Voltage drop with system powerup

sydney075 · Post by **sydney075** » Thu Nov 10, 2005 4:40 pm

Ok I was hoping to start a little project log with my next post but I have run into a problem that seems a little wierd and the search function has not been helpful in resolving it. I have made my power supply from 6 nimh aa's which gives me 7.2 volts this has been enough to run the system and the lcd separately but not when I went to wire them up together. As soon as I turn on the n64 the 7.2 volt line drops to around 6.5 volts and the 3.3 stays right about 3.3 were it should be.

I am running everything off of the 7.2 pack with a lm317 for the 3.3 line. Turning the lcd on creates no voltage drop so I know it is the system that is causing it. I am wondering if anyone else has had a similar problem becuase all the posts I could find talk about using a single 7.2 volt pack for both system and lcd. And as I stated I could not find a post relating to this problem.

Turbo Tax 1.0 · Post by **Turbo Tax 1.0** » Thu Nov 10, 2005 4:42 pm

try charging your batteries if you havnt

sydney075 · Post by **sydney075** » Thu Nov 10, 2005 4:52 pm

Been there done that.

Even used higher mah ones 2500 vs 2000 same problem.

daguuy · Post by **daguuy** » Thu Nov 10, 2005 4:55 pm

did you LED mod the screen? that'll lower the current draw so it might not make it shut down and maybe if you're just using a linear regulator, you should switch to something more efficient like DC-DC convertor or switching regulator to lower the 3.3v's draw

sydney075 · Post by **sydney075** » Thu Nov 10, 2005 5:06 pm

I plan to do a led mod but that will only affect the amperage not the voltage and 6.5 volts is still below the required amount for the screen. A dc-dc convertor is not really an option the as the amount of money I am spending at the moment is kinda fixed (no one seems to want to hire me

) I have all the parts that should be needed but as far as I can tell no one has had this problem with a system. It is not the regulator because while it may not be as efficent it does output the right voltage it is only when the system is turned on that the 7.2 line drops.

Post by **marshallh** » Thu Nov 10, 2005 5:10 pm

It can possibly be your batteries themselves. A lot of AA rechargeables simply aren't meant to handle high current loads. I used some Energizer nimh's for my n64 at first, and they would dip and literally get scathing hot. I'm using some AA's from a surplus site and they work fine.

Your lm317 is the 1 amp model, right? Well, the n64 draws more than that, intermittenly. Maybe it's overloading the regulator and that could be causing the voltage drop.

nos_slived · Post by **nos_slived** » Thu Nov 10, 2005 5:21 pm

Try disconnecting the 3.3V line from the LM317, and use two 1.5V AAs. If the power doesn't drop at startup, you know that the regulator is the problem.

superdeformed · Post by **superdeformed** » Thu Nov 10, 2005 6:20 pm

Have you checked the voltage of your battery set-up with them all fully charged? Six fully charged NiMH batteries should put out almost 9 volts with no load on them, and 7.2-7.5v with a load (batteries are not really a constant voltage source; current draw will effect them slightly and the voltage will also drop as they run out of charge). And as marshallh said, a lot of AA's just aren't meant for that much current draw. C batteries would work a fair bit better and you can get ones that will last a lot longer than AAs. If you're deadset on using AAs though, then you should get ones made for RC cars, as they should be able to handle the current draw better.

sydney075 · Post by **sydney075** » Thu Nov 10, 2005 10:57 pm

@marshallh - I've used 2 separate sets of batteries one 2000 mah and the other 2500 so I know it is not the batteries.

@nos_slived - Tired that after your suggestion still a power drop but only .3v less very odd.

@superdeformed - I am completely certain that the batteries are completely charged that was the first thing I thought of yesterday and as such charged them overnight. I was able to put one more battery inline and not get too much voltage to overload the screen before the unit was turned on. However he screen did not have quite enough to stay on. It was close though.

It looks like my final choice is to use a 9.6 volt pack (read 2 more aa's) and wire up another lm317 at 7.2 volts to absorb the extra voltage before the system is turned on. I do not want to trust a second power switch for just the screen and risk someone turning it on first. Don't look for an update on this for a while though as I don't have the components or the cash to get them right now.

Side note I hooked up the battery pack the other n64 and the same thing happens.

timmeh87 · Post by **timmeh87** » Tue Nov 15, 2005 6:52 pm

you said you cant afford a dc-dc converter, but you actually might be able to...

i am on the solar car team at my university, and electronics companies ship us free stuff all the time. they call them "samples". if you have, or know someone who has a university email address, it might be possible for them to obtain some free samples from texas instuments or whoever else makes dc-dc converters.

i know that theres like 20 of them just lying around the solar car office. we dont bother treating them with respect because we can always get more for free

.

im just thinking that using a reg wastes tons of power (i.e. they heat up) that could go towards battery life. i reccomend that anyone who can get their hands on a dc-dc uses one. (also, reduced heat means less heatsink, less airflow required)

[a quick google search revealed the efficiency of a lm317 is ~ <45%, vs 70 to as high as 90-something for a dc-dc] -->
http://pdfserv.maxim-ic.com/en/an/AN3560.pdf

as far as your problem - instead using 8 batteries in series, why dont you use 6 and 6 in parallel? this would add a lot of weight... but your problem seems amperage related, so i dont know if adding more batteries in series would help.

also, mAh is a rating of total power capacity, not max current draw. a higher mAh rating dosent *nessecarily* mean that you can draw more current.

bioniclebert · Post by **bioniclebert** » Fri Jan 20, 2006 6:49 pm

sorry to "bring this up" but Im wondering:

Im trying to power this N64, and heres the thing. I used a LM317 that outputted 3V. When I turn it on, the voltage dropped significantly, actually to 1.3V the 12V line only dropped 1V, but that was fine for the 7805.

So I'm wondering:
1. If I get a DC-DC converter, how can I be shure that it will not drop too low?

2. If I dont get a DC-DC converter, would it be safe to wire up 2 AAs, and then add one more to see if the power stays in place?

3. (if anyone could give me a direct link to send some thing to the DC-DC converter place, and get one that is explained how to hook it up, thanks!)

Post by **marshallh** » Sat Jan 21, 2006 5:55 pm

Most likely, you're not putting a high enough input voltage into this. My 5v switching regulator dips to 4.5v when enough load is applied (actually, when playing superfx games for snes), while a higher voltage is needed. Switching regs. might differ in this respect from linear regulators, though.

The LM317 is rated up to 1 amp. It WILL sag if you load it more than that, and will soon shut off if too much is drawn. I think the LM117 is 3 amps.

1. Make sure you read the datasheet and put a high enough voltage into it.

2. No. AA batteries realy can't cope with the current draw and will sag. However, if you get, say 6 and put them in 3 sets of parallel, you'll get more capacity and they can handle the current draw. However, there is much graphic distortion in the N64 below 3.05v.

3. Read the FREE DC-DC CONVERTOR thread by timmeh87.