Battery Charging Question - Fiberglass RV


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Old 08-15-2014, 09:49 AM   #1
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Battery Charging Question

I think I have a charging problem.

System and voltages

I have a 100 watt solar panel charging my battery. When I measure the voltage at connection from solar panel to charge controller I get 19+ volts. When I check connection from battery to charge controller I get about 13.4 volts. So far, so good.

Possible Problem

Yesterday the voltage dropped down to about 12.9 volts on battery side. The battery light on the charge controller was fast blinking which means the battery is fully charged. So this looked like a problem because the voltage is usually in the 13+ volts when fully charged.

This morning, the light was on solid indicating battery was charging. Voltage read about 13.4 volts. I just checked again and voltage has dropped to 12.9 volts and light is fast blinking again.

I'm at a loss how to trouble shoot this. The only things I can think of are:
  • Possible intermittent short in one of the connectors or cables
  • Intermittent failure in charge controller
Any ideas on what else might be causing this problem or things to measure?

ETA: I turned the fan on and disconnected the solar panel. I wanted to see if the battery light on charge controller would change to solid when the battery was discharged some. So far, it is still fast blinking and voltage has dropped from about 13.3 to 12.95.

ETA 2: With fan on, voltage dropped quickly to about 12.8. The light changed back to solid on, so I hooked solar panel back up. Voltage jumped to about 14.1. After a couple of minutes, battery light changed to fast blink again.

Maybe this is just how a cheap charge controller works.

New problem is why is fan pulling down voltage so fast?
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Old 08-15-2014, 11:07 AM   #2
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I don't think you're having a problem - the charge controller stops charging when the battery is fully charged, which it would be if you are seeing a voltage of 12.9v (12.6v is actually fully charged, some may argue 12.7v).
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Old 08-15-2014, 11:17 AM   #3
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Originally Posted by sarahspins View Post
I don't think you're having a problem - the charge controller stops charging when the battery is fully charged, which it would be if you are seeing a voltage of 12.9v (12.6v is actually fully charged, some may argue 12.7v).
I agree. In fact a good design would have some hysteresis, that is, on and off at different points, to avoid oscillation. Raz
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Old 08-15-2014, 11:26 AM   #4
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I will just consider myself educated then. And keep watching it to see if there is a pattern.
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Old 08-15-2014, 02:01 PM   #5
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Just because the LED indicates full charge, anything over 12.6 V, doesn't mean the controller is no longer charging. Most likely it is still charging, but at a lower rate.

What's the make and model of your controller?
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Old 08-15-2014, 02:52 PM   #6
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Just because the LED indicates full charge, anything over 12.6 V, doesn't mean the controller is no longer charging. Most likely it is still charging, but at a lower rate.

What's the make and model of your controller?
It's the Renogy 30 amp.
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Old 08-15-2014, 06:07 PM   #7
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If it's a Renology PWM1030, the manual, in the indications for the battery icon, shows: 'Green On: Battery level in the right range". (I guess that could mean anywhere from 11.58 to 12.6+ volts.) 'Green Slowly Flashing: Battery is full'.

I believe it's reasonable to assume that if the light isn't flashing green and not showing orange, the battery is charging. The flashing green I think would indicate that the battery is above 12.6 Volts, not necessarily that the charger has quit charging.

Do you have a battery monitor or DMM to check amp output when the light is flashing green? You may be surprised at what you find.

On my Morningtar SS-10-12V, on the state of charge LEDs, even when the battery shows full there may be some charging going on, though it may be at a very low level. Indications are as follows:
Green-on solid- battery nearly full.
Green-slow flashing, 1 flash/2 sec-full battery: float charge (13.7 Volts)
Green-medium flashing, 1 flash/sec-full battery: absorption charge (14.4 volts-3 hrs)
Green-fast flashing, 2 flash/sec-full battery: equalization charge (14.9 volts-3 hrs)

Then there is the Status LED which when the unit is charging, it is on, solid green, with a heart beat every 5 seconds. The SOC LEDs indicate the type of charging that is taking place.

As you can see there are 3 'full' levels where charging still takes place. The two most important ones are the absorption and float, as the equalization cycle takes place every 28 days.

Your LED indicators may not be this detailed, but I wouldn't be surprised if something similar is happening.
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Old 08-15-2014, 06:39 PM   #8
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It's the PWM30CC which is similar to the PWM10CC (10 amp), so the manual says PWM1030CC.

I checked amps, but got strange readings. At 1st it read a little over 4 amps, but when I retested I got 0 amps. I need to test again and see what the light is doing when I test.

In looking at the manual, 1 of the battery parameters is Load Reconnect 12.6V (12v). That's about the voltage when I noticed the charge led changed from blinking to solid.
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Old 08-15-2014, 06:47 PM   #9
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Its interesting that this conversation just arose today given that I just ran across the website linked below. There is a deep well of information about this very issue, much which will challenge your past knowledge, but can't recommend it enough. It will take some time to get through it all.

The RV Battery Charging Puzzle « HandyBob's Blog

Hope this helps
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Old 08-15-2014, 07:28 PM   #10
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Quote:
Originally Posted by Huck View Post
It's the PWM30CC which is similar to the PWM10CC (10 amp), so the manual says PWM1030CC.

I checked amps, but got strange readings. At 1st it read a little over 4 amps, but when I retested I got 0 amps. I need to test again and see what the light is doing when I test.

In looking at the manual, 1 of the battery parameters is Load Reconnect 12.6V (12v). That's about the voltage when I noticed the charge led changed from blinking to solid.
Were sun conditions changing when you did the readings? You might want to clip the VOM into the circuit for convenience and then sit and watch it a while during a full sun day to see if and how the reading change.

I don't think load reconnect applies here. As I understand it the load disconnect kicks in when voltage drops below the set point so that all the amperage goes to charging the battery.

If the charger just turns on an off when the battery is full, which your VOM will tell you, that sounds more like a shunt, or on/off controller. I read somewhere recently that there are some companies selling shunt controllers as PWM. While PWMs effectively turn on an off, it does so fairly quick, so much so that they can cause radio interference. PWM changes the time factor that the circuit is on, pulse width, thereby regulating the charge rate.

As a possible source of interference, a PWM controller, should operate within the limits of an FCC Class B digital device, just like your computer, and if so your manual should state that, probably somewhere in the first few pages under Regulatory Information.

The Morningstar has a slow switching mode that limits the frequency to a max of 10 Hertz if the default PWM setting causes noise or electronic interference.
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