SmartSolar MPPT 75/15 - Temperature Compensation Problem

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biborado asked Aug 1, '24

SmartSolar MPPT 75/15 - Temperature Compensation Problem

***UPDATE***

Added replies below initial post with more information
Looks like charge controller is working as designed, though this behavior really seems like a major design issue
Would greatly appreciate it if a Victron representative or expert can chime in
- Why does the temperature compensation stop and decrease voltage -20C? Colder should mean an increase in voltage compensation
- Why does the voltage dramatically drop between +48 to +60°C?
- Why does the voltage remain constant above +60C? This would 'cook' the battery if temperature compensation is enabled

For reference, I was recently on a trip where the outside air temperature alone was >+47°C. The battery sense detected a battery temperature in the +50 to +60°C zone causing the charger to stop charging all together.

Hello,

I've been troubleshooting an issue with my SmartSolar 75/15 which fails to output power to the battery even though all indications should allow the charger to output to the battery.

I believe I've figured out the conditions and have taken some screenshots and a screen recording of the events happening in real-time to help address the issue. This issue is easily reproducible and from what I've searched may be something others have come across but hadn't nailed down the exact conditions.

Using a heat gun, I heated up the SmartShunt temperature sensor causing it to start and stop charging depending on the VE.Smart Networking temperature sense.

Behavior:

CC stops charging when VE.Smart Networking temperature sense is between 50°C - 60°C
CC resumes charging outside of these ranges < 47°C or > 60°C
Disabling Temperature Compensation resumes charging
Leaving VE.Smart Networking resumes charging

Since the battery and SmartShunt temperature sense is in the engine compartment, the CC output is constantly turning on and off. This seems like a bug and doesn't make "sense".

Configuration

- SmartSolar 75/15 (VE.Smart Networking enabled)

- SmartShunt 500A w/temperature sensor (VE.Smart Networking enabled)

- Battery Type: Odyssey AGM (Operating temp -40°C to 80°C)

- Battery Location: Vehicle Engine Compartment

- SmartShunt Location: Vehicle Engine Compartment

- CC Location: Inside occupant cabin

MPPT SmartSolar SmartShunt Temperature Sensor VE.Smart Network temperature compensation

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biborado commented · Jul 30 at 11:49 PM

Stops charging @ 60°C

Resumes Charging @ 47°C

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biborado biborado commented · Jul 31 at 10:36 PM

MPPT appears to be working as designed per the manual, however I don't understand why it would stop charging between 50 - 60C. Looks like another user @Fra also noticed the same issue. (https://community.victronenergy.com/questions/162683/victron-temperature-compensation-graph.html)

Is there a reason why the temperature compensation would drop the voltage (effectively stop charging) between 50-60C? With a vehicle mounted lead-acid battery, it's very common for the battery temperature right in the middle of that 50-60C range. This seems deliberate but isn't obvious why.

It's causing the battery to be severely drained during the day. By the time the battery temp decreases to below 48C, there may not be enough sunlight left to fully charge the battery.

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biborado biborado commented · Jul 31 at 10:36 PM

And another user @GunnarH found the same thing with no resolution or response from Victron.

https://community.victronenergy.com/questions/164875/mppt-battery-temp-compensation-graphs-deep-voltage.html

I can understand if the charge controller needs to thermal throttle if it detects a high internal charge controller temperature however with an external temperature sense, assuming there's no overheating happening on the charger side it should continue charging in accordance with the voltage/temperature compensation as defined by the setting in the charge controller.

Adding an upper and lower voltage limit would also be useful.

I would expect the temperature compensation for an AGM battery to something like this (thank you Odyssey Battery):

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Answer 1 · 2024-08-02T01:27:51Z

klim8skeptic answered · Aug 02 at 01:27 AM

@Biborado Why does the temperature compensation stop and decrease voltage -20C? Colder should mean an increase in voltage compensation

Dunno much about LA batteries, but I do know the electrolyte will freeze at temps below 0c.

Attempting to charge frozen batteries is apparently bad and will lead to battery damage.

Could be the reason for the temp compensation offset at -30c.

Charging at High and Low Temperatures

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biborado commented · Aug 03 at 06:58 PM

AGMs are very resilient to low temperatures. Example, my Odyssey AGM has an operational temperature of -40°C to 80°C.

I think perhaps a fully discharged battery could freeze however if the battery has a charge then the electrolyte isn't susceptible to freezing until approximately -70°C.

The issue I'm really trying to address is the more warm temperatures. The problem is a normal day for my AGM is in the +50 to +60°C. The MPPT doesn't begin charging the battery until it is severely discharged below +12VDC.

Normal day:

Doesn't resume charging until the temperatures drop to +48°C regardless of Voltage or SOC.

In this case the battery was already full so it was only pulling in <17W after the temperature dropped. However if it was deeply discharged it would not have had enough time to charge up before sunset.

Notice the time 16:42. It would have missed out on almost 3 hours of charge time!

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klim8skeptic ♦ biborado commented · Aug 04 at 12:00 AM

@Biborado According to Odyssey Do not charge batteries if the temperature is above 104°F (40°C).

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biborado klim8skeptic ♦ commented · Aug 05 at 04:40 AM

I agree and do tend to see most AGM/Lithium battery manufacturers state an upper charge temp limit at 50°C. That does however seem more like a rule of thumb.

I think odyssey for example lists the lowest common denominator (RV & Marine) batteries as the high temp limit. My install uses the ODX-AGM variant.

Isn't the whole point of temperature compensation chart to help safely and effectively charge batteries at a range of temperatures?

Assuming Victron is trying to avoid charging over 50°C. That goes out the window at 60°C where the charge would resume.

Even if we were to assume that Victron were trying to prevent charge when >50°C, I had another issue. When I had the load output of the MPPT on, the charger remained off and didn't help offset the load being drawn directly from the MPPT and instead drained the battery. I would expect the charger would at least attempt to provide the direct connect loads with power when able.

Again, I think the whole point of temperature compensation is to use the offset (-24mV/°C in my case) to adjust voltage above and below the nominal 25°C charge settings.

The Victron temperature compensation graph isn't well defined in the manual as to why Victron does this. All it really does is hinder an effective charge where a properly set up temperature compensation offset would be sufficient.

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