Car doesn't start because of weak battery. But starts after 4 tries. Why?

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phucheneh

phucheneh

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Jun 30, 2012
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imagoon said:
It has more to do with running a device at or above 100% load for hours. A truly dead lead acid battery can draw quite a bit of power. A car with a 130amp alt running at 135+amps while still running the car itself will fry itself or the its diode set in a fairly short amount of time. There is no current limit between the battery and alt peg.
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But does the alternator (or rather, its control device) actually allow charging at 100% capacity? Also, I don't quite feel like doing math right now, but I don't think any battery would do well with hours of 100a+ charging.

My experience with carbon pile testers is that yes, you can load a battery down to the point where a standard 90-135a (I think that's about the reasonable range for most passenger cars) alt will peak at 150a or more...but at that time, due to the SEVERE load (the carbon pile is basically mimicking trying to jump start a couple other cars at the same time), your voltage is going to be in the 10-11v range, at best. The voltage drop is what induces the massive charging output.

To get any real empirical evidence, I'd have to get a bunch of cars, discharge their batteries to the 'barely has enough juice to start' level, and stick an inductive probe on them to see what the alternator charges at. I'm merely speculating, but I don't think it would be even half of the alt's rated output.

I know I've seen bad voltage regulators cause ~15v charging and boil all the electrolyte out of the battery, but at ~14.4v max, there really shouldn't be an issue...I'd have to get a little stronger on my EE-level 'battery theory' to understand charging voltage vs current flow (since a battery is in essence not a 'load,' right?), but anyhow, it is currently (hey a pun) my opinion that charging a battery with the alternator is not damaging to the car's charging system.

It's merely going to decrease the life of the battery through a) relatively rapid charging from a low level and b) having the battery at a habitually low charge. E.g. you discharge the battery to 10%, it is unable to start the car, you jump it, it manages to half charge the battery, you shut the car down. Then the battery may continue to hover in a state of, say, 30-60% charge, never actually reaching a 'fully charged' state (or taking a very long time to get there).

Number 'a' up there, again, I'm not so sure about...hard to get factual info in that area. I've just always started charging dead batteries at a slow rate, and only kicked up the charging after it's had a little while to 'trickle' (or at least stay below 10a or so). I have no way of knowing what is actually best without opening my own, uh, battery laboratory.
 
C

Charles Kozierok

Elite Member
May 14, 2012
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11.86V is pretty low. If that's after charging, yeah, it's dead. Even before charging, you don't want to leave a lead-acid below 12V any longer than necessary. (This depends on temperature, though. Cold batteries are full at lower voltages.)

As for the portapacks, the problem with them is that they usually don't have very good capacity. The other problem is that many of them are just junk.

Years ago I got one that actually had wheels and a handle and it worked really well and for a long time. It looked like this but yellow and only 600W. Unfortunately, they don't seem to make it any more.

This one has 28 Ah, which isn't bad, but rather uneven reviews.

There are no good solutions for what you want to do. Cars just aren't intended to be places to run things for long periods of time with the engine off.
 
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I

imagoon

Diamond Member
Feb 19, 2003
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phucheneh said:
But does the alternator (or rather, its control device) actually allow charging at 100% capacity? Also, I don't quite feel like doing math right now, but I don't think any battery would do well with hours of 100a+ charging.
Click to expand...

Yes,

One random example:

http://www.sparkys-answers.com/2010/01/2001-ford-windstar-alternator-burnt-up_25.html

It is really hard to find ones where people actually did the testing with the inductive load pickups.

Most alts are not all that smart really. My buddy also burned up the VR on his Harley when he loaded up to much power. I tested that one by attaching a a 13.5v power supply in place of the battery with the VR disconnected. Started the bike and popped all the switches to on. My supply registered total system draw at about 115% of the generators max. So it can happen.

I will not make the grandiose claim that they all will do it but you only really know if you do it and it fries so....
 
ProchargeMe

ProchargeMe

Senior member
Jun 2, 2012
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I've had a very 50/50 experience with optima batteries, they either work fine, or they're a complete pain in the ass. I'd say try to return it for a refund or exchange. Good luck!
 
fuzzybabybunny

fuzzybabybunny

Moderator<br>Digital & Video Cameras
Moderator
Jan 2, 2006
10,455
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How bad of an idea is this?

I have a 2A desulfinator and a 6A charger. Can I hook both up at the same time to the battery? Charge at 8A and desulfinate at the same time?
 
fuzzybabybunny

fuzzybabybunny

Moderator<br>Digital & Video Cameras
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LTC8K6 said:
Did you watch the vid? You said you had a desulfater. I'd just try it.
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I'm not currently in an area where I can watch it. So I can hook up my 2A desulfinator and my 6A charger simultaneously to the battery?
 
LTC8K6

LTC8K6

Lifer
Mar 10, 2004
28,520
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fuzzybabybunny said:
I'm not currently in an area where I can watch it. So I can hook up my 2A desulfinator and my 6A charger simultaneously to the battery?
Click to expand...

Just the desulfator. The vid is made by Optima and describes how to rescue their batteries from deep discharge and sulfation.

In the desulfate part, they use a small desulfator/charger similar to your BatteryMinder.
 
fuzzybabybunny

fuzzybabybunny

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Jan 2, 2006
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LTC8K6 said:
Just the desulfator. The vid is made by Optima and describes how to rescue their batteries from deep discharge and sulfation.

In the desulfate part, they use a small desulfator/charger similar to your BatteryMinder.
Click to expand...

Well, I hooked it up to a 6A charger and a 2A desulfator last night at the same time. The desulfator showed that it was working and when I got back in the morning the charger showed that it was done charging and in maintenance mode.

This was over about 8 hours.

Plopped it in the car and it still hesitated while starting. Possibly because I'm in Lake Tahoe and it was cold in the garage where the battery was charging.

Throughout the day, such as after skiing, the battery still shows hesitation starting up.

I don't have a Costco card and Walmart still charges $100 for a standard battery. The auto parts here do the same or $110. After tax that's $110-$120 just for a battery.
 
LTC8K6

LTC8K6

Lifer
Mar 10, 2004
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Why do you bother to ask questions? If you were going to do what you wanted to anyway, this thread could have been much shorter.
 
fuzzybabybunny

fuzzybabybunny

Moderator<br>Digital & Video Cameras
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Jan 2, 2006
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LTC8K6 said:
Why do you bother to ask questions? If you were going to do what you wanted to anyway, this thread could have been much shorter.
Click to expand...

What's the point of putting on a 2A desulfator for only 8 hours? Think about it. I needed to use the battery the following morning and I needed to make sure it would be good to go.

BTW that Optima video is oversimplifying the hell out of the process. They show that they can take a battery that's down to 8V and charge it back to 12.5v. That doesn't prove anything. It could very well not start the very next time because the capacity at that point is so far gone that it's only good for one start. Leave that battery overnight and I bet you it won't start the next morning.
 
disappoint

disappoint

Lifer
Dec 7, 2009
10,137
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fuzzybabybunny said:
Well, I hooked it up to a 6A charger and a 2A desulfator last night at the same time. The desulfator showed that it was working and when I got back in the morning the charger showed that it was done charging and in maintenance mode.

This was over about 8 hours.

Plopped it in the car and it still hesitated while starting. Possibly because I'm in Lake Tahoe and it was cold in the garage where the battery was charging.

Throughout the day, such as after skiing, the battery still shows hesitation starting up.

I don't have a Costco card and Walmart still charges $100 for a standard battery. The auto parts here do the same or $110. After tax that's $110-$120 just for a battery.
Click to expand...

I must have missed the part where you checked the voltage with and without load after charging/desulfinating.
 
LTC8K6

LTC8K6

Lifer
Mar 10, 2004
28,520
1,575
126
fuzzybabybunny said:
What's the point of putting on a 2A desulfator for only 8 hours? Think about it. I needed to use the battery the following morning and I needed to make sure it would be good to go.

BTW that Optima video is oversimplifying the hell out of the process. They show that they can take a battery that's down to 8V and charge it back to 12.5v. That doesn't prove anything. It could very well not start the very next time because the capacity at that point is so far gone that it's only good for one start. Leave that battery overnight and I bet you it won't start the next morning.
Click to expand...

A desulfator can take days to restore a battery...
 
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