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Old 12-08-2016, 18:30   #16
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Re: Battery @ 11.75v under sustained 8 amp load

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Originally Posted by 0urh View Post
So does this mean you have drunk all your beer by 6pm?
It either stays cold or i am too drunk too notice
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Old 12-08-2016, 18:42   #17
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Re: Battery @ 11.75v under sustained 8 amp load

You've been off-grid for a month. When's the last time you were really fully charged? May be that you are starting from a low charge state to begin with.
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Old 12-08-2016, 19:22   #18
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Re: Battery @ 11.75v under sustained 8 amp load

Yes, 8 amps is a lot -- maybe too much for our bank. Our old fridge is struggling. The cooler is not really well insulated. What can I say -- it's an old boat. It's been damn hot these last few weeks here on the lower Great Lakes. All this has exacerbated the problem.

My solar/wind charging system seems to bring the batteries back most days. I gage that by when my controller goes into cutoff/float mode. I can see the battery voltage rise slowly at first, then finish quickly with victron showing 20 amp-hr down (going to zero). Charge controller has a simple voltage cut off, which is now set to 15v. This allows the batteries to see a voltage of 14.5 (not 15.5 that I miss-typed earleier).

I'm on shore power for the next 36 hrs. Hopefully I can isolate the batteries to get stable voltage measures.

Robert, how big is your bank? I just wonder if I'm expecting too much from ours (which, although rated at 360 amp-hr, is probably less).

Mark, good idea with the timer. On hot nights I've turned the fridge off (after drinkin' time is over). This works fine, but maybe I just need more batteries ... or need to learn how to enjoy warm beer.


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Old 12-08-2016, 20:32   #19
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Re: Battery @ 11.75v under sustained 8 amp load

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Yes, 8 amps is a lot -- maybe too much for our bank. Our old fridge is struggling. The cooler is not really well insulated. What can I say -- it's an old boat. It's been damn hot these last few weeks here on the lower Great Lakes. All this has exacerbated the problem.

My solar/wind charging system seems to bring the batteries back most days. I gage that by when my controller goes into cutoff/float mode. I can see the battery voltage rise slowly at first, then finish quickly with victron showing 20 amp-hr down (going to zero). Charge controller has a simple voltage cut off, which is now set to 15v. This allows the batteries to see a voltage of 14.5 (not 15.5 that I miss-typed earleier).

I'm on shore power for the next 36 hrs. Hopefully I can isolate the batteries to get stable voltage measures.

Robert, how big is your bank? I just wonder if I'm expecting too much from ours (which, although rated at 360 amp-hr, is probably less).

Mark, good idea with the timer. On hot nights I've turned the fridge off (after drinkin' time is over). This works fine, but maybe I just need more batteries ... or need to learn how to enjoy warm beer.


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Mike our bank is not large, 420 amp hours in total BUT its a rare night that we ever use much more than 60 amp hours (Fridge and CPAP machine). By noon we have recovered most of the nights usage as well as kept up with the days use BUT batteries take a long time to get the last 10% charge into the batteries so its usually around 2 or 3 oclock before the controller starts to float the batteries at 13.4V. Its around then that we will start up the watermaker for an hour or two. I can tell you that even when crossing oceans with full time autopilot and fridge etc. and cloudy days I have never seen our batteries less than 12.4 volts. By the way we equalize the batteries monthly.
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Old 13-08-2016, 03:20   #20
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Re: Battery @ 11.75v under sustained 8 amp load

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Mike our bank is not large, 420 amp hours in total BUT its a rare night that we ever use much more than 60 amp hours (Fridge and CPAP machine). By noon we have recovered most of the nights usage as well as kept up with the days use BUT batteries take a long time to get the last 10% charge into the batteries so its usually around 2 or 3 oclock before the controller starts to float the batteries at 13.4V. Its around then that we will start up the watermaker for an hour or two. I can tell you that even when crossing oceans with full time autopilot and fridge etc. and cloudy days I have never seen our batteries less than 12.4 volts. By the way we equalize the batteries monthly.


Thanks Robert. I'm getting the picture that my charging has been inadequate due to a poor controller, and that I just may need more capacity -- or perhaps a new fridge.

Thanks to everyone for the assist.


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Old 13-08-2016, 05:43   #21
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Re: Battery @ 11.75v under sustained 8 amp load

Hi Mike, my bank is only 242amp/hr. Now I realize amp counters aren't that accurate but if in down 60amps over night I'm still around the 12.2-12-3v in the morning.

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Old 13-08-2016, 06:01   #22
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Re: Battery @ 11.75v under sustained 8 amp load

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Hi Mike, my bank is only 242amp/hr. Now I realize amp counters aren't that accurate but if in down 60amps over night I'm still around the 12.2-12-3v in the morning.

Sent from my vivo Y35 using Cruisers Sailing Forum mobile app

Thanks Dale. I'm certainly getting the sense I have a problem. Is your morning measure done under load? If so, under what load?

Under my 8 amp load my batteries fall below 11.9, but if I take the load off they immediately rise to near 12, and if I let the sit for say 15 minutes they're up to 12.1 - 12.2.


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Old 13-08-2016, 06:28   #23
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Re: Battery @ 11.75v under sustained 8 amp load

Hi Mike, they never get below 12.1v load or no load.

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Old 13-08-2016, 07:06   #24
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Re: Battery @ 11.75v under sustained 8 amp load

Mike I think it's your controller, you need something more sophisticated.
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Old 13-08-2016, 07:29   #25
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Re: Battery @ 11.75v under sustained 8 amp load

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Mike I think it's your controller, you need something more sophisticated.
I think you're right. I have a very simple controller which came with my windmill. Claimed to manage up to 500 watts of solar as well, which I thought great. But manages it like the windmill; on/off. I guess I gotta spend some more boat bucks to get a proper controller.
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Old 13-08-2016, 07:47   #26
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Re: Battery @ 11.75v under sustained 8 amp load

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I think you're right. I have a very simple controller which came with my windmill. Claimed to manage up to 500 watts of solar as well, which I thought great. But manages it like the windmill; on/off. I guess I gotta spend some more boat bucks to get a proper controller.
We use a Morningstar controller, works great but not the cheap seats.
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Old 13-08-2016, 09:46   #27
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Re: Battery @ 11.75v under sustained 8 amp load

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We use a Morningstar controller, works great but not the cheap seats.
That's OK. I'm frugal, not cheap . I don't mind spending big bucks on quality that will last or make my life better.

Which Morningstar do you have? I see there are multiple models.
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Old 13-08-2016, 16:24   #28
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Re: Battery @ 11.75v under sustained 8 amp load

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My basic question is: is this ok, or do I have a problem?

I have recently installed three new deep cycle Group 31 batteries maintenance-free, each claiming 120 amp-hr capacity. Single bank, so 360 amp-hr capacity. This is matched with solar/wind charger system that is rated at 400 watts each (800 total).

In the evening I can start with a fully charged bank (according to my Victron meter), but after ~ 8 to 10 hrs I'm measuring 11.75 volts while under 8 amp load. Lighten the load to 1 amp and the voltage rises to 11.9v fairly quickly, and might get up to 12v after a few minutes.

I understand that I need to look at the batteries at rest (fully charged, then no load/charge for hours), but we're out cruising right now, and that is a PITA to do.

All the readings I can find talks about at rest voltage measures. I'm hoping the gurus here can tell me if I have a problem, or should just enjoy my cold beer.


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A constant 8 A load is quite high (200 Ahrs / day).

However, we just completed a 3 week trip in the 1000 islands and it was so hot our fridge compressor ran almost continuous. (4 year old Nova Cool ice box conversion.)

That being said, with a fully charged 340 Ahr flooded wet cell bank, by the next morning we would read 12.5 volts. We would charge via solar and alternator to read 12.6 Vdc by about 8 pm. By the next morning we would read 12.3 Vdc (Compressor running for all measurements.)

If your batteries are good, I suspect you are not fully charged when your Victron meter indicates you are.
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Old 13-08-2016, 16:42   #29
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Re: Battery @ 11.75v under sustained 8 amp load

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That's OK. I'm frugal, not cheap . I don't mind spending big bucks on quality that will last or make my life better.

Which Morningstar do you have? I see there are multiple models.
You will need at least a 40A controller for your 400W array a 30A would be cutting it too close. The Morningstar TriStar 45 MPPT is a very, very good controller, dedicated volt sensing, remote temp, beefy terminals and programming options that cover everything you'd want, and then some. They also make a PWM version of that same controller for less money. On the budget end of things a Victron 100/50 would be another good option.
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Old 13-08-2016, 18:55   #30
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Re: Battery @ 11.75v under sustained 8 amp load

This link was posted a few times previous. It tells how your Victron meter will inadvertantly tell you tall tales, and how to get it more in line with reality.

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com
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