Connecting more than one pwm charge controller?

[Kimba]

I have 10A pwm charge controller and also two others spare, what I would like to know can I join them together as my solar system grows, or will I have to just get higher rated pwm charge controller 30A or something.

This is a mobile setup 12v 2x80watt panels, 10A pwm charge controller, I want to double the panels and maybe then some, as time goes by, but I understand there is a limit to how many panel watts a charge controller will allow, I don't want to change over to 24v I understand this doubles the charge controllers handling I wish to stay with 12v.

So simple question can I chain link pwm charge controllers.

[inetdog]

I have 10A pwm charge controller and also two others spare, what I would like to know can I join them together as my solar system grows, or will I have to just get higher rated pwm charge controller 30A or something.

This is a mobile setup 12v 2x80watt panels, 10A pwm charge controller, I want to double the panels and maybe then some, as time goes by, but I understand there is a limit to how many panel watts a charge controller will allow, I don't want to change over to 24v I understand this doubles the charge controllers handling I wish to stay with 12v.

So simple question can I chain link pwm charge controllers.

Simple answer: Yes.

Full answer: You do not have to chain, them. link them in any special way, etc. You just connect them both to the same battery bank. Neither one knows about the other, but since they both see the same battery voltage they work together. It does work best if they both have the same stage voltage settings, but even that is not 100% necessary, since during the bulk stage they both will be sourcing current rather than trying to set a voltage.

The limit to the number of panels that a CC will allow is just that if the panels produce more current (Imp) than the CC is rated for, the CC will not be able to send it to the batteries. PWM CCs will not tolerate a panel array with more current capability than the CC is rated for, but most MPPT CCs specify a certain tolerance for excessive power on the input side and simply do not deliver more than their rating to the batteries. Your 160 watts of nominal 12 volt panels is already at the limit for a 10 amp PWM CC.

Your statement about going to 24 volts "doubling the CCs handling" does not make any sense. If your current CCs have a switch to choose between 12 volt and 24 volt output, you can use them and just put your 2 80watt panels in series on the input and then add another two 80 watt panels in series, all with just the one CC. This is an advantage of using 24 volts.

You have not said anything about your battery bank. If you also describe it, we can give additional advice. You do not want to add more panels and CCs than the batteries can take, but you may be underpowered in panels right now.

[Kimba]

Simple answer: Yes.

Full answer: You do not have to chain, them. link them in any special way, etc. You just connect them both to the same battery bank. Neither one knows about the other, but since they both see the same battery voltage they work together. It does work best if they both have the same stage voltage settings, but even that is not 100% necessary, since during the bulk stage they both will be sourcing current rather than trying to set a voltage.

The limit to the number of panels that a CC will allow is just that if the panels produce more current (Imp) than the CC is rated for, the CC will not be able to send it to the batteries. PWM CCs will not tolerate a panel array with more current capability than the CC is rated for, but most MPPT CCs specify a certain tolerance for excessive power on the input side and simply do not deliver more than their rating to the batteries. Your 160 watts of nominal 12 volt panels is already at the limit for a 10 amp PWM CC.

Your statement about going to 24 volts "doubling the CCs handling" does not make any sense. If your current CCs have a switch to choose between 12 volt and 24 volt output, you can use them and just put your 2 80watt panels in series on the input and then add another two 80 watt panels in series, all with just the one CC. This is an advantage of using 24 volts.

You have not said anything about your battery bank. If you also describe it, we can give additional advice. You do not want to add more panels and CCs than the batteries can take, but you may be underpowered in panels right now.

Regards the 12v, 24v question now I understand it, thanks.

I was reading some advice given by someone, who has done research on solar and now I am bit concerned about his advice, let me quote him.



quote:

In order for the regulator to know the state of the battery, every so often it stops charging briefly and reads the Voltage of the battery.

If you have multiple regulators feeding the same battery bank what can happen is regulator A stops charging and reads the battery but sees the PV Voltage from regulator B rather than the actual state of the battery and believes that the battery is fully charged and stops charging.

I'd advise you oversize your regulator, you can add more panels and more batteries but I don't advise trying to feed multiple regulators into the same battery bank.
Of course you can get multiple regulators to feed multiple (separate) battery banks. That gives you redundancy.

It a little more awkward when it comes to loading as you need to distribute (or switch) your loads between your two or more battery banks.

Unquote:



This conflicts your information, as you say (Neither one knows about the other, but since they both see the same battery voltage they work together) he saying the CC's will see each other, I would like to join CC's as the system grows to the same bank, and what you’re saying is what I thought, and that it is quite ok to do.



My setup mobile is 2x80w and one 75ah Battery with 10A CC.

My off grid garden set up is 5x 80w with 30A MTTP CC, and this is running 4x75ah batteries, I would like to add 4 more would 400watts be enough for 8x75ah batteries.

Thanks again for your help.

[Sunking]

You can but would be foolish to do so. A 10 amp PWM controller at 12 volt battery is limited to roughly 170 watt maximum input power, and 340 watts @ 24 volts. Do yourself a favor and buy yourself a good 30 to 60 amps MPPT charge controller. It will be much less expensive in the long run. In your location if you use say a 500 watt panel input on a PWM CC will generate as much a a 300 watt panel with MPPT.

[Zardiw]

Am also considering multiple charge controllers off separate panel arrays, with different specs hooked to the same battery bank

And this quote also addresses a question I had: How do CC's know the battery bank status? The only way I see is if they quit charging for a second or 2 to determine what the status is:

Quote: "In order for the regulator to know the state of the battery, every so often it stops charging briefly and reads the Voltage of the battery.

If you have multiple regulators feeding the same battery bank what can happen is regulator A stops charging and reads the battery but sees the PV Voltage from regulator B rather than the actual state of the battery and believes that the battery is fully charged and stops charging."

Because if one CC is fully charging, the second one would see high voltage, correct? And then stop supplying power to the battery bank.

So it would seem that they need to be in 'synch' somehow and check battery bank status at the same time. i.e stop charging at the same time to see what the battery status is.

Now, I'm not certain how CC's work, so this could be all wrong.......but it certainly makes sense.

PS. Planning on using MPPT CCs

z

[Mike90250]

adding controllers in parallel (each with its own PV array) actually works well

[sensij]

Quote: "In order for the regulator to know the state of the battery, every so often it stops charging briefly and reads the Voltage of the battery.

I would question the accuracy of that quote.

[Zardiw]

adding controllers in parallel (each with its own PV array) actually works well

Yes.....supposedly it does.......however.....do they need to talk to each other for that to work?

And w/o disconnecting the charging from the battery, there is no way to tell what the status of the bank is........so it makes sense if the CC stops charging for a short time.....perhaps a few milliseconds.......to determine what's up with the batteries........

And if one CC is busy as a bee charging up the bank.......well the other CC would look at that and say.....My My.....what a great charge that bank has......and quit and go home for a nap.......

z

[sensij]

Yes.....supposedly it does.......however.....do they need to talk to each other for that to work?

And w/o disconnecting the charging from the battery, there is no way to tell what the status of the bank is........so it makes sense if the CC stops charging for a short time.....perhaps a few milliseconds.......to determine what's up with the batteries........

And if one CC is busy as a bee charging up the bank.......well the other CC would look at that and say.....My My.....what a great charge that bank has......and quit and go home for a nap.......

z

Maybe read Sunking's recent sticky on the stages of charging:

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/299490-bulk-absorb-float-equalize-what-does-it-mean

In bulk stage, voltage doesn't matter, just current. That current can come from a single CC or many, but the effect will be the same. When you get into a constant voltage stage (absorb), the voltage is maintained until current drops very low. All controllers will see and regulate to the same voltage, within calibration error of the voltage and temperature feedback.

The voltage being controlled is the applied charge voltage... not the voltage of the battery with charging shut off for a few ms. If your batteries are shot and have very high internal resistance, the controller will read them as "full" even when they aren't... this is what happens when the plates have been degraded by sulfation.

[Sunking]

Yes.....supposedly it does.......however.....do they need to talk to each other for that to work?

And w/o disconnecting the charging from the battery, there is no way to tell what the status of the bank is........so it makes sense if the CC stops charging for a short time.....perhaps a few milliseconds.......to determine what's up with the batteries........

And if one CC is busy as a bee charging up the bank.......well the other CC would look at that and say.....My My.....what a great charge that bank has......and quit and go home for a nap.......

z

PWM chargers are antiquated and very simple device. There is no need for them to stop charging the battery, Mo Controller does that. Some of the higher end MPPT Charge Controllers do have communications port so you can set a MASTER and the rest as SLAVES. But you are not going to find that in PWM controllers that I know of. Today there is no reason to use PWM controllers, they are to expensive and extremely inefficient. At Best if the panels are matched only 66% efficient, with 50% and less being typical.

To directly answer your question is you can Parallel PWM controllers. They do not need to communicate, nor can they do that. All the panels have to be matched up on each controller and in parallel using expensive battery panels with combiners and fuses.

[Zardiw]

Actually I was talking about MPPT CCs.....not PWM ....z

[Zardiw]

Maybe read Sunking's recent sticky on the stages of charging:

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/299490-bulk-absorb-float-equalize-what-does-it-mean

In bulk stage, voltage doesn't matter, just current. That current can come from a single CC or many, but the effect will be the same. When you get into a constant voltage stage (absorb), the voltage is maintained until current drops very low. All controllers will see and regulate to the same voltage, within calibration error of the voltage and temperature feedback.

The voltage being controlled is the applied charge voltage... not the voltage of the battery with charging shut off for a few ms. If your batteries are shot and have very high internal resistance, the controller will read them as "full" even when they aren't... this is what happens when the plates have been degraded by sulfation.

Unfortunately that sticky does not address MULTIPLE CCs

z

[sensij]

Multiple cc's will behave about the same as a single cc delivering the combined current, with any differences probably limited to the float stage. The sticky explains how each stage works... think about it.

In bulk, voltage doesn't matter. The voltage rise from delivering 40 A (for example) will be the same whether it comes from one or many cc's. The transition from bulk to absorb is just keeping that maximum voltage held constant, suo with good calibration, all the cc's will change state at about the same time.

[Zardiw]

Multiple cc's will behave about the same as a single cc delivering the combined current, with any differences probably limited to the float stage. The sticky explains how each stage works... think about it.

In bulk, voltage doesn't matter. The voltage rise from delivering 40 A (for example) will be the same whether it comes from one or many cc's. The transition from bulk to absorb is just keeping that maximum voltage held constant, suo with good calibration, all the cc's will change state at about the same time.

So you're saying that it's the voltage of the bank that determines whether or not the CCs go full bore to charge.

And as long as that voltage is below a certain level all of the connected CCs will pour charge into the bank.

Is that correct.

On a 24V bank, what would that voltage be approximately.....

Seems to me that if you have one CC hooked to a large array.........and another CC hooked to a small array.......that due to the large array supplying more voltage/amps it would make the smaller array CC stop supplying power, cause it would appear that the bank is Full...........

But maybe it doesn't work that way..........I wish somebody would explain in clear terms how it DOES WORK.........

z

[Mike90250]

the way electricity works, any point in a circuit that is properly connected with a wire, will have the same voltage as any other point does. Each CC senses the battery voltage and acts accordingly. i run 2 different brands each with a different sized array, and with a good low resistance setup, I have zero coordination issues.