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

For all of you smart electrical guys, I've got a question with my dual battery setup. I've got a dual battery setup, two Group 35s, connected with a BlueSea ACR. Attached to the aux battery I have a 100W solar panel with a Morningstar controller. I keep my Arb fridge in the back practically running 24-7. It's been great, but recently it seems like the aux battery is not staying charged as well. Also when my voltage gets to about 11.5V, my fridge trips offline, and the compressor starts and then stops. It flashes indicating under voltage. I have it on the LOW setting which I think goes down to 10.8V or something like that.

So my questions are...can the starting surge of the compressor be large enough that the voltage is dropping below the set point initially, preventing it from continuing to run. Also with the aux battery, I drive about 50 mins each way to work, so it should have plenty of juice from daily driving, but is there anything I should check or do to keep the battery in good health? Routine charger/conditioning, etc?

I just checked it again...Voltage of aux battery read 12.0V. I moved fridge temp from 35F to 33F. Compressor starts and shuts off on low voltage. Not sure if it's a problem with the fridge or my electrical set up. Thanks for the help!

 

Was that a typo? Did you intend to say it is not staying charged?

It could be an indication that the aux battery is having trouble holding a charge. Are both batteries the same age? Are they AGM types? I would try putting the aux battery on a 'smart' charger

CTEK (56-864) MUS 4.3 12 Volt Fully Automatic 8 Step Battery Charger

like this one that is designed for AGMs to see if that makes a difference.

You can also try swapping the two batteries. Putting the aux battery in the starting position to see if the other battery ends up behaving in the same way when it is in the aux position.

 

Oh yes...typo. Fixed it. Good idea to swap batteries and see how it responds. Yes both batteries were put in at the same time. Both are X2Power AGM batteries from Batteries Plus (I thought they were made by Northstar). Put them in just over a year ago. Not sure how the continuous cycling of the aux battery affects if lifespan. I've been looking at the CTEK chargers or Noco chargers to maybe give one of them a try.

Also for those of you that have battery monitors, what's the typical voltage that you see when running the truck? I show about 13.1-13.6V on engine battery and anywhere from 12.5-13.0V on aux battery. Off of memory I thought they're connected in parallel so ideally they should have same voltages when the ACR is closed right?

 

A battery is like a loaf of sliced bread. Every time it's discharged, you take a slice outta the loaf.

 

It isn't quite that simple. Some type of batteries handle and recover from discharges better than others. Deep cycle AGM types handle it much better that standard lead/acid batteries for instance. To use your analogy, the slices of bread are much smaller or there are a lot more of them in a deep cycle. FWIW, Northstar claims its AGM deep cycle batteries can handle up to 400 deep discharges (below 80% of capacity) before there is performance deterioration.

The differences could be due to voltage drop. What size wire did you use to connect the batteries? Where is the aux battery/how far is the cable run.

 

Yes, but when there's 365 days in a year and he's discharging it everyday, there won't be much battery left. Driving for only 50min to and from isn't gonna charge the battery enough to recover from full discharge.

 

Yes I understand that a battery only has limited life and a number of cycles. I was curious if people use there dual battery setups routinely and see similar performance?
Wire runs between batteries are 2AWG and right next to each other so only about a foot long wire run, so I don't expect close to a volt difference. Maybe I try to draw up a wire diagram to see if there's something I'm missing there. I haven't taken a voltmeter to the ACR to at least check that that is working right.

 

Any inductive motor will have an inrush current that will cause a voltage drop across it. Your arb fridge compressor can cause that voltage drop below its cutoff.

 

Finished this a few weeks ago. Now I need a pair of fuse blocks to clean up the wiring.

 

I thought of that but the low voltage cutout for ARB on low setting is 10.1V I think. Looking at some charts of 12V battery voltage and capacity, it looks like batteries are at 20% somewhere around 11.4-11.7V depending different tables found on the internet (with the battery being dead around 11-10.5V. I did find a ARB troubleshooting manual too that had a section to test the output voltage and then use an ARB tool that simulated the starting surge of a compressor and measure the voltage again. If the voltage droop is >0.5V, then to check the wiring. The specs for wiring seem a bit confusing though because it recommends 6mm diameter or 4.5 mm^2, which are two dramatically different gauge wires (if I'm reading those numbers right).

Poking around some more, I found out that it looks like I have a problem with the solar panel (100W) as it is putting out no voltage either. So I could drive before for two hours a day (~50 mins each way), but then the truck would still be outside and should be getting 2-5A from the panel, so the battery would be sustained just fine. Not realizing the panel wasn't providing output voltage, I didn't understand why it was killing my battery, so the issues too.

 

I've read through most of this thread, awesome, most comprehensive dual battery info I've found. Here's where I'm at.

Thanks to info on this board I follow the consensus the Blue Sea ML ACR is the way I want to go, picked one up for $155, which isn't bad considering the prices on them are steadily going up north of $200.

I've had an Odyssey PC1200 installed for more than 10 years and it's been awesome, but last 2 trips out I've drained it with my fridge while sitting for 24 hours plus, thus the reason I know I need an improved setup. I'd like to do a 100 watt solar panel and a Morningstar controller, but that's for another time.

I'm running a Cadillac eldorado alternator putting out 120 amps at idle, and my wiring had been cleaned up and accessories are on a Blue Sea fuse block, so basically I'm down to adding the second battery and wiring it all up with 1/0 awg welding cable.

With all this comes a pretty basic question-

Is there a good reason not to run a 10 year old battery with a brand new battery, am I smarter just biting the bullet and installing 2 brand new at the same time?

I don't know if I should pull the old one from the main battery and make it the accessory battery, or just run it as the main until it pukes then drop the second in its place and put a new one in the accessory battery spot, or if it will kill the new one faster no matter where I put it with the old one on its way out.

 

Interesting question. As I had not really thought much about it, I did a lot of googling. There doesn't seem to be an issue with mixing old/new batteries. There is an issue if you are running a LiPo battery as it requires a special charger, but for regular starter/deep cycle batteries there really isn't a lot info on running new and old at the same time. My guess would be as long as the old one is still holding a charge their shouldn't a problem. I would imagine if it was an issue there would be more info about it around the interwebs.

 

In typical TW fashion...

I was exactly where you are, about 6 months ago. I worried over this same question. Like you, I chose to use an ml-acr and 1/0. I decided to go with two brand new matching batteries. In a way, the decision was made easier when GB came along for Northstar AGMs because good batteries are not cheap. I also liked the idea that the batteries were evenly matched. Potentially anyway, they would take a charge and handle a load similarly. if that matters or not or if this behavior changes as a battery gets older.

Frankly, I think either way can work. But something to consider is that 10 years is at the long end of any batteries lifespan, including Odysseys.

 

Def agree, 10 years is starting to push it, especially after discharging it a few times. Probably gonna do a new one added to the old, but don't think I'll take too long getting the second installed. Mainly this is an issue of me being cheep and trying to be green, don't wanna ditch a battery that still holds a charge.

I may even buy a new second one and have it on the shelf and kill the old one, if it won't hurt the new running it with the old.

 

Im running a interstate SRM-4D deep cycle R.V. connected to a stinger heavy duty battery isolator. And then routed through the frame from the spare tire area. I have a custom battery holder\frame reinforcement cage welded into hold the 117 lb beast of a battery in place. Then its wired with 0 gauge wire for maximum power discharge into my sine wave 6000 watt invert-er with GFI grounded outlets. Then looped into a mini breaker 1 foot away from the main battery so i can jump the smaller truck battery from the mega RV battery if needed. But my isolator system only discharges the big battery when using the power.
The rear cage.

The side wiring Fully loomed!


and continuing through the the frame up to the cab. If you look close you can see the positive cable in the top of the frame. The body lift made it easy to do this and again fully loomed !!






going through the cab up to the invert-er.


the mini breaker and charge wiring. Sorry dirty engine bay after wheeling with my gap guards off what a mess!


Finally my stinger isolator and invert-er.

 

I had a similar setup on my old truck camper along with 300w of solar on top. Good job!

 

I'll leave this here.

https://www.tacomaworld.com/threads/blue-sea-ml-acr-7622-w-switch-for-dual-battery-setup-new.444921/

 

Finished my set-up last week:

Blue Sea Add-a-Battery Kit/Fuse Panel/285 Series Breakers
Offgrid Engineering Battery Tray
Pelfreybilt Fuse Panel Mount

 

Almost done with my install (Blue Sea ML ACR). I am looking for a "hot when the key is on" spot for the brown wire, in the fuse block under the hood, can't find one. All the open spots are hot all the time. How and where are you guys hooking up the brown wire, pictures please. I know a lot of people are not hooking up the brown wire, but some say their setup doesn't work without it. I want to be ready either way.

 

Qiorange 12v Car Add-a-circuit Fuse TAP Adapter Mini ATM APM Blade Fuse Holder Pack of 5

https://www.amazon.com/gp/product/B015GYN38A/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

There is a fuse in the cab under the steering wheel call "IGN" that's what I've tapped for key only on power.