AGM Batteries

[Paul L]

Originally Posted by Not Sure

Um, how can I put this nicely....that is not exactly correct. When you fast charge a battery (higher charging current) you create more gassing and higher temps, which is exactly what you're supposed to avoid with AGM's (and Gels).

The only actual benefit of AGM's is that they are supposedly 'spillproof', and they can't be refilled, which translates to .....they are popular with people who have little to no interest in messing with batteries, bottom line. The only benefit of Gel cells is that they can be put on standby for years with little to no maintenance, such as backup for a grid-tie solar powered home. Don't for a minute confuse either with being 'better' than the regular deep cell lead acid 'wet' cells. Other than for specific installations, they aren't. Sorry.

AGMs have a much lower internal resistance. That is why they can be charged at higher current rates than wet batts. Here is a table from one of the manufactures. http://www.energy1batteries.com/Tech..._batteries.pdf

Paul L

[Not Sure]

Originally Posted by Paul L

AGMs have a much lower internal resistance. That is why they can be charged at higher current rates than wet batts. Here is a table from one of the manufactures. http://www.energy1batteries.com/Tech..._batteries.pdf

Paul L

Yes, I'm sure that the manufacturers will tell you they are the greatest thing since sliced bread. That is what they initially claimed about the gel cells too. Unfortunately, in practice the reverse is true....the AGM's and gel cells are more suitable for very specific installations, or for people who want to install them and then leave them be. And many former proponents of AGM's (and gels) are quietly switching back to regular deep cycle wet cells. The fact is, if they were 'better' then wet cells they would be greedily adopted by the most hard-core users of batteries there is...off-grid solar/wind/hydro powered homes...and they haven't been, other than as previously stated, gel cells as standby/backup for grid tie installation (another instance of install-and-forgetaboutit), and people who aren't really interested in batteries or monitoring ('caring for') them.

[Paul L]

Originally Posted by Not Sure

Yes, I'm sure that the manufacturers will tell you they are the greatest thing since sliced bread. That is what they initially claimed about the gel cells too. Unfortunately, in practice the reverse is true....the AGM's and gel cells are more suitable for very specific installations, or for people who want to install them and then leave them be. And many former proponents of AGM's (and gels) are quietly switching back to regular deep cycle wet cells. The fact is, if they were 'better' then wet cells they would be greedily adopted by the most hard-core users of batteries there is...off-grid solar/wind/hydro powered homes...and they haven't been, other than as previously stated, gel cells as standby/backup for grid tie installation (another instance of install-and-forgetaboutit), and people who aren't really interested in batteries or monitoring ('caring for') them.

The point I was making was that you said that AGMs will not accept higher charge rates. In that you are just plain wrong. How about trying to at least keep the facts straight. As far as AGMs being 'more suitable for very specific installations'. Well, I agree with that statement. In my case I can fit AGMs into an area that keeps the weight well distributed and allows me to get in a large bank. No way would wet-cells of the same amp-hours have fit. They also allow me to re-charge at higher rate, thus reducing engine hours. Not for eveyone.

Paul L

[billyehh]

I agree with Paul L. Everything that I have read about AGM batteries indicate that accept a much higher charge rate. This is due to the Peukert Efect. I quote from von Wentzel's website.

• Flooded cells are usually bulk-charged at an ampere rate of about 25% of amp-hour capacity. For example, let's say you have to replace 100 Ah every day and chose to install a 400 amp-hour house battery bank. Using the 25% ratio, the maximum charge acceptance (the rate at which the battery can be safely charged) of your flooded battery during bulk charging would be around 100A. Assuming you have no other charge sources on board, after losses and other loads you would want to consider a 120 ampere (hot) rated alternator.
• If you use Gel cells, you can bulk charge with twice the current that flooded cells can sustain. A 400 amp-hour bank composed of gel cells can safely enjoy the benefits of a 200A charge source and bulk charge in less than 1/2 the time of a flooded cell (due to its higher charge conversion efficiency). Here, multiple small frame or a single large frame alternator may be ideal in order to reduce charge time and engine wear.
• The Lifeline AGM, is not current limited at all during bulk charging according to Concorde, the manufacturer. Theoretically, you could make your bulk charge time as short as you would like. In practice, people are charging AGMs with currents of up to 4x the amp-hour capacity. Accounting for conversion efficiency that would be 18x faster than your typical flooded cell but you'd have to install a charge system capable of delivering 1600 amperes to the battery bank (it would take about 5 minutes per day to replenish the 100 Ah with a 20 kW gen-set). In the real world, two large frame alternators may be more appropriate from a weight/cost standpoint.

It is a great source of information and can be found at How Lead Acid Batteries Work

That being said, where AGM's really shine is on a boat with alarge battery bank, with sophisticated multiple charging systems. It cantake an extremely large charge but is very sensitive to over voltage which will ruin the batteries in short order.

The caveat is that AGM's are not forgiving to non smart chargers, regulators or controllers. But if they are taken care of they will last as long as a Surrette or Rolls. Mine are almost 9 years old and passed a load test withflying colours last year.

[Not Sure]

So in other words, what you are both saying is that when confronted with physics, (i.e. higher charging current creates more heat, which creates more gassing, which evaporates the fluid more quickly, which can't be refilled in an AGM battery) you choose instead to believe what you are being told by manufacturers and whomever, rather than the science? Is that the position that you're taking here?

[Not Sure]

Originally Posted by billyehh

The caveat is that AGM's are not forgiving to non smart chargers, regulators or controllers. But if they are taken care of they will last as long as a Surrette or Rolls. Mine are almost 9 years old and passed a load test withflying colours last year.

And I've got 2 old used automobile batteries that every 2 weeks or so I drain down to near dead, then charge them back up using a 45watt 72v (that's 72 volts) solar panel, and I've been doing that for almost 3 years now, and the batteries are still taking a charge above 12.55v.

All that that proves, however, is that there are exceptions to every rule. It certainly doesn't mean that automobile batteries are suitable for deep cycling and high voltage charging, nor that they will last for years when treated in such a manner.

[billyehh]

You and your 2 old batteries are the perfect example of what I have been saying. Anyone who is hard on batteries should stick with the cheapest flooded batteries which can be replaced when you destroy them. Charging batteries at 72 volts and surviving means you have an minor miracle. Congratulations.

By the way Peukerts effect is part of physics the last time I checked and is the reason AGM's can take a higher charge.

Again for all those interested in a well thought out article on batteries I still recommend How Lead Acid Batteries Work

With a little search you can find many sites discussing the different merits of thevarious battery chemistries

[hellosailor]

"Um, how can I put this nicely....that is not exactly correct. When you fast charge a battery (higher charging current) you create more gassing and higher temps, which is exactly what you're supposed to avoid with AGM's (and Gels)."
Actually, when AGMs or any other type of lead acid battery are used with pulsed-DC charging, they can and will charge at a higher rate because the pulse charging allows micro intervals where the electrolyte cools enough so it does not buble. Bubbles create high resistance and high heat during a charge, so simply by using a PWM charger (MPPT, PWM-DC, etc.) you can often recharge a lead acid battery 10% faster without overheating it or doing any other damage.

The lab results and actual physics to back all this new stuff up are fairly recent and generally considered TRADE SECRETS and so not publicized in great detail by the folks making both the batteries and the chargers. Including alternators.

Sure, someone with somthing to sell is always suspect, but some of them have outstanding reps and can back their stories up with hard lab results. The information is out there and not hard to dig down to. Hidden pretty neatly by obsolete information and folks elling magic potions, but not really hard to find. Universities, government labs, other reasonably pobjective places all publish agreeing results.

You want to do things the old fashioned way with wet cells, that's your option. They're still the cheapest way to store power, and that's the only reason to still use them.

[hellosailor]

Not Sure, you've sure been lucky. Every auto battery maker (and that's an "SLI" battery, not an "auto" battery, to use the correct name) says that if you drain it nearly all the way and then recharge it, you might get six to ten full cycles out of it before it turns to junk. They're just not intended for deep cycling, and not one company making them will warranty them in that use.

Of course, it could be something in your "well the numbers don't matter its close enough" philosophy that is giving you misleading results. The difference between "dead" and 60% discharged is significant. As is the difference between 60% charged, and "full".

Apparently you've proved what Einstein said, that all the laws of physics are simply relative, and tend to vary from time to time and place to place.

[Paul L]

Originally Posted by Not Sure

So in other words, what you are both saying is that when confronted with physics, (i.e. higher charging current creates more heat, which creates more gassing, which evaporates the fluid more quickly, which can't be refilled in an AGM battery) you choose instead to believe what you are being told by manufacturers and whomever, rather than the science? Is that the position that you're taking here?

Not Sure,
OK, you win. The internal resistance of the battery does not matter as much as the resistance of the reader. Mind over physics.

Paul L

[Not Sure]

Originally Posted by billyehh

You and your 2 old batteries are the perfect example of what I have been saying. Anyone who is hard on batteries should stick with the cheapest flooded batteries which can be replaced when you destroy them. Charging batteries at 72 volts and surviving means you have an minor miracle. Congratulations.

By the way Peukerts effect is part of physics the last time I checked and is the reason AGM's can take a higher charge.

Again for all those interested in a well thought out article on batteries I still recommend How Lead Acid Batteries Work

With a little search you can find many sites discussing the different merits of thevarious battery chemistries

Actually the exact opposite is true. If you're prone to be hard on, or ignore batteries, then AGM's and gel cells are made for you, as you're easily able to run down to Walmart or Sears and grab another after you've ignored them and/or abused them for several years.

Batteries such as the Trojan 105's, however, are for those who take care of and monitor their batteries, fill them up with distilled water as needed, and otherwise try and cycle them not more than 50% down. It is ludicrous to claim that people who buy Sear's Diehard AGM Marine batteries (and the like) so that they don't have to monitor and take care of the battery, know more about what is the better battery and the proper way to take care of it then the off-grid energy users whose lives literally depend on keeping their regular wet-cell deep cycle batteries (such as the Trojan 105 'beginner'* batteries) well cared for.

*'beginner' - Trojan 105's are referred to as 'beginner' deep cycle in the off-grid power industry because they are used to teach battery owners how to properly care for expensive deep cycle batteries used in off-grid alternative power installations. They (T-105's) are robust and inexpensive, and there is not the monetary loss involved when new alternative power system owners neglect to properly care for them and/or deep-discharge them below 50%, which reduces the life of deep-discharge batteries and is costly if you're doing it to $800+ industrial quality deep cycle batteries as a 'learning' experience.

[Not Sure]

Originally Posted by hellosailor

"Um, how can I put this nicely....that is not exactly correct. When you fast charge a battery (higher charging current) you create more gassing and higher temps, which is exactly what you're supposed to avoid with AGM's (and Gels)."
Actually, when AGMs or any other type of lead acid battery are used with pulsed-DC charging, they can and will charge at a higher rate because the pulse charging allows micro intervals where the electrolyte cools enough so it does not buble. Bubbles create high resistance and high heat during a charge, so simply by using a PWM charger (MPPT, PWM-DC, etc.) you can often recharge a lead acid battery 10% faster without overheating it or doing any other damage.

The lab results and actual physics to back all this new stuff up are fairly recent and generally considered TRADE SECRETS and so not publicized in great detail by the folks making both the batteries and the chargers. Including alternators.

Sure, someone with somthing to sell is always suspect, but some of them have outstanding reps and can back their stories up with hard lab results. The information is out there and not hard to dig down to. Hidden pretty neatly by obsolete information and folks elling magic potions, but not really hard to find. Universities, government labs, other reasonably pobjective places all publish agreeing results.

You want to do things the old fashioned way with wet cells, that's your option. They're still the cheapest way to store power, and that's the only reason to still use them.

I see...it's 'trade secrets' and 'new physics', eh? LOL! Yeah, and 'Extends' (or whatever its called) is scientifically developed to make one's penis larger too, as seen on TV.

[Not Sure]

Originally Posted by hellosailor

Not Sure, you've sure been lucky. Every auto battery maker (and that's an "SLI" battery, not an "auto" battery, to use the correct name) says that if you drain it nearly all the way and then recharge it, you might get six to ten full cycles out of it before it turns to junk. They're just not intended for deep cycling, and not one company making them will warranty them in that use.

Of course, it could be something in your "well the numbers don't matter its close enough" philosophy that is giving you misleading results. The difference between "dead" and 60% discharged is significant. As is the difference between 60% charged, and "full".

Apparently you've proved what Einstein said, that all the laws of physics are simply relative, and tend to vary from time to time and place to place.

Actually, I don't believe I've been 'lucky' with those used automotive batteries (which aren't being used in a boat I might add, but rather in other remote 12v applications), particularly since I've got several more -- one an old 8D CAT battery -- that I treat the same way with similar results. I tend to take a more scientific approach. And that is that battery technology has improved to the point that even decent regular wet cell automotive-type batteries are built far better today than they were in the past and can take some repeated abuse, combined with the fact that my high-voltage (72v) solar panel is probably providing enough current to prevent the permanent sulfurization of the lead plates which occur with such deep discharges (and are what prevents the battery from taking a charge), that and the honeycombed lead plates of the automobile batteries are robust enough now that they are not deteriorating rapidly under such treatment, as they commonly did in the past. In other words...science.

[Not Sure]

Originally Posted by billyehh

Charging batteries at 72 volts and surviving means you have an minor miracle. Congratulations.

Uh, no. No 'miracle' necessary. The current, while 72 volts, is very low amps, and doesn't appear to put much stress on the batteries at all. I've left batteries charging on the 72v charger all day (8+ hours in full sun), with nary a hint of boiling over of the fluid, ever. The fact is, you can hold the 72volts in your hand and at peak output it only produces a mild burning sensation similar to touching your tongue to a 9v cell (which I assume everyone has done as a kid).

Do the math. 45 watts, 72volts. I'll let you figure the amps.


By the way, I've also taken completely dead used automotive batteries that have been sitting for several years dead, hooked them up to the 72v solar charger, and was able to bring them back to life in about 16 hours charging time.....again, approaching 12.5v as their new 'full' charge (measured after resting following charging, of course). Put that one in your pipe and smoke it. (It kinda goes against the grain of everything you've ever been led to believe about batteries, huh.)

If you want to make your own 72v solar battery charger/equalizer, I'll tell you what mine is made of. (Of course, I assume no responsibility if you blow something up, burn down something, or otherwise harm life or property, as this is for informational purposes only.)
Find an old Unisolar 45watt 72v direct-to-grid solar panel and wire up a jumper cable (with 1 set of ends left on for battery 'clamps') to the output leads of the solar panel. I clamp the jumper cable ends to either end of a 1"x12" block of wood when they are not being used, and make sure that they don't come in contact with anything while 'open circuit' (which can go as high as 90v or so).

[Not Sure]

Actually, I'll provide you the specs on the (amorphous) solar panel for science's sake -- yup, it even tolerates shade. (Solarex Millennia MST-43MV is the panel -- a subsidiary of BP Solar, and no longer in business) It's actually rated at 43watts, not 45w.
voltage at P: 72v
current at P: .6a
open circuit voltage(V): 98v
short circuit current: .8a
design max V: 117v
nominal voltage: 48v
minimum blocking diode: 3a
maximum system voltage: 600v
series fuse rating: 20a

In other words, if you wanted to hook this panel up to a battery bank permanently, it would need to be a 48v battery system with a 48v charge controller rated to take the 72v input. (Of course, you could hook it up permanently to a 12v battery if you ran it through a ceramic resistor that knocked the voltage down to around 12v, but then....what's the use, as you've effectively neutered the panel at that point, and it's low voltage low amperage output would be next to useless.....about 7watts or so)