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Solar Charge Controller Recommendation


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I am relatively new to the solar game. I have 160 watts of panels. I have a Samlex 300 watt pure sine wave inverter that I would like to power from the load terminals of the solar charger to take advantage of the settable low voltage shutoff feature. The inverter low power shutoff is 10.5 volts and is not adjustable. The primary items that I want to power from the inverter (satellite receiver and TV) total 100 watts. The charge controller that came with the panel kit is a 20Amp and says to limit load to 120 watts. I am looking for recommendations for a charger controller than would allow me to use more of the 300 watts of the inverter. I have found some like the Morning Star units, with costs between $150-200. Are there any more reasonably priced options?

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You do not connect an inverter directly to a solar charge controller.  That is not how the components are designed (at least not the ones intended for RV use) to work.  In an RV, the solar charge controller connects between the solar panels and the battery bank. It takes in DC power at various voltages and outputs DC power at a voltage a battery can accept.  The charge controller provides a charge to the batteries to replenish them or keep them topped off.

An inverter connects to a battery bank (a constant DC source).   The inverter uses power from the batteries to invert 120v AC power.  The batteries are a necessary piece of the puzzle in an RV.  The inverter needs constant 12v DC power to operate properly.  Otherwise you would not have inverter AC output after dusk/dark or in marginal conditions.  Additionally, the solar charge controller cannot consistently provide constant DC power at levels sufficient to power an inverter.  The solar panels connected to the charge controller are subject to lighting, weather, and other atmospheric and surrounding conditions.  These conditions affect the voltage being sent to the charge controlar and thus the voltage the charge controller can output.

In the residential grid tie world, inverters are built to take DC voltage power directly from solar panels and feed the inverted 120v AC power back into the grid.  This AC power being fed to the grid fluctuates based on conditions.  It is not constant.  It stays at 120 volts, but the amperage behind it fluctuates.  Grid tie inverters are not really intended to supply 120v AC directly for powering appliances, because of this fluctuating amperage.  They are simply meant to feed power back into the grid.  This is a different set up than an RV, which is a stand alone system and may or may not be connected to the grid.

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So why does the charge controller have a 12 volt DC load connection in addition to the battery connection? Why does it have a circuit that can be programmed to shut off the load at a specified battery voltage? Why do the controllers' manuals  specify that the load connected to the load output should not exceed X watts?  The controllers I am looking at from Morning Star and others (and the one provided with the panel kit) have input from the solar panels, output to the battery with programmable parameters, and load output with programmable parameters.  I am not looking to integrate the solar system into the RV power system with transfer switches, etc. at this time.

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I should have been a little more clear in my first response.  While it is technically possible to connect an inverter directly to a solar charge controller to supply 120 volt AC power from the DC solar panels, it would have severe functional limitations.  By adding a battery(s) into the system, it will function much better and will provide more useful service.

You would have to specify which controller models you are specifically looking at for me to answer the questions about the different connection lugs.

As for integrating the solar panels and inverter into your system, there is no need for "transfer switches, etc." to accomplish it.  The simplest way to install an inverter and solar to a 30 amp travel trailer would be to install the inverter and connect it to your existing battery(s).  Once the inverter is installed and connected, when you want power, simply plug the trailer power cord into an outlet on the inverter (with the proper adapter) and turn the inverter on.  If going this route, you would have to manually make sure 120 volt heavy draw items like air conditioners, converters, electric element on water heater, electric element on refrigerator, etc are all turned off or disabled at the breaker when running on inverter power.  Transfer switches, sub panels and other components are not required when powering 30 amp RV's.

To add solar to this same set up could be as simple as connecting a suitcase type portable solar set up with an in line charge controller to the battery bank to charge the batteries.  This whole set up would require minimal installation and would function fine within the limits of the components (as long as you remember to manually disable the heavy power draw items).  You can start with a set up like this and then upgrade or add as you like or need down the road.

This type of set up will function much better than trying to connect the inverter directly to the charge controller.

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47 minutes ago, trailertraveler said:

So why does the charge controller have a 12 volt DC load connection in addition to the battery connection? Why does it have a circuit that can be programmed to shut off the load at a specified battery voltage? Why do the controllers' manuals  specify that the load connected to the load output should not exceed X watts?  The controllers I am looking at from Morning Star and others (and the one provided with the panel kit) have input from the solar panels, output to the battery with programmable parameters, and load output with programmable parameters.  I am not looking to integrate the solar system into the RV power system with transfer switches, etc. at this time.

Those "Load" connections are there to allow a device to connect to, such as a 2 way radio or light. If battery voltage drops, the load will be disconnected, until the voltage comes back up. In some cases, this is done to prevent discharged batteries from freezing, but it also extends the battery life, by not running them flat dead.

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3 minutes ago, Chad Heiser said:

I should have been a little more clear in my first response.  While it is technically possible to connect an inverter directly to a solar charge controller to supply 120 volt AC power from the DC solar panels, it would have severe functional limitations.  By adding a battery(s) into the system, it will function much better and will provide more useful service.

You would have to specify which controller models you are specifically looking at for me to answer the questions about the different connection lugs.

As for integrating the solar panels and inverter into your system, there is no need for "transfer switches, etc." to accomplish it.  The simplest way to install an inverter and solar to a 30 amp travel trailer would be to install the inverter and connect it to your existing battery(s).  Once the inverter is installed and connected, when you want power, simply plug the trailer power cord into an outlet on the inverter (with the proper adapter) and turn the inverter on.  If going this route, you would have to manually make sure 120 volt heavy draw items like air conditioners, converters, electric element on water heater, electric element on refrigerator, etc are all turned off or disabled at the breaker when running on inverter power.  Transfer switches, sub panels and other components are not required when powering 30 amp RV's.

To add solar to this same set up could be as simple as connecting a suitcase type portable solar set up with an in line charge controller to the battery bank to charge the batteries.  This whole set up would require minimal installation and would function fine within the limits of the components (as long as you remember to manually disable the heavy power draw items).  You can start with a set up like this and then upgrade or add as you like or need down the road.

This type of set up will function much better than trying to connect the inverter directly to the charge controller.

Not sure why you think, I was not using a battery(ies). I do not want to plug the whole RV into the inverter. I have a separate dedicated 20 amp 120 volt AC circuit and outlets that can be plugged into shore power for additional electric heater(s) or to the inverter for TV and satellite receiver. Using your method, the inverter could draw the batteries down to its non-adjustable low voltage shutoff of 10.5 volts which would quickly kill the battery bank.

This is a typical product description for the controllers I am looking at "Solar panels produce 18-28 volts and this regulates voltage down to correct battery charge levels. It also monitors the load on your batteries passing thru the controller and will disconnect 12v devices when draw exceeds 40 amps. "

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6 minutes ago, Darryl&Rita said:

Those "Load" connections are there to allow a device to connect to, such as a 2 way radio or light. If battery voltage drops, the load will be disconnected, until the voltage comes back up. In some cases, this is done to prevent discharged batteries from freezing, but it also extends the battery life, by not running them flat dead.

That was my understanding and is why I asked for recommendations for a controller that would support more than the 120 watts maximum of the controller that came with the panels.

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10 minutes ago, trailertraveler said:

Not sure why you think, I was not using a battery(ies). I do not want to plug the whole RV into the inverter. I have a separate dedicated 20 amp 120 volt AC circuit and outlets that can be plugged into shore power for additional electric heater(s) or to the inverter for TV and satellite receiver. Using your method, the inverter could draw the batteries down to its non-adjustable low voltage shutoff of 10.5 volts which would quickly kill the battery bank.

This is a typical product description for the controllers I am looking at "Solar panels produce 18-28 volts and this regulates voltage down to correct battery charge levels. It also monitors the load on your batteries passing thru the controller and will disconnect 12v devices when draw exceeds 40 amps. "

I know you have batteries in your trailer, however you stated you want to run an inverter directly from a solar controller (so I assumed you meant no batteries in that system).  I am saying that is functionally not going to work and batteries are required to run an inverter.  This is why I gave an example of the simplest way to install an inverter since you said you did not want to add any extra components.  There are many ways to install inverters in an RV, but they all require batteries to make them functional.  You do not have to plug the whole 30 amp trailer into the inverter, but that is the simplest method to make things in the trailer work from the inverter.  You could also run extension cords from the inverter to the specific items you want to power so nothing else in the trailer is powered.  You can also permanently install secondary receptacles that are wired directly to the inverter.  You can also install a sub panel and transfer switch to power items from the inverter, and so on and so on.  There are many ways to accomplish powering 120 volt appliances from an inverter, however all those ways require the inverter to be connected to some sort of battery or battery bank to make it functional.

The load terminals you are describing on solar controllers are for small power draw loads like lights or a radio or the like as Darryl&Rita indicated.  They are not intended for high power draw items like an inverter.

Again, however, without the specific models of solar controllers you are looking at, I can't specifically address there capabilities.  I am happy to help in any way I can.  

Maybe if you describe what you are trying to power with the inverter we can give a better idea of the simplest way to accomplish this.  How often and when would the items you want to power be used?  This information will also help.

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15 minutes ago, Chad Heiser said:

...Maybe if you describe what you are trying to power with the inverter we can give a better idea of the simplest way to accomplish this.  How often and when would the items you want to power be used?  This information will also help...Again, however, without the specific models of solar controllers you are looking at, I can't specifically address there capabilities.  I am happy to help in any way I can...

I did in the original post.I am asking for recommendations for controllers that will support a 300 watt load so I don't have specific models in mind at this time.

5 hours ago, trailertraveler said:

...The primary items that I want to power from the inverter (satellite receiver and TV) total 100 watts. The charge controller that came with the panel kit is a 20Amp and says to limit load to 120 watts. I am looking for recommendations for a charger controller than would allow me to use more of the 300 watts of the inverter...

15 minutes ago, Chad Heiser said:

 

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Sorry, I missed that.  If you are only trying to power a TV and a satellite receiver, you do not need a very big inverter.  You do need to know the power draw of your TV and of your sat receiver to determine what size inverter will be needed to power them.  The 300 watt inverter you describe will probably be enough, but without knowing the draw of the TV and sat receiver, I cannot say for sure.  Both components should have ratings on them somewhere to give you an idea of how much power they will draw.  To truly know how much power they use, a Kill-A-watt meter can be used.  You can install your small point of use inverter in the entertainment center cabinet near the components and run cable to the power source to power the inverter.  

What is the voltage and amperage of your 160 watt solar panel?  

Do you plan to watch TV after dusk/dark or in the early morning/late afternoon (any time the sun is low in the sky)?  If the answer to any of this is yes, then the inverter must be connected to a battery bank.  Depending on the output ratings (amps and volts) of your solar panel, it might be possible to run them from the small inverter directly from a solar controller.  I doubt that single 160 watt panel will be able to produce enough power though, but the ratings will tell the tail.  If the ratings are enough, then you will still be limited to only a couple of hours in the mid day with full sun and no obstructions to the panels.  As I tried to indicate earlier, it is technically possible to do, but functionally not practical without the inverter being connected to a battery.

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19 minutes ago, Chad Heiser said:

...You do need to know the power draw of your TV and of your sat receiver to determine what size inverter will be needed to power them.  The 300 watt inverter you describe will probably be enough, but without knowing the draw of the TV and sat receiver, I cannot say for sure...

I know what the TV and satellite receiver draw.

6 hours ago, trailertraveler said:

..The primary items that I want to power from the inverter (satellite receiver and TV) total 100 watts...

The 300 watt inverter powers them fine. The 160 watts of panels will, once the battery is fully charged, run the inverter with the TV and Satellite receiver without drawing down the battery during daylight hours on a sunny day.

Again what I am looking for is a recommendation for a solar controller that will support a load of at least 300 watts and monitor and shutdown the load at adjustable low battery voltage. 

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47 minutes ago, Rich&Sylvia said:

You probably want to upgrade to the "ProStar-Gen-3" model by Morningstar.
See: ProStar Manual

Many solar controllers do not have "load" terminals, thus it's easy to confuse folks with your question.
Morningstar makes some good stuff.  You should find what you need within their product line.

Thanks for the link!!! I am curious about this statement in the ProStar Manual: "CAUTION:  Equipment Damage. Do not wire any AC inverter to the load terminals of the ProStar.  Damage to the load control circuit may result."

This raises the question of why, and whether any inverter can be powered through the load terminals of a solar control?

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6 minutes ago, trailertraveler said:

This raises the question of why, and whether any inverter can be powered through the load terminals of a solar control?

I thought I had been fairly clear about this, but maybe not.  This is not how solar controllers are designed to work.  Inverters are intended to be used with batteries, not directly connected to a solar controller with no battery in the loop.  Why are you so adamant about not having a battery in the system?  If you are afraid of running your trailer batteries down, use a stand alone battery just for the solar controller and inverter to connect to.

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Use the "Load" terminals to control a solid state relay. Wire the inverter direct to the batteries. Use the NO contact from the relay to kill power to the inverter. More than once you've been told not to do things the way you seem bent on. I predict smoke in your future.

I have been wrong before, I'll probably be wrong again. 

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25 minutes ago, Chad Heiser said:

I thought I had been fairly clear about this, but maybe not.  This is not how solar controllers are designed to work.  Inverters are intended to be used with batteries, not directly connected to a solar controller with no battery in the loop.  Why are you so adamant about not having a battery in the system?  If you are afraid of running your trailer batteries down, use a stand alone battery just for the solar controller and inverter to connect to.

I am not adamant about not having a battery in the system. In fact, I never said that I wanted to run the system without a battery.  If you bothered to take the time to read and understand what I have written, you would know that I do have a battery(ies) in the system. You would also have known that I knew what the TV and Sat receiver draw.  You obviously are not aware of the current products on the market and their capabilities such as powering a load. In the very first post I stated:

8 hours ago, trailertraveler said:

I would like to power from the load terminals of the solar charger to take advantage of the settable low voltage shutoff feature. The inverter low power shutoff is 10.5 volts and is not adjustable.

The load terminals are not the same as the battery charge terminals which you seem to think I am talking about. As I stated before, the controllers I am looking at have three sets of connections input from the panels, output to the battery and output to a "Load".

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I understand perfectly what you are talking about.  I know what load terminals are on a solar controller vs. the charging terminals.  I am very familiar with current equipment.  I have done a number of large and small solar and inverter installations.  I have also given multiple presentations on the subject.  I am trying to be as diplomatic as possible in telling you that you cannot run an inverter directly from a solar controller and expect it to work reliably or at all.  I don't have any more information that I can give you than that.

I asked you for some specific information on your equipment and the equipment you were looking at (model numbers, amp ratings, volt ratings) so I could help you get to where you want to go.  You supplied some basic information, but not the detailed information needed to fully answer your questions.

I apparently am not the right person to help you.  You seem set in your path and don't want to deviate at all.  I would like to help get you to a solution, but it can't be done the way you are trying to do it.

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9 minutes ago, Darryl&Rita said:

Use the "Load" terminals to control a solid state relay. Wire the inverter direct to the batteries. Use the NO contact from the relay to kill power to the inverter. More than once you've been told not to do things the way you seem bent on. I predict smoke in your future.

Thanks for piling on, you also are probably unfamiliar with the features of the newer products. As I stated before, the controllers I am looking at have three sets of connections: input from the panels, output to the battery and output to a "Load". This description "It also monitors the load on your batteries passing thru the controller and will disconnect 12v devices when draw exceeds 40 amps."  seems to indicate that the load is coming from the batteries and being monitored by the controller which is why the controller can shut the load off at overdraw or under voltage. I am concerned about the statement in the Morning Star manual that an inverter should not be used as the load powered by the controller.

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28 minutes ago, Chad Heiser said:

I understand perfectly what you are talking about.  I know what load terminals are on a solar controller vs. the charging terminals.  I am very familiar with current equipment.  I have done a number of large and small solar and inverter installations.  I have also given multiple presentations on the subject.  I am trying to be as diplomatic as possible in telling you that you cannot run an inverter directly from a solar controller and expect it to work reliably or at all.  I don't have any more information that I can give you than that.

So what are the load terminals suitable to power if not a small inverter that is less than the watt rating of the load terminals? I am concerned about the statement in the Morning Star manual that an inverter should not be used as the load powered by the controller and wondering why?.

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They are intended to supply power to small amperage items like a radio, lights, a fan or stuff like that.  An inverter is a high amperage constant draw and the load terminals on a solar controller are not designed to supply constant high amperage.  They may be able to support a high amperage draw for a short period like upon start up on a fan motor or something similar and then the amperage drops down to a lower more sustainable level.  This is why the Morningstar manual has the quote you referenced above to prevent people from trying to connect an inverter directly to the load terminals.  

Darryl&Ritas suggestion of using the load terminals to power a relay could be a possible solution to get you were you want to go.  Connect the inverter directly to the batteries.  Put a high amperage (rated high enough to match the inverters peak/surge ratings) relay in between the inverter and the battery bank.  Use the load terminals on the solar controller to open and close the relay based on the programmable settings you desire.  

For example, when the load terminals sense above X voltage, close the relay and allow power to pass from the batteries to the inverter.  When the load terminals sense below X voltage, open the relay to stop the inverter from drawing power from the batteries.  In this example the inverter is connected directly to the batteries, but the solar controller can control when it will be "on".

In this example, the solar panel ratings are irrelevant to the inverter operation.  The solar panels will provide a charge to the batteries through the solar controller when the sun powers them sufficiently to provide a positive charge to the batteries.

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31 minutes ago, Chad Heiser said:

...They are intended to supply power to small amperage items like a radio, lights, a fan or stuff like that.  An inverter is a high amperage constant draw and the load terminals on a solar controller are not designed to supply constant high amperage...

Thank you!!! It just seemed that a controller rated for a maximum load of 40 amp (480 watts) or 62.5 amps (750 watts) should be able to handle a 300 watt (25 amp) load.

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You need to look into the ratings a little deeper.  Not knowing specifically what model you are referencing, I can't look it up directly to get the information.  The ratings may be peek ratings.  If so, the unit is not intended to run at peak ratings for more than a short time period.  It may also have a working rating that is lower that it can sustain for longer periods of time.

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2018 Polaris RZR Turbo S (fits in the garage)
2016 Smart Car (fits in the garage or gets flat towed behind the DRV when the RZR is in the garage)
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14 minutes ago, Chad Heiser said:

You need to look into the ratings a little deeper.  Not knowing specifically what model you are referencing, I can't look it up directly to get the information.  The ratings may be peek ratings.  If so, the unit is not intended to run at peak ratings for more than a short time period.  It may also have a working rating that is lower that it can sustain for longer periods of time.

I really don't have any specific brand or model in mind. The ratings I mentioned in the last post were from some models I saw on line, but the ratings weren't all that good which is why I was asking for recommendations. The Samlex 300 inverter has a continuous output of 300 watts and a surge output of 500 watts. Maximum input 40 Amp. Voltage range 10.5 - 16.5 VDC.

If I go the relay route, would a 40 amp relay be enough? 

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The relay should at least be capable of supporting the maximum potential amperage draw of the inverter.  I might even go slightly larger than the inverter's maximum rating just to be on the safe side.  I have a couple of relays I use in my truck for different applications, but on the same principle.  I have them in line on some high draw items that I want to only be powered when my ignition switch is on or in accessory position.  Rather than run those high draw items through an accessory powered spot in my fuse panel, I have them connected directly to my battery bank with the relay in line and the relay is powered from the accessory power source.

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2017 DRV Mobile Suite 40KSSB4 with factory mods, dealer mods and personal mods - now in the RV graveyard
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2018 Polaris RZR Turbo S (fits in the garage)
2016 Smart Car (fits in the garage or gets flat towed behind the DRV when the RZR is in the garage)
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I would size the relay for 150% of the max draw you expect. The relay will live longer, and support any peak draws that were unexpected. Make sure that your inverter-battery wiring meets the inverter manufacturers specs. The other reason for a larger relay is matching wire size to lugs/terminals. Larger relays will make this easier. Your not talking about much current here, so the relay will not be very big.......

Jack & Danielle Mayer #60376 Lifetime Member
Living on the road since 2000

PLEASE no PM's. Email me. jackdanmayer AT gmail
2016 DRV Houston 44' 5er (we still have it)
2022 New Horizons 43' 5er
2016 Itasca 27N 28' motorhome 
2019 Volvo 860, D13 455/1850, 236" wb, I-Shift, battery-based APU
No truck at the moment - we use one of our demo units
2016 smart Passion, piggyback on the truck
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See our website for info on New Horizons 5th wheels, HDTs as tow vehicles, communications on the road, and use of solar power
www.jackdanmayer.com
Principal in RVH Lifestyles. RVH-Lifestyles.com

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