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zaczaller avatar image
zaczaller asked

MPPT reaches float when battery monitor voltage is not charged at all

All three screenshots are from this morning with the sun jus coming up. Last night the voltages read practically the same on both MPPT and Battery monitor but as soon as the sun rose the mppt went on bulk for a second and suddenly said my battery voltage was at 14.6 and hit float when clearly on the battery monitor it’s no where near charged. I am feeling a little hopeless as to what to do because I’ve followed the entire build process correctly and can’t figure out why this won’t charge my lithium battery properly.

BMV Battery Monitor
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zaczaller avatar image zaczaller commented ·

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3 Answers
snoobler avatar image
snoobler answered ·

Why are you starting a new thread? You already have the attention and assistance of smart folks in your other question. I don't see that you've acted on their recommendations.


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pwfarnell avatar image
pwfarnell answered ·

The behaviours here is completely in line with a high resistance somewhere in your circuit as I have been trying to tell you and get you to measure. When you have little current flow there is no voltage drop in the cabling, when current tries to flow it does not come through and creates a voltage drop. When you have solar power and the solar controller says 14.6 Volt and the BMV say 13.0 Volt you have to go out with your digital voltmeter and find out where that 1.6 volt drop is occurring. It could be in the cable terminals on the Solar Controller, it could be in the crimped on connectors, it could be in the connects where they are bolted to the busbars etc. etc.

As someone said, think of it as a pipe with a valve in it and some where in your system you have a valve that is cracked open a tiny little bit as an analogy for the high resistance. At night you have little solar generation, so analogy is a dribble of water (low amps) is trying to get through and you do not need much pressure (Voltage) to get a dribble through a tap that is cracked open. During the day you have more solar generation so you are now trying to get a firehose quantity of water to travel through a cracked open valve, no way can that amount of water get through and it builds up a lot of pressure behind the vale to get what little water it can through the valve. You need to find that valve and open it.

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bbmz avatar image
bbmz answered ·

I would like to crossreference to this thread

https://community.victronenergy.com/questions/116024/significant-difference-in-voltages-between-charge.html

The problem is the (insufficient) gauge 10 wiring between bus-bar and MPPT.

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