Battery question...

XFactor · Post by **XFactor** » Thu Mar 02, 2006 7:41 pm

Hey, thanks to all those who helped me in my previous post.

I have recieved all of the major parts for my portable from the seller; however, I am in a bind when it comes to the batteries.

I wanted a battery that would last 2-3 hours (w/a PSone Screen) and was compact enough that I wouldn't have to sacrafice significant case depth to house it. I found a battery that looks like it would suffice here: http://www.batteryspace.com/index.asp?P ... rodID=2362

I think it would be best to buy batteries that would not spontaneously explode...because I love my hands. I plan to buy 2 of these PCB-ready ones, making the entire energy output (as the site says..) 7.2v at 3000mAH. Would two of these be sufficient for the time/size?

Thanks to all those who can help. The next headache is figuring out which heatsinks will keep the case as slim as possible...

daguuy · Post by **daguuy** » Thu Mar 02, 2006 7:42 pm

yeah 2 of those would be good but you need a protection circuit so they don't blow up
EDIT: it says it has a built in protection circuit so maybe you could wire to parrallel but i'm not sure

XFactor · Post by **XFactor** » Thu Mar 02, 2006 8:19 pm

Yeah, the battery page mentioned that they could be wired for a parallel circuit.

But would they provide enough power and size compactness I need? I also read that the system requires 7.4v just to run. Would this cause the PSone screen to be dark or make the overall system run slower?

Secondly, how do you even go about wiring those batteries together so the PCB chips can protect the two of them at the same time?

daguuy · Post by **daguuy** » Thu Mar 02, 2006 8:28 pm

7.4v is perfect. 2 of those parrallel is 3000mah and should power it for 2.5-3 hours

timmeh87 · Post by **timmeh87** » Thu Mar 02, 2006 9:48 pm

keep in mind that near the end of their charge, they will drop off to about 3v apiece.

i happen to be in the process of designing a system to characterize li-poly cells for the solarcar our school is working on, and i have some data in front of me. under 1A of load, it looks like you get about 50% of your capacity somewhere above 3.5v, and the last 20% is below 3.2 (for these particular cells, which happen to be designed for laptop batteries.. 10Ah

) . i want to use polys for my own portable, and i have often wondered whether two cells in series really would be good enough.. i guess someone is just going to have to try it and find out.

alternatively, look for a dc-dc converter than can convert 3v to 8v, and put them in parallel

Post by **Skyone** » Thu Mar 02, 2006 9:52 pm

I thought you couldn't double mAh by parallel or series...?

timmeh87 · Post by **timmeh87** » Thu Mar 02, 2006 9:56 pm

voltage increases with series, capacity increases with parallel

Post by **Skyone** » Thu Mar 02, 2006 10:08 pm

Thanks for clearing that up for me!

XFactor · Post by **XFactor** » Fri Mar 03, 2006 12:14 am

timmeh87....would the power output of the type of batteries i want to use supply enough voltage to run the system effectively? Would 7.4v have a adverse side-effect like a dimmer screen or slower gameplay because its not say 9.6v?

The other thing is heatsinks. My cousin seems to be of the mind that small heatsinks are not effective. By small i mean heatsinks that don't have much height, and i just want to know how it really is because my cousin is often guilty of embellishment. I would like to go with heatsinks to keep everything compact; however, i have seen 30mm fans which i could place on the bottom of the unit to dissipate heat (however, when laying it down on a surface, air would not easily escape; so i sort of threw this out but felt to mention it). I was at the understanding that as long as you covered the entire surface area (the top) of a chip with a heatsink, it would be effective. The N64 is not a standard computer due to its obselecence, so i don't know what kind of effect modern heatsinks would have on it. Recommendations as to which types (if any) of heatsinks would be extremely welcome here.

I am just trying to sort out the kinks before i go ahead and order these batteries since they are rather expensive when bought in tandem. I will most likly get the heatsinks off of newegg.com or just shuffle on down to Best Buy to get them.

P.S: Where can you get a gamebit that will open the N64 where they don't hose you for shipping? I have found that oftentimes the shipping costs more than the bit; which is pretty ridiculous.

timmeh87 · Post by **timmeh87** » Fri Mar 03, 2006 8:23 am

everything except the 3.3v line in the 64 is regulated. that means it dosent matter what voltage you put in (as long as it is a valid voltage), the reg will drop it to the voltage that is needed (in the case of the n64 or the screen, 5v i think). if you dont put enough in, nothing will happen. how much is enough? most people on the forums quote a number between 7.2v and 7.6v.

now these regulators take in ~7.5v and output 5v. there is an inescapeaple loss of 2.5v in there. however, you can get "LDO" (low drop-out) regs that only need about .5v - 1v more than the output (so you would only need 6 volts). it is theoretircally possible to replace the regs on the 64 and screen with these, but i dont think anyone has ever tried it (at least on the n64)

so will two lithium batteries work? i do not know man. i have a suspicion that you will not get full power out of them, as the regs will drop out at around 60% or 70% discharge. like i said, look around for a 3v-8v dc-dc converter. this would basically solve your problem instantly. you could use the batteries in paralell, and always be guranteed 8v output.

heatsinks. there is no consensus on how small is too small. it is accepted that no heatsinks is bad. heat transfer is governed by three things, really.

1) mass. the more mass your heatinsks have, the more heat they can hold.
2) surface area. the greater the surface area, the faster heat will be transferred to the surrounding air (this is the ultimate goal)
3) material. different materials have different heat capacities, the amount of heat per unit volume that they can "absorb" i think aluminum has a higher heat capacity. this is a good thing.

so. yeah. this is basically a "use your best judgement" situation. try to find sinks that have high surface area (the kind that look like a pit of spikes are good). i understand that no one wants them to be that high but i think this is a situation where a compromise needs to be had. the one i chose (from an old pentium pro) is (or 'are', since i cut it up) about 2.5cm high.

also. you need to either glue the sinks to the chip, or use some special grease (or the stock pads that were there) and put some downward pressure on them. you want really good contact with the chip. there are many guides on doing this properly.

oh, and juut use the melted pen method, it costs less that a dollar. its gotta be the clear kind of pen made out of that hard, brittle plastic. and you gotta melt it before each screw.

XFactor · Post by **XFactor** » Fri Mar 03, 2006 2:12 pm

timmeh87, i am trying to look around for the regulator. Is the reg a 3v input to 8v output or is it an 8v input to a 3v output?

BTW, how much do regs typically go for?

I also am wondering if i should use 3 batteries of that type instead of two. Or, should i find a battery of near-proportional size that has a higher voltage and mAH level. I only ask because i like the size of those batteries; they would keep the case pretty compact.

Thanks for also addressing heatsinks; but i was wondering if i could sacrafice heatsink height (the spikes) if i put in a fan? My cousin and i were sort of contemplating a combination of smaller heatsinks and a fan, but i was hoping to get by with only small heatsinks (which by what you say really looks to be a dismal possibilty at this point). I obviously don't want the case to melt but at the same time i am trying to keep everything as compact as possible..

daguuy · Post by **daguuy** » Fri Mar 03, 2006 10:14 pm

Are the regulators on the 64 of the inefficient kind? I have heard there are two types of regulators: one which converts the extra voltage to heat, while the other doesnâ€™t waste it so much somehow.

yeah the 7805 is inefficient. the kind that doesn't waste as much power is a dc-dc convertor

would it not be better to use a LDO converter since you will get more use out of your batteries as their voltage drops towards the end of their charge?

no because LDO is still more inefficient than dc-dc. plus if the voltage dropped below 7v, the irreplacable 7805s on the psone screen would stop working

timmeh87 · Post by **timmeh87** » Sat Mar 04, 2006 1:43 pm

ok. some clarification:

there are two types of regulators: linear and dc-dc. linear regs just burn off the extra votage, where a dc-dc acts like a transformer

- (aside: the dc-dc is basically a transformer for dc current, but transformers only work with AC, so you cant just use a transformer for dc. the dc-dc basically rapidly turns the dc power on and off, through an inductor... its complicated to explain.. you can change the voltage like this...)-

within the "linear" category, you have LDO and just normal linear regs. LDO's are just as inefficient as normal ones, but they will accept a lower voltage before they "drop out" (turn off)

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the way a dc-dc works (rapidly pulsing the voltage), they introduce "noise" into your circuit. it causes ripples in the voltage. sometimes sensitive chips dont like this. i would be nervous about replacing the 7805 on the n64 for this reason. i will prbably try it at some point, but i still havent even wired my cartridge slot back on, one thing at a time..

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a fan will compensate for smaller heatsink size. it also uses up power and can be noisy. your call. mine is probably going to have a fan. but not on the heatsinks, just a general exhaust fan at the top of the unit.

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the only way to get every last bit of juice out of your batteries would be to stick in a LDO to produce 7.2v from the battery output

this makes no sense...

timmeh87 · Post by **timmeh87** » Sun Mar 05, 2006 12:25 pm

well you put a cap on the output with the intention of trying to eliminate noise. i guess it works pretty well, at least for the 3.3v line. who knows what surprises 5v will hold. i warn you though, i probably wont get around to it for months, at least.

codeman · Post by **codeman** » Sun Mar 05, 2006 1:13 pm

anotherperson wrote:I am familiar with how a transformer works, after all who doesn't enjoy playing with flyback transformers? I did not know that a DC-DC regulator operated on the same induction principle, though.

heh...are you sure it isnt a flyback converter instead of transformer? A flyback is actually a type of DC-DC converter, it just uses a transformer to provide isolation.
Anyway, I thought the 3.3V line on the N64 was the one that took the most current? The more current that's drawn through a DC-DC converter the worse the regulation, so if it's fine at 3.3V it should be better on the higher voltages.