I am trying to mimic a single AA NiMH battery performance with a 12vdc wall wart.
The load is basically a short circuit, a metal screen to produce heat in short durations.
So the datasheet says a new, fully charged AA at ambient room temp has .05R internal resistance. The current during short circuit should be around 24A? 1.2v/.05=24
Yes under these conditions the battery does not last very long and needs to be recharged constantly which is why I would like to figure out a way to get the same performance from a common household power supply.
I would think a voltage supply would not like a short for a load so would a current source be the way to go? I am worried that with a current source large voltages could be developed across the load if the screen's resistance increases due to heat.
Maybe a voltage source charging a super capacitor?
The load is basically a short circuit, a metal screen to produce heat in short durations.
So the datasheet says a new, fully charged AA at ambient room temp has .05R internal resistance. The current during short circuit should be around 24A? 1.2v/.05=24
Yes under these conditions the battery does not last very long and needs to be recharged constantly which is why I would like to figure out a way to get the same performance from a common household power supply.
I would think a voltage supply would not like a short for a load so would a current source be the way to go? I am worried that with a current source large voltages could be developed across the load if the screen's resistance increases due to heat.
Maybe a voltage source charging a super capacitor?
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You'd need a super capacitor that can handle being short circuited. That's probably a pretty tall order...
As you mention, the filament/screen will have much higher resistance when hot. If you know the material and have a rough idea of the temperature, you could look up the tempco and figure out the resistance - at least get a first order approximation. That would tell you what the steady-state current needs to be. You should be able to figure out what the cold resistance is, though, you'll probably have to use a 4-lead ohmmeter (Kelvin sense).
Another approach would be to find a buck converter that can deliver 1.2 V at some ungodly amount of current, say, 20+ A. Given the power requirements of modern CPUs and GPUs, that should not be too hard, actually... Set it up for 1.2 V out and a reasonable current limit and let 'er rip.
~Tom
PS: I suggest having this moved into the power supply forum.
As you mention, the filament/screen will have much higher resistance when hot. If you know the material and have a rough idea of the temperature, you could look up the tempco and figure out the resistance - at least get a first order approximation. That would tell you what the steady-state current needs to be. You should be able to figure out what the cold resistance is, though, you'll probably have to use a 4-lead ohmmeter (Kelvin sense).
Another approach would be to find a buck converter that can deliver 1.2 V at some ungodly amount of current, say, 20+ A. Given the power requirements of modern CPUs and GPUs, that should not be too hard, actually... Set it up for 1.2 V out and a reasonable current limit and let 'er rip.
~Tom
PS: I suggest having this moved into the power supply forum.
A heavy duty transformer is probably the way to go.
I wouldn't think it matters if it's AC or DC, and wouldn't think it has to be exactly 1.2v seeing how it's just powering a heater element. I found a 25VA from Hammond, part # 166S2, 10A @ 2.5v.
The heater element will only be "on" for periods of 10 seconds at a time. I couldn't find the secondary winding resistance on the transformer so not sure how much current will be pulled during a "short" or "on" cycle. I would think a 10 amp rating has a pretty thick secondary winding.
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