Question about external CMOS battery headers

Discussion about old PC hardware.

Question about external CMOS battery headers

Postby Cizkaro » 2018-3-08 @ 11:19

I have a Shuttle HOT-409 and naturally the old battery for CMOS has long since leaked and been removed. There is a external battery connector with 4 pins on this board I would like to utilize with a battery holder and AA batteries. I have looked around for a pin-out of this header but I am unable to find one. Perhaps someone here knows the pin-out or knows a way perhaps with a multi-meter I could determine which pins are + and - and what actual voltage this mainboard needs to retain CMOS information? I attached some links to the only info I have been able to find.

Links to what info I have found:

http://stephan.win31.de/hot409.htm

http://www.elhvb.com/mboards/shuttle/ma ... ot-409.pdf
User avatar
Cizkaro
Newbie
 
Posts: 11
Joined: 2018-2-25 @ 13:14
Location: Las Vegas, NV

Re: Question about external CMOS battery headers

Postby derSammler » 2018-3-08 @ 11:23

I don't see an external battery connector. J1 is a jumper, you don't connect a battery there. However, if there indeed is one, normally only pins 1 and 4 are used. Check which pin connects to GND and you have it (the other is plus then, of course). As for voltage, most RTCs can work with anything from 1V to 6V. 3V are best in most cases.
derSammler
Oldbie
 
Posts: 1748
Joined: 2017-4-14 @ 11:30
Location: Germany

Re: Question about external CMOS battery headers

Postby Cizkaro » 2018-3-08 @ 11:29

derSammler wrote:I don't see an external battery connector. J1 is a jumper, you don't connect a battery there. However, if there indeed is one, normally only pins 1 and 4 are used. Check which pin connects to GND and you have it (the other is plus then, of course). As for voltage, most RTCs can work with anything from 1V to 6V. 3V are best in most cases.




If you look above the keyboard connector on the actual board its there. Thanks for the info I will look into it! :cool:
User avatar
Cizkaro
Newbie
 
Posts: 11
Joined: 2018-2-25 @ 13:14
Location: Las Vegas, NV

Re: Question about external CMOS battery headers

Postby derSammler » 2018-3-08 @ 11:39

Cizkaro wrote:If you look above the keyboard connector on the actual board its there.

No, that is J1 and that's a jumper. You close 1-2 for an internal battery and 2-3 for an external one. Page 2 from the manual you posted yourself. ;)
derSammler
Oldbie
 
Posts: 1748
Joined: 2017-4-14 @ 11:30
Location: Germany

Re: Question about external CMOS battery headers

Postby timb.us » 2018-3-08 @ 16:14

Cizkaro wrote:I have a Shuttle HOT-409 and naturally the old battery for CMOS has long since leaked and been removed. There is a external battery connector with 4 pins on this board I would like to utilize with a battery holder and AA batteries. I have looked around for a pin-out of this header but I am unable to find one. Perhaps someone here knows the pin-out or knows a way perhaps with a multi-meter I could determine which pins are + and - and what actual voltage this mainboard needs to retain CMOS information? I attached some links to the only info I have been able to find.

Links to what info I have found:

http://stephan.win31.de/hot409.htm

http://www.elhvb.com/mboards/shuttle/ma ... ot-409.pdf


Generally these are four pin headers with one pin removed:
+ —
|_||

(If your header doesn’t look like this, simply buzz the GND pins out with the continuity function of your meter. They will be connected to one of the black wires of a 4-pin Molex power connector.)

The two GND (=) pins are connected together on the board, you only need to connect one to the battery pack. The + pin usually runs through two series connected diodes, dropping a 6V battery pack down to at least 5.5V (which is the max normal working voltage of most parts). This voltage connects to VCC on the CMOS ram and RTC (discrete or built into part of the chipset). There is also a connection to the same VCC pin from the normal 5V system supply, which goes through an NPN-PNP transistor combination (setup in a darlington configuration), this allows the power supply to override the batteries when the system is on. This setup will also explicitly *not* back feed current to the batteries, so you can use primary cells.

You can verify the series connected diodes by placing your multimeter into the diode test function and connecting between the External Battery + pin on the motherboard and the non-GND pin of the CMOS clear jumper. You should also do a voltage reading between Ext. Batt + and GND with the system turned on; verify you don’t get more than a few millivolts (this is to make sure current isn’t being fed to the batteries).

There should also be a 3W jumper that allows you to switch between an external or onboard battery. (This switches between two series connected diodes for a 6V pack and two back to back diodes for a 3.7V NiCd onboard battery (which allows charging).

On my 386 system I use a 4xAAA pack. Works great!

Also, if your system doesn’t have a pin header for an external pack you can always solder male pins to the battery footprint on the motherboard. In that case make sure you put a single 1N4148 diode in-line with the positive battery lead, to drop the voltage and prevent the pack from charging:

BATT 6V Pos +———+—[ >|—+——+ Motherboard
Any sufficiently advanced technology is indistinguishable from magic. (E.g., Cheez Whiz, RF, Hot Dogs)
timb.us
Newbie
 
Posts: 69
Joined: 2018-2-06 @ 01:23
Location: Virginia, United States

Re: Question about external CMOS battery headers

Postby Cizkaro » 2018-3-09 @ 07:13

timb.us wrote:
Cizkaro wrote:I have a Shuttle HOT-409 and naturally the old battery for CMOS has long since leaked and been removed. There is a external battery connector with 4 pins on this board I would like to utilize with a battery holder and AA batteries. I have looked around for a pin-out of this header but I am unable to find one. Perhaps someone here knows the pin-out or knows a way perhaps with a multi-meter I could determine which pins are + and - and what actual voltage this mainboard needs to retain CMOS information? I attached some links to the only info I have been able to find.

Links to what info I have found:

http://stephan.win31.de/hot409.htm

http://www.elhvb.com/mboards/shuttle/ma ... ot-409.pdf


Generally these are four pin headers with one pin removed:
+ —
|_||

(If your header doesn’t look like this, simply buzz the GND pins out with the continuity function of your meter. They will be connected to one of the black wires of a 4-pin Molex power connector.)

The two GND (=) pins are connected together on the board, you only need to connect one to the battery pack. The + pin usually runs through two series connected diodes, dropping a 6V battery pack down to at least 5.5V (which is the max normal working voltage of most parts). This voltage connects to VCC on the CMOS ram and RTC (discrete or built into part of the chipset). There is also a connection to the same VCC pin from the normal 5V system supply, which goes through an NPN-PNP transistor combination (setup in a darlington configuration), this allows the power supply to override the batteries when the system is on. This setup will also explicitly *not* back feed current to the batteries, so you can use primary cells.

You can verify the series connected diodes by placing your multimeter into the diode test function and connecting between the External Battery + pin on the motherboard and the non-GND pin of the CMOS clear jumper. You should also do a voltage reading between Ext. Batt + and GND with the system turned on; verify you don’t get more than a few millivolts (this is to make sure current isn’t being fed to the batteries).

There should also be a 3W jumper that allows you to switch between an external or onboard battery. (This switches between two series connected diodes for a 6V pack and two back to back diodes for a 3.7V NiCd onboard battery (which allows charging).

On my 386 system I use a 4xAAA pack. Works great!

Also, if your system doesn’t have a pin header for an external pack you can always solder male pins to the battery footprint on the motherboard. In that case make sure you put a single 1N4148 diode in-line with the positive battery lead, to drop the voltage and prevent the pack from charging:

BATT 6V Pos +———+—[ >|—+——+ Motherboard




I will look into this when I can get some time. My pin header does have 4 pins. Thanks for the useful information!
User avatar
Cizkaro
Newbie
 
Posts: 11
Joined: 2018-2-25 @ 13:14
Location: Las Vegas, NV

Re: Question about external CMOS battery headers

Postby timb.us » 2018-3-09 @ 22:40

Just to illustrate the description from my previous post, here’s a typical circuit for the CMOS/RTC Battery on 286/386/486 class motherboards that I whipped up in a simulator. It shows three states: External and Internal Batteries with the Power Off and Internal Battery with Power On (o show charging).

The CMOS/RTC is represented by an analog switch that presents a 250kOhm Load when off (simulating the standby current) and a 250 Ohm Load when on (simulating normal current draw). The comparator represents the Voltage Supervisor IC present on most boards and puts the CMOS/RAM into standby mode when System Power drops below 4.5V (in this simulation it’s used to control the aforementioned analog switch).

[attachment=0]362C3F19-638E-4D2A-8974-6C1960FDBDBB.png[/attachment]

[attachment=1]41A11CC1-7ABC-491A-8341-E09C917B2008.png[/attachment]

[attachment=2]AE36C274-58A4-4CDE-99E5-D3B109E24E63.png[/attachment]
Attachments
362C3F19-638E-4D2A-8974-6C1960FDBDBB.png
Power Off, External Battery
41A11CC1-7ABC-491A-8341-E09C917B2008.png
Power Off, Internal Battery
AE36C274-58A4-4CDE-99E5-D3B109E24E63.png
Power On, Internal Battery
Any sufficiently advanced technology is indistinguishable from magic. (E.g., Cheez Whiz, RF, Hot Dogs)
timb.us
Newbie
 
Posts: 69
Joined: 2018-2-06 @ 01:23
Location: Virginia, United States


Return to General Old Hardware

Who is online

Users browsing this forum: LHN91, luckybob, Unknown_K and 14 guests