car battery dead

My wife's car is dead. It's in the garage, a hard push uphill to get it out to jump-start, so I figured I'd build a battery charger. We still have our old DSL modem, and it has a huge 21-volt, 1.1 amp wall-wart, so I hooked that up. 3.1 amps... if I left that on all night, it would probably die... seems to be a 60 Hz xfmr-type, so probably has a thermal fuse. Adding my Makita belt sander in series, tie-wrap on the trigger, gets down to 1.3 amps, good enough in a cool garage. Maybe it will start in the morning.

So I should buy a real battery charger some day soon. Are they still big klunky transformer-rectifier things? I'd think that some nice small switcher could manage a few amps at least.

John

Reply to
John Larkin
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Or make one. Any 2 to 3 amp, regulated to a max of 13.8 volts will work. Add an ampmeter, and you're all set.

Reply to
PeterD

I've heard some dubious things about the cheap switcher types.. like they refuse to charge if the battery is too far gone.

It's not really a substitute, but I got one of those SLA based starter things for something like $60 (lighted alligators, etc). It takes forever to charge (10-15 hours) but starts the car right away and she can throw it in the trunk in case she gets stuck at her next stop.

I managed to destroy a xfmr-rectifier one by leaving it on the emergency start (60 or 80A claimed) for too long, and depending on the overtemperature thermostat to cut it off-- it actually smoked the xfmr), but I'd buy one again, at least until I'm sure they have got the cheap switchers done right.

Reply to
Spehro Pefhany

I "good" way to make a low cost charger is to run the electronics on the battery to be charged. You only need a power transformer and a gate drive transformer. You don't need any primary side power supply circuit to run any primary side electronics. The whole secondary side electronics could be a diode and single chip and a fuse.

Reply to
MooseFET

You could produce a nice one, but people (en masse) tend to gravitate to buying crap (cheap) rather than paying for decent, so it's probably a losing game. There are a number of dedicated control chips/microprocessors available, or you could do it with any number of general purpose ones, or even elegant old-fashioned analog design, though that's either harder or at least more subtle.

A good design would include temperature sensing at the clamps (at least a reasonable approximation of actual internal battery temperature, without requiring a separate sensor stuck to the battery) and separate charge/sensing leads (or just sense while shutting the charge off for a short period) with appropriate adjustments to charging voltages. Typical process would be constant current charge to a somewhat higher voltage (adsorb) for a few hours, followed by dropping back to a holding voltage (float). Inexpensive chargers don't do this, which is one reason why leaving them connected for a long time is bad news. Few expensive chargers even bother paying attention to temperature.

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Reply to
Ecnerwal

use the alternator. do the hard push uphill jumpstart routine once more, and drive it somewhere that sells batteries. Replace the failed battery.

Next time, replace the battery when it starts to fail instead when it is completely shot. Make sure there's nothing else draining the battery like a bad alternator when the car is stopped.

Reply to
AZ Nomad

Knowing the cause is essential. I have had dead batteries for years on vehicles not used much. I like putting deep discharges in those, as they seem to hold up better.

I think my trusty Schurer 4 amp is the longest lasting unit I have. I',ve built some using the Unitrode/TI analog IC. Those are currently not working for one reason or another. they were the best. Then I have a 10 charger, and a 50 amp my brother has. I use the 10 and I also use the Harbor Freight trickle charger that works very well.

I have left batteries on charge for up to a week on very bad cases. Thats when there is no current being drawn at first.

I keep thinking of adding that little solar charger to the truck.

greg

Reply to
GregS

John didn't say anything about battery *failure*...

I've found leaving the lights on, trunk or door open long enough will suffice, but my car is practically an antique (no more periodic mandatory emissions testing!)

Reply to
Spehro Pefhany

We have emmisions teasting based on number of miles driven. Isn't that how it should be ?

greg

Reply to
GregS

Nice thing about the big nasty Sears ones is that they tolerate amazing amounts of abuse and keep working. Once the price pressure really got to work on the switcher models, I'd expect them to croak if you touched the clips together.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
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Reply to
Phil Hobbs

She and I probably couldn't push it out of the driveway. Building a charger was the easy way. It worked.

The car wasn't used for a few days. Battery was 2.9 volts. Cause unknown. No obvious loads.

How do the authorities know how many miles have been driven?

John

Reply to
John Larkin

I suggest just going to Walmart or whatever and getting a battery charger. The first time you use it will prove its worth. You can solve a problem right in your driveway. You'll be glad you did.

Reply to
Gary Peek

On a sunny day (Wed, 05 Aug 2009 13:59:19 GMT) it happened snipped-for-privacy@zekfrivolous.com (GregS) wrote in :

In the winter, at -10C, my car battery was problematic with starting. So took it out in the evening, charged it with a car headlight in series as constant current source from something like 15 V unregulated DC, several amps... Full in the morning, and at a nice temperature so it would start, Sure Larkin must have a decent lab supply with current limiting???????? Using the bulb in series you can calculate how long you can leave it on (overnight) without overcharging (has he an amp meter????).

Anyways at the local store you can pick up a cheap charger for a couple of Euros, or just google via one of those price index sites on internet. For the non-technical without any equipment....

Reply to
Jan Panteltje

On a sunny day (Wed, 05 Aug 2009 10:22:06 -0400) it happened Phil Hobbs wrote in :

You can make a nice regulated one with one thyristor and an opamp, some LM317, with voltage and current limiting. Did that in the eighties, cooked a 100Ah battery with it too, think I have the volts a bit too high.. not sure..

Reply to
Jan Panteltje

In Ontario, light vehicles require emissions testing every 24 months unless the vehicle is >20 years old (at the time of sticker renewal-- which is typically due at yer birthday).

I don't know how they'd enforce a miles-driven rule, it would give people a fairly strong incentive to fudge the odometer declaration on their cars when they renew the license stickers.

The testing standards seem pretty lax- even with a bad oxy sensor (really rich mixture) my car passed. I think they're just looking for the extreme cases that are polluting 5x or 10x what is normal.

Reply to
Spehro Pefhany

I've replaced many batteries and never needed to know the cause unless the replacement battery showed up dead in a week (only happened once).

The rest of the time, the batteries simply failed because the previous owner never maintained them, or more recently it has been because the phoenix summer killed them.

Reply to
AZ Nomad

The way I did it as a poor student... light bulb, diode, extension cord. Make sure common is on the car chassis side ;-)

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Or a bad brake light switch... happened to me with a good battery. Finally, taking out trash on a really dark night, I noticed a slight glimmer of the brake lights :-(

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Yep. "Five year" batteries last two years in Arizona :-(

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

I bought one from this company to charge my 48v gokart. It's switching style,

3 stage charger. The smallest 12 volt charger they have is a 12 amp. Might be overkill for you but I wanted the 3 stage to better care for my gokart batteries.
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Mike
Reply to
amdx

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