House Bank health

[it4llc]

I've been wondering how healthy our house bank is. We have not spent tons of time on the anchor, but a few of the times, when reading the unit voltage on the chartplotter, it is down to 12.2, which I understand is ~50% discharge. However, we were only anchored for at most 3-4 hours. A couple of those times, we started with a warm fridge, so I wondered if that could be draining the batteries. I also started turning off the chartplotter to conserve. This past weekend, starting with a full bank (according to the solar charger panel) we went out and anchored for a little less than an hour. We started with a nice cold fridge before we unplugged from shore power. While anchored, we had on the chartplotter, VHF, fridge, wine cooler (which also started cold), stereo, and used the fresh water wash for maybe 5-10 minutes. We had medium sun out, so the solar would have been putting a little into the bank. Using the battery usage calculate spreadsheet from FM, my rough math is that we would have used about 22 amp hrs, or about 10% of our bank, which would correlate to ~12.55 volts. However, the unit voltage on the chartplotter was showing 12.2.

So my question is whether the unit voltage gauge on the chartplotter can be relied on? Should I get the batteries tested? (We got our boat new in Nov 2020 so the batteries should have some life left, unless they got run down too far at some point.). Any advice or tips would be appreciated.

 

[CruisingElvinRay]

First thing to do is install a Victron BMV 712 battery monitor. It will give you the information you are looking for. It’s hard to tell what’s going on with just the voltage.

The analogy I saw earlier: if a voltage monitor is a compass , a battery monitor is a GPS.

Sent from my iPad using Tapatalk

 

[it4llc]

First thing to do is install a Victron BMV 712 battery monitor.

Thanks - I've got the BMV-712 sitting in a box next to me. I've been debating whether to try the install myself or get it done professionally. Boat electrical is still somewhat new to me (in case my post didn't make that obvious) - I'm fine on a house but the wiring is a little more straight forward there. I watched your video and Submariner's and understand at a high level (thanks for taking the time to make and post it). I do have a few questions if I am going to do the install though:

1 - what gauge wire to use since I think I'll need at least one new wire to connect the bus bar to the battery - Is #2 wire big enough?
2 - what size bus bar do I need? Is a 150A bus bar sufficient?
3 - from your video, it looks like you just connected to one battery from a 2 battery house bank. The BMV-712 instructions show connecting to both batteries in the house bank to measure the mid-point. What's the advantage/disadvantage of these 2 options?

 

[Red Raven]

Before installing a battery monitor you can confirm the house battery voltage with several methods. First, there may be an analog (needle) gauge on your 12V panel with a switch to select the battery bank. The house should be battery #1 on the switch. If no gauge the solar panel remoter display should be able to display the house voltage on battery #1. You can also use a multimeter measuring directly on the house bank. If these alternative measures match the chart plotter unit voltage then you can rule out a poor reading for the unit voltage. You can also confirm the current draw with a DC clamp meter to see if it matches your assumptions.

A question I would have is why are you leaving the chart plotter and other systems on? They aren’t likely to be the cause of such a quick voltage drop but a general rule of thumb would be to shut off all non-essential systems when at anchor. Also if your propane solenoid is on that could be part of the issue. If you shut off all non-essential systems (e.g., all except fridge, stereo, and lights)and you still see 12.2 volts after 4 hours after full charge the batteries should be load tested and potentially replaced.

Curt

 

[it4llc]

Thanks Curt - good suggestions. I’ll use my meter to test as you suggest. I do usually turn off most equipment now, but knowing we weren’t going to stay long, and wanting to use the plotter to make sure we weren’t dragging, I kept most everything on.

 

[knotflying]

I would go along with some of the suggestions that Curt made. However, if you are concerned about battery condition a load test should be done. You can buy a load tester fairly inexpensively or take the batteries out and bring them to Advance auto or usually any auto supplier for the test. They should be fully charged and rested for about 30 minutes before doing the test. I personally like to keep things simple and have never installed a battery monitor. Yes, it will tell you a multitude of things, but power management and interpolating voltage to SOC have always worked for me. You know what your amp hour capacity is of your batteries and you should know what each item you use on the boat consumes and then do the math. As curt said, leaving the chartplotter on while anchored is a big draw. If you are worried about anchor drag use an app on your phone. I also know my historical data based on usage. When I wake up in the morning before sunrise (early riser) My house bank is usually at 12.4 volts. If I start to lose more than that and have not changed what I typically use then I either have a parasitic draw or my batteries are starting to lose capacity. For a parasitic draw search I will then use a clamp amp meter.

 

[Submariner]

The easiest way to test the house batteries is to run them. Sit at the dock, fully charge your batteries. Disconnect from shore power and run a handful of things. The refrigerator, the radio, the chart plotter. If you had a battery monitor installed it'll keep track of how many amp-hours are consumed. I did this to my boat and got to -8amps-hours consumed and hit 10.01 volts at 97% state of charge. Full charge to empty in 8 amp-hours. That's a bad battery. I repeated the test for the second battery and got the same result. It was exactly 30 minutes of run time on each battery. My batteries were toast. They both did pass a battery tester, by the way. Battery testers test cold cranking amps needed for starting the engine, not deep cycle. The only way I know of to test a deep cycle battery is by using them and seeing how long they can go.

 

[it4llc]

Thanks to all for the feedback. I've got a good excuse to go spend a day hanging out, I mean working from home 😀 , on the boat now to test the batteries... So far we've only overnighted at marinas on shore power, but are looking forward to some nights on the hook once I can get comfortable with our battery management.

 

[Submariner]

1 - what gauge wire to use since I think I'll need at least one new wire to connect the bus bar to the battery - Is #2 wire big enough?
2 - what size bus bar do I need? Is a 150A bus bar sufficient?
3 - from your video, it looks like you just connected to one battery from a 2 battery house bank. The BMV-712 instructions show connecting to both batteries in the house bank to measure the mid-point. What's the advantage/disadvantage of these 2 options?

1) Use the same size wire size as your current negative battery jumpers (yellow cables).
2) The R27-OB came with a 175 amp fuse for the house bank. I put in a 250amp bus bar for the negative side.
3) The mid-point monitoring is not relevant for batteries in parallel.