To pulse or not to pulse

It is accepted practice to maintain lead acid batteries at a float voltage of roughly 2.3 Volts per cell. The precise value depends on battery type and battery chemistry and ambient temperature. We have all done this for decades. Some charger manufacturers use a pulse scheme where they have a comparitor with hysteresis that turns the current off at say 2.3V and on at say 2.2V per cell. This is done at relatively small currents like C/100. I can see that this should represent a energy saving and I know that it is easy to implement by hardware or software. The question is: What is best for the life of the battery?

• Pipe ..Most power supplies take a idle current ,Example chinese artesyn 1500W pulls 22W to do nothing .If the circuit can spend most of its life shut down there will be an energy saving or average power saving . – Autistic Jan 30 '16 at 9:38
• The battery is alone but the SMPS say non china has 90% full load efficiency that is say 80% at 5% load but at 1% load it is 30% efficient .In a nutshell you set up the current where charger efficiency is reasonable .I will charge my leaf and smoke my pipe. – Autistic Jan 30 '16 at 9:51
• @pipe You can run the charger for ten minutes at 1A (plus 0.5A idle power) or for five minutes at 2A (plus 0.5A idle power) then turn it off entirely for five. Which uses less power in total? (All numbers entirely made up in this comment) – user253751 Jan 30 '16 at 12:18
• @pipe It demonstrates the principle the OP is trying to tell you, which is that the charger uses some power when turned on, regardless of the charge rate. So by turning it off except for short bursts you save energy. By "made up" I merely mean that I didn't get those numbers from any actual charger or battery. – user253751 Jan 30 '16 at 22:27
• if you want the battery to last you need a periodic equalizing charge in addition to the float charge. – Jasen Feb 7 '16 at 5:25

From Wikipedia's Lead-Acid Battery page, here are two quotes:

"Starting batteries kept on a continuous float charge will suffer corrosion of the electrodes which will also result in premature failure. Starting batteries should therefore be kept open circuit but charged regularly (at least once every two weeks) to prevent sulfation."

and

"There are commercial products claiming to achieve desulfation through various techniques (such as pulse charging), but there are no peer-reviewed publications verifying their claims. Sulfation prevention remains the best course of action, by periodically fully charging the lead-acid batteries."

So, the answer to your question, "What is best for the life of the battery?" it seems, has a surprise answer -- Don't Float Charge -- because it reduces battery life. And there is corrosion on the deep-cycle batteries too, it just doesn't affect them as much because their plates are thicker.

You could implement a "Smart Float Charge" feature that will allow the customer to still just keep your charger plugged in, turned on, and battery attached, for their convenience and peace of mind; but your charger wouldn't actually float charge, instead it would turn the charge completely off and wait the two weeks (as suggested in block quote #1 above), and then initiate a full charge. This will keep the battery ready for use whenever it is needed, which is the main purpose of the float charge, but it will cause much less corrosion, causing the battery of the customer to last much longer. A button to manually bring up the charge a few hours just before use might be nice. Also, don't forget to adjust your charge voltages for temperature -- Arizona charging is probably different from Alaska charging.

Also, during the main charge, you may want to pulse, because it supposedly knocks off the sulfation, also increasing battery life. Do google searches for this, because there's research (I saw it in passing, in searches to try to answer your question, but didn't read it -- just know it's there, and probably very helpful). You may need to pulse in a very specific way during your main charge to knock the sulfation off most effectively.

Since your answers are really in the realm of chemistry, if you want more information, I suggest that you ask further questions on the Chemistry stack exchange. They should be able to confirm or clarify what Wikipedia said (sometimes Wikipedia needs confirmation), more able to point you in the right direction, or answer your original question (which I am going to bet is "if you're going to float charge anyway, it's a low power charge and does not matter whether it is pulsed or constant".)

Hope this helps.

• .Interesting Answer .+1 .So you say it is good to pulse and bad to float. – Autistic Oct 15 '18 at 21:51

Flooded lead acid batteries are full at 12.7V and empty at 11.5V. Charging at more than 0.5V over the full charge "on the charger" is unnecessary and damages them. Each cell is about 2.1V and charging at 2.25V and watching the battery itself does not go over 2.1v is the way to go. Multiply by 6 for a 12V battery.

So, 13.2V to 13.8V on charger and be sure the battery does not rise above 12.7 V. Keep the batteries topped off and never discharge below 11.5V will keep them pretty good. I think a constant voltage is the way to go and as the battery fills it will naturally reduce current as above . I don't see pulsing it will help anything or save any power unless maybe you are in a float charge state ie ,holding it at 2.25V

• As I understand it, the OP is specificially asking about the regulation in the float phase and effects on battery life. While you give good advice in general, I think you do not answer what was asked. – Andreas Feb 26 '17 at 22:06
• "I don't see pulsing it will help anything or save any power unless maybe you are in a float charge state ie ,holding it at 2.25V" The chart is pertinent to establish where the true float stage is. – April Feb 26 '17 at 22:11
• A PID control would be able to use a nearly constant current in float phase. Would that prolong battery life? – Andreas Feb 26 '17 at 22:20