NiCd Power Supply Emulator

[ninefofo]

Please excuse this almost silly question. I need to build a power
supply that would mimic a 22VDC @ 1.7ah NiCd, using 120VAC as source.

The output will be approximatly 25 feet of 16 gauge stranded wire.

22VDC is the UNLOADED voltage, 18VDC is working.

Thoughts...Suggestions...

Thank You

Brad

 

[Luhan Monat]

Please excuse this almost silly question. I need to build a power
supply that would mimic a 22VDC @ 1.7ah NiCd, using 120VAC as source.

The output will be approximatly 25 feet of 16 gauge stranded wire.

22VDC is the UNLOADED voltage, 18VDC is working.

Looks like an 18volt 'wall-wart' to me. Assuming you actually mean 1.7A
and not 1.7ah - it may take a bit of luck at your local thrift store.

 

[TCS]

Looks like an 18volt 'wall-wart' to me. Assuming you actually mean 1.7A
and not 1.7ah - it may take a bit of luck at your local thrift store.

That's not a great assumption. A device might pull 5 amps off a 1.7ah
battery if it is only going to be momentary.

 

[Chris Dugan]

Looks like an 18volt 'wall-wart' to me. Assuming you actually mean 1.7A
and not 1.7ah - it may take a bit of luck at your local thrift store.

I'd love to see the 'wall-mart' that has the output impedence of any nicad
or nimh cell. 18V at 1.2V nominal a cell is 15 cells, 22V could be the
voltage straight off charge with each cell at approx 1.47V but depending on
the cell chemistry he's trying to emulate it'll drop to between 1.4 and 1.3
volts under load.

It'd be cheaper and easier to buy 1.7Ah NiCD cells and wire up a few packs
if this is for testing purposes. Otherwise you're looking at a power supply
capable of supplying a pulse current up to between 50-100A or more and with
an output impedence in the range of between 3.5 to 10 mOhm.

Chris

 

[John Woodgate]

Since the actual current draw was not specified, and the voltage drop
under load is quite large, it *could* be as simple as a wall-wart.

We need more specifics here to give a more definite answer.

The load is apparently specified as 25 feet of 16 gauge stranded wire. I
don't know that that is AWG, but if it is and it's copper, it's 100
milliohms, so the current at 18 V is ... a little too much for a wall
wart!

Alternatively, perhaps the OP didn't quite mean that!

 

[Luhan Monat]

I'd love to see the 'wall-mart' that has the output impedence of any nicad
or nimh cell. 18V at 1.2V nominal a cell is 15 cells, 22V could be the
voltage straight off charge with each cell at approx 1.47V but depending on
the cell chemistry he's trying to emulate it'll drop to between 1.4 and 1.3
volts under load.

It'd be cheaper and easier to buy 1.7Ah NiCD cells and wire up a few packs
if this is for testing purposes. Otherwise you're looking at a power supply
capable of supplying a pulse current up to between 50-100A or more and with
an output impedence in the range of between 3.5 to 10 mOhm.

Chris

Since the actual current draw was not specified, and the voltage drop
under load is quite large, it *could* be as simple as a wall-wart.

We need more specifics here to give a more definite answer.

 

[mike]

Please excuse this almost silly question. I need to build a power
supply that would mimic a 22VDC @ 1.7ah NiCd, using 120VAC as source.

The output will be approximatly 25 feet of 16 gauge stranded wire.

22VDC is the UNLOADED voltage, 18VDC is working.

Thoughts...Suggestions...

Thank You

Brad

Silly questions are not a problem.
The problem is that it's PART of a silly question.
What the heck does "mimic" mean?
Do you mean EMULATE? To what accuracy? Over what range of operation?
Wire is not often considered as load? What does output mean?
What do 22VDC and 18VDC mean? If you specify two fixed voltages, you
ain't emulating.
What do you want to do about the charging characteristics?

The fact that you specified two voltages implies that you don't want
just any old power supply to replace the power supplied by the battery.

To emulate, you're gonna be needing a BIG power supply that can supply
many amps. You'll need a microcontroller to accumulate charge/discharge
currents. You need to model the energy delivery as a function of load
current, the self heating on charge, voltage vs state of charge vs
charge current.

THIS IS A BIG PROBLEM.

Or maybe you really want to do something much simpler??
I've got the Psychic Friends Hotline number here somewhere.
Maybe they can tell me. ;-(

mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Wanted 13" LCD for Mitac 6133 Samsung HT13X13-201
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/