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Old 27-11-2018, 16:42   #1
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Overcharging Batteries

Does overcharging batteries with a dumb regulator reduce battery life and if so by how much? Dumb alternators never go to float voltage and stay at absorption voltage fore ever.
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Old 27-11-2018, 16:47   #2
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Overcharging Batteries

Your going to get varying answers to this, cause. In truth it does indeed vary.
Most alternators are set for 14V plus or minus .2V, that was the old automotive standard
Many,many automobiles run their batteries at 14V for thousands of hours and donít kill batteries, cause those batteries can tolerate it as can many of our banks.

Some batteries like Gel for instance, canít.

However itís my opinion that dumb alternators kill banks by never charging them, not by overcharging them, so if there isnít any supplemental charging like Solar or generator etc., then yes they contribute to a early death due to chronic undercharging.

See dumb alternators come from the automotive world, where an alternator isnít really used to charge a battery, itís used to run the electrical system, and ensure the battery isnít discharged.
Yes there is some charging of course, just maybe not a whole lot.

Oh, they donít stay at absorption forever, they stay in a voltage usually between absorption and float, so itís unlikely they overcharge, itís more likely they donít do much charging.
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Old 27-11-2018, 17:23   #3
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Re: Overcharging Batteries

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Does overcharging batteries with a dumb regulator reduce battery life and if so by how much? Dumb alternators never go to float voltage and stay at absorption voltage fore ever.
Depends on the battery type and voltages
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Old 27-11-2018, 17:34   #4
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Re: Overcharging Batteries

Will they just need watering more often? I know cars and trucks have dumb alternators but their batteries are starting batteries and not deep cycle batteries. They also have a constant flow of air around them to keep them cool.
Dumb alternators are actually very good at fully charging batteries if their voltage is set correctly. They stay at the set voltage and don't drop down to a float voltage prematurely. Trojan recommends a maximum of 4 hours in absorption I think.
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Old 27-11-2018, 18:43   #5
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Re: Overcharging Batteries

Charging a bit too low but all the time after full, no Float, will greatly shorten AGM lifetime, less so FLA.

Set to high end of spec more damage.

If it's a big expensive bank, put in external VR, or a DCDC charger.

Starter batt, who cares. , .
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Old 27-11-2018, 19:29   #6
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Re: Overcharging Batteries

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Does overcharging batteries with a dumb regulator reduce battery life and if so by how much? Dumb alternators never go to float voltage and stay at absorption voltage fore ever.
That's not quite correct. The sense wire will reduce voltage to a reasonable level even on a "dumb" charger. Consequently, you assumption the alternator stays at th higher rate is incorrect.
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Old 27-11-2018, 19:34   #7
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Re: Overcharging Batteries

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That's not quite correct. The sense wire will reduce voltage to a reasonable level even on a "dumb" charger. Consequently, you assumption the alternator stays at th higher rate is incorrect.
Huuuuum, what "sense" wire? The voltage will stay constant but the current will drop to whatever the battery will accept. That's what voltage regulators do.
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Old 28-11-2018, 06:24   #8
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Re: Overcharging Batteries

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Will they just need watering more often? I know cars and trucks have dumb alternators but their batteries are starting batteries and not deep cycle batteries. They also have a constant flow of air around them to keep them cool.
Dumb alternators are actually very good at fully charging batteries if their voltage is set correctly. They stay at the set voltage and don't drop down to a float voltage prematurely. Trojan recommends a maximum of 4 hours in absorption I think.
Yes just more watering assuming you are talking normal absorption voltage. I have my system set to stay in absorption for 6 hours and sometimes that isnít even really long enough based on acceptance. My 4 t105s use about 2 cups
Water every 2 months.
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Old 28-11-2018, 06:51   #9
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Overcharging Batteries

You guys are assuming a dumb alternator will overcharge a bank, and unless your motoring for days on end, I donít think it will.
As far as 14 V killing an AGM, how about the millions of AGM batteries in automobiles?

The BIG advantage of a three stage charger is that it will jump the voltage up considerably higher than 14 V so that your bank is actually being charged, and then turn itself back down when the bank is charged, not that it doesnít overcharge.
There are likely 100 boats out there with just stock alternator set ups for each boat with a three stage alternator controller, yet banks are not being destroyed left and right from overcharging.
Balmar and others arenít stupid with their marketing, if stock alternators were destroying banks, you would see advertising saying install our controllers and stop cooking your batteries, but you donít.
You see advertising install our controllers and have your banks charged better and faster, cause that is what happens.

On edit, 14V was picked long ago as a number that was high enough so that some charging would occur, but not so much so that if applied continuously that it would cook the average flooded battery.
Some aircraft we had adjustable voltage regulators and would turn the voltage up in Winter weather, and down in Summer weather, but never went to three stage chargers.
You would be surprised at how much some aircraft batteries cost
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Old 28-11-2018, 06:53   #10
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Re: Overcharging Batteries

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Yes just more watering assuming you are talking normal absorption voltage. I have my system set to stay in absorption for 6 hours and sometimes that isnít even really long enough based on acceptance. My 4 t105s use about 2 cups

Water every 2 months.


See, you have this battery stuff figured out. You used to say you didnít care, batteries were an expendable item, now you are obviously caring for them, and will of course save money.
But I think your right, average bank is chronically undercharged, very, very few are often overcharged
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Old 28-11-2018, 09:24   #11
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Re: Overcharging Batteries

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See, you have this battery stuff figured out. You used to say you didnít care, batteries were an expendable item, now you are obviously caring for them, and will of course save money.
But I think your right, average bank is chronically undercharged, very, very few are often overcharged
I always have cared and taken care of my batteries. I just donít obsess over them and treat them like Iím here to serve them, they are here to serve me.

Thatís what Iíve been saying and still believe over saving $50/year by praying to the expendable battery god on my boat
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Old 28-11-2018, 09:56   #12
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Re: Overcharging Batteries

So are we saying a stock single stage adjustable regulator could be better than an external three stage alternator? Or even a stock non adjustable alternator set at say 14.2 to 14.4 volts? I think external three stage alternators are more suited to trawlers that motor for days or weeks at a time.
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Old 28-11-2018, 10:46   #13
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Re: Overcharging Batteries

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The BIG advantage of a three stage charger is that it will jump the voltage up considerably higher than 14 V so that your bank is actually being charged,
Aren't the newer regulators set higher than that? A recently installed Beta onboard has an Iskra alternator set at 14.6v.
Certainly no point in me spending boat bucks on an external reg the trojans are unlikely to complain about sitting at absorption for a few hours beyond charge once in a while. Switching to float early is a more likely culprit for a battery trasher.......
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Old 28-11-2018, 11:13   #14
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Re: Overcharging Batteries

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So are we saying a stock single stage adjustable regulator could be better than an external three stage alternator? Or even a stock non adjustable alternator set at say 14.2 to 14.4 volts? I think external three stage alternators are more suited to trawlers that motor for days or weeks at a time.


No, cause at 14V for most batteries, not a whole lot of charging goes on, that plus the Yanmar alternators are very self protective, if they start making good power, they get hot and cut back on power, makes them last a very long time, but doesnít do much for charging.
Have to remember that a stock alternator is not meant or intended to charge a battery bank, itís meant to only replace the tiny bit of power removed from a single starting battery during engine starting.
A very good argument can be made that if your expecting to charge a discharged house bank with a stock Alt, your not using the right tool for the job.

A three stage controller if properly adjusted will work hard and charge the bank, then cut back to not overcharge, and of course is adjustable for your particular batteries voltage requirements
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Old 28-11-2018, 11:14   #15
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Re: Overcharging Batteries

Yes Conachair, I think that's right. The only advantage of an external three stage regulator is to charge quickly to around 80% SOC .
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