Float charger question

[markcal]

In my 12v automatic battery float chargers owners manual, it says the battery MUST be fully charged to at least 12 volts.

I know a float chargers purpose is to maintain and not charge a battery. Would you know why it needs to be 12v and if it's below that voltage, would it damage the charger or battery?

Thanks,
Mark

 

[Perrorojo]

Float probably holds to 12.7 volts and very low amps. It may not be able to withstand the draw from a low battery before it gets hot.

 

[American Locomotive]

The weird thing is, is that "12 Volts" is actually just about dead on a 12v lead acid battery. Typically around 12.6 volts is fully charged.

I suspect the float charger may not have enough current output to actually charge a battery.

 

[doorfx]

 

[Showkey]

Don't over think this..............

But........a solution buy a decent charger that charges the battery and then goes into float mode. Plus a decent chaerger will also sense the type of battery ( gel, wet, AGM) charge with the correct profile and float at the correct voltage for the battery chemistry.

 

[Shiftless]

My Deltran Battery Tender puts out only 1-2 amps and then automatically switches to float mode to maintain a battery indefinitely. It has charged a discharged battery but it took 12 hours. I have a 10 amp charger for quicker action but it doesn't have a maintain mode. Different tools for different purposes.

 

[PhysicsDude]

Its more of a safety mechanism than anything, worst case scenario is you have a bad battery that will not charge up to 12+ volts. The charger would pump juice into the battery 24/7 until you disconnect it, which could have bad results on the battery or the tender. More than likely its to prevent the tender from overheating. They're only meant to charge the battery sporadically.

Its really best to have a "smart" 10A+ charger to charge dead batteries anyway. Leaving a bad battery on a 10A charger for many hours can have very bad results. Leave the battery tenders for what they're made for - battery tending. As others have said, it takes 10+ hours to charge a dead battery with a tender... I've done it.

 

[Shiftless]

Just to make things clear, my 10 A. charger automatically switches off when the battery reaches full charge but doesn't have a maintain mode.
PhysicsDude is absolutely correct when he says that a charger that puts out a constant 10 amps needs a timer or it becomes a dangerous tool.

 

[Sal Bandini]

Battery needs to be at 12V because it will not charge a drained battery. If the battery voltage drops too low you need to charge it first with conventional charger.

 

[AntonLargiader]

Charging typically happens at a higher voltage than float maintenance. Depending on exactly what that charger does, the mfg probably doesn't want the user to think that it will add charge to a battery lest the user be disappointed by that. Sounds like a pretty unsophisticated tool, or one designed for a very specific use.

BTW that table is only accurate for some batteries. Maintenance-free batteries will usually have higher voltages than shown.

 

[Sal Bandini]

No, it doesn't have enough capability to charge. This is the same with some battery backup sump pumps. When mine is used and battery falls below certain level the charger will not charge the battery. I have to charge it with standard charger.

 

[MBfreak]

The reason float chargers need above some 11 Volts ( this threshold varies) to start charging is to avoid overcharging a battery with one or more cells shorted out. Since the float charger are mostly running without being manually observed a faulty battery on say 10 A chasing "fully charged " at some 14,15 V to get foldback of current level would cause a faulty battery with one cell shorted out to overcharge and start gassing . Hydrogen gas is very explosive at a certain concentration and requires only a very small spark to ignite.

Best regards

Ola

 

[jvitez]

It's also might be because the float charger will shut off if the voltage is below a certain level due to excessive amperage draw that charger doesn't have the power supply to handle. Ohm's law: volts x amps= watts.

Horses for courses. Huge amount of choices in the battery charging world. Use a standard automatic 10 amp charger to charge a battery till it shuts off, then switch it to the float charger. Automatic chargers also have a minimum voltage level under which they won't turn on. That's why I bought an old-school manual charger with battery boost. It'll get any battery above the minimum threshold so I can use my automatic charger and let it run.