[mik000000]

Sorry to revive the thread...
I am using a bank of 12 AA batts (2000ma) for my pimeta. According to the formula in the pint docs, my resister value should be 6R.
Is this correct?

 

[NeilR]

That's right.... 1.25/6 = 208ma.

You need to watch the power dissipation, though. That resistor will run very hot, dissipating a full 1/4 watt. I suspect you'll be pushing the envelope of the trickle charger design on that board/size/space, etc.

 

[mik000000]

thanks NEILR.
would i be better to aim for .05c with a 10-12R resistor instead? trickle is only to top up batts anyway. shoudl be sufficient as long as batts are not too discharged?

 

[NeilR]

That is your primary charger, unless you are pulling the batteries and charging them elsewhere? if your primary, you really want to get as close to 0.1C as you can.

I'm just trying to say you want the biggest, meanest, toughest 1206 part you can find and you want to keep an eye on it when you first fire it up. I'm curious how it works out for you because I've thought about these issues surrounding AA's but haven't tried it myself.

I took a quick look at Mouser for 1/4W 1206. They have very limited values. Your job will be to hunt down an acceptable value, I guess. Ideally you would want a 1/2W part to be a littel conservative.

 

[mik000000]

will be mainly desk powered, and occasionally battery. yes, circuit will be primary charger. I am putting pimeta, tread, charger circuit and 12 AA into hammond 1455k1601. is v/tight and will be difficult to remove batts to charge elsewhere. was planning 1/4" jack, but may have to revert to 3.5 for lack of room. I already will be going to parts place tomorrow to find shorter 470uf caps in order to fit..lol.

also what is and why 1206 type resistor? local parts store carries many values in 2-5w square ceramic pkg. i think is wirewound, but not sure. did not think it was critical item, and these are vv/cheap

 

[star882]

Quote:

Originally Posted by tomb There have been several posts lately about trickle chargers for battery-powered amps, and how to design/build them. Here are some building photos of trickle chargers for a couple of PIMETA's. The chargers are based on the LM317, with 2x9V, powered with a linear regulated 24VDC 500ma walwart (Jameco). The batteries are not pictured, but I'm using some 250mah, 8.4V "9V" batteries I got on e-bay. I will leave the calculations to others. The walwart is linear-regulated only to ensure good sound if the amp is operated under wall power. You will need higher voltage if you use 9.6V "9V" batteries. The idea started with __redruM and this thread a little over a year ago: http://www6.head-fi.org/forums/showthread.php?t=110663 One of the most recent detailed discussions was started by ozshadow here: http://www6.head-fi.org/forums/showthread.php?t=185796 __redruM essentially drew from Tangent's design for a charger in the PPA. Since then, what's shown in the schematic below is used in the PINT and the Mini3. The schematic and layout shown in the photos is as follows:

If the power supply is regulated, you can just use a resistor. Put it across D2 (omiting the regulator circuit) and calculate the value to make a slightly lower than design rate when fully charged. This way, it will charge faster when less than full charge (which you will want) and slow down as it charges up (also desirable). In some cases, if the regulated supply voltage is very close to the full battery voltage plus the diode drop, it can be designed to charge fast when discharged and essentially stop when charged. However, that generally doesn't work all that well with Ni-based batteries. Pb and Li-based batteries, however, work very well with that and in fact, that's the recommended way to charge them.

 

[tomb]

Quote:

Originally Posted by star882 If the power supply is regulated, you can just use a resistor. Put it across D2 (omiting the regulator circuit) and calculate the value to make a slightly lower than design rate when fully charged. This way, it will charge faster when less than full charge (which you will want) and slow down as it charges up (also desirable). In some cases, if the regulated supply voltage is very close to the full battery voltage plus the diode drop, it can be designed to charge fast when discharged and essentially stop when charged. However, that generally doesn't work all that well with Ni-based batteries. Pb and Li-based batteries, however, work very well with that and in fact, that's the recommended way to charge them.

All true, but charging faster is not what was wanted in this design. The idea was to use the amp indefinitely while connected to the wall power supply without a performance hit. Thus, the reason for a regulated circuit to trickle the batteries at a constant, trivial demand.

 

[NeilR]

Quote:

Originally Posted by mik000000 will be mainly desk powered, and occasionally battery. yes, circuit will be primary charger. I am putting pimeta, tread, charger circuit and 12 AA into hammond 1455k1601. is v/tight and will be difficult to remove batts to charge elsewhere. was planning 1/4" jack, but may have to revert to 3.5 for lack of room. I already will be going to parts place tomorrow to find shorter 470uf caps in order to fit..lol. also what is and why 1206 type resistor? local parts store carries many values in 2-5w square ceramic pkg. i think is wirewound, but not sure. did not think it was critical item, and these are vv/cheap

Don't pay any attention to me, I'm clueless

For some reason I thought you were working with a Pint and in that case the onboard parts are surface mounted. If you have the space, pick up a 1 watt resistor and you'll be fine. A 2-5W would be fine but probably overkill.

If it were me, I would go to a bigger case before I used a 1/8" minipin instead of a 1/4". The more I use minipins the more I hate em

 

[tomb]

PIMETA Pairs
Pics of the completed amps with the trickle chargers. The walwart used is a linear-regulated 24VDC @ 500mA, Jameco #174861 at $13.15. I can detect a subtle, slight loss in bass when using the walwart vs. pure batteries (fully charged, of course). So, it may not be up to the standard of the old Elpac (certainly not a TREAD), but it sure is convenient.

 

 
470uF Nichicon UPW (10x16mm shorty's)
Double stacked BUF634, single on Gnd, Class A bias trannies
AD8066/AD8065 in one, AD8620/AD8610 in the other
Batteries are 8.4V, 250mah from the Shoreline Market on Ebay.
Hammond 1455J1201 cases

P.S. Many thanks to Tangent and __redruM!

 

[gtp]

I dunno if this is a dumb question or not, so please bear with me.

Is it possible to set things up with a wallwart/circuit so I charge the batteries but do not power the amp? In other words, the amp always runs on batteries, whether a wallwart is plugged in or not. However, when a wallwart is plugged in, it charges the batteries (which may or may not be powering the amp at the time). This way I wouldn't need a linear regulated wallwart but could still charge the batteries. Further, the amp would always sound the same, not better with or without the wallwart.

Big Thanks,
GTP

 

[NeilR]

Not a dumb question at all. The problem is that you are sending a constant current to the battery. Lets say your amp draws 50ma and your charger is set up to deliver 20ma (0.1C to 9V batteries). If you charge and play at the same time, you have 20ma coming in and 50ma going out; you are losing ground

If you are fast charging a battery and the amp draws very little current, you might get away with it. The way I visualize it, the PSU would essentiually be powering the amp anyway and any noise from the PSU would flow into the amp.



Quote:

Originally Posted by gtp I dunno if this is a dumb question or not, so please bear with me. Is it possible to set things up with a wallwart/circuit so I charge the batteries but do not power the amp? In other words, the amp always runs on batteries, whether a wallwart is plugged in or not. However, when a wallwart is plugged in, it charges the batteries (which may or may not be powering the amp at the time). This way I wouldn't need a linear regulated wallwart but could still charge the batteries. Further, the amp would always sound the same, not better with or without the wallwart. Big Thanks, GTP

 

[tomb]

Having a little more time on these amps now, I would have to say that I can tell no difference - walwart vs. batteries. Some of it may have to do with the power caps getting broken in. They are definitely smoother now. The Jameco linear-regulated walwart is only $13 and change, so the cost-benefit ratio is much better than with the old, expensive Elpac.

As far as charging only, that is essentially what Tangent recommended in the first thread. As you say, it would only require the cheapest of walwarts. The simplest method would be to use a switched plug - so that if the walwart was plugged into the amp, the batteries would be out of the amp circuit. However, that would not accomplish exactly what you describe, but it would be pretty easy to do and is actually the more common method.

Edit: I take it back. Listening to my Senn's, there is a difference: more bass, but not as open on batteries; less bass, but much livelier on walwart. I guess that would correspond to more current/less voltage on batteries, but more voltage/dirty current on walwart. These differences go completely unnoticed with KSC75's or PortaPro's.

I am building some TREAD walwarts - I'll post back on how they do when finished.

 

[Alcaudon]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif [size=medium]PIMETA Pairs[/size] Pics of the completed amps with the trickle chargers. The walwart used is a linear-regulated 24VDC @ 500mA, Jameco #174861 at $13.15. I can detect a subtle, slight loss in bass when using the walwart vs. pure batteries (fully charged, of course). So, it may not be up to the standard of the old Elpac (certainly not a TREAD), but it sure is convenient. 470uF Nichicon UPW (10x16mm shorty's) Double stacked BUF634, single on Gnd, Class A bias trannies AD8066/AD8065 in one, AD8620/AD8610 in the other Batteries are 8.4V, 250mah from the Shoreline Market on Ebay. Hammond 1455J1201 cases P.S. Many thanks to Tangent and __redruM!

Wow!!! Very nice work!!!! Where did you get those knobs??? They look great!!

 

[tomb]

Thank you for the nice comments!

Those knobs are a two for $2.95 Radio Shack standard.

They've upgraded them since the pic on their website:
Silver Tone Knurled Knob

BTW, addressing that post above yours, a TREAD walwart loses no quality compared to the batteries.

 

[Alcaudon]

Just one more question tomb....

All I need to charge a couple of Ni-MH/Ni-Cd 9V batteries is just that simple circuit above and a wallwart of 24V and 500mA???? Nothing else to take care of???

I mean, I don't mind reducing battery life, I'm planning to build a small portable amp (something similar to a47) and I was planning just to take out the batteries and recharge them when necessesary (I want the amp as small as possible), but it might be worth a little more space on the board if I could just recharge them inside.

Thanks!!!!!!!!