Battery charger OK?

[Odyssey42]

I have a heavy 12V car battery recharger with 3 switches: manual, normal and deep cycle. When I recharge any size battery from auto to lawn mower, the charger charges at 15 amps for 10 seconds or so, then switches off for about the same period, then repeats-regardless of which position the switch is in.

I assume that the charger is going wheels up, but thought one or more of you guys that understand the electricals of this might be able to advise what is going on?

[SilentDeath]

That should be fine. most chargers will pause to monitor battery voltage/condition to make sure it doesnt get overcharged.

However 10 second pause sounds like a long pause, but this might reduce after its been on a while (5-10 mins?).

[KBeee]

No, a 15A charge is wrong.
The charger is broken

[Odyssey42]

SilentDeath-I left it on the battery overnight.

KBeee, Could you please elaborate on your comment. I am not looking at the charger, but recall that when a charger is plugged in, it normally starts the charge at 15 amps, no? If yes, I don't understand why you say that it is broken.

If no, are you saying that the charger is broken because it is charging at 15 amps? If this is the case, I need to have a look at the charger tomorrow to confirm that the "full on" rate is 15A.

Or are you saying that while it might start at 15 amps, the rate should reduce over time?

Or is it the on/off cycling that causes you to say that it is knackered?

If it is broken, can they be fixed or is it not worth the time and trouble? (BTW, it seems to charge up a car battery when someone leaves a light on overnight, even when it is doing this cycling business.)

[SilentDeath]

depends on type of charger. do you know if its constant current or smart?
usually constant current will be a lot bigger/heavyer, maybe with a ammeter (analog type) on the front, and cheaper but very slow

the smart type will be more expensive, small/lighter and a lot quicker at charging (1-4 hours for a full charge).

if its constant current type, then its definatly broken, but 7/15A is not a huge amount for a car sized battery (30/70Ah) - depending on how you got the 15A value. With a smart charger, the rate can be a lot higher.

[Odyssey42]

It does have an analog meter on the front and I guess weighs about 5 pounds. It is about 14 inches wide, 12 deep and 5 or 6 high (from memory). It is ten years old and then cost about $50.

Is there any way to tell from looking or labeling if it is constant or smart?

If it is charging up a car battery (even if it is doing this on/off thing), can it be broken?

Thanks.

[Odyssey42]

Anybody?

[KBeee]

15 amps is WAY too high for a normal 12 Volt lead/acid. If your battery is 100% dead, and been that way for a while, then it's buggered anyway (lead/acids don't like being left flat), but that'd be the only reason I could see it taking 15A at startup. Usually a peak of 1-5amps when first switching on the charger, dropping to a trickle charge. If you have the manual still available, read up on the various charging modes. I think you'll find that the Deep Cycle mode should only be used for wet alkaline cells (wet alkaline cells have a thing called the "memory effect", and unless they are fully drained then recharged every so often will never fully hold a charge), and specifically labelled eexpensive "Deep Cycle" batteries . However, lead/acids don't like getting totally flat (it sulphates the plates) and they don't suffer from memory effect.
Unless you're mistaking 15A for 15V, but even then 15V is a little on the high side. About 13 Volts is more normal for a 12 Volt L/A or SLA battery, and every 6 months give them a 14 - 15Volt kick-in-the-pants topping charge for an hour or two.

[SilentDeath]

I know un-sealed lead acid cannot be fast charged (1C = 1hour charge) like SLA can, but im sure they can be quick charged

Charging Rates

Batteries can be charged at different rates depending on the requirement. Typical rates are shown below:

* Slow Charge = Overnight or 14-16 hours charging at 0.1C rate
* Quick Charge = 3 to 6 Hours charging at 0.3C rate
* Fast Charge = Less than 1 hour charging at 1.0C rate

15A is about 0.25C and well within safe limits for a capable charger. a quick charger can be made with basic components only while fast chargers need a micro + the code and hardware design to run it, which is why they are more expensive. Yours is likely the second type in above list.

If this were a slow (trickle only) charger, KBeee would be correct. With these the charge rate is lower than what the battery can continuously dissipate meaning if you left it on permanently the battery would not get damaged from overheating/overcharging.

With 0.25C charge rate, on a 60Ah battery, thats 15Ah for 4 hours assuming 100% efficiency... you havent said how big the batterys are that your charging, but I assume that most cars will be using ~60Ah ones.

http://www.mpoweruk.com/chargers.htm#taper

explains the different types.