is there a solar charge controller that can do this?

[PaulDavis]

It seems like you have a fundamental misunderstanding of how lead acid charging works.

That's possible, but I don't think I do.

These solar controllers, and most chargers in general are voltage sources with current limits. The solar is limited to what the panels are producing, and charger is limited by its circuitry.

95% of the time, the power that my solar panels and charge controller deliver to my batteries is limited NOT by what the panels could produce at that instant, but by what the charge controller considers a suitable volt/amp combination given the battery SOC.

My batteries rarely drop below 70% SOC, and so I rarely see the panels deliver anything remotely close to what they are capable of. When SOC does drop to that sort of level, and the controller decides to be in a "bulk" charging regime, then I will finally see a limit based on what the panels (are|can) produce. But this is not the issue here.

I do not believe that the solar controller you are using is return current aware. For example, my outback solar controller interfaces with my battery monitor. It is set to charge until the return current drops below 1% of C at the absorb voltage.

Now you're more on point. As I said at the outset, and others have noted since, and as I've repeated, the problem here is when the load doesn't really shift the voltage seen by the charge controller very much at all. And as you've said, the core issue is that the controller (that I have) is not current aware, only voltage.

That's why I asked "is there are solar charge controller that can do this?"

 

[OrioN]

It seems like you have a fundamental misunderstanding of how lead acid charging works. These solar controllers, and most chargers in general are voltage sources with current limits. The solar is limited to what the panels are producing, and charger is limited by its circuitry. Charging lead acid from a charger that is less than the banks max charge current (which is usually the case) is done as follows.

Connect charger (or sun rises). Charger outputs its max available current. Voltage is wherever on the charge curve that current corresponds to. SOC will rise as the battery charges and so will charge voltage. At some point the batteries acceptance will drop below the chargers output. At that point the charger will hit its voltage setpoint, and the current will drop. The current will continue to drop while voltage holds steady until the chargers absorb timer (or return current for shunt aware units) is reached. If the charger is in absorb mode, and the voltage is below the absorb setpoint, this means the loads and the batteries acceptance are greater than the chargers output.

Once absorb is complete the charger will change its voltage setpoint to the float level. Usually around 13.3-13.5V. Note that many controllers prematurely go to float, causing unnecessary battery capacity loss.

I do not believe that the solar controller you are using is return current aware. For example, my outback solar controller interfaces with my battery monitor. It is set to charge until the return current drops below 1% of C at the absorb voltage.

If return current feedback is not an option, I would suggest setting a long absorb timer. For full-time live-aboard vehicles, I would suggest at least 4 hours, likely up to 6. Monitor your return current during the absorb cycle. If it doesn't drop below 1% during a typical day, extend the timer.

Are you using the Remote Sense feature?

 

[PaulDavis]

The problem is how to determine how much amperage the panel could deliver. Easy to determine how much power the controller is sending to the battery. The difference between the two amperages is what you are trying to measure.

Right now, there's an algorithm in the controller that ends up causing the controller to deliver a given V/A combination at any given point in time.

With my own eyes, I can see the difference between the amperage delivered from the controller and the amperage being delivered to the batteries, a difference that is accounted for by:

(a) wiring losses
(b) ongoing loads

All I need to do this is to read the amps on the controller and amps on the trimetric. The Morningstar controller doesn't do this, and so I was asking if there was one that could. If it could, it could increase the amps it delivers to the system until the level being delivered to the batteries matched the goal set by the algorithm. If there isn't enough power (from the panels) to do that, then just deliver the maximum available.

 

[OrioN]

Right now, there's an algorithm in the controller that ends up causing the controller to deliver a given V/A combination at any given point in time.

With my own eyes, I can see the difference between the amperage delivered from the controller and the amperage being delivered to the batteries, a difference that is accounted for by:

(a) wiring losses
(b) ongoing loads

All I need to do this is to read the amps on the controller and amps on the trimetric. The Morningstar controller doesn't do this, and so I was asking if there was one that could. If it could, it could increase the amps it delivers to the system until the level being delivered to the batteries matched the goal set by the algorithm. If there isn't enough power (from the panels) to do that, then just deliver the maximum available.

Create a custom profile/algorithm to mitigate this.


Step 1: Change the Float 'out time' from 60 minutes to 10 minutes, then the Bulk/Absorption restart.
Step 2: Study the Owner Manual & MSView Help.....

 

[PaulDavis]

Create a custom profile/algorithm to mitigate this.


Step 1: Change the Float 'out time' from 60 minutes to 10 minutes, then the Bulk/Absorption restart.
Step 2: Study the Owner Manual & MSView Help.....

That's not going to accomplish what I would like to see happen. As others have noted, to do the thing I'd like, the controller needs to be current-aware, not just voltage aware.

 

[OrioN]

That's not going to accomplish what I would like to see happen. As others have noted, to do the thing I'd like, the controller needs to be current-aware, not just voltage aware.

Are you using the Remote Sense feature?

Maximum current will occur during bulk stage. This stage can or will restart based on any voltage that it sense at the battery terminal or 'in/out' time limit you set. The voltage there will be indicative of both the SOC & load.



.

 

[autostaretx]

That's why I asked "is there are solar charge controller that can do this?"

And MidWestDrifter kind'a answered that when he wrote:

For example, my outback solar controller interfaces with my battery monitor. It is set to charge until the return current drops below 1% of C at the absorb voltage.

So we visit the Outback website: http://www.outbackpower.com/products/charge-controllers/flexmax-60-80
and download the manual: http://www.outbackpower.com/downloads/documents/charge_controllers/flexmax_6080/owner_manual.pdf
(which i'm currently plowing through... i'll obviously need to find their monitor, too)

... but i don't know if that's the model that MWD was describing (it does have "network" capabilities)

As for panel current vs battery current vs load current, my $35 MPW controller can display all three.
I know it's totally UNcharacteristic of me, but i haven't spent hours recording how they drift and correlate.
Since it is an MPW, the battery voltage drags the panel voltage down to a less efficient power level than an MPPT.

--dick

 

[Midwestdrifter]

I am using the flexnet dc with flexmax 60 as charge controller. Victrons gear has similar functions. If you are not seeing voltages at14 V or higher during your normal charge regime and low currents the charge controller profile may need adjusting.

Even without current feedback my charger will rapidly get to 14.4 volts and hold it for three or four hours minimum. Large loads may sometimes pull ir down for a bit but it would always return to the 14.4 setpoint.

 

[PaulDavis]

I think maybe I should restate this in simpler, less directed terms.

I know that at noon on February 12th under clear blue skies (thanks, Santa Fe), my panels can generate (at least) 220W because I've seen that number at noon on February 10th.

With SOC in the 80% range, the controller doesn't deliver that much power to my AGMs, but picks a lower value it believes is safe and healthy given the SOC. Let's say it is using 171W, 13.5V and 13A (numbers not far from reality but not necessarily real).

It's all good!

Now, plugin a 135W laptop charger, and turn on the inverter.

Controller meter continues to say 171W, 13.5V, 13A.

Can any controller provide extra power because it knows there is a load on the system above and beyond the "load" of recharging the batteries?

 

[OrioN]

I think maybe I should restate this in simpler, less directed terms.

I know that at noon on February 12th under clear blue skies (thanks, Santa Fe), my panels can generate (at least) 220W because I've seen that number at noon on February 10th.

With SOC in the 80% range, the controller doesn't deliver that much power to my AGMs, but picks a lower value it believes is safe and healthy given the SOC. Let's say it is using 171W, 13.5V and 13A (numbers not far from reality but not necessarily real).

It's all good!

Now, plugin a 135W laptop charger, and turn on the inverter.

Controller meter continues to say 171W, 13.5V, 13A.

Can any controller provide extra power because it knows there is a load on the system above and beyond the "load" of recharging the batteries?

Yes, this controller can.

As I stated before......

Create a custom profile.

For starters, set the profile to exit the float stage after 10 minutes (Currently set for 30). It will restart the bulking (maximum current) as it will read the 'load' induced battery voltage (assuming you are using the Battery Sense feature) as now being perhaps at 12.7v. If need be, adjust all the many other settings that are programmable....

 

[PaulDavis]

Yes, this controller can.

As I stated before......

Create a custom profile.

For starters, set the profile to exit the float stage after 10 minutes (Currently set for 60). It will restart the bulking (maximum current) as it will read the 'load' induced battery voltage (assuming you are using the Battery Sense feature) as now being perhaps at 12.7v. If need be, adjust all the many other settings that are programmable....

The voltage drop in this scenario is 0.1V. Also, I'm not normally in float stage. So I don't think this gets close to what I'm talking about.

Really, I just need lithiums. "Give me all the power you've got, right now, no questions asked". Then I can forget about the stupidity of my batteries actually seeing SOC decreasing under clear blue skies because the controller is trying to be careful.

Edit: real life scenario from right now. 203W from the panels, 13.2V / 15.4A. Batteries at 80% SOC. Current delivered to battery: 13.5A. Plugin laptop charger. Current delivered to battery drops to 12.7A. All other numbers remain the same.

 

[OrioN]

The voltage drop in this scenario is 0.1V. Also, I'm not normally in float stage. So I don't think this gets close to what I'm talking about.

Really, I just need lithiums. "Give me all the power you've got, right now, no questions asked". Then I can forget about the stupidity of my batteries actually seeing SOC decreasing under clear blue skies because the controller is trying to be careful.

Are you using the Battery Voltage Sense Terminals?

 

[Midwestdrifter]

As mentioned, what you are describing is not normal behavior. Either your controller is not configured properly, or your system has some type of fault, high resistance etc. It is tough to diagnose, but a pro could probably narrow it down in a hour or two. The morningstar controller is not watching return amps or watts. It is trying to reach voltage setpoints. If you are seeing 13.5V with no loads and clear skies, you are likely in float mode.

 

[PaulDavis]

Are you using the Battery Voltage Sense Terminals?

Yep.

 

[OrioN]

The voltage drop in this scenario is 0.1V. Also, I'm not normally in float stage. So I don't think this gets close to what I'm talking about.

Really, I just need lithiums. "Give me all the power you've got, right now, no questions asked". Then I can forget about the stupidity of my batteries actually seeing SOC decreasing under clear blue skies because the controller is trying to be careful.

Edit: real life scenario from right now. 203W from the panels, 13.2V / 15.4A. Batteries at 80% SOC. Current delivered to battery: 13.5A. Plugin laptop charger. Current delivered to battery drops to 12.7A. All other numbers remain the same.

Which meter is 12.7A current draw being read?

 

[PaulDavis]

Which meter is 12.7A current draw being read?

A trimetric.

 

[OrioN]

TriStar MPPT Operator’s Manual 32


Bulk Charge Stage
In Bulk charging stage, the battery is not at 100% state of charge and battery voltage has not yet charged to the Absorption voltage setpoint. The controller will deliver 100% of available solar power to recharge the battery.

Absorption Stage
When the battery has recharged to the Absorption voltage setpoint, constant-voltage regulation is used to maintain battery voltage at the Absorption setpoint. This prevents heating and excessive battery gassing. The battery is allowed to come to full state of charge at the Absorption voltage setpoint. The green SOC LED will blink once per second during Absorption charging.

The battery must remain in the Absorption charging stage for a cumulative 120 - 150 minutes, depending on battery type, before transition to the Float stage will occur. However, Absorption time will be extended by 30 minutes if the battery discharges below 12.5 Volts (25 Volts @24 V, 50 Volts @48 V) the previous night. The Absorption setpoint is temperature compensated if the RTS is connected.

Float Stage
After the battery is fully charged in the Absorption stage, the TriStar MPPT reduces the battery voltage to the Float voltage setpoint. When the battery is fully recharged, there can be no more chemical reactions and all the charging current is turned into heat and gassing. The float stage provides a very low rate of maintenance charging while reducing the heating and gassing of a fully charged battery. The purpose of fl oat is to protect the battery from long-term overcharge. The green SOC LED will blink once every two (2) seconds during Float charging.

Once in Float stage, loads can continue to draw power from the battery. In the event that the system load(s) exceed the solar charge current, the controller will no longer be able to maintain the battery at the Float setpoint. Should the battery voltage remain below the Float setpoint for a cumulative 30 minute period, the controller will exit Float stage and return to Bulk charging.

The Float setpoint is temperature compensated if the RTS is connected.

 

[OrioN]

The voltage drop in this scenario is 0.1V. Also, I'm not normally in float stage. So I don't think this gets close to what I'm talking about.

Really, I just need lithiums. "Give me all the power you've got, right now, no questions asked". Then I can forget about the stupidity of my batteries actually seeing SOC decreasing under clear blue skies because the controller is trying to be careful.

Edit: real life scenario from right now. 203W from the panels, 13.2V / 15.4A. Batteries at 80% SOC. Current delivered to battery: 13.5A. Plugin laptop charger. Current delivered to battery drops to 12.7A. All other numbers remain the same.

No... with LI's the exact same scenario you are having now will still occur.

 

[elemental]

With SOC in the 80% range, the controller doesn't deliver that much power to my AGMs, but picks a lower value it believes is safe and healthy given the SOC. Let's say it is using 171W, 13.5V and 13A (numbers not far from reality but not necessarily real).

It's all good!

Now, plugin a 135W laptop charger, and turn on the inverter.

Controller meter continues to say 171W, 13.5V, 13A.

Can any controller provide extra power because it knows there is a load on the system above and beyond the "load" of recharging the batteries?

I am not an expert, but my understanding of how these systems works may be slightly different than yours. My understanding is that current flows because of voltage (electrical pressure) differentials. A charger can't "force" current into a circuit (or a battery) without increasing the voltage (pressure); alternatively a voltage drop in a circuit will cause more current to flow if it is available from a current source. If you add a load into a circuit that is at a certain voltage level, the voltage will drop unless a current source with enough extra current to meet the new load is available. The extra current is either drawn into the circuit and the voltage doesn't drop, or insufficient current is available and the voltage drops.

If you have a charge controller (current source) with active electronics that is monitoring/maintaining a certain voltage level in a circuit that includes a battery (such as following a program to maintain a battery storage system) then the current flow from the charge controller is doing two things: it is satisfying any load in the system, and it is forcing energy into the battery (if and only if) the battery can accept more energy at the current voltage level. If you add a load to the circuit, the charge controller will have to increase the current flow (if it can) in order to maintain the voltage level in the circuit. Either the current flow increases, or the voltage drops. If neither of these occurs, something else must be supplying enough current to meet the load without dropping the voltage, such as the battery. But this would mean that the battery wasn't accepting any energy from the charge controller at the voltage the charge controller was maintaining in the circuit, or else it wouldn't be able to supply current at the circuit's voltage.

According to my understanding, if you add a load to your circuit (the inverter, powering your laptop through its AC adapter presumably) and neither the voltage drops or the current increases as seen by your charge controller, then the power to the inverter must be being supplied by the battery at a voltage equal to the voltage that the charge controller is already trying to maintain. Perhaps the amount of current required by the inverter/laptop is very small (for example, the laptop batteries might be near peak capacity and the laptop charger is not drawing any A/C current at the moment) and the additional current flow from the battery or the charge controller is thus very small and the voltage change is too low to be captured by the charge controller sensor? Alternatively, the battery wasn't really taking any energy from the charge controller at its current voltage?

I wonder what would happen if you tried the same experiment but with a larger known load on the circuit (something that you know draws a steady 5 amps at 12 VDC or so, which should translate to at least 60 watts), like a lightbulb or a resistive load like an electric heater in a coffee pot?

 

[HarryN]

I know that you are trying to get the charge controller to achieve:


(battery optimal charging at the given SOC)
+ (enough current going into the system so that it makes up for any loads when possible)

Just keep in mind that this is not the only way to charge a battery, especially Lifeline AGMs.

It is virtually impossible to have enough solar panels on a conversion van to keep up with the recommended bulk charge rate of a single size 31 Lifeline AGM battery.

(nominal 2C recommended bulk charge rate) x (120 amp-hrs) x (13 volts) = 3 kW.

In the real conversion van world, with a "real world solar output" of 5 - 10% of the recommended rates, the finishing charge conditions need to be changed to higher values in order to compensate.

If you contact Lifeline, they will provide suggestions on improved charge settings for these conditions. You might be surprised at how much higher current and time they can take at these finishing stages, essentially allowing you to never dial down your solar power input.