question

paul-neubert avatar image

Plenty of voltage from panels, no current from panels. Load discharging from battery instead.

Two 100W panels in series. 30+ volts consistently all day, but never more than about 1/10th amp showing as being produced. Multi-meter touched to wires as they enter the controller (so I suppose in parallel with the controller) read between 3 and 4 amps.


When load hooked up to load terminals at 1A draw (a 2 bay 18650 battery charger set to 1A charge rate), I see the amp coming off the battery, not the panels. I never see any amperage coming in from the panels.

I suppose this might be naive of me, but I assumed that if I was drawing a load, that the panels would attempt to fill the need before the battery did? Battery is a 12V lithium ion pack, so don't be concerned about is reading 11.59V. It can go a lot lower than that before any harm done.

Might also be worth noting that I have the float voltage set at 11.5V and Absorption set at 12.4V. I know I don't really need to float a lithium battery, which is why I have it set so low. I have the load output settings at 12.25V for the "reconnect load, battery is charged enough" and 10.35V for the "disconnect load, battery is getting too low".

Nothing appears to be reversed for polarization, and this battery has sort or trickle charged itself each day (graphs show me 10-20Wh per day input) to maintain roughly 12V over time. I haven't really had a load on it before today, so no significant battery charging has been needed.

We also have been dealing with all the wildfire smoke for the last week or so. Today was the first blue sky day. So first day I expected to see some panel efficiency.

Screenshot below.



Screenshot of my app.



input current
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3 Answers
wkirby avatar image
wkirby answered ·

Your float Voltage is set too low.
If the actual battery Voltage is higher than what you have set the Float Voltage to then it will not charge. It shouldn't charge if the actual battery Voltage is higher than the Float set point otherwise it'll never reach the Float level.. The battery will not reach the set Float Voltage unless it discharges to that value. So you can see that the acuall battery Voltage is 10.59V and Float is set to 10.5V.

I presume this is a 3S battery of 3.7V cells? 12.4V is good for Absorb, but I think you should set Float to 11.1V and see how that works.
The battery will discharge and PV will be zero until the battery Voltage comes down to 11.1V in the Float stage. Thereafter to will try to maintain that 11.1V Float point as long as there is enough PV power to do this and the load is not more than the PV can sustain.

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Makes sense. Yes, this is a cheap Chinese 3S8P pack. Just playing around with it. I think it is only something like 15 or 20 amp hours.


I will adjust the float!

Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

I think your charge settings are wrong. A normal LiFePO4 lithium battery has a absorption voltage of 14.2V and 13.5V float.

Take a look at the datasheet of your battery.

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Matthias;

Thanks for the quick reply. It isn't LiFePO4. Just regular old lithium ion. Here are the specs.

  • Standard voltage: 11.1 (V)
  • Working/Discharge voltage range: 8.5V ~ 12.6VCharging voltage: 12.4V ( 4.15v±0.05v)
  • Load voltage: 8.5~12.6V
paul-neubert avatar image
paul-neubert answered ·

Matthias;

Odd. It cut off about 3/4 of my "comment" back to you about the specs of the battery. Let's try it here in it's own comment.

It isn't LiFePO4. Just regular old lithium ion. Here are the specs.

  • Standard voltage: 11.1 (V)
  • Working/Discharge voltage range: 8.5V ~ 12.6VCharging voltage: 12.4V ( 4.15v±0.05v)

Do you think the charging parameters I have set would influence or cause the weird current limitations (basically zero current) I was describing in my original post? Load pulling from battery and not direct from panels when there is plenty of panel voltage? Perhaps that is how the charge controller is designed to operate and I am just not realizing it. The sun has gone down for the night and I am discharging the battery more than I have in the past. So the morning will tell me if the panels suddenly output some current to recharge the battery I suppose.

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