Odyssey AGM and solar experience?

[PNjunction]

Whoa! Thanks inetdog - I overlooked that.

In fact, I'm off to get some temp probes and perhaps an IR meter right now! You just saved my butt, and most likely my house.

[inetdog]

That makes it much clearer to me now. Thanks!

Batteries are gulping down 8amps solar as we speak.

While freaking out, I ran across an interesting page referencing Linden's Battery-Bible, (which was graciously pointed to in another thread on SPT - thanks again Sunking!) in regards to fast charging sealed VRLA's, that kind of put my mind at ease - basically stating that a properly functioning charger that doesn't go haywire with super high voltages should be safe:

http://www.powerstream.com/SLA-fast-charge.htm

Believe me, I'm not trying to sand-bag any thread here with later web cross-references!

Before any reader jumps the gun, I do NOT advocate going beyond a manufacturer's specified ratings.

Warning: That article does not mention the importance of monitoring the battery temperature during any fast charging process.

1. The desired fixed voltage, if you use one with a current-limited charger, is dependent on the battery temperature. Very hot or very cold batteries require different (temperature compensated) voltage settings.
2. If you do not monitor the battery temperature, you risk thermal runaway, in which the internal battery voltage goes down as temperature increases and therefore either the current increases or you continue charging after you reach full charge (which heats the battery even faster and causes it to vent and expire.

For fast charging (above the guaranteed-safe-reabsorbtion-rate current) you have to monitor not just the ambient temperature as most controllers do, but the temperature of the batteries themselves using a remote temperature probe attached to the charger.

If it is a series string, monitor the battery which has the least cooling, but also check the others periodically. Do not leave any battery on fast charge (above the Manufacturer's limit, or even at it the first time through) unattended.

"Stay cool, my friends!"

[PNjunction]

That makes it much clearer to me now. Thanks!

Batteries are gulping down 8amps solar as we speak.

While freaking out, I ran across an interesting page referencing Linden's Battery-Bible, (which was graciously pointed to in another thread on SPT - thanks again Sunking!) in regards to fast charging sealed VRLA's, that kind of put my mind at ease - basically stating that a properly functioning charger that doesn't go haywire with super high voltages should be safe:

http://www.powerstream.com/SLA-fast-charge.htm

Believe me, I'm not trying to sand-bag any thread here with later web cross-references!

Before any reader jumps the gun, I do NOT advocate going beyond a manufacturer's specified ratings.

[Sunking]

So for a properly configured charging system of either kind, the end voltage / Float voltage will be exactly the same (for a particular battery type)?

Exactly the same.

How does the fact that solar PV is only available for a limited number of hours at a time come into the picture?

Solar power is extremely extremely limited and you need the fastest charging algorithm to make the best use of the short time you have in a day. Time is not a problem from commercial power sources.

What happens if you are still in the first Stage when the insolation falls off? (With or without additional load on the battery before the next day comes around?)

You know the answer to that. Your battery sits less tan 100% charged up which is not a good thing.

[inetdog]

.... Constant Current and Constant Voltage charging. Fact is they are both very similar, only difference is the voltage set points.

So for a properly configured charging system of either kind, the end voltage / Float voltage will be exactly the same (for a particular battery type)?
How does the fact that solar PV is only available for a limited number of hours at a time come into the picture?
What happens if you are still in the first Stage when the insolation falls off? (With or without additional load on the battery before the next day comes around?)

[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.

[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]

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]

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]

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]

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.

[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.

[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.

[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]

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.