Electrical System

For our electrical system, we wanted to go without the need to hook up to shore power at all. That meant that we were looking to limit our energy usage as much as possible, and being able to charge the battery while driving (from the alternator) as well as when parked for a few days (solar).

We cobbled together a wiring diagram from a number of sources, as we couldn’t find an exact model of what we were trying to do. Sprinter-source had a couple of examples for auxiliary battery installations, and we ended up following broken granites guide almost exactly (sprinter-source.com). We bought a DieHard marine battery with 100 amp-hours at Sears (tip: check the Sears price online and walk in with a printout, this saved us $50). The battery, ACR (automatic charging relay, Amazon) and maxi fuse block (Amazon) are all installed below the passenger seat, and we used 4-gauge wire from the local auto parts store for all the connections.

So here’s our wiring diagram, and please excuse the 3-year-old handwriting:

wiring diagram

As for the solar installation, the conversion source book was invaluable and we ended up purchasing a set from AM Solar in Oregon. We opted for a 135W panel (made by Grape Solar) with the SunCharger 30 charge controller. The panel went up on the roof with 35mm mounting brackets to allow for air flow under the panel (you need at least 1 inch clearance) that are glued, not screwed to the roof using 3M VHB tape – we haven’t had any issues and have driven 10,000 miles with it. To guide the solar cable through the roof, we made a 1/2 inch hole and used a BlueSea cable clam (Amazon) to seal it.

Solar charge controller and fuse block (Amazon) for our appliances are mounted below the drivers seat (facing backwards). It’s a convenient location to monitor the charge current, and changing fuses is equally easy.

Lastly, our appliances:

  • Lighting: we bought Ikea LEDs – they’re great. Not expensive, bright, and most importantly, they run on 12V so you can simply connect them to your car battery. We also installed 3 light switches (Amazon) next to the kitchen counter, for the kitchen under-the-cabinet, living area, and bed area lighting.
  • Fridge: After much deliberation, we went with a 37qt ARB fridge (Amazon), which is expensive but has amazing reviews – Amazon had a good deal on it when we bought it. The size turned out to be perfect for us. We could probably do with a smaller fridge but we never seem to have trouble filling it up. Parkinson’s law definitely applies here. The fridge is incredibly efficient, using up only about 1.5 amps in 90 degree heat.
  • Ceiling Fan: We have the 5000 version of the Fantastic Fan (Amazon). It works well, and draws about 3 amps.
  • Inverter: We bought a cheap 300W inverter (Amazon) that charges our laptop and cordless drill.
  • USB plugs (Amazon) and 12V sockets (Amazon): We have a set of plugs next to our bed and the kitchen counter to charge up our phones and plug in the inverter. It’s a great location. Charging phones takes up almost no power.

A couple of other things we learned:

  • Watt = Volt x Amp. This was very helpful in figuring out what battery size we needed, solar panel size, as well as how much power we would end up using. The conversion source book has some more detail on this.
  • Always disconnect the system / fuses before any electrical work.
  • The car battery serves as the ground / negative on the car battery system. This allows you to only run the “plus” cable for your electrical system.
  • Wire cutters are great for crimping heavy gauge cables. You don’t have to buy the specialized tool.
  • We had no trouble installing all the electrical system after the furniture was pretty much built. But this may not be true depending on the layout of the van. Running wires behind furniture that’s built in can be a pain.
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  1. Hello. Nice post… this is similar to the system I am planiing. However I can’t seem to figure out how to monitor the charge on the battery. How do you do so?

    • Hey Logan, I was wondering about a good way to check the battery charge status as well when we first set up the system. The solar charge controller displays both the current battery voltage as well as the current (in amps) in the system. You can use the voltage at night to infer the charge status. You could also buy a battery monitor, but they also just show the voltage so we didn’t think it was worth it. Simply put, a battery is full at 12.6+ volts, it’s about 50% charged at 12.1 volts, and it’s at 0% below 11 volts. Temperature affects your battery as well (lower temperature = lower capacity). The way our system works, you can’t check the voltage while the battery is charging (i.e. car is running or sun is shining), so we monitor our battery at night and in the morning.

      With our system and our usage (fridge, LED lights, charging cell phones and occasionally laptop), we rarely tend to drop below 12.4 volts. The only time we’re lower is when we’re parked in the shade and don’t drive for a few days. Usually the battery is fully charged at night (12.7 volts or so) and then 12.4-12.6 volts in the morning, depending on whether we charged a laptop during the night and how much the fridge had to run at night (hotter outside temperatures means the fridge runs more).

      Hope this helps, let me know if you have other questions about the setup.

      • Excellent, thanks for the details! I am ridiculously confused about this process so this is very helpful! I am surprised that you are able to do so well with a single 100ah battery. Most of the conversions I have been studying use a 200-300 ah bank (like Geek on the Sprinter forum). I was looking at the BlueSea 500a ACR, 2 of the Diehard batteries and a 2000 inverter (as well as 200w worth of solar panel). We are planning for charging laptops, a maxi fan, fridge (probably the same one you are using), lights, stereo, and the occasional small appliance. Also, we are planning on sitting for anywhere from 2-7 days at a time… Thanks!!

  2. I thought I posted a comment yesterday, but I checked back and it wasn’t here. Anyway, great post! This is very similar to a system I am designing, however, I am very confused about how to monitor the charge in the batteries. I have read it is necessary to not run them below 50% in amp hours. With the ACR I can’t seem to find a solution to this. Any suggestions?

  3. Pingback: Electrical Update – Solar | Sprinter Van Diaries

  4. Awesome van and blog, I’ve been following you guys for a while now! Always amazing pics on instagram! I’m starting to plan out my travel/biking conversion van and I was curious if you’re happy with the placement of the fan? I was thinking of putting mine a bit further back so there would be a better draft while sleeping. Only downside I could think of would be less cooking ventilation? Also, I’m assuming you have to pop the front wheels of your bikes when you were traveling with them? Cheers!

    • We’ve often talked about how the additional draft while sleeping might be nice. The way we have it is great for cooking but we would probably move it further back next time.

      As for the bikes, we remove the front tires. This way they fit nicely into a space that is 65″ long.


  5. We are hooking up our ikea lights to the bluesea fuse box and getting no power to the lights but when you hold them directly to the battery we get light. What are we doing wrong? The fan is working fine on the fuse box with a 15amp fuse.

    • Ryan,

      Without knowing your exact setup, I’m not sure. Try using a multimeter on every connection that you’ve made. Try hooking up the lights directly to the fusebox. If you’re using a similar light switch setup as we are, check the connections there with a multimeter as well. My guess is that it’s either something around the switch wiring or the switch itself.


  6. Hey I was curious how you’ve found the battery charging to go with your setup. I’ve been doing a lot of research, and the two issues with this type of setup are 1) high charge rate when driving… lowest amp rating of alternator for sprinter is 90A, not sure what split goes to the house versus starting battery, but even if half did, 45A is a lot to send. I’ve read that this isn’t an issue with AGM batteries since they won’t gas out, but might be for lead acid… and 2) if you depend solely on this setup for charging, you can never top out a 12V battery.. you need shore power or solar charger to provide a higher voltage to actually top out the charge, which is something that ought to be done occasionally at least for battery health reasons.

    I have an AGM for my install, so I’m hoping the charge rate will not be an issue (on a side note, what size fuse did you use in the maxi-fuse block?). I bought a 15A charge controller to plug into shore power when available to top off battery occasionally. Think I won’t actually install the charger for now, and just have it at home to plug in with…

    thanks for the layout – it’s been a helpful guide!

    • Erik,

      Thanks for getting in touch. Like you, we were a bit concerned about the charging rate from the alternator, but haven’t found this to be an issue. I think the base alternator on the NCV3 Sprinter is 180A. We are using an 80A maxi fuse between the starter battery and ACR, so it’s definitely never higher than that. From what I’ve read a lot of people are using this setup and it hasn’t caused any issues. We do have an AGM battery, like you.

      On the second point, typically the alternator runs over 14V, and I believe that should be high enough to top out the 12V battery. I don’t think I’ve ever seen higher voltages from our solar charge controller than 14.5V. Do you think you need a higher voltage than that for battery health? I suppose you could just monitor the battery voltage for a while without the shore power and see how it does. Let me know what you find out!


    • Hey jakob, one more question for ya… did you connect a wire from the ACR to alternator to isolate aux battery during engine cranking? If so, where did you find the wire to make that connection?

      • I wanted to and spent a lot of time trying to figure out where the connection would be, but ultimately didn’t do it. As far as I know, nobody has done that on a Sprinter and documented it online. Under the driver seat there are 3 connection points that close circuits on 1) ignition off (always running), 2) ignition on, 3) engine running. I believe that would be the best place to connect. There’s more info on their location in the Sprinter upfitter manuals that you can find online. In the end I didn’t want to spend any more time on it, and it seems that our battery hasn’t suffered from cranking, so I haven’t regretted the decision. Please do let me know if you figure out how to do this, I will probably want to copy that!


  7. Jakob,
    No your solar charge setup should be good for battery health – 14.5V is enough to top them off… in fact many people put in solar panels as a means to keep the batteries topped off. The alternator charging is where lower voltages can be an issue with only taking up to ~80% or so. Because I haven’t fully thought my system out, I’ll just use the plug in IOTA charger for now, and hopefully install solar in the future so I can depend on plugging in less often.


  8. We’re about to start our sprinter build and i’ve been scouring the internet for wiring help. Thanks for your descriptions. I was curious about the ground off each battery. Normally a car battery doesn’t have an additional ground coming off the negative. Did you add one and if so what’s the rationale on that if you happen to know? Thanks!

    • Hey Drew, thanks for getting in touch and great to hear your building out your Sprinter. We didn’t add an additional ground from the starter battery to the body of the car (I believe that connection already exists, at least in the Sprinter). We did connect the negative of the house battery to the frame. Does that help?

  9. Hey Jakob!

    Finally got our van and am still working through the maze of electrical decisions. Another question, do you turn off your solar panels when using the alternator or does your system feed the battery at same time? Seems like some people have selector switches but I don’t think remembering that all the time is that feasible. Thnks!

    • Hey Drew,

      We don’t have a selector switch. The solar charge controller will take care of this automatically – i.e. if it senses that the battery voltage is quite high (e.g. when the alternator is running the system voltage will be around 14V or so, it doesn’t try to charge the batteries. This has worked really well for us, so I’m not sure you’ll need to add any manual switches.

      A manual switch (like this one) can be quite helpful when you want to override the ACR – the primary use case is if your starter battery dies, you can manually link the 2 batteries and start the car from both batteries combined. We don’t have it, but it’s something I’ve thought about adding.


    • I’ll try to get Nikki to put something together, but it’s difficult to get her off Instagram and focus on other things! Hopefully we’ll have something soon.

  10. Hello,
    I apologize about my naivety in advance. If i plan to run my power solely of my solar panels, do i need a fuse box? I thought i just needed the solar panels which connect to the charge controller then connect to the battery which then connects to my inverter which then connects to my fan and lights. Am i wrong by this? Thanks in advance. Im in my beginning stages of my conversion now. Any suggestions not on your page is appreciated and your page is very helpful and informative. Thanks

    • Bryce,

      You have the order of things pretty much right. Most likely your fan and lights will run on 12V, so you will connect them directly to the battery (instead of connecting to the inverter). Fuses will protect your appliances (lights, fan, etc.) from breaking in case of voltage swings – if for some reason system voltage is too high, you’ll just blow a fuse. Much better to replace a fuse than to fix a broken fan. The fuse box is just a convenience that allows you to have all fuses in one place. You’ll want to insert fuses between the battery and your appliances (fan, lights, inverter). Hope this helps, good luck with your build!



  11. Hello,

    First of all: Thank you so much for all this wonderful and helpful information! I was wondering, How much did your electrical setup cost overall? I’m working on a van myself and am wondering for the sake of budget. Thank you again!


    • Hey Carla,

      So let’s see: You’ll need a battery ($250), ACR to charge from the alternator ($100), fuse box ($50), cabling and connectors ($100), and a solar panel kit with charge controller (e.g. Renogy for $450). I’d say $500 for charging from the alternator and another $500 to add solar is a pretty reasonable budget. Hope this helps.


  12. When you put the solar panels in, where did you feed the wires through to the battery? We already sealed and installed our fan and we don’t want to have to cut another hole in our roof. Is cutting a hole for the wires a good idea? And what is the best way to make sure there will be no leaks through it?

    • Hey Lexi,

      We put a hole in the roof to route the cable, and I don’t think you’ll have much of a choice. To do so, we drilled a hole slightly bigger than the diameter of the cable, and mounted a cable clam on it. It’s for marine use and we never had any leaking issues with it. If you’re installing multiple panels, some people put a combiner box on the roof and then route just one cable to the inside of the van. Hope this helps.


  13. Hello there! This may be a super obvious question but I can’t seem to find out. Do you actually need to connect the deep cycle battery to the starter battery at all if you have the set up panel->charge controller->deep cycle battery->inverter? Why would you need to connect the battery to the car battery at all?

    • Maggie,

      You don’t have to connect the starter and house batteries at all, and many people choose not to do it. The reason we chose to connect them was that we wanted to be able to charge both batteries from the Sprinter’s alternator while driving; i.e. we wanted 2 sources for charging just in case (solar + alternator). The best way to do so is using an ACR that connects the 2 batteries when the car is running, and separates them when the car is turned off (to prevent the starter battery from draining). This added complexity may not be important to you, so you can leave it out.

      The one thing I want to flag is that in conventional car builds, oftentimes you attach the negative / ground wire of the system to the car body, which acts as the ground. When you create an isolated system (charged by panels), don’t ground the system to the body of the van. Let me know if you have questions about this.


  14. Hi Jakob,

    Thank you guys so much for documenting your amazing build! I just bought a 2011 144″ Sprinter and have been leaning on your blog for most of my decisions on the build. One thing I’m still scratching my head over is the placement of the aux battery. Were you able to fit yours under one of the front seats? Also curious about the placement of all the other items – maxifuse, ACR, fuse box. Any suggestions would be appreciated. Hope you are enjoying the vanofthesea adventures!


    • Yogesh,

      Thanks for the kind words! We fit almost all of the items you mentioned under the passenger seat (battery, maxifuse, ACR). It actually fit perfectly in the space. I bought some steel angle to secure the battery in place. I’d have to dig up some pictures to show you, but it’s very similar to this sprinter source build: http://sprinter-source.com/forum/showthread.php?t=28775&page=4

      I mounted the fuse box and solar charge controller on the back side of the driver seat pedestal. Check out our youtube video, you’ll be able to see what it looks like.

      Hope this helps! Let me know if I can give you any other specifics.


  15. Hey! Enjoy the website. You should consider bring extra fire fighting equipment when traveling especially in southern Mexico etc. From personal experience, fire response is sometimes non- existent. I like having multiple industrial fire extinguishers and fire-away spray up front. I’ve been there and seen it all as a 39+ year long hauler through the glorious country of Mexico.

    – John Kent

    • John,

      Thank you for your comment. Fire safety is definitely one of the neglected subjects on any of these van builds. We did carry a fire extinguisher and luckily never had any issues. I’ll definitely have to think about that aspect some more, almost regardless of where our travels may take us in the future.


  16. I do wonder how your aux battery is doing after 2 years of heavy cycling use and how much longer it’s going to last considering:

    a) you don’t actually know what is going on with the battery as you seem to have limited monitoring (look at something like Victron BMV or Bogart Trimetric)
    b) neither of your charging sources is optimized for AGM and, as far as I can tell, the charge controller is set to default values so the battery is unlikely to ever be completely charged
    c) AGM is less than ideal in RV use and have otherwise been proven to fail much more commonly and sooner than gel and flooded types

    • Jernej,

      Thanks for your comments. We had a lot of questions about our electrical system, and I think most experts can find fault somewhere within our system. Frankly, I still can’t tell a difference in battery capacity after 2 years of usage – our system has worked well, was simple to troubleshoot and cheaper than most alternatives. I find it difficult to justify spending $200+ on a battery monitoring system – what additional info does the average person know how to interpret? My approach was to design a reasonable, no-maintenance system at low cost, and I think those criteria were well met.

      What are your recommendations to improve the reliability of the system without increasing cost or maintenance?


      • Think you’ll find that Victron, Bogart or NASA Marine battery monitors are all in the 100-200$ range. Are they absolutely necessary? No. But battery voltage (or amps produced by the panel) is far from an accurate indicator of SOC when it comes to lead batteries under load/charge (in a van that would be nearly all the time). Under load the voltage will sag, sometimes quite low, possibly misleading you into thinking they are near empty. And during charging you have no idea how much of the charge you actually got back since it probably goes up to absorption voltage quite fast making some people think they are full when they anything but. Obviously a battery monitor doesn’t tell you everything either, but observing the amps going out, voltage under load and Ah actually drawn, you can estimate quite well what is going on and the health of the battery. Not absolutely necessary but beneficial to battery life.

        Secondly, from what I can tell your charge regulator can be programmed but based on what I read above you haven’t changed the defaults. I suggest you look at your battery manual or similar to work out what they recommend when it comes to charging. AGM batteries are very sensitive to correct charging regimes. A general discussion on AGM use in RV applications: http://www.aandncaravanservices.co.uk/agm-batteries.php

        Example manuals:
        Crown: http://cdn2.hubspot.net/hubfs/435823/Brochures/SafetyFirst-AGM-sec.pdf
        Trojan: http://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf
        Victron: https://www.victronenergy.com/upload/documents/Datasheet-GEL-and-AGM-Batteries-EN.pdf
        TAB: http://www.tab.si/pdf/katalogi/TAB_smalltraction_en/

        Note sometimes quite different voltage recommendations and variations due to usage patterns. I’ve set mine to max absorption and min float purely because the van can go for weeks just sitting on the driveway but when in use I need the fastest recharge possible. Obviously it’s a compromise that wouldn’t be optimal for full time cyclic use but to get the most out of your batteries you need to consider your own needs.

        Another useful link: https://handybobsolar.wordpress.com/

        • Thanks for sharing those links.

          Without a BMS, I usually took a look at our battery voltage twice a day – early in the morning and right before going to bed. In both situations, the system wouldn’t be charging, so I found the voltage read to be very helpful. Keep in mind that our system never had much of a heavy load (the fridge being the only constant draw, and even that would cycle on / off). I didn’t observe any sag in voltage, but I can’t speak for other systems than ours.

  17. Hey Jakob,

    Thanks so much for the response. I did notice that you mentioned the placement of the battery in your original post, so sorry for the redundant question. I’ve decided to put my aux battery under the passenger seat as well. I think I’m also going to try to squeeze and Espar D2 under there. Looks like a couple guys on the forum have been able to make that work.

    I checked out brokengranite’s build thread and really like the simplicity of that setup. Thanks for that. I’ve noticed a few other places on the forum people think the amp rating on that ACR is too low and that charging an AGM directly off the alternator is not optimal. Seems like you haven’t had any problems though?

    • Yogesh,

      Never had any problems – similar observation as brokengranite: Everyone says it shouldn’t work but it does. I never tried to measure current, but I used an 80amp fuse and it never blew, so clearly the current never exceeded that. A lot of people are concerned with charging AGMs from an alternator, but based on our experience it works just fine. Our thought was to just buy a new battery if it dies after 2 years, that’s a ~$200 fix if it happens – better than spending money on an “optimized” system that may break in some other way.

      Can you post a link to the forum? I’m curious how people put in the battery and heater under the passenger seat.


  18. Hey I was wondering if youve had any issues with charging your batteries simultaneously from the alternator and solar? Since your solar charge controller measures the voltage and status of your battery, as soon as the alternator is running your voltage will jump and the charge controller will get a false reading. Has that caused any issues? Im working on designing a system and havent figured out how to bypass that issue. Thanks for all your info! Definitely appreciated

    • Fred,

      This doesn’t create any issues. The charge controller will determine whether to charge the battery based on the system voltage. When the charge controller gets a higher voltage reading (i.e. >14V when alternator is running), it will not charge the battery from solar as the voltage indicates that batteries are full. So while the car is running the battery will only be charged from the alternator. When the car is not running, it is charged from solar. Hope this helps.


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