Is electricity stupid or what?

[Gibson]

Greetings to the forum,

I just finished my first solar system, nothing fancy, specs below. Mostly built use for camping and running Ham Radio’s and laptops for logging but I figure it can come in handy for basic needs during long term power outages too.

Specs:

Epever Tracer 4215BN with the MT50 interface.
GoWise 3000 watt inverter (intentionally oversized)
Battle Born 100ah x 2 (2 more in the works)
Rich 100 watt panels x 6

So here is my question…running a test with a 1000 watt radiant heater (actual consumption 960 watts per clamp on ammeter and ohms law) I a watched the MT50 interface. I never saw the PV watts go above 425 watts. With the heater on it basically pulled 425 watts for maybe a minute and then dropped into the 250-300 watts and held there. The battery icon started dropping, and dropping and dropping indicating that it was pulling the majority of power from battery power instead of the PV array.

I do not have the inverter connected to the "load" connection on the charge controller. I am wondering, if I changed that, does the controller have the logic built in that would draw the watts it needs from the PV array first and balance the rest from the battery? Obviously electricity is stupid and does not go where I want it. (I am being a wise guy). I surmise what is going on is that the inverter has a higher resistance than the batteries so the charger is putting what it can into the batteries based on the charging profile. Yes, no?

Simply stated, I guess my expectation was that I could run AC devices during the day and as long as I was not exceeding the max input of the array/ charger I would not be drawing the batteries down. Am I wrong or is there something else going on here.

PDF of how I wired stuff up with oversized wire since I had a bunch of welding cable. I am getting about 56-64 volts depending on sun, and should get 600 watts, or thereabouts.

PS...great site but there is an overwhelming amount of information to wade through.

 

[Supervstech]

A 15A charge controller cannot output over 210W at 14V… what voltage is the battery bank configured for?

 

[Supervstech]

I am guessing 24V series connected batteries. So, 420W max… depending on sun angle, getting 300WATTS isn’t bad.

 

[wattmatters]

I never saw the PV watts go above 425 watts. With the heater on it basically pulled 425 watts for maybe a minute and then dropped into the 250-300 watts and held there.

What is the charge current setting/limit of the solar charge controller? That sets the upper limit at which you can supply loads with PV without discharging the battery.

 

[Gibson]

@Supervstech: Unless I do not understand the specs, the 4215BN is a 40 amp charger. I am set up for a 12 volt system since all my radios operate on 12vdc.

@ wattmatters: Charge limit is set at 14.6. ...oh you asked current, the 14.6 are volts. Hmm, I don't know. It would have to be whatever the default setting is. I will have to look and see if I can find that in the menu. The only things I changed were the Temp. coef. to zero, charge limit to 14.6, float charge to 13.6 and equalize time to zero. All other settings are default.

Thanks!

 

[wattmatters]

According to the manual it's a 40A charger but the rated charge power for a 12V system is 520W. That's the most you'll pull from a PV array.

Also the manual says nothing about that charge controller working with Lithium chemistry.

 

[Smokin]

Electricity doesn't weigh anything so it can't be stupid.

 

[12VoltInstalls]

Unless I do not understand the specs, the 4215BN is a 40 amp charger. I am set up for a 12 volt system

So at the nominal 40A at 12V is 480W, tops, from the charge controller

The other factor: what was the sun angle to the panels? And atmosphere conditions?

Never mind inherent in efficiencies that reduce realized output (input?) your solar input at a nominal / static level is under 50% of the load you applied.

 

[Gibson]

According to the manual it's a 40A charger but the rated charge power for a 12V system is 520W. That's the most you'll pull from a PV array.

Also the manual says nothing about that charge controller working with Lithium chemistry.

The rated charge current is 40a, which seems to answer your question above. The rated charge power is 520 watts at 12v. However, the max PV array for the controller is 780w at 12volts. That being said, 600 watts PV array is within mfr.s specifications.

You are correct, the manual does not mention Lithium chemistry but it has the ability to create a custom profile. I spent a bit of time on the phone with Battle Born before hand and they were familiar with the charge controller and expressed no concerns. In fact, they said I would not need to change the default settings of the controller should I chose not to.

Circling back to my question but phrased in another manner : Let’s say the PV array is providing 600 watts to the charge controller, nice sunny day, and the batteries are fully charged. Now all of the sudden I have a 600 watt demand from the inverter. The charge controller has two outputs, one for the battery, the other is the “load” terminals. Does the charge controller have the logic to see that the batteries are fully charged and then take the full 600 watts from the PV array and send that power directly to the load terminal on the charge controller so it’s not drawing down battery power? I watched some of Will’s videos as a primer to my project and one of the things he mentioned is that he does not use “load" terminal on the Epever charge controller, but instead is connecting the inverter in parallel with the battery output circuit, but I don’t recall hearing the rationale behind it. Electricity is going to take the path of least resistance and not necessarily go where we want it to go…right? That being said, all I am trying to figure out is if charge controller has the logic built in to see where the power from the PV is best utilized, I.E., directly to the “load" terminal or to the battery terminal. If the logic is not built in then it is not really worth my time and effort to move devices around on my panel board and make new cables so that the inverter is connected to the charge controller "load" instead of being parallel as it is now. In the test I ran with a 1000 watt heater the controller would need a PID loop to balance the input to the two outputs, which gets more complex obviously. Thanks!

 

[Gibson]

So at the nominal 40A at 12V is 480W, tops, from the charge controller

The other factor: what was the sun angle to the panels? And atmosphere conditions?

Never mind inherent in efficiencies that reduce realized output (input?) your solar input at a nominal / static level is under 50% of the load you applied.

I was typing the above while you posted. I will have to return to this, need to earn a paycheck right now..thanks.

 

[wholybee]

The rated charge current is 40a, which seems to answer your question above. The rated charge power is 520 watts at 12v. However, the max PV array for the controller is 780w at 12volts. That being said, 600 watts PV array is within mfr.s specifications.

You are correct, the manual does not mention Lithium chemistry but it has the ability to create a custom profile. I spent a bit of time on the phone with Battle Born before hand and they were familiar with the charge controller and expressed no concerns. In fact, they said I would not need to change the default settings of the controller should I chose not to.

Circling back to my question but phrased in another manner : Let’s say the PV array is providing 600 watts to the charge controller, nice sunny day, and the batteries are fully charged. Now all of the sudden I have a 600 watt demand from the inverter. The charge controller has two outputs, one for the battery, the other is the “load” terminals. Does the charge controller have the logic to see that the batteries are fully charged and then take the full 600 watts from the PV array and send that power directly to the load terminal on the charge controller so it’s not drawing down battery power? I watched some of Will’s videos as a primer to my project and one of the things he mentioned is that he does not use “load" terminal on the Epever charge controller, but instead is connecting the inverter in parallel with the battery output circuit, but I don’t recall hearing the rationale behind it. Electricity is going to take the path of least resistance and not necessarily go where we want it to go…right? That being said, all I am trying to figure out is if charge controller has the logic built in to see where the power from the PV is best utilized, I.E., directly to the “load" terminal or to the battery terminal. If the logic is not built in then it is not really worth my time and effort to move devices around on my panel board and make new cables so that the inverter is connected to the charge controller "load" instead of being parallel as it is now. In the test I ran with a 1000 watt heater the controller would need a PID loop to balance the input to the two outputs, which gets more complex obviously. Thanks!

I am not familiar with your charge controller, but from what I know of others, no it is not smart enough to direct solar directly to the load terminals as you are thinking. Nor does it matter. The load terminals are just in parallel with the battery terminals, but can be turned off, and the current can be measured, allowing you to know home much current is going into charge and how much is going into the load.

A couple basics though. Nice sunny day. The batteries are fully charged. With no load, the PV panels are *not* providing 600W. It is important to understand that concept. The panels will provide no current, and no wattage, unless there is a load (charging is a load in this sense).

So now you turn on a load. Simply by paralleling the panels(solar controller output), load, and batteries, the panels will provide whatever current they are capable of, and the batteries will pick up the difference. If the solar is capable of fully powering the load, they will, as long as the float voltage is at or above the resting battery voltage, no current will flow out of the batteries. If the batteries are not fully charged, and the solar energy is enough, then current will flow to charge the batteries and to power the load. If the load is more than the solar can maintain, then the voltage from the solar will drop until it equals that of the batteries, and then current will flow from the batteries to support the load. There isn't any logic required in the charge controller to do this. It simply happens as long as the charging voltage is higher than the resting voltage of the batteries.

There is something that happens with Lithium though, because with Lithium the float voltage must be a bit lower than the resting voltage of the batteries. So what happens then, is that the batteries will discharge very slightly to the float voltage (to roughly 99%) and then be held there. From that point, it will work as above.

 

[12VoltInstalls]

The charge controller has two outputs, one for the battery, the other is the “load” terminals. Does the charge controller have the logic to see that the batteries are fully charged and then take the full 600 watts from the PV array and send that power directly to the load terminal on the charge controller so it’s not drawing down battery power

No, and. No.

First, forget the load terminals
(Run your inverter and dc loads direct from battery)

The general use charge controller only takes solar and profiles it into the battery bank. ALL power is provided from the battery; as voltage sags, drops, or declines, the charge controller gives the battery a charging current up to the limit of the output of the controller.
It’s a charge controller not a power source

If the load applied to the battery (s) is less than or equal to the max charge controller output (and you have enough solar panels in full sun) and the batteries are fully charged then theoretically (nominally only; some ‘losses’ occur) you will be using whatever load that is with 100% solar panel power. If the max output of SCC is 500W and you apply a 1000W load you theoretically will be using 50% battery and 50% solar panel (still essentially 100% solar LOL)

 

[Gibson]

Perfect...thanks. At this point I think what I want to do is connect some of my ammeters and voltage meters in some strategic locations so I can determine what the system is actually doing/ verify operation and compare those values to what I see on the MT50 interface. I know I know....I could buy external a shunt and other devices and install them in the system but I wont really care about it down the road. It's kinda cool to look at right now but as with all "lures" they tarnish with age. I am most appreciative you all taking the time to explain the sequence of operation. Two key points I take away: The load and battery on the controller are already in parallel and it's a charge controller, not a power source...duh...LOL. I should have made that distinction myself.