Slow Solar Charging and Go Power Display Questions

[KirkB]

The first thing I would suggest is to check the water level in your batteries. I found that the recharging via solar is less when the water level is lower.


I would also plug in to shore power if you can, even for a short while, to see if the converter charger can raise the voltage on the batteries faster than solar alone. You might keep plugged in until you are over 13V, then unplug to see how the solar does from there.


The solar charger will try to run a one hour bulk charge cycle each day at 14.4V. The power boost symbol (4 very small dots) are visible on the display until this cycle has completed. This cycle will not complete if the batteries cannot reach 14.4V of charge.

[canyonrider]

Interesting. After getting home yesterday afternoon the batteries were still around 80%, despite having at least partial direct sun all day. I plugged in to shore power for two hours. They went to 90% quickly, then stayed there. This morning the panel had direct sun again and was showing a charge of 4.1 amps, but batteries still stuck at 90%. I think my next step is to check water levels.

[float5]

Do you have the dual water heater with electric? If the propane is off, it is off. Electric, however, can be heard if you have that on.

The batteries can recover from deep discharges but that should only happen once in a great while or it will shorten their life. Try not to do it often and you need to do whatever you can to not use 12V for the refrigerator, as mentioned.

[padlin]

Might be worth checking the 12 volt voltage level with a meter of some sort, as opposed to just the GoPower's meter.

[hotfishtacos]

The first mistake I made boon-docking was to run the refrigerator on 12 volts instead of propane. This was a 4 day trip to the Anza Borrego Desert. Even with the 95watt solar panel and with the sun high in the sky it killed one of my two 6 volts batteries when the solar could not keep up. I replaced both of the batteries after that trip. The refer pulls way too much amperage to use boon-docking. As I added more batteries and panels I still never ran the refer on 12 volts while boon-docking, only when connected to the grid. ALWAYS use propane when off the grid.

[Brian B-P]

Originally Posted by padlin

Might be worth checking the 12 volt voltage level with a meter of some sort, as opposed to just the GoPower's meter.

I assume that the GoPower controller's meter is nothing but a voltmeter calibrated according to a table like that, adjusted by some formula based on current to try to compensate for the effect of charging. This isn't a monitoring system like the Bogart Trimetric that actually measures net current accumulated in and out of the battery.

It would make sense to me to remove the source of charge and any loads and let the battery sit to reach a more accurate indication of state of charge, based on resting voltage.

Originally Posted by canyonrider

After getting home yesterday afternoon the batteries were still around 80%, despite having at least partial direct sun all day. I plugged in to shore power for two hours. They went to 90% quickly, then stayed there. This morning the panel had direct sun again and was showing a charge of 4.1 amps, but batteries still stuck at 90%.

A problem with these charge level indications is that they are based simply on voltage, and at least some of these numbers are being read while a charger is pushing current into the batteries. The charger can make that number go up and down just by changing charging mode (absorption, bulk, float...) without any change in actual battery charge level. The steady 90% reading on shore power presumably just means that the charger was maintaining a constant output voltage, not that the battery wasn't charging, although any charging voltage is much higher than the 12.5 volts of a resting (not being charged or discharged) battery at 90% state of charge.

[Viajante]

Canyonrider, I question whether the gopower controller is operating properly. I might have a different model of gopower controller, but I haven't seen a charging voltage as low as 12.6 volts. If it has been in direct sun for 30 minutes and putting out 3.4 amps I would expect a voltage of between 13.6 and 14.4. 12.6 is what you might find after dark when not charging, and reflecting the status of the battery, not the charge voltage. Again, my controller might be a different model, but maybe worth a call to manufacturer.

[Brian B-P]

Originally Posted by canyonrider

They went to 90% quickly, then stayed there. This morning the panel had direct sun again and was showing a charge of 4.1 amps, but batteries still stuck at 90%.

I don't think that the batteries were stuck at 90%; I think that the controller's State of Charge calculation is stuck.

Originally Posted by Brian B-P

I assume that the GoPower controller's meter is nothing but a voltmeter calibrated according to a table like that, adjusted by some formula based on current to try to compensate for the effect of charging.

I found three manuals for what appear to be three different versions of GoPower's 30-amp solar charge controller, all called GP-PWM-30. One of them shows the logic to determine the State of Charge (SOC) value, which I can only guess is the same in all versions. It looks like my guess was half-right: it is a calculation based on voltage, but it doesn't even consider current.

Battery Voltage

State of Charge Displayed

• Shows only after full Boost or Equalization Cycle

  100%

• >= 12.8V

  90%

• < 12.8V and > 11.0V

  SOC = (BatteryVoltage V - 11.0 V)/1.8 V * 90%

• <= 11.0V

  0%

So once the battery voltage (or close to it, as seen by the solar charge controller) reaches 12.8 V - driven by the converter/charger - the display will show until the solar charge controller thinks the Boost cycle is complete... but the solar controller isn't doing the all of the charging, so who knows when it will think that?

[alanmalk]

Originally Posted by canyonrider

... despite having at least partial direct sun all day ...

Canyonrider, I'm a little worried about your use of "partial". You have mention this a couple of times. It may be significant because shade on a solar panel is the kiss of death. A single leaf shading one cell can cut the amps by half. Even shade of the width of a pencil across a full cell will be noticeable. Do your best to get 100% sun on the panel for at least a few hours when the sun is at its highest.

Also, you are welcome to visit our '21 here in Arvada and listen to the 'fridge. I have a very hard time telling when the propane flame is lit. On the other hand, I can hear the supplemental fans running on a warm day. Send me a PM (private message) if you are so inclined.

--
Alan

[J Mac]

Originally Posted by alanmalk

Canyonrider, I'm a little worried about your use of "partial". You have mention this a couple of times. It may be significant because shade on a solar panel is the kiss of death. A single leaf shading one cell can cut the amps by half. Even shade of the width of a pencil across a full cell will be noticeable. Do your best to get 100% sun on the panel for at least a few hours when the sun is at its highest.--
Alan

Your experience with shade on solar panels is exactly what I have experienced yet some forum members have stated that they receive a charge even with the cover on.

[KarenH]

After three years with my trailer and a single roof-mounted solar panel (90 watt), I am convinced (without any empirical data whatsoever) that sun angle is more critical than shade. My first year out I purposely camped in a canopied campground during the height of summer and I had no problem with recharging the next day. And since I am a winter camper, I added the additional 90-watt portable panel so I could point it at the sun during the day.

[Brian B-P]

The problem with partial shading is that a solar panel is a set of individual cells connected in series.

Each cell adds a "push" of voltage so the panel's voltage is the total of all the cells' contributions (about half a volt from each cell), just as the 12 volts from an Escape's dual battery setup is the total of 6 volts from each battery (and each 6V battery is in turn three 2-volt cells); if one of the three dozen or so cells of the panel isn't doing much that's not a big deal to voltage. The problem is that - again like dual batteries in series - exactly the same current passes through every cell in the series; if any one of them isn't getting enough light to pass much current, the whole panel's current is limited. If just one cell is completely shaded, the current output of the entire panel is hobbled by shading less than 4% of its area.

Imagine a bucket brigade, where each bucket-passing person represents one cell. If everyone in the line can handle a big bucket but just one person can only handle a teacup, the whole thing is limited to passing teacups.

(Better explanations from solar panel experts are welcome!)

An evenly shaded panel (even under a thin cover) still produces some power, and it seems like a partially shaded panel should do better, but the partial shading can dramatically limit useful output due to that current limitation.

[Brian B-P]

Looking for published sources to confirm or better explain the shading problem, I came across PVEducation. This site has excellent (in my opinion) explanations in a well-structured collection. The Shading section concludes:

Shading of a Module

The cells in a module are all connected in series. Shading a single cell causes the current in the string of cells to fall to the level of the shaded cell.

[padlin]

Another aspect. I can be in the shade from a tall tree and still get some power out of the panel, maybe 2 or 3 amps. Even under a thin trailer cover I'll see an .5 -1 amp. If I cover 1 cell with something like a piece of wood with the rest in the sun, I get nothing out of the panel. So it seems shade density has an effect too.

Although this has nothing to do with the OP.

[tdf-texas]

Originally Posted by padlin

If I cover 1 cell with something like a piece of wood with the rest in the sun, I get nothing out of the panel. So it seems shade density has an effect too.

I thought current panels all have bypass diodes to prevent that from happening.

[Brian B-P]

Originally Posted by padlin

Another aspect. I can be in the shade from a tall tree and still get some power out of the panel, maybe 2 or 3 amps. Even under a thin trailer cover I'll see an .5 -1 amp. If I cover 1 cell with something like a piece of wood with the rest in the sun, I get nothing out of the panel. So it seems shade density has an effect too.

That fits perfectly with the idea that the most-shaded cell limits the current.

Originally Posted by padlin

Although this has nothing to do with the OP.

The shading discussion came out of the observation that the batteries didn't seem to be charging as expected.

Originally Posted by tdf-texas

I thought current panels all have bypass diodes to prevent that from happening.

That makes sense, but I think bypass diodes are normally applied on a larger scale (that is, for a group of cells), not for each individual cell.
Bypass Diodes | PVEducation

For instance, the specs for the panels in the Samlex 100-watt and 150-watt kits say have three bypass diodes, so that would be one diode per group of 12 cells (since these are 36-cell panels as usual for nominal 12-volt operation).

[alanmalk]

Originally Posted by tdf-texas

I thought current panels all have bypass diodes to prevent that from happening.

Virtually all panels have a blocking diode. Only a very few specialized panels have bypass diodes on each cell. These panels do exist but I don't have a reference off the top of my head.

--
Alan