UM4980 board, battery voltage?

[RaptorZX3]

i finally know what's that "Mind" board now, it's a UM4980, v1.4. But like a dumbass, i forgot to take a picture of that battery plugged on the board, i remember it being 4 something volts, and being a NiCD i think (it looked like 3 x AAA batteryes wrapped together with 2 wires sticking out). Though i kept the connector + wires that go on the board before putting the battery in a bag with electronics to recycle.

So what kind of battery can i use on that board? can i safely use a 3V Lithium CR2032 battery?

My friend can make me a CR2032 socket with 2 wires soldered on it, with the little plugs that go on the board, so i can just replace the wires in the connector and plug this in the board...

I like this board because it's compatible with write-back on my 486DX2 66Mhz CPU (ID: SX955) on it, and i can just enable this in the BIOS (write-back feature for the CPU and the memory, and also can auto-detect hard disk and auto-configure memory).

 

[3pcedev]

Most boards are quite tolerant to a variety of battery voltages (within reason).

A 3V CR2032 will be fine - just make sure you get the polarity right.

 

[modem7]

..., i remember it being 4 something volts, and being a NiCD i think (it looked like 3 x AAA batteryes wrapped together with 2 wires sticking out).

It is very unlikely to have been NiCd. Why?

1. Photos, manuals, and diagrams of the UM4980 motherboard do not show a soldered-in battery, only connector J2, a standard 4-pin Berg connector for an external battery. Such a connector is for a non-rechargeable battery.

2. If the three AAA batteries were NiCd, the battery voltage would be 3.6V (3 x 1.2V), not the "4 something volts" you remember. "4 something volts" fits with three standard non-rechargeable 1.5V batteries.

 

[RaptorZX3]

i don't know if those batteries were AAA, but they looked like AAA batteries, together in a "battery pack" and yes it's a 4-pins connector, BUT there are only 2 wires in that connector, 1 is unused and 1 is for the key. I kept the wires inside the connector (red, and black) so i know which polarity goes where.

i'll make sure to use a velcro or something inside the case, far from the board just in case there's a leak from it.

So you're saying a 3V Lithium CR2032 battery, in a socket (with the wires of course) will work just fine? (it's easy to put back all the right settings in the BIOS, but it's a hassle everytime)

 

[modem7]

So you're saying a 3V Lithium CR2032 battery, in a socket (with the wires of course) will work just fine?

Well, 3pcedev is.

Unfortunately, the UM4980 motherboard manual does specify minimum battery voltage.

Even knowing which RTC chip or chipset is in use does not always give someone all of the information needed to determine minimum battery voltage. As what is possibly an extreme example: The IBM AT motherboard uses an MC146818 chip, a chip that has a minimum supply voltage of 3 volts. However, on the IBM AT motherboard, between the MC146818 chip and the battery connector are two diodes, diodes that result in the chip getting about 1 volt less than the battery voltage.

 

[RaptorZX3]

a friend of mine said that if the voltage is higher for NiCD battery on a board, it'll still be fine with a Lithium battery with a lower voltage. I wonder if that's true.

 

[Chuck(G)]

With the battery out, power up the board. Do you read any voltage across the battery terminals on the board? If so,it uses a secondary cells (i.e. NiMH, NiCD) Otherwise,a plain bog-standard CR2032 or a some alkaline cells will work just fine. As others have mentioned, the IC itself is very tolerant of voltage variations.

 

[RaptorZX3]

i can't try it right now, my friend is supposed to bring that to me soon...as i don't have a soldering iron and the stuff to make it myself.

 

[3pcedev]

Good point Chuck - I'd forgotten that some motherboards used secondary cells.

If it turns out your motherboard uses a secondary cell (i.e. voltage on the pins when the board is powered up) here is how to install a low voltage drop diode substitute:

http://www.vintage-computer.com/vcf...mbled)-computer-486DX2-80&p=351587#post351587

Works great in my old 486 - although as it turns out the battery I removed was not a secondary cell hence it really isn't necessary.

 

[RaptorZX3]

just think about that, it would be strange to NOT see a CR2023 socket on a main board nowadays. Yet this 486 board doesn't, but it's an external battery doing the job...