2 @295 watt panels in parallel

[MotorVation]

MotorVation, I wasn't referencing volts, I was referencing watts.

Yes, I understand. The description for the controller warned not to go over 150 volts or it will smoke it.

I was just on the Renogy site and their version is on sale too with the MT-50. They don't include the cable but with the cable and free shipping it comes out to about the same price as the one on Amazon. I'd rather buy it direct from them. I don't have my mind made up..still thinking things over. I know on a perfectly sunny day it will cost me a few watts..
Thanks..

 

[frater secessus]

I'm seriously considering this Solar Epic 40A MPPT controller. It's the same as the Renogy Commander. I don't mean it's similar, it's the same exact unit from the same manufacturer with a different sticker on the case. From what I've read, the firmware on the Renogy has been changed a bit so that the MT-50 that Renogy sells is only compatible with their unit.

That will be fine.  My sysem is a 99% match for yours and that controller works very well for me.  Well enough to donate power at the RTR.  
And the price, even without the discount, is probably as low as you'll find.
You can config setpoints from the MT50 display or via the cable using the free windows application. 

I realize that there are better controllers out there but I really don't want to spend 500 or so bucks on one right now.

There will always be commercial grade, marine grade, aerospace titanium nanocarbon grade components out there if you decide later on you need them.  Until then your controller will happily run the panels and battery bank.  Ignore the brainless battery graphic on the MT50 and all will be well. 

 

[frater secessus]

The two panels will be 590 watts, but the charge controller is rated to handle only 520 watts with a 12 volt battery bank.

As noted earlier, this controller will limit current by increasing Vpanel when needed.  It's not an unusual feature, since it is a function of a PPT controller's ability to run the panel at different voltages to match current requirements.  I notice a pattern that controllers with massive heat sinks allow/support  overpaneling in their documentation.  Those that forbid it tend to be smaller, more enclosed designs.  Horses for courses and not everyone wants to look at Big Metal Fins.    

Perhaps counterintuiitively, in practice overpaneled systems rarely need to clamp.  A couple reasons for this:

1. Overpaneled systems start collecting usable power earlier in marginal light.  I have observed that ny the time light levels are high enough to theoretically max the system out the charger has completed Bulk and the bank's current acceptance is dropping.  Also excels in rain and cloudy conditions.  In car terms, the overpaneled system trades away some of the panels high-end horsepower output for more low- and mid-range grunt.  Less sexy but could be more suited for use as a daily driver.   
2. Because of temperature derating the panels will usually be peaking at something like 400w.  Yes, perfect storms of altitude and cold can yield max+ power but clamping/limiting would address that.  

 

[MotorVation]

 @  frater secessus

Thanks for the info. I appreciate it.

 

[John61CT]

I like that torque analogy

 

[jimindenver]

When used as a battery charger only over paneling may not make a difference by the time the sun is high enough that the controller would see it. The bank may be far enough into absorb or float that it would be limiting the normal amount of watts accepted by the controller. Turn on a big load at noon and the controller will be pushed to its limits for the duration. The controller is going to get hot producing maximum amps especially if the panels are in series creating a high conversion situation. Heat is the bane of electronics. The controller controls the over paneling by controlling the voltage but it controls its own temperature by limiting output. once heated up you may see fewer amps than you would have seen without over paneling.

Designing a system is finding the right balance between equipment, needs and situation. I lived at what most consider high altitude where my panels exceeded expectations daily. I camped and now spend my summers in the nose bleed section at twice the altitude. So one persons perfect storm is another persons daily life.

 

[jimindenver]

To add

If you are only seeing 400 watts off of 590 watts....CLEAN YOUR PANELS

 

[frater secessus]

If you are only seeing 400 watts off of 590 watts....CLEAN YOUR PANELS

It was over 100F and 500' ASL.  Temperature derating is a real thing.

 

[frater secessus]

exceeded expectations daily. I camped and now spend my summers in the nose bleed section at twice the altitude. So one persons perfect storm is another persons daily life.

Agreed, hence the note that clamping would take care of that.

The controller OP and I are talking about has massive exposed heat sinks.

 

[jimindenver]

I use Morningstar TS-MPPT series controllers. The heat sinks are larger than the workings of the controller and account for more than 50% of the total mass of the units. In the A/C on solar torture test and the over paneling/mixed panels/high conversion test the controller got so hot it clipped its output to protect itself.

I spent a year with multiple panels in various conditions using nothing but a multi meter and temperature gun. I know the effect of temerature on a panel well enough. Heat affects the panel but not nearly as much as it does a controller.

 

[happiergnome]

Perhaps counterintuiitively, in practice overpaneled systems rarely need to clamp.  A couple reasons for this:

1. Overpaneled systems start collecting usable power earlier in marginal light.  I have observed that ny the time light levels are high enough to theoretically max the system out the charger has completed Bulk and the bank's current acceptance is dropping.  Also excels in rain and cloudy conditions.  In car terms, the overpaneled system trades away some of the panels high-end horsepower output for more low- and mid-range grunt.  Less sexy but could be more suited for use as a daily driver.   
2. Because of temperature derating the panels will usually be peaking at something like 400w.  Yes, perfect storms of altitude and cold can yield max+ power but clamping/limiting would address that.  

I'm trying to sponge up as much knowledge as i can but haven't come across this term clamping?  Is this what you're talking about?

https://en.m.wikipedia.org/wiki/Clamper_(electronics)

Am i right that it's basically taking the watt overage the batteries can't accept and somehow converting it into something they can? If we went to the extreme of too much solar or too little battery, what happens to that clamped input? Is this true for watt, volt, and amp? 

I apologize for any nuisance, thank you all for this discussion.

 

[John61CT]

When over-voltage can cause damage, a clamping circuit or device offers protection.

Can also apply to current (amps), but usually talk about current limiting.

 

[frater secessus]

I'm trying to sponge up as much knowledge as i can but haven't come across this term clamping?  Is this what you're talking about?

[Answering this again after the DB crash, for posterity]

Clamping in this context == the controller protecting itself by forcing the panel to produce less power.
Variously called clamping, clipping, overcurrent protection and a few other marketing terms.

I made a first run at describing how it's done: rvwiki - how MPPT controllers clip power.  I started to write it up here but the Preview/Draft editing functions aren't stable yet, and it'd clutter the thread.

 

[MotorVation]

Follow up on this thread. I just ordered the Morningstar TriStar 45 amp MPPT Solar Charge Controller and the Morningstar TS-RM-2 Remote Digital Meter.

I ordered from Northern Arizona Wind and Sun, the same place I bought the 2@295 watt mono panels.

I was really hesitant to spend that kind of money but after giving it serious thought, it seems to be the right choice for me. I'm paying for the durability, capacity, efficiency and 5 year factory warranty.

The vendor is having a 7% off sale (which pushed me over the edge) currently and I also received a further discount by having an account. All said and done, the controller and remote meter cost me 530.66 including shipping. I know, OUCH.

It will probably pay for itself over time.

I appreciate all the good advice and time everyone spent on pushing me in the right direction.
Thanks,
Bob

 

[John61CT]

For others looking for comparison, not saying it's better

https://www.invertersupply.com/index.php?main_page=product_info&products_id=4589

Or 2 of these, giving each panel its own MPPT optimization

http://shop.pkys.com/Victron-Energy...ontroller-with-built-in-Bluetooth_p_7182.html