[RE-wrenches] Mystery: C-40 controllers "stuck" in EQ mode

[Mick Abraham]

Hi, Detectives~

At a client's off-grid home I observed two side-by-side Trace C-40 PV
controllers, circa 1998, which were "stuck" in equalize mode. Day after day
they did the red/green blink and they would not throttle back the incoming
solar energy. This was with the jumper set for automatic EQ (should have
been once per 30 days). I changed the jumpers to Manual EQ and normal
behavior ensued: green blink with proper throttle back.

Clues: The battery is huge compared to the solar recharge current. The
battery is also old and may have high self-discharge. Internal shorts in one
or more battery cells are also possible. Because of these factors, the
battery voltage was not reaching a high value even though the controllers
were running wide open.

I thought that when the sun set, any auto EQ behavior on the C-40 would
cease, but that didn't happen in this case. A product failure seems
non-likely unless they both happened to break in the same way. Is there some
other condition which the C-40 must see in order to be satisfied that it's
OK to end the EQ?

Thanks in advance for helping me solve this mystery,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675
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