battery going flat. help needed

[Blakey]

I think you need to start your car at least once a week for atleast 5min, this should solve your flat battery problem.

U will run ur battery flat if u only run it for 5minutes, the starter motor draws something ridiculous like 30 - 40 Amps, so takes bout 30 minutes of running to get that charge back in, best is to just go for a cruise every week

you will find that the battery can do that a fair bit. and 5 min is heaps of time to replace that small amount of charge lost from starting.

our battery's are i think 80 or 90 Ah(Amp Hour) battery, so they can run at 80 - 90Amps for 1 Hr, (unlikely to happen, but that is what that rating means)

so 30 - 40 Amps for 5s isn't allot out of a battery, if it was something more like 300 - 400Amps for 5s then yes that would be allot more of a loss.

[smithsy]

Being a sparky I would have thought you'd understand that initially a motor will draw atleast around 5-7x it's operating load until the back EMF builds up in it. When you couple that with the fact it's been drawing a constant stand-by current for a week then it's a very real possibility that the alternator (and again this depends also on how the ECU regulates the usage of the alternator which can be quite complex in new cars for fuel efficiency reasons) won't be able be able to bring the battery back up to a full charge.

But ofcourse you would still know better from the book of facts in your ass, so lets do some very simple and primitive calcs that being a sparky and electronics 'guru' surely you would understand...

Going off a 0.04A standby current that gives you ~7Ah per week being drained from the battery. Given the alternator is 120A and assuming a theoretical 100% charge efficiency (something which you won't get in the real world, only a textbook) that equates to at least a 3.5minute run-time just to replenish the energy lost during the week. I'm also assuming that the ECU runs the alternator at full ball at idle to pump out the full 120A charging current (VE Commodores have had significantly problems with flat batteries because the engineers have put in all sorts of 'fancy' fuel saving alternator controls, so it's quite possible the Lancer ECU also has some 'magic' up it's sleeve) and ignoring the fact that the car still needs power to run the engine and auxiliaries.

So in fact he is very right to say that 5 minutes of run time a week will not be adequate once you take into account the starting power and the standby power the car has used through the week.

For an electrician who also claims to do uni, you never cease to amaze me how blindly lead all your comments are.... But then again seeing some of the electricians at work it doesn't exactly surprise me....

[AJjnr86]

I tend to disagree with u a bit here Blake, if it was an old car with a generator then it'll charge straight away, but newer cars will not charge all the time, this is to assist fuel consumption and emissions, I think they charge when the cruising, and if the car detects that it is absolutely required

[WTR]

My bet is a dead cell/sulphated battery - only way to tell is to have a "load test" done .... see your local auto electrician.

[smithsy]

I tend to disagree with u a bit here Blake, if it was an old car with a generator then it'll charge straight away, but newer cars will not charge all the time, this is to assist fuel consumption and emissions, I think they charge when the cruising, and if the car detects that it is absolutely required

^ BINGO!

Exactly why VE Commodores have problems according to NRMA (although Holden refute the claims) and it's like you say because they've tried to make the ECU too clever for it's own good and focus most of it's charging when the car is cruising and not under load. So like I said in my above post it's quite possible at idle it won't provide a full 120A charge current...

My bet is a dead cell/sulphated battery - only way to tell is to have a "load test" done .... see your local auto electrician.

Not sure how auto elecs do it, but when I was doing UPS maintenance we would use a meter worth a few grand that measured the 'conductivity' of the battery. Good batteries gave a high reading, duds gave a low reading. Generally we got about a 5year lifespan (the batteries would still work fine for say prawn lights/domestic use, but for a 'mission critical' UPS they simply didn't have enough charge capacity left) out of the batteries if they were well maintained in a temperature controlled environment. Generally I've found car batteries will last around the 5yr mark, but there's so many variables that can make this either shorter or longer.

[AJjnr86]

Smithy, I think Holden just need to have a few more trys at correcting the system, Benz have it right, but then we would have had it in round for a few more years and had more ppl researching and designing the idea

[smithsy]

Yeah I'm not saying the idea is flawed, it's a great idea, but as you say Holden have just mucked up their programming. I just mean that stuff like that just goes to assume you can't always assume now-a-days the alternator will pump out at full ball all the time, alot of it comes down to how well (or in Holden's case poorly) the code for the ECU control was written.

Much alike the glitchy programming of the Toyota Prius' electronic brake control, it's just showing that aspects of modern cars are now only as good as the team who've programmed it's micro-controllers...

[WTR]

@ Smithy - last time I had a suss battery, the auto electrician hooked up a box with a bunch of resistors (coils) directly across the terminals. It's like a stress test.

[smithsy]

Yeah sounds like wire wound resistors which would be just a cheaper way of testing the battery I guess, we used 500W halogen spot lights sometimes to load test (and also give a discharge cycle) to the smaller UPSs to see how long the batteries lasted....

Some places (such as battery World and Kmart Tyre and Auto) though i believe do use electronic based testing systems, but the cost of them is probably prohibitive for the average auto-elec to buy.

[AJjnr86]

Yea the electronic testers work well, cost bout $7500, that what we use to test batteries

[shamrockshirts]

Sounds like you've a dud battery mate. If its not holding charge and there is no drain then its the Battery Cells. You'll find the cold weather was shown its weak hence why its giving bother now.

New battery time!

Just check with Mitsubishi as its probably a warranty job too.

Cheers
John

[LZY_EYE]

I just replaced my battery.

It was obvious it was on its way out though as the car was struggling to start for a couple of weeks.

When there was no load on the battery it had its 12-13 odd volts. As soon as you attempted to start the car it dropped to 5.

The battery from Supercheap / Repco is about $165. I didn't shop around much as the car wouldn't start

I am pretty sure the batteries from Mitsu have a 1 year warranty. Best to double check though.

[Blakey]

Self-Discharge
The self-discharge rate is a measure of how much batteries discharge on their own. The Self-Discharge rate is governed by the construction of the battery and the metallurgy of the lead used inside.

For instance, flooded cells typically use lead alloyed with Antimony to increase their mechanical strength. However, the Antimony also increases the self-discharge rate to 8-40% per month. This is why flooded lead-acid batteries should be in use often or left on a trickle-charger.

The lead found in Gel and AGM batteries does not require a lot of mechanical strength since it is immobilized by the gel or fiberglass. Thus, it is typically alloyed with Calcium to reduce Gassing and Self-Discharge. The self-discharge of Gel and AGM batteries is only 2-10% per month and thus these batteries need less maintenance to keep them happy.