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Old 09-08-2020, 07:15 PM   #1
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Large alternator's

I'm looking to upgrade my alternator and the Surepower ones linked below caught my attention, but I have some concern about the output voltage. Once fully charged, a lead acid battery should be float charged at around 13.5 or so to avoid being above the gassing voltage at which the electrolite begins to boil the water out. The Surepower maintains as high as 14.5V even when sensing a fully charged battery. I wrote to their customer service dept and expressed my concern and received the reply below.

"The regulators have a float charge within them when they're sensing voltage to help keep the battery healthy and not over charge. So they'll still be at 14.4-14.5 but they'll be float charging because technically the battery is never full when the vehicle is in operation."

As the battery temperature increases, the max float voltage to avoid gassing decreases. At 50C (120F) which is an easy to reach under hood temperature, that max float voltage drops to 13.8, quite a bit above 14.5.

If the regulators have a "float charge within them", but never reduce the voltage, how does it safely float the batteries? This seems odd to me, anyone care to comment?



https://www.dcpowerinc.com/search?q=Ford+F-150+2000
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Old 09-08-2020, 08:38 PM   #2
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Because the alternator never really gets the battery fully charged. While the voltage is high, the current is limited to not fully charge the battery. So you don't really need a float stage.

-greg
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Old 09-09-2020, 11:03 AM   #3
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Because the alternator never really gets the battery fully charged. While the voltage is high, the current is limited to not fully charge the battery. So you don't really need a float stage. -greg
Well, I suppose that could be, but I'm having trouble wrapping my head around that kind of strategy when battery manufacturers advise against the higher float voltage, no matter the source, be it solar, shore power, or alternator. I guess I need to do some more research, but in the meantime I'll just accept it at face value. Thanks.........
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Old 09-09-2020, 11:25 AM   #4
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Originally Posted by arctictraveller View Post
Well, I suppose that could be, but I'm having trouble wrapping my head around that kind of strategy when battery manufacturers advise against the higher float voltage, no matter the source, be it solar, shore power, or alternator. I guess I need to do some more research, but in the meantime I'll just accept it at face value. Thanks.........
arctic, thought you presented a great question initially and been interested enough to see the outcome...not quite the response I expected either.

I simply don't have enough knowledge to comprehend the finer points of "electrical", consequently I would have concluded the same principle applies to pumping air into a tire without stopping...ultimately it blows.

Even thought it doesn't satisfy what I would interpret "logical", guess I too have to consider the source - Cant go wrong with advise from Scalf77.
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Old 09-09-2020, 12:11 PM   #5
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They could limit current using PWM rather than voltage regulation. But their website doesn't offer any such information. Or really much info at all...
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Old 09-09-2020, 12:51 PM   #6
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They could limit current using PWM rather than voltage regulation. But their website doesn't offer any such information. Or really much info at all...
Telling me that there is a ""float charge within them" seems really weak. It's the type of explanation one would expect from someone who doesn't really understand how something works. I much prefer a science / engineering based explanation.

[QUOTE=Twoxentrix;281205]"I simply don't have enough knowledge to comprehend the finer points of "electrical", consequently I would have concluded the same principle applies to pumping air into a tire without stopping...ultimately it blows."[QUOTE]

Actually, batteries can explode, but over charging a lead acid battery will first result in boiling the electrolyte, which will eventually dry it out completely. In the process, hydrogen gas is produced, and once the battery is completely or nearly completely dry, it heats up to the point where it can ignite the hydrogen and cause an explosion. But, it's highly unlikely this would happen in a vehicle because long before you got to this point, it wouldn't be able to start the motor. It could happen though if you were plugged into shore power for long periods and failed to keep the water level up.

Anyway, in the long run, I'm sure operating at a higher voltage level wouldn't show any real issues for quite some time, but could possably reduce battery life. So, I will continue to investigate and query some battery manufacturers. Stay tuned...................
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Old 09-09-2020, 01:09 PM   #7
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I suppose this is where the DC to DC charger rather than the alternator directly really helps.
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Old 09-09-2020, 02:26 PM   #8
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Actually, batteries can explode, but over charging a lead acid battery will first result in boiling the electrolyte, which will eventually dry it out completely. In the process, hydrogen gas is produced, and once the battery is completely or nearly completely dry, it heats up to the point where it can ignite the hydrogen and cause an explosion. But, it's highly unlikely this would happen in a vehicle because...
Yes, Sorry. This I'm aware of. I should have better clarified the use of my example: simply that delivering excess can/would have consequence...as in over-charging.
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Old 09-09-2020, 02:42 PM   #9
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Yes, Sorry. This I'm aware of. I should have better clarified the use of my example: simply that delivering excess can/would have consequence...as in over-charging.
Hey, no worries, I'm just stuck at home spouting off random stuff I think to be true, rather than getting my ass out in the hot garage and getting some real work done.
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Old 09-09-2020, 03:00 PM   #10
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Well, there is a big difference between the how the various chargers work, and pretty much why some will have a float charge or no charge. The alternator is the simplest of the charging systems, as it in essence controlled by voltage, as the voltage goes up less current is put out of the alternator. The current output is a function of voltage level, more load, or battery resistance the voltage drops and the current is increased. As the battery charges the voltage goes up , reducing current output of alternator. The voltage should be at least above 14.2 volts to charge most lead acid batteries.

When we move into a two stage or three stage charger, we have a completely different algorithm. The first phase is bulk, and is a constant current phase, if you have a 40 amp charger it will put out 40 amps of current, as the charge level goes up the voltage level will go up and induce the charger to go into absorption phase.

Absorption is constant voltage with controlled current. While in absorption, the charger will hold the battery at a voltage and start to tapper the current down, the current it provides is always a little more than would be needed so that it can fill the battery to full capacity. This is the phase of the charger that fills your battery to full SOC. The mechanism of leaving absorption , is usually based on current level derived from bank size, and/or time in absorption. The charger will then go into float charge and have become voltage controlled.

Even a long duration on proper float voltage, can reduce water levels and cause problems with wet lead acid batteries especially for chargers that are set for a AGM float voltage. A two stage charger is similar to three stage process but once charged it will then end, the battery will provide power and when the battery level drops enough it will begin the process over.

The two and three stage algorithms are usually used in shore power and solar controller. Their intent is to charge and maintain a deep cycle battery. The alternator uses a voltage regulator to provide the charge capacity of battery. The intent of the automobile alternator is to provide current to run the electrical system, and to charge the battery back up to provide current to start the car. to provide adequate cranking amps you don't need to push current back into the battery. It doesn't really matter if your alternator is putting out 14.2 volts or 14.5 volts, it is would be to high for a float voltage.

I agree their explanation may not have been great, but it is technically correct. They don't overcharge the battery because don't really ever reach full charge, the current level provided at regulated voltage will always be a little less then what is needed to fully charge the battery.

This is why you will not maximize the life of your house battery if you only have a alternator as your major charge source. This is also why I don't like auto bidirectional ACR's, if you plugin all the time, a long float charge could reduce your water level in start batteries.

Yes, this is one of the reasons DC to DC chargers have taken off.

-greg
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