AC charger smarter than the 3 stage "smart" charger?

[hellosailor]

"The AC charger is not going over the isolator, but the alternator's regulator is,"
There ya go, you've answered the question. The isolator, if it is a conventional diode isolator, will have about a 0.3-0.4v drop across it. Unless you've compensated for that in the regulator's sense lead and charging lead, the alternator may be leaving the batteries "full" when they are 0.3-0.4V too low (less likely, high). So you've got two chargers, one thinking "This is 12.6 volts" and the other thinking "This is 12.6 volts" and one of them has been deluded by 0.3-0.4 volts.

You'll need to confirm the voltage drop in the isolator, and how the wiring is set up (to compensate or not) to track it down further.

[btrayfors]

"The AC charger is not going over the isolator, but the alternator's regulator is"

Well, my friend, there you have it! You really should have checked this out earlier.

An isolator contains diodes which DROP THE VOLTAGE, usually about 0.7 volts in the isolators used on boats.

In other words, and depending on how it's hooked up, your alternator/ regulator thinks the battery voltage is 0.7V higher than it actually is. If your alternator/regulator is putting out, e.g., 14.2 volts, the battery is seeing only 13.5 volts.

The battery charger doesn't have this problem because it's not going through the isolator.

Anyway, this might well be part of the problem. You need to draw out your complete charging circuits on a piece of paper, then puzzle out what's really going on.

[CSY Man]

There ya go, you've answered the question.

Well, my friend, there you have it! You really should have checked this out earlier.

Not so fast there boys...

You are assuming the voltage drop is not compensated for: It is! The ships charging system works just fine, never had a problem with it.

After I switched the AC charger to HOT, instead of WARM, the indications are all normal.

The problems was the AC charger pumping too much and over-charging the batteries.
Having tried the new setting on the charger for 6 hours, I only see + 4 AMPS instead of + 40.

The HOT setting was for batt temps over 80F, which is about what we have inside the boat here in Florida in the summer.

Xantrex sells a temp sensor, but I did not spring for it.
Perhaps I should re-visit the price list and see how much they go for...?

[btrayfors]

Glad you're happy.

But, you shouldn't be complacent re: the readings you've been getting, or believe that the temp compensation was the only problem.

"You are assuming the voltage drop is not compensated for: It is! The ships charging system works just fine, never had a problem with it." This is a feel good statement which, without details and measurement data, is meaningless. Apparently, you DID think there was something wrong, and that was the reason for your original post.

There's no way you're gonna pump 40AH into a fully charged battery. A battery will accept only as much charge as it's going to accept, then, everything else is converted to heat, gassing, boiling, etc.

This is the problem with trying to diagnose complex problems piecemeal at a distance, without the benefit of adequate information on the installation itself, test equipment, or test data.

Bill

[CSY Man]

But, you shouldn't be complacent re: the readings you've been getting, or believe that the temp compensation was the only problem.

Well, can;t say I am complacent, yet the problems seems to be gone after I flipped the switch.

"You are assuming the voltage drop is not compensated for: It is! The ships charging system works just fine, never had a problem with it." This is a feel good statement which, without details and measurement data, is meaningless. Apparently, you DID think there was something wrong, and that was the reason for your original post.

Well, if you feel my statements are meaningless, you should quit reading them...

The reason for my original post was to get ideas on why the charging was different from different sources.

If indeed the voltage over the isolator was not compensated for, I would never get full charge on the batteries while underway. (Running the engine)
But that is not the case, again, I have never had a problem with the charging systemt: The boat was re-wired and all the electrical components proffesionally installed by an boat electrician. Not added picee by piece by various previous owners without a clue, as is often the case with old boats.

In this case I had not switched the temprature setting from (Florida) winter to summer, hence got an overcharge situation that showed up on the Battery Monitor.

My fault as I did not switch it in a timely manner, but never looked at myself as complacent, don't think anybody has done as much preventive maintenance on a sailboat as I have.

Thanks for all the help and advice.

[hellosailor]

Manually switching the charger for ambient temperature. Hmmm. I would have thought the charger could sense that by itself, not sure why they'd use a manual switch to do that. Even a decent car alternator knows how hot IT is.<G>
Without knowing what it changes which way, I'd still think putting a temp sensor on the battery is a better way to go. In theory that's just a $2 thermocouple. WIth a $2 splice and $2 more wire and $5 more handling and a couple of retail markets. Shouldn't be more than a $50 part.<G>

[btrayfors]

From the Xantrex TrueCharge 40 amp manual...

Quote
Cold battery temperature. If you choose the Cold setting,
Truecharge + delivers, for example, 14.8 volts in absorption mode and
13.9 volts in float for a Flooded battery.

Hot battery temperature. If you choose the Hot setting for the same
battery, the charger delivers 14.0 volts in absorption mode and 13.1 volts
in float, nearly one volt of difference from the cold battery charge.

Consequence of wrong selection. If you choose a cold temperature
setting for a hot battery, you risk overcharging your battery. If you are in
doubt about which to choose, or if you are leaving the charger connected
for an extended time, select Hot to reduce the risk of overcharging. The
same is true for Gel and AGM type batteries. The life of your battery will
be extended if all banks are in a similar temperature environment and you
make sure the switch setting is correct each time you charge. You should
consider purchasing a Xantrex battery temperature sensor if you expect
wide temperature fluctuations. Unquote

From the Trojan Batteries website:

Quote. Correct the charging voltage to compensate for temperatures above and below 80o F. (Add .028 volt per cell for every 10o below 80o F and subtract .028 volt per cell for every 10o above 80o F). Unquote.

They go further to recommend, for 80 deg F, the following charging voltages:

"Daily Charge 14.8V"
"Float 13.2V"
"Equalize 15.5V"

Why the "hot battery" setting on the Xantrex isn't the default setting is beyond me, given the potential of the "cold battery" settings (14.8V absorbtion and 13.9V float) to damage flooded batteries if not watched closely.

Bill

[CSY Man]

Yeah, I should look into the temp-sensor and all that.

The West price is $35.00, probably cheaper on the internet.

Same for the Xantrex Battery Monitor, it has a temp option, more like $80.00.

Spent so much money on the boat that I hesitate to pour more money into stuff that is not critical, but if I make some overtime in the near future, I may open the purse strings....

[Rick]

O.K. here is what is going on. First please read my previous submissions regarding how fasy you can charge your battery as well as noting the concept of charging using the Amp-hour law and how the so-called 3-step charging regulators crudely approximate the implementation of the Amp-hour law charging method.

The problem is that your alternator regulator does not have a sufficiently high setting for the acceptance voltage (as measured at the battery terminals, not the alternator output terminals). 14.2 to 14.4V is too low at 70 deg. F. 14.4V is "specified" by many regulator suppliers and battery suppliers at that temperature yet the battery will possibly reach full charge at that setting it will not successfully have achieved full potential capacity after several sequential charge/discharge cycles.

I'm betting that the shore charger is giving you a slightly higher acceptance voltage and/or a longer time spent in acceptance before going to float and that is sufficient to replenish more of the lost charge than experienced using the alternator as a source.

Please note that a more exacting method of reading your battery's state of capacity is to use the Link10 (or 2000 or 1000) "almost hidden" data indicating kW-hrs consumed and replenished which is true energy. Amp-hours do not indicate true energy and, therfore, any comparison between Amp-hours consumed divided by Amp-hours replenished is NOT a valid indication of charge/discharge efficiency and any rule of thumb to replenish 20% more Amp-hours than a consumed indication is almost meaningless. Without knowing the voltage you are in never-never land in this regard because the discharge voltage is always less than the charge voltage.

A great use of Amp-hours "missing" from the battery with a Link10 is to use that value to set the acceptance voltage (assuming that your alternator controller lets you do that as does a simple Alpha 3-step regulator) so that the acceptance voltage allows the alternator to deliver the same number of Amps as the scalar value of the number of Amp-hours missing as indicated by the battery monitor. This lets you incrementally force the use of the Amp-hour charging and you may be surprised as to how few adjustments you will have to make. Initially you will discover that the first setting will be at or above 14.7V. Your battery charge acceptance will drop continuously and start to follow the Amp-hour law charging curve almost without decreasing from that value (this will surprise you) until about 20 min before having to go to float whereupon you might decrease the setting down to around 14.5 V or so depinding upon what your monitor tells you. You can always keep the charge current slightly above the Amp-hour law conservative values as long as you are not in a quite hot environment for the battery.

Force float when the charge current drops to 2% of the Amp-hour rating of the battery and at 14.5V near 20 deg.C.

Hope it is amber, not the very dark rum.
Regards,
Rick

[CSY Man]

This is the Battery Monitor Mr. Rick, not the Link 10 or 1000. They may work the same for all I know, never tried the Linkys.

Hope it is amber, not the very dark rum.

It is amber, but uh, I drank it myself, 'cause I solved the problem by moving the switch on the charger from WARM to HOT...



Will read yer post again a few times (After the rum wears off) so I can understand it better, a bit over my head right now. (Got a low ceiling on my boat.. )

[hellosailor]

A very clever monitor, Rick. I didn't realize they could control the charge based on the kWh expended. That's some nice programming.

[Rick]

I don't know if the monitor that you show is programmed internally to track kW-hrs like the Link series was. Problem is that Xantrex either "let go" or ran off all of the legacy engineers who really know about batteries and applications. The power design engineeers from the original Xantrex, along with the ones hired later, are competent in their areas yet not knowledgeable about RV and marine and alternative energy applications (based upon my observations). Do you detect a sour note here?

[CSY Man]

Do you detect a sour note here?

Yeah, uh because of the rum...?

[CSY Man]

Charge Efficiency Factor (CEF)

Not all energy transferred into the battery during battery charging is

also available during discharging of the battery. The charge
efficiency of a brand new battery is approximately 90%, meaning
that 10 Ah must be transferred to the battery to get 9 Ah actually
stored in the battery. This efficiency figure is called Charge
Efficiency Factor (CEF) and will decrease with battery age.
The Xantrex Battery Monitor automatically calculates the CEF of the
battery as the battery is discharged. The level at which the CEF is
recalculated is variable and is linked to the discharge floor set in
F05. The CEF algorithm starts operating when 10% of the difference
between 100% and the discharge floor is discharged from a fully
charged battery.
----------------------------------------------------------

The above note from the users manual.

Tried to dig through the thing and look for Kw-hours, but no mention of it.

I did however order the batt temp. kit for the monitor, found it cheaper on the 'net.
Should be helpful when equalizing the batteries as well as daily monitoring.

(Have not equilized the batteries since bought new banks a year ago...Probably should..)

Rich, there is a bottle of amber left here, what is yer address? :cubalibre

[hellosailor]

CSYman, did you ever stick a digital voltmeter on those batteries to see what voltage which charger was actually DELIVERING to them?

Amber rum...the things we have to "make do" with when the Gossling's has run out. (Sigh)