By Rusty Latenser
Most lockouts don’t “just happen.” The controller almost always warns you first.
Message Board controllers provide a steady stream of data about battery health, solar harvest, and system stress. Operators who know how to read these numbers can spot trouble days before a sign goes dark. This article breaks down the four parameters that matter most — and how to interpret them in the field.
Voltage Trends
Voltage is the single best early‑warning indicator of battery health and upcoming lockouts.
What to watch:
Resting voltage (no load). Fully charged lead-acid = 12.-12.8V, LiFePO4 = 13.6V
What is Resting voltage?
Nothing is connected to it (no load)
It has not been charged for 30–60 minutes
This is the true state‑of‑charge indicator for both lead‑acid and LiFePO₄.
Why “no load” matters: Resting voltage is the only voltage that accurately reflects State of Charge (SOC) and Battery health
LiFePO₄
- Treat 13.2–13.4V as “healthy and ready.”
- Anything 12.8V or below means you’re already under ~30–40% SOC.
- Below 12.5V, you’re in the danger zone for winter autonomy.
Lead‑Acid
- 12.6–12.8V = full
- 12.2V = ~50% SOC (where cycle‑life damage begins)
- 11.9V = ~40% SOC (sulfation accelerates)
What it means:
Declining voltage with load added = battery stress
If voltage sags every time the message activates, the battery is struggling to support the load.
For PCMS units, voltage sag during message activation is one of the earliest indicators of: Failing lead‑acid batteries, cold‑soaked LiFePO₄, low SOC due to poor solar harvest (somewhat fixable by using MPPT controllers)
For your field crews, sag will appear as:
Voltage drops from 12.8V → 11.5V when the message turns on
Or LiFePO₄ dropping from 13.2V → 12.0V under load
Message flicker or dimming
Controller rebooting
Solar charger showing “low voltage” even though the battery seems “charged”
Voltage never fully recovering during the day
Expect a lockout within 24–72 hours unless conditions improve.
Operator rule:
If voltage is trending down for two days in a row, act before the sign shuts down.
Charge Current
Charge current tells you how much power the solar array is actually delivering to the batteries.
What to watch:
Peak charge current at midday
Charge current during clear skies
Charge current vs. panel rating
Charge current vs. battery voltage
What it means:
Low charge current despite full sun = shading or wiring issue. Even a small shadow can cut current by 50–80% (especially if your equipment uses PWM controller – 6 out of 7 manufacturers use this cheaper controllers. Only INEX provides it as standard equipment).
Charge current stuck at low values all day. Panels may be dirty, mis‑angled, or partially disconnected.
Charge current spikes but doesn’t sustain. Indicates intermittent shading, loose connections, or panel mismatch.
Operator rule:
If charge current is less than half of expected output at noon, inspect the panels immediately for damage, snow, or dirt.
Solar Input (Wattage or Voltage)
Otherwise known as Panel voltage (Vmp): the total voltage coming into the solar charger at its maximum power point. It is not a fixed number — it shifts with temperature, irradiance, shading, dirt, snow, and angle. For example. Heat → lowers Vmp and Cold → raises Vmp.
What to watch:
Panel Vmp
- The voltage the panel produces at its maximum power point
- Varies with sun angle, dirt, snow, temperature
- It goes into the charge controller
- It is not the voltage sent to the battery
Controller Output Voltage
- Determined by battery type
Fully charged lead-acid = 12.-12.8V, LiFePO4 = 13.6V
(Lead-acid, AGM, Gel or LiFePO4) and charge stage
- Typically, 12–14.6V for 12V systems
- Independent of panel Vmp
For PCMS units, this distinction is critical because:
- PWM controllers force panels to operate at battery voltage → big winter losses
- MPPT controllers allow panels to operate at Vmp → 15–40% more harvest in cold weather
This is why your MPPT retrofit specs matter so much for winter autonomy tables.
What it means:
Solar voltage collapsing = shading or panel failure
When a shadow hits even one solar panel cell, panel voltage can crash.
Why shading matters (the part most operators miss)
Even small amounts of shading can dramatically reduce output because:
• Solar cells are wired in series, so one shaded cell drags down the entire panel or string.
• Shading can cause hot spots, which damage panels over time.
This is why PCMS units with low winter sun angles, snow on the bottom edge, or tree shadows lose far more energy than operators expect. Another reason why cleaning snow off solar panels is important.
Solar voltage normal but charge current low
Batteries may be full, cold, or the controller is limiting output.
Temperature
Temperature affects both charging and battery capacity.
What to watch:
Battery temperature
Controller temperature
Solar panel temperature (if available)
Ambient temperature trends
What it means:
Cold batteries charge slowly
Below freezing, charge current is automatically limited if your system has Temperature Compensation built into it or charging is blocked entirely. Temperature Compensation is your friend: it ‘trickle’ charges the batteries to prevent damage.
Hot batteries lose capacity
High temps accelerate voltage drop and shorten runtime. Lead-acid really hate heat.
Controller overheating
Can cause throttling, reduced charge current, or shutdowns.
Operator rule:
If battery temperature is below freezing or above 120°F, expect reduced charging and faster SOC decline.
Putting It All Together: Predicting Lockouts
A lockout rarely comes from a single parameter. It’s usually a pattern.
Common lockout pattern:
Solar input drops (shade, dirt, bad angle)
Charge current stays low
Voltage declines each day
Overnight voltage falls below safe limits
Controller locks out to protect the batteries
Early intervention checklist:
Increase panel tilt if that is possible,
Northern half of USA (not Alaska)
- Best year‑round tilt: 32.3°
- Best summer tilt: 17.3°
- Best winter tilt: 47.3°
Southern half of USA
- Best year‑round tilt: 28.6°
- Best summer tilt: 13.6°
- Best winter tilt: 43.6°
Clean the panels (about a 5% impact on power generation)
Reduce message brightness (not ideal since this may reduce operational distance to below 800 feet or 650 feet legibility (a MUTCD requirement).
Check wiring and fuses for rust or looseness.
