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Old 20th October 2006, 10:44 PM   #1
zobsky is offline zobsky  India
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Default How much trickle current can fixed bias cathode batteries stand?

I blew up a set of AAA duracells by mistakenly connecting a VR tube between a pentode screen grid and cathode pin, pumping reverse current through the cells working in fixed bias between cathode and ground.

My fault admittedly. I plan to connect the VR tube between the screen and ground next time. But I'd like to know how much trickle current regular cells can handle (my tubes are biased at around 25mA idle).

Thanks
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Old 20th October 2006, 11:01 PM   #2
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Default Re: How much trickle current can fixed bias cathode batteries stand?

Quote:
Originally posted by zobsky
I blew up a set of AAA duracells by mistakenly connecting a VR tube between a pentode screen grid and cathode pin, pumping reverse current through the cells working in fixed bias between cathode and ground.

My fault admittedly. I plan to connect the VR tube between the screen and ground next time. But I'd like to know how much trickle current regular cells can handle (my tubes are biased at around 25mA idle).

Thanks

Do you mean they will sustain an anode current when could not sustain a grid one?

Did not you think of a cheap PNP transistor with collector on the ground, and a Zener between base and collector? Your chassis can work part time as a good enough heatsync...
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Old 21st October 2006, 02:16 AM   #3
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Wavebourn is correct. You can't use alkaline cells in the cathode circuit.

You must use pre-charged rechargeable cells in the cathode circuit. NiMH gets the nod. 25 mA. is fairly substantial. I'd use "C" size, perhaps "AA", definitely not "AAA".
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Old 21st October 2006, 03:23 AM   #4
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Quote:
Originally posted by Eli Duttman

You must use pre-charged rechargeable cells in the cathode circuit. NiMH gets the nod.
At least they don't blow up with a fire like litium batteries do.
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Old 21st October 2006, 05:31 AM   #5
zobsky is offline zobsky  India
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Thanks, I picked up a bunch of NiMh AA cells this evening. I plan to solder them in tomorrow. They are rated at 2000mAh, so using the "rule of max trickle current less than 1/10 x mAh", they should be able to survive the 20 - 25 mA of idle current (the batteries are in a cool part of the chassis, so I'm not worried about heat in this case)
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Old 21st October 2006, 03:51 PM   #6
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Trickle charge is a lot less than 0.1C that rate is the SLOW CHARGING RATE of a battery. If I'm not mistaken NiMH don't like trickle charge much at any rate. certainly 0.1C is too high. I'd Google Nickel Metal Hydride cells and see what is recommended for standby service. That is closer to what you are doing. It isn't cyclic service.
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