Two stage battery charger

[muddasirwaheedmalik]

hi.
I am designing a 2 stage battery charger for my 48V lead acid battery 150A. The first stage would use ELTEK twin power plus rectifier set at 56.4 Volts with constant charging current around 50A (C/3). Now i need a circuit which senses the current reduced to 10A (as the batteryELTE termainal voltage rises) , i will then disconnect the ELTEK mains (through (SSR) and connect the mains (through SSR ) of smaller Eltek Flat pack rectifier set at 54V .Hence the two stage charging.

I have a shunt resistor which gives 60mv at 100A (60mv/100=0.6 mOhm resistane) by which i read charging current through panel type digital ammeter, 10A charger current will give 6mV , can i have any circuit which turns on/off a solid state relay by sensing current below 10A, or voltage below 6mv ?????

Regards

 

[tpetar]

You can use microcontroller ADC to sense mV on current shunt when is under 10A and then do the job.

This second phase is float charge ?

 

[muddasirwaheedmalik]

yes thanks, but microcontroller ???? isnt it too much just for charger change ? the reason i am using this topology is that i already have two SMPS supplies, i have adjusted voltages now for two stage charging i just need to switch them in sequence, constant current first at 56.4 and when current drops below 10A switch charger with lower float voltage 54V. BTW which micro controller ADC u were refereing to and can any one get pin configuration for ELTEK TWIN power pack plus rectifier it seems to have remote shut down function/float function pins indicated on it but how to wire them is not known .I tried grounding and giving high rails but nothing. Any help here?

 

[D.A.(Tony)Stewart]

THis depends if this is just for you or a commercial design. Can you specify budget, efficiency & time constraints? Beware of the risks of charging defective cells with 10kW chargers.

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My previous warning was to ensure you consider safety 1st not last...

o Low mains alarm
o High mains alarm
o Low output voltage alarm
o Over voltage shutdown alarm
o Current limit alarm
o Current sharing alarm
o Fan Alarm
o Temperature alarm
o Rectifier failure alarm

 

[muddasirwaheedmalik]

thanks. the rectifiers already have these features built in, so its not an issue. its for personal use. its not 10KVA its 3000VA SMPS for constant current stage where voltage will be brought up to 56.4 Volts during bulk stage and when when current will fall below 10A the charger is to be switched to a 1500VA SMPS charger at 54V volt and may be a separate trickle charger after that .
Issue is how to use current sensing with shunt resistance , i tried 741 but it would not work may be i need split voltage rails , and the swithcing smps 220v mains through SSR doesnot seem a very good option, with full load at startup the smps will be drawing around 15A for about an hour and i expect a 50A SSR even with good heat dissipation would be quite lossy ? Any how can any one suggest a current sensing ciruit to get me a trigger signal below 10A, the shunt produces 60mV at 100A so at 10A the voltage will drop below 6mV.

 

[D.A.(Tony)Stewart]

Use a TI Current Shunt monitor instead of the 741 for best results **broken link removed**

Hard to guess without a schematic but use a 56.4 V ref to shutdown 1st stage charger which can be diode or'd with voltage trickle charger.

 

[muddasirwaheedmalik]

any suggestion on second line? how to do it?

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any Constant current design for existing SMPS ??? IGBT based as current regulator as the charger starts charging at 50A which is C/3 so the battery voltage rises rather faster and gets to 54V output after around 45 min of 50% discharge after which the charging current declines rapidly, i think it should be charged at 30A which is C/5 ? any suggestions how to implement constant current, i assume i have to boost up the voltage to 56V and regulate current with a sink circuit ??

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any IC for diode OR application?