circuit board for battery backed ST clock

[rcgldr]

This board replaces the 6301 in the keyboard, and the 6301 plugs into the board. The red and black wires go to a rechargeable battery pack. I use 3 x AA NIMH batteries (2400 mah). The board is called a "time-saver". I got this back in 1985 or 1986 when I got my 520 ST as part of a developer kit.

 

 

Edited March 19, 2020 by rcgldr

[+Stephen]

Thanks for the battery info.  I found one of these in an ST I took apart, but IIRC it had the 9-volt battery "soft plug" but nothing plugged in.  Very glad I did not just plug a 9-volt battery into it!  Question - I see you are using NIMH batteries in it.  I assume that means this device recharges the batteries when the computer is turned on?

[rcgldr]

23 hours ago, Stephen said:

I assume that means this device recharges the batteries when the computer is turned on?

I'm not sure how much of a recharge occurs. I measured 4.2 volts from the circuit board, but I don't have a way to measure the current. Nimh batteries self-discharge even with zero load. A single cell li-po battery has the right voltage range, 3.8 v (low charge) to 4.2 v (max charge), and virtually no self discharge. I would need to buy connectors to create a cable for this. 

 

An alternative would be using two packs, charging one externally, and swapping packs while the ST is on. 

 

Then again, I'm concerned about the 6301 running 24/7 over an extended period of time, so most of the time, I leave the battery pack disconnected.

Edited March 22, 2020 by rcgldr

[rcgldr]

On 3/21/2020 at 2:41 PM, Stephen said:

I see you are using NIMH batteries in it.  I assume that means this device recharges the batteries when the computer is turned on?

I did a crude test with a 3 x AA 2400mah NIMH pack at 3.97 volts. After about an hour it was up to 4.00 volts, so the circuit board is recharging the batteries. I then used an offline discharger / charger to get an idea of the mah charged, running it at it's minimum of 100 ma discharge / charge. At close to 4 volts, my guess is the circuit board outputs about 12 or so ma (could be more). I recall a comment that the circuit board draws about 1.3 ma. That would translate into about 2.5 hours per day to break even. However, the 4 volts is close to the unloaded 4.2 volts from the circuit board. At lower voltages it may generate more current. It came with a 2 x AA pack, but I don't recall what type of batteries it used, and 2 rechargeable batteries would normally have 2.6 to 3.0 volts, but doesn't seem like enough to power the 6301. Maybe special batteries were used?

 

If the recharge rate is too low, an option would use 2 packs, charging one offline, and swapping packs when the Atari is on.

 

Still there's the issue of running the 6301 and circuit board 24/7, so I have the battery pack unplugged most of the time.

 

 

Edited March 25, 2020 by rcgldr

[rcgldr]

I've since confirmed what I suspected, that 2 x AA 2400 mah NIMH batteries don't work, not enough voltage to keep the 6301 running. The original battery holder specifies 2 UM-3 AA batteries, which would be non-rechargeable zinc-chloride batteries, 1.5 volts (or a bit more when new), versus rechargeable AA's which are 1.2 to 1.4 volts each. The 3 x AA 2400 mah NIMH pack is working, but avoid charging over 4.2 volts, since that is what the board outputs to an empty battery holder.