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Old 31-10-2014, 00:27   #1
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MPPT solar controller

Hi,
I recently installed a Tracer 3215RN MPPT solar controller. It works fine except that the battery voltage shown on the controller is much higher than what is showing at the battery. The result is that when the controller shows 14.4 volts and regulating the amps down, the batteries show 13.7 volts. does anyone know of a way to rectify this?
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Old 31-10-2014, 01:06   #2
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Re: MPPT solar controller

Sounds like voltage drop between the bat and the controller to me. Either that high resistance in the the cables leading to a mis-read.

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Originally Posted by Paul Klein View Post
Hi,
I recently installed a Tracer 3215RN MPPT solar controller. It works fine except that the battery voltage shown on the controller is much higher than what is showing at the battery. The result is that when the controller shows 14.4 volts and regulating the amps down, the batteries show 13.7 volts. does anyone know of a way to rectify this?
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Old 31-10-2014, 07:37   #3
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Re: MPPT solar controller

Without pulling the manual, I suspect that the controller has a provision for voltage sensing input and, if so, it was not installed. Voltage sense is connected directly to the battery bank or its buss bars and provides the input to the controller so that the controller can raise its output voltage to compensate for voltage drop in the conductors between the controller output and the battery bank.

That said, 0.7V voltage drop is almost 5% which isn't terrible. I suggest you increase the size of your conductors to achieve a voltage drop <3%.
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Old 31-10-2014, 08:56   #4
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Re: MPPT solar controller

I have a 40A TRACER MPPT controller and have to say that , although I am very satisfied by the performance of the unit , I do not trust the MeTer .
I monitor the state of charge my batteries with a TRIMETRIC , and the data shown by this (reliable) unit is nowhere close to the one shown by the Tracer Meter (sometimes .3V to .4V off !!!
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Old 31-10-2014, 09:17   #5
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Re: MPPT solar controller

What is the current when you see this voltage mismatch? If the current is high then it is likely conductors that are too small, poor connections, or something similar and you are losing power (and heating wires or connectors).

On the other hand, if the current is low when you see this mismatch then it is unlikely that it is wiring/connections, instead one (or possibly both) of the meters is wrong. If you can stop the current entirely and still keep the MPPT meter display up, if there is a delta then the problem is in the meters. If there is no delta V with no current then the problem is in losses between the controller and battery. In that case you can beef up the wires and/or add a sense wire if the controller accepts same.
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Old 31-10-2014, 09:40   #6
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Re: MPPT solar controller

Check the voltage difference at night when there is no solar current to see if you have a wiring issue or just a cheapo voltmeter in the MPPT.
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Old 01-11-2014, 05:06   #7
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Re: MPPT solar controller

Thanks for the replys. I have used very heavy wiring (7.91 mm2 Rated to 74 amps) from battery to controller. The wiring from the panels to the controller is 4.50mm2 rated to 38 amps (maximum current from the panels is 25 amps). I did discover today that the battery negative at the controller was loose, again, and very hot. This time I crushed the soldered ends with vice grips and re secured all wires. I will check tomorrow if this has made a difference in the two previously mentioned voltages. Thanks again for the advice
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Old 01-11-2014, 05:30   #8
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Re: MPPT solar controller

Hot is not good and it sounds like you have found a bad connection.

To correctly size marine wiring the usual limiting factor is not the maximium current rating of the wire, but the voltage drop. This is something you need to calculate. Those wire sizes are quite small and are likely to have some significant voltage drop.

My solar array is a similar size and my wires are 35mm2
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