Battery Voltage versus Amps

[tdellaviola]

Hello all,
I realize a lot of topics on the forum has info related to batteries, but I could not find exact fit, so I thought I would ask the group. I have a battery question. I changed out my 6 batteries on my 2014 C30 last year, but am having challenges with the house bank. I thought I had a parasitic draw, so based on the early online events put on by Ranger I purchased a Victron battery monitor. From what I can tell no parasitic draw. So the issue: Batteries are fully charged after traveling to a destination, Volts at 12.7 soon after engine is turned off, sit on anchor for 18hours, consume about 14amps. 4 Batteries combined (according to manufacture have 260 amp hours), so after the 18hours on the hook my Victron indicates I have 95% capacity still to go. But voltage has significantly dropped to 11.8 volts, which from my understanding means almost dead battery.
So with using so little amps, but having voltage drop by so much, does that mean my 1 year old house batteries are shot?

 

[BB marine]

If you have full capacity batteries 110 ah each 440 ah capacity using 50% 220ah of the battery capacity would put the batteries at 12.2 V . 18 hours on the hook drawing 14 amps per hour =252 ah which would put your batteries at 60% discharge which would be approximately 12.0V. 11.9 V would be considered 100% discharge. I would say your batteries are doing what they are supposed to do. If you discharge them that much all the time they will not do that for a long time. It is not a good Idea to let them fall below 12.2 if they are AGM batteries

 

[tdellaviola]

woops, was not clear . My total amp hours are 260 (batteries are approx. 65ah each) for the house bank. The 14 amps used over the 18hours was total amps, not 14amps per hour). All I was running was the fridge, radio and 30 minutes of lights in the evening.

 

[SassyRed]

I am not trying to be picky here, and I'm not trying to correct your terminology for the sake of correcting you. I am only trying to get us all talking the same way. An amp is a measure of how much instantaneous current is flowing in a wire. Amp hours are how much total current has flowed over a given time. So when you say you have consumed 14 amps, it is confusing. Did you consume a maximum instantaneous of 14 amps at some time, or did you consume a total of 14 amp hours?

Example of why this is could be a bit confusing:
A Nova Kool refrigerator should consume something like 4 or 5 amps when running. If it has say a 50% duty cycle, it averages 2.5 amps over 18 hours, which means it consumes 45 amp hours. These numbers are my guesses/approximations, not necessarily real.

A radio might consume another 2.5 amps times say 10 hours- or another 25 amp hours.

So with the above, you would have consumed 70 amp hours of your battery capacity.

None of that necessarily explains why you are draining your batteries, but there are only a few possibilities:
1) the batteries are not getting fully charged
2) you are running the batteries down. Your battery monitor should be able to read total amp hours consumed, and if hooked up close to the battery, should be able to tell you total usage in amp hours out of the battery. You could also hook up a clamp-on meter to verify for sure you don't have anything you don't know about generating load. Lights, flushing toilet, fresh water pump, navigation mfd's, bilge pumps, partial short to ground somewhere or to a seawater-connected fitting, anything else?
3) batteries aren't holding a charge.

Good luck with looking into this.

If you knew all this, I apologize. I wasn't lecturing, I was trying to better understand your issue.

 

[Red Raven]

woops, was not clear . My total amp hours are 260 (batteries are approx. 65ah each) for the house bank. The 14 amps used over the 18hours was total amps, not 14amps per hour). All I was running was the fridge, radio and 30 minutes of lights in the evening.

Something is not right here. First, there is no such thing as Amps per hour or even total Amps. Amperes, or amps, or just A, is an instantaneous measurement of current (think a flow, like GPH). You will be drawing X number of amps at any given moment. Amp Hours (AH) is an energy (think capacity) measurement (amps x hours). So, if you draw an average of 0.78A over 18 hours you will have used 14AH.

However, only 14AH consumed over 18 hours is highly unlikely with a refrigerator running. The typical refrigerators on the Fluid Motion boats average around 2 to 2.5A and would use 36 to 45AH over 18 hours. More likely, you are talking daylight hours when the solar panel was contributing charge to the batteries. 14AH may in fact be the net amp hours used after adding in what the solar panel added back in to the batteries.

As to why your battery voltage is so low when the state of charge on the Victron disagrees it could be several things. The voltage, current, or energy readings could be wrong or misunderstood, the Victron could be installed or programmed incorrectly, or your batteries may be shot.

It would be good idea to use a Clamp Style multimeter that can measure DC current to confirm the currents the Victron is reporting and confirm the voltages as well from an alternate source.

Edit. Just saw this is essentially a repeat of Sassy Red’s post!

Curt

 

[knotflying]

A couple of things. I personally like the simple method, interpolate voltage to state of charge. Using two different measurement mediums will almost always give different readings and then which one do you believe. In this instance I would say the voltmeter does not lie. It is my understanding that the Victron has to be calibrated and it self adjusts over time before it is accurate. Also, what one thinks they are consuming in power over time is many times underestimated. Over time I know what to expect when I get up in the morning and look at my voltmeter after 15 hours on the hook. I have two house batteries and the thruster joined. After 15 hours I will have 12.37 to 12.45 volts. This does not necessarily answer your question, but sit down and accurately estimate how many amps you are consuming as a first step. or as curt suggested throw on a amp meter while all your equipment is powered up and see what you get and then do the math.

 

[Levitation]

https://pveducation.com/solar-concepts/ ... y-voltage/

A picture is worth 10,000 words :mrgreen:

 

[Levitation]

And specific gravity IS the bottom line on state of charge

EZRED SP101 Battery Hydrometer - on Amazon

 

[BB marine]

woops, was not clear . My total amp hours are 260 (batteries are approx. 65ah each) for the house bank. The 14 amps used over the 18hours was total amps, not 14amps per hour). All I was running was the fridge, radio and 30 minutes of lights in the evening.

As Curt stated there is not a true measurement of APH (amps per hour) but in using that statement it helps to understand Amp hr capacity. The terminology is not correct but the theory is easier to understand (Amp x Hours) It is an equation not a electrical measurement.

The first comment I would make as to your low voltage at the end of 18 hours on the hook is you installed the wrong house batteries. If you want to anchor for 18 hrs and expect to maintain 50 % battery capacity at the end of your stay. Batteries rated capacity of 65 AH are either small light duty dual purpose or group 27 or 31 high amp cranking batteries. Neither would be the batteries that should be installed as house banks in boat with all 12V accessories in a 30 Cutwater. A battery if group 27 or 31 with high cranking amp capacity would be a good engine battery. I will go back to my original post. The measured capacity 65 AH of your batteries is the batteries rated total capacity. This is a new fully charged battery rating. If the batteries installed have been discharged repeatedly below 50% (12.2 V) there is a possibility there is damage to the batteries or a battery. Dropping a battery 50% or lower can cause sulfating. To prevent sulfating a battery must be charged enough to prevent it from dropping below 12.4 volts. 2 effects or sulfation is longer charge times and shorter running times between charges. If you use Sassy Red's numbers which I believe are conservative numbers but realistic. 70 ah used of the capacity of 260 ah that is only 30 % the bank should be reading around 12.4 V. if the batteries were fully charged.

Things that use current during a 18 hour anchorage

Anchor light
Head when flushed
water pump when using fresh water
radio
refrigerator
bilge pump
shower sump
Chart plotter

All of these items are used for limited time but can add up.

Before you anchored was the house bank charged to full capacity 14.2 to 14.4 V The only time my house batteries ever see a full charge is when charged on shore power when 12 Volt requirements are limited or when cruising for several hours after an anchorage. When we are cruising we are using several devises on board that require 12V power to run. The helm- auto pilot, chart plotter, a couple 12V fans, refrigerator ,VHF, radio, inverter, fresh water pump, head, I have engine compartment exhaust blowers running when the engine is running. All of this is being drawn from all battery banks along with the engines demands for 12V power and the occasional thruster. Remember when you are running and charging all batteries, house, engine and thruster are one battery bank. The battery banks are not charged separately once the requirements of the ACR are met. The Voltmeter should read 14.2 to 14.4 V for all batteries to be 100% charged

If you question the battery condition of your 1 year old batteries start there. Fully charge the batteries, let them rest until they stabilize at the fully charged condition. Test the batteries individually. look for a battery that possibly is damaged. One bad battery in a bank will be a draw on the rest of them. That could be your culprit.

What batteries are installed in the boat? Brand, type, model ?

 

[tdellaviola]

Thank you very much for you insights. I apologize for the poor wording related to Amps, still learning. I believe the vitron battery monitor is doing the reading correctly. The batteries were fully charged as I traveled 4 hours to the anchorage. And yes much of the time was during the day when I would be getting help from the sun, plus we were good about keeping the fridge door closed. I checked Amp draw randomly during the day and it was usually net 0.4 to 0.6 A. Based on some of you feedback, I think I purchased the wrong batteries for house. PLUS I messed up on getting all the same as I assumed 2 house batteries not 4. I consistently drop below 12 Volts so likely damaged them?
I have 2 Optima D34M (55Ah) and 2 Optima D31M (75Ah) for a total 260Ah.

 

[Red Raven]

Yes, the wrong batteries for this application. However, even with only 130Ah of useable capacity with only one refrigerator running you should be able to get through the the night. Also, your Victron should not be indicating 95% state of charge if it is calibrated right and the batteries are in passable condition.

Regarding the batteries: Check what the current draw is when the sun is down. During the day you could be getting up to 10 amps from the solar panel and thus your net draw of .4 to .6 A could mean your draw overnight could actually be as high as 10amps if you have other items running. 10 hours at that draw is 100AH so this could easily explain your low voltage in the morning especially if the batteries are no longer able to deliver full capacity. Also, you may not be getting a full charge after a short run. 12.7 volts could be more like 80% state of charge as it takes a while for the voltage to settle.

Regarding the battery monitor: Check that it has been set up with the correct AH’s available as well as any other calibration parameters. If the net AH used over 18 hours really was 14 AH then the 95% state of charge would be accurate for a brand new battery in perfect condition. Volts should then be near 12.7volts. If the calibration checks out such that the net AH’s are correct then the batteries are likely shot. You’ll want to get 4 new 110 AH batteries anyway to make your setup usable for multi day cruising so at this point consider the old batteries the cost of education. 😀

Curt

 

[scross]

Completely agree with Brian and Curt.
But power management is not just about battery capacity. In addition to increasing your battery AmpHr capacity, also think about cutting power consumption and increasing your solar charging capability.
Consumption: Make sure ALL lights on your boat are LEDs. The non-LED anchor light is a big power suck. If your stereo has an amplifier see if there’s a way to turn the amp off when on the hook. Try not to use the inverter at all while on the hook or if you must, keep its use to an absolute minimum.
Solar: MPPT Controllers in general are more efficient than the older PWM controllers. Consider replacing that obsolete 140 Watt solar panel with a new 180-210 Watt panel. And/or add a second panel if possible.

 

[tdellaviola]

Just wanted to thank everyone for the responses, probably some expensive education here.....