question

dan avatar image
dan asked

75/15 mppt floats below the set voltage

screenshot-20210328-143016.jpgHi, i have a victron 75/15 mppt with blutooth dongle attached with no battery temp monitor. i have set up a maintenance setting (pic attached), the problem is that it its floating @13.09v and its set to 13.35v.screenshot-20210328-143036.jpg

Ive also noticed there is intermitant data on the history and i have set absorption and float the same setting values, it seems that it reaches the 13.35screenshot-20210328-131019.jpgvoltage in bulk or absobsion then drops to 13.09v.

I also have another seperate system but with a batt monitor and no dongle but blutooth, both are set to the same config through the phone app and it keeps the correct float voltage except for the battery monitor adjustments.

Just cant work it out

Some conflicting pic data, inital data is Set float voltage 13.35v and it sits at 13.09v.

Currently the 13.15voltage is dropping back due to checking voltage setup and now its set at 13.30v so i expect it to drop lower than 13.09v, maybe 13.04v float.

MPPT Controllers
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2 Answers
Paul B avatar image
Paul B answered ·

Hi you dont mention what type of batteries you have, but all your settings look wrong .

your absorption voltage is the same as your float voltage. Absorption should be around 14 to 14.6 volts normally depending on your battery specs and float around 13.6v


also for the mppt to start charging the voltage difference between the PV voltage and the batteries must be more that 5Vs or the MPPT will not start charging. so I suspect that your panel voltages maybe to low. so if you have more than one you should maybe change them to a series configuration to bump there voltages upto 36 volts

Just a couple of comments. for you


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dan avatar image dan commented ·

The voltage is in float mode that means its charging its already gone through the bulk and absorb cycle, the voltage is not the issue, if i adjust the float up to 13.7v it will charge to 13.45v or so..

The absorb and float are set the same because the batterys are not on load during the day they are in maintenance mode for months or untill we go camping, thats why the tail is .5v so a quick bulk and absorb are achieved.


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dan avatar image dan commented ·

Todayscreenshot-20210328-182419.jpg

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screenshot-20210328-182419.jpg (386.2 KiB)
JohnC avatar image
JohnC answered ·

Hi @Dan

If you scroll down your Settings screen a little further you'll see Temperature Compensation. That will affect your target voltages.

What value is entered there?

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dan avatar image dan commented ·

I dont have any temp info, there isnt any on the mppt is there?, only if i have a battery temp monitor which is on my other one, only.


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JohnC avatar image JohnC ♦ dan commented ·

@Dan

Yes it has, but it only uses it when starting at daybreak, else any casing heat would be misrepresented.

This from my settings (48V bank, hence the high TC):

1616925816257.png

(Must be a negative value).

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dan avatar image dan JohnC ♦ commented ·

Oh yes, its on tge page.screenshot-20210328-212841.jpg

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screenshot-20210328-212841.jpg (277.9 KiB)
JohnC avatar image JohnC ♦ dan commented ·

@Dan

That's ok. but your mppt must be in a hot place to under-target the set V's at dawn. You could try setting the TC to zero, then maybe awaiting a new day.. Just to see if it follows uncorrected setpoints.

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dan avatar image dan commented ·

screenshot-20210328-201912.jpg

Just now

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klim8skeptic avatar image klim8skeptic ♦ dan commented ·

edit..........

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dan avatar image dan commented ·

So this is the other unit with the temp monitor on the battery, it has the same user set and its in the driveway with the other unit in the sun, the batts would be the same temp i reckon.screenshot-20210328-202020.jpg

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screenshot-20210328-202020.jpg (312.0 KiB)