A (hopefully) easy house bank charging question

[Mooseflyer]

Hi all,
I'm trying to get good handle on how to properly charge my house battery bank to ensure long battery life and good performance. My new (to me) boat has 6 golf cart batteries wired in series/parallel to provide 696 Ah of capacity at 12 volts. The batteries are Interstate GC2-XHD (232 Ah each). My inverter/charger is an Outback FX2012 coupled with a Mate controller.

The battery manufacturer's website recommends the following:
Charge current = 23.2
Charge voltage = 7.23
Absorb voltage = 7.65
Absorb time = 2 to 4 hours
Float voltage = 6.7
Equalization voltage = 7.8
Equalization time = 2 hours

Next time I'm at the boat, I want to make sure my charger was set to the proper values by the previous owner. Figuring the proper voltage set points is easy - just double the numbers above for 12 volts instead of 6. My question is this: what should my charge CURRENT be limited to? 69.6?

Thanks for any info. I tell ya, the learning curve with a new boat is STEEP!

PS - doesn't the manufacturer's recommendation for absorb and equalization voltage seem high, at 15.3v and 15.6v respectively? I have always heard not to exceed 15 volts. But then, I'm not a battery manufacturer.

[noelex 77]

They seem like unsual specifications.

With your 6x6v batteries you are correct in assuming that the recomended voltages should be doubled and the maximium current multiplied by x3

I am not sure what they mean by "Charge current" and "Charge voltage" Perhaps they mean that that the maximum charge current should not exceed 23.2A unless the voltage is below 7.23v. This would translate in your configuration to 69.6A and 14.46v.

The absorption voltage is high as you have noted. Normally battery manufacturers recommend reasonably conservative settings and I would want to check they were not a misprint before using them.

[roetter]

I checked the instructions and must say they are strange. They mix standard terminology around. For example they give a Bulk Charge voltage. There is no such thing.

Bulk charging is the state were the voltage constantly rises while the charger is at its maximum amperage capacity. The bulk charge state ends when the absorption voltage has been reached.
Bulk = constant maximum amps - voltage rising
Absorption starts when the charger starts keeping the voltage constant at absorption level while slowly reducing the amps.
Absorption = amps going down - voltage constant


The absorption voltage they give is way too high. It is almost equalization voltage.

14.4V for absorption makes sense. Also the 13.2V for float.

I personally would go to 14.6V absorption.

Call customer service. The number is on this instruction document for your batts. http://www.interstatedealers.com/pdf/201535.pdf


Rolf

[noelex 77]

Originally Posted by roetter

I checked the instructions and must say they are strange. They mix standard terminology around. For example they give a Bulk Charge voltage. There is no such thing.

Some batteries do recommend a different bulk and absorption voltage.

If the bulk voltage was was say 14.8v and the absorption voltage was 14.6 with an absorption time of 2 hours.

This means that the charging algorithm is for the voltage to rise until it reaches 14.8v. The regulator will then switch to absorption mode and try to maintain 14.6v for a total time of two hours.

The voltage is rising during the bulk phase, but the end point is referred to as the "bulk voltage".
For a lot of batteries the recommended bulk and absorption voltages are identical. The voltage is then simply referred to as "absorption voltage"

[noelex 77]

This is a graphical example of a lead acid charge algorithm with a separate bulk and absorption voltage. BMax is the bulk voltage.

[Mooseflyer]

Thanks for the replies gents. Nice find on the PDF Roetter. It's not the same document I had found, but yours is much better - it's printed and will go in the "boat book".

You both bring up an interesting point WRT the published figures. In this case, the absorb voltage (15.3) is actually HIGHER than the listed "charge (i.e. bulk) voltage" (if there is such a thing), at 14.4. I haven't heard of that before, but I'm quite a novice. If, as Roetter says, bulk charge ends when absorb voltage has been reached, then this will theoretically never occur. Or, at least bulk will continue to 15.3, which defeats the purpose of the manufacturer listing a "charge voltage".

It does seem like some clarification is needed, so I'll give customer service a call next week. I'll report back. Thanks again gents.

PS - Thanks Noelex for the confirmation of charge current. I was none too sure. Like I said - the new boat learning curve is steep, and college was some time ago. Sometimes I think I purchased a retirement hobby......20 years too early, lol.....

[blackswan555]

The reason they give "strange" numbers is they are Motive batteries, Usually used in Golf carts/fork lift trucks and similar applications, Whilst they are basically the same as a normal deep cycle FLA (apart from some have trick watering/stirring systems) Due to their usage patterns, The charge regime is different, Eg The high charge voltage to charge them faster, It results in a shorter battery life, But when downtime is a issue, can make up the costing many times over,
Settings, You need to get a hydrometer to get your absorb time right, But below is standard FLA,
Charge current, 5 to 15% of 20hr is normal, so you 69.6A is good, Your inverter is 230v ? if so the outback setting will be 4.2AAC (4.2AAC x 230v = 966W /12v =80.5A @12DC, lose around 10% in conversion, About 70 amps)
Charge voltage, 14.4 is standard, As I mentioned, you can go up to decrease charge time, But it results in more plate shedding ( every charge/discharge cycle a little bit of lead comes off plates, The higher the voltage the more)
Absorb time, You need a hydrometer to get it right, measure SG's around your normal "time to charge" Extend absorb time to max, Check and record SG's every hour ish untill they stop rising, Absorb time start untill SG's stop rising is your "time",
Does the system have a battery temp sensor on it ? You need one if not :-)

Tim

[Mooseflyer]

Thanks very much for your additional comments Tim. You bring up a very good point regarding down time in a commercial application costing $$$. I re-read my Outback charger manual and it recommends almost the same procedure as you describe in your last few sentences, regarding taking SG readings periodically to find my "personal" absorb time. My inverter/charger is 120v, and yes, it does have a temperature sensor installed.

Last week I spoke with a manufacturer's representative. He confirmed all the figures on the spec sheet as being correct. He also said the reason for limiting the current is to keep the battery temperatures reasonable while charging. Even though he said it's just fine to charge the batteries as per the spec sheet, I think I'll drop the voltage down a bit based on the recommendations here and from what I've read elsewhere in the last week.

Last week I also bought a hydrometer and tested all the batteries. They all showed a pretty uniform reading indicating about 50% state of charge. I adjusted the settings on my Outback to the manufacturer's recommendation and began to charge. Unfortunately I wasn't able to finish due to personal time constraints, so I'll continue this week.

Thanks again to all!

[Maine Sail]

Originally Posted by noelex 77

This is a graphical example of a lead acid charge algorithm with a separate bulk and absorption voltage. BMax is the bulk voltage.

Sadly this is marketing mumbo jumbo. What they are calling boost is CC/bulk. What Roetter wrote is spot on.

Bulk is constant current and anyone who understands this stuff will readily admit to that, even the marketing folks at Balmar who invented the term "bulk voltage". They made this up FOR MARKETING PURPOSES. Everyone else jumped on the stoopidity band wagon...

Any stage where the voltage becomes the controlling factor is CV or constant voltage charging. Call it absorption, maintenance, float, absorption #1 & absorption #2 but a CV limited stage of charging is NOT bulk (unless you are in the marketing department)..

Sadly the charger manufacturers have realized the buying public is largely stoopid and they can get away with tricking the naive consumer into believing bulk is a CV stage of charging and they are actually getting something they don't in a "less smart" charger.

The term bulk voltage, as it is used by charging equipment manufacturers, is pure rubbish.. Bulk is constant current, limited only by the current capability of the charging source, it is not a voltage limited stage of charging, simple stuff.

Just this morning I was on the phone with a very well respected company trying to sort out a software glitch. The first tech I got started to repeat the party line of "Our chargers are smarter than everyone else and know exactly how much current to send the battery to keep it safe". I said "You mean that new invention called constant voltage charging and Ohm's law?".. He shut up quickly and moved me to the next level support..... D'oh.....

The Interstate batteries the OP has could be made by US Battery. US Battery used to make them for Interstate, and may still, but Interstate is now owned by JCI and many of their golf car batteries are now JCI not USB.... They do like a high charging voltage but for a marine application I would use 14.7V max and Fred W. at US Battery suggests this too. Problem is in a marine application we never know how long charging will take because there are far to many charge sources and variables such as how long we may have to run the engine today...

Fred W. at US Battery (Georgia plant) can answer just about any question you have, if the batteries are USB (with a picture of the case I could likely tell). The folks at Interstate I find are less good on tech support knowledge. This is likely because that battery is physically made by another company who may know more about it.. 14.6V -14.7V will be fine for the Interstates....

[blackswan555]

Outback has a very active forum which may be of help OutBack Power Technologies User Forum • Index page , There's even someone on there with the same "blackswan555" name as me,,,, Err that might be me :-)
Tim

[blackswan555]

Yes, Agree with below

The term bulk voltage, as it is used by charging equipment manufacturers, is pure rubbish.. Bulk is constant current, limited only by the current capability of the charging source, it is not a voltage limited stage of charging, simple stuff.

Put in different terms, Bulk is give it all the amps you have (within bat design specs, 5 to %15 of 20hr FLA) to get the bank up to Absorb voltage, The you start your voltage limited stage, Absorb,
As a rough guideline, Bulk puts back %80 of charge removed and takes %20 of the time, Absorb %20 of charge removed & 80% of time,
Tim

[barnakiel]

They only take as much as they can. Self limiting current. Limit voltage, not current.

b.