When is AGM 100% full charged at Float voltage?

[JmanC]

Say your charger is set in power supply mode to 13.8V & you just keep it at this voltage all the time. Is there some tail current % figure at Float voltage that means full? I have read that at absorption voltage full means tail current of 0.5% of capacity, so just curious.

thanks

[a64pilot]

It should I believe be roughly the same.
If 13.8 is your float voltage and the only voltage your charger outputs, you will see a charge if the bank is down, it won’t be nearly as much charge current as higher voltages of course, but it will eventually charge.

Don’t quote me, but it will I think be a lower amperage, but ought to be close.

Of course if this is your float voltage then of course you want to leave the charger on always whenever possible

I don’t think being an AGM is relevant.

The .5% pertains to Lifeline batteries, it may be a different manufacturer uses a different number, although many or most don’t specify

[john61ct]

The manufacturer's spec'd definition of Full will be measuring trailing amps at Absorb voltage.

Once you drop to a much lower Float voltage anywhere near that point, very little current will flow.

Best to get to the 100% Full before dropping to Float,

it would be possible (but not easy) to cross-reference to get to the same SoC at Float, but doing that regularly is not recommended, could easily take days.

[sailinglegend]

Originally Posted by JmanC

Is there some tail current % figure at Float voltage that means full? ....

All you do is turn the charger back on and it will go to 14.4v and the tail current should 0.5% of the Ah capacity.

[Maine Sail]

Originally Posted by JmanC

Say your charger is set in power supply mode to 13.8V

What brand/model charger?

[JmanC]

Originally Posted by Maine Sail

What brand/model charger?

Hi, It's Sterling pro ultra charge 50A.

[john61ct]

Originally Posted by sailinglegend

All you do is turn the charger back on and it will go to 14.4v and the tail current should 0.5% of the Ah capacity.

Yes unfortunate that such kludgey workarounds are needed.

Sterling's PCU units' algorithm is certainly much better than a dumb egg-timer, and their user-defined setpoint programming is great.

But apparently they do not allow the Absorb Hold Time to be adjusted directly for current conditions?

_____
From Maine Sail's HowTo
https://marinehowto.com/installing-a...ttery-charger/

In an *ideal recharge* a battery charger would not drop to float voltage until the battery bank had attained the 99.5% to 100% SOC point. Almost all battery chargers out there, for marine use, drop to float before the battery bank has attained 100% SOC. While this makes them “safe“, for the manufacturers lawyers, it also means that in order to get back to 100% SOC it just takes a bit longer. At a dock this is not a huge deal, if we are getting into the mid to upper 90’s before the float transition. Once the charger drops to float this dramatically extends the time it takes to get to 100% SOC. The absorption cycle is perhaps the most important stage of charging and if it is too short, due to an egg-timer, the batteries can become chronically under charged and suffer the effects of sulfation.
…
Even the best AGM batteries still require well over 3 hours of absorption charging, under ideal conditions, to get anywhere near 100% SOC from 50% SOC, even when being changed at rates as high as 40% of Ah capacity or 40A for a 100Ah battery.

[a64pilot]

Why would you use it in power supply mode with the batteries still connected?

[Maine Sail]

Originally Posted by JmanC

Hi, It's Sterling pro ultra charge 50A.

Power supply mode is just the old "battery charger" mode and it should still do bulk, absorb & float but not do the CEC turn-off thing.. The only way to get it to do 13.8V constant would be to set both absorption & float to the same value in the custom settings.

When they came out with California Energy Compliance chargers they kept the original battery charger mode and they just call it PS mode.

[JmanC]

Originally Posted by john61ct

Yes unfortunate that such kludgey workarounds are needed.

Sterling's PCU units' algorithm is certainly much better than a dumb egg-timer, and their user-defined setpoint programming is great.

But apparently they do not allow the Absorb Hold Time to be adjusted directly for current conditions?

From what I can tell with AGM presets, the absorption timer is too short (premature float) when sized to large banks, like 50A for 300-400AH, but when sized so it's 0.2C min charge rate in bulk it actually stays in absorption too long, usually until tail current is alot below 0.5%.

[JmanC]

Originally Posted by Maine Sail

Power supply mode is just the old "battery charger" mode and it should still do bulk, absorb & float but not do the CEC turn-off thing.. The only way to get it to do 13.8V constant would be to set both absorption & float to the same value in the custom settings.

When they came out with California Energy Compliance chargers they kept the original battery charger mode and they just call it PS mode.

Thanks for that. I had no idea it worked like that in PS mode, alot more flexible.

[JmanC]

Originally Posted by a64pilot

Why would you use it in power supply mode with the batteries still connected?

My understanding is. In a situation where there is mains power 24/7 & I have lead acid, I would use it so the battery stays full & is less cycled & the charger supplies loads. Power supply is the same as float & 13.8V just seems like a good set & forget voltage.

[a64pilot]

Originally Posted by Maine Sail

When they came out with California Energy Compliance chargers they kept the original battery charger mode and they just call it PS mode.

Didn’t know that. I assumed power supply would have been a single voltage

[john61ct]

Yes that is what those words usually mean, no varying stages at all.

[sailinglegend]

Originally Posted by JmanC

My understanding is. In a situation where there is mains power 24/7 & I have lead acid, I would use it so the battery stays full & is less cycled & the charger supplies loads. Power supply is the same as float & 13.8V just seems like a good set & forget voltage.

I think you have misunderstood Mr Sterling's badly written instruction manual. PS mode is used when no batteries are connected.

PS mode is a permanent Float setting so if you go sailing and come back to 24/7 shorepower the charger will not go up to an Absorption voltage so it will not charge the batteries properly.