EFB and AGM batteries charge faster?

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I see the blurb on these batteries being able to charge a lot faster than standard flooded batteries. But how does it charge faster if the alternator is not modified to put out more current?
I read that on older cars that dont use smart alternators the charge current to the battery is around 5amps. So does that mean efb and agm will not be charged any quicker than a regular battery?
 
Originally Posted by slybunda
... But how does it charge faster if the alternator is not modified to put out more current?
I read that on older cars that dont use smart alternators the charge current to the battery is around 5amps. So does that mean efb and agm will not be charged any quicker than a regular battery?
Recharge current to a typical car's battery is not fixed, and normally has very little to do with the peak current capacity of the alternator. It depends not only on the battery type, but also several other factors, including applied voltage, and the size, state-of-charge, and condition of the battery.
 
But even if its a small alternator e.g 50amp you cant charge a battery at full 50 amps otherwise the battery would heat up and explode. Or is that not the case?
 
From my understanding, unless a car uses algorithm-controlled charging in the form of coding a power control/distribution module like a BMW or PCM-controlled charging that regulates the alternator, the car will charge an AGM/EFB like any other battery at a constant rate.

Toyota installs EFBs as default in the Prius and the aftermarket has responded with AGMs but there isn't any programming needed for the DC-DC converter within the inverter that provides 12V output for the auxillary loads.
 
The battery accepts as many amps as it wants at the system voltage reaching the battery terminals, upto the maximum output of the charging source.

Higher voltage sought means more amps flow.

Agm batteries have less resistance than flooded and can charge faster with higher electrical pressure and a alternator capable of delivering a lot of amperage above that required to run the vehicle and accessories
 
Originally Posted by wrcsixeight
The battery accepts as many amps as it wants at the system voltage reaching the battery terminals, upto the maximum output of the charging source.


i have read from here: https://www.impactbattery.com/blog/2017/05/how-fast-can-i-charge-my-car-battery/ and here: https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

that charging car battery with high ampage is not possible since battery can blow up.
so i dont get how for example a 70 amp alternator can dump all its current into a battery in one go, it would cause the battery to heat up considerably and blow up.
most of those websites i have checked say that charging lead acid batteries should be no more than 20% of the ah rating, most suggest 10%. so a 50ah battery should be charged at 5amp or so.

nthach's post above makes sense that the cars alternator/control module needs to be programmed to work with a battery that accepts a higher charge rate.
so what happens if you put an EFB or AGM battery in an older car that was designed to work with just a normal flooded battery? does it charge at the same rate as the flooded battery or will it actually charge up faster?
 
At least for Odyssey AGM there is no initial current limit.
I have discharged the Group 65 Odyssey in my Crown Vic to 12.0V which is pretty much completely discharged, started the engine and using a current clamp noted that it was charging at 100A. I have a 130A alternator. This is faster than any standard battery can accept. The alternator doesnt care about what battery is attached. It is just trying to meet its regulation voltage. If its looking for 14.2V then it will increase its output until it meets that, or the field duty cycle is 100%. A AGM has low internal resistance which means it can accept more current so the alternator will put out more current. This low resistance also means the battery will not heat up as much while accepting that much current.
Provides for very quick charging. It works fine with no changes to the vehicle, however, the issue with AGM is they like a bit higher charge voltage, so I need to go into the PCM and turn up the voltage control a couple tenths one of these days..
 
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Ahh. So if a battery is discharged will it pull down the alternator voltage making the alternator put out more current to get the voltage back up?
I know this happens in my car if i put something electrical on like the rear windscreen defogger the volts drop for a split second and then go back up.

If batteries can be charged at high amps why are those websites saying that they shouldnt be charged up with high amps?

Is alternator voltage adjustable on all cars? Can it be done on my celica?
 
Originally Posted by slybunda
Ahh. So if a battery is discharged will it pull down the alternator voltage making the alternator put out more current to get the voltage back up?
...
If batteries can be charged at high amps why are those websites saying that they shouldnt be charged up with high amps?

Is alternator voltage adjustable on all cars? Can it be done on my celica?

correct.

It will only charge at 100A or 60A or 40A for a few minutes, to get the battery voltage back up to pre-starting level - not long enough to 'heat up' the battery to cause damage, just replacing the recent 'start-discharge'.

You DONT want to charge a battery at 100A for hours and hours..... those charging chart currents are for 'continuous' charge

not adjustable on most cars/alternators...
 
ahh this is starting to make sense now. so does the alternator see a discharged battery as a load like a regular accessory?

what determines the maximum charge acceptance current of a battery?
 
Originally Posted by slybunda
ahh this is starting to make sense now. so does the alternator see a discharged battery as a load like a regular accessory?

what determines the maximum charge acceptance current of a battery?

Yes it does.
Charge acceptance current will be based on the internal resistance....Lower resistance battery will take more amperage for the same voltage than a bettery with higher resistance. Look up Ohms law calculators and play with the resistance vs current. Youll see that if you keep the voltage the same, the current will vary drastically based on the resistance.

And I measured near 100A into the battery for about 10 minutes before it started tapering off....I had sucked a lot of juice out of the battery running my radio in the garage.
 
thanks for this info.

i also read that for my cars that use regular flooded batteries i cant use an AGM battery due to its higher charging voltage requirements. but is an EFB battery a direct replacement/upgrade for a regular flooded battery or does EFB also have particular charging requirements?
 
I'm using AGM batteries in both the 2005 Buick for three years so far, and the 2007 Honda for two years so far. They are working fine, no problems to report. I usually get about 5 years from a battery and thought I would try AGM to see how long they will last in comparison. I bought each one at a decent sale price at Canadian Tire, so I thought worth a try.
 
Did some reading on EFB batteries, and yes, they do appear to be a direct replacement for standard flooded cell batteries.
 
The wiring will limit the current fed to the battery more than anything else. A discharged AGM like an Odyssey can accept huge amps initially, and the alternator will be whining pretty good delivering as much as the twinned 8GA wires will carry. With a better conductor (than the sad 8GAs), that batt could see even more amps. Wouldn't want to stress the alt or fry the diodes though.
 
Battery manufacturer recommendations as to charging amps are intended to minimize the possible return percentage

My northstar 90 ah agm regularly sees 40 amps. 65 amps when i stack chargers when well depleted. And the alternator can do upto 108 amps, When cold and 2200+ rpm when my voltage regulator is seeking 14.7v. If i ask it for only 13.6 amps at the same level of depletion about 30 to 40 amps flow.

This battery now has 1000 deep cycles on it and turned 5 year's old last month.

The higher $ agms want huge amperage when depleted. The lesser agms say 30% of ah max.

My battery warms up with huge charge rates. But has never exceeded 110 f in 90f ambient.

Ithe battery is only going to accept huge amps when depleted below 80% state of charge.

The issue with alternator recharging depleted batteries is not too much current. It is the voltage regulator rolling back voltage way too early.
 
Originally Posted by slybunda
but is an EFB battery a direct replacement/upgrade for a regular flooded battery or does EFB also have particular charging requirements?

From my understanding, a EFB is more or less a flooded battery that is sealed and has valve-regulated venting.

The earlier Miatas and Prius(or any Toyota/Lexus hybrid that doesn't use a group 51R battery in the engine bay for the 12V auxiliary loads and "booting") are the more common EFB applications. And if you loosely apply the definition of an EFB, the original Delco Freedoms could be considered EFBs, as well as Dekas due to their sealed lids.
 
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