# If controller is to small?



## budgetprepp-n (Jul 8, 2015)

HI
I'm going to put up two panels they are 245 watt ea. And I'm running 12 volts 
so,, 245 +245 = 490 watts -divided by 12 volts= 40.8 Amps 
I see that I should have a 40 amp charge controller but all I have right now is a 30 Amp
If the controller is to small will the controller be damaged or will it just be sort of
a bottle neck and hold back any power over 30 Amps?


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## cowboyhermit (Nov 10, 2012)

Unfortunately, the answer is... it depends.

First off, the actual charging pathway (semiconductor) of a charge controller WILL overheat and be damaged at a specific amperage and ambient temperature. It will not, intrinsically, limit the power to a specific amperage. However, many charge controllers have such "overload protection" built in to them. The overload protection typically shuts the unit down either momentarily or with the need to be reset. Another thing to consider is that many units are built to handle overcurrent, while others should actually be derated at certain temps. I know the simple non-digital morningstars could handle much more than rated. Also, if voltage on the input side gets too high the unit may shut down.

So, it depends on the manufacturer, type (PWM, MPPT, digital, heck even old shunt type, etc), voltage, and temps. :dunno:


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## mosquitomountainman (Jan 25, 2010)

What's the model number and manufacturer of the controller? What's the manufacturer, model number, and rated output in volts of the panels? (Look on the data plate on the back of the panels.) 245 watt panels are probably not designed for a 12 volt system unless you're using an MPPT controller. If you are using a 12 volt PWM, digital, etc. controller you'll probably be producing far less power than the panel's maximum output.


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## LastOutlaw (Jun 1, 2013)

If you wire in series rather than parallel your voltage will increase but your amps will not. Let your charge controller convert back to 12 volts before the batteries.










Keep in mind higher amps need thicker (more expensive) wire.


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## mosquitomountainman (Jan 25, 2010)

LastOutlaw said:


> If you wire in series rather than parallel your voltage will increase but your amps will not. Let your charge controller convert back to 12 volts before the batteries.
> 
> 
> 
> ...


That will only work with an MPPT controller. If it's a PWM controller he just lost about half of the available power from the panels.

Some PWM controllers can be used for 12/24/36/48 volts in which case the battery bank must match those voltages. We could get by with only one PWM controller with our solar array by going to a 24 volt system but then we'd need a 24 volt battery bank (not a problem) and a 24 volt inverter (is a problem) plus we would lose our 12 volt DC system which I would rather keep.


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## LastOutlaw (Jun 1, 2013)

Considering the size and expense of the panels I think it would make sense to use an mppt controller anyway. From what I understand the mppt will produce more power in the mornings and evenings and cure the amperage output as well. 

I have a cheap pwm controller that I wired to one small panel to keep my bank on float. (Bank is not connected to any other panels, is recharged from a gen using an iota charger daily when I am there.) Works well for that use but getting the most output possible from my panels is important and I have an mppt for them.


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## Caribou (Aug 18, 2012)

I currently have four 250W solar panels. I would like to at least double that. Any recommendations on a charge controller would be appreciated.


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## LastOutlaw (Jun 1, 2013)

There are a lot of options when it comes to solar depending on how you wire your panels, how you wire batteries, how long the run is from panels to charging station, charge controller voltage and amperage limits, and what power inverter is used.

For instance: panels can be wired for higher voltages and lower amperage or vice versa depending on the limits of your charge controller and battery bank voltage and power inverter limitations.

You will need to research what you have and possibilities of different wiring scenarios and what you want out of it all.


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## Viking (Mar 16, 2009)

mosquitomountainman said:


> That will only work with an MPPT controller. If it's a PWM controller he just lost about half of the available power from the panels.
> 
> Some PWM controllers can be used for 12/24/36/48 volts in which case the battery bank must match those voltages. We could get by with only one PWM controller with our solar array by going to a 24 volt system but then we'd need a 24 volt battery bank (not a problem) and a 24 volt inverter (is a problem) plus we would lose our 12 volt DC system which I would rather keep.


After running an MPPT controller for our solar system on the motor home, I wouldn't use any other controller, they are perfect for high voltage panels when charging lower voltage battery systems. For our home solar backup system I have eight 195 watt panels that will be series/ parallel for 70.4 VDC maximum output going into a 60 amp. MorningStar MPPT controller which is set to charge a 24 volt battery bank.


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## mosquitomountainman (Jan 25, 2010)

Caribou said:


> I currently have four 250W solar panels. I would like to at least double that. Any recommendations on a charge controller would be appreciated.


That will depend on several factors. What brand and model number are the panels? What brand and model numbers will you add to them? What's the brand and model number of your controller?

For example: I run two controllers on my 930 watt solar array at 12 volts (wired parallel) If I went to 24 volts (wired parallel/series) I'd only need one controller because my controllers are rated in amps. Double the voltage and the watts remain the same but the amps are cut by 50 percent.

930 watts divided by 12 volts equals 77.5 amps
930 watts divided by 24 volts equals 38.7 amps

I now have two PWM, 40 amp controllers.

An MPPT controller is figured a little differently. I would always use an MPPT controller unless it's a simple and small 12 volt system.  They are much more efficient and you can save enough on new panels to more than make up for the extra cost of an MPPT controller. (It's all in my book.)


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## Fn/Form (Nov 6, 2008)

budgetprepp-n said:


> HI
> I'm going to put up two panels they are 245 watt ea. And I'm running 12 volts
> so,, 245 +245 = 490 watts -divided by 12 volts= 40.8 Amps
> I see that I should have a 40 amp charge controller but all I have right now is a 30 Amp
> ...


It's kind of like asking if your 750 cold cranking amps battery in your car will blow up your the phone charger you plug in the cigarette lighter socket. The charger only uses what it needs. Make sense?

Remember that 40A is the potential; it doesn't mean it's somehow force feeding the 30A controller.

The charge controller current limits itself. A good design should run at 30A continuous duty in the specified environmental conditions.


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## mosquitomountainman (Jan 25, 2010)

Fn/Form said:


> It's kind of like asking if your 750 cold cranking amps battery in your car will blow up your the phone charger you plug in the cigarette lighter socket. The charger only uses what it needs. Make sense?
> 
> Remember that 40A is the potential; it doesn't mean it's somehow force feeding the 30A controller.
> 
> The charge controller current limits itself. A good design should run at 30A continuous duty in the specified environmental conditions.


I think you're comparing apples and oranges here. Too much input current could fry the controller. At the very least the unit will shut down at times to protect itself. Cowboyhermit covered it well in the second post on this thread.



cowboyhermit said:


> Unfortunately, the answer is... it depends.
> 
> First off, the actual charging pathway (semiconductor) of a charge controller WILL overheat and be damaged at a specific amperage and ambient temperature. It will not, intrinsically, limit the power to a specific amperage. However, many charge controllers have such "overload protection" built in to them. The overload protection typically shuts the unit down either momentarily or with the need to be reset. Another thing to consider is that many units are built to handle overcurrent, while others should actually be derated at certain temps. I know the simple non-digital morningstars could handle much more than rated. Also, if voltage on the input side gets too high the unit may shut down.
> 
> So, it depends on the manufacturer, type (PWM, MPPT, digital, heck even old shunt type, etc), voltage, and temps. :dunno:


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## cowboyhermit (Nov 10, 2012)

The amount of current running through a basic circuit is determined by Ohm's law I=V/R. Rather than using a cell charger that is in fact a separate circuit it is easier to compare with something like a 12V fan motor. It is completely true that the size of battery, power supply, alternator, what have you has no bearing on the current flowing through the fan. It is determined simply be the voltage of the system and the resistance inside the fan motor.

In contrast, a solar charge controller's charging mechanism, is required to have an exceptionally low resistance to function well. So, when you apply the same formula; I=V/R with R=a fraction or decimal it becomes obvious how different the situation is.

The charge controller has ways to limit power, that is what it is intended to do, but it has to be an active process built into the system that measures heat or current, and many do not have that capability.

Just googled for a quick example;


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## LincTex (Apr 1, 2011)

My largest system uses a C35 (35 amp) Trace/Xantrex charge controller. It stands alone on that system, but what if I want to combine systems.....


Scenario: Solar array could put out 90 amps in full sun (absolute max)

Q: Can I mix and match 3 different brand 30 amp charge controllers, each one handling 1/3 the array, to all feed one large 12 volt battery bank (simultaneously) without the charge controllers "fighting" or arguing with each other?


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## Caribou (Aug 18, 2012)

What are the types of charge controllers? 

What are their strengths and weaknesses? 

What does the controller control? Volts? Amps? 

Isn't the controller there to protect the battery bank? If so how does that affect the sizing of the controller?


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## mosquitomountainman (Jan 25, 2010)

LincTex said:


> My largest system uses a C35 (35 amp) Trace/Xantrex charge controller. It stands alone on that system, but what if I want to combine systems.....
> 
> Scenario: Solar array could put out 90 amps in full sun (absolute max)
> 
> Q: Can I mix and match 3 different brand 30 amp charge controllers, each one handling 1/3 the array, to all feed one large 12 volt battery bank (simultaneously) without the charge controllers "fighting" or arguing with each other?


Like my example in the previous response I made on this thread, (if) you can increase the voltage of the controller/battery bank to 24 volts instead of 12 volts your (pwm) controller can handle twice as many watts of solar panel output because the amps will remain the same.

You can mix controllers as long as the output voltage is the same. I have two controllers from two different manufacturers on our home system. They work fine together. One is adjustable and I set the outputs as close as I could to the other controller. I shut off the 30 day automatic equalization cycle on one controller because they were each doing their thirty day equalization charge on different times. However, by doing that the equalization cycle is being done by only half of the panels. It still works okay though and the batteries don't use nearly as much water that way.

If the output voltages don't match exactly you'll find one controller going through it's cycles at different times than the other. For example, one might go from the bulk phase to the absorption phase then to the float phase earlier than the other controller(s). Overall it won't hurt your batteries or your system performance.


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## cowboyhermit (Nov 10, 2012)

I don't have time or brain power for detailed responses, hope this makes sense;



Caribou said:


> What are the types of charge controllers?
> 
> Realistically, PWM (pulse width modulation) and MPPT, there are/were other types that aren't really worth mentioning.
> 
> ...


I don't have much knowledge or experience mixing MPPT controllers, but as far as PWM they seem to play well enough together, especially the simple ones. Even among the same brands though, there are often different settings for battery type that if wrong can cause one charger to be going into float mode while the other is still charging.

IMO, best to make sure to run separate lines to the bank though, for each charger, or sense wires, to keep voltage fluctuations from altering readings.


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## BJ-Solar (Aug 5, 2015)

*Solar Panel amperage*

Hi if you look up the specs from the manufacturer HESPV amp ratings you will find the 250 Watt panel only provides max 8.36 amps each at 29.9v. The recommended fuse is 20A. You're only have app 17 amps through the charge controller. I have some charts that may assist at.


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## Fn/Form (Nov 6, 2008)

mosquitomountainman said:


> I think you're comparing apples and oranges here. Too much input current could fry the controller. At the very least the unit will shut down at times to protect itself. Cowboyhermit covered it well in the second post on this thread.


*could* if you're using a cheapy charge controller. New system owner beware. You will notice no max input current listed on the decent and reliable models. When you talk to the manufacturer some will say you can over PV by 300%, others say there is no max (MPPT especially).


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## BJ-Solar (Aug 5, 2015)

This equation cannot be used to determine amps. If an appliance uses 245 watts then / 12 =running amps 
245 +245 = 490 watts -divided by 12 volts= 40.8 Amps
8.36 + 8.36 = 16.72 amps 
This panel cannot delivery more than manufacturers claims.


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