Ok so after replacing 3 alternators in 4 days and finally finguring out that it was one of my big 140a fuses AND one of my smaller 7.5 amp fuses that was causing the alternators not to charge the battery... i'm STILL having a charging problem. Or rather this time a discharging problem. When i try to start my max after sitting all night the battery is usually very discharged and its hard to start, but today it was fully discharged. When the cars running the alternator is feeding the batter enough voltage (i had it checked and my battery checked at 2 places, both checked out fine although they got a low voltage warning at autozone saying my alternator wasn't putting out quite as much voltage as it should be. Everything runs great when the cars running, although i have noticed several little nusense problems like my sub amp cutting out on me while driving sometimes. Then it cutting back on when (check this) i turn my ac fans on. It always works... whenever my subs cut out i can turn my ac fan on and they work just fine, even after i turn them off again. So basically i'm thinking i have a short somewhere that is discharging the battery can causing these weird problems. Anyone have any guesses as to where, or at least an idea of where and how i should start looking. Taking this to the dealer would cost me way too much since there'd be insane diagnostic charges. So Any help would be appreciated.

 

Start off with all wires that you touched or was working on. A wire may be touching a ground causing it to stay on. You may need to see a mechanic that is savy in electrical to pin point the problem.

Also try looking in the FSM and how the car charges the system. Your going to have to start reading the electrical plans of the car and one by one check the wiring system.

 

simple start would be replace your battery connectors.

 

Disconnect your sub and run the car without it for a few days.

 

I know it's a simple thing but make sure battery connections are clean none of that corrosive build up at the terminals. Otherwise I agree with SVI 30 start disconnecting circuits over night.

 

those battery tests are not conclusive. I would start by replacing the battery, especially if it is more than a few years old. when batteries go bad they can do strange things, discharge intermittently, etc. even if the battery is relatively new, it can fail.

the blown fuses are a bit suspicious, and you may indeed have some other fault. but I'd first eliminate the battery as the source of trouble. you can always return it if it turns out to be something else.

 

ok what u need to do is gram a ammeter and disconnect the positive terminal of the battery and see how much is being drawn.... then just start disconnecting all the crap that u have installed one by one untill u find the one that is causing it...

 

that's not a bad suggestion, except that you'd have to know how much current the car should normally draw with key off. it will not be 0. if he measured, say, 3mA would that be too much?? how about 30? 300? I suppose one of us with a healthy system could get a baseline for him.

 

if it draws more than 25 mA then u have a problem.....

 

and where did you get that from?

 

i calculated it...

 

I trust this guy he's pretty good with electrical stuff.
Also I personally know this guy.

 

OK i'll try that when i get off work today. I really need to find this problem soon, or there will be a 5 speed max for sale for cheap. I'm moving across the country to san diego at the end of the month and i planned on driving there...

 

Hey, f550maranello2 you want a good electrical problem check out post windows won't roll down sunroof out. I've been working with this guy for three days, Wally>

 

you calculated it? please share your calculations with us. what is the basis of your analysis? (are you assuming a certain amp-hr rating? a certain discharge time?). what maxima-specific assumptions are you making, if any?

you said >25mA is bad. are you saying 25mA is a hard cutoff? for instance, if he measures, say, 50mA are you then suggesting that would be the cause of his overnight discharge? whereas 24mA would allow the battery to stay sufficiently charged for months on end without charging cycles? clearly these two scenarios are not compatible, so I'm wondering how you came up with 25mA...

in my view, there are only 2 ways to approach this from an empirical perspective -- quiescent draw design spec or battery capacity.

taking the capacity route , he needs to know the battery's C/8 rate (e.g. how much current it takes to discharge the battery in 8 hours, or overnight). for a typical healthy car battery the C/8 rate will range between about 5 and 15 amps - that's full amps, not mA (most modern car batteries are rated between about 75A-hrs and 200A-hrs at the C/20 rate - use Puekert's law to find the C/8 rate) -- this means 25, 50, or even 500mA isn't going to drain a *healthy* car battery overnight (operative word being healthy). of course if the battery is not healthy it will take much less current to drain it, and you need a new battery anyway - hence my original suggestion to buy a new battery.

alternately, if he knew the car's quiescent draw spec (e.g how much current the nissan engineers designed the car to draw with key off) then he could measure his actual draw and compare it to the spec. but unless the measured draw is several orders of magnitude higher than spec he will not be any closer to solving this mystery.

if the measured draw was only 2x or 3x the design spec, it could indeed indicate a problem somewhere -- but this would not be the cause of his overnight discharge. and again, you'd have to know what the Nissan engineers had in mind to draw any sensible conclusions from this, and you'd *still* have to replace the battery (any battery that can't deliver a 2, 3, or even 10x Q load overnight needs to be replaced).

BTW -- by my calculations a typical 100A-hr battery can deliver about 25mA for about 11 months, assuming it is rated at the C/20 rate and n=1.2 at room temperature. But this doesn't mean Nissan designed the quiescent draw to be 25mA, and it doesn't mean that if you measured more than 25mA that you have a problem. perhaps Nissan feels 6 months/40mA is an acceptable quiescent discharge profile? or perhaps they based their calculations on a higher capacity battery?? neither you nor I know what they had in mind.

So again I ask -- how did you arrive at 25mA?? why do you believe that is the magic number he should be looking for?

to the OP -- take your measurements. IMO if you get anything over a few hundred milliamps then you should take a hard look at what is draining your battery, just know that by itself is not enough to drain a healthy battery overnight. if you only get 5, 50, or even 100mA or so then you probably don't have a draw problem at all. in any case, if you get less than a couple full amps then your battery is fubar and needs replacement anyway. so again - I think it would be prudent to just start with a new battery and go from there.

 

^^^man this guys is always on my *** about something...

dude i pulled it out of my A.ss.. ok....

the point is to see if there is a draw.. ok.... i had 25-35 milliamp draw on my car and after 3 days the battery was dead this being on a new battery... then i traced it to the starter which was the problem... thats not "months and months ok!!"

then on a neighbors boat with a New battery he ha the same exact problem it would just discharge after a day or two... came out to be the same damn problem 120 mA this time....

now the point here is to replace as little parts as possible why the crap would u just go and replace the battery? if something is drawing current from the battery... ok..

this is the first step in trouble shooting.. ok if u engine runs like crap ur not just gonna go and replace the engine ur gonna take a look at other stuff before

now take ur googled explanations and stick them up ur A$$!!!

be a man and accept others advice before doubting others... ok

 

dude you need to calm down.

first off, your advice is bad, for all of the reasons I have stated above. you send a guy off to measure voltage without telling him what to look for or why. he's not going to have a clue what to make of his measurements. that's bad advice.

second, as I have already demonstrated, 25mA is not enough to drain a car battery in 3 days. your "new battery" was faulty, or you are lying.

third -- my "googled" explanations are the result of a master's degree in electrical engineering, coupled with over 6 years design experience in the electronics industry. in other words, I know my sh*t.

now you be a man and learn to accept when you have been corrected instead of hurling insults at the person who keeps this forum honest.

 

Yea i am lying.... thats why it fixed the problem and it never came back on 2 separate occasions.. thats not to say that the draw was a constant 25 mA.. who knows what it might have been as temperature increased and as time went on... when it was checked thats what it read.. so get off my ***...



i have a bachelors in electronic engineering, and i work with CNC machines i have seen **** that will boggle the mind and not make any sense but it turns out to be the root cause of the problem..... so i know my **** as well...
you dont have to flex your muscle here cuz ur not the only one here that has an education..

 

Certainly draining down a charged battery would not be in the milliamp range. A fully charged battery would be in the 50-60Ah range. So it would take a few amps to drain it overnight.

He has a sub amp hooked up. These amps have MOSFETs that are connected direct without any switch in between the battery and the MOSFETs. They are just put in tri-state mode via control gates. And given that they are consumer electronics, it is usually built as cheaply as possible. So the likelihood is his sub amp is acting up.

A quick check is to see if the amp is warm with the car off. That much energy has to create heat somewhere.

 

that's certainly a good possibility. and a quick check. I thought those things had relays to disconnect the fet's source (or is it the drain?) from the supply lines? and a separate turn-on wire to close the relay? maybe he tied the turn-on wire to the +bat supply line instead of running it to his head unit...

 

I've read where approximately 25mA is the typical draw for an automobile that is just sitting there and turned off (this maintains the memories such as radio presets). I would expect an automobile that is draining down the battery to draw considerably more, 100-200mA maybe more. The problem is the guy who has the problem may not know how to use or interpret an ammeter that is why I recommended he should just disconnect suspect circuits such as his sub amp. Never checked draw on my properly working Maxima but that is what I would expect to find.

 

alright -- just to put some additional factual data behind this, I just measured my "key off" current draw (what I'm calling quiescent draw).

when the ammeter is first connected in series the draw is about 250mA (this is probably capacitors charging). then after about 4 seconds it drops incrementally down to about 90mA, and seems to level off there. I repeated this 7 or 8 times, and it was the same every time. I didn't have the patience to sit and watch it for more than 5 minutes to see if it subsequently dropped below 90mA. my assumption is not.

so, key off draw = 90mA (for a '99 fully loaded SE).

when locking the doors it spikes to about 7.5A (when the turn signal lights are flashing), then settles down to 90mA.

when unlocking the doors it spikes to about 1A, then settles to about 890mA (presumably because the interior lights are on).

I have occasionally left my car dormant for several weeks at a time without problems (I travel a lot). and I presume Nissan designed the system to hold sufficient starting charge for at least a couple months.

bottom line - 25mA, 35mA, or even 135mA isn't going to discharge the battery overnight, after a week, or even after an entire month of inactivity - so long as the battery is in good working order and fully charged to begin with. of course, with some basic understanding of battery capacity ratings and discharge curves we already knew this. but now we have an actual field measurement to validate the theory.

f550 - I will accept your apology if you choose to offer it.

TonyGotSkilz - check your amp first like SVI30 says. then if you measure the key off current and don't come up with >1-2A draw in steady state, then your battery is shot. and it is probably shot even if you do. and you could quite possibly have other problems too.

 

blah blah blah. you both need to kill it.