Vanlife Essentials: Installing a Smart Battery Isolator

Last Updated on

This post may contain affiliate links. Learn more >>

Send me epic build guides and kickass vanlife tips

Send me epic build guides and kickass vanlife tips

Having solar power in your van is just plain awesome. It means you can live completely off the grid with lights, a fridge, phones and computers – all while not worrying about electric bills or power outages.

But sometimes solar power just isn’t enough, especially if your budget doesn’t allow you to throw down for a huge multi-panel system. Cloudy weather, wildfire smoke, and camping in shady forests limits the amount of sunlight getting to your panels. Even with our larger four-panel solar system, we’ve run into problems with battery drain after 4-5 days in poor sunlight conditions.

That’s why we highly recommend installing a battery isolator in your DIY van build. A battery isolator is a great way to supplement your solar panels and make sure your batteries stay topped off no matter the weather. And if you’re on a tight budget, you can even skip the solar and still have basic electricity with nothing but a good isolator and a deep cycle battery.

Adding our KeyLine Chargers Iso-Pro140 Smart Isolator to our rig was a game changer for us. Read on to learn why having a battery isolator is essential for vanlife, and how you can install your own.

What is a Battery Isolator and Why Do You Need One?

Every vehicle has an alternator, which is a device that converts the mechanical energy from your van’s engine into electricity and uses that electricity to charge your starting battery. A battery isolator is a device that allows you to charge a second (auxiliary) battery from your van’s alternator.

You can easily use your alternator to charge your auxiliary battery simply by connecting the positive terminals of both batteries. But connecting your batteries this way means that when the engine’s off, your electrical loads will also drain the starting battery – not good if you want to start your van in the morning!

That’s where a battery isolator comes in. An isolator isolates your batteries so that your alternator will only charge your auxiliary battery when the engine is running, and your electrical loads won’t drain your starting battery.

Battery isolators are essential for vanlife. Life on the road means a fair amount of driving, and having the ability to charge your batteries from your engine is a great way to increase your power efficiency and make sure you have electricity when you need it.

On a budget? Start with a battery isolator.

A good battery isolator paired with a deep cycle battery is the easiest and cheapest way to add electricity to your van build. You can always expand your system and add solar later.

Why You Want a Voltage-Sensing “Smart” Isolator

There are three types of battery isolators out there: solenoid, solid state, and voltage-sensing “smart” isolators. In our opinion, a smart isolator is far and away the best choice. Here’s a rundown of each type:

Solenoid Isolators are essentially mechanical switches – electrical current causes the switch to close, sending charge to the auxiliary battery. These isolators are the cheapest (around $20 or so), but they’re also the most complex to install. To prevent draining your starting battery, you’ll need to wire it into a circuit that’s only active when the vehicle’s running. Since they have moving pieces, they also come with some risk of mechanical failure.

Solid State Isolators use electrical diodes to split the charge coming from the alternator between the starting and auxiliary batteries. But these types of alternators are not nearly as efficient, introducing about 0.7A of voltage drop. This means it will take longer to charge your batteries, and neither battery may reach full charge. Solid state isolators are generally in the $50 range.

Voltage-Sensing “Smart” Isolators automatically sense the voltage of your starting battery. When the voltage reaches 13.3V (meaning the engine is on and the battery is fully charged), the isolator “cuts in” and sends 100% of the alternator’s current to your auxiliary battery. When the starting battery voltage drops to 12.8V, the isolator “cuts out” to prevent your starting battery from draining. A smart isolator will run you about $60-$80+, but the efficiency, reliability, and ease of installation are definitely worth it.

Recommended Battery Isolators

KeyLine Chargers Iso-Pro140

12V 140 Amp Dual Battery Smart Isolator by KeyLine - VSR - Voltage Sensitive Relay Specially Designed for ATV, UTV, Boats, RV's, Campers 5th Wheels Off Road Vehicles Rhino Polaris Artic Cat ETC

We had the KeyLine Chargers Iso-Pro140 Smart Battery Isolator installed in our van initially, and we can’t recommend it highly enough. It’s small and compact, it’s very simple to install (the hardest part is running battery cable from the engine compartment to the rear of your vehicle). And it’s IP65 certified, which means you won’t have to worry about it failing after driving the dusty road to Burning Man. IFor durability and reliability, this isolator is an excellent choice.

Wirthco Battery Doctor 125A/150A

WirthCo 20092 Battery Doctor 125 Amp/150 Amp Battery Isolator

This the battery isolator that we have now, and we highly recommend it. Although we think the Keyline isolator is excellent, we decided to switch to the Wirthco Battery Doctor to pick up one key feature: the ability to reverse the current and jump the starting battery from the aux battery. This is a handy feature to have if your starting battery dies in the middle of nowhere. The Wirthco Battery Doctor is also more affordable and comes with clearer instructions than the Keyline.

Installing a Battery Isolator in Your Van

Step 1: Disconnect the Negative Battery Terminal

disconnecting negative battery terminal

This is an important safety step that isolates the starting battery so you won’t get shocked.

Step 2: Mount the Battery Isolator in the Engine Compartment

mounting isolator bracket

Find an easily-accessible spot near the starting battery to mount your isolator. The Iso-Pro140 comes with a rear mounting bracket. Use this as a template to mark where to drill, and drill the holes for the mounting screws. Screw down the mounting bracket using the two short screws.

Note: Depending on how your engine compartment is arranged, you may need to temporarily remove your starting battery for this step (we had to).

Step 3: Connect Black Ground Cable to Vehicle Body

connect grounding wire

Crimp a blue ring terminal onto the isolator’s black ground wire. Attach the ground wire to the metal vehicle body. The best option here is to add it to an existing ground screw.

Step 4: Cut and Crimp Battery Cable and Attach to Back of Isolator

cables on back of isolator

Cut your battery cable to length – one short cable to connect the isolator to the positive terminal of the starting battery, and one longer cable to connect to the positive terminal of the auxiliary battery. Crimp battery terminals onto the ends of the cables. Then, attach the cables to the posts on the back of the isolator (which post goes to which battery should be marked).

Step 5: Attach Short Cable to 150A Inline Fuse, Then Run Wire to Positive Terminal on Starting Battery

positive terminal on starting battery

Attach the other end of the short cable to a 150A inline fuse or circuit breaker. Mount fuse/breaker in the engine compartment if needed. Run a short piece of wire from the fuse to the positive terminal on the starting battery.

Important Note on Fuses

The in-the-box instructions for some battery isolators (including the one we have) does not call for any fuses. But adding two 150A inline fuses (one as close as possible to your starting battery and another one close to your auxiliary battery) is an important safety feature.

The purpose of a fuse is to break the circuit in case of an electrical short. When you install an isolator, you’re likely running electrical wire underneath your van. If that wire somehow shorted out and both of your batteries were not fused, you could have a serious problem on your hands.

So – it’s a good idea to fuse both batteries when you install a battery isolator. When in doubt, add a fuse!

Step 6: Run Long Cable Underneath Vehicle to Auxiliary Battery

cable under vehicle

String the long cable underneath the vehicle back to where you have your auxiliary battery, tying it out of the way with zip ties as you go. You may need to drill a hole up through the floor to get the cable up to your auxiliary battery (make sure to seal the hole with silicone caulk). Then, attach the end of the cable to a 150A inline fuse/breaker, and run a short cable from the fuse to the positive terminal on your auxiliary battery.

Step 7: Reconnect Starting Battery and Make Sure Everything Works

After reconnecting your starting battery, test your system to make sure it works. First, turn on your engine. Wait a few minutes for the system to reach cut-in voltage. Using a multimeter, voltmeter, or battery monitor, check the voltage on your auxiliary battery. It should be above 13.0 to indicate that it’s charging. Now you should be good to go!

Electricity on the Road in Any Conditions!

We think a battery isolator should be one of the first things you add to your van’s electrical system. Sometimes solar isn’t enough, or you may not have the budget for solar right away. In either case, a battery isolator is great solution.

No matter if you’re traveling in overcast climes, in the deep forest, or other areas where you may not get enough sunlight, having a battery isolator ensures that you can keep your batteries charged in all conditions.

For more build guides and vanlife tips, be sure to follow us on Instagram @gnomad_home and on Facebook. Cheers!

Did this page help you?

Send me epic build guides and kickass vanlife tips

Send me epic build guides and kickass vanlife tips

More Dope Sh...enanigans

Build Your Van

The Ultimate Van Build Guide

Planning a van build? Read our free guide. We cover just about everything you need to know - from planning, to insulation, to solar and electrical, to picking appliances, to essential tools. Get started today so you can get out there on the road!

103
Leave a Reply

avatar
38 Comment threads
65 Thread replies
35 Followers
 
Most reacted comment
Hottest comment thread
44 Comment authors
JohnTravisMonica Fischmankyle boschChris Hill Recent comment authors
  Subscribe  
newest oldest most voted
Notify of
alexander fowl
Guest
alexander fowl

With the battery isolator does it shut off when the secondary batteries are 100% charged? Just wondering because I know some batteries you don’t want to over charge them or it can ruin them.

Topher
Guest
Topher

Did y’all connect the negative ends of the starter and aux batteries?

Freya Heeks
Guest
Freya Heeks

Hi! Just wondering how you went about having the batteries charging from using both the isolator and the solar panels and how it’s all connected. Thanks

Ian
Guest
Ian

what’s the approximate time scale that it would take to charge up a 135ah deep cycle with this? Something on the order or 10min, an hour, 5 hours? Thanks.

Keefe
Guest
Keefe

This is the best info yet for isolator I have found; I’m sold! What gauge wire did you use to run under your van? This might be a dumb question…I’m not sure. Looks like 2 maybe?

Brett
Guest
Brett

Did you replace your starter battery with a deep cycle battery as well? I know it generally kills batteries when you have two different types of batteries wired together. Does the isolator prevent this from happening?

Mary
Guest
Mary

Of all the information I’ve seen about batteries and solar this has been informative. Thsnks so much for this info on isolators. Greatly appreciated

Stephen O
Guest
Stephen O

I’m wondering about the need for a DC-DC charger / charge controller. Much like a solar charge controller manages the various stage of solar charging (Bulk, Absorption, Float, etc), i.e. you don’t just connect a solar panel to your battery, shouldn’t there also be something like this installed for the voltage coming from the alternator to ensure your batteries are being charged efficiently/effectively/correctly? I have no knowledge / experience of RV electronics. I’ve seen other posts about people using such things and am wondering what your thoughts are, because I have to say, your post is so well documented it… Read more »

Joe J
Guest
Joe J

Did y’all use any fuses for this system?

Todd Bushman
Guest
Todd Bushman

So I want to set up a smart isolator (the second one you recommend since the keyline is sold out) to charge an auxiliary battery off the alternator of my van. I am using a goal zero yeti 400 chained to an additional battery of the same size (33ah 12v deep cycle) to run devices off of in our van. Goal zero told me I can connect the isolator into the anderson port of the yeti directly. I’m not convinced since in your description you only run the positive battery cable from the isolator back to the aux battery (so… Read more »

Nick Cheply
Guest

Hey guys! I’m going to be starting my can build in a few weeks and have spent the past few months researching online. Love your blog and your super detailed explanations of things; I know I’ll be using this a lot during my build!! I’m trying to sort out our electrical situation and I am thinking of relying primarily on the alternator to charge our cabin battery via a smart isolator but am also going to get a 100 watt solar panel to have to supliment it when we are camped in one place for long periods. I was just… Read more »

Chad
Guest
Chad

Absolutely the most useful site out here for van conversions!! THANK YOU SO MUCH for the enormous amount of effort you’ve put into this site. My question is this: I’ve got a cruiser van with tons of DC outlets and interior lights already wired in. There is no auxiliary battery, however. How can I most easily hook up the deep cycle and isolator without reconnecting every individual thing to it? Sorry if this is a dumb question, but I know absolutely nothing about this topic.

Randy Skidgel
Guest
Randy Skidgel

Great info guys, just purchased my first van. As an avid fly fisher I’m tired of hotel prices.
Thanks again.

90d
Guest
90d

I recently upgraded my alternator to a Bosch 150A. I noticed the isolator you recommend is rated for 140A. Will I run into problems if I follow this guide? Can you update your post to include your alternator specs, for the curious? Love your blog!

Dan
Guest
Dan

Thanks for the great article. I couldn’t agree more about multiple forms of incoming charge. I’m currently working on building a bank. Probably only 200 or 400 amp hours to start out. I’m in a MB Sprinter v6 diesel. I have looked up the alternator and it appears to have a 180 amp output. Any suggestions on how to properly size the isolator?

Apple Customer Support
Guest

The use of solar power for making power, energy is the very wisest idea because solar energy is a renewable source of energy but if you don’t have enough budget then solar energy is not enough. Also, the given information on installing battery isolator is properly explained here.

michael pigneguy
Guest
michael pigneguy

i haven’t researched too widely but from what i can gather, the info you provide here is priceless, thanks s much for this. I have one question (for now), can this set up of battery and isolator be used with the Renogy 1000Watt 12V DC to 120V AC Pure Sine Wave Inverter Charger ?

Chris
Guest
Chris

Thanks for this info John! Still getting a little lost. Could you post a schematic drawing of what you’re recommending? Thanks a bunch!

Jayne
Guest
Jayne

HI there! Awesome site.. so beautifully done. This isolater help was very much needed. With that said.. I ran into an issue. I have a ’18 Promaster. After everything was hooked up I turned on the van and bam. No start. I think the van is in an “anti- theft” mode and locked the key in the ignition. The key will not come out. Has anyone run into this issue??? Help! I’ve heard that it’s the Promasters way of saying there was short and that I’ve blown a fuse. I have no idea where to start looking or if that’s… Read more »

Eugene
Guest
Eugene

Jumping in here. This site is heaven-sent thank you so much. I have a promaster and was going to install this weekend (crazy I just caught this comment). I was going to use 4 awg wire with a 125A fuse to protect the wire. I don’t know much about what could’ve happened there but would love an update! I will see if I can find anything to help.

Josh Andrews
Guest
Josh Andrews

HEy there! Love the site, it’s helping me tons! Was wondering though if I’m running two aux batteries how I would run the isolator with them? I am horrible with electricity!

Jazmyn
Guest
Jazmyn

Hey! What size wire did you use to wire the Isolator your house batteries?

JOe
Guest
JOe

HEy guys
Is it ok to use 8 awg cable instead of 4 awg to run the connection ? I have a lot of 8 awg cable left over

slp
Guest
slp

Hi I bought a smart battery isolator through your site but now am doubtful of using it. One this video https://www.youtube.com/watch?v=9jjh3Y4xIL8 mentions not to use an isolator with vehicle with a computer controlled alternator. I’ve also read on the sprinter forum that alternators want the same type of battery they are tuned for(your starter battery). Thanks for any thoughts!

Bruce A Kathol
Guest
Bruce A Kathol

Hello, Great site. I’m wondering can you charge your auxiliary battery with your van running, charging from your alternator and charge the auxiliary battery with the solar at the same time with your wiring setup? Say it’s a nice sunny day and your driving down the road.

Mike Fye
Guest
Mike Fye

I’ve reading your blog with great interest. Really a great resource. My home-brew camper van has a totally separate solar system feeding 3 deep cycle AGM batteries. I want to install a smart battery isolator. My van motor is a GM 6.6 turbo-diesel that has 2 full-sized starting batteries. The second battery is mounted under the van about mis-ship and almost directly underneath where my ‘house batteries’ . So my question is: can I mount the isolator to (and next to) the second starting battery rather than the battery under the hood? If so, I could do the whole install… Read more »

Rob
Guest
Rob

The fuse link is for a 100a fuse and you refer to using a 150a fuse…is the 100a fuse sufficient?

BEN
Guest
BEN

Incredible post. Just finished installing the isolator (used your amazon link 🙂 for my Honda Element. Thanks for answering the questions below cause that helped me out when I installed mine.

Your directions are a little confusing. You’ve g
Guest
Your directions are a little confusing. You’ve g

You’re directions are a little confusing. You’ve got the in-line fuse connected to the positive terminal and you’ve got the isolator connecting to the positive terminal

Max
Guest
Max

Hi there, awesome tutorial!
You do t happen to have a full circuit diagram for this setup, so it can be visualised as a whole product!
Thanks a lot

Ben
Guest
Ben

John, I got a big 100 amp hour battery by Renogy.

Any suggestions on how to put some safety measures in place in case of a crash?

My goal is to build or buy something if it already exists, that would keep the battery from flying (and hitting me) in the event of a big crash.

Cheers,

Ben

Alex
Guest
Alex

I have my isolator installed in my van, and when the solar panels are engaged, the isolator makes a constant clicking noise. I believe it’s the isolator cutting off the attempt by the aux batteries to draw power off of the starter, but I haven’t seen the sound referenced anywhere, so want to make sure my hookup is actually working correctly and charging while I’m driving :\

The Wandering Sun
Guest
The Wandering Sun

Thank you so much for all this useful information! We would be lost without you guys!

CZA
Guest
CZA

Thx! Great article, as usual for your site. What I don’t know is how you determine what amperage you need for the isolator and the fuses. Is it based on the alternator amps, or what? And how do you choose a fuse that is neither too high (as to properly protect) or too low (being tripped when you don’t want it to be)?

Chris Hill
Guest
Chris Hill

This is a great site! I am finding so much useful information. Thank you for sharing! I have a ProMaster 2500 159. It has a 180 Amp Alternator. Do you think this witch 150 would work for me?

kyle bosch
Guest
kyle bosch

Happy I found this I wanted to add a battery to battery set up in my 18 transit I just ordered everything u guys used and am gonna copy u… I’m new to all this so I asked on forums for help and everyone was confusing the crap out of me saying battery’s have to have the same chemistry and this is. Isolater not a charger blah blah I’m only running a maxfan water pump andfew usb outlets so I ordered a 100ah battery to supply them … so I hope this works for me seems pretty straight forward I… Read more »

kyle bosch
Guest
kyle bosch

I ordered the 75-100 battery isolater my battery is a 100 ah batter says max amp charge is 30 amps so would I need a smaller isolater

Monica Fischman
Guest
Monica Fischman

Hello! I’m completely clueless to anything electric and was wondering where I should look for help with this. I was thinking car audio shop? Any ideas on what to even google to find some assistance? Also what kind of power are you going to get from this? I really am in need of some type of AC, was considering a swamp cooler so I would just need power to run a 12v fan. Halp!

BTW love you guys, thank you so much for all this valuable and FREE info! Y’all are awesome!

Travis
Guest
Travis

What is the reason for installing the B2B charger in the main engine area or close to the van battery? Could the B2B Charger be installed in the rear of the van by the rest of the electrical components?

Want to build your own DIY campervan?READ THE GUIDE
+
Scroll to Top

Send this to a friend