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Old 11-01-2020, 21:20   #1
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My float voltage is too high despite correct settings.

I have just installed a new bank of Lifeline AGM's. I'm currently on a walk-on mooring so I have my Mastervolt charger permanently plugged in. I haven't yet hooked up the temperature sensor as I'm trying to get my settings accurate before lettting the charger automatically adjust the voltages due to temperature. The charger supplies power to the few loads that I have without draining the batteries so it constantly supplies up to 8 amps for fridge etc...The batteries are therefore fully charged and in float mode. The trouble is, the batteries are sitting at 13.8v in float although I've set the float voltage to 13.3v as per manufacturers instructions. It seems to me that no matter what power the charger is supplying the loads, the float voltage should remain at the correct settings?
Any advice would be appreciated.
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Old 11-01-2020, 21:29   #2
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Re: My float voltage is too high despite correct settings.

What are you using to measure the 13.8? A multimeter or battery monitor etc.
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Old 12-01-2020, 05:38   #3
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Re: My float voltage is too high despite correct settings.

You could try setting the Float lower to see if the voltage comes down a bit to verify the controller is working properly.
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Old 12-01-2020, 06:03   #4
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Re: My float voltage is too high despite correct settings.

There are multiple device Voltages "negotiating" to produce a "compromise" result on the circuit.

When the bank is truly 100% Full as per Lifeline specs, say

14.4V held until 0.005C endAmps

that is the **charging** voltage.

Isolate the bank completely, and 24+hrs later you will see a much lower **resting** voltage.

Given a newish healthy battery, some of that might still be a "surface charge", so drawing say half an Ah will be a better reference point "X".

That bank is still at 100% SoC

So, an input voltage **any higher** than that X will be enough to Float the bank, keeping it at 100%.

As long as the sources' current is sufficient to cover any loads fed, no current is drawn from the bank, stays at 100% SoC and the circuit voltage is maintained at that "negotiated" point Y.

But, when current drawn is **greater** than sources' input, then current must come from the bank, and both SoC and Voltages start to drop.

Depending on the load current rate, then circuit voltage Y will drop much faster than bank voltage X, which can be seen by isolating the bank, and watching bank V "bounce back".

So TLR, try dropping your bank SoC% down lower than say 70%, and see how that changes the numbers you are reporting.
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Old 12-01-2020, 06:27   #5
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Re: My float voltage is too high despite correct settings.

Many multimeters are inaccurate so it is possible that the 13.8v is just wrong. Are you measuring the voltages at the same location? The other possibility is that the voltage sensor in the charger is out of calibration. Finally, without a temperature sensor connected, what temperate does the charger default too? Try plugging in a sensor.

You should be able to set a custom setting to adjust for any discrepancies, but given the large error I would try and track down the source first.
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Old 12-01-2020, 08:06   #6
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Re: My float voltage is too high despite correct settings.

The digital gauge on my charger and my Xantrex battery monitor are both showing 13.8v. My multi meter at the terminals shows a reading of 13.55v. Even allowing for a bit of error that's still a bit above the float voltage of 13.3v?
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Old 12-01-2020, 08:14   #7
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Re: My float voltage is too high despite correct settings.

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Originally Posted by Privilege View Post
The digital gauge on my charger and my Xantrex battery monitor are both showing 13.8v. My multi meter at the terminals shows a reading of 13.55v. Even allowing for a bit of error that's still a bit above the float voltage of 13.3v?
Yes, it is significantly different. Small variations in these charge set points make a large difference in the current the battery will accept, and therefore factors such as the time taken to fully charge the battery, and if the battery is being over or undercharged.

It is worth checking the voltages carefully and making adjustments for any poor calibration or voltage drop even with much smaller errors than you are reporting.
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Old 12-01-2020, 10:32   #8
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Re: My float voltage is too high despite correct settings.

Had this same issue when we bought our boat with Mastervolt chargers and Lifeline AGMs.

What are your "Battery Type" dip switch settings on the Mastervolt charger set to? Dip switches should not be set for "AGM" if you are manually setting float to 13.3V. Per Mastervolt Tech Support: for 12V, the "AGM/Gel" setting just adds 0.55V in float. Since float voltage is already programmed manually at 13.3V (+/- with temp compensation), the dip switch setting will add and overcharge your batteries during float. The extra .55V would give you the 13.8V you're seeing.

If you have the means to customize all the settings on the charger (i.e. USB interface, MasterAdjust software, etc), best would be to set the battery type dip switches to "Standard" and manually configure all the parameters to Lifeline specs. If not, you could stick with the AGM setting but drop the float voltage 0.55V.

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Old 12-01-2020, 12:40   #9
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Re: My float voltage is too high despite correct settings.

Noelex is right about meter accuracy or lack thereof. Most meters specify accuracy as a percentage of the full-scale voltage. With most digital meters, you’re measuring 12v using a 20v scale. So, a meter that is specified as "accurate to +/- 1%" can vary +/- 0.2 volt from the true voltage. To that inaccuracy, digital meters can vary at least one number in the low-order digit. So a good meter, like my Fluke 177 will specify the accuracy as "+/- 0.09% +2" counts.

So, with an actual voltage of 13.50 volts, the voltage reading might be anywhere between 13.50 +/- 0.018 or 13.518 to 13.482. Since the meter only displays to two decimal digits, you’ll see a voltage displayed between 13.48 and 13.52.
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Old 13-01-2020, 18:23   #10
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Re: My float voltage is too high despite correct settings.

Do you have access to a calibrated meter?

It will have the calibration stick attached

I have several at work, but since my battery voltage is usually within .3 -.5 volts of my Float setting, I really don't worry about it

My voltage at Float now is exactly at 13.8 (which is the Victron default) but in Summer it's usually closer to 13.5 or so

Most probably a temperature thing.

One day I'll take a calibrated meter onboard and get the real voltage
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Old 14-01-2020, 12:26   #11
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Re: My float voltage is too high despite correct settings.

I got my problem sorted so thought I’d let everyone know and for anyone else with the same problem. Chris hit the nail on the head. My Mastervolt charger was set to AGM charging via the dip switches. I returned them to the factory default settings and it brought the float voltage back to 13.3 where it should be. Thanks for everyone’s help.
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Old 14-01-2020, 12:32   #12
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Re: My float voltage is too high despite correct settings.

Congrats, forum hive mind at its best!
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Old 15-01-2020, 20:55   #13
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Re: My float voltage is too high despite correct settings.

Glad to hear that worked for you and you got it sorted!
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