Amiga 4000cr Rev D CN181 EXT BAT. How to use it?

[Hanzu]

Amiga 4000cr Rev D motherboards have connector CN181 EXT BAT for external battery.

Original A4000 battery in Rev B schematic details battery is "Varta V80H Ni-MH" or in the scematic picture itself battery is marked detailed with "3/600K Ni-CD 3.6V 60MAH". Ni-MH and Ni-CD is same document is a little confusing.

From Anthonys nice theory I see A4000 Rev B will recharge its battery with 4mA current.

Because there are no schematics for Rev D where CN181 EXT BAT connector is visible I don't know if it will recharge its internal battery or external battery connected to CN181 EXT BAT. Does anyone know this?

I already tried SAFT LS14250 3.6V Li-SOCl2 and it seems to keep time and date, but this battery type is not rechargeable and all recharging operations to it are forbidden, so how can I check if recharging current comes to CN181 EXT BAT or not?

[Hanzu]

Found an article from 2001 by Robert Williams (?)
http://www.totalamiga.org/pdf/totalamiga_8.pdf
and from there page 34 of scanned paper (Page 18 of PDF)

"Lithium
These batteries are not rechargeable, they
are usually in the form of a single coin cell
and have the great advantage over NiCds
that they very rarely leak so even if your
lithium battery is dead you don’t need to
rush to replace it. As standard Lithium
cells were only used on the revision D
A4000s"

and later

"Fortunately this motherboard also has an
external battery connector (at the front left
marked EXT BAT) where you can attach a
3.6V lithium battery pack."

In pictures A4000cr Rev D internal battery seems 3V non-rechargeable Lithium coin type. So what puzzles me is why EXT BAT accepts 3.6V non-rechargeable Lithium?

[Castellen]

Because there are no schematics for Rev D where CN181 EXT BAT connector is visible I don't know if it will recharge its internal battery or external battery connected to CN181 EXT BAT. Does anyone know this?

I already tried SAFT LS14250 3.6V Li-SOCl2 and it seems to keep time and date, but this battery type is not rechargeable and all recharging operations to it are forbidden, so how can I check if recharging current comes to CN181 EXT BAT or not?

Easy to check; simply connect a voltmeter to the outer two pins of the external battery connector.  If you measure next to nothing while the computer is powered on, it means the computer will not supply charging current to the external battery connector.

Anyway, I'm fairly sure the A4000cr RTC circuit is nearly identical to the A4000T RTC circuit.  See the nasty scan of my tatty schematic sheet here.  The external battery connector (CN180) is designed to connect directly to a T1AA/C lithium battery.  These are still commonly available from electronic parts wholesalers such as Element14, RS, DigiKey and some computer parts stores may stock them.  Google will find a source for you.  This should be fine for the A4000cr as well.

[Matt_H]

The external battery port does not supply charging power. (Neither does the built-in battery circuitry on rev D 4000s and all 4000Ts, which is why non-rechargeable lithiums are installed by default). The internal battery on my 4000T has been dead since before I got the machine in 2004. I'm now on my second external battery pack, replaced about a year ago. This is what I'm using now.

[Hanzu]

Thank you both of you. Now I feel confident to plug 3.6V lithium to EXT BAT of A4000cr Rev D and A4000T too, if I ever manage assemble my empty PCB for it.

Still I don't understand why internal battery for A4000cr Rev D adn A4000T is 3V when EXT BAT is 3.6V. I guess the circuitry is not that picky about extra 600mV.

[Castellen]

Still I don't understand why internal battery for A4000cr Rev D adn A4000T is 3V when EXT BAT is 3.6V. I guess the circuitry is not that picky about extra 600mV.

Exactly.  Check the RP5C01 datasheet and you'll see that the minimum required voltage to retain RTC data is 2.2V.

[Amiga_CDTV]

Nice, re-drawn schematics of some Amigas are available here.

Looking at the A4000T schematics around the RTC:
- in A4000T schematics there is option for either Ni-Cad or Lithium internal battery (a resistor or a diode is installed depending on which is used)
- for internal or external lithium usage there is (a resistor and) a diode, which should drop the voltage to about 3v

RP5C01 datasheet gives "Data preservation voltage" as 2.2-5.25v.

The A4000 schematics looks identical but the bit about the lithium battery is removed (also there is no mention of the external connection, which seems to be present in the CR-version).