Three-Stage Charger Actually Two-Stage?

[cal40john]

This is coming from a thread drift of the battery ventilation thread.

I believe that some 3 stage chargers are 3 stage due more to wording than to fancy electronics.

CharlieJ posted this 3 stage chargers graph in the vent thread:

http://www.cruisersforum.com/forums/...2&d=1260805238

(Actually I believe that the current graph in the bulk stage is wrong. It should be a flat line at the max current heighth.)

This graph indicates to me that there is a voltage setpoint. As long as the voltage is below the setpoint the current output is maximum. Once the voltage setpoint is reached, the current output is throttled as needed to maintain that setpoint. This is the transition from bulk to acceptance. This is no different than how a dumb car regulator operates. In this sense you would call your car regulator a 2 stage regulator. What is different is that the voltage setpoint is higher than what you would normally set your car regulator to. And since this would eventually overcharge your battery the smart regulator has a transition, it changes the set point after a suitable time transitioning you from the acceptence to the float stage.

From an electrical standpoint, a battery has an internal resistance that increases with increasing state of charge. Using Ohm's law this means once the battery reaches a certain state of charge there would be no way of maintaining full current output without raising the voltage above the acceptance voltage.

I'm not saying that these chargers do not charge faster, they do because the setpoint before the cut back is higher, but if you set your car regulator to that same voltage it would behave exactly the same. The additional electronics that you are getting with the 3 stage charger turn down the voltage set point to float at a later time.

There are what I would consider true 3 stage regulators. Balmer and Iota are two examples.

The Balmer defaults to 0.2 volts higher on the bulk stage than the acceptance. It also decides how long to stay in the bulk stage by estimating how full the battery is by looking at the fraction of time that the alternator is turned on to maintain the voltage.

http://www.balmar.net/PDF/2005-mc-612-manual.pdf

3. Bulk Charge - The most aggressive of the charging stages. Voltage is held at a pre-set level, specified by battery program
selected, for a set time period. Factory-set bulk time is 30 minutes.
4. Calculated Bulk Charge - Holds voltage at bulk level for six minutes, then calculates battery condition by comparing
existing voltage, time at voltage, and field percentage to target values. If values are met, the regulator advances to the
next stage. If values are not met, the regulator extends the bulk charge time by an additional six minutes and compares

real-time to target values. This will re-occur until all values are met.


Iota's IQ also has a higher bulk voltage set point than the acceptance, but they don't go into how the stages advance.

IQ Smart Charger for DLS Series Battery Chargers from IOTA Engineering

John

[Mexbungalows]

The three charging stages should be referenced as to "how the battery is responding to the charging source".

1-Regulated volt set point has not been reached

2-Regulated volt set point has been reached-

3-Regulated volt set point has been reached and charging amperage has declined to a predetermined value. At this stage the voltage should be reduced to an appropriate level to maintain battery charge without creating excessive gassing or plate/paste erosion.

[Rick]

caljohn40;
Battery internal resistance DECREASES with increased state of charge. Battery charge current acceptance decreases as well due to the voltage-per-cell increase during charge.

Keep in mind that multiple-step charging for deep-discharge batteries is merely a first approximation to Amp-hour law charging for which no commercial product is available. Limits for acceptence voltages limits and acceptance-time limits before transition to float voltage limits are, therefore, largely a compromise without a regulation regimen closely tied to a particular battery size, chemistry, and state of charge. The closest that a commercial alternator regulator came to being less than arbitrary was the Link 2000R which utilized the battery monitor function to control the voltage limits and transition times.

Magnum energy makes a sine inverter/charger/transfer switch with optional monitor that does a decent job with setting voltage limits and transition times for shore/gen charging.

[CharlieJ]

Battery internal resistance DECREASES with increased state of charge.

Rick-Everything that I have seen on three stage charging algorithms (like the one I posted as referenced in #1 of this thread) shows the absorption phase as constant voltage with decreasing current. Ohm's Law tells me the only way that will work is if resistance increases as the battery is charged.

What am I missing?

Charlie

[cal40john]

Let's see if I figured it out based on Rick and a couple of web pages. The internal resistance is related to the concentration of the acid. Discharged battery has very little acid. The conductivity of the solution is low. Charge the battery and acid concentration goes up, conductivity of the solution goes up, internal resistance down, current into the battery is up.

But going in the opposite direction as the battery charges and the internal cell voltage rises, the potential difference, voltage difference between the internal battery and the applied charging voltage is decreasing, so current is down for a given resistance.

c = charger
ib = internal battery

I = (V(c)-V(ib))/R(ib)

So for the current going into the battery to decrease the internal voltage of the battery has to rise fast enough that the difference between charger voltage and battery internal voltage becomes proportionally smaller faster than the internal resistance is falling. Going to take more time with the chem book and redox and nernst eqns to see if I can make that work.


Rick I have read your posts before about the Amp-hour law and have learned a lot, but what I was complaining about was that the original 3 stage chargers were a bit of a hype unless people were calling regular car regulators 2 stage regulators. And I don't remember anyone calling car regulators that.

John