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Old 11-18-2014, 06:37 PM   #21
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Brian,
I have a 25w panel serving just the genset battery(6D/150ah) via a regulator. Probably more panel than needed. I`m sure it extended the life of the previous battery.
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Old 11-18-2014, 08:37 PM   #22
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Originally Posted by Aquabelle View Post
I think on my set-up, this is 12.0V....but that point is programmable by you. I would have thought 10.5V is much too low...there is something clearly wrong with the battery bank if inverter loads draw the V down to that level and you want to cut out well before that.
Under no-load conditions, I would agree with you Aquabelle, but we're talking about the inverter placing a load on the house bank and the voltage reading under load, understanding that this load reading is different than that which would normally be read 12-24 hrs later after rest. 10.5V under load on healthy batteries could easily read 12.1-12.3V after a long period of rest without further charge.
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Old 11-18-2014, 08:58 PM   #23
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Wow... why does this have to be so complicated? Oh, well...

Ski in NC - your idea is brilliant in its simplicity. Will commence such a test at earliest opportunity! (I'll just repeat it in .5 volt steps down, and when it gets to a point that the engine won't start, I'll just add back .5 or even 1.0 volts, and set the LowBatteryCutOff voltage at that.)

Aquabelle, there is no draw on the genset's starting battery, and it's practically brand new - so maybe the trickle charger is overkill, as you suggest. We'd never go 2 months without running the genset for some reason or other, I don't think.

And the inverter is always on, because someone lives on the boat (probably a detail I should have included), and the fridge and freezer work only when the inverter is on.

Thanks, everyone, for all of your fantastic input! I'm starting to feel pretty good about the electrical setup on This Old Boat.
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Old 11-19-2014, 03:30 AM   #24
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2. We do have a SOC meter - brand new,
I just installed one last week. Haven't even taken the boat out of it's slip since and still I have no idea how I took so long to fit it.
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Old 11-19-2014, 06:12 AM   #25
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I installed an SOC meter a year ago and relied entirely on it's State of Charge reading. We anchor a lot and one morning a couple of months ago I checked the SOC reading as I usually do first thing in the morning and it read in the high 60's percent like it normally does, but unlike I normally do I check the voltage and it read 10.8 volts.

I know that a batteries SOC can only accurately be determined by checking voltage after 24 hrs no load/no charge so I knew the voltage reading was not an accurate reading of SOC but I felt something didn't seem right.

After a good charge I disconnected all the batteries from my 4 battery house bank and checked voltage after 12 hours or so. I found one of the batteries dead.

I removed the dead battery from the bank, readjusted the bank ah on the SOC meter and now watch voltage in addition to SOC. I don't let voltage get below 12.2 regardless of SOC before recharging.
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Old 11-19-2014, 08:46 AM   #26
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I installed an SOC meter a year ago and relied entirely on it's State of Charge reading. We anchor a lot and one morning a couple of months ago I checked the SOC reading as I usually do first thing in the morning and it read in the high 60's percent like it normally does, but unlike I normally do I check the voltage and it read 10.8 volts.

I know that a batteries SOC can only accurately be determined by checking voltage after 24 hrs no load/no charge so I knew the voltage reading was not an accurate reading of SOC but I felt something didn't seem right.

<snip>
My understanding from reading all the documentation for our new system is that the SOC is really just a report of the current status of the net charge/discharge since the last time the system believed the batteries were fully charged. The DC shunt tracks all of that, pretty accurately on the discharge, but only estimating the charge (due to the fact that charging is not 100% efficient, so you program in the Charging Efficiency). When certain parameters are met, it says "OK, batteries are now fully charged", and it resets the counter to 0.

How it displays the SOC is up to the unit. I think our old Xantrex did it by displaying the net charge / discharge in Amp hours since the last charge. I think our new Magnum Energy takes that a step further and converts it to a percentage of a full charge - but of course, it's up to me to tell it what a full charge is (in Amp hours, the total capacity of the battery bank).

So, if all of the above is correct, the SOC meter is really only to be believed when it's pretty close to 100% (and even that assumes you've programmed it to know when it's at 100%, with all those parameters). (Kinda like a fuel guage in a plane - the FAA says the only time it has to be accurate is when it's showing EMPTY!).

Lesson, I think, it to get to know YOUR system, as your SOC indication (net Ah, %, or whatever) is going to be specific to your boat.
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Old 11-19-2014, 09:46 AM   #27
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Yes Brian I think you're right. The meter estimates SOC by subtracting the amps used from the bank capacity the user initialized the unit with when installed.

In the case I mentioned above the fully charged state was not accurate because one of the batteries in the bank was dead, thus making the bank capacity less than what the unit was initially programed with.

I suppose the point I'm trying to make is that relying on just SOC may give you a false indication of the state of your batteries.

And again as you mentioned the bank capacity is just a guess so when initializing the meter you are in effect guessing. Garbage in Garbage out.
I don't have the SOC manual in front of me but I believe it says that the typical battery bank will loose 3% of it's capacity every year. I think with as much use as I've given my batteries (charge cycles) it's much more than 3%.
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Old 11-19-2014, 09:56 AM   #28
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'Zactly - don't rely solely on the SOC. Corroborate it with a voltage reading every time - takes an extra 3 seconds if you have a volt meter in the panel (which we do). And even then - before you're going to be in a situation in which your batteries CAN'T let you down (on the hook in the Bahamas, for example), take a specific gravity reading of every cell in every battery. (You're going to be checking the electrolyte level and topping off anyway before such a trip, so get out that hydrometer.)

At least, that's what Mr. Calder would advise.
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Old 11-19-2014, 02:23 PM   #29
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Yes, so in summary check the voltage against the SOC reading knowing that both the voltage and SOC will not give an accurate indication of the batteries true state of charge.

The SOC reading is just an estimation based on the users input of the banks capacity which will diminish over time.

The voltage reading though accurate will not indicate the batteries true state of charge until no load or charge has been applied for 24 hrs. Impracticable to determine in normal use.

So what I do is recharge my batteries when the voltage reaches 12.2 ish. According to the manufacturer my AGM's are at 50% SOC at 12.3 volts. Knowing that if my batteries are at 12.2 volts while in use, their real unloaded 24 hr voltage will be higher, I've kind of built in a safety factor.

I think we've beat this horse to death!
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Old 11-19-2014, 02:51 PM   #30
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I think we've beat this horse to death!
But you beat it with great accuracy.
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Old 11-19-2014, 03:45 PM   #31
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Whoever set up your system did a good job.


A simple solution is to not use the both position for one pair and keep it as start or backup house. That way you will know when the on line set gets low and decide then what to do. I am not a fan of paralleled batteries and would switch between banks in normal operation anyway. If one battery in a parallel bank fails it will draw down all the others and in your case all those batteries will dump current into the one failed battery boiling it among other exciting things.
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Old 11-19-2014, 04:11 PM   #32
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I am not a fan of paralleled batteries and would switch between banks in normal operation anyway. If one battery in a parallel bank fails it will draw down all the others and in your case all those batteries will dump current into the one failed battery boiling it among other exciting things.
So you're not a fan of 6V golf cart batteries wired in parallel/series to form a large house bank, I take it. Lot of folks do this and understand the meaning of battery bank voltage. When monitored, it can indicate a failed cell or battery.
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Old 11-20-2014, 08:14 AM   #33
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The big fear with a house only , no dedicated start is FLAT BATT..

Folks with an undervoltage alarm need to be aboard to start the recharge.

Leaving for a day trip , with a light on or a bilge pump stuck on can bring the house to dead in time.

The start batt for the engine solves the DEAD horror with little effort , no Sea Tow , batt cables .....
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Old 11-20-2014, 09:16 AM   #34
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I assume that this discussion is aimed at lead acid batteries, can anyone confirm if the discharge percentages etc are the same for AGM batteries? As I have just replaced my old lead acids with AGM's it would be good to know
Slightly different:
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Old 11-20-2014, 09:51 AM   #35
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I wired my last boat with 2 35watt panels, one for generator start, one for forward bow thruster. Both stand alone. Thruster batt next to thruster with no big cables strung through the boat for charging or running the thruster, just 12ga for panel charging. House and main start charged from alternator or charger. Charger powered from shore or genset. Controller shared charging for house or main.
I had some jumper cables that would reach from the main start and house to reach Genset start should it go south, and they would reach the thruster from the main/house. Never needed the jumpers. This worked good, and for peace of mind many redundancys.
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Old 11-20-2014, 02:05 PM   #36
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I assume that this discussion is aimed at lead acid batteries, can anyone confirm if the discharge percentages etc are the same for AGM batteries? As I have just replaced my old lead acids with AGM's it would be good to know
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Slightly different:

Heron, I can't quite tell what your meaning is here. Is the pic relevant to Andy's question?

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Old 11-20-2014, 02:08 PM   #37
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Heron, I can't quite tell what your meaning is here. Is the pic relevant to Andy's question?

-Chris
Yes...Shows the different % Charge numbers VS Voltages for both battery types..
I understood that is what he was asking...
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Old 11-20-2014, 02:34 PM   #38
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in series no problem. In parallel if one cell shorts you have a 10.5 V battery in parallel with a 12V battery both being charged by the alternator. I know this is common practice but that does not make it without problems. What do think happens when the one batter in a parallel set up fails?


The OPs switch set up at least allows him to switch things out.
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Old 11-20-2014, 02:38 PM   #39
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Yes...Shows the different % Charge numbers VS Voltages for both battery types..
I understood that is what he was asking...


Hmmm... I often have trouble seeing things that are right in front of me...

But all I can see is wet and gels, not AGMs...

??

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Old 11-20-2014, 02:43 PM   #40
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Fly:
What do think happens when the one batter in a parallel set up fails?
The voltage drops precipitously.
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