question

ares1 avatar image
ares1 asked

Mppt 150/35 float stuck problem

Hello I have 250watt x2 panels in series. I have 4×220 Ah battersea (total 880 Ah). I folow my battery voltage from BMV 700 monitör and also from the mesurment device on my inverter. Now both shows 11.7 Volt . My problem is during night time when the mppt is off I see same volt on my mppt application in my phone. So normally the morning it should be bulk but in a very short time it goes float since it shows 13.8 Volt float voltage limit. From settings I increase float limit to 14 volt . In a second it is ön float volt showing batteries voltage 14 volt I again decrease 13.8 volt and system shows 13.8 and remain float. What could it be the reason stucking in float mod?

MPPT Controllers
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wkirby answered ·

When the MPPT Voltage is reading 13.8V or 14V, what Voltage does the BMV read?
I suspect there is a bad connection somewhere between the MPPT and the battery.

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ares1 avatar image ares1 commented ·

11.75 volt

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wkirby avatar image wkirby ♦♦ ares1 commented ·

So therefore, the battery is not connected to the MPPT battery output terminals.
Check for bad connections, open fuses or circuit breakers.

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ares1 avatar image ares1 wkirby ♦♦ commented ·

Thank you. I check my connection and fuse. And I found melted fuse. What might be the reason for melting of the fuse?img-20201101-wa0018.jpeg

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img-20201101-wa0018.jpeg (925.1 KiB)
wkirby avatar image wkirby ♦♦ ares1 commented ·

Oh no, that looks bad. I'm glad you have found the problem.

I have found that those fuse holders don't realy work well with continuous high current. The fuse terminals (the flat part) was most likely getting hot due to the contact not being 100%. The design of the fuse holder means that you would not be abble to detect or see a poor connection.
Then, to make matters worse, the fuse holder is thermally insulated, so any heat cannot get out and then whole thing just gets hotter until it melts like that.

You could try and use the physically larger type of blade fuse in a better holder which allows cooling and you can see if the blade terminals are making good contact, or you can feel that it is firm when you push the fuse in.
The best would be the Mega style of fuse which is bolted in place which offers very good contact and takes any heat away from the fuse through the bolt terminals.

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