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48V float charger

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kubeek

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I am trying to work out how to make a float charger for a 48V AGM battery.
The problem I am facing is that the charger will be supplied by a full-wave rectified sine at 80-100Vpeak (this is a system requirement and there is really no good way around that). I tried to make it with just two opamps and an output transistor, but the whole thing is not very stable (see the schematic).

How would I calculate the feedback or what should I change so that the battery current after the initial charge at 0.5s settles and is with little ripple?
 

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I am trying to work out how to make a float charger for a 48V AGM battery.
The problem I am facing is that the charger will be supplied by a full-wave rectified sine at 80-100Vpeak (this is a system requirement and there is really no good way around that). I tried to make it with just two opamps and an output transistor, but the whole thing is not very stable (see the schematic).

How would I calculate the feedback or what should I change so that the battery current after the initial charge at 0.5s settles and is with little ripple?
How much current?
 
Well the manufacturer says that at 25°C the float current drawn by the batteries should be somewhere around 10mA.
I might need to feed some 400mA to an allways on solenoid which is not too picky about current, but needs to be connected to the battery in case the main charging supply gets interrupted. The power dissipation in the linear driver can be managed without any concern, but the main point is that the current to the battery according to manufacturers needs to have as little ripple as possible. When the battery is on float charge the manufacturer says that the current must not be alternating, that is a few hundred amps in an then a few hundred amps out alternating at 100Hz is a no go.

But even if my linear approach is not going to be implemented, how would I go about stabilising the feedback so that it does not ocillate and is not a square wave along with the mains feed frequency, just from the theoretical point of view?
 
Being lazy I took the easy way first with a LM317HV and a little filter cap.
I'm still working on the hard way. :D
 

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  • 48v float.asc
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Thank you Ron :)
Here is another to play with.
To compensate it I just use a pulse at power on and make it well behaved at the output. Then do the same with a step in current on the output. See C3. Some smart guy could probably calculate it.:woot:
 

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