Battery condition discrepancy

[colin k]

Hi. So i have a 55 watt solar array with a pathetically CHEEZY charge controller(thank you costco).

My charge controller has 3 led lights. The first light tells you you have 75% + battery charge.
The second light tells you ,you have between 25-75% charge.
The third light tells you you have 25% or less charge.
So after charging my battery to 100%, i run my fantastic fan for about 10 minutes on medium and my charge controller tells me my battery is now at 75% and lower. Hmmm. Brand new battery from wallyworld rv deep cycle 120 amp/hr rating.

Then

I decided to let my fridge(12v fridge) run my battery down to the third led light which is the 25% and less battery charge indicator.
I hook up my fancy digital battery charger which tells you the charge on the battery. The battery charger reads 70% charge.

Hmmm. My cheezy charge controller reads below 25% and my fancy battery charger reads 70%.

Comments,suggestions welcomed.

[Paddy Morris]

Bummer, I think I have the same little charge controller, I used my inverter to tell me the state of the batter as I don't really trust those three little lights. While testing the solar set up at home the controller jumps from one light to another for no apparent reason sometimes. My inverter seemed more accurate. I'm pretty sure that controller is the lower end of the market. At Emily the congtroller behaved though. Pat

[Steve C.]

Hi. So i have a 55 watt solar array with a pathetically CHEEZY charge controller(thank you costco).

My charge controller has 3 led lights. The first light tells you you have 75% + battery charge.
The second light tells you ,you have between 25-75% charge.
The third light tells you you have 25% or less charge.
So after charging my battery to 100%, i run my fantastic fan for about 10 minutes on medium and my charge controller tells me my battery is now at 75% and lower. Hmmm. Brand new battery from wallyworld rv deep cycle 120 amp/hr rating.

Then

I decided to let my fridge(12v fridge) run my battery down to the third led light which is the 25% and less battery charge indicator.
I hook up my fancy digital battery charger which tells you the charge on the battery. The battery charger reads 70% charge.

Hmmm. My cheezy charge controller reads below 25% and my fancy battery charger reads 70%.

Comments,suggestions welcomed.

Most of these led battery charge displays only read the output voltage of the battery, and rely on the fact that a battery at full charge will be 12.6-12.7 volts, half charge at approximately 12.0-12.1 volts and dead at around 11.5. Unfortunately, these voltages only reflect the battery's condition when it is at rest. That is, no current drawn out or put in for several hours at least. If you are charging or drawing current recently or in the last few hours, the battery voltage reading simply will not reflect the actual state of charge.

As you have discovered, this, coupled with the broad range covered by the leds, makes for a somewhat crude indication of battery condition. A more accurate measurement of charge is possible using a temperature compensated battery hydrometer, or a programmable amp-hour meter.

Steve.