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Michael J. Kidd edited this page Aug 25, 2021 · 18 revisions


On October 13th of 2015, we embarked on a new adventure.  That, you see.. is the day we picked up our first Tesla electric vehicle!  A 2015 Tesla Model S 90D.  But, we are a bit atypical in that we also travel the country full time in a motor coach.  Initially, we thought we could charge the Tesla off of the RV-30 amp plug while we power the coach off of the 50 amp connection.  This ultimately did not work out so well.

There were a few issues with the 30 + 50 amp plug use.

  • Many RV parks are not wired to support the use of both the 30 and 50 amp connections at the same time.
    • You see, the wire size needed to supply 80 amps to the pedestal is quite expensive, and RV parks often require very long runs to supply the sites.  Since RV park designers and engineers don't have an expectation that both will be used, they tend to run smaller gauge wire to save installation costs for something that no one thinks is necessary in the first place.
  • Many RV parks allocate a portion of the lot rental fee to cover expected electrical usage.
    • There's no expectation that both the 30 and 50 amp plugs would be used, so the fee portion charged to cover electricity consumption doesn't include enough to cover this dual plug use.  In order for the RV parks to stick around for us to use, we have to ensure they can remain profitable.  While this may be a small amount compared to other costs, every little bit adds up and we shouldn't take advantage.
So, what to do?  Could you safely power the coach AND charge your EV from the same 50 amp plug?  Let's talk this through.
Can you safely power the coach AND charge your EV from the same 50 amp plug?
Yes! But you need to have some things setup first, otherwise you'll trip the breaker pretty quickly.
With these big coaches, is there enough power left over to charge an EV?
Yes! It's quite surprising how often even the biggest RVs use only a small fraction of the available power. There's plenty left over to charge up an EV!
How do you keep the breaker from tripping when the load changes?
That's where a bit of hardware and a bit of software come in. Keep reading...
Which Electric Vehicles will this work for? Only a Tesla?
Actually, this setup will work with the parts listed below for any EV that has an ability to charge from a J1772 plug. This includes practically every EV sold in the US. However, you should confirm your EV can use a J1772 plug for charging BEFORE purchasing any equipment for this project.
What about EVs that need a Type 2 Mennekes plug?
The shop for the EVSE we use (OpenEVSE) does list a Mennekes Kit bundle. It does not include the input power cord, nor do they seem to offer one fully assembled. However, if you're comfortable putting the kit together, it should work. Since we have no experience with Type 2 Mennekes vehicles, we simply cannot guarantee comparability.

Theory of Operation

  1. The House Energy Monitor device monitors the current used by the coach.
  2. It provides these readings to the Raspberry Pi via your existing WiFi network.
  3. The software running on the Raspberry Pi receives notice of the current use change and recalculates the amount that's left over for the EV to charge with.
  4. The software publishes the new EV charge limit via your existing WiFi network for the OpenEVSE to use.
  5. The OpenEVSE unit sends the new EV charge limit to your EV.
  • If the EV4RV software doesn't receive an update from the Coach Energy Monitor device for 30 seconds, it will disable the OpenEVSE so that your vehicle stops charging and prevents tripping the power pedestal breaker.
  • Once readings return, EV4RV will automatically re-enabled charging on the OpenEVSE.

You can use the Table of Contents at the right to see more details.

EV4RV Introduction Video