Battery charger output 11 volts.

[maxcampbell]

One (actually two) of those chargers with a silly green light that's supposed to light up when the battery's full. The light's on all the time, even when not connected to a battery, let alone only when connected to a full one, and putting a voltmeter across the clips, max reading I get is about 11 volts - is the charger F*****d, am I doing something wrong? Seem to remember similar thing in the past which spontaneously rectified itself - would a shake or an irish screwdriver help?

 

[VicS]

One (actually two) of those chargers with a silly green light that's supposed to light up when the battery's full. The light's on all the time, even when not connected to a battery, let alone only when connected to a full one, and putting a voltmeter across the clips, max reading I get is about 11 volts - is the charger F*****d, am I doing something wrong? Seem to remember similar thing in the past which spontaneously rectified itself - would a shake or an irish screwdriver help?

You dont say what make and model it is.

If you connect it to a slightly discharged, but otherwise good, battery then plug it in and switch it on what happens.

Can you do that while monitoring the battery volts and the current? If so do you see a current flow and how does the battery volts respond.

If no current flow and /or no change in battery volts most likely cream crackered unless an internlal fuse has blown.

 

[superheat6k]

Automotive chargers often have a relay to prevent incorrect polarity connection, requiring the battery to have some life to pull the relay in. With these there is a click as the leads are connected, but once connected the output voltage should be above the terminal voltage, so measure this pre connected then whilst on charge. The on charge voltage must be higher, but on a small charger with lo current (amps) output perhaps not by very much.

If you have a completely flat battery then you need another voltage source to get the relay pulled in, but once in the charger output will hold this in.

 

[born2sail61]

i bought a 'smart' charger for a coupla quid at car boot sale.had to rewire 240v in and 12v out leads cos a dog had chewed them,hence the price. When testing i could only get a very low voltage on the meter,but as soon as it was connected to a load(a flat battery) the voltage increased to correct level. Is that any help?

 

[theoldsalt]

I think the circuit works in a similar way to the power supply unit in a PC. There is low/zero off-load voltage. The correct output voltage only occurs when a load is applied.

 

[maxcampbell]

Well, thanks for replying. One is branded as Halfords, the other is Absaar. The battery I'm trying to charge is hidden within a sprayer, and I don't know whether it's actually charged or not - I had expected more zing from the motor, but maybe that's all it does. I don't think I can lay my hands on a reliably discharged battery.

I had thought that a charger would be pushing 14v or something, and I don't understand why the green "battery full" light is on all the time, whether connected or not.

 

[VicS]

I don't think I can lay my hands on a reliably discharged battery.

Wife's car battery! Switch the lights on for a little while to discharge the battery a bit. Then see how the charger will perform when connected to it.

Expecting to see the volts start off at 12.something and to slowly rise to 14 to 14.4 ish ...even higher if its not an automatic charger.

Expecting to see a few amps initially, falling as the battery is recharged to less than 1 amp, but depends on the charger, and the battery.

 

[jimmcgee]

12v 20 watt bulb from the pound shop or 24 hour asda , stick it on the charger and measure the voltage simples

 

[VicS]

12v 20 watt bulb from the pound shop or 24 hour asda , stick it on the charger and measure the voltage simples

Charger may not operate if you do that.

Mine wont unless connected to a battery........ If I then connect a load IIRC it goes into "recondition" mode.

Not so simple at all!

 

[William_H]

Lastly almost certainly OP is testing voltage with a digital volt meter which has very high input resistance. Which means it will detect and measure voltage with very low current drawn from the device. This means that it can measure voltage through very large resistance. In practice this means it can almost smell voltage that is in practical terms not really there. You need a light bulb or similar in parallel with the meter to drag current to measure what is really there. But then as said maybe it is not meant to provide power until it senses a battery of correct polarity and voltage. good luck olewill