Super Capacitor CMOS Battery Replacement

[alec006]

So I have an old motherboard that just turned 20 years old in October of this year. It still works and I plan on turning it into a DOS/ Windows 95 machine in the future. The thing that worries me the most is the battery is also 20 years old. I tested it with a multimeter and it still has a 3.6v charge even though it hasn't been on in ages. It's a rechargeable NiCd barrel battery rated at 60 mAh. The thing that worries me the most is since it's so old it could give at anytime, and I really don't want to replace it with another NiCd.

So my question is could one replace it with a 5.5v 1.5F Super Capacitor instead? The specs say the cap is rated up to 5.5v so 3.6 or lower doesn't hurt it. I've seen some people replacing their Sega CD batteries with Super Caps without any problems, so I thought why not with my old motherboard?

The other alternative I thought of was to have a regular CR2032 coin holder installed and have a blocking diode on the positive side so that it doesn't charge the battery.

[MaxWar]

So I have an old motherboard that just turned 20 years old in October of this year. It still works and I plan on turning it into a DOS/ Windows 95 machine in the future. The thing that worries me the most is the battery is also 20 years old. I tested it with a multimeter and it still has a 3.6v charge even though it hasn't been on in ages. It's a rechargeable NiCd barrel battery rated at 60 mAh. The thing that worries me the most is since it's so old it could give at anytime, and I really don't want to replace it with another NiCd.

So my question is could one replace it with a 5.5v 1.5F Super Capacitor instead? The specs say the cap is rated up to 5.5v so 3.6 or lower doesn't hurt it. I've seen some people replacing their Sega CD batteries with Super Caps without any problems, so I thought why not with my old motherboard?

The other alternative I thought of was to have a regular CR2032 coin holder installed and have a blocking diode on the positive side so that it doesn't charge the battery.

Yeah remove that nasty barrel asap, these things leak all the time and they ruin boards. Ive never heard of anyone using a supercap as replacement though.

Most of these old motherboards have an external battery connector. Its usually near the battery. This is for non-rechargeable batteries and it is your best option. I normally use either a remote CR2032 holder or a 3xAAA batterie pack. Works great. If you lack the external battery connector, You can use the diode trick.

[alec006]

Yeah remove that nasty barrel asap, these things leak all the time and they ruin boards. Ive never heard of anyone using a supercap as replacement though.

Most of these old motherboards have an external battery connector. Its usually near the battery. This is for non-rechargeable batteries and it is your best option. I normally use either a remote CR2032 holder or a 3xAAA batterie pack. Works great. If you lack the external battery connector, You can use the diode trick.

Well I removed it by just putting a knife between the contacts and snapping them off the board, only a few scufs of damage where the battery used to be but no traces were broken.

http://i103.photobucket.com/albums/m...psfddcd136.jpg

http://i103.photobucket.com/albums/m...ps7897b481.jpg

And I actually do have an external 4 pin battery connector on the board. I'm guessing pin 1 would be positive,pin 4 would be negative and the two in the middle are grounds from what little research I've done but to be sure how could I test the points with a multimeter?

Where would I obtain a CR2032 holder that has a connector like that, I'm guessing Mouser or some electronics specialty supplier. Also I found this, looks like it uses those old Macintosh PRAM 3.6v batteries.

http://www.alancomputech.com/nec-tad...tl-5009-w.html

[MaxWar]

Yeah, looks like you had no battery leak at all. Thats pretty nice for a 20 yrs old board. You took that barrel out in time

You can find the ground pin by measuring continuity/resistance with any other ground point. Normally i just use the screw pads or something. Typically I think the center pins are NC or grounded , one of the extremity will be grounded, the other extremity is your + . But double check the traces to be sure. If you find the diagram for your motherboard, as you often can online, the polarity and pinouts are usually provided.

The connector that goes there is just normal header type connector. I usually scavenge them off dead fans or broken computer cases so i have a small supply of them. But You can probably get them at most electronic stores. If you do not find a 4 pin connector you could always use 2 one pin connectors or 2 two pin connectors, anyway you get the idea...

[alec006]

Thankfully

What sucks is my board seems to be super rare or not many were made and I can't find any manuals or diagrams of it anywhere. I found a few places that sold them but that's about it.

Ask for that connector, I switched it to the 20k Ω Ohms setting on my multimeter and placed the negative probe on a screw pad ground. Pin 1 showed 1 , pin 2 showed 1, pin 3 showed 0.00 and pin 4 showed 0.00. Exactly what does that mean I'm abit confused there.

1 shows up on the multimeter by default when the probes are not torching anything.

1 Also shows up when the positive probe touches pins 1 or 2 on that connector and the negative probe is touching a screw pad ground.

When the probes are shorted by touching each other the screen shows 0.00.

I'm not too knowledgeable when it comes to electronics so I'd really like to know what the multimeter is telling me.

[MaxWar]

Well, alot of multimeters have a simple continuity function, often with a useful Beeper. This is what i would use here. But otherwise just set it to the smallest Ohm range possible.

You should get < 1 ohm resistance when testing direct continuity so the 20k range it not adequate. It is possible that you have a ++-- setup on your header, so it is actually compatible with 2,3 or 4 pin connectors.

[alec006]

Well, alot of multimeters have a simple continuity function, often with a useful Beeper. This is what i would use here. But otherwise just set it to the smallest Ohm range possible.

You should get < 1 ohm resistance when testing direct continuity so the 20k range it not adequate. It is possible that you have a ++-- setup on your header, so it is actually compatible with 2,3 or 4 pin connectors.

Yea guess I need a new multimeter with a beep. The one I have is a cheap $5 one I bought at Harbor Freight. I switched it to the lowest possible Ohms setting which is 200. Pins 1 & 2 still remained 1 with no decimal which I'm guessing means infinite? However after jumping around a lot of numbers for a few seconds pins 3 and 4 finally showed 01.0 as a common number. So I'm guessing ++-- as you said. Thanks for the help!

[MaxWar]

Yeah, looks like it. I guess your multimeter deals in whole number and you read 1 ohm.
You can also check between pin 1 and 2. If they are both ok for the + they should be linked. You can even look at the board for visible traces connecting them.

Good luck with your retro computing project!

[APE992]

What sucks is my board seems to be super rare or not many were made and I can't find any manuals or diagrams of it anywhere. I found a few places that sold them but that's about it.

Sadly that is all too common for mobos from the late 80s/early 90s. There were probably a good sum made but the assumption back then was that all you needed to pack in was a sheet or three showing what the jumper settings did and maybe pin header pinouts if even that. Today we may have an "enthusiast" crowd but they aren't anything like people were back in the day where far more knowledge was simply assumed when you bought something.

Best you could do is find schematics/datasheets on the chips and work out what the board is capable of.

[Niku-Sama]

the only problem i see with using a "super" cap is that sure its rated at 1.5 farads with a 5.5v rating but at 3.3v its rating may be much less and might not be enough.

just because its 2/3rds the voltage doesent mean your going to get 2/3rds the capactanceif you find a spec sheet it should tell you