[MikeW]

I recently built a Mini3, all the intial checks are fine except one.. The battery charging circuit, it only reads as 03.12ma for current. supposed to be 16ma. Voltage is fine @ 12.17 volts. I double checked the R8 resistor and it reads 74.6r. I double checked polarity of C2 seems fine. Im at a loss, wonder if im reading it right, using my craftsman auto-ranging VM. set to ma/current readings. The rest of the amp seems to work great.
 
I also tested the current ma, output of my power adapter, a reiliapro 15v 500ma unit, the voltage was 21 volts, and current reading on my VM said 05.85ma. makes me wonder if im reading it wrong or not understanding the measurement. Maybe a decible point off? so it should be 585ma? i don't know. If that's the case though i'd be getting 31.2ma in my charging circuit, that's still way off the mark. This was a glass jar audio kit btw.
 
p.s the charge led does come on, and the battery does charge. but it takes forever.

 

[MisterX]

Sounds like the AC adapter could be the problem.
But let's be sure before jumping off the conclusion bridge....
How are you trying to measure thre output current from it?

 

[MikeW]

bah, fuse in multimeter was either blown or questionable.. i don't know. I looked at it, looked ok. but I bypassed it with a piece of wire and my measurments are all what they are supposed to be. 16.67 ma , 25.5 quiescent. I took a quiescent current early on in the intial checks, and tried to take it again a few times and could not get a reading, i thought i was doing it wrong, but the VM was not passing the power though, that's what made me check the fuse and bypass it. I must have done something to blow that fuse. Thanks for the quick help MisterX. I did have another question, the battery contacts each have 3 solder joints, are the  other 2 joints important, or is it just the center one that matters? are they just support for the contact, they are all 3 "shorted" right? I had to de-solder my battery contacts and trim them up to get my battery to fit after the fact, and i slightly lifted/damaged one of the 3 solder pads. They are still on there, but they look a little rough.

 
I think it takes like 18 hours to get a full charge on this battery, but i guess that is normal with 16ma charge rate.
 
I actually built this Mini3 awhile back, a few months ago, and i never did the intial checks (shame on me) but it sounded great, i recently splurged on the AMB face plates and decided while i've got it all apart i should do those checks, everything checks out fine.
 

 

[MisterX]

http://www.amb.org/audio/mini3/mini3_pcb_big.png
 
Yep, the front/center pin is the only pin of each battery connector that is connected to anything on the PCB.

 

[Beftus]

I think it takes like 18 hours to get a full charge on this battery, but i guess that is normal with 16ma charge rate.

If you lower the value of R8 you can increase the charge current. Soon after I built per spec it I modified the value of R8. Mine uses a 47 ohm resistor now, charge current is 26.3mA. The charge current should not exceed ~35mA to prevent U1 from overheating.

 

[MikeW]

yeah, i've thought about it, that would lower charge time to about 10 hours. I do like being able to set it and forget it though. It's good to know if you forget about it for 3 days your ok. I guess there's no free lunch. I think I did read somewhere that the zeener diode actually bleeds off the excess current once the battery is full? I may not be understanding that right though.

 

 

[amb]

No, the D4 zener is to prevent the circuit from "seeing" over-voltage from the wallwart (and be damaged) if you remove the battery.