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Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Woke up to this and decided to make a portable 400V supply the easiest way possible!
I read up on NiCd batteries and it seems the easiest way to charge them is to just give them C/10 for 16 hours at constant current (from full discharge).
I want jury rig a charger that I can use while designing something more sophisticated.
Would it be okay to use a NST to charge the pack? I can attach a full wave rectifier to the battery pack so the voltage is always reasonable across the diodes and just plug the pack into the output of the transformer to charge it, and just manually disconnect it after ~16 hours or so, or have a microcontroller cut off a relay between the mains and primary.
Not sure whether this should be in General Science or High Voltage. Figured I'd put it here since it's more about the battery than the HV.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Thank you for the feedback. I am putting them all in series and would prefer not to handle it after assembly unless something fails. I bought extra, but how will I know if something has failed?
A boost converter would work but I have a neon sign transformer that has an output current about equal to the charging current I need. I was wondering if there was anything conceptually wrong with rectifying, smoothing, and using that to charge the whole series bank. I can monitor the current with a shunt resistor and clamp the output with a series resistor+mosfet to switch to float charging upon the voltage reversal exhibited by fully charged NiCd cells.
Registered Member #1565
Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159
a NST should do the job nicely.
Just remember something to shut down the NST in case of open circuit.
As for failed cells, you would probably have to measure them all. Doing the battery in sections can be of great help there. Even neon-lamps connected over cells may be able to tell if the voltge is too high (more than 60V where there should be less at all times). If the pack starts to light up (the neons) then terminate charge and check all.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I've decided to put a normally-on clamp (just a mosfet with a pullup resistor) right after the rectifier that will be triggered to go open when connected to the battery. Might have to put a pfc cap on the primary to help limit the idle current draw. Or I could just not leave it plugged in...
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Charging a ~400V NiCd Battery
