Author Topic: 20v from panel....12v entering regulator ?  (Read 2149 times)

Offline Bernard

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20v from panel....12v entering regulator ?
« on: April 29, 2020, 12:20:35 PM »
I've had no battery backup at night for bedroom light and gadgets.

The battery is half car battery size. Panel is 22v @ 55watts. I get 20v at the end of the cable.

As soon as I clamp the cable into the regulator I only get 12v. (Back probe)

What am I missing ? Lol

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Offline Bernard

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Re: 20v from panel....12v entering regulator ?
« Reply #1 on: April 29, 2020, 12:26:15 PM »
The voltage in the lower photo is 12.5v

Offline chrisc

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Re: 20v from panel....12v entering regulator ?
« Reply #2 on: April 29, 2020, 12:27:29 PM »
The no-load voltage is much higher in this instance as it is not a regulated supply

Lead-acid batteries are not too fussy about incoming voltages since the internal resistance increases greatly as it reaches its capacity, which is 13,85V (and the current it is able to absorb drops)

However, this is not a long-term solution.  Cannot you change it to between 13,65 and 13,85 volts?   All that will happen is that the battery life will shorten and get hot
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Offline Bernard

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Re: 20v from panel....12v entering regulator ?
« Reply #3 on: April 29, 2020, 01:19:58 PM »
Thanks Chris...I don't know enough to open it up to change anything in the regulator. lol
I just can't figure out that I get 20V at the end of the cable .... until I clamp it in.

Being a regulator I simply assumed it would still be 20v +- from the panel and the regulator would do it's job and "regulate" it to 13v or so ??

Do you think 4 years is "time up" for one which has "lived" in almost perfect conditions ?

Offline Bernard

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Re: 20v from panel....12v entering regulator ?
« Reply #4 on: April 29, 2020, 02:39:28 PM »
OK...checked again... the input voltage is now 13.26V
Still have no idea what happens between the 20V and the 13.26V. lol

Offline DACMan1

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Re: 20v from panel....12v entering regulator ?
« Reply #5 on: April 29, 2020, 03:08:54 PM »
OK...checked again... the input voltage is now 13.26V
Still have no idea what happens between the 20V and the 13.26V. lol

That is the way those cheap PWM chargers work. Basically, if the battery is low, it connects the battery directly to the panel. This means you waste quite a bit of the capacity of the panel, but if you want to use it all, you have to get an MPPT controller.

Offline Bernard

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Re: 20v from panel....12v entering regulator ?
« Reply #6 on: April 29, 2020, 03:26:43 PM »
But this is the bit I can't wrap my head around. Item1. Lead not connected, gives me 20V.

Item 2. Lead connected to regulator. Voltage at the end of the same lead is now 13.26V Before ..... it reaches the PCB.

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Offline DACMan1

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Re: 20v from panel....12v entering regulator ?
« Reply #7 on: April 29, 2020, 04:23:36 PM »
A PV panel is a current source. The PWM regulator measures the battery voltage, if it is below a threshold, it connects it to the battery, if it is above another, it disconnects. (It is slightly more complicated, but that is it for the most part)

If you connect the PV to your battery, being a current source, the voltage will drop to that of the battery with the given current the panel is able to supply at that point of it's I/V curve.

What you are seeing is completely as expected.

(if you disconnect the battery and load with only the panel connected, you will see nearly the same 20V as with it floating.)

Offline chrisc

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Re: 20v from panel....12v entering regulator ?
« Reply #8 on: April 29, 2020, 05:55:11 PM »
The meter presents a tiny load to the power supply
So you will see whatever comes out, no loss whatever

Its a very small unit.  I am very suspicious of the 30 amp claim.  There is no heatsink I can see or voltage regulation

My Mecer charger can deliver 20 amps.  It is 10 times the size and has 2 fans inside
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