What's a Safe Voltage to Discharge to ?

[bazzer]

Thanks to all that replied. In fact I had the answer on my iPad all the time with the lifeline AGM manual I had saved in iBook a while ago. You can use a voltmeter if there is no load on the battery for four hours, AGM life Is dependent on how much you discharge them before recharging. There is a graph to explain this. But discharging below 12 volts would not be a good idea since this will shorten battery life, but not wipe them out.
I know this is a approximation but it should do for now.
Thanks

[djmarchand]

I think that AGM batteries can accept a deeper discharge rate than flooded cells without damage. I suspect it has to do with sulphating.

Sulphating occurs when a battery is left discharged. Lead sulphate (or some other sulfur compound) precipitates out if the battery is left uncharged. This can occur when the battery is partially discharged.

In flooded batteries this precipitate drops to the bottom and can eventually kill the battery by shorting the cells. In AGMs it stays in the electrolyte and may recombine when the battery is recharged. That is why AGMs are less vulnerable to deep discharge damage.

[hellosailor]

"rough And ready"
Then you recharge at 12.0 volts, which is 50% discharged. If your batteries go down to 11.5V that's fully discharged--no real useable power even if things still can run off it--and they will be damaged by being run down all that far.

You should also be aware that even digital voltmeters are deceptive. Most have some published accuracy figures, typically a tolerance of 1% or 1/2% on the 20VDC scale. And then they have some "float" in the rightmost digit, also known as the LSD or least significant digit. If your meter has four digits and can display 20.00 as the maximum voltage, the rightmost digit may be off by 2-4 digits due to this float. If the meter only displays three digits, 12.x or 20.x, then you've got a bigger problem because it may DISPLAY "12.0" while the real voltage is 11.5 to 12.5 due to those errors.

So you look into that as best you can, and meanwhile assume that whatever it shows for a fully charged but rested battery (i.e. 12.6 on the morning after a full charge, allowing the surface charge to dissipate) you can use about 1/2 volt below that, and then you'd want to recharge. .4 volts to be on the safe side, assuming your batteries aren't brand new to start with.

[Mark Johnson]

Originally Posted by barnakiel

What you need even more is understanding of what is going on, how to use the batteries and how to measure the battery's condition.

My observation is that many, many owners who have battery monitors onboard do not know how to calibrate, reset them, nor do they know how to interpret the readings. On the other hand, many long time cruisers will do very well with the simplest of tools.

Not to say battery monitors are useless. I think they are great. But they do need to be set up properly and then reset temporarily, which too many users tend never to do! It also takes some reading thru the manual and some exercising to get the swing of the tool.

b.

b.

Ah yes... You're talking about the complicated "Pukets Exponent"! You are right that if you don't install them correctly, connecting the wires in order, JUST like the instructions, and calibrate them to tell the little computer brain the "size" and "type" of battery bank that you have, they will not work properly.

The first time, calibrating it was a bit intimidating, but the installation was merely time consuming. (one day) When it comes time to fire it up, there is a temptation to call for help. The instruction book said that ALL of the answers were in the book, but if you need ANY help, feel free to call. HOWEVER, If after answering your question, they could show that it was in the book, there would be a $100 charge for their service! YIKES!

They were right, the answers ARE in the book, so we just figured it out. Took about an hour and a half. (It is in fact very intimidating, I admit that). There was only one other time, when we changed batteries, that we had to calibrate it. This time it took 30 minutes! This is the ONLY effort that has gone into this device in it's totally accurate and reliable 15 year life. Never a moments effort again. Since we top off the batteries every day, the meter re-zeros every day, and automatically starts the computation over again. We know to the tenth of an amp / hour, how much juice has gone out and the exact state of charge left in the house bank. We can access another function and know how much is going out at that moment, how much ANY device on the boat consumes in amps, the boat's line voltage, or the number of hours that we can run @ that moment's consumption rate.

Since we have power going in, (solar), while power is also going out (lights & stereo), it tells us what we need to know... the net amount of power going in or out. If the solar is putting out 10a, but the electrical draws are 5a, the "Link 10" will say + 5a. Push the button again and it goes from amps to amp/hours. If it says -10 ah, That's how much the batteries are down. With 5a going in, we will be topped off in two more hours of solar. Then it says "0" on amp hours, and starts to blink... batteries are full.

It has been hassle free, zero maintenance, and never needed recalibration, (except the one time), and the difficult 1.5 hour set up, is a small price to pay to know exactly what is going on with our batteries and charge devices. It allows us to properly take care of the batteries and get a 10 year + lifespan out of them.

The only other simple way to know the batteries charge, is to take the specific gravity with a hydrometer several times a day. Voltage means NOTHING unless you have no power in or out all day, you have an incredibly accurate digital readout, and their is NO line loss in the sensor wires. (never the case). Even with all of these qualifications, v mostly tells you if you are almost dead, or full. It is not accurate about the inbetween points.

This leads to over charging, under charging, or getting stuck with low batteries when you need them, and a shorter battery life.

Getting some sort of smart monitoring device is probably the most "money well spent" item on the entire boat. IMO.

Mark

[Maine Sail]

Originally Posted by Extemporaneous

Is it out of the question to get a proper battery monitor? Now that you have the rest of the good stuff.....

That's certainly what I'd do if I could.

Regards,
Extemp.

Ditto. The OP spent some good $$ on AGM's and a Victron BMV-600 is only $158.10 at Jamestown Distributors.

Terminal voltage is rather tough when cruising as most folks don't have the time to do it correctly. The generally accepted "industry" rule of thumb is to discharge the bank no more than 50%. Of course the less deep you discharge the longer life you get. AGM's also like to get back to a full 100% SOC quite often to get the most out of them..

Here's a direct quote from Lifeline:

"For maximum battery life in cycling applications, do not discharge the battery bank below 50%. Discharging the bank repeatedly to 100% will shorten the battery life. The open circuit voltages listed below correspond to the various states of charge:"

12.2 Volts on a Lifeline AGM is 50%.


They also say this:
"For maximum battery life, a battery must be recharged to 100% capacity. Recharging to less than 100% may result in premature battery failure. Lifeline batteries are not covered under warranty if they are not recharged properly. For more information, please refer to our warranty policy"



Without solar or wind getting back to 100% can be tough when charging off an alternator alone.

[S/V Illusion]

Originally Posted by bazzer

All I want to know is a rough And ready method of assessing the state of charge of my batteries without going into Phd and spending a lot of cash, preferably none. I do have voltmeters and the knowledge on how to use them.
Thanks

There isn't much to add to this except reiterate that standing voltage isn't a good way of measuring state of charge. I understand you don't want to spend money needlessly but for the price of your Ipad or phone, you could buy a decent monitor and save money in the long run by not killing your battery bank prematurely. Think value rather than simply price.

[Extemporaneous]

Assuming the OP got the answers he wanted, I have a question for Mark.

Hi Mark,
Great Post.
One thing/question. Originally and subsequently on occasion, did/do you run your bank down to empty (10.5V under its 20hr rated load) to confirm and/or reestablish your Battery banks capacity?

BTW, I also chose the Link 10 as it was the ONLY Battery monitor that both was able to tell me Watt hours, and could use a temperature sensor to properly equate things. There may be other out there now??

Cheers,
Extemp.

Originally Posted by Mark Johnson

Ah yes... You're talking about the complicated "Pukets Exponent"! You are right that if you don't install them correctly, connecting the wires in order, JUST like the instructions, and calibrate them to tell the little computer brain the "size" and "type" of battery bank that you have, they will not work properly.

The first time, calibrating it was a bit intimidating, but the installation was merely time consuming. (one day) When it comes time to fire it up, there is a temptation to call for help. The instruction book said that ALL of the answers were in the book, but if you need ANY help, feel free to call. HOWEVER, If after answering your question, they could show that it was in the book, there would be a $100 charge for their service! YIKES!

They were right, the answers ARE in the book, so we just figured it out. Took about an hour and a half. (It is in fact very intimidating, I admit that). There was only one other time, when we changed batteries, that we had to calibrate it. This time it took 30 minutes! This is the ONLY effort that has gone into this device in it's totally accurate and reliable 15 year life. Never a moments effort again. Since we top off the batteries every day, the meter re-zeros every day, and automatically starts the computation over again. We know to the tenth of an amp / hour, how much juice has gone out and the exact state of charge left in the house bank. We can access another function and know how much is going out at that moment, how much ANY device on the boat consumes in amps, the boat's line voltage, or the number of hours that we can run @ that moment's consumption rate.

Since we have power going in, (solar), while power is also going out (lights & stereo), it tells us what we need to know... the net amount of power going in or out. If the solar is putting out 10a, but the electrical draws are 5a, the "Link 10" will say + 5a. Push the button again and it goes from amps to amp/hours. If it says -10 ah, That's how much the batteries are down. With 5a going in, we will be topped off in two more hours of solar. Then it says "0" on amp hours, and starts to blink... batteries are full.

It has been hassle free, zero maintenance, and never needed recalibration, (except the one time), and the difficult 1.5 hour set up, is a small price to pay to know exactly what is going on with our batteries and charge devices. It allows us to properly take care of the batteries and get a 10 year + lifespan out of them.

The only other simple way to know the batteries charge, is to take the specific gravity with a hydrometer several times a day. Voltage means NOTHING unless you have no power in or out all day, you have an incredibly accurate digital readout, and their is NO line loss in the sensor wires. (never the case). Even with all of these qualifications, v mostly tells you if you are almost dead, or full. It is not accurate about the inbetween points.

This leads to over charging, under charging, or getting stuck with low batteries when you need them, and a shorter battery life.

Getting some sort of smart monitoring device is probably the most "money well spent" item on the entire boat. IMO.

Mark

[Mark Johnson]

Originally Posted by Maine Sail

Ditto. The OP spent some good $$ on AGM's and a Victron BMV-600 is only $158.10 at Jamestown Distributors.

Terminal voltage is rather tough when cruising as most folks don't have the time to do it correctly. The generally accepted "industry" rule of thumb is to discharge the bank no more than 50%. Of course the less deep you discharge the longer life you get. AGM's also like to get back to a full 100% SOC quite often to get the most out of them..

Here's a direct quote from Lifeline:

"For maximum battery life in cycling applications, do not discharge the battery bank below 50%. Discharging the bank repeatedly to 100% will shorten the battery life. The open circuit voltages listed below correspond to the various states of charge:"

12.2 Volts on a Lifeline AGM is 50%.


They also say this:
"For maximum battery life, a battery must be recharged to 100% capacity. Recharging to less than 100% may result in premature battery failure. Lifeline batteries are not covered under warranty if they are not recharged properly. For more information, please refer to our warranty policy"



Without solar or wind getting back to 100% can be tough when charging off an alternator alone.

This last part is so true. With a big battery bank, you might be at 90% full after an engine run, and the last 10% will be SOO time consuming to accomplish this way. And talk about inefficient! The huge 150a alternator might only be putting in 10a, because near the top of their charge, the batteries want a slow trickle charge. That's all they will accept.

Even if one only has enough solar to do the top half of the daily required recharge, the panels are the perfect way to do this. (No need to run the engine for hours, just one, first thing in the morning).

Mark

[Mark Johnson]

Originally Posted by Extemporaneous

Assuming the OP got the answers he wanted, I have a question for Mark.

Hi Mark,
Great Post.
One thing/question. Originally and subsequently on occasion, did/do you run your bank down to empty (10.5V under its 20hr rated load) to confirm and/or reestablish your Battery banks capacity?

BTW, I also chose the Link 10 as it was the ONLY Battery monitor that both was able to tell me Watt hours, and could use a temperature sensor to properly equate things. There may be other out there now??

Cheers,
Extemp.

VERY good question. One can't take their battery capacity for granted if they want it correct. The rating might be wishful thinking.

I got a new set of Trojan batteries two years ago, because I killed the previous pair, as I had stupidly let them run out of water. Otherwise they might've made it to 15 years old! This screw up was too easy to do. With HydroCaps, and my very shallow cycles, I only needed water twice a year! (These batteries have HUGE sumps in the bottom) Now, I check the first day of every season!

Anyway, these new batteries were one and a half years on the distributor's shelf, and it concerned me. They did reassure me that they had gotten a charge once a month.

When I got all 300 pounds home, I charged them up and did a few complete cycles... with equalizes at the top. This exercises them, for better performance. Then I put a 1a load on them untill the 10.5v point, and figured the real a/h capacity of the batteries. It was about 8% less than the rating!

I called Trojan, kinda pissed, and they said that 8% under rating was great! Apparently very few batteries are up to their rating. Anyway, I set up the Link 10 to the REAL measured capacity! I think that one reason I have never gotten a running error, is that we top off the batteries daily, (as a rule), so it starts over. I suppose for folks who don't do this, it can be a bit more problematic. We never had a problem.

At well over $500 a pair, I want these batteries to last a LONG time. BTW, anyone shopping for batteries, that can live with 14" or even 16" tall, 6v, wet cell batteries, in series... (340 & 380 a/h per pair @ 12v total) These puppies will out last ANY 12 v battery, even theirs, 2 or 3 to 1. They're rugged!

Mark