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Old 04-14-2018, 04:01 PM   #1
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Default Deep Cell Battery Charge Over 15?

quick question: just switched solar controller from cheapie pwm to cheapie mppt - under pwm voltage never went over upper 13s - with mppt it has gone over 15 - is this okay?
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Old 04-14-2018, 05:25 PM   #2
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quick question: just switched solar controller from cheapie pwm to cheapie mppt - under pwm voltage never went over upper 13s - with mppt it has gone over 15 - is this okay?
Please post screen shot.
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Old 04-14-2018, 05:38 PM   #3
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Please post screen shot.
i don't understand what screen shot to post...

basically all i am saying is i had a pwm solar charge controller for over a year which at most went to 13.7 or 13.8 volts - when i switched to a mppt controller i saw that the voltage (the next day) was at 15.1 volts - so i am wondering if this will do any harm to my two wet cell 12v batteries

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Old 04-14-2018, 06:03 PM   #4
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That is too high for charging any of the lead acid batteries, but before you get too concerned, make sure you are looking at the correct voltage. The voltage coming from the panels will be higher than the voltage going to the batteries, often by as much as 5 volts. Different controllers call everything different names, so check to make sure you are looking at battery charging voltage or output from the controller and not panel or input voltage.

That said, the controller could also have an equalize feature that accidentally got activated during setup. Check the instructions to see how to tell if equalize has be initiated.
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Old 04-14-2018, 07:09 PM   #5
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I stuck one of those plug-in voltage meters into one of the 12volt sockets connected to the house batteries and it showed the higher amount as well - so is that telling me the batteries are being over charged?
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Old 04-14-2018, 07:17 PM   #6
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Does your controller have a remote with information or does the unit have any indicator lights to let you know what it thinks it is doing?

Brand and model number would help, so we can look up the manual and see how it is supposed to be installed and function.
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Old 04-14-2018, 08:02 PM   #7
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It is a cheapo controller with minimal user manual - on Amazon it is called "CPY-2420 12V/24V 20A USB MPPT Solar Panel Battery Charge Controller" - it claims it has overcharge protection but there is no way to configure the thing
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Old 04-14-2018, 08:37 PM   #8
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From the small amount of information there is, they mention 12/24v "autowork", so the assumption has to be it autoselects the voltage based on what it sees for a battery. That may be what is messed up.

You might want to put a voltmeter on the panel to controller input to see what it is reading for volts. I wouldn't be surprised if it will read the same as you see on the outputs within a small amount, if it is just passing through the voltage due to a defect. Some places were selling those for just over $25?
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Old 04-14-2018, 09:59 PM   #9
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From the small amount of information there is, they mention 12/24v "autowork", so the assumption has to be it autoselects the voltage based on what it sees for a battery. That may be what is messed up.

You might want to put a voltmeter on the panel to controller input to see what it is reading for volts. I wouldn't be surprised if it will read the same as you see on the outputs within a small amount, if it is just passing through the voltage due to a defect. Some places were selling those for just over $25?
so, i went out and measured as you suggested and here's what i found: note that the sun was well past its peak - the voltage coming off the panels was over 14 and the batteries were at below 13 - interesting, right?
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Old 04-14-2018, 10:22 PM   #10
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Very interesting for sure. Time to wait until tomorrow for more sun to see what it does then, I think.

Almost like it went to float, but still doesn't explain the 15v.
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Old 04-15-2018, 02:04 PM   #11
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It is a cheapo controller with minimal user manual - on Amazon it is called "CPY-2420 12V/24V 20A USB MPPT Solar Panel Battery Charge Controller"
I bought one for experiments ($25) and it is exceedingly squirrely. I can't tell what it is doing by watching the input/output. I gave up on it.

The earlier versions of this model were doing at least rudimentary MPPT. Later versions (at least the ones that work) are doing something different and potentially interesting. They seem to be running the panels a volt or two higher than Vbatt and bucking down the incoming voltage. Not PPT but more power than PWM might make.

Anyhow, for more info on the controller in question, Adam Welch has youtube testing on both the other older and newer models.
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Old 04-17-2018, 08:27 PM   #12
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Very interesting for sure. Time to wait until tomorrow for more sun to see what it does then, I think.

Almost like it went to float, but still doesn't explain the 15v.
There hasn't been a lot of sunshine the past few days but what appears to be happening is the cheap mppt controller is stepping down by 2 volts whatever the panel is producing onto the batteries- not good. Going back to my tried and true pwm for now.
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Old 04-17-2018, 11:42 PM   #13
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I was thinking of upgrading my cheap pwm that came with my panel when I installed it but I think I will just stick with it. Thanks for this thread. It may have saved me some high blood pressure.

Paul
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Old 04-18-2018, 08:42 PM   #14
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I always encourage folks to get the most out of what they have before buying something new.

Here's a quick wiki page on tweaking a PWM for max output.
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Old 04-18-2018, 11:13 PM   #15
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fratermus, thanks. That is great information. The chart in the link you provided is a good one to print out and have a copy on board.

Paul
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