Question about Auto batteries

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explode,

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I miss read this as you meant A/H and CA/CCA being the same thing. Sorry. It was getting early. I have always charged to the A/H and it comes out consistent with DMM and hydrometer before that. Really not significant when posting to someone wanting to short out batteries though.

Have never seen a battery explode or one that had exploded. I'm sure I came very close, many decades ago, when jumping a 6 volt car with a 12 volt car. Have only seen a few starters burnt up from over cranking either. Most people know not to do it.

Voltage and current are not mutually exclusive If current draw is high enough then it drops the voltage. Either from resistance or lack of battery capacity. If ignition voltage is dropped enough the plugs don't fire. However it happens it's the heat that kills. That certainly wouldn't be any kind of an engine a person could use for a year round driver around here.

on load current will be far higher though.

NT

Not a problem. It just didn't read the same to me :)

There is not a big difference between the charge and discharge currents, but it does generate some waste heat.

When I was a kid my dad had a Ford station wagon. It went through starters like crazy, and was hard to start. He went to a junkyard and bought a 6 volt starter and battery cables for a few bucks. He put them in the 12 volt Ford station wagon. After that, it only took one try to start it because it turned over much faster.

That's one bad thing about the sunny south. You rarely get any warning that a car battery is getting old. You stick the key in and it doesn't turn start. Sometimes the solenoid doesn't even click, even though you had driven a while and shut it off minutes earlier.

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Michael A. Terrell
Central Florida

All of the RV power converters I've had were nothing more than the transformer, a pair of diodes and a power switch. The were intended to run 12 VDC motors and lights, so they had no filter capacitors They were not intended to charge a battery.

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Michael A. Terrell
Central Florida

Either that or it was hosed out immediately, before the acid could start attacking the metal. The paint under a lot of hoods is poor, because most car owners never look under the hood, and when they do, they rarely look up. That paint has lots of tiny pinholes, and it doesn't take long for the acid to attack the metal through the holes.

Maybe the emergency vent is plugged? Some batteries have a small channel that runs across the top of the battery to vent pressure, to prevent an explosion.

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Michael A. Terrell
Central Florida

Well yeah, 70 amps no-load is a huge draw. Hundreds of amps under load is not uncommon though. Big difference.

I've heard this is a common hack for Wankel engine conversions on VW Beetles. A stock VW starter won't crank a Wankel fast enough to fire. But if you run a 6 volt starter off 12 volts, it will.

I never worked on VWs, but I have a neighbor and a friend who are VW fanatics. I preferred mid '60s Pontiacs, and I always kept the shop's service trucks on the road. From a Corvair van, all the way to a Chevy step van. There was even a 53 Ford panel truck at one shop. :(

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Member of DAV #85.

Michael A. Terrell
Central Florida

I could test a car starter on my electronics bench at one time. The adjustable, regulated DC bench supply would put out over 75 amps continuous, and 95 amps short term. I used to rebuild my starters and alternators. Less than $10 in parts, and a half hour, and I was back in business. Brushes or bearings were cheap and easy to replace. Open windings meant that the unit was scrap.

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Member of DAV #85.

Michael A. Terrell
Central Florida

All of the 'off-vehicle' battery chargers that I've seen here in the UK, are just a transformer, couple of diodes and a fuse and meter. I've never even thought about them having filter caps. I don't actually see why they would need them. The battery being charged represents a very low impedance cap (electrically) anyway, doesn't it ? For this reason, all of the electronic circuitry in modern cars, runs quite happily, with not a sign of a big cap anywhere, including on the alternator output, to where the battery is glued pretty much directly. I've also read somewhere I think, that charging with a 'pulsy' waveform is good for breaking down inter-plate sulphation. Could be wrong on any of this - auto electrics not really my subject, but have owned and maintained cars for more years than I care to remember.

Interesting about the exploding batteries. I'm sure that temperature must be a big factor in this. I've been in Florida when there has been sustained heat. The UK does get that hot, but only for a day or so at a time. I have never had a car battery explode on me, and I can't think of ever having heard of any friends or colleagues that have either. On the other hand, we do get sustained periods of cold ( or at least we used to ) in the winter, and I don't recall ever having heard of a battery freezing. Looking around on the net, the freezing point of sulphuric acid, seems to be around the -20C mark depending on concentration, so that might be why batteries don't typically freeze here, but what happens when these things are in use up in the north of Canada or wherever ? Do freeze inhibitors have to be added ? Does a frozen battery cease to produce any current at all, and does it recover if left to unfreeze ?

Arfa

OK, I'm jealous.

[Sucks breath through teeth]

Even my 10 year old Halfords one is a bit more sophisticated than that. ;-)

Most decent modern ones will also change to a float charge when the battery is fully charged. So called 'sealed' - actually low maintenance types - don't like being left to gas heavily as once was the norm.

[snip]

It used to be fairly common when garages had battery charging areas - mechanics would plug or unplug one from the communal charger and a spark would do the rest. But H&S regs would probably make sure any such area these days was properly ventilated. But I'd agree with you - I've not known one explode on a car.

I remember stories long time ago about those in Scandinavian countries etc with severe winters taking the battery indoors at night. That would be a pain these days with all the memories on a modern car.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Arfa Daily wrote: > On the other hand, we

Actually, the freezing point of a fully charged battery is much lower than that. According to the well-respected and independent site

the electrolyte in a fully charged battery freezes at -77F (-67C). A freezing point of -20C represents an almost fully discharged battery. I'm also under the impression (though I haven't a reference at the moment) that when it freezes, it first turns slushy, and only at somewhat colder temps does it turn solid. However, apparently when it gets cold enough to turn solid, it will crack the case, ruining the battery.

Also pertinent to your question - when a battery gets cold, its terminal voltage drops, so it won't crank a car engine as well. Unfortunately a car engine is harder to crank when it is cold, so these two things are moving in opposite directions, with the result that a car can be very hard to start on a cold morning. When I lived in central Maine in the late 60's, I had a Chevy Blazer with a sizable V-8 engine. I remember that I wrapped an electric heat-tape around the battery, and wrapped the whole thing in a thin insulation blanket. When the overnight temp was expected to be -25F or lower, I would run an extension cord out to the car and plug in the heat tape - it was the only way I could be sure it would start. I was quite often the only one in the entire student apartment complex who could start a car in the morning, so I would use jumper cables to start two other cars, and then go off to school. In a rare show of social co-operation, the drivers of each of those two cars would usually jump start two others, and before long the entire apartment complex was up and running.

In places like Fairbanks, there are electrical outlets on the parking meters ...

Bill Jeffrey

Some people try to use the "Power Converter" top power electronics, then complain when the smoke pours out. The high ripple and high peak voltages destroy cheap stuff.

These devices are used while parked, to keep the load off the vehicles battery and electrical system.

I have seen a lot of conflicting views on the subject but a quality car battery should last five years or more, with proper use and care.

I spent a year in Alaska back in the '70s. We had small electric heaters that wrapped around the battery to prevent freezing. We also had dipstick heaters to keep the oil thin enough to start, and a lower heater hose heater that kept the coolant above its freezing point. You were limited to a single 20 amp, 120 volt circuit to protect your vehicle, and you needed a permit to use the outdoor outlets on the Army base. It dropped below -20 F quite often, and sometimes low enough that the battery would still freeze.

If the electrolyte does a full, hard freeze the battery case cracks. A little less than that can distort the plates and short them out, or break the connections at the top where the connect between cells. I have autopsied a number of damaged batteries before turning in the scrap lead. Its amazing the damage a little frozen electrolyte can do to a lead acid battery.

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prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Don't be, I had to get rid of both of them about 20 years ago but they were fun while I owned, and drove one of them. (the other was a parts car)

There was a mistake on the engine number I took the crankshaft out of. I had it acid cleaned and it measured less than .0005" wear so I used it, only to find out the engine was an earlier version, and wouldn't bolt to the torque converter. On top of that, it was from a 421 engine, not a 389. That thing would idle at about 300 RPM, according to the factory tach.

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Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Thanks all. Very informative stuff. Sorry to cause the teeth sucking Dave ( don't do it too much - you might get mistaken for Gordon Brown and we wouldn't want that ... ;~} ). I must admit that I've had my Halfords' charger since I was a kid with my first Moggy Minor, and it's still going strong. Haven't looked inside one for years, so I'll take your word for it that we now have to charge brute force lead acid batteries with an electronically controlled feather touch. But how does that stack up against charging it on the vehicle with an alternator ? That hasn't got much more in it than it ever had, has it ? Three phase bridge, pretty basic voltage regulator, yes ?? Still fundamentally a brute force charging device, relying on the battery to self smooth the charging voltage, without help from caps, and to stop drawing charging current when it's had enough, much like in the old days. There are plenty of 10 or more year old vehicles out there with very conventional alternators on them. Is there supposedly an issue then, when a new generation sealed maintenance free battery is fitted to one of these cars ?

Arfa

I'm waiting to see the new cars with a 42 volt electrical system, and how they handle starting in less than ideal situations.

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Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

In Alaska, battery heaters are normal, and engine heaters essential.

I suspect they'll start more easily, for the same reason 12 volt cars start more easily than 6 volt ones. Higher voltage means lower current, and lower current means lower resistive losses in the cables and connections.