Boost charge question

mcgivor · March 2017

Regarding setting a CC to have a higher bulk voltage than absorbtion, the manual for the Schneider 60 -150 MPPT states that it is advantageous to do so in an off grid cyclical application, the raised voltage is held for one hour before dropping back down. This makes sense in that it will stir the electrolyte and prevent sulfation, albeit at the cost of water loss. The battery manufacturer gives no mention of charging voltages other than to state the equalized voltage for 24V nominal is 28.8V, which where I currently have the bulk/absorbtion set. So the question is what would a reasonable setting be for the boost charge? Battery is FLA.

Marc Kurth · March 2017

Generally, the Bulk phase of the charge cycle is called the "constant current" phase because the charging source is running at maximum current and/or the battery bank is sucking up everything being fed to it - at that voltage. Raising the voltage will simply drive the battery to pull more current, assuming that it is available from the source.

In a classic "low battery" scenario, the starting voltage is lower than set point at the beginning of the charge cycle because the batteries are demanding more current than the system can supply. The charging system modulates the voltage to maintain the current. The charging voltage gradually climbs to reach the desired set point as the battery accepts the charge. The transition from Bulk to Absorb isn't a "switch", it is simply the point where the output voltage reached design output and the current draw of the batteries begins to drop.

Of course if the charging capacity of the system is large compared to the battery bank, or the batteries are only mildly discharged - the Bulk and Absorb phases operate the same way.

So, assuming you have the charging capacity available, raising the Bulk voltage will increase the charging current and reduce the charging time. Then dropping back to the 28.8v will allow the batteries to slowly absorb the final charge. The actual voltage setting for the boost will depend upon how hard you are intending to push the batteries.

Some people use a "finishing charge" at 29.6v when the batteries approach full charge instead of boost at the beginning. I suggest working with your battery manufacturer to determine what is optimum for their product.

oil pan 4 · March 2017

The boost charging I'm used to is on forklift traction batteries.
No voltage specs just keep it under 20% to 25% of the name plate amp hours and stop charging if the battery gets near 110°F or starts off gassing.
I think you generally want to keep the volts under equalization

mcgivor · March 2017

Marc Kurth said:

Generally, the Bulk phase of the charge cycle is called the "constant current" phase because the charging source is running at maximum current and/or the battery bank is sucking up everything being fed to it - at that voltage. Raising the voltage will simply drive the battery to pull more current, assuming that it is available from the source.

In a classic "low battery" scenario, the starting voltage is lower than set point at the beginning of the charge cycle because the batteries are demanding more current than the system can supply. The charging system modulates the voltage to maintain the current. The charging voltage gradually climbs to reach the desired set point as the battery accepts the charge. The transition from Bulk to Absorb isn't a "switch", it is simply the point where the output voltage reached design output and the current draw of the batteries begins to drop.

Of course if the charging capacity of the system is large compared to the battery bank, or the batteries are only mildly discharged - the Bulk and Absorb phases operate the same way.

So, assuming you have the charging capacity available, raising the Bulk voltage will increase the charging current and reduce the charging time. Then dropping back to the 28.8v will allow the batteries to slowly absorb the final charge. The actual voltage setting for the boost will depend upon how hard you are intending to push the batteries.

Some people use a "finishing charge" at 29.6v when the batteries approach full charge instead of boost at the beginning. I suggest working with your battery manufacturer to determine what is optimum for their product.

The maximum recommended charge current is 25A per battery , there are 2 strings parallel, the maximum charge current is set at 30A, 15A per string, given that this current is not exceed, raising the voltage would be a sort of be a mild equalization without dumping the maximum current the array can supply into the battery. This setting is about 12% of the capacity of the battery, so limiting the current and raising the voltage should be benificial in that it stirs the electrolyte without overcharging, being that this "boost" is limited to one hour, my assumption is that the voltage would be slightly higher, not at equalization voltage, say in the mid 29v range. The manufacturer offers no information regarding such settings, the only voltage stated is the equalized voltage, float and equalization are dependent on the charger. See attached Pdf, Battery is EB 130

Estragon · March 2017

So with the "boost" charge, it would go something like:
Bulk- 3 hours at max 30a until voltage gets to eg. 30v.
Boost- 1 hour held at 30v with tapering current
Rest- however long it takes with no current for voltage to drop to 28.8v
Absorb- tapering current to set EndAmps or TimeOut.

IMHO it would be better to get batteries charged then do EQ if needed. They would be only part charged after boost phase and might take a while to drop to Vabsorb and start charging again, and may not finish before dark. I'm not sure what the advantage is of doing the sort-of-EQ before absorb is, or of doing it daily.

mcgivor · March 2017

Estragon said:

So with the "boost" charge, it would go something like:
Bulk- 3 hours at max 30a until voltage gets to eg. 30v.
Boost- 1 hour held at 30v with tapering current
Rest- however long it takes with no current for voltage to drop to 28.8v
Absorb- tapering current to set EndAmps or TimeOut.

IMHO it would be better to get batteries charged then do EQ if needed. They would be only part charged after boost phase and might take a while to drop to Vabsorb and start charging again, and may not finish before dark. I'm not sure what the advantage is of doing the sort-of-EQ before absorb is, or of doing it daily.

Currently the bulk/absorbtion is set at 28.8v, 30A max. When the bulk stage reaches 28.8v it transitions into absorbtion until 2% of the battery Ah is met then goes into float. Introduction of the boost would raise the voltage , say 30v for example , for the first hour of the absorption. The time taken to rest until the voltage drops would be negligible as the battery cannot hold that high a voltage, so transition to absorbtion would be almost seamless. On most days the time taken to complete bulk/absorb is around 5 hours from sunrise, so float is reached at 11:30am to noon with loads, so array capacity is not an issue.Below are the pages from the manual associated with the boost setting.

Estragon · March 2017

At my latitude I get to float at about the same time in summer, but not in fall/winter so that would be an issue for me, but not you. My batteries seem to bubble pretty well at Vabsorb and EQing as needed (roughly every 3mos) seems to be working.

Assuming the boost stage is temp compensated and voltage not too high, I guess it wouldn't hurt to enable boost. Might mean fewer EQs?

mcgivor · March 2017

Estragon said:

At my latitude I get to float at about the same time in summer, but not in fall/winter so that would be an issue for me, but not you. My batteries seem to bubble pretty well at Vabsorb and EQing as needed (roughly every 3mos) seems to be working.

Assuming the boost stage is temp compensated and voltage not too high, I guess it wouldn't hurt to enable boost. Might mean fewer EQs?

Yes it is temperature compensated, at 28.8v bulk /absorb there is mild gassing but as the voltage rises and current drops, much less. This is a new CC, so learning new things, have set a boost of 29.6V and see what happens tomorrow. Being at 17 Deg from the equator certainly helps, in fact winter is better than summer, less cloudy and cooler, except April and May when it's hot, 40C plus, which is when I place the batteries in a water bath to moderate their temperatures.

Estragon · March 2017

At 40C plus, you would have to put ME in the water bath. At -40C like we occasionally get, we can dress for it.

mcgivor · March 2017

Estragon said:

At 40C plus, you would have to put ME in the water bath. At -40C like we occasionally get, we can dress for it.

You drink about 10 liters of water per day and don't visit the bathroom much, so you are in a constant water bath, so to speak, lived in Northern Canada, the cold is dry cold but I'm a tropical person and prefer the heat, you acclimatize, overall its cheaper in the tropics, less clothing, no heating and you can grow food all year, I'm not only off grid but 80% self sufficient and working towards 100%.

Marc Kurth · March 2017

mcgivor said:

You drink about 10 liters of water per day and don't visit the bathroom much, so you are in a constant water bath, so to speak, lived in Northern Canada, the cold is dry cold but I'm a tropical person and prefer the heat, you acclimatize, overall its cheaper in the tropics, less clothing, no heating and you can grow food all year, I'm not only off grid but 80% self sufficient and working towards 100%.

Nice!!

WaterWheel · March 2017

I have a Schneider controller with boost capability. Since I'm not looking to do a mini-EQ on a daily basis which the boost function is capable of yet still appreciate the benefits of a tiny electrolyte stir regularly I just set my boost voltage .1v higher than my absorb. I suspect going .2v higher wouldn't hurt a bit. I would not suggest getting anywhere close to EQ voltages if you use the boost feature.

The way I look at it since charging heats the batteries you get a little extra electrolyte stir before the batteries get warm as they do further into the absorb cycle.

mcgivor · March 2017

WaterWheel said:

I have a Schneider controller with boost capability. Since I'm not looking to do a mini-EQ on a daily basis which the boost function is capable of yet still appreciate the benefits of a tiny electrolyte stir regularly I just set my boost voltage .1v higher than my absorb. I suspect going .2v higher wouldn't hurt a bit. I would not suggest getting anywhere close to EQ voltages if you use the boost feature.

The way I look at it since charging heats the batteries you get a little extra electrolyte stir before the batteries get warm as they do further into the absorb cycle.

It's all a balancing act I guess, watch the temperature, the gassing etc, it's so easy to change the parameters, one could find the sweet spot sooner or later, it's just interesting to hear other's opinions and results, it just seems that the Schneider is not popular, for reasons I don't understand, seems to be well made and offers an abundance of settings in a simple yet sophisticated unit.

Boost charge question

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