Lead acid end amps

mountainman

In winter What are the consequences of a daily  extended absorb and end amps less than 1℅

Estragon

Assuming flooded and Vabs high enough for some gassing, I would expect some extra water loss, heating, and maybe some extra grid corrosion?

If not temp compensated and the bank is cold though, summer absorb voltage may not be high enough to gas.

Marc Kurth

mountainman said:

In winter What are the consequences of a daily  extended absorb and end amps less than 1℅

Much will depend upon how long the "extended absorb" time is. For many PV systems, excessive absorb time is not an option in winter. End amps can be specific to the manuacturers particular design, so this is best ansered by them. 

mountainman

I have tried to over size my system
With an average 800 watt hour daily usage. And Nearly 800 watts of pv.
And over 4 Dec sun hours
Except for several over cast days.
charging doesn't seem to be a problem.
Was wondering how bad over charging 
Might be for the batteries.
By 10:30 I'm usually at 1℅
by around noon with absorb set for 3 hours
Im seeing 2 amps on a  400 ah bank.

Marc Kurth

What are the manufacturer's recommendations for absorb parameters for your battery brand?

Remember that a little extra time in absorb and a good amount of time in float tends to help your batteries balance to each other. This, in turn, tends to help reduce the natural imbalance between strings. Keep it within reason, monitor your water consumption - and your batteries will serve you well

Undercharging is the enemy and you are avoiding it!

Marc

mountainman

Manufacturer says 2.58 volts per cell 
Hold for 2-4 hours then stop. 
Sg should be 1.275
Im not sure if the electronics in my old camper could take 15.5 volts?
So I set vabs at 2.48

mike95490

mountainman said:

Manufacturer says 2.58 volts per cell 
Hold for 2-4 hours then stop. 
Sg should be 1.275
Im not sure if the electronics in my old camper could take 15.5 volts?
So I set vabs at 2.48

With lower Vabs, you will need to increase the absorb time, so you really need to monitor the Sg.

mountainman

Does any gc battery manufacturer other than us battery.
Recommend a 15.5 daily charge
I thought that was eq volts.
I haven't equalized in 6 months
SG says  I haven't needed to.
And  i have read that eq is hard on Batteries. 
It was overcast yesterday.
Today was clear all day
 floating by noon
With vabs set at 14.9
At 5:30 pm  My SG is.
1.275 1.270 1.265 1.265

Estragon

US Battery is 15.5 recommended absorb? 

I think recommended on my US Battery flooded L16s is 2.45vpc (25°C) = 14.7 @12v bank..  Actual charging is generally higher with temperature compensation on my cool/cold banks.

mountainman

From us battery website

mountainman

mountainman

Maybe I'v misinterpreted their instructions?

mcgivor

The charging recomendations are based on grid supply, in an offgrid application it is not possible to achieve the amount of time required, therefore higher amperage charging rates are needed to to compensate for the window of opportunity available. There are some who recommend higher voltages to premote saturation within the limited window of opportunity, however that differs depending on depth of discharge, no two systems are identical.

One needs to monitor the parameters of their particular system to gain knowledge, it's actually more complicated than simply following recommendations as there are so many variables associated with lead acid, there is generally no monitoring system to prevent errors, which is the reason I've personally abandoned the obsolete technology. Having said that it is possible to dance on the head of a pin and have success, but there are more failure reports than success or so it seems, most news is bad news. There is a place for lead acid where environmental conditions favor their use, outside that there is little reason to consider a more advanced technology, my opinion naturally.

Estragon

The above method uses a lower absorb (2.4vpc) then a sort of mini-eq at the higher voltage than I use.  As McGivor says, this may be preferable with grid charging.

With solar,  higher absorb voltage (2.45vpc)  gets my banks to very close to full more often than a lower Vabs would, and I can EQ opportunistically and only as needed.  US Battery would call that 2 stage charging.

Much of the year, the first way would take too long for me.  I'm guessing it would also mean a fair bit more watering.

mvas

mountainman said:

Maybe I'v misinterpreted their instructions?

Are you using the US 1800 XC2 6 Volt 208 AHr Golf Cart battery ?

Then per US Battery, their recommended 3-Stage charging cycle is ...
Bulk = Constant Current @ 21 Amps until 14.7 Volts
Absorb = Constant Voltage @ 14.7 Volts until down to 6 Amps
Finish = Constant Current @ 6 Amps for 2 - 3 hour or when less than 24mv dv/dt per hour

Float = 13.02 Volts

Equalization = Constant Voltage @ 15.3 Volts until hourly SG stop increasing

https://www.usbattery.com/wp-content/uploads/2019/03/usb_1800_data_sheet_2019.pdf
Note: Temperature compensated
Note: The above amps is per string ( I think, you have 2 strings ) 

mountainman said:

In winter What are the consequences of a daily extended absorb and end amps less than 1℅

When does your SG stop rising?
a) If the SG does not stop rising before "sunset" then you may be slightly under-charging
b) If the SG is constant for the last hour of good sun, then you are reaching 100% SOC
c) If the SG is constant for many hours in Absorb Mode, then you are only slightly over-charging

If you have a different % DOD every morning and/or
a different number of Sun-Hours every day, then the answer may be ... a, b or c.

Your "extended" Absorb charge will take longer to reach 100% SOC than
the suggested US Battery "Bulk + Absorb + Finish" charge cycle
With only 2 amps flowing into a 400 AH Battery bank ( 1 amp per string ) at Noon,
then that is not that much more than FLOAT.
I think, it is difficult for your configuration to adversely over-charge your 416 AH 12 Volt Bank in the winter

The "Finish" charge, recommended by US Battery, is a mini-Equalization - they claim it extends the overall life.

mountainman said:

Does any gc battery manufacturer other than us battery.
Recommend a 15.5 daily charge

Trojan also recommends a "Finish" charge

mountainman

Thanks all  I think I'M finally getting my answer. There is no set and forget it. 
Each days sun and my usage is different.
So there is no definitive answer.
You just have to keep the hydrometer stuck in the battery till you bust the bulb.
Hence the term dancing on the head of a pin.