What is the trade off on high voltage charging?

[paulcheung]

Hi all,

What is the trade off with high voltage charging? say the 48 volt battery bank charged for 1 hour or two daily between the 58.8 volt to 62 volt range at bulk mode when the water level and temperature is carefully monitored?

Thanks

[Sunking]

Over charging or too high of a voltage does two things, gasses the electrolyte which will expose th eplates. 2nd is grid corrosion. It adds up to shorter cycle life and diminished capacity.

[inetdog]

In addition to requiring more maintenance to replenish the electrolyte by adding distilled water, heavy gassing can also vent acid vapor out the caps, causing other maintenance problems.
That family of damage, as mentioned by Dereck, can be managed if there is a good reason for the high rate charging.
The plate corrosion damage, however, is irreversible. The degree to which plate corrosion occurs will vary somewhat with plate (electrode) composition and physical design.

What it all comes down to is that you have to have a really good reason for wanting to do that kind of charging to justify the bad side effects.

[Sunking]

Paul you have Rolls batteries correct?

If so follow Rolls recommendations. For a FLA battery:

Bulk/Absorb = 2.5 vpc.
Float = 2.19 vpc

So for a 48 volt that means:

Bulk/Absorb = 60 volts
Float = 52.6

ROLLS OWNER MANUAL

[paulcheung]

The grid corrosion is causing by high voltage? or chemical reaction? Can I set the volt on absorb=60 volts?

The reason I ask is when 11:30 am to 12pm the charge controller start go over the 58.8 volt and put the charge to absorb mode and decrease the charge current, the battery is not fully charge yet and by 2pm we usually have a lot cloud past by if not over cast or rain. it is really feel bad to see the current being wasted. sometime I turn on the water heater to get 30 minutes to heat up the water a bit. if I can set the absorb voltage to 60 then it is better than 58.8 volts.

Thanks guys.

[inetdog]

The grid corrosion is causing by high voltage? or chemical reaction? Can I set the volt on absorb=60 volts?

The reason I ask is when 11:30 am to 12pm the charge controller start go over the 58.8 volt and put the charge to absorb mode and decrease the charge current, the battery is not fully charge yet and by 2pm we usually have a lot cloud past by if not over cast or rain. it is really feel bad to see the current being wasted. sometime I turn on the water heater to get 30 minutes to heat up the water a bit. if I can set the absorb voltage to 60 then it is better than 58.8 volts.

Thanks guys.

AFAIK, the grid corrosion is caused by a combination of chemical reaction which can only happen at high voltage and mechanical damage resulting from local violent gassing.
Do not set the absorb above the recommendation of the battery manufacturer if those recommendations are actually given for the three stage constant current, constant voltage, constant voltage profile that CCs use.

The problem of losing charging capability from the panels because of the transition to absorb can be minimized by following Sunking's recommendation. Take a look at it and see if you can figure out what the result will be. If you cannot, then just try it!

Oh, and remember that all of the voltage recommendations or custom settings have to be automatically compensated for battery temperature changes.
If your CC does not have this capability or you are not using a remote battery temp sensor, then you need to be all the more careful about getting close to the manufacturer's maximum values.

And are you measuring that voltage at the battery terminals or at the CC output? Some of your problems could be related to voltage drop in the wires and terminals, which you would need to correct.

[Sunking]

Do not set the absorb above the recommendation of the battery manufacturer if those recommendations are actually given for the three stage constant current, constant voltage, constant voltage profile that CCs use.

The problem of losing charging capability from the panels because of the transition to absorb can be minimized by following Sunking's recommendation. Take a look at it and see if you can figure out what the result will be. If you cannot, then just try it!

Well you are hitting on a point I keep trying to drive. 3-stage charging is useless in a solar application as there is just not enough Sun Hours in a day to get topped off. Unfortunately battery manufactures do not make that clear in their documentation. The only way you learn call the manufacture and ask. What you end up with is 2-Stage

But here it is in a Nut Shell. Varies a bit from one manufacture to another, but this gets you real close.

Bulk = Absorb = 2.5 vpc
Float = 2.2 vpc

How do you know when you get it right. Only your hydrometer can tell you that.

So Paul set Bulk/Absorb to 60 volts, and float to 52.6. When it switched to Float check the specific gravity and adjust Bulk/Absorb accordingly until you get it right. Be sure to keep distilled water on hand and check electrolyte levels.

[paulcheung]

Ok Thanks.

[Shockah]

How do you know when you get it right. Only your hydrometer can tell you that.

What about AGM batteries... is there a way to tell without the hydrometer?

TIA.

[Sunking]

What about AGM batteries... is there a way to tell without the hydrometer?

TIA.

Nope.

[paulcheung]

One more Question,

One more question,

If I remember right, I have read somewhere that if high voltage are used to charge the batteries frequently it help reduce the need of equalization, is that true? does high voltage charging help reduce sulfation ?

Also, do those Power Pulse Battery Charger real help? do they have any place in the solar world?

Thanks.

[Sunking]

Higher voltages do help to dissolve lead sulfate crystals. That is the whole point of applying a EQ charge. Low specific gravity is a result of sulfation. However there are limits. Once the lead sulfate crystals harden, they cannot be dissolved.

As for the pulse chargers, there is no credible evidence they prevent sulfation. With that said most battery manufactures do not object to them being used. IMHO it is more snake oil and marketing than real benefit.

EQ does two things.

1. Dissolves soft lead sulfate crystals.
2. Gasses the electrolyte which causes agitation thus reverses stratification. In other words it stirs up the electrolyte.

[inetdog]

Higher voltages do help to dissolve lead sulfate crystals. That is the whole point of applying a EQ charge. Low specific gravity is a result of sulfation. However there are limits. Once the lead sulfate crystals harden, they cannot be dissolved.

As for the pulse chargers, there is no credible evidence they prevent sulfation. With that said most battery manufactures do not object to them being used. IMHO it is more snake oil and marketing than real benefit.

EQ does two things.

1. Dissolves soft lead sulfate crystals.
2. Gasses the electrolyte which causes agitation thus reverses stratification. In other words it stirs up the electrolyte.

The other, more specific reason to do an EQ charge is if your series string of cells has become unbalanced for some reason. That is the SG and end of charge voltage differs by more than a set amount from one cell to another. A well designed system will not get into this situation often, but it can happen.
The higher EQ voltage applied to the string will force current through a fully charged cell or cells, gassing madly, to deliver the needed charge current to a cell or cells which has not yet reached full charge.
In cases of really bad cell to cell imbalance, the first requirement is to figure out how they got into that state rather than blindly trying to correct it.
The second step is to decide whether you want to stress the whole string to take care of one battery, or whether you want to take that battery out of the bank and charge it separately.

The "equalization" name for the procedure refers to balancing unbalanced cells, but that is no longer the main reason that the EQ setting and high voltages are actually used.

[paulcheung]

Ok understood, Thanks a lot.