# APS battery powered SCSI

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Joined: Dec 20 2003
Posts: 361

I have this APS SCSI drive that's battery powered but lack the external charger. I would have thought it would take a DC adapter but on opening the case on the circuit board where the external power supply connects it says AC but no voltage. Inside is 7.2 volt NiCad battery and a 2.5" SCSI drive. The FCC ID is IDKAPS-9000. I've looked on the net without finding anything. I'm hoping someone might have one and could give me some info on the external power supply.

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Joined: Nov 16 2011
Posts: 2422
Re: APS battery powered SCSI

hello Wayne,
although i don´t have a similar unit i´ll asume some basics:
if the unit is for use with an ac-input the PCB must have at the inputarea some kind of bridgerecitifer ( usualy containing 4 Diodes ) to convert the ac voltage to dc voltage and at least thereafter a electrolytic capacitor to smothen the voltage and a resistor in the positiv branch to limit the current to the battery to avoid an overloading....

usualy the NiCad- batteries are loaded with an amount of 5% maximum of the capacity of the battery - so assuming that the 2.5 drive has a demand of something like 250mA all together the NiCad-battery probably is labeled with a value of something like 2000mAH.... with such a value the powersource should give an amount of 100mA to 150mA and the voltage should be to maximum of 9 to 10 Volt...

some volt is lost by the conversion from ac to dc and the voltage drops by 0,7 Volt while passing the diodes in the bridgerecitifer and the voltage should keep slightly above the final loadcapacity of the NiCad-battery

the NiCad batteries climb up to 8,4 Volt when fully charged....

so when the external powersource is pluged in the voltage at the loading electrolytic capacitor after the bridgerecitifer should not be much more than 8,4 Volt otherwise there is a danger of overloading the NiCad-batteries

the limiting resistor in the positiv branch behind the loading capacitor will keep the voltage then behind itself below the critical voltage.

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Joined: Dec 20 2003
Posts: 361
Re: APS battery powered SCSI

I was having similar thoughts. But there's no rush on this. I'll wait a month and hopefully someone replies that has one. If not, I'll dig through my case of odd wall warts and see what I have between 7 & 9 volt. If it was DC then I'd have dozens but AC is a lot less common power supply output. Hopefully there won't be any magic smoke escaping.

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Joined: Nov 16 2011
Posts: 2422
Re: APS battery powered SCSI

There is no need for that.... ac can only be converted once to dc... if you connect a dc supply the only thing that happens - is that the dc just runs along one path in the reticifer-branch and the other branch for the oposite wavepart will be unused.... the only effect will be that you must calculate the loss of 2 times 0,7 volt from the source to the point behind the diodes.... it´s just even regardless how you connect the source it will allways just only pass one path of the bridgereticifer and it´s regardless which one it will use....

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Joined: Dec 20 2003
Posts: 361
Re: APS battery powered SCSI

I decided to proceed by taking out the battery and using the same voltage of wall wart to power it. It spun up right away so I shut it down and looked for the handiest Mac to connect it to. That happened to be a 6500. I hooked everything up and turned on the drive and it went sprt sprt sprt and didn't spin up. Disconnected it from the 6500 and turned it on and it spun up. Tried it with just a regular 50 to 25 SCSI cable and the same spt spt spt. Tried a different cable and the same.
So I went digging for an old powerbook and a HDI-30 SCSI cable. The topmost one was a 520c. Connected everything up, drive spun up and once the 520c booted, I could read and write to the external drive.
Now I guess I'll see if the battery happens to still take a charge. After that try and figure out a use for it

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Joined: Dec 20 2003
Posts: 361
Re: APS battery powered SCSI

Charged the battery and used it a bit on battery power. Was surprised, usually after the battery sits dead for a few years it won't take a charge.