Hi,
I have laptop charger whose output is 19V 3.42Amp.
Can I use it to charge 12V 1.2 Amp battery?
Is it safe to connect it directly to battery or I have to do some changes to reduce its output voltage and current?
thanks in anticipation.

 

If you connect the 19V/3.42Amp power to the 12V/1.2A battery then it could be destroy the battery, because the voltage is too high, so don't do that, and different battery has different voltage charing condition, maybe using 12.8 V or 13.8V or other voltages, so you have to know what kind of battery that you are trying to charge.

Search LM317 circuit to adjust the output voltage to suit what the battery can afford it.

 

Hi,
I assume you are talking about those small 12V 1.2Ah SLA battery. You need to reduce to voltage to 13.8V-13.9V for Standby and 14-14.4V for cyle use. Also for this small battery the initial charging current should be less than 1A I think. You could get one of those cheap DC-DC down buck converters like a cheap LM2596 with both voltage and current adjustment or XL4015 etc. or get those small motorcycle 12/6V 800mA lead acid chargers.
Do not use that 19V laptop adapter directly. You boil off all the electrolyte and destroy the battery.Plus it could heat up and explode too.

 

I thought I would mention this unit is very stable and offers some nice features. There is somethings that I think could be better. Like the ability to change modes and have them modes saved to what you wanted the last time at that mode. Main issue I have with it, When you want to use the USB you need to make sure that it is set around 5 volts and will flash to remind you that it isn't the right volts when used in different mode.

One of the nice things is it can be set for charging your battery at your rate of current you want. Then once it sees that it is charged it will change over to a Charged LED

Most important to this and why I thought it would work good for your needs. I have it working off a Laptop power supply that is 19.5v at the input and works great. Has nice dual LCD display that shows Volts and amps at the same time. There are some that are cheaper without displays so I don't want you to think this is only one out there for your needs. Just one that I thought may be the best for the money..

http://www.ebay.com/itm/32V-5A-DC-t...c-Case-X4O3-/351849950946?hash=item51ebe42ee2

 

Hi,
I have laptop charger whose output is 19V 3.42Amp.
Can I use it to charge 12V 1.2 Amp battery?
Is it safe to connect it directly to battery or I have to do some changes to reduce its output voltage and current?
thanks in anticipation.

No - assuming the PSU survives, it will boil the battery dry and probably warp the plates.

The absolute simplest would be a current limiting resistor to drop the excess voltage - but it will gas the electrolyte away if you leave it charging too long.

A simple constant current circuit would be better - but not much.

You need to limit the voltage to 14.4 under any circumstances - and it will still gas dry if you leave it charging.

Most commercial "smart" chargers detect full charge and throttle back to 13.6V to prevent excessive gassing.

 

Hi,
I assume you are talking about those small 12V 1.2Ah SLA battery. You need to reduce to voltage to 13.8V-13.9V for Standby and 14-14.4V for cyle use. Also for this small battery the initial charging current should be less than 1A I think. You could get one of those cheap DC-DC down buck converters like a cheap LM2596 with both voltage and current adjustment or XL4015 etc. or get those small motorcycle 12/6V 800mA lead acid chargers.
Do not use that 19V laptop adapter directly. You boil off all the electrolyte and destroy the battery.Plus it could heat up and explode too.

In a fully flat lead acid battery; all the acid is in the plates and the electrolyte is heading in the general direction of distilled water - actual 100% pure distilled water is not conductive.

Normal procedure is current limiting at 1/3Ah capacity with about 29V available.

As charge current recovers, it will pull the voltage down - at around 10.8 - 11.5V, you should switch to constant voltage charging. That phase of bulk charging is 14.4V for flooded cell batteries - it may be different for SLA.

 

In a fully flat lead acid battery; all the acid is in the plates and the electrolyte is heading in the general direction of distilled water - actual 100% pure distilled water is not conductive.

Normal procedure is current limiting at 1/3Ah capacity with about 29V available.

As charge current recovers, it will pull the voltage down - at around 10.8 - 11.5V, you should switch to constant voltage charging. That phase of bulk charging is 14.4V for flooded cell batteries - it may be different for SLA.

Yes, but in normal case the battery is not usually discharged below 30% to prolong its life. He should charge at about 400mA. I think the 1.2Ah cells are only available in AGM SLA form factor. Its best to get an automatic smart type charger for SLAs while flooded ones are more forgiving and we can always refill with water.

 

Yes, but in normal case the battery is not usually discharged below 30% to prolong its life. He should charge at about 400mA. I think the 1.2Ah cells are only available in AGM SLA form factor. Its best to get an automatic smart type charger for SLAs while flooded ones are more forgiving and we can always refill with water.

You can refill a SLA - it just voids the warranty, that's all.

 

You can refill a SLA - it just voids the warranty, that's all.

Yes. We can but the issue is that unlike flooded we can't see the water level and the acid might overflow while charging. But yeah, you can get some juice out of it.Actually I do it to most of my SLA cells. This way I've managed to get batteries beyond 3 years.

 

Yes. We can but the issue is that unlike flooded we can't see the water level and the acid might overflow while charging. But yeah, you can get some juice out of it.Actually I do it to most of my SLA cells. This way I've managed to get batteries beyond 3 years.

I used to have free access to scrap UPS boxes - the batteries were always gassed out. This leaves a small amount of concentrated acid and the battery sulphates even when charged.

The antics I used to recover a few of them are verboten on this forum................