Made with in our van.

Sharing this tool with others is the best way to say thanks if you found it useful. Thanks for supporting us and for keeping this website alive! See you on the road 🙂

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Van Electrical Calculator

12V DC
LOADName of the appliance. CUR
(A)AVERAGE CURRENT (in amps) drawn during operation. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.
(A)AVERAGE CURRENT (in amps) drawn during operation. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.


120V AC
LOADName of the appliance. PWR
(W)MAX POWER (in watts) of the load. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.
(Ah)[(POWER/12) x HOURS] / 0.85
INVThis column is used to size the inverter. Check all the appliances that you plan on using simultaneously. Note that the biggest load is automatically selected by the calculator. PWR
(W)MAX POWER (in watts) of the load. Find this info on Google, product's website, owner's manual, technical sheet.
(h)How many HOURS per day this appliance is in operation. It's a guesstimate.
(Ah)[(POWER/12) x HOURS] / 0.85
INVThis column is used to size the inverter. Check all the appliances that you plan on using simultaneously. Note that the biggest load is automatically selected by the calculator.


Battery Type

Your Type


1- Size Your Main Components
Use the calculator above
Daily Energy Usage

? Ah

Battery Bank

? Ah

Solar Panels

? W

Solar Charger


Alternator Charge

? A

Shore Charger

? A


? W

Manual Mode Enabled.
Bold options = automagic values.
2- Size Your Wires, Fuses & Breakers
+ Wire Lengths & Terminals Calculator

Appropriate wire gauge (AWG) varies with length & load and therefore is unique to each installation. Our wiring diagram automatically sizes the wires gauge, fuses & breakers to ensure that your own system is safe and performs as it should. Bonus: it also calculates all the wires lengths & terminals that you'll need by type/gauge, which will make STEP 3 (customize your items list) super easy to complete. No other diagram does this!

3- Customize Your Items list

Fill these tables per your wiring diagram:




Cost EstimateIncludes everything on your Items List, except the 12V & 120V loads (appliances) and Tools. Prices on Amazon change frequently, so our estimate is subject to change.


Items List

The list below defines your entire electrical system. Click on "ADD ITEMS TO AMAZON CART" section-by-section; make sure that all the items are valid (links to Amazon products sometime change, please let us know if that's the case!) and make sure all items are in stock at the moment.

#ItemDescriptionQuantityView on Amazon
1Terminal Fuse Block with Fuse 250ABlue Sea (Catastrophic Fail Safe. Connects directly to battery post.)1View
2System SwitchBlue Sea (Main System Switch)1View
3Bus Bar (250A, 4 studs)Blue Sea2View
4Cover for Bus Bar (for 250A 4 studs)Protect the Bus Bar2View
540A Breaker/Switch, Surface MountBetween Fuse Block and Bus Bar1View
6Fuse Block (12 circuits)Blue Sea (12V Distribution Panel)1View
7Fuses KitAssorted Fuses (2A 3A 5A 7.5A 10A 15A 20A 25A 30A 35A)1View
8Battery MonitorVictron BMV-712 with BlueTooth1View
#ItemDescriptionQuantityView on Amazon
1Heat Shrink Butt Connector, Ancor MarineTo connect to Loads (75 Pack Kit)1View
2Heat Shrink Disconnect, 10-12 AWG Cable, 1/4″ Tab, Female
To connect to certain loads (i.e. 12V Sockets) , to make “removable” connections (i.e. Fridge, LEDs) and to connect cable of different gauge together (i.e. LED Dimmer) (25 Pack)
3Heat Shrink Disconnect, 10-12 AWG Cable, 1/4″ Tab, Male1View
4Heat Shrink Disconnect, 14-16 AWG Cable, 1/4″ Tab, Female1View
5Heat Shrink Disconnect, 14-16 AWG Cable, 1/4″ Tab, Male1View
6Heat Shrink Disconnect, 18-22 AWG Cable, 1/4″ Tab, Male1View
73M Scotchlok Quick Splice with Gel (14 AWG stranded)We used that to parallel our LED lights (25 Pack)1View
8Heat Shrink Tubing Kit (with adhesive)To protect lug after crimping1View
9Split Loom Tubing, 3/8″ diameter 25 feetTo protect wire bundles1View
10Split Loom Tubing, 1/2″ diameter 25 feetTo protect wire bundles1View
11Split Loom Tubing, 3/4″ diameter 10 feetTo protect wire bundles1View
12Nylon Cable Clamps KitTo secure cable/split-loom to wood1View
13Zip Tie Mount with AdhesiveTo secure cable/split-loom to metal1View
14Nylon Zip Ties KitTo secure cable/split-loom1View
15Rubber Grommet KitTo protect wire from sharp edge (going through metal hole)1View
12V Loads

These are the appliances we personally use in our van:

#ItemQuantityBuy LinkMore Info
1Maxxair 6200K Roof Fan1AmazonFan Installation
2LED Ceiling Lights (Dimmable)3Amazon
3PWM Dimmer for LED Lights, 12V, Slider1Amazon
4Blue Sea 12V Socket4AmazonElectrical System Guide
5Shurflo Revolution Water Pump, 3 GPM1Amazon
6ON/OFF Switch for Water Pump1Amazon
7Webasto Air Top 2000 STC Gasoline Heater1eBayWebasto Installation
8Propex HS2000 Propane Heater1DealersPropex Installation
9Novakool R5810 Fridge, 12V only1Campervan-HQFridge Guide
10Sirocco ii Gimbal Fan, 12V1AmazonSirocco ii Installation / Review
11Nature’s Head Composting Toilet1AmazonToilet Installation
12Propane Solenoid Shutoff Valve1Amazon
13ON/OFF Switch for Propane Solenoid1Amazon

These are essential to build your electrical system. Do NOT cheap out on tools (e.g. using pliers to crimp) or you'll compromise the performance and safety of your system.

# Item Description QTY View on Amazon
1 Crimping Tool, Single-Crimp (8-22 AWG) Single-Crimp should be used with Heat Shrink connectors to prevent tearing the insulation and loose the watertight connection (corrosion prevention) 1 View
2 Cutter / Stripper for 10-22 AWG Stranded Wire Nothing to add! 1 View
3 Hydraulic Crimping Tool (2/0-12 AWG) Provides adequate, repeatable results for larger gauge lugs. 1 View
4 Cutter for up to 4/0 Cable For large gauge cables 1 View
5 Heat Gun for Heat Shrink Connectors 1500W, Dual Fan Speed, Variable Temperature Control 1 View
6 Digital Multimeter (Voltage, Current, Continuity, Resistance) You don’t need it until you need it! Your friend when you need to troubleshoot… 1 View


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about us

Nice To Meet You.

Hello! We’re Isabelle and Antoine 🙂 In 2017 we sold our house (and everything in it), quit our engineering careers and moved into our self built campervan. We’ve been on the road since then and every day is an opportunity for a new adventure; we’re chasing our dreams and hopefully it inspires others to do the same!

72 thoughts on “Van Electrical Calculator”

  1. Awesome info on your website. I am building my van now. First time in the winter as well…. and pandemic and crazy USA situation! anyway , do you have any great ideas for hot water heater that uses minimal electricity? I am looking at the mini 2.5 gal Bosch, but even that uses 1450 Watts. I could get a 2000Watt inverter, and I only need 20 minutes to heat there water for a shower every other day ( song bath in between or friends house if needed). I am trying to stay away from propane ( just a 1 gal bottle for my cooker). I am new to this and would appreciate your help if you know of anything MUCH OBLIGED!!!

  2. Thanks for compiling this!

    The Sterling Pro Batt Ultra B2B Charger is unavailable on Amazon (not just out of stock). I did however find the Renogy 60A DC to DC Battery Charger, is that an acceptable replacement?

  3. Hi folks, let me say I have probably funded your next trip since I not only bought your builder’s pack but have spent about $4500 so far on Amazon using your affiliate links! But now I have two questions if you don’t mind helping me out. First, I bought the Samlex 1230 based on your calculator even though so many forums say not to use this with a LiFePo battery. But you do so I’m trusting your experience. What DIP settings are you using? In the manual it looks like I should use “battery with load” both dip off but I have a feeling you’re using S1 off, S2 on, Flooded/AGM. Can you please enlighten me so I don’t blow my batteries up?
    Second, your calculator in Acrobat Pro doesn’t show a fuse between the hot bus and the 2000 watt invereter but Mac Preview (which I know your calculator doesn’t support) shows a 250 amp Bussman battery terminal fuse between the bus bar and the inverter. I assume that is correct?

    • First, thank you for your support, it means a lot 🙂

      Samlex 1230: S1 off/S2 on, LiFePo4 battery charging profile is similar to AGM battery, so no issues here.

      The wire between the bus bar and inverter will be protected by the 250A fuse that is located between the battery and the bus bar. However, if that fuse blows up because something goes wrong with your inverter, your whole electrical system is down. Having a fuse between the bus bar and inverter could isolate issues with your inverter from the rest of your system; assuming this is the one to blow!
      When going with a smaller inverter, wire can be smaller and must be protected by a smaller fuse (175A/200A).

      • Thank you so very much, that’s just what I needed! One thing I do see missing from your site (and this might be planned) is any photos of your electrical system. I can look at your calculators but was hoping to find some photos of how you laid yours out. I watched your video of the van tour but it only shows Antoine opening a tiny cabinet then closing it again. I can’t believe all of those wires, components and breakers fit in that tiny cabinet. At any rate, your site has been indispensable and I am creating my entire electrical system and propane system directly from your diagrams. What an amazingly helpful resource.

  4. Is it possible that there is an error in the AH calculation in the 120 volt section of your electrical calculator. I have always though that the wattage needs to be divided by the voltage to obtain the amperage. In the calculator, the wattage is divided by 12 instead of 120. Am I wrong?

    • But remember that your energy source (the battery) is 12V!
      – So between the battery and the inverter (where the voltage is 12V), the current is AMPS=WATTAGE/12V (and in fact, even more amps because of the efficiency loss of the inverter);
      – Between your appliance and the inverter (where the voltage is 120V), the current is AMPS = WATTAGE/120V

      Hope that makes sense.

      • We have the same question…
        When we type in 1050 watts for our microwave for 0.25 hours it gives us 27.5 amp hours. This doesn’t seem possible… Whereas if we divide by the 120V it then gives us 2.57 amp hours.
        Just looking for further clarification on this.


        • Here is the calculation:
          Current as seen by the inverter (120v): Amps = Watt/Volt = 1050W/120V = 8.7.A
          But look at what’s going on at the battery bank:
          Current as seen by the battery bank (12v): Amps = Watt/Volt = 1050W/12V = 87.5A
          Total energy draw at the battery bank: Ah = A * h = 87.5A * 0.25h = 21.9Ah
          The calculator also includes conversion loss (120V > 12V) from the inverter of 85%: 21.9Ah/0.85= 25.7Ah

          So using your microwave for 15 minutes draw 25.7Ah from the battery bank. If you start with 200Ah (2 batteries at full charge), the remaining energy left in your battery bank is: 200-25.7 = 174.3Ah. So you went from 100% charge to 87% charge.

          Hope that clear things up!

  5. First, thanks for making such a helpful guide. I was wondering, what made you choose the 60A b2b charger if your alternator could theoretically handle more. We have a transit with a 250A heavy duty alternator, and we’re big time snow chasers, so we figure the more we can pull from the alternator in the winter, the better. is there anything dangerous about going with a 100A b2b?

    We were also wondering, do you think it would be possible to route the b2b through one of the transit auxiliary switches? The idea would be to try to use it less in the summer when we can count on solar to save wear and tear on our alternator, but turn it on in winter or any other time we need the boost. Is there any merit to that idea?

    Thank you so much!

    • First, we don’t think it is dangerous to go with a 100A B2B. We wanted to go with Sterling and they don’t recommend using the 120A for automotive application. We felt 60A was enough for our needs.

      As for the auxiliary switches, they won’t provide enough current. And since we installed breaker before and after the B2B, we simply use them to shut down the B2B charger (it can also be done on the charger itself). This article will provide you with more information about our installation:

  6. Wow… just wow. You guys have created such an incredible resource here and I’m so thankful. This would take me uncountable hours to figure out if I were piecing it together from all the different web sources. I think I may build my entire van out using the resources you’ve created, so THANK YOU! I’m so impressed at the level of detail you guys go to, and the electrical usage calculator with autofill options might be the coolest thing I’ve seen yet. Thanks again for everything you guys have created, super stoked to build our van, and we’ll be sure to use your Amazon affiliate links for everything we can!

  7. I purchased the van electrical calculator, but it doesn’t appear to work for me. It says I need more than 500Ah of battery and more solar than your calculator can handle, so I’m not getting the component or wire gauge calculations that I need. What can I do?

  8. Hi and thank you for such amazing resources!

    When calculating needs, my setup estimates 46ah per day, however recommends 200ah lithium batteries. Since lithium can be used completely, can you explain why 100ah wouldn’t be sufficient?

    Thanks so much!

    • You could go with one (selecting Sun Seeker option should also give you 100Ah). However, it doesn’t give you a lot of autonomy in case you can’t charge everyday.

  9. For the Main Component Sizing, what are some of the assumptions? Is it assuming 2-days capacity? I came up with 190Ah usage. In Sun Seeker mode with Lithium battery, it recommended 400AH battery capacity, or 600AH AGM. I’m sure it’s making assumptions about re-charge from solar, solar panel efficiency… But is it assuming more than one day worth of capacity?

    • Hi! For reference, this page goes through the calculation step-by-step (including the formulas):
      You’ll find in section 3.1.2 that the formula for Sun Seeker lithium is: Battery capacity=(Daily Power Usage x 1.5)/0.8.

      190Ah usage seems unusually high… Can you take a screenshot of the calculator (with your inputs) and send it to faroutride at gmail dot com ?

  10. Hi there! I am so very impressed with people like you who have such detailed knowledge like this. I kind of make it up as I go and learn along the way 🙂

    Anyway, I am in a learning phase right now. I have a 90w fridge that runs 7.5 amps and two macbook pros between my gf and I. That would need some charging mot days. 2 iPhones and a camera and drone with batteries.

    We have 160W solar and 2, 100ah AGM batteries that are also connected, in parallel, to a split charge system. Would love your thoughts on if you think our system will be adequate? TIA!

  11. Hi Antoine and Isabelle, why is a terminal fuse block included in the ‘inverter’ section with a 1000W and 1500W inverter, but not with a 2000W inverter? Thanks!

    • Because the wire between the inverter / bus bar is already protected by the 250A fuse (located at the battery terminal). When you choose a 1000W or 1500W inverter, the smaller wire is not rated for up to 250A and therefore must be protected with a smaller fuse. Hope that makes sense!

  12. We used your old calculator (love the new one though!) and ended up with a 600W inverter and 100Ah battery. We just decided we wanted to use the Pakt coffee kit in our van which has a kettle that draws up to 500 Watts. I’m worried that we should’ve gotten a 1000W inverter now… Do you think we can still get away with using our 600W inverter and 100Ah battery? We use an alternator charger and drive at least an hour a day so I’m not too worried about having power, just don’t want to ruin our system trying to draw too much… Thank you for any advice!

    • I’d give it a try, you won’t damage your system. Here’s what will happen if you have an overload (extract from the Samlex manual):

      10.1.2 Overload: If there is a continuous overload of 110% to 115% for 2 to 3 sec, the
      output voltage will be shut down. Red LED marked “OVERLOAD” (3, Fig 6.1) will turn ON,
      the Status LED on the GFCI outlet (5C, Fig 6.1) will be OFF and buzzer alarm will sound.
      The Green LED marked “POWER ON” (2, Fig 6.1) will continue to be lighted. The unit will
      be latched in this shut down condition and will require manual reset. To reset, switch OFF
      the unit using the ON/OFF Switch (1, Fig 6.1), wait for 3 minutes and then switch ON the
      unit again. Before switching ON, determine and remove the cause of overloading.

  13. Isabelle, Antoine,

    First off, you two are beasts for compiling everything on this website. Couple of inquiries for you: Please explain the need for the 250-amp catastrophic fail safe. Considering a system where the only input is 540-W of solar with the respective Victron 100/50 MPPT with the Battle Born BMS’s and the assorted circuit breakers, is the fail safe necessary? Seems like there is plenty of redundancy with respect to fail safes.
    Additionally, the shore power charger by Samlex you recommend is apparently not intended for Li cells per the manufacturer’s manual. Is there a 120-12v converter you like or have heard about for the popular battle born batteries?



    • The 250A fuse would be useful in the case of an accident, or even during installation if pos/neg cable touch by mistake; that’ll protect you from getting electrocuted or starting a fire.
      Battle Born FAQ mentions that a charger with AGM settings works fine, since the charge profile is very similar.


  14. How are you calculating the fridge only being active for 8.4 hours a day? is it assuming this is the amount of time that the system is not running from Solar?


    • Hey Kieran,
      most campers are using a compressor fridge, that means the fridge only consumes power when the compressor is working. Over the day, it is only active for a few hours (depending on the outside temperature) and the rest of the time the cold is stored.

      I hope I could help you too


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