Amiga battery replacement

[demolition]

Originally Posted by Jope

Let's see when the first diode failure / exploded coin cell happens. Lots of guys have been fitting these with just the diode. :-)

I think diodes are quite trustworthy and it's very rare to see a failing one..
But yes, it would be best to have a resistor in there just to make sure the battery will not explode if it happens.

[Photon]

Yeah, problem with all the solutions is as always that "time will tell" who's right, and even if your replacement was done 3 years ago it's inconclusive if it's proper and safe. But surely the battery manufacturer has that experience, they didn't have to put that in a battery datasheet, but they did. Just seemed so definitive to me.

[RiP]

I had a question, how does Amiga 2000 charge the battery?

[Daedalus]

Power from the 12V rail passes through the resistors and diode and charges the battery. The diode then prevents the battery from trying to power your hard drive when the 12V rail is down.

[demolition]

Originally Posted by RiP

I had a question, how does Amiga 2000 charge the battery?

When +12v is present, current will flow through R801, D801 and then R803 into the battery. The +12v supply will drop to ~5.7v after R801 (+5v plus the voltage drop across D800), then drop to ~5v after D801 (reduced by one diode forward voltage) providing U801 with 5v Vcc. The battery will be charged by this 5v through R803. Obviously this is a higher voltage that the nominal battery voltage, but I guess it should be acceptable or they would have designed it differently.

[RiP]

Thanks all possible to use 140mAh instead of 60mAh battery?

http://patriotgaming.com/075-3-6v-varta-stacked.html

[demolition]

As long as it will fit physically, the capacity is not important.

However, instead of putting another Ni-MH battery in there, I would consider replacing it with a CR2032 Lithium cell which will not leak:

http://amigakit.amiga.store/product_...oducts_id=1093

[Capitaine]

Originally Posted by demolition

However, instead of putting another Ni-MH battery in there, I would consider replacing it with a CR2032 Lithium cell which will not leak:

http://amigakit.amiga.store/product_...oducts_id=1093

About that Lithium Coin Cell Clock Battery Adapter....

My board had a Ni-Cd 3.6v battery


But CR2032 are 3v. Is it still safe to upgrade ?

[demolition]

Sure, as long as the battery is protected against charging, it is fine. The RTC chip will work fine with 3V - my experience is that it keeps working until the voltage comes down to around 2V, so there is some headroom.

[Capitaine]

Thanks

[ubermick]

So planning on putting together a quick coin cell board to replace the old Varta in my A500+. Quick question tho, does it matter which positive pin I solder the diode/resistor to? Negative is straightforward obviously, but with two positive pins I'm *ASSUMING* that for one is voltage out and one is voltage in? (Or is only one used, and if so, which one?!)

[demolition]

The direction of the diode is important as it controls which way the current can flow.

There is an explanation here.

And the schematic from that site:


The 'line' of the diode symbol corresponds with the ring/line that you can see on the diode.

[Jope]

Originally Posted by ubermick

with two positive pins I'm *ASSUMING* that for one is voltage out and one is voltage in? (Or is only one used, and if so, which one?!)

They're both the same pin, it's like that to stop people from mounting the battery in reverse.

[ubermick]

Originally Posted by Jope

They're both the same pin, it's like that to stop people from mounting the battery in reverse.

Ah. So only one of the pins needs to be routed to positive?

[Jope]

They're connected together anyway, so pick the one that's more convenient. :-)