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Battery management worries

2333 Views 6 Replies 4 Participants Last post by  Goldfinger
Sorry for the long post but I 've had a few electrical things change on my 33ft sloop and need some reassurance that all is okay or advice on how to move forward… so hence the detail here.

I have a house bank (Main) with 2 identical 110Ah sealed batteries and a start (Aux) 70 Ah AGM battery, all 4 years old. The boat lives on a swing mooring and gets a trickle charge from a 75 watt solar panel, almost never shore power. All this is monitored by an Enerdrive ePro battery monitor.

About 5 months ago, after a couple of difficult starts, a marine electrician diagnosed a faulty Voltage Sensing Relay and replaced it which seemed to fix the problem. (He tested the start battery and found it healthy.)

BUT the new VSR seems to work differently, or at least causes the battery monitor to deliver different information than before. So I am worried… should I be?

Concern 1:

As a default, the new VSR switches the Main and Aux banks together in parallel. This delivers an identical voltage from each bank (the average of all 3?) to the battery manager. Usually 13+V. If the voltage drops to 12.7 under load then, as designed, the relay isolates the start battery to protect it from further discharge.

Previously the battery manger always showed different voltages between the two banks at any time, never identical.

Is having different types of batteries in parallel most of the time, damaging to either or all of them?

Concern 2:

Shortly after the new VSR was installed, I saw .4 amps going into the Main bank when there was nothing generating power (no engine; night, so solar panel inactive) indeed we were drawing down power for lights. So can only assume this was coming from the Aux bank in some sort of equalisation. I haven't observed this recently, but is this normal or to be expected?

Concern 3:

Previously the battery manager almost always showed "Full" when I returned to the boat after a week of Australian sun shining on the solar panel. Now it is almost never "Full" but shows say 99.5% + or -, sometimes 100% (the step before it shows "Full") after the engine has been running.

The new VSR does burn a LED when actively switching both banks together (which is most of the time). But would this be enough to explain the change?

Concern 4:

The fridge operation has changed.

The fridge is 240V and runs off the house bank via an inverter, according to the battery manager it pulls 30+ amps. Not ideal but that's what I've got. I only run it if we are going out overnight. Almost as soon as the fridge is started the voltage drops and the VSR disconnects the two banks which isn't surprising. To run the fridge up to cold drains the Main bank to about 85% capacity. BUT with the bank at this capacity, the inverter won't run the compressor again when the thermostat triggers it, showing a "high amp" fault when it tries. I have to run the engine to get it going again.

The Main bank used to run the fridge compressor as low as 60% capacity ( I never let capacity fall below this). Perhaps this is just the batteries getting old but it is the timing that worries me. i.e. coincident with the new VSR.

A Final question:

The battery manager is calibrated to expect the Main bank to have 220 Ah but with the Aux almost always switched in parallel, should I be recalibrating the Main to include the start/Aux battery i.e.290Ah?
Any thoughts? I only know the basics of 12v systems, so feel free to answer a question I don't know enough to ask myself.

Thanks in advance.
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What VSR and what battery monitor?

In addition to MS's programming link, a longer description of programming:

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.
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