2 or more 140watt panels on 10amp controller.

[MooChaqa]

Hi there,

Will the controller only deliver what it can and excess production is wasted? Or does my house get toasted?

I have an 85ah battery, 1 x 140watt 12v panel and a 10amp controller. In best conditions I am generating around 8 amps, although this drops significantly late in the day and in cloud, obviously.

What I am asking is can I add an additional 140 watt panel to this to increase my average production, and the top end production wont exceed the capabilities of the system/controller.

I don't want to buy a new controller or increase my battery bank.

Cheers!

[Wy_White_Wolf]

NO.

[Sunking]

You do not want to push more than 8 amps into a 85 AH battery. Max charge rate if it is a flooded lead acid is C/8 so 85ah / 8 a = 10.6 amps.

[inetdog]

85ah / 8 a = 10.6 amps.

Make that 85ah / 8 h = 10.6 amps and we have a deal!

[Naptown]

Make that 85ah / 8 h = 10.6 amps and we have a deal!

Ah but a 10A CC is the deal breaker.

[Sunking]

Make that 85ah / 8 h = 10.6 amps and we have a deal!

Doh, what a dunce I am. A 5th grader knows A = AH/H

[MooChaqa]

Hey thx for the replies.

Remember I do not want to create more than the 8 amps max. But how about when conditions result in a 4 amp charge. The question is can I use more than 1 panel through the 10 amp CC but not overload the max, just increase power generated when conditions would be less.

I wonder if I am still making myself clear or not.

Its sunny. I am generating 8 amps. I add another panel but the 10a CC will stop me generating what would potentially be 16amps.

Its a little sunny. I am generating 4 amps. I add another panel and am now generating 8 amps.

Is this correct or can the 10a cc simply not be used with an array exceeding 10 amps?

[Sunking]

Remember I do not want to create more than the 8 amps max. But how about when conditions result in a 4 amp charge. The question is can I use more than 1 panel through the 10 amp CC but not overload the max, just increase power generated when conditions would be less.

I wonder if I am still making myself clear or not.

You are making yourself clear, you just do not understand how the current is regulated. What you want to do can be done, but requires special equipment which will be a custom design.

[MooChaqa]

You are making yourself clear, you just do not understand how the current is regulated.

The reason I wasn't sure is that your previous answer was irrelevant.

I was aware that I shouldn't charge the battery at a rate faster than C/8 or the rule of thumb I was adhering to, no more than 10% of battery capacity. So in my case 8.5ah. Soooooooooo. The question I had relates to how the CC manages charging current above and beyond it's rating of 10amps.

I am imagining eitherL:
A: You can't use a 10a CC with 20amps of panels. The CC will explode in a great colourful display of ignorance. or
B: It will regulate all incoming charge to a maximum of 10amps regardless of the amount of panels connected.

Help me understand by explaining what happens to this surplus energy.

Many thanks.

[epsgunner]

My MorningStar TS45 (PWM) handles upto 45 amps normally.. If I went with 6 panels at 8.05 amps.. I'd be at 48.3 amps..

The controller also has a overage allowance upto lets say 10%.. so lets say 49.5 amps.. the max for the controller before over amp disconnect is say 50 amps (for my controller).

Good controllers will just CLIP the amps down to there max.. my case 45 (if there was no 10% per se)..

I stopped at 5 panels and 40.25 amps as I didn't want to go OVER the rated limit (though I know I could use 6 technically speaking)..

Thats why he said it would just limit you to your CC rated capacity (or explode pending on cheapness of the model.. LoL)....

When in doubt call the manufacturer.. (thats what I did to double check)..

[daz]

The reason I wasn't sure is that your previous answer was irrelevant.

I was aware that I shouldn't charge the battery at a rate faster than C/8 or the rule of thumb I was adhering to, no more than 10% of battery capacity. So in my case 8.5ah. Soooooooooo. The question I had relates to how the CC manages charging current above and beyond it's rating of 10amps.

I am imagining eitherL:
A: You can't use a 10a CC with 20amps of panels. The CC will explode in a great colourful display of ignorance. or
B: It will regulate all incoming charge to a maximum of 10amps regardless of the amount of panels connected.

Help me understand by explaining what happens to this surplus energy.

Many thanks.

The current (and voltage) ratings on charge controllers are the maximum working values. The components in the controller are designed specifically for those maximum values. Therefore, exceeding them will damage the controller!

[inetdog]

The reason I wasn't sure is that your previous answer was irrelevant.

I was aware that I shouldn't charge the battery at a rate faster than C/8 or the rule of thumb I was adhering to, no more than 10% of battery capacity. So in my case 8.5ah. Soooooooooo. The question I had relates to how the CC manages charging current above and beyond it's rating of 10amps.

I am imagining eitherL:
A: You can't use a 10a CC with 20amps of panels. The CC will explode in a great colourful display of ignorance. or
B: It will regulate all incoming charge to a maximum of 10amps regardless of the amount of panels connected.

Help me understand by explaining what happens to this surplus energy.

Many thanks.

Well, probably the best way to understand where the surplus energy goes is to realize that it does not go anywhere. If you have a 150HP engine and it is idling, you usually don't ask where the surplus 149HP is going. It is not being generated. Similarly, the solar panel has a curve of voltage versus current for a particular amount of light hitting it. If you do not draw current from it, no power is being generated (the sunlight just produces heat and the panel is being ultimately inefficient.) The charge controller will draw enough current from the solar panels to deliver the needed current to the batteries. That will lead to the corresponding amount of power being produced by the solar panels. The only surplus you have is the ability to generate more power, and you are just not using that capacity.

On the other side of things, an MPPT controller will not be overloaded by any amount of panel capacity. It will draw no more current than it needs as long as the open circuit voltage of the array does not go above the design voltage of the controller.

A PWM controller could be designed either to rely on the solar array to not be able to deliver more current during each pulse than the controller can handle or to shut down if the current goes too high. The components in the PWM controller that switch the current on and off have two performance limits:
1. The average current flowing based on the on and off time of the pulses. This is based on the heat dissipation of the device and the maximum temperature before it melts down.
2. The peak current during a pulse before there is immediate damage.
Depending on the design of the controller, either it will regulate to meet condition 1 and the current for condition 2 is limited by the size of the solar array, or it can regulate both 1 and 2 to protect itself. The first kind may fail if you connect too large an array to it, the second kind will shut down to protect itself. Either way, you are wasting panel capacity.

[Naptown]

Well, probably the best way to understand where the surplus energy goes is to realize that it does not go anywhere. If you have a 150HP engine and it is idling, you usually don't ask where the surplus 149HP is going. It is not being generated. Similarly, the solar panel has a curve of voltage versus current for a particular amount of light hitting it. If you do not draw current from it, no power is being generated (the sunlight just produces heat and the panel is being ultimately inefficient.) The charge controller will draw enough current from the solar panels to deliver the needed current to the batteries. That will lead to the corresponding amount of power being produced by the solar panels. The only surplus you have is the ability to generate more power, and you are just not using that capacity.

On the other side of things, an MPPT controller will not be overloaded by any amount of panel capacity. It will draw no more current than it needs as long as the open circuit voltage of the array does not go above the design voltage of the controller.

A PWM controller could be designed either to rely on the solar array to not be able to deliver more current during each pulse than the controller can handle or to shut down if the current goes too high. The components in the PWM controller that switch the current on and off have two performance limits:
1. The average current flowing based on the on and off time of the pulses. This is based on the heat dissipation of the device and the maximum temperature before it melts down.
2. The peak current during a pulse before there is immediate damage.
Depending on the design of the controller, either it will regulate to meet condition 1 and the current for condition 2 is limited by the size of the solar array, or it can regulate both 1 and 2 to protect itself. The first kind may fail if you connect too large an array to it, the second kind will shut down to protect itself. Either way, you are wasting panel capacity.

Red text is untrue
MPPT controllers can be overloaded and will have a maximum output current
Make sure the input voltage is within parameters and output amperage at full power from the array is below the amperage rating on the voltage battery bank it is connected to.

[billvon]

MPPT controllers can be overloaded and will have a maximum output current.

Which MPPT controllers do not limit current?

[inetdog]

Which MPPT controllers do not limit current?

I don't doubt that they may exist, but the first two I looked at were protected, although in different ways: (from the specifications and manuals for the models named.)

Example 1: Blue Solar MPPT 70/15
"Maximum PV power at 24volt battery setting: 400W (note a)"
Max Battery Current: 15A (more available peak into combined battery and load)
"a) If more PV power is connected, the controller will limit input power to 400W"
So there is a regulated maximum output, which is the design or name current for the model. And adding too much PV will not damage the unit. The output current does have to be matched to the batteries for the bulk phase though.

Example 2: Outback MX60 PV MPPT
The maximum output current is regulated/protected at 60A, but can be adjusted lower. Higher power PV array will not cause that output to be exceeded, BUT the manual indicates that regardless of voltage, the maximum current from the array must not exceed 48A, and be fused appropriately. Not that the controller would necessarily be damaged, but that it would be operating outside the range for which it is NEC compliant by testing and approval if a fault occurs.

Any MPPT controller has to be able to limit the output current as needed to hit the target voltage on the batteries, and it is not a big jump to providing a means to limit the maximum output current directly, regardless of the battery voltage. But I guess that does not mean that all of them will.
(The controller will only seek to the Maximum Power Point of the array if all of that power is needed.)