miya avatar image
miya asked

Charging - Bulk, Absorption and Float

Hi All

Can someone help validate / correct my understanding on the above.

I am trying to understand in simple terms what is happening in these states of charge. I have read Energy Unlimited - and other documents - I think I've got my head around it - but fear I haven't understood it correctly. Be gentle with me if I am being stupid :-).

Bulk -

The charger throws amps in to the battery - as many as it can (while being limited by any specific limits set in the charger). As loads of amps pile in to the battery - the battery voltage rises. When the battery voltage reaches the specified absorption V - bulk stops - and absorption starts. This phase will simply go on as long as it takes - to get to the battery V to the set absorption V. This could take 1 minute, 1 hours, 3 hours....

Absorption -

The charger continues to throw amps at the battery - but in this phase it doesn't allow the voltage to go above the specified absorption V. So, as time goes on, in this phase, the number of Amps drop off, as the battery gets fuller, the charger requires less amps to maintain the battery at the specified V. Eventually the number of Amps being thrown at the battery drops to almost nothing - to hold the battery at the specified absorption V. At this stage, or, when hitting the time limit set for absorption, the charge stops absorption and switches to float. This phase will go on for as long as it takes, or, for a specified time if time limited in settings of any given charger.

Float -

The charger now just holds the battery at a lower specified voltage - trickling the lowest number of Amps in to the battery that it can- to maintain the float Voltage.

Feedback please - am I way off the mark ?



battery charging
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eddo avatar image eddo commented ·
and when is triggered the change between bulk-absorption-float?
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Alexandra avatar image Alexandra ♦ eddo commented ·


Bulk and absorption are usually the same target voltage. So the difference between the two stages is the current being drawn.

Then float is a specific voltage the batteries drawn down to.


The red line is voltage and the blue line is current.

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Luis (Tiki) Verdiales avatar image Luis (Tiki) Verdiales commented ·

ca3e3a7e-8ea0-4eae-9ca8-4f727018d390.jpegHow can you edit lifePo4 settings float and absorption values? My batteries have different recommended values (56.5) both float and ansorption, see images

ed2f11da-b2b1-43df-a297-dffff8785178.pngIts like in expert mode values are preset and cannot be edited. Thanks!

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2 Answers
JohnC avatar image
JohnC answered ·

Hi @Miya

You seem to have a pretty good handle on it. So yes, validated.

Other makers may use other terminology, but that's pretty much what's meant here.

There's more to it than that of course, like Equalization and Storage phases, which might apply in specialized situations. Ask if you need to know, or Google, there's volumes been written on these things..

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miya avatar image miya commented ·

Thanks so much JohnC - much appreciated.

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Salim Naufal avatar image
Salim Naufal answered ·

Is Float required for LiFePo4 batteries? I have been reading that it came from the Led Acid batteries environment.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

The resting (or open circuit) voltage of a NiFe battery, appears to about 1.4 volts per cell.

Probably as good a voltage to "float" the cells at, maintaining capacity, while getting some use of available solar energy. Should you be the type who cycles their battery daily.

Dunno what ppl program in should the batteries be for stand by use.

As always, follow manufacturers recommendations.

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