Mx60 Absorb And Float Limits

System

The mx60 absorb and float default settings (for a 24 volt system) are 28.8 and 27.2, respectively.
A friend of mine recommends to RISE those limits, in order to get more reserve capacity in my batteries.
Is it wise to rise the limits? If so, what settings do you recommend?

My system: 6 kyoceras 130 (wired at 36v); mx60; 4 exide batteries (24v); exceltech 1100 inverter

crewzer

Re: Mx60 Absorb And Float Limits

Amilkar,

A higher absorb voltage (ref 77 F / 25 C) might be warranted for some flooded-cell batteries. However, a lower voltage may be required for AGM batteries, and is definitely required for gel batteries.

Can you tell us more about the batteries (make, model, type, etc.)?

More later,
Jim / crewzer

System2

Re: Mx60 Absorb And Float Limits

Crewzer:

Four Exide golf cart batteries, flooded lead acid, 6 volts each, in series, 210 amp each.

I have been using them for just 3 months now, and so far they have worked perfectly, except that I feel they need more reserve capacity

crewzer

Re: Mx60 Absorb And Float Limits

Amilkar,

For your generic GC2 batteries, I'd recommend you following Trojan Battery's guidelines. Here's a link to their manual:

http://www.trojanbattery.com/Tech-Support/BatteryMaintenance.aspx

I'm not sure that I understand what you mean by "need more reserve capacity".

HTH,
Jim / crewzer

System2

Re: Mx60 Absorb And Float Limits

Crewzer:

Thanks.
I am not sure, either.
What I was trying to say is that, perhaps, if I raise the absorb and float limits, more energy would be put into the batteries and, thus, more watts would be available for the night period. Since my inverter's manual says that the exeltech 1100 works happyly with 27.6 volts, and at night the battery voltage is NEVER so high, I thought that raising those limits could keep the voltage AT LEAST above 26 when the mx60 is not charging. (Keep in mind that when the mx60 is charging and reads "27.9", for example, the actual voltage of the batteries is not 27.9, but less, since that reading takes into account the current that is been pump into the batteries, not only the pure voltage of them.)

Hope you understand my poor english.

mike95490

Re: Mx60 Absorb And Float Limits

The specific chemistry (Lead, calcium, tin, copper, antinomy etc...) that the battery manufacturer has chosen, determines the exact voltage output. It's the reaction of the metal alloy and the acid, that creates the voltage.

Charging at a higher than needed voltage, only bubbles the electrolyte faster, requiring you to add more makeup distilled water (when the voltage is too high, the electrolyte breaks down via electrolysis into oxygen and hydrogen.) This is done one a month, only with flooded cell batteries, in what is called an "Equalizing Charge" or "Equalization", with the thought that any low cells in the string, will eventually be fully charged, and that the bubbles, stir and mix the acid in the batteries, preventing stratifaction.

Sometimes, new batteries need 20 or so, charge and discharge cycles to get to full capacity. Running an extra "equalize" cycle should not hurt them, your charger should have a way to initiate an Equalize Cycle manually. It should have an automatic timer to do one monthly.

boB

Re: Mx60 Absorb And Float Limits

Raise the ABSORB voltage as your friend says...

Check the water level more often but you won't have to equalize as often.

boB

crewzer

Re: Mx60 Absorb And Float Limits

Amilkar,

OK… now I understand. There are considerable differences between battery voltages when the battery bank is being charged, when it’s at rest, and when it’s under load. This is normal.

While being charged, your “24 V” battery voltage will rise to about 29.6 V. However, once the charger is removed and there are no loads, the battery voltage “at rest” will gradually drop to ~25.4 V after several hours. Once loaded, the battery voltage will immediately drop, and will continue to drop until the load is removed, at which point the battery voltage will recover a bit.

These false high and low voltages are called “surface charge”, and they’re the result of thin layers of high (or low) specific gravity electrolyte in direct contact with the battery plates. These layers dissipate over time once the charging source or loads have been removed.

In short, if you’re going to use battery voltage as a means of determining battery state-of-charge (SOC), you’ll need to do take the voltage measure several hours after all charging sources and loads have been removed.

I thought that raising those limits could keep the voltage AT LEAST above 26 when the mx60 is not charging

This won't happen. The batteries will read ~25.4 V when they're full, the MX60 is not charging, there's no load, and they're rested. The Trojan reference I provided includes more information as well as a voltage vs. SOC chart.

HTH,
Jim / crewzer

niel

Re: Mx60 Absorb And Float Limits

amilkar,
i think we can summarize this into what you refered to as reserve capacity, was only the suface charge that will slowly retreat back to its resting voltage no matter what you do. this means do fully charge your batteries, but DO NOT keep trying to get this surface charge to stay or go higher or you could overcharge the batteries and boil out the electrolyte with possibly ruining them. the inverter will operate just fine with those normal battery voltages as it was designed to.

System2

Re: Mx60 Absorb And Float Limits

OK.

Thanks to all.

One final question: Am I to understand that the "real" voltage of my batteries (ignoring the "surface charge" mentioned) will never be higher than 25.4?

crewzer

Re: Mx60 Absorb And Float Limits

Am I to understand that the "real" voltage of my batteries (ignoring the "surface charge" mentioned) will never be higher than 25.4?

Amilkar,

I don't know about "never", but you'll certainly rarely see an "at rest" voltage of greater than ~25.46 V from your healthy and well-maintained flooded-cell deep-cycle lead-acid batteries in your environment. Any higher reading should be a small and short-term difference.

"Full" voltages for VRLA (AGM and gel) batteries at rest are a bit higher.

Regards,
Jim / crewzer

System2

Re: Mx60 Absorb And Float Limits

Thanks again, all the information is appreciated.