AGM vs. Lead Acid for solar (in 2017)

[dwh]

To charge a battery to a specific voltage, the power supply must have a voltage potential equal to or higher than whatever battery voltage you are shooting for. This is why "12v nominal" solar panels are built to have a Vmp (voltage max power (under load)) of generally at least 16v.

If you directly connected a 12v nominal solar panel to a 12v nominal battery, theoretically the solar could eventually push the battery voltage up until it reached the solar panel's Vmp. The primary purpose of a solar charge controller is to prevent that by insuring that the battery voltage is never allowed to rise too high.

Optimizing the charging of the battery is a secondary function.

Cheap solar "regulators" don't optimize battery charging at all; it's just an on/off switch. When the battery voltage drops to a certain point, say 13.6v, they connect the solar to the battery and leave it connected until the battery voltage rises to a certain point, say 14.4v, then they disconnect the solar and wait for the battery voltage to fall. Rinse and repeat. Basically the same way a non-computer-controlled voltage regulator in a vehicle behaves.

A PWM is also an "on/off switch" voltage regulator, but with a computer controlled high speed chatterswitch that can regulate voltage very accurately. Since it's computer controlled anyway, it's no big deal to add a bit of programming to control the rate (pulse width) at which the switch chatters (hardly chatters at all during bulk stage), and while you are at it you might as well add a bit of programming to have it regulate at several different voltages. Tada! Multi-stage charging (though technically, float is not a charging stage). Added benefit: The pulsing of the power to the battery helps keep the electrolyte in the battery agitated, and helps to knock sulfation off the plates. Icing on the cake.

MPPT adds a circuit to regulate the voltage on the solar side to keep the solar operating at Vmp (get the most watts), then feed that through a voltage converter to lower the voltage to the battery side (same watts, but as volts goes down, amps goes up), and then feeds that through a PWM switch to regulate the voltage on the battery side.

Then some PWM and MPPT controllers get real fancy and add tempuature compensation and some even provide an interface to allow the settings in the computer to be changed.

But all of that is secondary. The primary purpose is to prevent the battery voltage from rising to the solar's Vmp.



Odysseys are freaks that require special care and feeding. Something about that particular high-pressure thin plate pure lead (TPPL) / absorbed glass mat (AGM) sandwich recipe makes them prone to misbehave if they aren't regularly pushed up to the 14.7v/14.7v bulk/absorb that keeps them healthy.

One known issue is that in regular automotive use they don't get the voltage they like, and over time their full charge resting voltage drops and stays dropped. Odyssey has a recommended proceedure to fix it: Run the battery dead and then recharge to the specified voltage using a C*.4 current (40a charge current per 100ah of battery capacity). Odyssey will sell you a charger that can do that. No other charger will, except a large high-zoot programmable like a Xantrex TruCharge.

I've tried to figure out why that happens, and the only answer I can come up with, is that it must be something to do with electrolyte stratification. I've never seen that confirmed though, so at this point it's just a theory that fits the observed facts.


Very few other lead-acid batteries are as picky as Odysseys. Most can be charged just fine by raising the battery voltage up over 14v and holding it there long enough for the electrolyte to absorb all the electrons it can.

HandyBob is right though, going to a higher voltage will get it done a lot faster, and be healthier for the batteries...as long as you are careful not to go too high.

 

[Step-Hen]

[snip] I've tried to figure out why that happens, and the only answer I can come up with, is that it must be something to do with electrolyte stratification. I've never seen that confirmed though, so at this point it's just a theory that fits the observed facts.


Very few other lead-acid batteries are as picky as Odysseys. Most can be charged just fine by raising the battery voltage up over 14v and holding it there long enough for the electrolyte to absorb all the electrons it can.

Firstly, "chatterswitch" is the best word I've learned in the past 20 years, besides perhaps "feckwit."

Secondly (and this is a question, I'm not disputing your assertion,) do AGMs stratify to a significant extent?

Lastly, are Odysseys pickier than other batteries, or is the company just picky about specifying the optimal charging and recovery conditions? Again, that's really a question, not an argument.

 

[dwh]

Firstly, "chatterswitch" is the best word I've learned in the past 20 years, besides perhaps "feckwit."

"I calls 'em like I sees 'em. And if I don't sees 'em, I makes 'em up."

Secondly (and this is a question, I'm not disputing your assertion,) do AGMs stratify to a significant extent?

Dunno. Makes sense that they could/would...electrolysis certainly happens, hydrogen and oxygen certainly rise and then recombine...so there must be some separation of water and acid going on.

But how much? Haven't seen any published data. Your guess is as good as mine.

Lastly, are Odysseys pickier than other batteries, or is the company just picky about specifying the optimal charging and recovery conditions? Again, that's really a question, not an argument.

The batteries are pickier. The drop in resting voltage, Odyssey's recommended fix and the special battery chargers are all documented facts.

And like I said, the only theory I've got to explain it is stratification, and the recommended fix is probably about as close as you're going to come to doing an EQ on a SLA without forcing open the blow-off valve.

 

[SSage]

I would just put a Group 31 AGM in a plastic box and call it a day. Sam's Club here sells an AGM 12 volt for $179, 105 AH or the true deep cycle 6 volts for the same $179 in AGM. I've used the AGM Deka type and its not bad for the money. I think advanced auto sells the same battery too for more money, I picked up one on the road and it was in a Deka case. Or pick your favorite brand, they are all fairly similar in the 12 volt AGM flavor. If you want to go for more run time and much better life get two 6 volt AGM golf cart batteries.The key to battery life is getting it fully charged often and staying above 50%. You want enough charging capacity to get the batteries into float mode occasionally, always staying under charged will kill them early. W4SGE

 

[Ducky's Dad]

One known issue is that in regular automotive use they don't get the voltage they like, and over time their full charge resting voltage drops and stays dropped.

True dat. I tried to keep an Odyssey 31M happy with a 160amp alternator and long highway mileage, and the battery crapped out at three years on the nose. Replacement Odyssey 31M in the same truck got the 160amp alternator and occasional shore power charging/reconditioning on a high tech AGM-optimized charger that went to 14.6V. Battery failed again at a little more than three years and Odyssey told me I needed 14.7V-15.6V during bulk charge, and high amperage, preferably 50amps. Third Odyssey 31M in the same truck got a 270amp alternator and occasional shore power charging/reconditioning on an Odyssey 40amp charger (because the 50amp unit was no longer available), and now it gets 24-48 hours about twice a month on a 7amp Ctek AGM charger. I'm using the 7amp Ctek because with it I can simultaneously charge the big Odyssey and and the Optima G34 house batteries simultaneously (Optima recommends max 10amp charge for their batteries, but I think that's bogus). My current Odyssey 31M is getting close to two years old and its typical resting voltage now stands at about 12.45V , while 100% charge is 12.85V or higher. So, I'll probably have to go back to the 40amp Odyssey charger. I probably won't be able to get it much above 12.65V.

Odyssey has a recommended proceedure to fix it: Run the battery dead and then recharge to the specified voltage using a C*.4 current (40a charge current per 100ah of battery capacity). Odyssey will sell you a charger that can do that. No other charger will, except a large high-zoot programmable like a Xantrex TruCharge.

Odyssey recommends 50amp chargers for their G31 batteries, but they no longer sell a 50amp charger. And they no longer sell a 40amp charger. Both were discontinued in favor of their new line of chargers that maxes at 20amps. Supposedly, the bigger chargers are coming. Odyssey told me that their newish 20amp charger will work on the G31, but that bigger would be better. They show the Ctek 25amp charger on their tech data pages as being suitable for the G31.

I have a Northstar G31 in another truck. It has never been on shore power, never been reconditioned, never failed to start that truck in infrequent driving. It's the same age as the Odyssey G31 that requires lots of attention.

 

[FJR Colorado]

I can tell you that a yellow Top Odyssey AGM deep-cycle battery works great with the 100W Renogy panel and it would be good for your in-cab application.

More details in my 2006 Tundra build thread.

 

[FJR Colorado]

Removing duplicate post

 

[Ducky's Dad]

I can tell you that a yellow Top Odyssey AGM deep-cycle battery works great

If it's yellow, it's not an Odyssey. Probably an Optima.

 

[devero4]

Man, what a wealth of knowledge this thread has become. A little update though: Yesterday I bought this East Penn Intimidator battery. I know a lot of you have mixed feelings on RV/Marine batteries, but the place I purchased it from told me that a lot of ranchers use it for solar gates to get in and out of their property. I also like how it tells me the recommended float charge. Paid $180 after tax... What do you guys think? Again, using it with a 100w Renogy panel and 20amp PWM controller to power a fridge. Did I make the right decision?

Sent from my iPhone using Tapatalk

 

[Joe917]

For your purposes AGM was the right choice but that is not a deep cycle battery.

 

[Step-Hen]

...Odyssey told me I needed 14.7V-15.6V during bulk charge, and high amperage, preferably 50amps.

Did they say why? Were they thinking that you were chronically undercharging the battery, and the higher volts/amps would ensure that it gets fully charged more often?

 

[dwh]

55ah might be a touch undersize depending on how much your fridge draws. Then again maybe not.

On the upside, a smaller battery is more likely to get fully charged and thus less likely to suffer from the effects of chronic undercharging.

You paid your ante, now it's time to play your cards and find out. Let us know how it works.

You might consider tossing one of these in the mix just to keep an eye on things:

https://www.amazon.com/gp/aw/d/B014...ower+meter&dpPl=1&dpID=41z+tg37tJL&ref=plSrch


Look around Amazon and you'll find a ton of those by different manufacturers rated for all sorts of voltages and amperages.

 

[devero4]

Thanks for the link, a good friend of mine recommended the same thing. This battery has a 2 year warranty, and 2 years prorated after that, so that was another selling point that made me feel a little better about the price. Never bought a battery that expensive before :Wow1:

 

[devero4]

Fridge is the Engel. Should draw around 2.5 amps on high

 

[Rbertalotto]

REAL Deep Cycle AGM batteries have come way down in price. $179 each.....
I've had two of these Duracell, Group 31 AGM batteries in the travel trailer for two years with great performance.
https://www.samsclub.com/sams/searc...eahead_group-31-agm-battery&_requestid=414160
AGM batteries require a different charge criteria that flooded batteries. A search will reveal the need for four stage charging if you want the absolute best battery life and performance.
I 'm charging with 320 watts of solat through Bogart charge controller which offers all kinds of charge parameters to maintain the batteries correctly.