AGM battery chargers vs normal battery charger?

Re: AGM battery chargers vs normal battery charger?

A good place to start is reading the Battery FAQ.

Basically, AGM batteries are very sensitive to overcharging vs flooded cell batteries.

When you overcharge, the battery generates hydrogen gas by breaking down the water into hydrogen and oxygen. In a flooded cell battery, when this happens you simply add distilled water to bring the electrolyte level back up.

With an AGM battery, several things happen differently. There is still hydrogen and oxygen being generated--but there is a small platinum (or similar?) catalyst in the battery cap. This recombines the hyrodgen and oxygen back into water. This both "wears out" the catalyst and generates heat. Do this often and with enough current, it will cause the battery to overheat and "vent"--letting gas and water out of the sealed battery. And you have no way to refill the battery or replace the catalyst (not quite true--there are some people that have successfully replaced the water and put on new caps--the caps are not cheap, and you don't know how much water to replace without special equipment).

About charging a deep cycle battery (flooded cell)--the batteries will charge on a battery charger--but they are usually not designed to be left on the charger. Either the charger will over charge the battery (too much current into the battery will "boil" the electrolyte--hydrogen and oxygen--causing the battery to fail over time and/or overheat)--Or, not charge with high enough voltage (for a couple hours) to properly equalize the battery (get all cells to 100% charge and mix the electrolyte).

Chargers designed for long term charging of flooded cell (or AGM) batteries will frequently have a remote temperature sensor (battery charging voltage is temperature sensitive) and 2-3+ charging stages--with the last stage a "float" voltage setting (backs charging voltage back to around 12.7-13.6 volts to prevent boiling a battery dry) and/or an automatic or manual equalize setting (which can be turned off/adjusted for AGM/sealed batteries).

If you put the battery on charge until the current is reduced/voltage peaks--and don't leave the battery on charge for days on end--you should be OK.

Also, if you are using AGM's--they have low self discharge and should be able to sit for a few months between charges (see vendor specs.). You can use an accurate volt meter to estimate the battery state of charge (or measure the specific gravity of the electrolyte for a flooded cell) and recharge it when it gets down near 80% state of charge (20% discharged). Bad things happen to batteries when they are stored below ~75% state of charge for days or longer (sulfates harden and battery storage capacity is permanently reduced).

-Bill

PS: You can check out this thread about small/good quality maintenance chargers.

Re: AGM battery chargers vs normal battery charger?

Lloydy,

I am not exactly sure what you are asking about...

Generally -- you have a power source (120 VAC, solar panel, etc.), goes to a Battery Charger (or Charge Controller) which may shift the power (from 120 VAC to 15 VDC) and provides current to a battery bank in an appropriate manner.

At least, from a definitional point of view--A Battery Charger and a Charge Controller are sort of the same thing...

However, there are many types of Battery Chargers/Charge Controllers out there that are designed for specific uses...

You have the normal Car Charger (120 VAC to 15 VDC).

You have simple Solar Charge Controllers (manage the solar panel current/voltage to the battery bank).

And you have sophisticated Solar Charge controllers (MPPT Type) which optimize the solar panel's I*V curve to the battery bank's I*V curve (maximize power transfer)...

There are even charge controllers that take energy from a 24/48 VDC battery bank and drop it down to charge a 12 volt battery bank (high voltage truck or something and 12 VDC accessory like a HAM/CB radio).

And then you have other specialized controllers (one common type known as a shunt controller) which "bleeds" power from the battery into a load (air or water electric heater typically) because the charging source (wind or water turbine) cannot allow to be "unloaded" or they will overspeed and self destruct. The turbine simply outputs as much power as it can into the battery bank + load--and the shunt controller turns on when the battery is fully charged and dumps the current into the load/resistor bank as waste heat.

And some of the Solar RE controller have multiple function and can actually be setup to operate either as a "pass through" or "shunt" controller--depending on the need of the installation.

So--if you have a particular application, describe your needs rather than trying to "fit" your need to a particular controller--I think we can help better that way.

-Bill