Voltage Drop in AGM Under Load?

[chala]

Originally Posted by neelie

1) I never equalize.. My rudimentary understanding is that this is not necessary on AGMs... .?? Am I wrong?

I do equalize LA and other recommends it.

Originally Posted by Maine Sail

Shallow cycles do lead to longer life but with Lifeline AGM's getting to 100% as often as possible, proper float voltages, equalizations and high charge rates are also important to the longevity.

Originally Posted by Maine Sail

They also need to be equalized periodically depending upon your use.. .

Originally Posted by neelie

the 100AH pack will struggle at 180A draw..

Victron specification for a 12.8V 90Ah, maximum continuous discharge current 270Ah. And you have a 100Ah pack.

Originally Posted by neelie

3) What makes you say that my batteries are being run lower than 50%? I already stated that as per my BMS they never get below 70%.

Originally Posted by neelie

Load 5A; V = 12.5

With 700 W of solar, not really a charge voltage.

Originally Posted by neelie

Ps... Recently, we motored for over 12 hours. By all accounts, the battery should have been close to 100%

Did you achieve?

Originally Posted by Maine Sail

Lifeline batteries are not "full"/ 100% until net accepted current is 0.5% of Ah capacity at 14.4V..

[hellosailor]

"Posted by neelie
1) I never equalize.. My rudimentary understanding is that this is not necessary on AGMs... .?? Am I wrong?"

It is physically impossible to equalize the vast majority of AGM batteries. You would generate so much gas pressure that they would be damaged by venting, or explode. That's simply how they are made, and how their makers tell you to use them.

The singular(?) exception to this is with LifeLine/Concorde AGMs, which are military aviation batteries constructed to withstand much higher pressure, and capable of being equalized without damage. Which is why that company will tell you to equalize their batteries.

Whether equalizing does or does not have any purpose or gain in AGM batteries is another question entirely. But for most of them, you might as well put them in a campfire instead of trying to equalize them. You'll get similar results.

[Paul L]

Originally Posted by hellosailor

"Posted by neelie
1) I never equalize.. My rudimentary understanding is that this is not necessary on AGMs... .?? Am I wrong?"

It is physically impossible to equalize the vast majority of AGM batteries. You would generate so much gas pressure that they would be damaged by venting, or explode. That's simply how they are made, and how their makers tell you to use them.

The singular(?) exception to this is with LifeLine/Concorde AGMs, which are military aviation batteries constructed to withstand much higher pressure, and capable of being equalized without damage. Which is why that company will tell you to equalize their batteries.

Whether equalizing does or does not have any purpose or gain in AGM batteries is another question entirely. But for most of them, you might as well put them in a campfire instead of trying to equalize them. You'll get similar results.

I think Lifeline is the only manufacturer that publishes the equalization directions. I doubt that it has to do with their construction being better than the others. Maybe they've had a too many field failures that they wanted to try and recover. When my North star AGMs failed, the factory had the distributor go through 2 bench equalizations on them.

[hellosailor]

Paul-
If you run some fast numbers, Lifeline's batteries come out as "different". The average sealed lead battery (of any kind) is designed to operate at sea level, and maybe up to 5000 feet (Denver) and similar elevations. And they have a fairly low over-pressure valve setting, designed so they will ventilate (permanently depleting electrolyte in gas form) at pressures that are adequate for that use.
In contrast, Lifeline are designed to go up and down, to 30,000 feet, 40,000 feet, 50,000 feet...military operating altitudes, not just civilian aviation. Check out the air pressure difference at 40,000 feet, and you'll see that battery has to be built differently from anything that is restricted to earthbound use.
And if you've ever cooked off a battery while recharging it...it doesn't take much extra voltage for very long to pop pressure valves.
Northstar told you to equalize as a remediation step, to try to recover something. OK, but did they say to do it as routine preventive maintenance? The "big three" battery makers in the US (JSI, Deka, and I'm forgetting the third) all say NEVER to equalize their AGMs. I have no idea what or why Northstar said to, haven't looked at their product, just have this nagging memory of that name, that blue color, and a "China special" at the time.

[Paul L]

You got me interested. If you go to the Lifeline website they mention milspec designations, but they don't tell you which ones. So it really says nothing. Are you saying the marine batteries are flight qualified or the same construction as the flight qualified batteries?

[hellosailor]

Paul-
I'm saying neither. Only that they build for a different market, and it is very possible that "all" of their AGMs are built to the higher spec, simply to take advantage of the economics of scale. Same case, same valve, etc. for everything, could be simpler and more profitable for them. If nothing else, their engineering staff would have a different knowledge and different considerations in house, compared to the average mass-market company.
Or, of course, everyone else could be incompetent liars when they say not to equalize other products, that they would be damaged. (I wouldn't bet on that.(G)

[Paul L]

Lifeline didn't start out suggesting equalization. It was only after a lot of issues that they, seemingly reluctantly, published the directions. I spoke with the guys at Rolls on their AGMs and they did not want to recommend equalization. It seems that with AGMs the issue is more that you get them to 100% charge regularly, than that you try and fix the problems latter with equalization. In practice in a cruising situation, I don't think that Lifeline has proven to be any more robust than many of the other AGM vendors.

[Wotname]

FWIW, the Concorde maintenance manual (for the RG Platinum series) suggests "conditioning" their AGMs in order to recover capacity. I carry this out if the capacity drops below 85% (when measured at the C1 rate). Sometimes I have found it to be fairly effective and other times not so much. I had improvements from 65% back to 95% although it appears that the capacity at higher discharges (say 10C1) isn't so good.

Their "conditioning" charge is to charge at a constant current of 0.1C1 for 16 hours and they caution that each conditioning cycle decreases battery life and suggest it only be used when necessary.

As they are robust AGM batteries, I wouldn't suggest this method can be transferred to other makes or models within due consideration to the standard potential dangers of any battery charging (heat / pressure etc).

[sailinglegend]

Originally Posted by hellosailor

.... Lifeline are designed to go up and down, to 30,000 feet, 40,000 feet, 50,000 feet...military operating altitudes, not just civilian aviation. Check out the air pressure difference at 40,000 feet, and you'll see that battery has to be built differently from anything that is restricted to earthbound use....

Lifeline/Concorde are not the same batteries!
Lifeline make batteries for RV/MARINE use, and now Racing AGMs. Concorde make aviation batteries.

Full River also recommend equalising their AGMs.

[neelie]

Ok.. I have had the batteries checked and the result is disappointing.

Prior to checking, I charged the batteries to what I believed to be 100%, rested the batteries for 4 hours and checked the voltage, they were all between 12.7 and 12.8 V.

Temperature is 32C or 90F

Battery capacities were checked and they averaged 93AH (the range was +/- 3AH)

So here is the annoying part...

My batteries are rated at 125AH each, they are 10 months old and have "lost" around 30% of their advertised capacity possibly due to the high operating temperatures.

I have corrected my BMS to reflect this new capacity minus 10%...I.e. 500AH.

So it looks like Chala and Mainsail were correct! My batteries when indicating 80%SOC for C=750 were in all likelihood only around 50% SOC for the real SOC of 550.

Thank You everyone for your advice and comments, it added to mine and a lot of other peoples learning experience!

As for total voltage loss, there was another 0.6V lost in the 12 feet of 4/0 cable running through a battery switch did not help either.

Regarding equalization, the Lifeline documentation states it should be done if capacity is lost due to excessive discharges and should be performed by a battery technician.

So back to the LFP vs AGM debate.. My 6 AGMs of allegedly 750 AH (in reality only 500AH) cost a lot more than a 400AH pack of LFPs. Both have similar useable capacity.

In this context, LFPs are clearly cheaper,lighter and smaller. It's no longer a contest.

[Paul L]

Originally Posted by neelie

.....So back to the LFP vs AGM debate.. My 6 AGMs of allegedly 750 AH (in reality only 500AH) cost a lot more than a 400AH pack of LFPs. Both have similar useable capacity.

In this context, LFPs are clearly cheaper,lighter and smaller. It's no longer a contest.

Not sure doing a comparison between failed AGM and healthy LFP is that valid. It will be interesting to see the failure rate of LFPs once they are get beyond the bleeding-edge type users and into the hands of the AWB users -- who may not be as diligent with them as they may require.

[Ex-Calif]

Originally Posted by neelie

Ok.. I have had the batteries checked and the result is disappointing.

Sorry this sucks for you but I am wondering if there is a learning moment here.

I have long felt for AGMs the best thing that can be done for them is to not discharge anywhere close to 50%. This means lots' of charging ability needs to be available to keep up with daily loads.

I have lost the plot a bit. How far down on average would you say you discharged your batteries over the year?

And the 12 foot run seems long as well. I am sure battery location is probably somewhat fixed for you. Bigger primary supply cable to reduce v-drop?

[neelie]

Paul,
No comparison can ever be valid.
But in this case, my AGMs had not failed, I have been told this is pretty normal for one year old AGMs in the tropics. The heat reduces capacity, it's between 32-38C in the battery compartment.

Also, I was only comparing purchase price for similar useable capacities, no allowance for installation. Of course LFP will be way more expensive to install.

I made the comment because the early resistance to LFP was based on purchase cost.

My experience with my "learner" 100Ah LFP pack is that they are remarkably robust, and I did abuse it to see what would happen.

The bulk of the issues stem from EV's who have 144V systems and have very high C draws.. In the order of >3C and the same with charging. Most cruisers rarely exceed 0.25C thus the probability of cell imbalances are reduced.

Hey Ho.. My 0.02c worth. But my next storage system will be LFP.

[neelie]

Originally Posted by Ex-Calif

Sorry this sucks for you but I am wondering if there is a learning moment here.

I have long felt for AGMs the best thing that can be done for them is to not discharge anywhere close to 50%. This means lots' of charging ability needs to be available to keep up with daily loads.

I have lost the plot a bit. How far down on average would you say you discharged your batteries over the year?

And the 12 foot run seems long as well. I am sure battery location is probably somewhat fixed for you. Bigger primary supply cable to reduce v-drop?

Yes, you are correct, do not let SOC be less than 50% and longevity will be increased.... Or so they say!

In my case, I never let SOC run below 70% .. But that was on the nominal 750AH which the marketing people claimed. So, as far as AH counted, 30% of 750 = 225AH used.

So on my new and realistic capacity of 500AH, it looks like SOC was never less than 55%.

The reduction in useable capacity, is apparently to be expected in a hot environment.

My cable is 4/0.. Do they make it any bigger? According to the electricians calculations, a draw of 180A will result in approximately .5V drop over 12 feet.

It's a 50ft boat.. Not sure one can reduce the run by much more and still keep the inverter outside the battery compartment (H2 off gassing and sparks make a heady mixture).

I think the lesson here is for owners in tropical regions with AGMs to get their capacities checked. A rude shock is in store for them.

So, from my perspective, it's either plain old vanilla FLA golf cart batteries (excellent bang for the buck) or LFPs. AGMs are an overpriced, underperforming option.

[Paul L]

I'm not buying 30% reduction in capacity after 1 year of use is standard and to be expected. It is a failure in my mind. Does their warranty cover anything after a year?