# How does pulse or burp charging work?

I've been doing some research about how to fully charge a lead-acid and AGM battery. However I have some questions and need some guidelines for proper implementation.

Basically I am trying to find out if:

1. There is an optimal voltage or current to use during pulse charging. I know the voltage can be higher but does the .1C charging current rule apply for example?

2. If I were to setup a solar PV system, would you recommend modifying the circuit in such a way that pulse charging technique is applied to the battery array for charging?

Would really appreciate some sort of open source reference for this especially from someone who's tried it as it seems a good amount of documentation around this is proprietary or patented.

• The "burp" aspect of lead-acid charging goes back as far as I can remember as a studying child. I remember reading an article on the idea in the late 1960's. As charging takes place, bubbles form on the plates. These bubbles impede the growth of lead as it precipitates out from solution. It's supposed to precipitate right on the plates, but with bubbles in the way it makes quite a "furry mess" of things. Every so often, they suggested reversing the charge voltage (flip with a relay, even) for a moment --sufficient to "shake" the bubbles loose which then float to the surface and out of the way. – jonk Sep 1 '16 at 2:11
• 1. During which phase of the charging? When already fully charged? 2. It's a compromise. You can float charge it to a low enough voltage to never cause enough outgassing to be a problem in the first place. Here you trade a slightly lower SOC for less outgassing. You can tickle-charge it to a slightly higher SOC without signigicatly increase the outgassing. – winny Sep 1 '16 at 10:34

There are two fundamental rules of battery charging: you shouldn't let the battery get too hot, and, you shouldn't let the voltage get too high.

The .1C charge rule is a rule-of-thumb to protect you from both of the real rules.

Particularly when you have cheap charging equipment that can't shape the charge curve, and/or Particularly when your real skills are at manufacturing batteries at a competitive cost, not battery chemistry, and you don't know any better.

You can use much higher rates for short periods because (1) If it's short, the battery won't over-heat, and (2), If it's very short, it's just charging the battery capacitance, so the voltage won't go too high.

If the ambient temperature is low, you can use medium-higher rates for medium-length-periods when the battery voltage is low, because the battery voltage won't go too high until is is partly charged.

Most battery charging is done with pulses, from switch-mode power supplies.

Most solar-system charging is done with systems where the charge rate is limited by the solar panels, so you couldn't get too much pulse current if you tried.

Burping the batteries is probably a bad idea. Experiments which have tried it report reduced battery life.

• Hi @david Thanks for your answer. What if you charge with a lower current than .1C? I'm also curious of what you make of this topic as they claim they pulse charging and burp are about the same and tend to lead to better battery life. Any evidence or reference is highly appreciated. – Chibueze Opata Sep 1 '16 at 10:45

Lead-acid batteries suffer from two annoying problems. The first problem is that if voltage exceeds about 2.4V per cell the water in the electrolyte will break down into hydrogen and oxygen (electrolysis). Apart from the risk of explosion, the lost water needs to be replaced or the battery won't work properly. A 'flooded' or 'wet cell' battery can be topped up with deionized water, but sealed batteries cannot.

The reason this is a problem is that to prevent gassing the voltage must be kept safely below the point of electrolysis, so the battery can only be charged at maximum rate for a few hours. Current must then be progressively reduced to stop the voltage from rising, and the battery gets charged slower and slower (taking 20 hours or more to get a full charge).

AGM (Absorbent Glass Mat) sealed batteries get around this slow charging issue by recombining the hydrogen and oxygen rather than venting gas. However this increases pressure inside the battery, so it can only handle a limited amount of gassing. A charging system that is designed for AGM batteries can charge them a bit faster than normal SLA (Sealed Lead-Acid).

Pulse charging may be able to charge at even higher rates without gassing if it can get a burst of current into the cell before it starts to gas. However it is possibly more useful for dealing with the second lead-acid battery problem - sulphation. This is the formation of lead-sulphate crystals that occurs when the battery is left in a partially discharged state for a long time. The crystals have low solubility and are not easily dissolved by normal charging. A sulphated battery loses capacity because there is less acid available, and it may also have reduced current carrying capacity due to the crystal's poor conductivity.

Pulse charging aims to break the crystals down so they will dissolve faster and restore capacity. The technique does work, and can even use the battery's own power to do it! However there isn't much point applying it to a battery that is in good condition.

• Very informative. I've found quite a few 2V Lead batteries and have considered using them as well... But interestingly, I found some guys called IronEnergy that uses nickel and iron to create 1.2V batteries. – Chibueze Opata Sep 3 '16 at 14:30
• Nevertheless, what I'm precisely after is learning or understanding if pulse charging for example can work with any voltage or current or if there're some minimum and maximum specs. And secondly you say it is much useful for helping ensure crystals don't form or breaking them down, however, is it not possible that these crystal formation slows down the charging process hence the need for 'trickle charging'? – Chibueze Opata Sep 3 '16 at 14:30
• Typical pulse charge current is around 1C, 1 pulse per second with maximum on/off ratio of 80-98%, reduced as necessary to keep peak voltage below 2.45V/cell. 'Burp' charging applies short charge and discharge pulses of about 2-3C and 5ms duration. "Controversial claims have been made for the improvements..." mpoweruk.com/chargers.htm#pulse – Bruce Abbott Sep 3 '16 at 16:36

Summary

• Standard well tried well documented methods usually are "not too bad".

• Super 'patented' chrome plated pulse methods MAY work better. Or not. Unless they are certainly superior and have no hidden problems, there may be no good reason to use them.

Pulse charging tends to lie somewhere in the realms of some mix of:
Advanced real world science understood only by the illuminati (or technocrati) / Common sense / Accidental discovery that works, sometimes, sort of / Magic and-or Scam (oxygen free copper-crystals-phase-of-moon-bank-holidays-dead-fish-nsfw-ymmv-dnttah-ianal , ...) / Other.

Deciding which is which can be difficult to impossible.
IF a method is of clear capability, reasonably priced and does not damage the battery, then consider it. Otherwise, tried and true methods are in widespread use and probably preferable.

Whatever Trojan Battery USA say is a good starting point. (I have no association with Trojan - just admire their products)

Battery university are usually not terrible although some choose to slang some of their stuff.

Super patented chrome plated pulse methods MAY work better. Or not. )

Reputable battery manufacturers usually have a good idea of what works with their batteries. If the spec sheet is deficient in this area then, if you care, changing brands may be in order.