ok....I'm trying to find out and haven't yet found what I'm looking for.....if a charger input wattage is say recorded as '250' - is it less at float? Like would that be what it drawers at its maximum? Or doesn't it matter whatever stage the charger is in?
-- Edited by Grubbygypsy on Wednesday 14th of June 2017 12:50:32 AM
for lead acid batteries the charger generally puts out its maximum amperage (or wattage) when in "bulk" mode, if the battery voltage is under mid-13v.
If over mid-13v the charger will generally ramp down its output (absorb phase) until the battery reachess mid-14v.
The charger will then maintain mid-14v (float) at the level of output required. This is usually only slight compared with bulk or absorbing amps but may still be significant if the battery is large or tired in age.
For example my large AGM battery takes around 150 watts at 14v to maintain float. My figures are a bit ambiguos due to the varied battery types, chargers and settings available but you get my drift?
Thanks heap bagmaker
It helps a lot. That's the only items that requires 240v I haven't been able to get a read on.
My new charger has the documentation - but only at that one rate. I was sort of assuming that in float they'd take very little. I suppose it is in the scheme of things (a small amount), but I just pays to have the knowledge. Especially when confronted with limited power.
>For example my large AGM battery takes around 150 watts at 14v to maintain float.
Some confusion I think: what you write suggests the battery is consuming around 12A when it's being float charged - this is near to impossible.
GG:
Lead acid batteries are pretty simple but modern chargers like to make them look more complicated.
Essentially a sealed 12V lead acid has two charge conditions: charging and float. When charging the charging voltage should be around 14V5 and should remain there until the current has stabilised for a couple of hours. Once that has happened the battery should be put on float charge which means its charging voltage should be reduced to 13V8. These voltage numbers vary, very slightly, across manufacturers and temperature.
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"I beseech you in the bowels of Christ think it possible you may be mistaken"
Oliver Cromwell, 3rd August 1650 - in a letter to the General Assembly of the Kirk of Scotland
As a rough guess your charger is rated at 15 A. As the battery is reaching the charge where the charger rolls over into the absorption stage it would be putting around 200 W of power into the battery, the charger would be at least 90% efficient so it would be drawing around 220 W power from the mains. The manufacturers would have rounded that up to 250 W to be safe in their specifications.
As the battery comes into the absorption stage the current will drop off so the power supplied will drop off. The power drawn from the mains will = V x I / X where V is the battery terminal voltage, I is the current is current drawn by the battery and X is the percentage efficiency of the charger divided by 100.
For example, if during the absorption stage the voltage is 14.3 V, the charge current is 4 A and the efficiency of the charger is 90% then the power drawn from the mains will be 14.3x4/.9=63.5 watts.
Many manufacturers will claim an efficiency of 95% or more but that will be at the most optimal operating conditions. As the output current reduces the efficiency drops off and will be considerable less during trickle charging but the power draw will still be much less than the 250 W figure quoted.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
I would like to add that if the charger is a switch mode design, which most of the fancy ones are, it is difficult to accurately measure the power being being put into the battery, particularly in float mode, because the chargers "pulse" the current. So using a normal cheaper style multi meter you may not get reliable reading of the current or voltage. They are only designed for steady DC or sinewave AC readings. Just because you get a reading to 4 or 5 digits it is not necessarily actually what is happening. Just pointing this out for those interested.
They are only designed for steady DC or sinewave AC readings. Just because you get a reading to 4 or 5 digits it is not necessarily actually what is happening. Just pointing this out for those interested.
