is there a solar charge controller that can do this?

PaulDavis

Member
It's now the start of year 5 in the story of our Sprinter conversion. We recently sold our home in Philadelphia, and are once again "full timing" in the van, except that we've already fallen in love with and bought a home in Santa Fe.

Everything continues to be fine with the van (more or less, I won't get started) but the behaviour of our solar charge controller bothers me and I have been wondering if there are alternatives that can do what I think it should.

We have a Morningstar MPPT controller, along with the associated TriStar "remote meter". We also have a Trimetric battery meter.

The Tristar shows me the current being delivered by the charge controller; the Trimetric shows me the current arriving at the batteries. Obviously, in almost all cases, the Trimetric current reading is less than the value on the Tristar - no problems with that.

The charge controller is doing its "clever" thing where it limits the power delivered to the (AGM) batteries based on their current charge state. We're mostly in the high 80%-95% range, so it tends not to deliver a lot of power even in clear overhead sun. Although I'd prefer lithiums so that we could just absorb as much power as the sun can give us, I understand that in terms of the health of our batteries, the controller is being smart about it.

Here's what bothers me. The Trimetric can see that the actual current (and voltage and thus power) arriving at the batteries is less than the values displayed by the Tristar, because of ongoing loads on the electrical system. The fridge may be drawing power, or a laptop charger, or the Espar D2 or whatever. But the charge controller appears to have no understanding of this at all. Its power delivery is based entirely on its understanding of the battery state, not the current system state.

I am wondering if there's a charge controller that can use a measurement point like the Trimetric, understand that we're actually drawing power from the system while it is charging, and increase the power delivery from the panels while this is happening.

Specific case in point: charge controller is delivering 150W (from 540W of panels) at 10A to the batteries. Trimetric shows 9.2A being delivered ... we're good. Now plug in a 135W laptop charger. The charge controller does NOTHING different. I'd like one that understands what has just happened and responds by increasing the delivery from the panels.

Does this exist?
 

HarryN

Well-known member
I don't know the answer, but I will tell you that I have had long conversations with some of the solar charge controller companies regarding algorithms.

Some of them will essentially "turn off" and let a battery get 25% depleted while the sun is shining in the middle of the afternoon, then kick on the charging just before sun down due to dinner time power demand. This is particularly true for 12 volt mppt types. Crazy.

In spite of its lower efficiency (due to being a pwm design), the trimetic solar charge controller "might" be able to do this. The trimetic monitoring information is fed to the charge controller, so this capability "might" be built in.

The owner of Bogart Engineering (trimetic) is an off grid RV / solar guy, so if anyone understands what you are asking, they would.

_________

Midnight solar builds a Kid mppt controller that includes the "trimetic like" functionality using a shunt and feedback to the controller. It has a very high degree of programmability, so this capability might be in there. Their phone support is actually pretty decent, as is their "user run forum". If the functionality is not in the product, they definitely will not add it. Sometimes you can trick it though.

_________________________

There are a few other possibilities, but if those can work they will be the most simple to implement.

___

The battery charging algorithm area, especially for simultaneous charging and load draw is a bit of a controversial area, especially on forums. IOTA developed a custom charge algorithm for a major customer with both battery charging and loads. (120 vac charger) The end customer was very happy, so they released it as an option to the general market and got no end of flack for creating a "battery ruining algorithm". Sometimes it is hard to help people.

____________________

Edit - just thought of something. Some chargers allow you to program in higher currents for finishing stages vs the typical recommended currents. It is not quite what you are asking, but if you are regularly using 100 watts of load during the day, it might be just fine to program it this way.
 
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HarryN

Well-known member
Enjoy Santa Fe. It is a pretty nice town. About as optimal as you can get for generating solar power, just be careful of the very high UV index.
 

autostaretx

Erratic Member
I have to admit that i'd think the controllers DO accidentally compensate/correct for loads when they're in the constant voltage stage of their charging cycle.
But they probably don't "properly" handle loads during the earlier "constant current" stage.

The "constant voltage" stage (if only seeing batteries, not loads) will see the current diminish as the battery "finishes up".
If a load comes on-line, the current will increase to keep the voltage "constant". So the battery is still being treated nicely.

The killer to that is if the load is high enough to pull the battery (and charger) down to a noticeably lower voltage ... that would probably convince the charger to switch back to "constant current" since it would think the battery is at a significantly lower level of charge.
And by that, you've lost the "load compensation".

From my casual reading, many of the mid- and lower-priced controllers were designed for the telecommunications industry: solar-powered microwave repeaters in difficult locations. The loads were known and controlled, and the battery capacity made them NOT draw the batteries down unexpectedly (in fact, the loads were pretty much constant (except for perhaps "night lights", which is why the controllers with "load" outputs activate them with loss of solar input).

That's something to look at: if your controller has "load" outputs ... and you're using them (like i do), does the net current to the batteries properly follow the battery's desired charging curves?
My controller certainly knows the currents flowing through all three connections: panels in, battery (net), loads out.
But i haven't sat down and tested/recorded what happens

Controllers without Load outputs wouldn't know what's going on ... all they'll see is the battery (whatever its load).

--dick
 
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OrioN

2008 2500 170" EXT
If the one you have the Morningstar Tristar MPPT60, it is custom programmable and can do what you require.

Read the manual to learn how you can create your desired algorithm with the MSView program utility.
 

HarryN

Well-known member
Hi Dick, thanks for the comments.

It is always fascinating what tricks and protections are built into chargers. Liability and risk drive a lot of decisions when it comes to potential algorithm enhancements.

The typical charger that I have tested highly limits the current in the absorption and float stages. They make assumptions about the charge state based on the programmed sequence.

I have observed the same behavior you have regarding the impact of heavy loads. Start pulling 1 - 2 kW from an inverter and the pack voltage will sag sufficiently to trigger a full charge sequence, starting with the healthy currents supplied in bulk stage.

The tricky area is pulling low / moderate currents when the battery is in that 80+% SOC area. The charger thinks that it is doing its job supplying small currents for the ABS and Float stages, and the load can be sufficient that SOC is actually decreasing.

A taper charge solves this, but not everyone is on board with the concept and it requires some additional hardware to deal with its behavior. I have a few in installations where they make sense.
 

Graphite Dave

Dave Orton
Some of them will essentially "turn off" and let a battery get 25% depleted while the sun is shining in the middle of the afternoon, then kick on the charging just before sun down due to dinner time power demand. This is particularly true for 12 volt mppt types. Crazy.
The Morningstar SunSaver MPPT 15 amp solar controller does not turn off and let the battery get depleted to 75%. I have never had my house battery below 75% SOC. The SunSaver does charge the battery back to 100% SOC no matter what the SOC is above 75%.
 

OrioN

2008 2500 170" EXT
The Morningstar SunSaver MPPT 15 amp solar controller does not turn off and let the battery get depleted to 75%. I have never had my house battery below 75% SOC. The SunSaver does charge the battery back to 100% SOC no matter what the SOC is above 75%.
Try this....

One summer morning, when you get up, deplete the bank to 75%. Let your solar fill it back up. 15 minutes after it is full, deplete again to 75%. Then tell us what your solar charger is doing. You may be unpleasantly surprised....
 

Graphite Dave

Dave Orton
Try this....

One summer morning, when you get up, deplete the bank to 75%. Let your solar fill it back up. 15 minutes after it is full, deplete again to 75%. Then tell us what your solar charger is doing. You may be unpleasantly surprised....
I assume you are telling me that it would not work. Should not be an issue because I never get below 75% SOC anyway much less getting below 75% SOC twice in a row.
 

Midwestdrifter

Engineer In Residence
As mentioned most MPPT controllers(including this one) are going to output as much current as they can in an attempt to reach the voltage setpoint. Once the setpoint is reached the charge rate it limited by the batteries acceptance at the voltage. If you have other loads consuming power, and there is not enough solar to meet the charge acceptance and the loads, then the voltage will drop below the setpoint until which time the solar exceeds the acceptance+loads. Lead acid, especially as it ages, will accept less and less current at the same SOC. Once you break 95% SOC, you will not see more than 2-3% of C in charge rates at absorb voltage.
 

elemental

Wherever you go, there you are.
I am wondering if there's a charge controller that can use a measurement point like the Trimetric, understand that we're actually drawing power from the system while it is charging, and increase the power delivery from the panels while this is happening.

Specific case in point: charge controller is delivering 150W (from 540W of panels) at 10A to the batteries. Trimetric shows 9.2A being delivered ... we're good. Now plug in a 135W laptop charger. The charge controller does NOTHING different. I'd like one that understands what has just happened and responds by increasing the delivery from the panels.

Does this exist?
There are charge controllers that use a remote battery monitor so that the charge controller can sense the voltage at which it is charging the battery directly at the battery. That helps solve the problem of voltage drop in the cabling leading from the charge controller to the battery. If there was a load pulling the voltage down I would expect the charge controller to increase the voltage in the system if it had enough supply (i.e., enough sun on the panels if it is solar PV) so that the voltage at the battery measured what it expected at that point in the charge cycle.

Someone in the thread mentioned a charge controller that has separate "load" connections from the battery charge/discharge connections. That sounds like it would make the charge controller even smarter with respect to battery state versus system state.

Wizardry usually has its price, so there are probably tradeoffs in terms of the component cost to have a smarter system that you would weigh against the payback either in extended battery bank life or more usable power on the daily cycle.
 

PaulDavis

Member
If the one you have the Morningstar Tristar MPPT60, it is custom programmable and can do what you require.

Read the manual to learn how you can create your desired algorithm with the MSView program utility.
I have the manual. I see how to reprogram the bulk/absorb/float stuff. But that's not what I desire. I'm quite happy with the current programming.

I just want a solar array that can deliver the correct charging current to my AGM's (given their current SOC) but ALSO deliver more to the system if there is a current draw other than the batteries.
 

PaulDavis

Member
The tricky area is pulling low / moderate currents when the battery is in that 80+% SOC area. The charger thinks that it is doing its job supplying small currents for the ABS and Float stages, and the load can be sufficient that SOC is actually decreasing.
Precisely.
 

autostaretx

Erratic Member
Reading the Morningstar MPPT manual, it would appear to only be a VOLTAGE controlled/sensing device (with one overcurrent exception).

So it's going to be putting out as much current as it can for the voltage levels it's trying to achieve.
The only current *limiting* it does is if the battery is accepting more than 130% of the controller's rated output.
At which point the controller will shut down for 10 seconds. And blink LEDs at you.

So if the unloaded battery is accepting less than full-rated current due to a high state of charge, AND you turn on your load, the controller's current output WILL increase to keep the battery up at the desired voltage, to the limits of its output rating. If it achieves that goal (the battery reaching the float stage, for example), then you could say that all of the controller's output is actually going to the load ... and the battery's just along for the ride.

--dick
 
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downunder

Active member
Hi Paul,
Perhaps have a look at an Enerdrive DC2DC+ epower charger? Multi stage, multi source with MPPT.
Apparently when in float stage it can support additional loads like lighting or refrigerators, effectively using the charger as a dc power supply.
It may also be available under the Kisae name?
I don't know enough about it; it may satisfy your query, but hope this is of some help
 

hein

Van Guru
We have the Sunsaver MPPT which has a 'load' connection.
Says it provides 'battery' power for lights, etc.
We don't have anything connected there in our van.

All the best,
Hein
 

MsNomer

Active member
I have both the TriMetric meter and charger. I’m not sure I understand what you are saying the Morningstar does/doesn’t do, but the TriMetric shows me when excess solar is available for other purposes when the batteries are not taking in all that is available.
 

PaulDavis

Member
I have both the TriMetric meter and charger. I’m not sure I understand what you are saying the Morningstar does/doesn’t do, but the TriMetric shows me when excess solar is available for other purposes when the batteries are not taking in all that is available.
I mostly want the reverse. I want the charge controller to know when the panels can deliver more than the batteries should receive AND there's a load above and beyond charging that can use the extra.

Eg. batteries at 85% SOC, charge controller decides to deliver 13.0V at 10A to keep the batteries healthy. Now add a load (e.g. a 135W laptop charger, or a refridgerator or whatever) ... the charge controller can deliver a lot more power "into" the system without harming the batteries, while still continuing to charge them at the optimum rate.

But the charge controller doesn't know this because the only measurement it has is voltage in the system, and these loads don't change the voltage sufficiently for the controller to do anything differently. If it watched the current arriving at the batteries, like the Trimetric does, it would know that something else is sucking power from the system, and it could increase its output accordingly.
 

Midwestdrifter

Engineer In Residence
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.
 
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Graphite Dave

Dave Orton
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.

How can you determine the maximum output available from the panel when battery is full?

If you knew the difference how would you change your electrical usage during the time excess power was available? What else would you power?
 
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