Battery charging

[pebe]

With the present spate of bad weather my car is not getting enough use to keep the battery charged up enough to ensure it can turn the starter.

I have an old charger giving rectified, unsmoothed AC. But I have read somewhere that when using this type of charger the battery should be disconnected to charge it otherwise diodes in the alternator could be damaged.

Is there any truth it that? If possible, I don't want to disconnect it because of the hassle of resetting the radio code when I reconnect.

[Tim W]

pebe wibbled on Friday 15 January 2010 11:32

Not that I know of. The battery will act a big fat smoothing device anyway.

What you want to avoid is excessive overcharging leading to the car battery voltage going much about 14.5V - that could do the battery harm and might be of some risk to the car's electronics.

[Timothy Murphy]

I don't know if it is true, but my Nissan Micra manual does say exactly that.

[Harry Bloomfield]

pebe submitted this idea :

Best dump it and get a modern one. Modern ones will not damage your battery by over-charging and so can be left on almost permanently.

Unlikely, unless it is a really large charger.

A modern charger is what you need. Lidl/Aldi have them regularly on special offer for around £10.

[Usenet Nutter]

Does that not suggest that your battery is shot .I have used my Mondeo about twice locally in the last 3-4+ weeks and I have started it several times apart from that and it starts no problem.

[pebe]

No, my battery is just 2years old. The fault showed itself because the starter solenoid would not engage. I suspected the battery but it would run full headlamps and foglamps on together without dimming when I tried to start as a test. So I suspected a faulty starter and had it towed in (it's an automatic so it would not bump-start). The garage only found the battery was flat. Yes.....I was amazed too! I think the system's microcontroller measured the battery voltage at the time the solenoid engaged, found it pulled the battery voltage down too much, and dropped it out again. All within a couple of milliseconds, so the lights did not blink.

That's the only thing I can think of.

[dennis]

The lidl one specifically tells you to disconnect the battery to charge it.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember pebe saying something like:

Generally, no. That's not to say there might be some out there that will be damaged, but I've never heard of it actually happening.

[Harry Bloomfield]

dennis@home laid this down on his screen :

Which is back side covering. I never have, use it regularly and the thing only chucks out 3.6amps at a touch lower voltage than your alternator. Your alternator can put 10 times and more that level of current into your battery, with numerous large voltage spikes.

[dennis]

I used it last night, I didn't disconnect the battery either.

[pebe]

Thanks everybody for your replies. I am bidding on ebay for a newer charger that can be used with the battery still connected.

[Richard Russell]

Please don't assume that means the battery is OK. Our car has had three batteries in the space of four years from new, each replacement being free under the terms of the warranty (Toyota); one only lasted a few months. Some batteries just seem to die prematurely.

Richard.

[tony sayer]

5 and their still fine:)..

[ransley]

No you dont need pure DC, What is important is how its charged, and to what voltage, and that is about 13.3v.

knows more than me. I find the older charger best as chargers go out of calibration and a calibration Pot can usualy be found inside good old units. My old charger wasnt charging well I found it was only putting out 12.5v, but 12.5v only is a 50% charged battery, I adjusted the charger.

[terry]

A small anecdote. Couple of years ago we repaired a nominal 12 volt charger. With unit working we then measured the output voltage using a DMM (digital display multimeter). And got a seemingly crazy (high) voltage reading on the DC Voltage setting. The meter was probably trying to read the peak of the rectified AC voltage! We attached a battery in reasonably good condition and got a sensible reading. IIRC somewhere around 13.8 volts (or around 2.3 volts per cell for a 6 cell nominal 12 volt lead acid battery). Agree 12.5 volts barely enough to put anything into a battery. Maybe just enough to put a small amount ihtona completely dead battery? By the way high quality stationary batteries, telephone exchanges etc., are often continuously 'floated' (maintained) at either 2.15 or

2.17 volts per cell, depending on the administration and to a slight extent on the type of lead acid cells, just to maintain them at full charge for immediate use. For six cells 2.15 per cell =3D 12.9 volts and 2.17 =3D 13.02 volts. This being the 'maintaining' not a 'charging' voltage.

[Dave Liquorice]

replacement

lasted a

Agreed car batteries shouldn't die so quickly unless they are being abused. I reckon 5 years is a good life time.

Abuse, lights being left on and moderate discharges happening or a fault with the car probably the alternator over charging.

Modern throw away society strikes again, battery dies replace it. Fine the first time though a bit suspicious in a new car. Second time ought to have flagged up the running a few basic tests to find out what is killing the battery, third time definately. This is all warranty work as well so will be on the computer no excuse of not knowing so poor service from the garage.

[Dave]

Modern batteries are not the same as we were brought up on.

We have 2 Rover 45's. One petrol, the other diesel. Wife goes away and I am using the diesel every day for two weeks. Come to get the petrol car ready for her home coming and the battery is knackered, it wouldn't even work the radio and I had a hell of a job getting past the security. Went to the garage and the boss tells me that it has died because the battery has not been charged for more than 2 weeks. Something to do with the chemistry of modern batteries. He lends me a battery and I get the car back to him, he fits a new battery and I have had no problem for well over two years now, But I did use the car while she was away for three weeks over Christmas and new year.

Dave

[The Natural Philosopher]

NOT the chemistry of modern batteries. The habit of having electric door locks, clocks and trackers permanently wired across them.

[Dave]

No, it was the chemistry of the battery. They are no longer lead acid.

Dave

[ransley]

If not lead acid than what, Potatos and Beer? Any 12v car battery I know of is lead acid maybe the solution is gell but its sulfuric acid. Low voltage sulfates plates ruining them, with clocks, alarm, a car needs to be driven every dew days or voltage drops and sulfation starts