Battery drain

F

Fishpants

Active member
Joined
Jun 27, 2015
Messages
28
Fluid Motion Model
C-30 S
Vessel Name
Doug
Hi all,

I’ve struggled a bit to fully understand battery specs, and am not sure if my house bank is draining faster than it should. My batteries (AGM) are only about 3 years old, and the boat doesn’t get heavy use. It stays plugged into charger year-round. I have had the house bank fully drained once due to service guys leaving house on and not plugging charger in. Other than that, I’ve been pretty cautious about keeping them up. Rarely would I let them get below about 12.5V- 12.6V.

This week we’ve been up in the Broughtons, and while we’ve been careful, I do have concerns. For example, after motoring for about 5 hours, and arriving to our anchorage with a full charge around 6pm, this morning they’re at 12.58V, which if I’m correct, is a bit under 75%. But to lose 25% overnight seems a bit much. Other than careful use of lights, (which I assume aren’t a large draw anyway) the biggest draw would be the galley and cockpit fridges. We turned both down to around 3 to keep them just cold enough. I didn’t even have an anchor light on, as I felt the spot we were in was low-risk for traffic.

The weather has been spotty, so solar will contribute on some days, but even that doesn’t seem to help much. We just spent less than 2 days at anchor, but had to get going in the morning to charge batteries, as they had already dropped way below where I had planned, at around 12.2V.

Should I be concerned, or does this sound normal? Thanks in advance for any input.

-David
 
David,
According to the table I have been using below, 12.58 volts is 90% capacity, not 75%. So maybe not as bad as you think.

Percentage of Charge.
12 Volt Battery Voltage

100. 12.70
95. 12.64
90. 12.58
85. 12.52
80. 12.46
75. 12.40
*********************
70. 12.36
65. 12.32
60. 12.28
55. 12.24
50. 12.20
45. 12.16
40. 12.12
35. 12.08
30. 12.04
25. 12.00
20. 11.98
15. 11.96
10. 11.94
5. 11.92
Discharged. 11.90

Are all lights on boat (cabin, cockpit, navigation and v-berth) LEDs? That will make a significant difference in your power consumption.
With our 180 watt solar panel, MPPT controller, 4 house batteries, all LED lights, never using inverter and being miserly with consumption we can go 4 days easily -even on cloudy days.
 
David, from my experience I feel what you’ve described seems about normal. I’m guessing you have the Northwest Package and therefore no generator? If that’s the case you should run your engine for an hour or so to charge the batteries back. We have a generator on Kismet. Currently we’ve been on the hook for 2 nights. This morning the batteries showed 12.5, after a few more days they may dip down to 12.3 to 12.4 by morning. In the morning I run the generator, if we’re not on the move, for an hour or so to heat the water, charge the house batteries, charge electronics etc, this gets the house batteries back to normal. I would think running the engine would do the same for you but I’d like to hear from others.

Jim F
 
This looks like normal performance. You could have some reduction in capacity due to the full drain episode but that can not be confirmed from the data you provided. When you get home you can have the batteries tested to confirm. In the mean time consider the following:

1) With 4 110AH batteries you had a total capacity of 440 AH when new. At three years old this will be less. Let’s assume however you have 400AH, 200AH of which are useable.

2) Two refrigerators will draw somewhere around 5 amps on average around the clock. That’s 120AH a day not including other draws on the battery. 2 days on the hook with no solar output will likely take you to at or below 50%.

3) The output of one Solar panel is at the very best around 50AH per day in direct sun on a long summer day. If there are even just partial clouds this can be reduced significantly and with full clouds our rain will likely be less than 10% of this.

4) The battery voltage is affected significantly by what is currently running and the solar charger. If both refrigerator compressors are actively running you may see an additional drop of at least a tenth of a volt. It is best to check you battery state before the sun comes up and when the refrigerator compressors are not running.

Given the above, 12.58V in the morning after one night on the hook is very good (as across stated close 90%). Unless of course the sun was starting to hit your panel when measured. 12.2V after nearly two days on the hook would also be normal assuming limited solar charging during the day. This reading could actually be closer to 12.3V assuming one or both refrigerator compressors were running.

When you see 12.2V its time to start your engine.

Curt
 
There was a great "As the Prop Turns" on power management and they have power usage calculators that can help determine how much power you are generating and using. Check it out - https://www.youtube.com/watch?v=Uj_am-ecSt4
 
Huge thanks to all of you who replied so quickly! I do feel a bit better based on your input. What an amazing time we live in when we can reach out for technical assistance and advice from the comfort of a secluded anchorage!
 
Curt,
Would you please clarify a point you made for me? For the refrigerator you mention that both of them use about 5 Amps per hour for each hour they are running. This is less than the RT folks used in their Power Management seminar where they used 4.5 Amps for each refrigerator. Also, RT folks said that a typical amount of run time for the refrigerator was about 4 hours per day. I assumed that this means the refrigerator is cycling on and off triggered by a thermostat of some sort. This assumption of 4 hours run time per day resulting in each refrigerator using about 20 AHrs per day.
In your calculation you have each refrigerator running continuously at 24 hours per day - each using 60 AHrs per day. How do I reconcile these different refrigerator run time assumptions?
 
Hi Al,

Each refrigerator uses 4.5amps when cycling on. I have found that ours cycle on with a 50% duty cycle, so 2.25 amps each on average. I just rounded to 5 amps for the two of them to make it simple.

If you turn your refrigerator way down and don’t open the door the duty cycle probably goes down some but I chose to focus on a typical use scenario without active conservation.

We have a refrigerator and a freezer as well as a battery monitor. We regularly see about 50AH of drain overnight so my numbers are based on that. We have two solar panels so in full sun we can keep up indefinitely. With little sun we are down after two days with two house batteries.

Curt
 
Thanks Curt!
I guess the RT folks should adjust the numbers used on that Power Management slide.
We are keeping our refrigerator on full time while in storage in the hard. After a nearly 4 week period (6/30 to 7/26 during lots of rainy and cloudy days in Burlington) the data from the VictronConnect app shows the lowest voltage reading at 12.45 volts. So the solar panel is keeping up with our draw while on the trailer without a problem. We seem to be averaging 650 Watt-Hours or about 52 Amp-Hours of charging per day during that same rainy and cloudy period.
 
To reduce unnecessary power consumption, we installed toggle switches in series with the water tank gauge and the DC volt meter. We also paralleled the DC volt meter with as cigarette lighter socket in which we keep a small digital volt meter for a more precise measurement of battery voltage.

Barry and Lynne Thompson
TOUCAN, R-27 Classic
 
scross":1nyuek83 said:
Thanks Curt!
I guess the RT folks should adjust the numbers used on that Power Management slide.
We are keeping our refrigerator on full time while in storage in the hard. After a nearly 4 week period (6/30 to 7/26 during lots of rainy and cloudy days in Burlington) the data from the VictronConnect app shows the lowest voltage reading at 12.45 volts. So the solar panel is keeping up with our draw while on the trailer without a problem. We seem to be averaging 650 Watt-Hours or about 52 Amp-Hours of charging per day during that same rainy and cloudy period.
Click to expand...

Hi al,

The power management slides and spreadsheet are correct. When Andrew uses 4 hours that was relative to the 4 hour trip up to the islands. Later he talks about Power Management at anchor and clearly states the refrigerators run on a 50% duty cycle (though the spreadsheet shows the refrigerator drawing less when running at 42 watts (3.5 amps). He then uses 12 hours for a day of run time in the spreadsheet.

Your 52AH/day fairly closely closely matches the more conservative 60AH I used per refrigerator. Note that while in storage you are not opening the refrigerator so it will use less power. Also, Your 180 watt panel and MPPT controller likely will produce about about 50% more charge than the factory (PWM controller and 140W panel) setup in the same conditions. With two extra batteries (I think?) you have a great setup!

Curt
 
There is one other factor that would affect the duty cycle power consumption.

With the boat is occupied versus in "storage" or left on a mooring. there could be a big difference.

If the boat is occupied, the windows are open and the interior would be at "room temperature". But when the boat is all buttoned up the interior can easily run up to 100+ degrees.

First, with higher interior temperatures, the heat load (rate that cabin BTU's are conducted into the fridge through the insulation) can come close to doubling. That would double the duty cycle.

Second, the heat that the refrigeration system extracts from the interior of the fridge has to be rejected to the exterior of the fridge... i.e. the cabin. If the cabin is already hot, that rejection temperature (and pressure) has to be higher. This causes the compressor to work harder... more amps.

As a side note, I have never verified where the rejected heat ends up but as far as I can tell it is in the space behind it and the cabinets. Not to put too fine a point on it, opening the cabinet doors and ventilating that space could help.

Lots of nerdy tests that I'd like to run, but driving the boat around is too much fun.
 
Everyone that owns a Ranger Tug needs to invest in a Victron BMV-712 Battery Monitor for around $200.00
This will give very accurate readings on usage and SOC (current State Of Charge) and help you understand power management much better. You can actually see exact power draw when the Frig cycles on and off. No more guessing. Also consider switch battery bank out to Battle Born Lithium batteries. Expensive but well worth it. One major pulse is that you have use of 100% of the battery before recharging, not 50% like AGMs. Also half the weight.
 
two weekends in a row. with just the fridge and anchor light on overnight. Im at 88% SOC by the morning. (according to my balmar smart guage) voltage is impossible to use unless you can turn off all draws and let the batteries settle. If the fridge is running at the time you read the volts, the voltage displayed will be lower than the actually SOC is, as the fridge draw is dragging down the volts on the battery.

the fridge basically draws 2.5Ah. so 10 hours is 25A out of a capacity of 100Amp (assuming no less than 50% SOC on a 200AMp Battery pair) which suggests Im doing better than 2.5Ah and around 1.2Ah on the fridge.

Since upgrading the solar panel to a 340W and an MPPT controller. within 3 hours of sunrise SOC is starting to creep back to 100%.
 
Thanks Curt!
The original owner put in the two additional house batteries. Don’t know how we could do our cruises without the four house batteries.
Even with four house batteries, last summer in Desolation Sound we ran into issues. With very short engine runs between different anchorages, the batteries were not getting a full recharge.
And after determining that the entire solar panel and solar controller install would cost less ($900) than a single lithium battery, or even three AGMs, solar seemed like the best solution. We are sticking with our flooded batteries that have been lasting 4+ years. If Our Journey had the factory solar set-up I think I would have upgraded to MPPT and a higher watt solar panel.
Will be back in the water next week for an 18 day cruise with 13 nights on the hook. Nice to be able to do that and not worry about your batteries!
 
In the “Power Management” virtual seminar, Andrew discussed the value of monitoring battery voltage from the Garmin Chartplotter. I have searched my Chartplotter (8612) menus and can’t find the right information to put on a customized screen. Under “Edit Overlays” “Data” “Power” there are the choices “DC Current”, “DC State of Charge”, “DC Time Remaining” and “DC Voltage”. “DC State of Charge” and “DC Voltage” sound promising but both have no value (“—.—“) with ignition and/or engine off. Doesn’t matter if Engine battery switch is on or off. Does any one know where to look within Garmin menus to find appropriate data to view (presumably voltage?) to monitor House and Engine battery status?

I appreciate that a battery monitor (like Victron BMV-712) is a better answer and I am looking into how best to install in my 2020 R29S.
 
You must log in or register to reply here.

  • Tugnuts.com is the community hub for Ranger Tug, Cutwater, and Solara owners. Since its inception in 2008, the Tugnuts forum has grown into an active and thriving community of more than 9,000 members. It serves as both a meeting place for the best boating community online, and an invaluable archive of information.

  • User menu
Back
Top