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Discussion Starter · #1 ·
Was reading Maine Sail's battery monitor article (Installing A Battery Monitor Photo Gallery by Compass Marine How To at pbase.com), and he states when talking about synching:

Rule #1 of Ah counters: Disable the "auto synch" feature and use manual "known full" re-sets.

What is known full?

*Voltage at 14.4V+ - Check

*Net "accepted current less than 1.5% of Ah capacity - Check

*Okay to reset to full

NOTE: Battery voltage MUST be at absorption level NOT a float voltage.

I don't understand why this is. Seems like if I leave it to charge, when it is full it will be at float voltage. For example my batteries have been charging on shore power for 3 days. The charger is in Float mode. I would assume they are full and I can reset, but voltage is at 13.55.

Can someone explain this to me?

Thanks,

Brian
 

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Was reading Maine Sail's battery monitor article (Installing A Battery Monitor Photo Gallery by Compass Marine How To at pbase.com), and he states when talking about synching:

Rule #1 of Ah counters: Disable the "auto synch" feature and use manual "known full" re-sets.

What is known full?

*Voltage at 14.4V+ - Check

*Net "accepted current less than 1.5% of Ah capacity - Check

*Okay to reset to full

NOTE: Battery voltage MUST be at absorption level NOT a float voltage.

I don't understand why this is. Seems like if I leave it to charge, when it is full it will be at float voltage. For example my batteries have been charging on shore power for 3 days. The charger is in Float mode. I would assume they are full and I can reset, but voltage is at 13.55.

Can someone explain this to me?

Thanks,

Brian
This is because many chargers are simply not as "smart" as the label says they are.

Also 1.5% - 2% acceptance at 13.4V is simply not a full battery. It would be full at 14.4V & 1.5 - 2% (or your batteries acceptance rate) but not 13.4 and 1.5% - 2%.

If you are seeing .05% acceptance at 13.4V then yes that would be full. You can get batteries full at float voltages but it takes a long, long time. Some chargers even use simple egg timer programs to transition to float regardless of ever even attaining absorption. One "big name" charger start a 4 hour timer from the minute you turn it on. At 4 hours it drops to float. With a big enough bank it can go from bulk straight to float....

The best way to confirm is absorption & net accepted current but float can work too the current will just be lower, like below .05%...
 

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Discussion Starter · #3 ·
This is because many chargers are simply not as "smart" as the label says they are.

Also 1.5% - 2% acceptance at 13.4V is simply not a full battery. It would be full at 14.4V & 1.5 - 2% (or your batteries acceptance rate) but not 13.4 and 1.5% - 2%.

If you are seeing .05% acceptance at 13.4V then yes that would be full. You can get batteries full at float voltages but it takes a long, long time. Some chargers even use simple egg timer programs to transition to float regardless of ever even attaining absorption. One "big name" charger start a 4 hour timer from the minute you turn it on. At 4 hours it drops to float. With a big enough bank it can go from bulk straight to float....

The best way to confirm is absorption & net accepted current but float can work too the current will just be lower, like below .05%...
Just to be clear, .05% acceptance on a 225 AH battery is .113 amps?

My monitor currently shows I = .31 amps, so basically it is still charging, just slowly? I should wait until it reads I = .113 amps or less before I do the synch?

As instructed I am only doing manual synchs, so just want to make sure I am pushing the synch button at the right time. The charger is an Iota 55, which I just installed. Long term I will be using this charger only as a backup and my solar controller will be the primary charging source.

Thanks,

RD
 

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Just to be clear, .05% acceptance on a 225 AH battery is .113 amps?

My monitor currently shows I = .31 amps, so basically it is still charging, just slowly? I should wait until it reads I = .113 amps or less before I do the synch?

As instructed I am only doing manual synchs, so just want to make sure I am pushing the synch button at the right time. The charger is an Iota 55, which I just installed. Long term I will be using this charger only as a backup and my solar controller will be the primary charging source.

Thanks,

RD
My bad should be .5% or 1.125A can be considered full..

BTW here is a 400Ah Trojan bank at 14.4V. This is really "full"...

Yes that is 0.1A of accepted current at 14.4V or 0.025% net accepted current......



This is why even small unregulated solar panels can still cook batteries!!
 

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Discussion Starter · #5 ·
Here is my confusion: I thought the bank would only be at 14.4 volts if the charger is still in absorption mode. I also thought with a properly designed charger, it should almost never be full and in absorption mode at the same time. As soon as the acceptance drops to a suitably low level, the charger should switch to float mode. Is this not how it works in theory? Or is it just that my idea of "properly designed charger" is naive?
 

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In theory a charger would always switch from absorption to float at 98-99% SOC.. Sadly chargers are voltage devices and many really, really suck at determining when to transition. Most cheap chargers simply use a timer, 2 hours, 4 hours, 6 hours etc... Better smart chargers use variable time, voltage, time to attain voltage, time in bulk etc. and even power supply output current in an attempt to calculate and determine a more proper time necessary for absorption.

Unfortunately other parameters such as on-board loads can get in the way of even the best smart chargers.. Just because a charger has entered float does not mean the batteries got full during absorption so they may still be filling during float but at a much lower rate due to the lower voltage. If in float you see .5% or close to it feel free to do a reset. If it has been floating for days then obviously you can reset.

The big problem for owners is not resetting the BM at the dock but rather when off cruising. This is when using 1.5% - 2% and absorption voltage is most handy because no one wants to run the motor long enough to even enter float.

Many chargers, charge controllers and regulators switch to float "prematurely" and this is why I stress 14.4V and 1.5-2%. because it is easy to see 13.6 and 1.5-2% if it went into float prematurely but this would not represent "full"...
 

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Can one reasonably out fox a charger by turning it off and then back on after four hours and get a full charge?
Take the scenario - sailed all day, tied up in a marina and plugged into shore power. Let it charge for four hours, turn it off (how long?) turn it back on and let it charge until tomorrow's departure. Would that give you anything close to a full charge?
John
 
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