as a result are near-as-makes-no-difference eliminated. Which is the purpose of the RedArc beyond it's batt maintenance routines.
Still think OP needs at least 100Ahrs in the rear and solar to make it several-days viable tho, given how little the engine is running.

Or move to 24V (it's what I did, otherwise I'd be happy to take the 1240 off OPs hands lol) tho this requires devices to be purchased again in 24v models (i.e. RedArcs 2420 BCDC) if 12v versions are already in hand.
Yes it can be converted but that's 'conversion reversion' and negates a good bit of the advantage.

 

[e9999]

^ OK, not sure if I got that ("knows the status of charge") right, but sounds like the weak point in the approach you describe is that the charger has to know the level of charge of the battery at all times. Short of measuring directly the voltage there, it'd have to do some historical calculations based on some presumably known initial condition. IOW, keeping track of how much energy has flown into the battery knowing how charged it was before. That would be quite an iffy proposition, I think, given particular unknown battery specs and condition, inefficiencies and the like. I suppose you could charge something like that but to expect it would be charged optimally that way seems like a long shot. Then again, I'm probably missing something. Interesting topic.

 

[sdnative]

1) The biggest reason to run a BCDC is to overcome the voltage loss encountered when running a smallish wire intended to carry respectable current over a distance.

Not sure I agree with this.

The function of the DC-DC charger is two fold:
1. convert one DC voltage to another to provide proper voltage to charge the battery
2. manipulate the input voltage to control current flow into the battery being charged

The charger can overcome a low input voltage and convert to a higher output voltage as needed, but it expects that voltage to remain fairly constant during its full range of output. That's why the recommendation is no more than a 3% voltage drop at full capacity.

Problem with too small of a wire is during low power charging everything may work fine, but when the charger is outputting high current, the voltage sensed at the input terminals may drop significantly causing the charger to shut off on low voltage shutoff threshold or engine off detection.

This is a good watch:

using it's charge profiles knows the status of charge and how much current and at what voltage is needed to charge the batt to full.

Essentially, the alt sees a constant load regardless of charge state of the second batt, until the RedArc presents a 'full batt' charge state to the alt. (basically raising the circuit voltage as seen by the alt, and the alt lowering the current flow as a result)

The DC-DC charger (Redarc or any other) does not present a constant load to the alternator. The charger uses a constant current / constant voltage (CC CV) charging profile to charge the battery. The load to the alternator is only constant during the bulk phase.

Step 1 is Bulk charging (CC stage). The charger will output maximum current until the voltage of the charging battery reaches absorption voltage.
Step 2 is Absorption charging (CV stage). Once the battery voltage reaches this point, the charger will keep voltage constant while the current falls. Once the current reaches some minimum level, charging is complete or the charger will enter a float stage depending on battery chemistry and charger configuration.
Step 3 is Float (optional). This is a reduced voltage to maintain charge.

Which is the purpose of the RedArc beyond it's batt maintenance routines.

The charger is a very simple device. It doesn't have any purpose other than to charge the battery. The devices connected will see the battery terminal voltage or the charger output voltage or somewhere in between (hopefully these voltage will be very close).

The charger only measures the output voltage (which should be the same or very close to battery voltage), and manipulates the input voltage to control current flow through the charger.

 

[e9999]

^ the typical charging scheme described above is indeed ideally what would be best for a (lead acid) battery, but an issue is that this nice scheme is what the charger outputs, not what the battery sees, unless the battery is right next to the charger. Unless there is some battery voltage sensor, the charger only knows and controls what it outputs, it does not actually know the load battery voltage. And then there is the temperature compensation issue. The charging scheme should depend on the battery temperature. That issue in practice is also mitigated if the charger and battery are physically (thermally) close to each other and the charger itself has a temperature sensor, thankfully; otherwise you best have a battery temperature sensor as well.
IOW, in practice, I would locate the charge controller right next to the house battery if I can at all, that will reduce some potential problems... The good thing is that a smart modern DC-DC converter is quite forgiving of input voltage variations.

Having said all this, we can probably debate all sorts of subtleties about charge controller and its location etc, but that may all be a moot point if OP only drives 12 miles a day while running a fridge 24/7 in AZ summer... For practical purposes, if you have access to mains power, just use a big enough charger during some of the day or at night to top up the batteries. Or if not, or for off-grid purposes, I would put a solar panel on the roof and help charge the house battery with that (assuming you can park in the sun during the day, of course).