There is not much reason to monitor our inverter/charger, although there is a really good reason to be able to control the inverter/charger. But it turns out monitoring the inverter/charger is easy, and controlling it is hard. In this post we will explain what we did and why we didn’t do what we really wanted to do.
The Inverter
Our Inverter/Charger is a Magnum Dimensions MS2012, which is a 2000W Pure Sine Wave Inverter. It takes a 12 volt DC input and creates a 120 volt AC output. A while it does a great job of making AC out of DC, it does not offer a modern interface to be controlled by a computer. The main problem is the communication protocol is proprietary and only allows for one remote device to control the inverter.
In a typical RV setup, the inverter is controlled by dedicated display and control unit. In our case, this is the ME-RE from Magnum Dimensions. The status of the inverter and charger can be quickly determined from dedicated LEDs and changed from dedicated buttons. It is very easy to use, and probably why Magnum has this interface. The LCD panel allows for more complex functions and configuration, but these are hardly ever needed.
What we really want is to do is, be able to monitor and control the inverter and charger from two devices; keeping the remote control unit as the primary device and adding our computer as a second option. The communication protocol used by the inverter/charger has a significant limitation and only allows control from a single device.
But not all is lost. The inverter/charger uses a 2-wire RS485 network to communicate to its controller. And RS485 supports multiple devices being connected at the network at the same time. So, electrically we can add more devices to the network, we just can’t add more devices which are controllers. We can and did add a computer to the existing RS485 network. The computer is able to listen to or eavesdrop on all of the existing communications between the inverter/charger and its controller. This might seems like a bit of a hack, but RS485 fully supports multiple devices, in fact upto 32 networked devices. The limitation is in the proprietary communication protocol not the specification of the RS485 network. As a side note, RS485 dates back to 1998 which is around the same time our inverter/charger was designed. And at that time, RS485 was a modern standard and probably a great choice.
So in summary, we have added our computer to the RS485 network and we can monitor all of the existing messages, we just can’t control the inverter/charger in our setup.
Controlling the Inverter/Charger
But what we really want to do is control the inverter. Below are some options, all of which we have rejected.
Option 1. We could disconnect the existing Magnum Dimensions (ME-RC) controller from the network and replace it with our computer. This is possible as there would be only one controller on the network, and the computer can act like the original controller. The inverter/charge would not be able to detect the difference as long as the computer faithfully implements the proprietary protocol. The problem with this option, we would no longer have the original controller. So we can only control the inverter/charge from the computer, and this is not nearly as convenient as using the original dedicated controller. If it is a choice between the original controller and the computer, the original controller will always win.
Option 2. This is actually the same as option 1. Magnum Dimensions sells a gateway product which is specifically designed to allow a computer to interface with the inverter/charger. It is the ME-RVC. However, just like using a computer on the RS485 network, when the ME-RVC is connected, then the original controller has to be disconnected. Again, the original controller wins.
As a side note, we purchased the ME-RVC device, and option 2 would be preferred over option 1, as we can rely on the ME-RVC device to correctly implement the proprietary protocol and can use the more modern CANBUS and RV-C communication protocol.
Option 3. This is where things get tricky and we enter the nefarious world of hackery. We connect the computer to the inverter/charger on one RS485 network with the computer acting like a controller and then we connect the computer to the original controller but on a separate RS485 network, and on this second network the computer acts like an inverter/charger. The computer fools the inverter/charger into thinking it is talking to the original controller and vice-versa. In this arrangement, messages from the controller can be altered allowing the computer to control the inverter/charger but also allowing the original controller to control the inverter/charger. This sounds like the magic solution, but has one significant drawback. If the computer is turned off or has a fault, then this system is not going to work. But having said this, should the computer fail, then the original controller can be disconnected from the computer and plugged into the inverter/charger, and all is returned to a conventional configuration and everything works again.
One day we will wire-up option 3, at least with a twist. The original remote will use a RS485 network, but the inverter/charger will be wired to a ME-RVC gateway device and then to the computer. A project for the future.
Other Options. Also worth noting, Magnum Dimensions sells two web monitoring devices, ME-MW-E and ME-MW-W, one based on ethernet and one on wireless, which allows the inverter/charger to be remotely monitored. Neither of these devices allow the inverter/charger to be remotely controlled.
Controlling the Inverter/Charger
Why all the fuss about controlling the inverter/charge. Well, there are two main reasons. Firstly, we want to be able to the turn off the inverter automatically under certain conditions, like there has been no load for 5 mins. There is no reason to keep the inverter on when there is no load, as the inverter uses quite a bit of energy, even when it is not inverting. In idle or search mode it uses about 25 watts, which is a lot for doing noting. The inverter has to be completely turned off to prevent this. We mainly use the inverter to make coffee, boil water or charge our electronic devices. But when we are finished doing these thing we turn the inverter off. The computer can turn it off for us if we forget. Might seems like a small reason, but this small feature will save us energy. The second reason is to turn off the charger when the batteries reach 90% state of charge. In our setup there is no reason to fully charge the batteries from shore power, and it would be ideal to turn off charging and allow the solar to top-up the batteries. It might be possible through the charger settings to achieve the same result, but we have not been able to figure out how to do that (yet!).
Neither of these reasons are very compelling, and is the reason we have not worried about controlling the inverter/charger from the computer. But wanted to share all the details.
What Can we Monitor
More to come on this.
