Solar Controller Wiring

[camelracer]

When I installed my Morningstar SunSaver MPPT controller several years ago I followed their instructions which stated that no inverters should be connected to the load output terminal. Since I don't have an inverter - no problem. I just wired the camper master switch to the controller load terminal. This allowed the Morningstar controller to log current out put and amp hour usage plus provide low voltage disconnect.

Recently I was looking at the Morningstar web site and found out they changed the installation instructions to not attach any inductive load to the controller load terminal. This includes inverters and motor driven devices (compressor fridge, heater, water pump, vent fans & etc).

I contacted Morningstar and their tech rep said that I've been lucky to not have had any problems so far and it may have to do with the combination of items that are on and their cycling sequence. He recommended these items be powered through a relay and flyback diode and sent this article.
http://support.morningstarcorp.com/wp-content/uploads/2014/07/ALL.DIG_.Load_Control_Using_
A_Relay.01.EN_.pdf

This would be an easy mod but I would loose the load usage logging capability. I think I would rather loose that capability than try to find a replacement solar controller in Mulege next year.

Can any of you EEs out there weigh in and give this ME some advice.

 

[PaulT]

camelracer,

Your charge controller is charging batteries, right? Batteries are good for absorbing transients. Ask Morningstar how to wire their controller into a system with an inverter and batteries. Why would anyone buy their product if it couldn't be used in a typical RV system. These commonly include inverters driven off batteries and charged by charge controllers.

It may be that the tech guy you contacted, thought that the Morningstar was directly driving devices without batteries in the circuit. Worth asking.
I did look at the link. Your load is a mix of items and not just a pump, motor, or inverter.

Paul

 

[rando]

If it hasn't been an issue for the past couple of years, I don't see much reason to worry about it now. If you really want to be safe you could put a 'flyback' or clamp diode across the load terminals. The issue with the inductive loads is something called field collapse - when you suddenly shut off the power to the coil the collapse of the magnetic field can cause a negative voltage spike that back feeds the driving circuit. In the case of your fridge, when the thermostat cycles off it is disconnecting the power to the compressor at the thermostat - so any field collapse spike won't make it back to your solar controller. The only time you could have an issue is when the controller turns off the load terminals while the fridge compressor is running. You can address this by adding a reverse biased Schottky diode across the terminals of the load output. That way if the solar controller dumps the load while the compressor is running the negative voltage will flow through the (now forward biased) diode as opposed to the MOSFET inside the controller.

 

[camelracer]

Paul
I could run an inverter and/or motors safely if those loads were connected to the battery and that could be a solution. The problem is they are now connected to the load output of the controller which has a solid state switch to shut off the load when battery voltage gets too low or the current draw exceeds 15 amps. I guess this switch and other electronics in the controller can be damaged by the voltage spikes resulting from a collapsing magnetic field.

Rando,
That makes sense. The worse case scenario would be if the controller turned off the load terminal when I have all the inductive loads running. Since the controller load is only turned off for over current or under voltage conditions it hasn't happened yet. That may be why I haven't had any problems. The diode on the load terminal would be good insurance. I'll have to figure out what a Schottky diode is or can a 1N400X type be used.

Thanks for the help guys - Dick

 

[ntsqd]

If it can be fixed with a simple diode, why isn't Morningstar already doing that? The unit cost at their volume can't be much.

Space permitting this sort of thing is why I've long tended to shy away from all-in-one solutions.

 

[rando]

If you are going to add this, you probably want something a little heftier than a 1N4XX - something like this:
https://www.digikey.com/product-detail/en/fairchild-on-semiconductor/SB1245/SB1245CT-ND/2179164

would be fine.

As for why Morningstar isn't doing it - clearly it is not a major problem as nothing bad has happened to CamelRacer so their engineer probably just didn't think of it. I am guessing somewhere along the line they had a failure or two, so they took the easiest route - update the manual as opposed to a redesign of their product. It is not really an issue with an integrated product, just a pre-emptive approach from morningstar to address a minor problem.

 

[Happyjax]

I'm a bit confused......okay so that's normal but....

I thought the purpose of a solar charge controller was exactly what it says, to control the amount of charge your batteries receive from your solar panels.

I know many have a load take off but I thought that was often to use wasted power when your batteries were up to snuff or a quick power connection for a light or something small.

My understanding is we have batteries to supply our needed power and they are made to handle current and supply lots of amps on request.

I cannot imagine putting even the smallest inverter or any motor/inductive load on the load output of a controller which is coming off of the panels. I don't believe solar panels are really suited for that especially in the wattage amounts that we tend to use. That might be why there is no special diode on those terminal, they aren't really made for that....

So if I am wrong please enlighten me as I do want to understand this all better. I will eventually be putting something on the camper I will eventually be buying....lol

Thanks!

 

[rando]

The 'load output' is just a connection to the battery through a solid state relay (MOSFET). It is not a direct connection to the panels or anything like that. It is kind of a legacy from when solar power was use primarily for lighting - you could attach your light to the load output, and the controller would switch it on when the sun set (ie when solar power went to zero) and off when the sun rose.

One advantage of using the load output is that some controllers monitor the current on this output (eg Morningstar, Victron) so you can read what your loads are and keep a better eye on state of charge. However, the primary advantage is that it acts as a Low Voltage Disconnect which will save your battery from damage if you leave something on and then park in the garage. The load output is usually rated for whatever the charge controller is rated for, so there is no reason not to use it if your loads are lower than this number. Connecting an inverter to this would be pushing it (and they usually have their own LVD built in anyway), but connecting your fridge/fan/lights/propane alarm etc through this is totally fine and gives you peace of mind.

 

[Happyjax]

Cool I have learned something today. Life is good

 

[camelracer]

Good explanation Rando and thanks for the diode recommendation.

 

[Alley-Kat]

Connecting an inverter to this would be pushing it (and they usually have their own LVD built in anyway), but connecting your fridge/fan/lights/propane alarm etc through this is totally fine and gives you peace of mind.

So if I'm thinking correctly, my summary is; the inverter is a HIGH amperage draw unit and the fridge/fan/lights/etc. are LOW amperage draw units, thus Morningstar is concerned about any high amperage draw units?

I've used the same solar charge controller that camelreacer has for over 6 years now, using the LOAD off the Morningstar to feed all my low amperage draw units and I've not had any issues. I don't have any high amperage draw units in my camper.

I have no electrical connection to the truck in any way. Completely solar powered.

 

[craig333]

My inverter is the only thing that doesn't go through the charge controller. For as seldom as its used I don't mind that the trimetric is unaware. Unlikely as it is to harm the shunt its not impossible.

 

[Vic Harder]

ditto load terminals for everything but inverter

 

[ntsqd]

There are two shunts available. As I recall one is a 50A and the other is 500A. I realize that there's like a degradation in the reading with the 500 over the 50, but the TriMetric calibrates for either.