Odyssey AGM and solar experience?

[Sunking]

Put the battery in the fridge and charge them.

[inetdog]

During the bulk phase, I'm well below the absorb voltage setpoint - in practice, I'm in the "float" voltage arena during the bulk process, where larger amounts of current beyond the common 0.3C shouldn't be a huge issue. By the time the battery reaches the fixed absorb setpoint where the CC is now in control, I'm already well below 0.3C. So two controllers are in charge here - in bulk the battery runs the show until it reaches absorb, then the CC takes over signaled by reaching 14.4v (or whatever you have set it to). The CC is now overcharging the battery on purpose, but nowhere near the current levels seen in bulk.

??

I'm not trying to prove a point, just trying to um, absorb it all in my head if you will.

Well, you can try absorbing this, if I state it correctly:

1. When you are in Absorb, you are not yet overcharging the battery. Your CC thinks that it has found the point at which constant current might lead eventually to overcharge and so it switches to constant voltage mode. When the current drops to a certain level at the correct Absorb voltage for the batteries, you are on the threshold of overcharge, and going to the Float voltage will allow the CC to just replace internal losses in the battery and maybe charge it slightly.
An controlled overcharge (AKA Equalization) will happen when you increase to voltage to the Equalize voltage, which is higher than that for Bulk, Absorb, or Float.
This voltage will produce a substantial current through the batteries even after they have fully charged and will expend all of its energy in electrolyzing water and heating the battery.
2. The complication, which makes it more difficult to understand in detail, is that you are usually working with a series string of cells, either within one battery or in the form of a string of batteries. Since the SOC and capacity of different cells may eventually vary, even if they have the same life history, applying the Equalize voltage to each of the cells simultaneously is not going to happen. They will all get the same current, but may be at different voltages. As a result, if one cell is still, effectively, in Absorb or Bulk in terms of accepting charge, the other cells in the string will be getting an even higher voltage applied than just Veq/N where N is the number of cells.
Or in the other direction, one of the cells may not have been discharged as far as the others and will be fully charged while the others are still at the Bulk or Absorb level. In this case, the voltage across that one cell has to increase to make up for the lower voltages at all of the others. It is now getting a super overcharge.
These two possibilities are one very good reason that you need to check the individual battery or cell voltages and watch temperatures on all batteries during Eq.

[Sunking]

These two possibilities are one very good reason that you need to check the individual battery or cell voltages during Eq.

Just one little problem with that. You cannot do that with any SLA battery and is why they should never be EQ. Well if you have 2 volt SLA batteries you can monitor voltage.

[PNjunction]

As usual - great info for me to chew on. I also like Sunking's advice, although instead of the battery, I should put my head in the fridge.

One thing I may be overlooking too is that I am starting from no lower than a 50% DOD when I pump 0.5C into the general purpose agms. As I understand it, internal resistance is lowest when fully charged, and highest resistance when fully discharged. Maybe that is the reason I seem to be getting away with it as I'm not at the highest resistance but somewhere in the middle when I start charging - but this is pure speculation on my part.

Anyway, I'll do more testing, but will give you guys a break and thanks for input - it is definitely appreciated.

Maybe the best move is to stop piddling around with these general purpose agm's, and just enjoy life with the Odyssey's as they'll take anything I can throw at them.

[PNjunction]

NOCO 3500 ac charger results

As promised, I tested the 50% DOD 7ah powersonic agm with the NOCO 3500 in 85F ambient temps.

Note that the charger has a high and low output. The manual clearly states that for my 7ah size, I should be using the low (800ma output) rate. However, I tried the high rate (3.5a max), under SAFE conditions.

It started out at a steady 3.5A (0.5C) for a few minutes, and then ramped down to a steady 2.9A (about 0.4C) until 40 minutes later, the battery reached 13.2 volts, and dropped the current to 880 milliamps which remained steady until reaching 14.7 volts, and then dropping to a trickle of 80 milliamps in the space of a little over 2 hours. Sidenote: NOCO calls this transition from 13.2 to 14.7v absorb, although I would have preferred it to actually absorb longer at 14.7 volts.

At no time was the battery more than 3 degrees hotter than ambient temp. A discharge test shows it maintaining capacity as it should. I guess I'm not afraid of going to 0.5C SAFELY, which might come in real handy when my solar insolation is only like 2 hours and the battery is no lower than 50% DOD to start with. The battery won't be fully charged, but maybe 90 - 95% charged will get me through to the next day.

[Sunking]

I would have preferred it to actually absorb longer at 14.7 volts.

No you should not prefer that with an AGM as that is above the gassing voltage of 14.4

[PNjunction]

You are right - why I'm fixating on 14.7 I don't know.

My limited testing so far, and interpretation of Linden seems to be saying to me that one can apply much higher levels of current than 0.3C, as long as that is during the bulk stage. Thermal runaway / venting etc is pretty much certain if your charging environment exceeds this for whatever reason (failure / misadjustment) BEYOND the bulk stage. By designing your system in such a way that it is electrically impossible to go beyond 0.3C, you have a built-in safety factor.

I'm going to to test these general purpose types safely to 1C (during bulk only) and monitor the charge profile. Protective eye/face gear, gloves, temperature probing, and a non-flammable environment will accompany me. 1C doesn't really interest me from a solar standpoint, but I feel like I need to know more first hand. KEEPING that hand is a priority, so safety in testing is the most important part - a stupid battery is not worth injuring yourself or others, so that's way I'm being very respectful and careful about it.

One issue I'm going to research more is that even if this seems to work without overtemp or vent-blowout, elevated levels of hydrogen may be seeping through the case itself going beyond a safe level.

[PNjunction]

Test at 1C successful

Cranked things up to 1C and again no detectable heating / gassing.

DUT: Powersonic 3.4ah agm, at 50% DOD.
NOCO 3500 charger at the high rate (high rate not recommended by manufacturer for this size)
Ambient temp: 85F
Time to completion of charge: 1 hour, 10 minutes.

Initially it started with 3.6 amps for about 1 minute. It then dropped to 2.9 amps continuous for 16 minutes while voltage rose. After that, it dropped back to 880 milliamps continuous until it hit 14.7 volts and went into trickle. No appreciable heating detected. I'll try this again with my pwm charge controller and solar panel.

I guess all I can say is that I take personal responsibility for going beyond the manufacturer's limit. And only with this battery, which is not a TRUE deep-cycle with thick plates. But from a safety standpoint then yes, the manufacturer's limit would be wise to follow in any case. And with that, I think I'm done.

[Sunking]

You are right - why I'm fixating on 14.7 I don't know.

My limited testing so far, and interpretation of Linden seems to be saying to me that one can apply much higher levels of current than 0.3C, as long as that is during the bulk stage. Thermal runaway / venting etc is pretty much certain if your charging environment exceeds this for whatever reason (failure / misadjustment) BEYOND the bulk stage.

Close but no cigar friend.

Maximum charge rate for AGM varies from manufacture to manufacture, and model to model within a manufacture. Since this is a solar forum I can safely say C/4 (or .25C) is the maximum charge rate. I say this because I am certain that does exceed any manufacture maximum rate. But primarily because in a solar system anything excess of C/4 is going to be overkill on panel wattage making utilization efficiency really poor. For example you are just throwing money away putting in panel wattage capable of generating say 2 Kwh/day in winter when you only design and size the battery for 1 Kwh/day. In practice the only time you would ever reach a C/4 charge rate is for those poor suckers in the north where winter insolation gets to 2 hours or less. For example in in Seattle for a 1 Kwh/day battery system @ 12 volts requires a 400 AH battery and a 1200 watt solar panel pumping 100 amps. Take that same requirement to Tuscon you still need a 12 volt 400 AH battery but only a 400 watt panel pushing 33 amps. In Seattle you are forced to use a much more expensive shorter life AGM battery, and in Tuscon a much less expensive longer lasting FLA.

But back to your statement. For AGM you only want a 2-stage charging algorithm of Absorb and Float. Absorb and Float are constant voltage with current taper. You would set the ABSORB voltage set point to just below the GASSING VOLTAGE say 14.38 volts, and Float to 13.6 volts. So let's say the battery is 30% DOD. Morning rolls around. full sun hits the panels and battery demands charged with its voltage sitting down around 12.3 volts. Charge controller turns full ON and delivers full current that the panels can deliver and will continue to do so until the voltage of the battery comes up to about the 14.38 set point. Once it hets 14.38 volts the current tapers off but the voltage never goes above 14.38 volts. The current finally tapers down to say 3% then switches to FLOAT. So the point here is, the C rate is not important. It can be C/20 or 5 C. As long as the charge current does not exceed the maximum manufacture charge rate, there should be no problem as you never go above the GASSING VOLTAGE. Now this assumes the battery is good operating condition.

Now take note the most common failure point in AGM batteries is a shorted cell, and a shorted cell has ZERO or close to ZERO volts. Your charge does not know when that happens. All it can do is tell the battery voltage and is looking for say 14.4 volts. But an AGM with a shorted cell fully charge voltage is now 12 volts, and 14.4 is well above the GASSING VOLTAGE and will go into THERMAL RUNAWAY. Kaboom

[PNjunction]

In practice the only time you would ever reach a C/4 charge rate is for those poor suckers in the north where winter insolation gets to 2 hours or less. For example in in Seattle for a 1 Kwh/day battery system @ 12 volts requires a 400 AH battery and a 1200 watt solar panel pumping 100 amps.

Or guys like me that go camping that despite good solar insolation, may be time-limited due to the environment, the need to get a move-on to another site, or want to explore, but need to secure the system to deter theft. I may not be grid-tie, or use 2kw of power, and even though one may classify them as 12v toys, they are still following the same rules as the larger systems do for the most part, and are a valid application of solar. Doing it correctly here is good training if one wants to take it to the higher levels.

I will add one thing to what you said that makes this kind of current unrealistic for the larger systems is also the need to make sure that all the wiring infrastructure can handle it as well.

So the point here is, the C rate is not important. It can be C/20 or 5 C. As long as the charge current does not exceed the maximum manufacture charge rate, there should be no problem as you never go above the GASSING VOLTAGE. Now this assumes the battery is good operating condition.

No problem with that as I've found out. My issue is that manufacturers may be very conservatively limiting the rate in their documentation, possibly for liability reasons more so than engineering reasons. I see words of "can", "may" cause thermal runaway etc, yet in my testing, I found not even a hint of it up to 1C- of course we are talking about these ups-style agm's with well-designed chargers / controllers. I love my superior Odysseys for sure, but these little general purpose agm's are going to be used on occasion with plenty of panel to take advantage of short insolation. With small systems, I have that luxury and plan to use it.

I found this very interesting just today: In the circa 2000 Yuasa NP Application Manual, while they "recommend" 0.25C, there is a max rate of 1C for 2-stage constant-voltage charging, which they say is the most preferred method. This max limit of 1C is in parenthesis in that document under that section. (it is a direct link to a pdf, so I won't post it as a direct link, but it comes up easily enough linked through google). Of course they list the proper voltages desired to do it most efficiently. BUT dig this:

The circa 2006 Enersys Genesis NP line - not the "tppl purelead" type, but the gp type (Enersys now owns Yuasa I believe) has nearly the exact same model numbers and application manual - yet here, that line showing a 1C max has been removed. I can't believe that the new Genesis NP is a less capable product than the older Yuasa! I tend to believe this is more for liability than anything else, but I am not a lawyer. And again, I am probably wrong, but think that some other manufacturers are just basing their own limits on what the big-boys say to do in their docs.

The helpful hints section about building a charger that has current limiting, short protection, reverse polarity etc only tightens the brim of my conspiracy-theory hat that this might be a liability CYA move for the battery due to it's ultra basic common-sense that any engineer would be a fool to ignore.

Late Update: As a consumer, I also have to wonder how much of this is due to trying to market those "thin-plate-pure-lead" types. The Genesis XE and EP appear to be Odysseys in ups-style casings. In their excellent application manual for the XE/EP, they point out that "other manufacturers" may only limit their inrush to 0.25C(10). Like their own Genesis NP line now. I like the "tppl" agm's for sure, yet their admission in the application manual that battery charging specs are dynamic and not static lead me to believe that as long as I follow the Ampere-Hour-Law, I might be ok taking it to 1C for the general purpose types under normal conditions of charge - as long as battery / charging quality is good to start with. Yet I'm sure the sales guys don't want me using anything but TPPL if I take it slightly above 0.25C.

Shorted cell? Sure, but that is a problem under normal conditions anyway.

Again for lurkers - these are only MY observations, and I don't recommend going beyond manufacturer's specifications.

[PNjunction]

You have to reach the Gassing Voltage of about 2.39 volts per cell before any gassing occurs. This is why voltage regulation is mission critical when charging VRLA battery types. This is why monitoring the temperature of VRLA batteries is important to monitor to prevent thermal runaway. In the event a cell fails shorted (common failure mode), the voltage drops and fools the charger into thinking the battery needs more charge current and this causes the remaining individual cell voltages to rise above the gassing point and where heat begins to build up causing the voltage to drop even lower which causes even more current and heat. The effect is regenerative feedback and called Thermal Runaway. If left unchecked can cause a violent explosion and fire.
.

I had to read this again. And yet again before it sunk in.

Despite being able to find instances of where I could go beyond 0.3C with the general-purpose agm's, and additional real-world testing showed no problem with properly operating solar controllers and chargers going up to 1C, (basically being under the gassing voltage during bulk, and current naturally ramping down to .3C or lower once it reached absorb), all it would take is a shorted cell. So far, I've been lucky.

I don't like depending on luck to be safe.

For my low solar-insolation / high charge current needs, it looks like I'll be making the Odyssey's which are designed at the outset to go beyond 0.3C my safest bet.

[inetdog]

I had to read this again. And yet again before it sunk in.

Despite being able to find instances of where I could go beyond 0.3C, and additional real-world testing showed no problem with properly operating solar controllers and chargers going up to 1C, (basically being under the gassing voltage during bulk, and current naturally ramping down to .3C or lower once it reached absorb), all it would take is a shorted cell. So far, I've been lucky.

I don't like depending on luck to be safe.

I don't know how an Odyssey or other high-quality agm's that are purposely built to go beyond .3C will react with a shorted cell, but it must certainly be safer than with one of these general-purpose types.

Short of a computerized system of voltage history monitoring to alert you to a shorted cell, your best protection against disaster is constant automatic battery temperature monitoring. It may not save you from electrolyte venting, but it will at least avoid a full china syndrome meltdown. (The battery enthusiasts with high energy density Li-ion cells refer a lot to "venting with flame.")

[PNjunction]

Below-spec current on Odyssey not optimal but ok

On a related note about charge currents for the Odyssey ...

Odyssey says that the minimum bulk charge current for their tppl batteries is .4C - but I had always wondered if going lower would be doing harm. It isn't always perfectly sunny during my charge periods to get the max out of my panels.

Apparently the Odysseys have a denser oxide, and the .4C minimum is needed to be effective - BUT that is if you go further than a 50% DOD. So you can use a lower bulk current, but it really won't be very efficient at all when deeply discharged beyond 50% DOD. I found this interesting information in another forum direct from Enersys:

http://www.bmwmoa.org/forum/showthread.php?t=42030&page=10

Even though I don't plan on going beyond 50% DOD, I'm still going to hit them as hard as I can. But it is good to know that no harm from lower current is happening (other than being inefficient).

[PNjunction]

I'm going beyond 15 volts - warranty immediately void!

I guess I'm straying a bit from a pure solar application - but in the end my testing is to see if I might want to use a custom charge controller that goes to 14.8 volts. Temp compensated and thermal sensor for detection of thermal runaway.

The quick rundown is that I'm inspired by the testing of Nigel Calder, and also by Joel Wisman's extensive experience with the Odysseys, where 15v might be a simplification, given that the Odyssey's own chargers (Sure looks like a Schumacher charger) also go above 15v under certain conditions:

http://advrider.com/forums/showthread.php?t=765630&page=6

My test setup now includes an Odyssey PC-525 and PC-625, along with a Sears Diehard Platinum P3 (an Odyssey inside), a Sears Diehard Platinum charger 71227 model (looks like schumacher as well), and also a Schumacher SSC-1500A charger. Neither one of these chargers are on Odyssey's approved list. Quick rundown - the Sears charger runs up to 14.9 volts at absorb, and ramps down slowly to 14.8 before float. The Schumacher runs all the way up to 15.35 at absorb, and then, goes into a cyclic 13.45 - 16+ volt operation before float. As measured at the battery terminals on my Fluke 87V.

Anyway, I don't want to turn this into a charger thread, but I am glad to report that the Odysseys seemed to have survived multiple 15-16+ volt specialized operations without any complaint, and my resting OCV has improved, especially on my 2 year old 525 that never had a charge before I got it. I don't plan on using it every day - that's what my panels are for!

Obviously my warranty is totally void, and I'm totally respectful of thermal runaway / gassing and testing in a safe and sane environment. I'm just testing this on my own, so again, I do NOT recommend anyone go beyond the manufacturers limits like I have.

[PNjunction]

Quick note: the methodology I'm using with the Schumacher ssc-1500A charger with the PC-535 / 625's are after a 25% discharge, recharge them with the 10amp rate set for agm (being cautious limiting it to a little below the 1C rate just for now) Once the cyclic operations start (panel indicates full charge, rate leds go out but cycling continues), I reset it by changing the rate to 2amps where it continues again for awhile until it starts cycling again. I don't have an officially approved Odyssey Ultimizer Omax-6A-1b to compare with.

The 535 was received after a 2-year manufacturing date, and had a resting voltage of 12.43 out of the box. Solar charging with my pwm controller at 14.4 over many days at 8amps charge never got the 12-hour resting soc above 12.93. Load testing at 1 - 2 amps seemed to follow the conventions listed in their manual. I was pretty happy but wanted to do better. Resting voltages after charging as above nets me about 13.05 v.

Continued testing will tell if these short-term gains will result in expensive lumps of lead.