(un)Realistic AGM specifications?

liamg

Hello,

I'm in the market for a new battery bank (48V/250Ah) and I've just discovered an AGM model (Hoppecke sun.power VR M, 6V/250Ah block) having some unrealistic(?) parameter: 2000 cycles @ 60% DOD. The price is pretty decent, too.

The manufacturer is a very reputable one thus I tend to believe those specifications.

Anyway, I didn't find any similar product on the competitor's portfolio.

Is there any proprietary breakthrough technology involved? Does anyone have any experience with this battery model?

Thank you in advance for any piece of information.

Marc Kurth

Yes, the company has a good reputation. It is my understanding that they rate their battery life cycles based on a very high discharge rate. By putting a big load on the battery and draining it to only 1.8v/cell, they get a higher number - resulting in fewer amp-hours being drawn out per cycle. BCI standards call for a high rate, but what number do they use?

Note that in their capacity tables, the amp hour rating for a 100 hour rate is actually lower than the 50 hour rate. I have never seen another battery that does this. For other deep cycle batteries, the slower you draw the power, the more total AH you get.

Buy a set and let us know what you think!

mcgivor

Whilst doing research, one of the batteries I was looking into was Hoppecke, although the flooded opzs variety which had an impressive cycle claim, even higher than the block AGM, after reading through the installation manual, there claims are based on a 20°C or 68°F battery temperature, which would mean a climate controllled environment, for most operators. The claim for the mono block type are more than likely based on these temperatures, for me personally the temperatures are unrealistic, I experience 30°C regularly and being off grid a controlled environment is unrealistic, at this point in time. At double the cost versus golf cart batteries, I went with tthe latter, if however ones environmental conditions are favorable, ie. a cold climate, perhaps they could perform the 2000 cycles, the 2V AGM  cells have a 2500 cycles rating at 60% discharge, going much higher at lower discharge rates.

liamg

This AGM block model is a top selling one in Germany, as a reserve power (during nighttime) for the ongrid installations.

They are usually sold as a storage rack (including a metallic case, connections and a fuse) to be mounted in a garage/shed hence I doubt the cycle specifications are rated at 20°C. Actually, I've read in an operating instruction manual that the recommended room temperature should be in the 10-30°C range with a maximum allowable of 40°C or so.

Anyway, it's still hard for me to choose between these AGMs and an equivalent traction tubular flooded block/cells, the price being almost the same for identical capacity.

The AGM advantage (beside no maintenance) is the increased charging efficiency and the greater maximum charging current, which are very useful for my offgrid installation.

Anyway, I'm still afraid of a charger fault leading to an uncontrolled overcharge aka AGM battery sure(?) death.

What will you recommend between the two options? Am I too paranoid?!

liamg

Marc Kurth said:

Note that in their capacity tables, the amp hour rating for a 100 hour rate is actually lower than the 50 hour rate. I have never seen another battery that does this. For other deep cycle batteries, the slower you draw the power, the more total AH you get.

Actually, the 100 hour rating is referenced to 1.85V/cell (discharge limit) whilst the 50 hour rating is referenced to 1.80V/cell (that's why the former capacity looks higher). 

@mcgivor:

You were right: all those specifications are based on a 20°C temperature (Germany average climate, maybe?). That's a quote from the operating instructions manual:

The recommended operating temperature range for lead-acid batteries is between 10 °C and 30 °C. The technical specification applies for the nominal temperature of 20 °C. The ideal operating temperature range is 20 °C ± 5 K. Higher temperatures decrease the service life (a temperature increase of 10 °C halves the calendar service life). Lower temperatures reduce the available capacity. The limit temperature of 55°C must not be exceeded. Continuous operating temperatures of 45 °C or more must be avoided.

The specifications are still good for a nominal temperature of 25 °C (1500 cycles/60% DOD) but, then again, should I better go for the tubular flooded (traction) ones?

mcgivor

If I were you, which I'm not, flooded would be the preferred route to go, maintenance not withstanding, flooded are more forgiving, being easier to understand, the ability to measure the state of charge with a hydrometer is an advantage, something that can't be done with AGM, the chemistry is basically the same, but easier to understand with flooded, the history is over 100 years old so better understood. Hoppecke flooded cells are more impressive than the AGM, in terms of cycles, the added advantage is a series battery can be made up of the required cells of a given capacity, rather than going parrallel. Obviously discharging to 60% on a regular basis is not the best thing to do, a shallower discharge will render more cycles, 8000 cycles  at 20% for the flooded is outstanding, even if one could get 6000, that is still impressive. Food for thought.

liamg

Thanks for your advices! I'm currently a "flooded" user but I thought I could give AGM a chance (after all, it was supposed to be an enhanced flooded technology).

I was not looking for the 60% DOD neither, it was for reference purpose only. Still, AGM/gel has some advantages over flooded technology: increased charging efficiency and higher charging/discharging currents (as the chemistry take place over the whole plate surface simultaneously).

If no one votes for the AGM, I'll go with the FLA then. I only have few days left to decide..   

Estragon

It comes down to the application and personal preference. As well as the advantages you noted, AGMs also don't generally vent gas, can be installed multiple orientations without spilling, and have lower self-discharge.

For me, none of the advantages except low self discharge are of much use to me for my main banks, and the ability to monitor SGs is important to me, so I use flooded. I do use AGM for other applications though.

liamg

Looks like I need all those advantages (off-grid installation, daily cycling) but being unable to restore the electrolyte level (in case of an accidental overcharging) is a giant NO.

Btw, speaking of rated temperature: I've seen some manufacturers referencing the battery parameters to room temperature (20°C, by example) while others using the electrolyte temperature (usually, 10°C higher than room temperature) as a reference.

That's it, 20°C (room temperature) or 30°C (electrolyte temperature) it's actually the same thing.

Estragon

My electrolyte only gets 3°C or so warmer than ambient during normal daily cycling, and only in the last hour or so of charging. Most of the time it's about ambient temp.

liamg

Oops.. you're right. I was under the impression of the manufacturer (biased) operating instructions.

Well, then it's a big difference between 20°C and 30°C rated life cycles.

I'm very disappointed that such a reputable manufacturer make use of these cheap marketing tricks to "enhance" his product specifications.

I think I"ll go with a flooded tubular traction battery then. At least, its life cycle (1200 at 80% DOD) is more realistically rated at 30°C.

Many thanks for keeping an eye on my further investment..