Odyssey AGM and solar experience?

[PNjunction]

For experimentation, I just picked up a small Odyssey PC535 agm (around 13-14ah) to pump 8a into with my panels. Odyssey specs .4C as the minimum here!

I knew from the beginning that this is the wrong application, and my pwm charge controller method immediately voids the warranty, but I wanted to see what going well beyond the typical C/4 rate for THIS agm felt like. It felt GOOD!

I can't say what will happen now, since I am starting off on the wrong foot - the Odyssey I picked up on a deal was already new-old-stock at 2 years old, and only had 12.43 volts open-circuit. Someday I'll get enough to doing it right with an RE-designed battery, but for now I'll see if I only get 50 cycles out of this thing.

I'm just wondering if anyone else has put solar to an Odyssey and what their experience was.

[Sunking]

Well I cannot say I have used them in Solar Applications, but no worries mate as it will be hard to do any harm to them. The only thing to remember with them is do not apply a voltage greater than 15 volts. 14.1 to 14.7 is the sweet spot depending on Temperature.

The battery line you have is a dual purpose hybrid made for both Cranking and Cycling. It is a direct competitor to Optima battery line up. They have very low internal resistances which is a good thing if you have a 20 AH battery trying to power a 200 watt inverter. The CCA on you model is 200 amps out of a 14 AH battery. That means when fully charged the internal resistance is around [12.8 volt - 7.1 volt] / 200 amps = .0285 Ohms. So that battery can deliver 35 amps with only 1 volt drop at the terminals. That is a heck of a current for a little 14 AH battery in excess of 2C.

Do not worry about pumping 8 amps into the battery, as long as it is cool and you stay below 15 volts you can pump 70 amps into it. Heck you can draw as much as 535 amps for 5 seconds out of it if you want. The battery is designed as a Motorcycle starting battery, and popular with the FIGHTING ROBOT crowds or anyone who needs a lot of current from a small package.

As for solar, it will work, just not a lot of cycle life, but you already know that. Hopefully someday we will get an affordable battery with 5C rates and 10,000 cycles.

[PNjunction]

Well, even only after 5 cycles, I can say i LOVE hammering agm's that can take it! I'll cycle it 15 or more times before I try to determine what the capacity really is after having sat around for 2 years with no charge - so nothing definitive yet on how much harm that did.

What I'm trying to plan for is winter - even here in SoCal where the solar insolation is not too shabby, I am often hit by intermittent high-altitude cloud cover that tends to linger right in the middle of the good insolation hours. When the sun does finally peek through, I'm dealing with a fast moving shadows from obstructions that are also long, limiting my portable ground mounting. What was good before can turn ugly in 15 minutes and ruin my um, wait for it - daily solar harvest. Frustrating when it is relatively bright outside. One lingering cloud or long shadow can ruin my day.

Even though this little Odyssey is a test/trainer, from what I've seen so far, I KNOW I'll be picking up a Sun-Xtender and hammering that as well with a bit more panel. This little thing is built like a tank, was packaged really well, and I love the docs. Too bad Enersys doesn't make Sun Xtenders in anything smaller than 35ah, so this Odyssey will have to do for now. I'm hooked now. I had to laugh when I stood back and saw 145 watts of total panel power going through my morningstar CC and hitting up a 13ah battery. Wild!

[PNjunction]

2 year old Odyssey is promising

Well, after only 8 cycles, the 2 year old 13ah Odyssey is living up to their storage claim.

I pulled 1.2 amps from it for 6.5 hours, and after a 6 hour waiting period of no charge/load, it measured 12.17v ocv - pretty much what is in the manual on their second chart for just under the 50% OCV status.

I used my Fluke 87V and a watts-up inline metering gadget to measure. While not lab-accurate, I do feel that yes indeed, an Odyssey can survive 2 years of no charge neglect - provided it is cool (and as long as it doesn't go below 12.0v first - mine came purchased at 12.43v)

Putting 8 amps surge from my panels into the PWM charge controller set for 14.4v (temp compensated) is working ok. To make sure I get a good charge for this initial analysis, I made sure that I spent some extra time in the sun getting the current down to about 150ma or so before I lost my solar insolation for the day. So while it only took about about 60 minutes to get to absorb, I spent another 4-5 hours to make sure it was really charged well after each cycle. I probably won't have that luxury in the winter.

I was so happy / amazed at something living up to it's promises, that I bought a second Odyssey - the PC 625 - which is cheaper yet has more storage capacity. Thing is, I gotta' stop buying these things because it is eating into my Sun Xtender budget. Until that day comes, I'll be keeping tabs on the life-cycle as I don't plan on getting too close to 50% DOD anyway.

[PNjunction]

Minimum current requirement is very true

Sorry to get so bloggy, but this may be important for those trying to duplicate my efforts...

Discovered what the engineers meant by needing a minimum of .4C to be effective.

With only a single 15watt panel attached to the 18ah PC625 as a test, 1amp will flow into the battery, but you'll never get a terminal voltage above 13.7 volts. All the meanwhile, that 1 amp (as measured on my Fluke) is going in doing something else - heat perhaps?

Found this out accidentally: I totally discharged it by unintentionally leaving my load on overnight, waking to only 11.2 volts ocv measured after a 6 hour rest. Pumped my total of 8 amps from the panel into it, and it recovered just fine in a few hours. Way to go Odyssey!

Then wanted to see if any of my chargers would improve upon a fully charged battery when I ran out of sun. Results:

Noco Genius 7.2amp charger: immediately ramps up to 14.7 volts and goes into trickle.
Noco Genius 3.5 amp charger: same thing as above.
Noco Genius .9 amp charger (3500 in low power mode). STRUGGLES to reach 13.7 volts where it sits, and continues to pump 900ma into it forever just like the undersized panel test did. Yikes.

It doesn't appear to be sulfation since I can consistently measure specified capacity loads after all this was over...

This poses a dilemna for solar: When the solar insolation gets so bad (clouds, haze etc) that there is hardly a shadow, my 8amps of panel current usually turns into 1/10th of it's capabilites. Yup - about 800 milliamps. But with the Odyssey, instead of just slow charging, it is now just heating things up. (I think). This can't be good.

Seems like I'll have to ensure that I have good solar insolation during the timeframe I'm charging them. While they do charge quickly with a lot of current, when there is little current to be had due to clouds or whatever, I may be just generating heat.

Why can't I just for once outsmart the engineers?

[Sunking]

Why can't I just for once outsmart the engineers?

It is not about outsmarting engineers, it is about the Law of Physics. Unlike man made laws, you cannot violate the Law of Physics. For those who do not believe that next time you see a full moon out, get a running start and try to jump over it.

[PNjunction]

Whoa - you guys know I'm joking right? I must have struck a nerve..

I think all I have done here is verify what the engineers at EnerSys (Odyssey, Lifeline, Concorde, Sun Xtender, Genesis) had to say about minimum rates. I didn't find it in the Odyssey manual, but I did find it in the Lifeline and Sun Xtender manuals.

Essentially, when under the minimum current input level, you'll just cut down your cycle life, and as I've found when waaay too low, it is too inefficient to be practical.

For the Odyssey: .4C
For the Lifeline and Sun Xtender: .2C

So while I love playing solar with the Odyssey's, I kind of knew going in that it was the wrong application. The Lifeline or Sun Xtender would be the best bet.

Even the ups-style Genesis NP tech manual was awesome, and answered a minimum current question asked in another thread for these types. (basically none, but I'd put my money on .15C as the minimum for practical use for the small general purpose types.)

[Sunking]

Whoa - you guys know I'm joking right? .

Of course I was throwing it back at you.

Just keep in mind not all AGM batteries have a minimum limit. Obviously common sense should tell any designer anything below C/20 is useless and impractical. But when you see a minimum of like C/5 to C/2 or very high charge rates on AGM is because they cannot be Equalized to to dissolve lead sulfate crystals that form on the plates. So they recommend high charge rates to keep lead sulfate from building up in the first place. You can get away with that on AGM because of their low internal resistance and sealed jars which recombine the Hydrogen and Oxygen gasses that result from high charge rates. You cannot do that with flooded types.

Floodeg and AGM's have their plus and minuses. Your application will dictate which to use. Without going into a lot of detail generally you would prefer Flooded because they can take quite a bit of abuse and last quite a bit longer with proper care.

[inetdog]

But when you see a minimum of like C/5 to C/2 or very high charge rates on AGM is because they cannot be Equalized to to dissolve lead sulfate crystals that form on the plates. So they recommend high charge rates to keep lead sulfate from building up in the first place. You can get away with that on AGM because of their low internal resistance and sealed jars which recombine the Hydrogen and Oxygen gasses that result from high charge rates. You cannot do that with flooded types.

I would also imagine that the lower internal resistance, associated with higher plate surface area, allows them to accept a higher charge rate without gassing nearly as much in the process (as long as you stay below the cutoff voltage for that charge rate.) Is that correct?

The recombination would keep them from losing electrolyte due to overcharging as long as the pressure stays below the relief valve level. So no need to add water.

[PNjunction]

Once again, both of you guys are making the CFL inside my head light up....

You don't want to tickle agm's. For the longest time, as a consumer I thought that an agm's enhanced "charge acceptance" with it's low internal resistance meant low-current charge efficiency. NOT SO. There IS a minimum, and I think I saw a "knee" of performance with my totally undersized panel/charger test on the Odyssey. What the low internal resistance does is make the agm accept a much higher rate without wasting/damaging power as heat. In the case of the very small ups-style agm's, that's about 0.25C to 0.3C max. Higher quality agm batteries have much higher minimums, but they can also utilize much higher maximums, like C/5, C/2, or even C*4 for example, as long as you keep it within safe guidelines.

That commonly accepted C/20 rate seems ridiculous now (about 3 times too low at least for a cyclic minimum), unless all one wants to do is put in a superficial surface-charge, or maybe use that to "top off" or float the battery. At any level of decent discharge, it seems that C/20 will just slowly roast the battery since it is not enough to activate a chemical reaction properly.

The secondary benefit of using a higher charge rate, is a bit of a lessening of a need for EQ an an agm. Provided you start from a known good quality battery.

The third benefit I immediately see is that while you can get up to say 90% charged very quickly, as a solar hobbiest, that give you much more time to spend in the absorption phase on the back end! Typically in my 4-hour solar insolation day, I might have been lucky to just barely reach absorption. It would take another half-day or whole day (depending on conditions) to get down to a real float level! With my Odysseys charging up in 90 minutes or so, that leaves me 3 hours to spend in absorb because I'm hitting it hard initially to get up to absorb fast.

Looks to me that if you really want to take care of your agm's, it will cost you in panel capacity, BUT you will be treating your expensive batteries much nicer overall. Maybe the additional cost would even out with longer battery life ?

I'm hooked now on the more capable agm's, that's for sure.

[Sunking]

Well I have to blow a hole in your analogy.

Lets' pretend you need 500 watt hours per day, 12 volt system, 3 Sun Hour winter insolation.

Panel wattage = 250 watts
MPPT Charge = 20 amps
12 Volt Battery = 200 AH

So if you insist on using say a .3 charge current what has to happen?

Well what it boils down to is spend a whole lot more money because it would require 750 watt panel and 60 amp charge controller.

[PNjunction]

Wow - thanks for the reality-check! Looks like the only sizes I'll be hammering with large currents from solar are my motorcycle-sized batteries. It's a heck of a lot of fun though.

[Sunking]

Wow - thanks for the reality-check! Looks like the only sizes I'll be hammering with large currents from solar are my motorcycle-sized batteries. It's a heck of a lot of fun though.

Now you understand why I am not keen on using AGM's. They do have their place, but an expensive option.

[PNjunction]

Solar AGM confusion!

Wow - having a mental breakdown trying to figure this out - all the while showing my ignorance.

The question is: While a solar panel is considered a current source, can it be considered a CONSTANT current source in regards to solar panel charging? Even though the battery is doing the regulating with my little pwm cc setup?

Reason I ask -

A) I'm having no problems charging up my Odyssey agm's with a charger. I'm having no problem charging them via my limited 8amps of solar. Yet when I think about it, the application here is for vehicle charging, ie Constant - Voltage from an alternator or outboard charger.

B) While looking at the application manual for a similar Enersys Genesis XE TPPL-type (not the general purpose Yuasa rebadge), it has much the same specs. While not created specifically for SLI, the XE is shown to be ok for solar. BUT the application manual goes into MUCH more detail on the differences between Constant-Voltage vs Constant-Current charging. What raises the hair on my head is that under Constant-Current, the charge limit is 0.33C, NOT an unlimited rate. You can see the application manual for the Genesis XE here:

http://www.enersysreservepower.com/productDocuments.asp?id=100&brandID=3

Given the similarities between the Odyssey and the Genesis XE (both Enersys), I'm wondering just which direction to obey when using solar - unlimited inrush current, OR a 0.33C max for constant-current as per the Genesis manual? Odyssey doesn't go into constant-current much of course because the application is mainly directed at vehicle installs.

Ack! I'm freaking right now having put them through a handful of solar charge cycles already...

[Sunking]

The question is: While a solar panel is considered a current source, can it be considered a CONSTANT current source in regards to solar panel charging?

No it is a current source of unknown capacity that varies with the light input.

I'm freaking right now having put them through a handful of solar charge cycles already...

You just do not undertand the difference between Constant Current and Constant Voltage charging. Fact is they are both very similar, only difference is the voltage set points.

Let's start with Constant Voltage method first. In a 4 stage battery charger Absorb, Float, and Equalize are all Constant Voltage algorithm's. For example if I use a rectifier for a Telephone Office battery system is just a fancy name for a 2 stage battery charger which has 2 modes of Float and Equalize. So let's say it is a 100 amp 48 volt rectifier set in the Float mode connected to a deeply discharged 1000 AH battery. The Float voltage is set to 54 volts. When you initially connect the rectifier to the battery the rectifier goes into Current Limit of its rated capacity of 100 amps, and stays there until the battery voltage reaches the Set Point of 54 volts. That will take a few hours. When the set point is reached the current will taper off from 100 amps and gradually go to almost 0 amps when the battery becomes fully charged. The rectifier will will now hold the battery at 54 volts indefinitely holding the battery at 100% SOC. If a load is turned on, the rectifier supplies the power not the battery as long as the load does not demand more than 100 amps. The battery remains 100% fully charged up and does nothing and remains in STAND BY until a power failure. This is how all Telecom Battery Plants and UPS system operate. So ho wdid the rectifier operate? It operated as a constant current source until it reached the set point.

OK now let's discuss the contant current mode which in a 3 or 4 stage charger is the BULK Mode or Constant Current mode. Same 48 volt battery of 1000 AH, except this time we use a 3 Stage Battery Charger which is a fancy name for a Rectifier that has 3 voltage settings of Bulk, Absorb, and Float. Battery is severely discharged and we have the BULK voltage setting to 57.6 volts. The charger supplies a constant current of 100 amps until the battery voltage reaches 57.6 volts. At that point the Bulk charge is terminated, and the charger switches to Absorb with a set point to 57.8 volts. Initially when it goes to 57.8 volts 100 amps are supplied but the battery voltage raise very quickly to 57.8 volts and the current begins to taper off. The voltage is now regulated to 57.8 a Constant Voltage and the current will taper off toward 0 amps and the battery charges up to the new voltage. We keep this voltage applied until the current tapers off to about 1 to 3% at which point the Absord cycle is terminated and switches to Float mode. In Float mode the voltage is lowered to 54 volts, and all power demand now comes from the Battery charger exactly like above. The battery just sets there in Standby until either the power demands exceeds the charger capacity or there is a power failure.

So what is the difference between a Float Constant Voltage charger and a 3 stage charger? One is faster than the other. Float chargers can take up to 24 to 48 hours if properly sized. A 3-Stage charger can do it in 6 to 10 hours if properly sized. Well in the case of AGM if you use a C/3 charge rate, 3 to 5 hours.