power thread deally (again)

[geekbait111]

Hihi
I have a couple of questions with batteries. But I really only want 4 nimh batteries, otherwise 6 takes as long as 8 to charge (I think). First of all: alkalines AA’s have a quick discharge rate at the beginning, soon it becomes/stays at 1.2 V for a while then later goes down more where it’s usless. And yet you can have a PSone screen/model 2 gen (or whatever) with only 4 AA’s! Nimh on the other hand stays a 1.2V for a long time and eventually goes down and dies for recharging. Theoretically, couldn’t I supply a PSone screen/model 3 with 5V (rounded) and be OK?

To make the equation more balanced, though, I should lower the requirements of the PCB’s by bypassing… that’s where I have a problem

1) How/what’s the definition of bypassing?

2) How do I bypass a sega model 3 (something with the 7805 perhaps?)

3) How do I bypass the PSone screen if possible

-Thanks! This would help me a ton if I could do it!

[Skyone]

PSOne screen requires ~7.5v.

Bypassing is simply ignoring a part or group of components. Skipping a 7805 that need 7.2v is an example. By bypassing it, you apply 5v to the output of the 7805, rendering the 7805 useless.

To bypass the 7805 in the Genesis 3, just plug 5v into the output pin of the 7805.


*image from talkingelectronics.com*

What do you want to bypass on the PSOne screen? "Bypassing the PSOne screen" means not using a PSOne screen...

[vskid]

I've had the PSone screen work down to about 7v, 7.2v is considered the minimum, 7.5v is just what sony says it needs.

[geekbait111]

Can NiMH batteries be substituted for alkaline batteries even though they are only 1.2 volts?

Yes, for most high drain electronic applications NiMH batteries are ideal substitutes and you needn't worry about the apparent voltage differences. Even though alkaline batteries are rated at a nominal 1.5 volts, they only deliver 1.5 volts when they are fully charged. As they begin to discharge the voltage of alkaline batteries continuously drops. In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. That's very close to the 1.2 volts of a NiMH battery. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for most of their discharge cycle.There are a couple of cases where their actual voltage difference may be important to you. In the case of a device like a radio, where a higher voltage can mean a stronger signal, a fresh alkaline battery may be more desirable - but more expensive - than a rechargeable NiMH battery. This is also true for a flashlight, which will be brighter with the initial higher voltage of alkaline cells. This minor difference may not be important to you and is probably offset by the much lower cost of operating NiMH batteries. And keep in mind that the alkaline battery only has a higher voltage when it is fully charged. Once it gets to 50% capacity or less, it will be delivering a lower voltage than a NiMH battery.

The one time when the voltage difference of the two is important would be in the case of a device that checks the voltage of a battery to estimate the amount of charge left on the battery. Because the voltage of an alkaline battery drops at a very predictable rate it's possible to estimate the amount of capacity left in an alkaline battery based solely on its voltage. (1.5 volts - fully charged, 1.25 volts - 50% charged, 1.0 volts - almost fully discharged). But a NiMH (or NiCd) battery stays at about 1.2 volts until it is nearly completely discharged. This makes it almost impossible to know the amount of capacity left based on its voltage alone. When a device that's using NiMH batteries indicates the battery is low, it's time to change the batteries now!

from: http://www.greenbatteries.com/nibafa.html



So that means that an alkiline AA is 1.25 V when around 50% through its life cycle. And yet: A person made a gen. 2 + PSone screen with 8 alkaline AA's (4 wired in parallel then wired in series with another pair of 4 alkaline AA's wired in parallel... well you get the idea basicly the volt equavilent of 4 alkaline AA's)

So theoretically shouldn't the screen die after about 1/2 the batterys' capacity?


If I find it again, I'll post the link (I think somewhere on benheck)


P.S Nimh AA's are definatley going to be my power source because of cost and cheapness at sams club . (maybe later I'll move to Li-ion)



edit
this isn't quite what I saw but look!

The PSOne screen has a 7805 inside it that takes the 7.5 volts and drops it to 5 Volts, AFAIK. Bypass it and it'll run on 5 Volts.

some website/blog so I think it'll work if I bypass it.
http://www.hardforum.com/showthread.php?t=892708

[Skyone]

The PSOne screen has a 7805 inside it that takes the 7.5 volts and drops it to 5 Volts, AFAIK. Bypass it and it'll run on 5 Volts.

some website/blog so I think it'll work if I bypass it.
http://www.hardforum.com/showthread.php?t=892708

That doesn't work. The 7805 only works for the audio or something...

[geekbait111]

oh... I regret getting a PSone screen now instead of a hip pad or whatever . But oh well, guess I'll have to get 6 AA's.

Well... thanks!

edit: wait... so how does 4 alkalines sustain a PSone screen/gen 2 for its entire life?
when it's at 50% it only has 1.2V, same as a Nimh through its entire life nearly!